Transmission device

Abstract

A transmission device (21) comprises an input shaft (22), an output shaft (23), a planetary continuously variable transmission mechanism (24), a direct coupling mechanism (27), an idler element (28), a multistage transmission mechanism (26), and a controller (25). The controller (25) controls the rotation speed of a first variator (33) of the planetary continuously variable transmission mechanism (24) and the fastening and release of a first clutch (27C) of the direct coupling mechanism (27). The controller (25) can switch the transmission device (21) to three power transfer states: a first power transfer state (continuously variable transmission); a second power transfer state (internal lock-up); and a third power transfer state (external lock-up). The controller (25) switches between the second power transfer state (internal lock-up) and the third power transfer state (external lock-up), according to the rotation speed of the output shaft (23).

Description

Transmission

[0001] The present disclosure relates to a transmission device mounted on a vehicle such as a wheel loader.

[0002] For example, Patent Document 1 describes a construction machine that transmits power using a planetary continuously variable transmission that combines a planetary gear mechanism and an electric motor. According to the construction machine of Patent Document 1, the use of the planetary continuously variable transmission is thought to reduce sudden changes in engine rotation speed and suppress sudden changes in the operating speed of the loading and unloading machine.

[0003] JP 2008-247269 A (Patent No. 5095252)

[0004] The transmission may be configured with a planetary continuously variable transmission mechanism and a multi-stage transmission mechanism connected to the planetary continuously variable transmission mechanism. In this case, the transmission may be configured to have three modes: a mode in which power is transmitted to the multi-stage transmission mechanism while the planetary continuously variable transmission mechanism is continuously variable; a mode in which power is transmitted to the multi-stage transmission mechanism by internally locking up the planetary continuously variable transmission mechanism; and a mode in which power is transmitted to the multi-stage transmission mechanism by an external lockup mechanism that does not pass through the planetary continuously variable transmission mechanism. However, in this case, a high load is placed on the power source when switching between the internal lockup and external lockup modes, which may cause a rapid decrease in vehicle speed.

[0005] SUMMARY OF THE INVENTION One object of the present invention is to provide a transmission that can smoothly switch between internal lockup and external lockup.

[0006] The present invention preferably includes an input shaft rotated by a power source mounted on a vehicle, an output shaft that outputs rotation to a running device of the vehicle, a planetary continuously variable transmission mechanism provided between the input shaft and the output shaft and that changes the speed of the rotation of the input shaft side and transmits it to the output shaft side, a direct-coupled mechanism that transmits the rotation of the input shaft side to the output shaft side bypassing the planetary continuously variable transmission mechanism, an idler element that mechanically couples the output side of the planetary continuously variable transmission mechanism and the output side of the direct-coupled mechanism, and a transmission path for switching the transmission path of meshing gears to gradually change the rotation of the output side of the planetary continuously variable transmission mechanism. and a multi-stage transmission mechanism for changing speeds, the direct-coupled mechanism having a direct-coupled clutch provided between the input shaft and the idler element, the planetary continuously variable transmission mechanism being a planetary mechanism having three members: a first member connected to the input shaft side, a second member serving as an output side, and a third member connected to the idler element and serving as an output side separate from the second member; and a hydraulic rotating machine performing pumping or motoring, the first variator having a rotating shaft connected to the second member of the planetary mechanism; and a hydraulic rotating machine performing pumping or motoring, the first variator having a rotating shaft connected to the second member of the planetary mechanism; a second variator capable of transmitting power to and from the first variator through a pair of main lines, the transmission further comprising a controller that controls the rotational speed of the first variator and engagement and disengagement of the direct-coupled clutch, wherein the controller disengages the direct-coupled clutch and changes the rotational speed of the first variator to change the rotational speed of the second member, causing rotational motion with two degrees of freedom between the first member, the second member, and the third member, and transmitting the power transmitted from the power source to the planetary continuously variable transmission mechanism to the multi-stage transmission mechanism; a second power transmission state in which the rotation of the second member is stopped by disengaging the direct-coupled clutch and stopping the rotation of the first variator, and one-degree-of-freedom rotational motion is performed between the first member, the second member, and the third member, thereby transmitting the power transmitted from the power source to the planetary continuously variable transmission mechanism to the multi-stage transmission mechanism; and a third power transmission state in which the direct-coupled clutch is engaged and the power transmitted from the power source to the direct-coupled mechanism is transmitted to the multi-stage transmission mechanism, bypassing the planetary continuously variable transmission mechanism, and the controller isThe second power transmission state and the third power transmission state are switched in accordance with the rotation speed of the output shaft.

[0007] According to the present invention, switching between the internal lockup (second power transmission state) and the external lockup (third power transmission state) can be performed smoothly.

[0008] 1 is a left side view showing a wheel loader equipped with a transmission according to an embodiment. FIG. 2 is a partially cutaway side view showing the transmission in FIG. 1. FIG. 3 is a configuration diagram showing a transmission according to a first embodiment. FIG. 4 is a configuration diagram showing the transmission in FIG. 3 together with the inside of the planetary mechanism. FIG. 5 is an enlarged view of part (A) in FIG. 6. FIG. 6 is an enlarged view of part (B) in FIG. 6. FIG. 7 is a configuration diagram showing an example where the first variator, second variator, power absorption device, etc. of the planetary continuously variable transmission mechanism in FIG. 3 are configured using hydraulic equipment. FIG. 7 is an explanatory view of the planetary mechanism in FIG. 4 viewed from the power source side. FIG. 8 is a characteristic diagram showing the relationship between the rotational speeds of the members of the planetary mechanism in FIG. 4. FIG. 9 is a driving force diagram showing an ideal relationship between vehicle speed and tractive force of a wheel loader. FIG. 10 is a driving force diagram showing an example of the relationship between vehicle speed and tractive force of a wheel loader (driving force diagram for the configuration in Table 1 described below). FIG. 11 is a driving force diagram showing another example of the relationship between vehicle speed and tractive force of a wheel loader (driving force diagram for the configuration in Table 2 described below). 3 is a configuration diagram similar to FIG. 3 , showing a first modified example (a configuration in which internal lockup is performed by a brake). FIG. 4 is a configuration diagram similar to FIG. 4 , showing a second modified example (a configuration in which the input shaft is connected to the first sun member and the first variator is connected to the carrier). FIG. 4 is a configuration diagram similar to FIG. 4 , showing a third modified example (a configuration in which the input shaft is connected to the first sun member and the first variator is connected to the second sun member). FIG. 4 is a configuration diagram similar to FIG. 4 , showing a fourth modified example (a configuration in which the second variator is connected to the output shaft). FIG. 7 is a configuration diagram similar to FIG. 7 , showing a fifth modified example (another example in which the first variator, second variator, power absorption device, etc. of the planetary continuously variable transmission mechanism in FIG. 3 are configured with hydraulic devices). FIG. 8 is a characteristic line diagram showing an example of time changes in rotational speed and pressure when switching from internal lockup to external lockup. FIG. 9 is a characteristic line diagram showing an example of time changes in rotational speed and pressure when switching from internal lockup to external lockup in a configuration equipped with a brake mechanism. FIG. 10 is a characteristic line diagram showing an example of time changes in rotational speed and pressure when switching from external lockup to internal lockup. 1 is a characteristic diagram showing an example of time-varying rotational speed and pressure when switching from external lockup to internal lockup in a configuration equipped with a brake mechanism, and FIG. 2 is a characteristic diagram showing an example of time-varying rotational speed, pressure, and reduction ratio when switching from continuously variable transmission to internal lockup.1 is a characteristic line diagram showing an example of time variations in rotational speed, pressure, and reduction ratio when switching from continuously variable transmission to internal lockup in a configuration equipped with a brake mechanism. 2 is a characteristic line diagram showing an example of time variations in rotational speed, pressure, and reduction ratio when switching from internal lockup to continuously variable transmission. 3 is a characteristic line diagram showing an example of time variations in rotational speed, pressure, and reduction ratio when switching from internal lockup to continuously variable transmission in a configuration equipped with a brake mechanism. 4 is a characteristic line diagram showing an example of time variations in pressure when switching a speed stage of a multi-stage transmission mechanism. 5 is a characteristic line diagram showing an example of time variations in pressure and rotational speed when switching from internal lockup to external lockup and switching a speed stage of the multi-stage transmission mechanism. 6 is a characteristic line diagram showing an example of time variations in pressure and rotational speed when switching from internal lockup to external lockup and switching a speed stage of the multi-stage transmission mechanism in a configuration equipped with a brake mechanism. 7 is a characteristic line diagram showing an example of time variations in pressure and rotational speed when switching from external lockup to internal lockup and switching a speed stage of the multi-stage transmission mechanism. 36 is a characteristic line diagram showing an example of time variations in pressure and rotation speed when switching from external lockup to internal lockup and changing the speed stage of the multi-stage transmission mechanism in a configuration equipped with a brake mechanism. 37 is a characteristic line diagram showing an example of time variations in reduction ratio when switching from internal lockup to external lockup and changing the speed stage of the multi-stage transmission mechanism. 38 is a characteristic line diagram showing an example of time variations in reduction ratio when switching from external lockup to internal lockup and changing the speed stage of the multi-stage transmission mechanism. 39 is a characteristic line diagram showing an example of time variations in reduction ratio and pressure when switching from continuously variable transmission to external lockup and changing the speed stage of the multi-stage transmission mechanism. 39 is a characteristic line diagram showing an example of time variations in reduction ratio and pressure when switching from external lockup to continuously variable transmission and changing the speed stage of the multi-stage transmission mechanism. 39 is a characteristic line diagram showing an example of time variations in reduction ratio and pressure when switching from external lockup to continuously variable transmission and changing the speed stage of the multi-stage transmission mechanism. 39 is a characteristic line diagram showing the relationship between the rotation direction of the variator and the direction of torque (load). 39 is a configuration diagram similar to FIG. 4 showing a second embodiment. 39 is an enlarged view of part (C) in FIG. 36. Fig. 37 is an explanatory diagram of the planetary mechanism in Fig. 36 as seen from the power source side. Fig. 38 is a characteristic diagram showing the relationship between the rotational speeds of the three members of the planetary mechanism in Fig. 36. Fig. 39 is a configuration diagram similar to Fig. 36, showing a sixth modified example (a configuration in which the input shaft is connected to the ring member and the first variator is connected to the carrier).FIG. 37 is a diagram similar to FIG. 36, showing a seventh modified example (a configuration in which the input shaft is connected to the carrier and the first variator is connected to the ring member).

[0009] Hereinafter, a transmission according to an embodiment and a modification thereof will be described in detail with reference to the accompanying drawings, taking as an example a case where the transmission is applied to a vehicle (wheel loader).

[0010] Figures 1 to 9 show a first embodiment. In Figure 1, a wheel loader 1 is a representative example of a vehicle (work vehicle). The wheel loader 1 is configured as an articulated work vehicle in which a front body 3, which is provided with left and right front wheels 2, and a rear body 5, which is provided with left and right rear wheels 4, are connected so as to be able to bend in the left-right direction. In other words, the front body 3 and the rear body 5 constitute the body of the wheel loader 1. A center hinge 6 and a steering cylinder (not shown) are provided between the front body 3 and the rear body 5. The front body 3 and the rear body 5 bend in the left-right direction about the center hinge 6 by extending and retracting the steering cylinder. This allows the wheel loader 1 to be steered while traveling.

[0011] A loading and unloading machine 7, also known as a working device, is mounted on the front body 3 of the wheel loader 1 so that it can be raised and lowered. The loading and unloading machine 7 is equipped with a loader bucket 7A. Meanwhile, the rear body 5 of the wheel loader 1 is equipped with a cab 8, the interior of which serves as a driver's compartment, an engine 9, a hydraulic pump 10, a speed change device 21, which is a transmission (power transmission device), and the like. Inside the cab 8, there is provided an accelerator pedal 8A as an operating member for accelerating the vehicle, and a forward / reverse switch lever 8B (hereinafter referred to as FNR lever 8B) for switching between forward and reverse movement and gear positions of the vehicle. Also provided inside the cab 8, although not shown, are a driver's seat, a steering wheel, a brake pedal, a parking brake switch, and the like.

[0012] The accelerator pedal 8A is provided with an operation amount detector 8C that detects the operation amount θ1 of the accelerator pedal 8A. The FNR lever 8B is operated by the operator to switch the wheel loader 1 between forward and reverse and to change the gear position. The operator switches the FNR lever 8B to the forward position (F) when moving the wheel loader 1 forward. The operator switches the FNR lever 8B to the reverse position (R) when moving the wheel loader 1 backward. The operator switches the FNR lever 8B to the neutral position (N) when continuing to stop the wheel loader 1 without traveling, or when wanting to stop the wheel loader 1 while traveling. The operator rotates the FNR lever 8B about the lever axis when changing gear positions.

[0013] The engine 9 is the power source (prime mover) of the wheel loader 1. The power source can be constituted by the engine 9 alone, which is an internal combustion engine, or, for example, by an engine and an electric motor, or by an electric motor alone. The hydraulic pump 10 is connected to the engine 9. The hydraulic pump 10 is a hydraulic source for operating the loading and unloading machine 7. As shown in FIG. 3 and other figures, which will be described later, the hydraulic pump 10 is connected to the engine 9 via gears 10A and 10B.

[0014] A front axle 12 extending in the left-right direction is provided below the front vehicle body 3. Left and right front wheels 2 are attached to both ends of the front axle 12. Meanwhile, a rear axle 13 extending in the left-right direction is provided below the rear vehicle body 5. Left and right rear wheels 4 are attached to both ends of the rear axle 13.

[0015] The front axle 12 is connected to the transmission 21 via a front propeller shaft 14. The rear axle 13 is connected to the transmission 21 via a rear propeller shaft 15. The transmission 21 changes the speed (increases and / or decreases) of the rotation of the engine 9 and transmits it to the front propeller shaft 14 and the rear propeller shaft 15. That is, the power from the engine 9 is transmitted to the transmission 21 coupled to the engine 9.

[0016] The power from the engine 9 has its rotation speed and rotation direction adjusted by the transmission 21, and is then transmitted from front and rear output shafts 23A, 23B of the transmission 21 to the front axle 12 and rear axle 13 via the front propeller shaft 14 and rear propeller shaft 15. That is, as shown in Figure 2, the transmission 21 includes an input shaft 22 connected to the engine 9, a front output shaft 23A connected to the front propeller shaft 14, and a rear output shaft 23B connected to the rear propeller shaft 15. The transmission 21 changes speeds and switches between forward and reverse rotation between the input shaft 22 and the output shafts 23A, 23B by switching the power transmission path within the transmission 21.

[0017] FIG. 10 shows an ideal driving force diagram for the wheel loader 1. FIG. 10 shows an ideal driving force line Lf in the forward direction and an ideal driving force line Lr in the reverse direction (reverse direction). When moving forward, high tractive force is required for excavation, and high vehicle speeds (0 to 40 km / h) are required for deadheading. The wheel loader 1 also needs to be able to stably climb uphill slopes with various gradients found in quarries and the like. For this reason, it is desirable for the tractive force to be equal in horsepower regardless of vehicle speed, for example, at speeds of 3 km / h or higher.

[0018] Range A in Fig. 10 indicates the range where a high tractive force is required for excavation, i.e., range A of the driving force lines during excavation. Range B in Fig. 10 indicates the range where a constant horsepower tractive force is required regardless of vehicle speed, i.e., range B of the driving force lines of constant horsepower in the forward direction. Range C in Fig. 10 indicates the range where a constant horsepower tractive force is required regardless of vehicle speed, i.e., range C of the driving force lines of constant horsepower in the reverse direction.

[0019] 3 and 4, the transmission 21 according to the first embodiment includes a planetary continuously variable transmission mechanism 24, a direct-coupled mechanism 27, and a multi-stage transmission mechanism 26. In this case, the transmission 21 has a mode in which power is transmitted to the multi-stage transmission mechanism 26 while the planetary continuously variable transmission mechanism 24 is continuously variable, a mode in which power is transmitted to the multi-stage transmission mechanism 26 by internally locking up the planetary continuously variable transmission mechanism 24, and a mode in which power is transmitted to the multi-stage transmission mechanism 26 by an external lockup mechanism (direct-coupled mechanism 27) that does not pass through the planetary continuously variable transmission mechanism 24. Power transmission by internal lockup is achieved by stopping the rotation of the member (e.g., first sun gear 29B) connected to the first variator 33 out of the three members (e.g., carrier 29A, first sun gear 29B, second sun gear 29C) of the planetary gear mechanism 29 that constitutes the planetary continuously variable transmission mechanism 24.

[0020] On the other hand, power transmission by external lockup is performed via an external lockup mechanism (direct-coupled mechanism 27) attached to the outside of planetary continuously variable transmission mechanism 24. In this case, power transmission by external lockup is performed in a state where power transmission by planetary continuously variable transmission mechanism 24 is stopped. This stopping is performed by releasing (or reducing the torque of) a member (e.g., first sun gear 29B) connected to first variator 33 out of the three members (e.g., carrier 29A, first sun gear 29B, second sun gear 29C) of planetary gear mechanism 29.

[0021] Furthermore, according to the first embodiment, as shown in FIGS. 4, 5 and 8, the planetary gear mechanism 29 of the planetary continuously variable transmission mechanism 24 includes two sun gears 29B, 29C, a planet gear 29D and a balance gear 29E that rotate while revolving around the central axis S (FIG. 8) of the two sun gears 29B, 29C, and one carrier 29A that rotatably supports the planet gear 29D and the balance gear 29E and rotates around the central axis S of the two sun gears 29B, 29C.

[0022] The transmission 21 according to the first embodiment will be described in detail below. While FIG. 3 shows the planetary gear mechanism 29 of the transmission 21 as a box (rectangular frame), FIG. 4 also shows the interior of the planetary gear mechanism 29, i.e., the specific gear arrangement of the planetary gear mechanism 29. To avoid overcomplicating the drawings, FIGS. 3 and 4 simply represent the output shaft 23 of the transmission 21 as a common output shaft 23 (= output shafts 23A and 23B) that transmits power to both the front axle 12 and the rear axle 13. That is, FIGS. 3 and 4 omit a configuration that splits power between the front output shaft 23A and the rear output shaft 23B via, for example, a center differential mechanism. The same applies to FIG. 7 , which will be described later. Also, the hydraulic pump 10 and gears 10A and 10B are omitted from FIG. 7 .

[0023] 3 and 4 are mechanical diagrams of a transmission 21 according to a first embodiment, more specifically, a transmission 21 equipped with both an internal lockup and an external lockup. The transmission 21 includes an input shaft 22 as an input member, an output shaft 23 as an output member, a planetary continuously variable transmission mechanism 24 as a continuously variable transmission mechanism (main transmission mechanism), and a controller 25. The transmission 21 also includes a multi-speed transmission mechanism 26 as a stepped transmission mechanism (auxiliary transmission mechanism), and a direct-coupled mechanism 27 as an external lockup mechanism. The direct-coupled mechanism 27 includes a first clutch 27C that is engaged when power is transmitted through the direct-coupled mechanism 27.

[0024] The transmission 21 also includes an idler element 28 (idler shaft 28A, first idler gear 28B, second idler gear 28C) that mechanically couples the planetary continuously variable transmission mechanism 24, the multi-speed transmission mechanism 26, and the direct-coupled mechanism 27. Furthermore, as shown in Fig. 7 , which will be described later, the transmission 21 also includes a first speed detector 49, a second speed detector 50, a first pressure detector 51, a second pressure detector 52, and a third pressure detector 53.

[0025] The input shaft 22 of the transmission 21 is rotated by the engine 9, which serves as a power source (prime mover) mounted on the vehicle (wheel loader 1). That is, the input shaft 22 is connected to (the drive shaft of) the engine 9. A gear 10B for transmitting power to the hydraulic pump 10 is provided on the input shaft 22. An input gear 27A of a direct-coupled mechanism 27 is also provided on the input shaft 22. The input shaft 22 is connected to a planetary continuously variable transmission mechanism 24 (more specifically, a planetary gear mechanism 29) via a first connecting member 30. Meanwhile, power is output from an output shaft 23 of the transmission 21. The output shaft 23 of the transmission 21 also serves as an output shaft 77 of the multi-speed transmission mechanism 26, which will be described later. The output shaft 23 outputs rotation to the front wheels 2 and / or rear wheels 4 via the front axle 12 and / or rear axle 13 of the wheel loader 1.

[0026] Power input to the transmission 21 from the input shaft 22 is transmitted to the idler element 28 via the planetary continuously variable transmission mechanism 24 or the direct-coupled mechanism 27. The power transmitted to the idler element 28 is output from the output shaft 23 via the multi-speed transmission mechanism 26. The planetary continuously variable transmission mechanism 24 is provided between the input shaft 22 and the output shaft 23 (specifically, between the input shaft 22 and the multi-speed transmission mechanism 26, more specifically, between the input shaft 22 and the idler element 28). The planetary continuously variable transmission mechanism 24 changes the speed of rotation on the input shaft 22 side and transmits it to the output shaft 23 side. The input side of the planetary continuously variable transmission mechanism 24 is connected to the input shaft 22 on which the input gear 27A of the direct-coupled mechanism 27 is provided. The output side of the planetary continuously variable transmission mechanism 24 is connected to the idler shaft 28A of the idler element 28.

[0027] The planetary continuously variable transmission mechanism 24 enters an internal lockup state by stopping the second connecting member 31 that connects the planetary gear mechanism 29 (e.g., the first sun gear 29B) and the first variator 33. This internal lockup state is achieved, for example, by braking the first variator 33 to stop the second connecting member 31. The braking operation of the first variator 33 will be described later. When the planetary continuously variable transmission mechanism 24 is in an internal lockup state, the power input from the input shaft 22 is transmitted to the idler element 28 (first idler gear 28B) via the "first connecting member 30 that connects the planetary gear mechanism 29 (e.g., the carrier 29A) and the input shaft 22," the "planetary gear mechanism 29," and the "third connecting member 32 that connects the planetary gear mechanism 29 (e.g., the second sun gear 29C) and the idler element 28."

[0028] In the first embodiment, the transmission 21 can arbitrarily select from the following three paths (A), (B), and (C) as a power transmission path for transmitting power input from the engine 9 to the input shaft 22 to the multi-stage transmission mechanism 26. (A) An infinitely variable speed path (first power transmission path) for transmitting power input from the engine 9 to the input shaft 22 to the multi-stage transmission mechanism 26 while the planetary continuously variable transmission mechanism 24 is continuously variable. At this time, the first clutch 27C, which serves as a direct-coupled clutch, is released, and the second clutch 36 and the third clutch 37 of the planetary continuously variable transmission mechanism 24 are engaged (connected). The state in which power is transmitted via the infinitely variable speed path is referred to as a first power transmission state. (B) An internal lockup path (second power transmission path) for transmitting power input from the engine 9 to the input shaft 22 to the multi-stage transmission mechanism 26 while the planetary continuously variable transmission mechanism 24 is internally locked up. At this time, the first clutch 27C, which serves as a direct-coupled clutch, is disengaged, and the second clutch 36 of the planetary continuously variable transmission mechanism 24 is engaged (connected). The third clutch 37 is engaged (connected) as needed. The state in which power is transmitted via the internal lockup path is referred to as the second power transmission state. (C) An external lockup path (third power transmission path) that transmits power input from the engine 9 to the input shaft 22 to the multi-stage transmission mechanism 26 via the direct-coupled mechanism 27. This external lockup path is a power transmission path that passes through the direct-coupled mechanism 27 without passing through the planetary continuously variable transmission mechanism 24. At this time, the first clutch 27C, which serves as a direct-coupled clutch, is engaged (connected), and the second clutch 36 and third clutch 37 of the planetary continuously variable transmission mechanism 24 are disengaged as needed. The state in which power is transmitted via the external lockup path is referred to as the third power transmission state.

[0029] In the embodiment, when it is appropriate to infinitely change the speed of the planetary continuously variable transmission mechanism 24, power is transmitted by infinitely changing the speed of the planetary continuously variable transmission mechanism 24. When it is appropriate to internally lock up the planetary continuously variable transmission mechanism 24, power is transmitted by internally locking up the planetary continuously variable transmission mechanism 24. When it is appropriate to transmit power via the direct drive mechanism 27, power is transmitted via the direct drive mechanism 27.

[0030] Table 1 below shows combinations of power transmission paths for the transmission 21 equipped with both internal and external lockup. In this case, the multi-speed transmission mechanism 26 has three forward speeds and one reverse speed. That is, the multi-speed transmission mechanism 26 can select one of the following speeds: first forward speed, second forward speed, third forward speed, and first reverse speed.

[0031]

[0032] As shown in Table 1, when traveling forward, the power transmission states are set in the order of "forward 1st speed infinitely variable," "forward 1st speed internal lockup," "forward 1st speed external lockup," "forward 2nd speed internal lockup," "forward 2nd speed external lockup," "forward 3rd speed internal lockup," and "forward 3rd speed external lockup," in ascending order of vehicle speed. When traveling backward, the power transmission states are set in the order of "reverse 1st speed infinitely variable," "reverse 1st speed internal lockup," and "reverse 1st speed external lockup," in descending order of vehicle speed.

[0033] Fig. 11 shows a driving force diagram of the transmission 21 having the power transmission state of Table 1. As shown in Fig. 11, forward speed can be changed in seven stages: first forward speed infinitely variable speed Lf1, first forward speed internal lockup Lf2, first forward speed external lockup Lf3, second forward speed internal lockup Lf4, second forward speed external lockup Lf5, third forward speed internal lockup Lf6, and third forward speed external lockup Lf7.

[0034] On the other hand, reverse can be shifted to three stages: reverse 1st gear infinitely variable Lr1, reverse 1st gear internal lockup Lr2, and reverse 1st gear external lockup Lr3. Transmission 21 having the power transmission states shown in Table 1 can obtain high tractive force when starting in reverse, can obtain high vehicle speeds (0 to 16 km / h) during transportation and when being sent out of service, and can stably climb uphill slopes with various gradients.

[0035] It should be noted that a power transmission state of infinitely variable speed operation may be provided when the speed stage of the multi-speed change mechanism 26 is the second forward speed and / or the third forward speed. For example, a combination of power transmission paths such as those shown in Table 2 below may be adopted.

[0036]

[0037] As shown in Table 2, when traveling forward, the power transmission states may be set in the following order from the lowest vehicle speed: "forward 1st speed infinitely variable", "forward 1st speed internal lockup", "forward 1st speed external lockup", "forward 2nd speed infinitely variable", "forward 2nd speed internal lockup", "forward 2nd speed external lockup", "forward 3rd speed infinitely variable", "forward 3rd speed internal lockup", and "forward 3rd speed external lockup". When traveling in reverse, the conditions are the same as those in Table 1.

[0038] Fig. 12 shows a driving force diagram of the transmission 21 having the power transmission state of Table 2. As shown in Fig. 12, forward speed can be changed in nine stages: forward first speed infinitely variable Lf1, forward first speed internal lockup Lf2, forward first speed external lockup Lf3, forward second speed infinitely variable Lf4, forward second speed internal lockup Lf5, forward second speed external lockup Lf6, forward third speed infinitely variable Lf7, forward third speed internal lockup Lf8, and forward third speed external lockup Lf9.

[0039] The advantages of providing the forward two-speed infinitely variable speed Lf4 and the forward three-speed infinitely variable speed Lf7 are found when changing the power transmission state from the forward two-speed infinitely variable speed Lf4 to the forward first-speed external lockup Lf3, and when changing the power transmission state from the forward three-speed infinitely variable speed Lf7 to the forward two-speed external lockup Lf6. When the wheel loader 1 is transmitting a tractive force through the transmission 21 that is 70% or more of the vehicle speed corresponding to the Lf line shown in Fig. 12, it is preferable not to use the forward two-speed infinitely variable speed Lf4 or the forward three-speed infinitely variable speed Lf7 in order to save fuel. This is because the power transmission efficiency of the transmission 21 is inferior to that of internal lockup or external lockup in the infinitely variable speed state.

[0040] On the other hand, when the transmission 21 transmits a tractive force of 40% or less of the vehicle speed corresponding to the Lf line, it is preferable to use the forward second-speed infinitely variable transmission Lf4 or the forward third-speed infinitely variable transmission Lf7 to save fuel. This is because, although the power transmission efficiency of the transmission 21 is inferior to that of the internal lockup or external lockup in the infinitely variable transmission state, the efficiency of the engine 9, which is the power source, drops even more. In this case, the combined efficiency of the transmission 21 and the engine 9 can be improved by reducing the rotational speed of the engine 9 to improve its efficiency. Specifically, the forward third-speed infinitely variable transmission can save fuel when the transmission 21 transmits a tractive force of 40% or less of the vehicle speed corresponding to the Lf line in the vehicle speed range of 0 to 16 km / h. The forward second-speed infinitely variable transmission can save fuel when the transmission 21 transmits a tractive force of 40% or less of the vehicle speed corresponding to the Lf line in the vehicle speed range of 0 to 9 km / h.

[0041] Next, the planetary continuously variable transmission mechanism 24 will be described with reference to Fig. 3. The planetary continuously variable transmission mechanism 24 includes a planetary gear mechanism 29 as a planetary mechanism, a first variator 33, a second variator 34, a transfer element 35, a second clutch 36, and a third clutch 37. The planetary gear mechanism 29 is connected to the input side (engine 9 side) via a first connecting member 30. The planetary gear mechanism 29 is connected to the first output side (first variator 33 side) via a second connecting member 31. The planetary gear mechanism 29 is connected to the second output side (idler element 28 side) via a third connecting member 32.

[0042] The first variator 33 and the second variator 34 are configured as electric motor-generators (electric motors, electric generators) or hydraulic pump-motors (hydraulic pumps, hydraulic motors). Specifically, when the first variator 33 is configured as an electric motor (electric generator), the second variator 34 is configured as an electric generator (electric motor). When the first variator 33 is configured as a hydraulic pump (hydraulic motor), the second variator 34 is configured as a hydraulic motor (hydraulic pump). As shown in FIG. 7 (described later), in this embodiment, the first variator 33 and the second variator 34 are configured as hydraulic pump-motors (hydraulic rotating machines that perform pumping or motoring operations, more specifically, hydraulic rotating machines).

[0043] The first variator 33 (hereinafter also referred to as the first hydraulic pump motor 33) and the second variator 34 (hereinafter also referred to as the second hydraulic pump motor 34) are configured to be able to transmit power between the first variator 33 and the second variator 34 while continuously changing speeds when the rotational speeds of the first variator 33 and the second variator 34 differ. For this purpose, a transfer element 35 for transmitting power between the first variator 33 and the second variator 34 is provided between the first variator 33 and the second variator 34. The transfer element 35 is configured, for example, by electrical wiring or hydraulic piping. As shown in FIG. 7 , in this embodiment, the transfer element 35 is configured by a pair of main lines 35A, 35B (a first main line 35A and a second main line 35B).

[0044] A power absorbing device 38 is provided midway along the transmission element 35. The power absorbing device 38 is a device that absorbs (disposes of or stores) power. The power absorbing device 38 absorbs (disposes of or stores) the power of the first variator 33 that exceeds the power that the second variator 34 can absorb. The power absorbing device 38 also absorbs (disposes of or stores) the power of the second variator 34 that exceeds the power that the first variator 33 can absorb.

[0045] The power absorption device 38 may be configured, for example, as a device for storing power (power storage device) using a hydraulic accumulator or an electrical storage device (storage battery). Furthermore, the power absorption device 38 may be configured, for example, as a device for disposing of power (power disposal device) using a communication valve (relief valve, on-off valve) or a resistance device (electrical resistance). As shown in FIG. 7 , in this embodiment, the power absorption device 38 is configured using variable relief valves 38A, 38B (first variable relief valve 38A, second variable relief valve 38B). The functions of the first variator 33, the second variator 34, and the transfer element 35 may be configured using an infinitely variable transmission (IVT). Furthermore, when the first variator 33 and the second variator 34 are electric motor-generators, an inverter-converter may be provided as necessary.

[0046] A second clutch 36 is provided between the planetary gear mechanism 29 and the first variator 33, i.e., between the second connecting member 31 and the first variator 33. The second clutch 36 is configured, for example, by a friction-connected clutch (friction plate), a dog clutch, or a synchromesh dog clutch. The second clutch 36 mechanically couples (connects) and releases the second connecting member 31 and the first variator 33. In other words, the second clutch 36 switches between the transmission and release of power between the planetary gear mechanism 29 and the first variator 33.

[0047] The controller 25 includes, for example, a microcomputer equipped with an arithmetic circuit (CPU), memory, etc. The controller 25 controls the engagement and release of the first clutch 27C, the engagement and release of the second clutch 36, and the engagement and release of the third clutch 37. The controller 25 controls the rotational speed of the first variator 33. The controller 25 controls the rotational speed of the second variator 34. The controller 25 controls the power absorption device 38 (variable relief valves 38A, 38B). The controller 25 controls a brake mechanism 55 ( FIG. 13 ), which will be described later, as necessary. Furthermore, the controller 25 controls the engagement and release of a forward first-speed clutch 69, a reverse first-speed clutch 70, a forward second-speed clutch 75, and a forward third-speed clutch 76, which will be described later, of the multi-speed transmission mechanism 26.

[0048] Here, the controller 25 controls the engagement and disengagement of the second clutch 36. For example, when power transmission by the planetary continuously variable transmission mechanism 24 is not required, the controller 25 outputs a signal to disengage the second clutch 36, thereby disengaging the second clutch 36. This makes it possible to stop (or reduce) the rotation of the first variator 33, thereby reducing power loss due to the rotation of the first variator 33.

[0049] The second variator 34 is connected to the idler element 28 via a third clutch 37. The third clutch 37 switches between transmitting and releasing power between the second variator 34 and the idler element 28. That is, the third clutch 37 is provided between the second variator 34 and the idler element 28. The idler element 28 includes an idler shaft 28A and a first idler gear 28B and a second idler gear 28C provided on the idler shaft 28A. The idler shaft 28A is connected to a lockup gear 27B of the direct-coupled mechanism 27 (more specifically, to a rotating shaft 27B1 of the lockup gear 27B) via a first clutch 27C.

[0050] The idler shaft 28A is connected to the second variator 34 via the transmission 39 and the third clutch 37. The first idler gear 28B meshes with the third connecting member 32 and is connected to the planetary gear mechanism 29 via the third connecting member 32. The first idler gear 28B is also meshed with the counter gear 64 (reverse first-speed gear 67) and the forward third-speed gear 73 of the multi-speed transmission mechanism 26. The second idler gear 28C is also meshed with the forward first-speed gear 66 and the forward second-speed gear 72 of the multi-speed transmission mechanism 26. As a result, the first idler gear 28B and the second idler gear 28C are connected to the multi-speed transmission mechanism 26.

[0051] A transmission 39 that changes gears between the second variator 34 and the idler element 28 (idler shaft 28A) is provided between the second variator 34 and the idler element 28. This transmission 39 may be omitted. In that case, a third clutch 37 is provided between the idler shaft 28A of the idler element 28 and the rotating shaft of the second variator 34 (second rotating shaft 43), and the third clutch 37 can engage (connect) and disengage the idler shaft 28A and the rotating shaft of the second variator 34.

[0052] The third clutch 37 is configured, for example, by a friction-connected clutch (friction plates), a dog clutch, or a synchromesh dog clutch. The third clutch 37 mechanically couples (connects) and disengages the second variator 34 and the idler element 28. The controller 25 controls the engagement and disengagement of the third clutch 37. For example, when power transmission by the second variator 34 is not required, the controller 25 outputs a signal to disengage the third clutch 37, thereby disengaging the third clutch 37. This makes it possible to stop (or reduce) the rotation of the second variator 34 and reduce power loss due to the rotation of the second variator 34. However, under these conditions, the third clutch 37 does not necessarily have to be disengaged.

[0053] The power transmitted from the engine 9 to the first connecting member 30 is distributed by the planetary gear mechanism 29 to the second connecting member 31 connected to the first variator 33 and the third connecting member 32 connected to the idler element 28. The power distributed to the second connecting member 31 is transmitted to the idler element 28 via the second clutch 36, the first variator 33, the transmission element 35, the second variator 34, the third clutch 37, and the transmission 39. The power distributed to the third connecting member 32 is transmitted to the idler element 28. The torque distribution ratio between the second connecting member 31 and the third connecting member 32 is always constant and depends on the type of the planetary gear mechanism 29 and the meshing radius of the gears.

[0054] However, because the torque distribution ratio between the second connecting member 31 and the third connecting member 32 is constant, power is not always transmitted from the first variator 33 to the second variator 34, but may be transmitted from the second variator 34 to the first variator 33. The power transmitted from the third connecting member 32 to the idler element 28 has less loss than the power transmitted from the second connecting member 31 through the first variator 33 and the second variator 34. For this reason, the planetary continuously variable transmission mechanism 24, which combines the variators 33, 34 with the planetary gear mechanism 29, has higher power transmission efficiency than a continuously variable transmission that transmits power using only a variator.

[0055] 7 shows a specific configuration of the first variator 33, the second variator 34, the transmission element 35, and the power absorbing device 38. As shown in FIG. 7, the planetary continuously variable transmission mechanism 24 includes a planetary gear mechanism 29, a hydrostatic continuously variable transmission mechanism 41, a second clutch 36, and a third clutch 37. The hydrostatic continuously variable transmission mechanism 41 includes a first rotating shaft 42, a first hydraulic pump motor 33 corresponding to the first variator 33, a pair of main lines 35A, 35B (first main line 35A, second main line 35B) corresponding to the transfer element 35, a second hydraulic pump motor 34 corresponding to the second variator 34, a second rotating shaft 43, variable relief valves 38A, 38B (first variable relief valve 38A, second variable relief valve 38B) corresponding to the power absorption device 38, a connecting line 44, bypass lines 45, 46, and check valves 47, 48.

[0056] The first rotating shaft 42 corresponds to the input shaft of the hydrostatic continuously variable transmission mechanism 41. The first rotating shaft 42 corresponds to the rotating shaft of the first hydraulic pump motor 33. The second rotating shaft 43 corresponds to the output shaft of the hydrostatic continuously variable transmission mechanism 41. The second rotating shaft 43 corresponds to the rotating shaft of the second hydraulic pump motor 34. The first hydraulic pump motor 33 is connected to the output side of the planetary gear mechanism 29 via the second clutch 36. When the first rotating shaft 42 is rotationally driven, the first hydraulic pump motor 33 circulates pressure oil through the pair of main lines 35A, 35B.

[0057] The first hydraulic pump motor 33 is configured, for example, by a variable displacement, swash plate type or bent axis type hydraulic pump motor (hydraulic rotary machine). The first hydraulic pump motor 33 is a hydraulic device (hydraulic pump or hydraulic motor) that functions as a hydraulic pump when power is input from the first rotating shaft 42, and functions as a hydraulic motor when power is output to the first rotating shaft 42. The first hydraulic pump motor 33 has a regulator 33A for adjusting the capacity (pump capacity, motor capacity). The regulator 33A receives a command (command signal W) from the controller 25 and adjusts the capacity. Ｐ ) is variably controlled based on the

[0058] A pair of main lines 35A, 35B connect a pair of supply and discharge ports of the first hydraulic pump motor 33 and a pair of supply and discharge ports of the second hydraulic pump motor 34. The second hydraulic pump motor 34 is connected to the first hydraulic pump motor 33 via a pair of main lines 35A, 35B (first main line 35A and second main line 35B). The second hydraulic pump motor 34 is rotated by pressure oil supplied from the first hydraulic pump motor 33. The second hydraulic pump motor 34 is connected to the idler element 28 (idler shaft 28A) via a third clutch 37 and a transmission 39. The second hydraulic pump motor 34 circulates pressure oil through the pair of main lines 35A, 35B as the second rotary shaft 43 is rotationally driven.

[0059] The second hydraulic pump motor 34 is configured, for example, by a variable displacement, swash plate type or bent axis type hydraulic pump motor (hydraulic rotary machine). The second hydraulic pump motor 34 is a hydraulic device (hydraulic motor or hydraulic pump) that functions as a hydraulic motor when power is output to the second rotating shaft 43, and functions as a hydraulic pump when power is input from the second rotating shaft 43. The second hydraulic pump motor 34 has a regulator 34A for adjusting the capacity (motor capacity, pump capacity). The regulator 34A receives a command (command signal W) from the controller 25 and adjusts the capacity. Ｍ ) is variably controlled based on the

[0060] The hydrostatic continuously variable transmission mechanism 41 includes variable relief valves 38A, 38B with variable set pressures (relief set pressure, relief start pressure) and check valves 47, 48 that allow hydraulic oil to flow in one direction and prevent hydraulic oil from flowing in the opposite direction. Specifically, the first main line 35A and the second main line 35B of the hydrostatic continuously variable transmission mechanism 41 are connected by a connecting line 44. The first hydraulic pump / motor 33 and the second hydraulic pump / motor 34 transmit power by hydraulic oil flowing between them through the pair of main lines 35A, 35B. For example, when the rotation of the input shaft 22 is changed in speed and transmitted to the output shaft 23, the pressure in the first main line 35A becomes higher than that in the second main line 35B. Furthermore, when the rotation of the output shaft 23 is changed in speed and transmitted to the input shaft 22, the pressure in the second main line 35B becomes higher than that in the first main line 35A. A pair of check valves 47, 48 are provided in a connecting pipe 44 that connects the first main pipe 35A and the second main pipe 35B.

[0061] One check valve 47 (hereinafter also referred to as the first check valve 47) allows pressure oil to flow from the second main line 35B toward the first main line 35A and prevents pressure oil from flowing in the reverse direction. That is, the first check valve 47 allows the flow of hydraulic oil from the second main line 35B to the first main line 35A to be communicated, and blocks the flow of hydraulic oil from the first main line 35A to the second main line 35B. The other check valve 48 (hereinafter also referred to as the second check valve 48) allows pressure oil to flow from the first main line 35A toward the second main line 35B and prevents pressure oil from flowing in the reverse direction. That is, the second check valve 48 allows the flow of hydraulic oil from the first main line 35A to the second main line 35B to be in a communicating state, and blocks the flow of hydraulic oil from the second main line 35B to the first main line 35A.

[0062] Bypass lines 45, 46 that bypass the respective check valves 47, 48 are connected to the connecting line 44. The first bypass line 45 branches off from the connecting line 44 and is connected to the connecting line 44, bypassing the first check valve 47. The second bypass line 46 branches off from the connecting line 44 and is connected to the connecting line 44, bypassing the second check valve 48. The adjustable relief valves 38A, 38B are provided midway along the bypass lines 45, 46.

[0063] That is, the first variable relief valve 38A is provided in the first bypass line 45. The first variable relief valve 38A blocks the flow of hydraulic oil from the first main line 35A to the second main line 35B when the pressure in the first main line 35A is equal to or lower than a predetermined pressure, and opens the flow when the pressure exceeds the predetermined pressure. On the other hand, the second variable relief valve 38B is provided in the second bypass line 46. The second variable relief valve 38B blocks the flow of hydraulic oil from the second main line 35B to the first main line 35A when the pressure in the second main line 35B is equal to or lower than a predetermined pressure, and opens the flow when the pressure exceeds the predetermined pressure. The variable relief valves 38A, 38B are controlled by a command signal (command signal W) from the controller 25. Ａ , W ＢThe set pressures (relief set pressures, i.e., relief start pressures) of the variable relief valves 38A, 38B are changed in response to a command signal (command signal W Ａ , W Ｂ ) is carried out based on this.

[0064] The first speed detector 49 is provided on the input shaft 22 of the transmission 21. The first speed detector 49 is a rotation detection sensor that detects the rotation speed and rotation direction of the input shaft 22. The rotation speed of the input shaft 22 corresponds to the rotation speed of the engine 9 (hereinafter referred to as engine rotation speed Vin). The first speed detector 49 outputs a detection signal corresponding to the engine rotation speed Vin to the controller 25. The second speed detector 50 is provided on the output shaft 23 of the transmission 21. The second speed detector 50 is a rotation detection sensor that detects the rotation speed (hereinafter referred to as output rotation speed Vout) and rotation direction of the output shaft 23. The output rotation speed Vout corresponds to the vehicle speed. The second speed detector 50 outputs a detection signal corresponding to the output rotation speed Vout and rotation direction to the controller 25.

[0065] The first pressure detector 51 is provided in the first main line 35A. The first pressure detector 51 is a pressure sensor that detects the hydraulic pressure (pressure) of the first main line 35A. The first pressure detector 51 detects the hydraulic pressure P Ａ The second pressure detector 52 is provided in the second main line 35B. The second pressure detector 52 is a pressure sensor that detects the hydraulic pressure (pressure) of the second main line 35B. The second pressure detector 52 detects the hydraulic pressure P Ｂ The controller 25 outputs a detection signal corresponding to the detected value.

[0066] The third pressure detector 53 is provided in the first clutch 27C. The third pressure detector 53 is a pressure sensor that detects the clutch pressure (pressure) of the first clutch 27C. The third pressure detector 53 detects the clutch pressure P ＣThe operation amount detector 8C (see FIG. 1) is provided on the accelerator pedal 8A. The operation amount detector 8C is an operation amount detection sensor that detects the operation amount θ1 of the accelerator pedal 8A. The operation amount detector 8C outputs a detection signal corresponding to the operation amount θ1 of the accelerator pedal 8A to the controller 25. The controller 25 also receives an output value (capacity θ2) of a capacity sensor (not shown) of the first hydraulic pump / motor 33 and an output value (capacity θ3) of a capacity sensor (not shown) of the second hydraulic pump / motor 34.

[0067] As shown in FIG. 7, the first clutch 27C receives a command from the controller 25 (command signal C １ The engagement and disengagement of the first clutch 27C is controlled by a command from the controller 25 (command signal C １ The second clutch 36 is controlled based on a command (command signal C ２ The second clutch 36 is engaged and disengaged in response to a command from the controller 25 (command signal C ２ The third clutch 37 is controlled based on a command (command signal C ３ The third clutch 37 is engaged and disengaged in response to a command from the controller 25 (command signal C ３ ) is controlled based on

[0068] Next, the planetary gear mechanism 29 will be described. In Figures 3 and 7, the planetary gear mechanism 29 is indicated by a box (rectangular frame). The planetary gear mechanism 29 has three members (rotating members): a first member connected to the engine 9, which is the power source; a second member connected to the first variator 33; and a third member connected to the idler element 28 on the output shaft 23 side. In the first embodiment, the planetary gear mechanism 29 is composed of a carrier and two sun gears (first sun gear, second sun gear). Table 3 below shows combinations of the components of the planetary gear mechanism 29 (carrier, first sun gear, second sun gear).

[0069]

[0070] 4, 5, and 8, in the first embodiment (i.e., No. 1-A in Table 3), planetary gear mechanism 29 includes carrier 29A corresponding to the first member, first sun gear 29B corresponding to the second member, second sun gear 29C corresponding to the third member, planet gear 29D, and balance gear 29E. Note that first sun gear 29B, second sun gear 29C, planet gear 29D, and balance gear 29E do not necessarily need to transmit power through meshing of gears, and may transmit power through friction of rollers (outer circumferential surfaces), for example.

[0071] The engine 9 is coupled to the carrier 29A via a first connecting member 30. The first sun gear 29B is connected to a first variator 33 via a second connecting member 31. The second sun gear 29C is connected to the idler element 28 (first idler gear 28B) via a third connecting member 32. The first sun gear 29B meshes with a planet gear 29D. The second sun gear 29C meshes with a balance gear 29E. The balance gear 29E meshes with the planet gear 29D.

[0072] The rotation axis Sp (FIG. 8) of the planet gear 29D and the rotation axis Sb (FIG. 8) of the balance gear 29E are supported by the carrier 29A. Therefore, the planet gear 29D and the balance gear 29E rotate while revolving around the central axis S (FIG. 8) of the planetary gear mechanism 29. The planet gear 29D includes a gear portion 29D1 that meshes with the first sun gear 29B and a gear portion 29D2 that meshes with the balance gear 29E.

[0073] According to the first embodiment, the balance gear 29E is provided between the second sun gear 29C and the planet gears 29D, but it may be provided between the first sun gear 29B and the planet gears 29D. Also, the balance gear 29E may be provided both between the second sun gear 29C and the planet gears 29D and between the first sun gear 29B and the planet gears 29D, or it is not necessary to provide the balance gear 29E at both locations.

[0074] 8 is a cross-sectional view of planetary gear mechanism 29 as viewed from the power source side. Carrier 29A, first sun gear 29B, and second sun gear 29C are arranged concentrically. That is, the central axes S (rotational centers) of carrier 29A, first sun gear 29B, and second sun gear 29C are aligned. First sun gear 29B meshes with gear portion 29D1 of planet gear 29D. Second sun gear 29C meshes with balance gear 29E. Balance gear 29E meshes with gear portion 29D2 of planet gear 29D. Balance gear 29E and planet gear 29D are free to rotate in the rotational direction by carrier 29A but are constrained in the revolution direction around center axis S so that the respective gears mesh. Therefore, the planet gear 29D rotates about the rotation axis Sp, which is the central axis of the planet gear 29D, and revolves around the central axis S of the carrier 29A. Therefore, the locus Cp of the central axis (spinning axis Sp) of the planet gear 29D forms a circle centered on the central axis S of the carrier 29A. The balance gear 29E rotates about the rotation axis Sb, which is the central axis of the balance gear 29E, and revolves around the central axis S of the carrier 29A. Therefore, the locus Cb of the central axis (spinning axis Sb) of the balance gear 29E forms a circle centered on the central axis S of the carrier 29A.

[0075] The meshing radius rs1 of the first sun gear 29B is the meshing radius on the first sun gear 29B side when the first sun gear 29B and the planet gear 29D mesh with each other. The meshing radius rp1 of the gear portion 29D1 of the planet gear 29D is the meshing radius on the gear portion 29D1 side when the first sun gear 29B and the planet gear 29D mesh with each other. The meshing radius rs2 of the second sun gear 29C is the meshing radius on the second sun gear 29C side when the second sun gear 29C and the balance gear 29E mesh with each other. The meshing radius rp2 of the gear portion 29D2 of the planet gear 29D is the meshing radius on the planet gear 29D side when the balance gear 29E and the planet gear 29D mesh with each other.

[0076] In the first embodiment (No. 1-A in Table 3), carrier 29A is connected to a member (terminal) connected to engine 9, i.e., first connecting member 30, and therefore torque Tc of carrier 29A is the torque that can be generated by engine 9. First sun gear 29B is connected to a member (terminal) connected to first variator 33, i.e., second connecting member 31, and therefore torque Ts1 of first sun gear 29B is the torque that can be generated by first variator 33. Second sun gear 29C is connected to a member (terminal) connected to idler element 28, i.e., third connecting member 32, and therefore torque Ts2 of second sun gear 29C is the torque reaction force received from idler gear 28B.

[0077] The ratio between torque Ts1 of first sun gear 29B, torque Ts2 of second sun gear 29C, and torque Tc of carrier 29A remains constant while planetary continuously variable transmission mechanism 24 is transmitting power. Based on this law, controller 25 outputs a signal to control first variator 33 and controls the torque of second connecting member 31 (e.g., first sun gear 29B) connected to first variator 33. That is, controller 25 controls the torque of second connecting member 31 (e.g., first sun gear 29B) by controlling first variator 33. In this way, controller 25 indirectly controls the torque of first connecting member 30 (e.g., carrier 29A) connected to engine 9 and the torque of third connecting member 32 (e.g., second sun gear 29C) connected to idler element 28. As a result, the transmission torque can be controlled between the first connecting member 30 (e.g., carrier 29A) connected to the engine 9 and the third connecting member 32 (e.g., second sun gear 29C) connected to the idler element 28.

[0078] FIG. 9 shows the relationship between the rotational speeds of the planetary gear mechanism 29. Assume that the rotational speed of the carrier 29A is constant. In this case, increasing the rotational speed of the second sun gear 29C decreases the rotational speed of the first sun gear 29B. Conversely, decreasing the rotational speed of the second sun gear 29C increases the rotational speed of the first sun gear 29B. Based on this law, the controller 25 outputs a signal to control the first variator 33 and controls the rotational speed of the second connecting member 31 (e.g., the first sun gear 29B) connected to the first variator 33. In other words, the controller 25 controls the rotational speed of the second connecting member 31 (e.g., the first sun gear 29B) by controlling the first variator 33. Thereby, the controller 25 indirectly controls the rotation speed of the first connecting member 30 (e.g., carrier 29A) connected to the engine 9 and the rotation speed of the third connecting member 32 (e.g., second sun gear 29C) connected to the idler element 28. As a result, it is possible to control the gear ratio between the first connecting member 30 (e.g., carrier 29A) connected to the engine 9 and the third connecting member 32 (e.g., second sun gear 29C) connected to the idler element 28.

[0079] When the "rotational speed of the second sun gear / rotational speed of the carrier" is 0, the second sun gear 29C rotates at 0 min. Since the second sun gear 29C is connected to the output shaft 23 via the third connecting member 32, the idler element 28, and the multi-stage transmission mechanism 26, the second sun gear 29C rotates at 0 min. -1 In this case, the vehicle speed is 0 km / h. In other words, the speed ratio of the planetary continuously variable transmission mechanism 24 is infinite. As shown in a second modified example in FIG. 14 (i.e., No. 1-B in Table 3), the planetary gear mechanism 29 may have the first sun gear 29B connected to the first connecting member 30 that is connected to the engine 9, the carrier 29A connected to the second connecting member 31 that is connected to the first variator 33, and the second sun gear 29C connected to the third connecting member 32 that is connected to the idler element 28. As shown in a third modified example in FIG. 15 (i.e., No. 1-C in Table 3), the planetary gear mechanism 29 may have the first sun gear 29B connected to the first connecting member 30, the second sun gear 29C connected to the second connecting member 31, and the carrier 29A connected to the third connecting member 32.

[0080] Next, the internal lock-up operation of the planetary continuously variable transmission mechanism 24 will be described. The power transmission efficiency between the planetary gear mechanism 29 and the idler element 28 is higher through the power transmission path via the third connecting member 32 than through the power transmission path via the second connecting member 31, the first variator 33, the transmission element 35, the second variator 34, the third clutch 37, and the transmission 39. Therefore, in order to increase the transmission efficiency, the rotation of the second connecting member 31 connected to the first variator 33 can be stopped to prevent power transmission between the first variator 33 and the second variator 34. In this case, the power supplied from the engine 9 to the planetary gear mechanism 29 through the first connecting member 30 is not distributed to the second connecting member 31 connected to the first variator 33, but is entirely transmitted to the third connecting member 32 connected to the idler element 28.

[0081] To place the planetary continuously variable transmission mechanism 24 in an internal lockup state, it is sufficient to stop the rotation of the second connecting member 31 connected to the first variator 33, out of the three connecting members 30, 31, 32 connected to the planetary gear mechanism 29. When the first variator 33 and the second variator 34 are hydraulic pump motors, the controller 25 maintains the displacement of the hydraulic pump motor of the first variator 33 at a predetermined value or more (preferably 10% or more of the maximum displacement), and controls the displacement of the hydraulic pump motor of the second variator 34 to zero.

[0082] The internal lockup state may also be achieved by fixing the rotating shaft of the first variator 33 to a non-rotating portion to stop the rotation of the first variator 33. For example, as in a first modified example shown in FIG. 13 , the internal lockup state may be achieved by fixing the second connecting member 31 to a non-rotating portion (e.g., the case of the transmission 21) with a brake mechanism 55. The brake mechanism 55 may be configured to fix the second connecting member 31 connected to the first variator 33 to the non-rotating portion by frictional coupling or mechanical meshing coupling. In particular, when the first variator 33 is a generator, it is desirable to fix the second connecting member 31 to the non-rotating portion with the brake mechanism 55 from the perspective of power loss.

[0083] In the case of the transmission 21 capable of performing internal lockup operation and external lockup operation of the planetary continuously variable transmission mechanism 24, power is transmitted by continuously changing the speed of the planetary continuously variable transmission mechanism 24 during starting and excavation. During transportation and deadheading, power is transmitted by internally locking up the planetary continuously variable transmission mechanism 24 or by using the external lockup mechanism (direct-coupled mechanism 27). As a result, during starting and excavation (e.g., 0 to 7 km / h) when continuously variable speed change is required, power transmission efficiency can be improved by continuously changing the speed of the planetary continuously variable transmission mechanism 24. On the other hand, during transportation and deadheading (e.g., 7 km / h or higher) when continuously variable speed change is not required, power transmission efficiency can be further improved than with continuously variable transmission by internally locking up the planetary continuously variable transmission mechanism 24 or by using the external lockup mechanism (direct-coupled mechanism 27).

[0084] Next, the direct-coupled mechanism 27, which is an external lockup mechanism, will be described with reference to Figures 3 and 4. The direct-coupled mechanism 27 transmits power supplied from the engine 9 to the idler element 28 by meshing of gears without passing through the planetary continuously variable transmission mechanism 24. The direct-coupled mechanism 27 includes an input gear 27A provided on the input shaft 22, a lockup gear 27B meshing with the input gear 27A, and a first clutch 27C. A rotating shaft 27B1 provided with the lockup gear 27B is connected to an idler shaft 28A of the idler element 28 via the first clutch 27C.

[0085] The first clutch 27C is provided between the input shaft 22 (more specifically, the rotating shaft 27B1) and the idler shaft 28A. The first clutch 27C is configured, for example, by a friction-bonded clutch (friction plate), a dog clutch, or a synchromesh-equipped dog clutch. The first clutch 27C mechanically couples (connects) and disengages the lockup gear 27B (the rotating shaft 27B1) and the idler element 28 (the idler shaft 28A). By disengaging the second clutch 36 and engaging the first clutch 27C, the power input from the input shaft 22 is transmitted to the idler element 28 (the first idler gear 28B and the second idler gear 28C) via the input gear 27A, the lockup gear 27B, and the first clutch 27C. As a result, the power supplied from the engine 9 can be transmitted to the first idler gear 28B and the second idler gear 28C via the direct-coupled mechanism 27, which is an external lockup mechanism, without passing through the planetary continuously variable transmission mechanism 24.

[0086] Here, the external lockup rotation speed ratio Ir is defined as in the following equation 1. In this case, the number of teeth of the input gear 27A is "N27A", and the number of teeth of the lockup gear 27B is "N27B".

[0087]

[0088] In the case of a transmission 21 that is equipped with an external lockup mechanism (direct-coupling mechanism 27) and performs internal lockup operation, it is desirable that the external lockup rotational speed ratio Ir be equal to or greater than the internal lockup output speed ratio Ip. Preferably, in order to more widely and effectively utilize the speed ratio of the planetary continuously variable transmission mechanism 24, the external lockup rotational speed ratio Ir is made greater than the internal lockup output speed ratio Ip. This allows the speed-up range of the planetary continuously variable transmission mechanism 24 to be more widely and effectively utilized. The internal lockup output speed ratio Ip is defined by the following equation 2. In this case, the number of teeth of the third connecting member 32 connected to the first idler gear 28B is "N32," the number of teeth of the first idler gear 28B is "N28B," and the internal lockup speed ratio is "In."

[0089]

[0090] The transmission 21, which is equipped with an external lockup mechanism (direct-coupled mechanism 27) and performs internal lockup operation, can transmit power, for example, as follows: When starting and excavating (vehicle speed: 0 to 7 km / h), which require infinitely variable speed, power is transmitted via the planetary continuously variable transmission mechanism 24 while performing infinitely variable speed. When transporting and deadheading (vehicle speed: 7 km / h or higher), which do not require infinitely variable speed, power is transmitted via the planetary continuously variable transmission mechanism 24 while operating the internal lockup. When transporting and deadheading (vehicle speed: 10 km / h or higher), which do not require infinitely variable speed, power is transmitted via the external lockup mechanism (direct-coupled mechanism 27). This allows the transmission 21 to select the power transmission path with the highest power transmission efficiency during all operations, including excavation, starting, transporting, and deadheading.

[0091] Next, the multi-speed transmission mechanism 26 will be described. The multi-speed transmission mechanism 26 is a transmission mechanism that changes speed by meshing gears, switching clutches, and switching brakes. The multi-speed transmission mechanism 26 corresponds to, for example, a planetary transmission, a countershaft transmission, a manual transmission, an automated manual transmission, a dual clutch transmission, etc. In the first embodiment, the multi-speed transmission mechanism 26 is configured by a countershaft transmission with three forward speeds and one reverse speed.

[0092] The multi-speed transmission mechanism 26, which is a countershaft-type transmission, will be described with reference to Figure 6. The multi-speed transmission mechanism 26 includes a low-range shaft unit 61, a high-range shaft unit 62, an output shaft unit 63, and a counter gear 64. The low-range shaft unit 61 includes a low-range shaft 65, a forward first-speed gear 66, a reverse first-speed gear 67, a low-range gear 68, a forward first-speed clutch 69, and a reverse first-speed clutch 70. The high-range shaft unit 62 includes a high-range shaft 71, a forward second-speed gear 72, a forward third-speed gear 73, a high-range gear 74, a forward second-speed clutch 75, and a forward third-speed clutch 76. The counter gear 64 is a gear for reversing the rotational direction of the output shaft 77 of the output shaft unit 63. The output shaft unit 63 includes an output shaft 77, a low-range output gear 78, and a high-range output gear 79. The output shaft 77 of the output shaft unit 63 (i.e., the output shaft 77 of the multi-speed mechanism 26) corresponds to the output shaft 23 of the transmission 21.

[0093] The first reverse gear 67 is constantly meshed with the first idler gear 28B via the counter gear 64, and rotates together with the first idler gear 28B. The third forward gear 73 is constantly meshed with the first idler gear 28B, and rotates together with the first idler gear 28B. The first forward gear 66 is constantly meshed with the second idler gear 28C, and rotates together with the second idler gear 28C. The second forward gear 72 is constantly meshed with the second idler gear 28C, and rotates together with the second idler gear 28C.

[0094] The reverse first-speed clutch 70 engages (connects) and disengages the reverse first-speed gear 67 and the low range shaft 65. Connecting the reverse first-speed gear 67 and the low range shaft 65 by the reverse first-speed clutch 70 enables power transmission between the first idler gear 28B and the low range shaft 65. The forward first-speed clutch 69 engages (connects) and disengages the forward first-speed gear 66 and the low range shaft 65. Connecting the forward first-speed gear 66 and the low range shaft 65 by the forward first-speed clutch 69 enables power transmission between the second idler gear 28C and the low range shaft 65.

[0095] The forward second-speed clutch 75 engages (connects) and disengages the forward second-speed gear 72 and the high range shaft 71. Connecting the forward second-speed gear 72 and the high range shaft 71 by the forward second-speed clutch 75 enables power transmission between the second idler gear 28C and the high range shaft 71. The forward third-speed clutch 76 engages (connects) and disengages the forward third-speed gear 73 and the high range shaft 71. Connecting the forward third-speed gear 73 and the high range shaft 71 by the forward third-speed clutch 76 enables power transmission between the first idler gear 28B and the high range shaft 71.

[0096] The low range gear 68 of the low range shaft unit 61 is always meshed with the low range output gear 78 of the output shaft unit 63, and the low range shaft 65 and the output shaft 77 rotate together. In addition, the high range gear 74 of the high range shaft unit 62 is always meshed with the high range output gear 79 of the output shaft unit 63, and the high range shaft 71 and the output shaft 77 rotate together.

[0097] That is, when the reverse first-speed gear 67 and the low range shaft 65 are coupled (fastened) by the reverse first-speed clutch 70, the first idler gear 28B, counter gear 64, reverse first-speed gear 67, reverse first-speed clutch 70, low range shaft 65, low range gear 68, low range output gear 78, and output shaft 77 rotate integrally. As a result, the power transmitted to the idler element 28 (idler shaft 28A, first idler gear 28B) via the planetary continuously variable transmission mechanism 24 or the direct-coupled mechanism 27 can be transmitted to the output shaft 77.

[0098] When the forward first-speed gear 66 and the low-range shaft 65 are coupled (fastened) by the forward first-speed clutch 69, the second idler gear 28C, forward first-speed gear 66, forward first-speed clutch 69, low-range shaft 65, low-range gear 68, low-range output gear 78, and output shaft 77 rotate integrally. This allows the power transmitted to the idler element 28 (idler shaft 28A, second idler gear 28C) via the planetary continuously variable transmission mechanism 24 or the direct-coupled mechanism 27 to be transmitted to the output shaft 77.

[0099] When the forward second-speed gear 72 and the high range shaft 71 are connected (fastened) by the forward second-speed clutch 75, the second idler gear 28C, forward second-speed gear 72, forward second-speed clutch 75, high range shaft 71, high range gear 74, high range output gear 79, and output shaft 77 rotate integrally. This allows the power transmitted to the idler element 28 (idler shaft 28A, second idler gear 28C) via the planetary continuously variable transmission mechanism 24 or the direct-coupled mechanism 27 to be transmitted to the output shaft 77.

[0100] When the third forward gear 73 and the high range shaft 71 are connected (engaged) by the third forward clutch 76, the first idler gear 28B, third forward gear 73, third forward clutch 76, high range shaft 71, high range gear 74, high range output gear 79, and output shaft 77 rotate integrally. This allows the power transmitted to the idler element 28 (idler shaft 28A, first idler gear 28B) via the planetary continuously variable transmission mechanism 24 or the direct-coupled mechanism 27 to be transmitted to the output shaft 77. Table 4 below shows the operation (engagement / disengagement) of each of the clutches 69, 70, 75, and 76 of the multi-speed transmission mechanism 26.

[0101]

[0102] In reverse first gear, the reverse first clutch 70 is engaged (locked), and the forward first clutch 69, forward second clutch 75, and forward third clutch 76 are disengaged. In forward first gear, the forward first clutch 69 is engaged (locked), and the reverse first clutch 70, forward second clutch 75, and forward third clutch 76 are disengaged. In forward second gear, the forward second clutch 75 is engaged (locked), and the forward first clutch 69, reverse first clutch 70, and forward third clutch 76 are disengaged. In forward third gear, the forward third clutch 76 is engaged (locked), and the forward first clutch 69, reverse first clutch 70, and forward second clutch 75 are disengaged.

[0103] In the embodiment, the second variator 34 is connected to the idler element 28 (idler shaft 28A) via the third clutch 37 and the transmission 39. Alternatively, as in a fourth modified example shown in Fig. 16, the second variator 34 may be connected to the output shaft 77 of the multi-speed mechanism 26 (output shaft 23 of the transmission 21) via the third clutch 37 and the transmission 39.

[0104] Now, consider the case of configuring a transmission capable of six speeds. In this case, if the configuration does not switch between internal lockup and external lockup, a six-speed sub-transmission mechanism (multi-speed transmission mechanism) is required. In contrast, if the configuration switches between internal lockup and external lockup, six speeds (2 × 3 = 6) are possible with a three-speed sub-transmission mechanism (multi-speed transmission mechanism). Therefore, by configuring the sub-transmission mechanism (multi-speed transmission mechanism) to switch between internal lockup and external lockup, the number of speeds (number of gears) of the sub-transmission mechanism (multi-speed transmission mechanism) can be reduced, making the sub-transmission mechanism (multi-speed transmission mechanism) smaller and less expensive. However, in this case, as shown in Tables 1 and 2 above, for example, it becomes necessary to change speeds (switch) of the sub-transmission mechanism (multi-speed transmission mechanism) simultaneously with switching between internal lockup and external lockup, making it very difficult to switch the power transmission path.

[0105] That is, consider a state in which power transmission by internal lockup and power transmission by external lockup occur simultaneously when switching between internal lockup and external lockup. In this case, power generated by engine 9, which is the power source, is transmitted to idler element 28 through direct-coupled mechanism 27, which is an external lockup mechanism, and attempts to return to engine 9 from idler element 28 via planetary continuously variable transmission mechanism 24. However, because the "reduction ratio from engine 9 to idler element 28 in internal lockup state" differs from the "reduction ratio from engine 9 to idler element 28 in external lockup state," a high load will be applied to engine 9 if this state is left as is. This may cause engine 9 to stop and idler element 28 to suddenly stop rotating, resulting in a rapid decrease in vehicle speed.

[0106] Therefore, switching between internal lockup and external lockup, and in turn, simultaneously shifting (switching) the auxiliary transmission mechanism (multi-stage transmission mechanism), can easily lead to vehicle stalling and sudden stops, posing a major problem. Therefore, in this embodiment, smooth switching between internal lockup and external lockup can be performed, and in turn, smooth shifting (switching) the auxiliary transmission mechanism (multi-stage transmission mechanism) can be performed simultaneously with this switching. This makes it possible to configure a compact, low-cost multi-stage transmission mechanism. These points will be explained in detail below.

[0107] As shown in Fig. 7, the planetary continuously variable transmission mechanism 24 includes a planetary gear mechanism 29 and a hydrostatic continuously variable transmission mechanism 41. A pair of main lines 35A, 35B of the hydrostatic continuously variable transmission mechanism 41 are connected by a connecting line 44. The connecting line 44 is provided with a first variable relief valve 38A, a second variable relief valve 38B, a first check valve 47, and a second check valve 48. The set pressures (relief set pressures, i.e., relief start pressures) of the variable relief valves 38A, 38B are controlled by a command signal (command signal W Ａ , W Ｂ The variable relief valves 38A, 38B correspond to communication valves that can switch between a communication state and a cutoff state between the pair of main lines 35A, 35B.

[0108] The controller 25 can set the adjustable relief valves 38A, 38B to a blocked state, i.e., a blocked state in which the pair of main lines 35A, 35B are blocked, by increasing the set pressures of the adjustable relief valves 38A, 38B. The controller 25 can set the adjustable relief valves 38A, 38B to a communicating state, i.e., a communicating state in which the pair of main lines 35A, 35B are communicated, by decreasing the set pressures of the adjustable relief valves 38A, 38B.

[0109] The relief pressures of the variable relief valves 38A, 38B are normally set to a predetermined value on the high-pressure side (e.g., 35 MPa to 50 MPa). That is, when power is transmitted via the planetary continuously variable transmission mechanism 24, the controller 25 sets the relief pressures of the variable relief valves 38A, 38B to a predetermined value on the high-pressure side (e.g., 35 MPa to 50 MPa). At this time, the working fluid flowing from the first hydraulic pump / motor 33 to the second hydraulic pump / motor 34 via the first main line 35A, the working fluid flowing from the first hydraulic pump / motor 33 to the second hydraulic pump / motor 34 via the second main line 35B, the working fluid flowing from the second hydraulic pump / motor 34 to the first hydraulic pump / motor 33 via the first main line 35A, and the working fluid flowing from the second hydraulic pump / motor 34 to the first hydraulic pump / motor 33 via the second main line 35B can be sent without being bypassed by the connecting line 44 along the way. This allows power to be transmitted between the first hydraulic pump motor 33 and the second hydraulic pump motor 34 .

[0110] Furthermore, for example, when the pressure in the first main line 35A becomes high (e.g., 40 MPa or higher) equal to or higher than a predetermined pressure and exceeds the relief pressure of the first adjustable relief valve 38A (a predetermined value on the high-pressure side), the hydraulic fluid in the first main line 35A flows to the second main line 35B through the connecting line 44, the first adjustable relief valve 38A, and the second check valve 48. When the pressure in the second main line 35B becomes high (e.g., 40 MPa or higher) equal to or higher than a predetermined pressure and exceeds the relief pressure of the second adjustable relief valve 38B (a predetermined value on the high-pressure side), the hydraulic fluid in the second main line 35B flows to the first main line 35A through the connecting line 44, the second adjustable relief valve 38B, and the first check valve 47. This makes it possible to prevent damage to the first hydraulic pump-motor 33 and the second hydraulic pump-motor 34 caused by the pressure of the hydraulic fluid becoming excessively high.

[0111] On the other hand, the controller 25 can shut off hydraulic power transmission within the hydrostatic continuously variable transmission mechanism 41 by bringing the variable relief valves 38A, 38B into a communication state (i.e., by connecting the pair of main lines 35A, 35B). For example, the controller 25 can lower the relief pressure of the first variable relief valve 38A to allow the hydraulic fluid in the first main line 35A to flow to the second main line 35B through the connecting line 44, the first bypass line 45, the first variable relief valve 38A, the connecting line 44, and the second check valve 48. As a result, the hydraulic fluid sent from the first hydraulic pump / motor 33 to the first main line 35A bypasses the second hydraulic pump / motor 34 and returns to the first hydraulic pump / motor 33. As a result, the first hydraulic pump / motor 33 is unable to transmit power to the second hydraulic pump / motor 34 via the first main line 35A. Similarly, the hydraulic fluid sent from the second hydraulic pump motor 34 to the first main line 35A bypasses the first hydraulic pump motor 33 and is returned to the second hydraulic pump motor 34. As a result, the second hydraulic pump motor 34 is unable to transmit power to the first hydraulic pump motor 33 via the first main line 35A.

[0112] Furthermore, for example, the controller 25 can lower the relief pressure of the second adjustable relief valve 38B to allow the hydraulic fluid in the second main line 35B to flow to the first main line 35A through the connecting line 44, the second bypass line 46, the second adjustable relief valve 38B, the connecting line 44, and the first check valve 47. As a result, the hydraulic fluid sent from the first hydraulic pump / motor 33 to the second main line 35B bypasses the second hydraulic pump / motor 34 and is returned to the first hydraulic pump / motor 33. As a result, the first hydraulic pump / motor 33 is unable to transmit power to the second hydraulic pump / motor 34 via the second main line 35B. Similarly, the hydraulic fluid sent from the second hydraulic pump / motor 34 to the second main line 35B bypasses the first hydraulic pump / motor 33 and is returned to the second hydraulic pump / motor 34. As a result, the second hydraulic pump / motor 34 is unable to transmit power to the first hydraulic pump / motor 33 via the second main line 35B.

[0113] Furthermore, for example, the controller 25 can bypass the hydraulic fluid in both directions between the first main line 35A and the second main line 35B by lowering both the relief pressure of the first adjustable relief valve 38A and the relief pressure of the second adjustable relief valve 38B. In this case, power cannot be transmitted in both directions between the first hydraulic pump / motor 33 and the second hydraulic pump / motor 34. Note that it is not necessary to provide both the first variable relief valve 38A and the second variable relief valve 38B; only one may be provided and the other may not be provided. Also, it is not necessary for both the first variable relief valve 38A and the second variable relief valve 38B to be electromagnetic relief valves; one may be an electromagnetic relief valve and the other a relief valve with a fixed relief pressure (fixed relief valve).

[0114] The hydrostatic continuously variable transmission mechanism 41 shown in FIG. 7 uses variable relief valves 38A, 38B as means for shutting off hydraulic power transmission within the hydrostatic continuously variable transmission mechanism 41. Alternatively, as in a fifth modified example shown in FIG. 17 , a first on-off valve 81A may be provided in parallel with the first variable relief valve 38A, and a second on-off valve 81B may be provided in parallel with the second variable relief valve 38B. The first on-off valve 81A and the second on-off valve 81B switch the pair of main lines 35A, 35B between a communication state and a cut-off state. That is, in the fifth modified example shown in FIG. 17 , the first on-off valve 81A and the second on-off valve 81B are provided between the pair of main lines 35A, 35B, switching the pair of main lines 35A, 35B between a communication state and a cut-off state. The on-off valves 81A and 81B correspond to communication valves that can switch between a communication state and a cut-off state between the pair of main pipes 35A and 35B.

[0115] That is, the first on-off valve 81A and the second on-off valve 81B can be switched between an open position corresponding to a communication state and a closed position corresponding to a cut-off state. The switching of the first on-off valve 81A and the second on-off valve 81B is controlled based on commands (command signals Wc and Wd) from the controller 25. That is, the on-off valves 81A and 81B are configured as electrically operated on-off valves (e.g., electromagnetic on-off valves) that open and close based on the command signals (command signals Wc and Wd) from the controller 25. In this configuration, the relief setting pressure of the first adjustable relief valve 38A can be set to a low pressure to establish communication between the pair of main lines 35A and 35B by opening the first on-off valve 81A. Furthermore, the relief setting pressure of the second adjustable relief valve 38B can be set to a low pressure to establish communication between the pair of main lines 35A and 35B by opening the second on-off valve 81B.

[0116] 17 , by opening the first on-off valve 81A and the second on-off valve 81B, the pair of main lines 35A, 35B are brought into communication with each other, thereby blocking the transmission of power by hydraulic pressure within the hydrostatic continuously variable transmission mechanism 41. When the first on-off valve 81A and the second on-off valve 81B are provided, the first variable relief valve 38A and the second variable relief valve 38B may be changed to relief valves with a fixed relief pressure (fixed relief valves). Furthermore, it is not necessary to provide both the first on-off valve 81A and the second on-off valve 81B, and only one of them may be provided.

[0117] In this state of internal lockup, power is transmitted from the engine 9 to the output shaft 23 via the planetary continuously variable transmission mechanism 24 and the multi-speed transmission mechanism 26. The power transmitted from the engine 9 to the planetary gear mechanism 29 via the first connecting member 30 is transmitted to the third connecting member 32, while a torque is generated in the second connecting member 31 to maintain one degree of freedom of rotation of the planetary gear mechanism 29. In order to stop the rotation of the second connecting member 31, during internal lockup, it is necessary to generate torque in the first hydraulic pump / motor 33 or to operate a brake mechanism 55 ( FIG. 13 ), which serves as a lockup mechanism.

[0118] In the case of Fig. 9, one degree of freedom means fixing the gear ratio of planetary gear mechanism 29 at the intersection of line Y1 and the horizontal axis (rotational speed of first sun gear / rotational speed of carrier) or the intersection of line Y1 and the vertical axis (rotational speed of second sun gear / rotational speed of carrier). Similarly, in the case of Fig. 39 described below, one degree of freedom means fixing the gear ratio of planetary gear mechanism 29 at the intersection of line Y2 and the horizontal axis (rotational speed of sun gear / rotational speed of carrier) or the intersection of line Y2 and the vertical axis (rotational speed of ring gear / rotational speed of carrier).

[0119] When performing internal lockup using the torque of the first hydraulic pump motor 33, the controller 25 controls the command signal W so that the volume of the first hydraulic pump motor 33 is 10-100%. Ｐ and outputs a command signal W so that the displacement of the second hydraulic pump motor 34 becomes 0. Ｍ When the second hydraulic pump motor 34 does not rotate, the hydraulic fluid generated by the rotation of the first hydraulic pump motor 33 does not flow through the first main line 35A and the second main line 35B. On the other hand, when internal lockup is performed by the brake mechanism 55 serving as a lockup mechanism as in the first modified example shown in FIG. 13 , the controller 25 engages the brake mechanism 55 to stop the rotation of the second connecting member 31.

[0120] Next, a case where the set pressures of the adjustable relief valves 38A, 38B are high, that is, where the adjustable relief valves 38A, 38B are in the shut-off state, will be described.

[0121] First, we will explain the case where the engine 9 (power source) rotates clockwise in the direction of the output shaft 23 (axle) and applies clockwise torque to the first connecting member 30. In this case, clockwise torque acts on the second connecting member 31, causing the first hydraulic pump / motor 33 to rotate clockwise. This is referred to as "unidirectional." At this time, hydraulic fluid flows from the first hydraulic pump / motor 33 through the first main line 35A, the second hydraulic pump / motor 34, and the second main line 35B in this order, and attempts to return to the first hydraulic pump / motor 33. However, because the volume of the second hydraulic pump / motor 34 is zero, the flow rate through the second hydraulic pump / motor 34 is very small. Therefore, the flow rate of hydraulic fluid through the first main line 35A and the second main line 35B is effectively zero. As a result, a counterclockwise torque can be applied to the second connecting member 31 even if the first hydraulic pump / motor 33 does not rotate.

[0122] On the other hand, a case will be described in which the engine 9 (power source) rotates clockwise in the direction of the output shaft 23 (axle), applying a counterclockwise torque to the first connecting member 30. In this case, a counterclockwise torque acts on the second connecting member 31, causing the first hydraulic pump / motor 33 to rotate counterclockwise. This is referred to as the "opposite direction." At this time, hydraulic fluid flows from the first hydraulic pump / motor 33 through the second main line 35B, the second hydraulic pump / motor 34, and the first main line 35A, in that order, before returning to the first hydraulic pump / motor 33. However, because the volume of the second hydraulic pump / motor 34 is zero, the flow rate through the second hydraulic pump / motor 34 is very small. Therefore, the flow rate of hydraulic fluid through the second main line 35B and the first main line 35A is effectively zero. As a result, a clockwise torque can be applied to the second connecting member 31 even if the first hydraulic pump / motor 33 does not rotate.

[0123] In this way, by shutting off both the first adjustable relief valve 38A and the second adjustable relief valve 38B, the controller 25 can set the operating state of the first hydraulic pump / motor 33 to a state in which torque (load) acts in both directions. In this case, internal lockup power transmission is possible in both the "one direction" and the "reverse direction."

[0124] Next, a case where the set pressure of the first adjustable relief valve 38A is high and the set pressure of the second adjustable relief valve 38B is low, i.e., the first adjustable relief valve 38A is in a closed state and the second adjustable relief valve 38B is in a connected state, will be described.

[0125] First, we will describe a case where the engine 9 (power source) rotates clockwise in the direction of the output shaft 23 (axle), applying clockwise torque to the first connecting member 30. In this case, clockwise torque acts on the second connecting member 31, causing the first hydraulic pump / motor 33 to rotate clockwise (one direction). At this time, hydraulic fluid flows from the first hydraulic pump / motor 33 through the first main line 35A, the second hydraulic pump / motor 34, and the second main line 35B, in this order, before returning to the first hydraulic pump / motor 33. However, because the volume of the second hydraulic pump / motor 34 is zero, the flow rate through the second hydraulic pump / motor 34 is very small. Therefore, the flow rate of hydraulic fluid through the first main line 35A and the second main line 35B is effectively zero. As a result, counterclockwise torque can be applied to the second connecting member 31 even without the first hydraulic pump / motor 33 rotating. In other words, internal lockup power transmission is possible.

[0126] On the other hand, a case will be described in which the engine 9 (power source) rotates clockwise in the direction of the output shaft 23 (axle), applying counterclockwise torque to the first connecting member 30. In this case, counterclockwise torque acts on the second connecting member 31, causing the first hydraulic pump-motor 33 to rotate counterclockwise (opposite direction). At this time, hydraulic fluid flows from the first hydraulic pump-motor 33 through the second main line 35B, the connecting line 44, the second variable relief valve 38B, and the first check valve 47 to the first main line 35A and then back to the first hydraulic pump-motor 33. As a result, no clockwise torque is generated in the second connecting member 31. In other words, the power transmission of the internal lockup is interrupted.

[0127] In this way, by placing the first adjustable relief valve 38A in a blocked state and the second adjustable relief valve 38B in a connected state, the controller 25 can change the operating state of the first hydraulic pump / motor 33 to a state in which torque (load) acts in one direction and torque (load) does not act in the opposite direction. In this case, the "opposite direction" blocks the power transmission of the internal lockup, and the "one direction" allows the power transmission of the internal lockup.

[0128] In the internal lockup state, power is transmitted from the engine 9 to the output shaft 23 via the planetary continuously variable transmission mechanism 24, the idler element 28, and the multi-speed transmission mechanism 26. In the external lockup state, power is transmitted from the engine 9 to the output shaft 23 via the external lockup mechanism (direct-coupled mechanism 27), the idler element 28, and the multi-speed transmission mechanism 26. When the "reduction ratio from the engine 9 to the idler element 28 in the internal lockup state" is compared with the "reduction ratio from the engine 9 to the idler element 28 in the external lockup state," the reduction ratio in the internal lockup state is set to be larger. For example, in the configuration shown in FIG. 11 (the configuration in Table 1 described above), when the first forward speed internal lockup Lf2 is compared with the first forward speed external lockup Lf3, the first forward speed external lockup Lf3 increases the rotation of the output shaft 23 relative to the rotation of the engine 9.

[0129] In other words, when internal lockup and external lockup are operated simultaneously, the power generated by the engine 9 is transmitted to the idler element 28 via the external lockup mechanism (direct-coupled mechanism 27), and attempts to return from the idler element 28 to the engine 9 via the planetary continuously variable transmission mechanism 24. However, because the "reduction ratio from the engine 9 to the idler element 28 in the internal lockup state" is different from the "reduction ratio from the engine 9 to the idler element 28 in the external lockup state," if left as is, a high load will be applied to the engine 9. This could cause the engine 9 to stop, and the rotation of the idler element 28 to suddenly stop, resulting in a rapid decrease in the speed of the wheel loader 1 (vehicle). For this reason, switching between internal lockup and external lockup poses a major challenge.

[0130] To solve this problem, it is necessary to interrupt the internal lockup power transmission state in the "reverse direction" and enable the internal lockup power transmission state in "one direction." Figure 18 is a characteristics diagram (time chart) showing an example of the changes over time in the rotational speed of the engine 9 (power source), the rotational speed of the second connecting member 31, the pressure of the first clutch 27C, and the pressure of the second clutch 36 when switching from "internal lockup" to "external lockup." The first clutch 27C is a clutch (direct-coupling clutch, external lockup clutch) of the external lockup mechanism (direct-coupling mechanism 27). The second clutch 36 is a clutch that connects the planetary gear mechanism 29 and the first hydraulic pump / motor 33.

[0131] From time B to time E in FIG. 18 , the controller 25 controls the variable relief valves 38A, 38B to stop rotation in one direction of the first hydraulic pump / motor 33 and allow rotation in the opposite direction. That is, by shutting off the first variable relief valve 38A and connecting the second variable relief valve 38B, the controller 25 sets the operating state of the first hydraulic pump / motor 33 to a state in which torque (load) is applied in one direction and torque (load) is not applied in the opposite direction. In this state, from time C to time E in FIG. 18 , the controller 25 engages (boosts) the first clutch 27C. This makes it possible to avoid interference in power transmission between internal lockup and external lockup. In FIG. 18 , the rotational speed of the engine 9 (power source) decreases from time C to time D (a command to reduce the rotational speed is input to the engine 9).

[0132] On the other hand, when internal lockup is performed by the brake mechanism 55 as in the first modified example shown in FIG. 13 , the controller 25 releases the brake mechanism 55 (reduces pressure) from time E to time F as shown in FIG. 19 . In this case, from time D to time I in FIG. 19 , the controller 25 controls the adjustable relief valves 38A, 38B so that the operating state of the first hydraulic pump / motor 33 stops rotation in one direction and allows rotation in the opposite direction. That is, the controller 25 shuts off the first adjustable relief valve 38A and opens the second adjustable relief valve 38B, thereby changing the operating state of the first hydraulic pump / motor 33 to a state in which torque (load) acts in one direction and torque (load) does not act in the opposite direction. In this state, from time G to time I in FIG. 19 , the controller 25 engages the first clutch 27C (increases pressure).

[0133] On the other hand, Figure 20 is a characteristic diagram (time chart) showing an example of changes over time in the rotational speed of the engine 9 (power source), the rotational speed of the second connecting member 31, the pressure of the first clutch 27C, and the pressure of the second clutch 36 when switching from "external lockup" to "internal lockup." From time B to time F in Figure 20, the controller 25 controls the variable relief valves 38A, 38B so as to stop rotation in "one direction" and allow rotation in the "opposite direction." That is, by bringing the first variable relief valve 38A into a shutoff state and the second variable relief valve 38B into a connected state, the controller 25 brings the operation state of the first hydraulic pump / motor 33 into a state in which torque (load) acts in one direction and torque (load) does not act in the opposite direction. In this state, from time D to time F in Figure 20, the controller 25 releases the first clutch 27C (reduces pressure). This makes it possible to avoid interference in power transmission between internal lockup and external lockup. In Figure 20, the rotation speed of the engine 9 (power source) increases from time E to time F (a command to increase the rotation speed is input to the engine 9).

[0134] On the other hand, when internal lockup is performed by the brake mechanism 55 as in the first modified example shown in FIG. 13 , as shown in FIG. 21 , the controller 25 controls the adjustable relief valves 38A, 38B to stop the operation of the first hydraulic pump / motor 33 from time B to time F, so as to stop rotation in one direction and allow rotation in the opposite direction. That is, the controller 25 shuts off the first adjustable relief valve 38A and opens the second adjustable relief valve 38B, thereby causing the operation of the first hydraulic pump / motor 33 to apply torque (load) in one direction and not apply torque (load) in the opposite direction. In this state, the controller 25 releases (decreases pressure) the first clutch 27C from time D to time F in FIG. 21 . Thereafter, the controller 25 engages (increases pressure) the brake mechanism 55 from time G to time H, completely transitioning to the internal lockup state.

[0135] Next, a case where the set pressure of the first adjustable relief valve 38A is low and the set pressure of the second adjustable relief valve 38B is high, i.e., the first adjustable relief valve 38A is in the open state and the second adjustable relief valve 38B is in the closed state, will be described.

[0136] First, a case will be described in which the engine 9 (power source) rotates clockwise in the direction of the output shaft 23 (axle), applying clockwise torque to the first connecting member 30. In this case, clockwise torque acts on the second connecting member 31, causing the first hydraulic pump-motor 33 to rotate clockwise (one direction). At this time, hydraulic fluid flows from the first hydraulic pump-motor 33 through the first main line 35A, the connecting line 44, the first variable relief valve 38A, and the second check valve 48 to the second main line 35B and then back to the first hydraulic pump-motor 33. As a result, no counterclockwise torque is generated in the second connecting member 31, allowing it to rotate freely. In other words, power transmission due to internal lockup is interrupted.

[0137] Now, let us consider a case where the engine 9 (power source) rotates clockwise in the direction of the output shaft 23 (axle) and applies a counterclockwise torque to the first connecting member 30. In this case, a counterclockwise torque acts on the second connecting member 31, causing the first hydraulic pump / motor 33 to rotate counterclockwise (opposite direction). At this time, hydraulic fluid flows from the first hydraulic pump / motor 33 through the second main line 35B, the second hydraulic pump / motor 34, and the first main line 35A, and then attempts to return to the first hydraulic pump / motor 33. However, because the volume of the second hydraulic pump / motor 34 is zero, the flow rate through the second hydraulic pump / motor 34 is very small. Therefore, the flow rate of hydraulic fluid through the first main line 35A and the second main line 35B is effectively zero. As a result, a counterclockwise torque can be applied to the second connecting member 31 even without the first hydraulic pump / motor 33 rotating. In other words, internal lockup power transmission is possible. In this way, by placing the first adjustable relief valve 38A in a communicating state and the second adjustable relief valve 38B in a blocked state, the controller 25 can change the operating state of the first hydraulic pump / motor 33 to a state in which torque (load) is applied in the opposite direction and torque (load) is not applied in one direction. In this case, the "opposite direction" allows power transmission of the internal lockup, and the "one direction" blocks power transmission of the internal lockup.

[0138] However, to switch between internal lockup and external lockup, it is necessary to cut off the power transmission state of the internal lockup in the "opposite direction" and enable the power transmission state of the internal lockup in "one direction." Therefore, to switch between internal lockup and external lockup, the relief pressure of the first variable relief valve 38A needs to be variable, but the relief pressure of the second variable relief valve 38B may be fixed.

[0139] Next, a case where the set pressures of both the first and second adjustable relief valves 38A and 38B are low, that is, where both the first and second adjustable relief valves 38A and 38B are in a communication state, will be described.

[0140] In this case, it is not possible to generate both clockwise and counterclockwise torque in the second connecting member 31. In other words, by bringing both the first adjustable relief valve 38A and the second adjustable relief valve 38B into a communication state, the controller 25 can set the operating state of the first hydraulic pump / motor 33 to a state in which torque (load) does not act in both directions. In this case, the internal lock-up state is released in both the "one direction" and the "reverse direction."

[0141] Next, a case where the power transmission state of the planetary type continuously variable transmission mechanism 24 is switched from "continuously variable transmission" to "internal lockup" will be described with reference to FIG.

[0142] For example, in the configuration of Table 1, switching from continuously variable transmission to internal lockup is assumed when the multi-speed transmission mechanism 26 has first forward gear and first reverse gear. Furthermore, in the configuration of Table 2, switching from continuously variable transmission to internal lockup is assumed when the multi-speed transmission mechanism 26 has first forward gear, second forward gear, third forward gear, and first reverse gear. Figure 22 is a characteristic diagram (time chart) showing an example of time variations in the rotational speed of the engine 9 (power source), the rotational speed of the second connecting member 31, the pressure of the third clutch 37, and the reduction ratio of the planetary continuously variable transmission mechanism 24 when switching from "continuously variable transmission" to "internal lockup." The third clutch 37 is a clutch provided between the second hydraulic pump / motor 34 and the idler element 28.

[0143] In the continuously variable speed state from time A to time B in FIG. 22 , the controller 25 engages the second clutch 36 and the third clutch 37 and disengages the first clutch 27C. In this state, the controller 25 adjusts the rotational speed of the first hydraulic pump / motor 33 and the rotation of the second connecting member 31 to achieve the target reduction ratio. To switch from continuously variable speed to internal lockup, the controller 25 reduces the rotational speed of the first hydraulic pump / motor 33 and stops the rotation of the first hydraulic pump / motor 33 from time B to time C in FIG. 22 . This stops the rotation of the second connecting member 31. From time C in FIG. 22 onward, the reduction ratio of the planetary continuously variable speed mechanism 24 becomes constant, and the system switches from continuously variable speed to internal lockup. The third clutch 37 is disengaged after time C to reduce power loss. For example, from time E to time F in FIG. 22 , the controller 25 disengages the third clutch 37. In FIG. 22, the rotation speed of the engine 9 (power source) decreases from time B to time C (a command to decrease the rotation speed is input to the engine 9).

[0144] On the other hand, a case where the power transmission state of the planetary continuously variable transmission mechanism 24 is switched from "continuously variable transmission" to "internal lockup" in a configuration in which internal lockup is performed by a brake mechanism 55, as in the first modified example shown in FIG. 13, will be described with reference to FIG. 23.

[0145] In the continuously variable speed state from time A to time B in FIG. 23 , the controller 25 engages the second clutch 36 and the third clutch 37 and disengages (depressurizes) the first clutch 27C and the brake mechanism 55. In this state, the controller 25 adjusts the rotational speed of the first hydraulic pump / motor 33 and the rotation of the second connecting member 31 to achieve the target reduction ratio. To switch from continuously variable speed to internal lockup, the controller 25 reduces the rotational speed of the first hydraulic pump / motor 33 and stops the rotation of the first hydraulic pump / motor 33 from time B to time C in FIG. 23 . This stops the rotation of the second connecting member 31. The brake mechanism 55 begins to engage (increase pressure) after time C in FIG. 23 , achieving a complete internal lockup state. For example, from time D to time E in FIG. 23 , the controller 25 engages (increases pressure) the brake mechanism 55. After time C in FIG. 23, the reduction ratio of the planetary type continuously variable transmission mechanism 24 becomes constant, and the transmission switches from continuously variable transmission to internal lockup.

[0146] Next, a case where the power transmission state of the planetary continuously variable transmission mechanism 24 is switched from "internal lockup" to "continuously variable speed" will be described with reference to Figure 24. Switching from internal lockup to continuously variable speed is assumed when the speed stages of the multi-speed transmission mechanism 26 are first forward speed and first reverse speed in the configuration of Table 1 described above. Also, in the configuration of Table 2 described above, switching from internal lockup to continuously variable speed is assumed when the speed stages of the multi-speed transmission mechanism 26 are first forward speed, second forward speed, third forward speed, and first reverse speed.

[0147] In the internal lockup state from time A to time D in FIG. 24 , the controller 25 engages the second clutch 36, stopping the rotation of the first hydraulic pump / motor 33 and therefore the rotation of the second connecting member 31. The first clutch 27C is disengaged. In the internal lockup state, the third clutch 37 may be engaged or disengaged. When the third clutch 37 is disengaged, the controller 25 completes the engagement of the third clutch 37 by time B in FIG. 24 in order to switch from internal lockup to continuously variable speed. Thereafter, from time D to time E in FIG. 24 , the controller 25 adjusts the rotation speed of the first hydraulic pump / motor 33 and adjusts the rotation of the second connecting member 31 to achieve the target reduction ratio. As a result, from time D in FIG. 24 onwards, the reduction ratio of the planetary continuously variable transmission mechanism 24 becomes continuously variable, and the system switches from internal lockup to continuously variable speed. In FIG. 24, the rotation speed of the engine 9 (power source) increases from time D to time E (a command to increase the rotation speed is input to the engine 9).

[0148] On the other hand, a case where the power transmission state of the planetary continuously variable transmission mechanism 24 is switched from "internal lockup" to "continuously variable transmission" in a configuration in which internal lockup is performed by the brake mechanism 55, as in the first modified example shown in FIG. 13, will be described with reference to FIG. 25.

[0149] In the internal lockup state from time A to time D in FIG. 25 , the controller 25 engages the second clutch 36, engages (increases pressure on) the brake mechanism 55, and stops the rotation of the first hydraulic pump / motor 33, thereby stopping the rotation of the second connecting member 31. The first clutch 27C is disengaged. In the internal lockup state, the third clutch 37 may be engaged or disengaged. When the third clutch 37 is disengaged, the controller 25 completes the engagement of the third clutch 37 by time B in FIG. 25 in order to switch from internal lockup to continuously variable speed. The controller 25 disengages (decreases pressure on) the brake mechanism 55 between time B and time C in FIG. 25 . Thereafter, from time D to time E in FIG. 25 , the controller 25 adjusts the rotation speed of the first hydraulic pump / motor 33 and adjusts the rotation of the second connecting member 31 to achieve the target reduction ratio. As a result, after time D in FIG. 25, the reduction ratio of the planetary continuously variable transmission mechanism 24 becomes continuously variable, and the internal lockup mechanism changes to continuously variable transmission.

[0150] Next, a case where the power transmission state of the planetary continuously variable transmission mechanism 24 is switched from "internal lockup" to "external lockup" will be described with reference to FIG.

[0151] In the configurations shown in Tables 1 and 2, for example, switching from internal lockup to external lockup is assumed when the multi-speed transmission mechanism 26 is in first, second, third, and reverse first gears. In the internal lockup state from time A to time B in FIG. 18 , the controller 25 engages the second clutch 36 and disengages the first clutch 27C. The controller 25 also controls the first hydraulic pump / motor 33 to either a "state in which rotation in both directions is stopped (a state in which torque is applied in both directions)" or a "state in which rotation in one direction is stopped and rotation in the opposite direction is allowed (a state in which torque is applied in one direction and not applied in the opposite direction)." For example, the controller 25 closes the first variable relief valve 38A and closes the second variable relief valve 38B or opens or closes the second variable relief valve 38B. This stops the second connecting member 31. In an internal lockup state, the third clutch 37 may be disengaged or engaged, but is preferably disengaged to reduce power loss.

[0152] To switch from internal lockup to external lockup, the controller 25 changes the control state of the first hydraulic pump / motor 33 from time B in FIG. 18 to a state in which rotation in one direction is stopped and rotation in the opposite direction is allowed (a state in which torque is applied in one direction and torque is not applied in the opposite direction). For example, the controller 25 sets the first variable relief valve 38A to a shutoff state and the second variable relief valve 38B to a connected state. The "one direction" refers to the rotation direction of the second connecting member 31 that is provided to transmit the power transmitted from the engine 9 to the planetary gear mechanism 29 through the first connecting member 30 to the third connecting member 32. Using the characteristic line of the rotational speed of the second connecting member 31 in FIG. 18 as an example, this is a state in which rotation in the negative direction is permitted and rotation in the positive direction is prevented. The "one direction" corresponds, for example, to the rotation direction of the engine 9. Time B in FIG. 18 may be immediately before switching from internal lockup to external lockup, or there may be no period between time A and time B, and the control state of the first hydraulic pump / motor 33 may always be "a state in which rotation in one direction is stopped and rotation in the opposite direction is free (a state in which torque is applied in one direction and no torque is applied in the opposite direction)."

[0153] However, the wheel loader 1 often travels on uneven road surfaces. For this reason, there is a problem in that fluctuations in acceleration and deceleration from the road surface are transmitted from the output shaft 23 to the engine 9, causing the engine 9 to act as a brake, resulting in a decrease in vehicle speed. For this reason, it is also preferable to perform the following control when the internal lockup state is in effect. That is, when the operator depresses the accelerator pedal 8A and power is being transmitted in a direction in which the wheel loader 1 is accelerating, the control state of the first hydraulic pump / motor 33 is always set to a "state in which rotation in one direction is stopped and rotation in the opposite direction is allowed (a state in which torque is applied in one direction and torque is not applied in the opposite direction)." On the other hand, when the operator releases the accelerator pedal 8A and the engine 9 acts as a brake, and it is necessary to decelerate the wheel loader 1, the control state of the first hydraulic pump / motor 33 is set to a "state in which rotation in the opposite direction is stopped and rotation in one direction is allowed (a state in which torque is applied in the opposite direction and torque is not applied in one direction)."

[0154] The controller 25 starts engaging the first clutch 27C from time C in FIG. 18 and completes the engagement at time E. As a result, an external lock-up state occurs from time E onwards. From time E in FIG. 18 onwards, the controller 25 maintains the control state of the first hydraulic pump / motor 33 in a "state in which rotation in one direction is stopped and rotation in the opposite direction is allowed (a state in which torque is applied in one direction and torque is not applied in the opposite direction)", or switches the control state of the first hydraulic pump / motor 33 to a "state in which rotation in both directions is allowed (a state in which torque is not applied in both directions)". For example, the controller 25 sets the first variable relief valve 38A in a blocked state or a connected state, and sets the second variable relief valve 38B in a connected state. From time G in FIG. 18 onwards, the controller 25 switches the control state of the first hydraulic pump / motor 33 to a "state in which rotation in both directions is allowed (a state in which torque is not applied in both directions)" or a "state in which rotation in one direction is allowed and rotation in the opposite direction is stopped (a state in which torque is not applied in one direction and torque is applied in the opposite direction)". For example, the controller 25 places the first adjustable relief valve 38A in a communicating state and the second adjustable relief valve 38B in a blocking or communicating state. The second clutch 36 can be released from time E in Figure 18 onwards. In an external lockup state, the second clutch 36 may be released or engaged, but is preferably released to reduce power loss.

[0155] On the other hand, a case where the power transmission state of the planetary continuously variable transmission mechanism 24 is switched from "internal lockup" to "external lockup" in a configuration in which internal lockup is performed by the brake mechanism 55, as in the first modified example shown in FIG. 13, will be described with reference to FIG. 19.

[0156] In the internal lockup state from time A to time B in Figure 19, the controller 25 stops the rotation of the second connecting member 31 by engaging (increasing pressure) the brake mechanism 55. The first clutch 27C is disengaged. In the internal lockup state, the third clutch 37 may be disengaged or engaged, but is preferably disengaged to reduce power loss. The second clutch 36 may be either disengaged or engaged. To switch from internal lockup to external lockup, the controller 25 begins engaging the second clutch 36 from time B in Figure 19 and completes engagement at time C. This operation is unnecessary if the second clutch 36 has been engaged before time A.

[0157] From time D in Figure 19, the controller 25 changes the control state of the first hydraulic pump / motor 33 to a state in which rotation in one direction is stopped and rotation in the opposite direction is allowed (a state in which torque is applied in one direction and not in the opposite direction). Thereafter, the controller 25 releases (reduces pressure in) the brake mechanism 55 between time E and time F in Figure 19. From time G in Figure 19, the controller 25 starts to apply the first clutch 27C, and completes the application at time I. As a result, from time I onwards, an external lockup state is established.

[0158] After time I in FIG. 19 , the second clutch 36 can be released. In an external lockup state, the second clutch 36 may be released or engaged, but is preferably released to reduce power loss. In FIG. 19 , the second clutch 36 is released (pressure reduced) from time J to time K. After time I in FIG. 19 , the controller 25 maintains the control state of the first hydraulic pump / motor 33 in either a "state in which rotation is stopped in one direction and free rotation in the opposite direction (state in which torque is applied in one direction and torque is not applied in the opposite direction)" or a "state in which free rotation in both directions is possible (state in which torque is not applied in both directions)." After time K in FIG. 19 , the control state of the first hydraulic pump / motor 33 is changed to a "state in which free rotation in one direction and rotation is stopped in the opposite direction (state in which torque is not applied in one direction and torque is applied in the opposite direction)" or a "state in which free rotation in both directions is possible (state in which torque is not applied in both directions)."

[0159] Next, a case where the power transmission state of the planetary continuously variable transmission mechanism 24 is switched from "external lockup" to "internal lockup" will be described with reference to FIG.

[0160] In the configurations of Tables 1 and 2 described above, for example, switching from external lockup to internal lockup is assumed when the speed stages of the multi-speed transmission mechanism 26 are forward first, forward second, forward third, and reverse first. In the external lockup state from time A to time B in Figure 20, the controller 25 engages the first clutch 27C and disengages the second clutch 36. The controller 25 also sets the control state of the first hydraulic pump / motor 33 to a state in which it can rotate freely in both directions (a state in which torque is not applied in both directions). In the external lockup state, the second clutch 36 and the third clutch 37 may be engaged or disengaged, but are preferably disengaged to reduce power loss.

[0161] To switch from external lockup to internal lockup, the controller 25 sets the control state of the first hydraulic pump / motor 33 to a state in which rotation in one direction is stopped and rotation in the opposite direction is allowed (a state in which torque is applied in one direction and torque is not applied in the opposite direction) from time B to time F in FIG. 20 . In other words, in terms of the characteristic line of the rotational speed of the second connecting member 31 in FIG. 20 , this is a state in which rotation in the negative direction is allowed and rotation in the positive direction is blocked. The controller 25 completes the engagement of the second clutch 36 between time B and time C. As a result, the second connecting member 31 rotates integrally with the first hydraulic pump / motor 33. Note that time B in FIG. 20 may be immediately before switching from external lockup to internal lockup, or the second clutch 36 may remain engaged at all times without being present between time A and time C.

[0162] The controller 25 starts disengaging the first clutch 27C from time D in Figure 20 and completes the disengagement at time F. This completes the switch from the external lock-up state to the internal lock-up state. After time F in Figure 20, the controller 25 maintains the control state of the first hydraulic pump / motor 33 in a state where rotation in one direction is stopped and rotation in the opposite direction is free (a state where torque is applied in one direction and no torque is applied in the opposite direction), or switches it to a state where rotation in both directions is stopped (a state where torque is applied in both directions).

[0163] On the other hand, a case where the power transmission state of the planetary continuously variable transmission mechanism 24 is switched from "external lockup" to "internal lockup" in a configuration in which internal lockup is performed by the brake mechanism 55, as in the first modified example shown in FIG. 13, will be described with reference to FIG. 21.

[0164] In the external lockup state from time A to time B in Figure 21, the controller 25 engages the first clutch 27C, disengages the second clutch 36, and disengages (reduces pressure) the brake mechanism 55. The controller 25 also sets the control state of the first hydraulic pump / motor 33 to a "state in which it can rotate freely in both directions (state in which torque is not applied in both directions)." In the external lockup state, the second clutch 36 and the third clutch 37 may be engaged or disengaged, but are preferably disengaged to reduce power loss.

[0165] To switch from external lockup to internal lockup, the controller 25 sets the control state of the first hydraulic pump / motor 33 to a state in which rotation in one direction is stopped and rotation in the opposite direction is allowed (a state in which torque is applied in one direction and torque is not applied in the opposite direction) from time B to time F in FIG. 21 . In other words, in terms of the characteristic line of the rotational speed of the second connecting member 31 in FIG. 21 , this is a state in which rotation in the negative direction is allowed and rotation in the positive direction is blocked. The controller 25 completes the engagement of the second clutch 36 between time B and time C. As a result, the second connecting member 31 rotates integrally with the first hydraulic pump / motor 33. Note that time B in FIG. 21 may be immediately before switching from external lockup to internal lockup, or the second clutch 36 may remain engaged at all times without being present between time A and time C.

[0166] The controller 25 starts to release the first clutch 27C from time D in Figure 21 and completes the release at time F. At time F in Figure 21, the controller 25 maintains the control state of the first hydraulic pump / motor 33 in a state where rotation is stopped in one direction and free rotation in the opposite direction is possible (a state where torque is applied in one direction and no torque is applied in the opposite direction), or switches the control state of the first hydraulic pump / motor 33 to a state where rotation is stopped in both directions (a state where torque is applied in both directions). From time G to time H in Figure 21, the controller 25 engages (increases pressure in) the brake mechanism 55 to completely stop rotation of the second connecting member 31. This completes the switch from the external lock-up state to the internal lock-up state. After time H in Figure 21, the control state of the first hydraulic pump / motor 33 may be a state where rotation is stopped in both directions (a state where torque is applied in both directions) or a state where rotation is free in both directions (a state where torque is not applied in both directions). For example, the controller 25 sets the first adjustable relief valve 38A and the second adjustable relief valve 38B to a blocked state or a communicating state.

[0167] Note that Figures 18 to 25 and Figures 33 and 34 described below show, as an example, gear changes (switching) while the vehicle speed is maintained constant, but this is not limiting, and gear changes (switching) may also be performed while decelerating or accelerating.

[0168] Next, a description will be given of speed changes (switching) by the multi-speed change mechanism 26. As shown in Table 4 above, the multi-speed change mechanism 26 can change (switch) speeds to first forward speed, second forward speed, third forward speed, and first reverse speed.

[0169] The gear changes (switching) are assumed to be from forward first gear to forward second gear, from forward first gear to forward third gear, from forward first gear to reverse first gear, from forward second gear to forward first gear, from forward second gear to forward third gear, from forward second gear to reverse first gear, from forward third gear to forward second gear, from forward third gear to forward first gear, from forward third gear to reverse first gear, from reverse first gear to forward first gear, from reverse first gear to forward second gear, and from reverse first gear to forward third gear. The gear changes of the multi-speed transmission mechanism 26, i.e., the switching of the speed stages, are performed by engaging and disengaging the forward first gear clutch 69, reverse first gear clutch 70, forward second gear clutch 75, and forward third gear clutch 76 shown in Table 4.

[0170] 26 is a characteristic diagram (time chart) showing an example of changes over time in the pressure of the primary clutch (a clutch that is switched from engagement to release), the pressure of the secondary clutch (a clutch that is switched from release to engagement), and the pressure of the asymmetric clutch (a clutch that remains released) when a gear change (switching between speed stages) is performed in the multi-stage transmission mechanism 26. When a gear change is performed in the multi-stage transmission mechanism 26, the clutch that is engaged before the gear change is referred to as the primary clutch, the clutch that is engaged after the gear change is referred to as the secondary clutch, and the clutch that is released both before and after the gear change is referred to as the asymmetric clutch.

[0171] For example, when shifting from first forward speed to second forward speed, the first forward speed clutch 69 serves as the primary clutch, the second forward speed clutch 75 serves as the secondary clutch, and the first reverse speed clutch 70 and the third forward speed clutch 76 serve as the asymmetric clutches. Between time A and time B in FIG. 26 (i.e., before the shift), the primary clutch is engaged and the secondary clutch is disengaged. The controller 25 reduces the pressure of the primary clutch from time B in FIG. 26 . The controller 25 completely reduces the pressure of the primary clutch at time D in FIG. 26 , thereby completing the release of the primary clutch. The controller 25 increases the pressure of the secondary clutch from time C in FIG. 26 . The controller 25 completely increases the pressure of the secondary clutch at time E in FIG. 26 , thereby completing the release of the primary clutch. Thus, the shift of the multi-speed transmission mechanism 26 is completed at time E in FIG. 26 . The asymmetric clutch is always disengaged before and after the shift.

[0172] Next, a description will be given of simultaneous switching of the planetary continuously variable transmission mechanism 24 and the multi-speed change mechanism 26. First, a case where the planetary continuously variable transmission mechanism 24 is switched from "internal lockup" to "external lockup" and the multi-speed change mechanism 26 is also shifted (switched) will be described with reference to FIG.

[0173] In the configurations of Tables 1 and 2, for example, this shift (switching) is expected to take the following steps: from forward first gear internal lockup to forward second gear external lockup, from forward first gear internal lockup to forward third gear external lockup, from forward second gear internal lockup to forward third gear external lockup, from forward second gear internal lockup to forward first gear external lockup, from forward third gear internal lockup to forward second gear external lockup, and from forward third gear internal lockup to forward first gear external lockup. In other words, this shift (switching) does not involve switching the power transmission states shown in Tables 1 and 2 in the order shown in the tables, but rather corresponds to a case where a shift is performed by skipping some steps (jump-step shift). Figure 27 is a characteristic diagram (time chart) showing an example of the change over time in the pressure of the first clutch 27C of the planetary continuously variable transmission mechanism 24, the pressure of the second clutch 36, the pressure of the primary clutch (clutch that switches from engagement to release) of the multi-stage transmission mechanism 26, the pressure of the secondary clutch (clutch that switches from release to engagement) of the multi-stage transmission mechanism 26, and the rotational speed of the second connecting member 31 during this gear change (switching).

[0174] In the internal lockup state from time A to time B in Figure 27, the controller 25 engages the second clutch 36, disengages the first clutch 27C, engages the primary clutch, and disengages the secondary clutch. The controller 25 also controls the first hydraulic pump / motor 33 to either a "state in which rotation in both directions is stopped (a state in which torque is applied in both directions)" or a "state in which rotation in one direction is stopped but rotation in the opposite direction is allowed (a state in which torque is applied in one direction but not the opposite direction)." This stops the second connecting member 31. In the internal lockup state, the third clutch 37 may be either disengaged or engaged, but is preferably disengaged to reduce power loss.

[0175] To switch from internal lockup to external lockup, the controller 25 changes the control state of the first hydraulic pump / motor 33 to a state in which rotation in one direction is stopped and free rotation in the opposite direction is permitted (a state in which torque is applied in one direction and torque is not applied in the opposite direction) from time B in FIG. 27 . The controller 25 starts engaging the first clutch 27C from time C in FIG. 27 and completes engagement at time G. As a result, the second connecting member 31 begins to rotate in the opposite direction, and from time G onwards, the external lockup state is reached. Meanwhile, the controller 25 starts releasing the primary clutch from time D in FIG. 27 and completes release at time F. That is, the controller 25 starts reducing the pressure of the primary clutch from time D and completes the release at time F. Furthermore, the controller 25 starts engaging the secondary clutch from time E in FIG. 27 and completes engagement at time H. That is, the controller 25 starts increasing the pressure of the secondary clutch from time E and completes the engagement at time H.

[0176] Thereafter, the controller 25 disengages the second clutch 36 from time I to time J in FIG. 27. That is, the controller 25 reduces the pressure of the second clutch 36 from time I to time J. After time H in FIG. 27, the controller 25 switches the control state of the first hydraulic pump / motor 33 to a state in which the first hydraulic pump / motor 33 can rotate freely in one direction and is stopped from rotating in the opposite direction (a state in which torque is not applied in one direction and torque is applied in the opposite direction) or a state in which the first hydraulic pump / motor 33 can rotate freely in both directions (a state in which torque is not applied in both directions). The second clutch 36 can be disengaged after time H in FIG. 27. The second clutch 36 may be either engaged or disengaged, but is preferably disengaged to reduce power loss.

[0177] Although not shown, the pressure of the non-target clutches (i.e., clutches other than the primary clutch and secondary clutch) of the multi-speed transmission mechanism 26 is always reduced to zero (the non-target clutches are disengaged) before and after the gear shift (switching). In this way, when the planetary continuously variable transmission mechanism 24 is switched from "internal lockup" to "external lockup" and the multi-speed transmission mechanism 26 is also changed (switched), the switching of the planetary continuously variable transmission mechanism 24 from "internal lockup" to "external lockup" begins prior to the gear shift (switching) of the multi-speed transmission mechanism 26. In other words, the increase in pressure (engagement) of the first clutch 27C begins prior to the start of the decrease in pressure (disengagement) of the primary clutch and the increase in pressure (engagement) of the secondary clutch.

[0178] On the other hand, a case where, as in the first modified example shown in FIG. 13 , an internal lockup is performed by the brake mechanism 55, the power transmission state of the planetary continuously variable transmission mechanism 24 is switched from “internal lockup” to “external lockup”, and the multi-speed transmission mechanism 26 is also shifted (switched) will be described with reference to FIG. 28 .

[0179] In the internal lockup state from time A to time B in Figure 28, the controller 25 stops the rotation of the second connecting member 31 by engaging (increasing pressure) the brake mechanism 55. The first clutch 27C is disengaged. In the internal lockup state, the third clutch 37 may be disengaged or engaged, but is preferably disengaged to reduce power loss. The second clutch 36 may be either disengaged or engaged. The control state of the first hydraulic pump / motor 33 may be either a "state in which rotation in both directions is stopped (state in which torque is applied in both directions)" or a "state in which free rotation in both directions is possible (state in which torque is not applied in both directions)."

[0180] To switch from internal lockup to external lockup, the controller 25 starts engaging (pressure increase) the second clutch 36 from time B in FIG. 28 and completes the engagement (pressure increase) at time C. Thereafter, from time D in FIG. 28 , the controller 25 switches the control state of the first hydraulic pump / motor 33 to a state in which rotation in one direction is stopped and free rotation in the opposite direction is permitted (a state in which torque is applied in one direction and torque is not applied in the opposite direction). The controller 25 releases (decreases pressure) the brake mechanism 55 from time E to time F in FIG. 28 . The controller 25 starts engaging the first clutch 27C from time G in FIG. 28 and completes the engagement at time J. As a result, the second connecting member 31 begins to rotate in the opposite direction, and the external lockup state is established from time J onwards. Meanwhile, the controller 25 starts releasing the primary clutch from time H in FIG. 28 and completes the release at time K. That is, the controller 25 starts reducing the pressure in the primary clutch from time H and completes it at time K. Also, the controller 25 starts engaging the secondary clutch from time I in Figure 28 and completes the engagement at time L. That is, the controller 25 starts increasing the pressure in the secondary clutch from time I and completes it at time L.

[0181] After time L in FIG. 28 , the controller 25 switches the control state of the first hydraulic pump / motor 33 to a state in which the first hydraulic pump / motor 33 can rotate freely in one direction and is stopped from rotating in the opposite direction (a state in which torque is not applied in one direction and torque is applied in the opposite direction) or a state in which the first hydraulic pump / motor 33 can rotate freely in both directions (a state in which torque is not applied in both directions). The second clutch 36 can be disengaged after time L in FIG. 28 . In FIG. 28 , the second clutch 36 is disengaged from time M to time N. That is, the controller 25 reduces the pressure of the second clutch 36 from time M to time N. The second clutch 36 may be disengaged or engaged, but is preferably disengaged to reduce power loss.

[0182] Although not shown, the pressure of the non-target clutches (i.e., clutches other than the primary clutch and secondary clutch) of the multi-speed transmission mechanism 26 is always reduced to zero (the non-target clutches are disengaged) before and after the gear shift (switching). In this way, when the planetary continuously variable transmission mechanism 24 is switched from "internal lockup" to "external lockup" and the multi-speed transmission mechanism 26 is also changed (switched), the switching of the planetary continuously variable transmission mechanism 24 from "internal lockup" to "external lockup" begins prior to the gear shift (switching) of the multi-speed transmission mechanism 26. In other words, the increase in pressure (engagement) of the first clutch 27C begins prior to the start of the decrease in pressure (disengagement) of the primary clutch and the increase in pressure (engagement) of the secondary clutch.

[0183] Next, a case where the planetary continuously variable transmission mechanism 24 is switched from "external lockup" to "internal lockup" and the multi-speed transmission mechanism 26 is also shifted (switched) will be described with reference to FIG.

[0184] In the configurations of Tables 1 and 2 above, for example, this gear change (switching) can be envisioned as a gear change from forward first gear external lockup to forward second gear internal lockup, a gear change from forward first gear external lockup to forward third gear internal lockup, a gear change from forward second gear external lockup to forward third gear internal lockup, a gear change from forward second gear external lockup to forward first gear internal lockup, a gear change from forward third gear external lockup to forward second gear internal lockup, and a gear change from forward third gear external lockup to forward first gear internal lockup.

[0185] In the external lockup state from time A to time B in Figure 29, the controller 25 engages the first clutch 27C, disengages the second clutch 36, engages the primary clutch, and disengages the secondary clutch. The controller 25 also controls the first hydraulic pump / motor 33 to either a "state in which it can rotate freely in one direction and is stopped from rotating in the opposite direction (a state in which torque is not applied in one direction and torque is applied in the opposite direction)" or a "state in which it can rotate freely in both directions (a state in which torque is not applied in both directions)." In the external lockup state, the second clutch 36 and the third clutch 37 may be either disengaged or engaged, but are preferably disengaged to reduce power loss.

[0186] To switch from external lockup to internal lockup, the controller 25 sets the control state of the first hydraulic pump / motor 33 to a state in which rotation in one direction is stopped and rotation in the opposite direction is allowed (a state in which torque is applied in one direction and torque is not applied in the opposite direction) from time B to time I in Figure 29. The controller 25 completes the engagement of the second clutch 36 between time B and time C. This causes the second connecting member 31 to rotate integrally with the first hydraulic pump / motor 33. Note that time B in Figure 29 may be immediately before switching from external lockup to internal lockup, or the second clutch 36 may remain engaged at all times without being present between time A and time C.

[0187] On the other hand, the controller 25 reduces the pressure of the primary clutch from time D to time F in Figure 29 to disengage the primary clutch. Also, the controller 25 increases the pressure of the secondary clutch from time E to time H in Figure 29 to engage the secondary clutch. The first clutch 27C starts to disengage from time G in Figure 29 and completes the disengagement at time I. This stops the rotation of the second connecting member 31. From time I in Figure 29, the controller 25 changes the control state of the first hydraulic pump / motor 33 to a state in which rotation is stopped in one direction and rotation is free in the opposite direction (a state in which torque is applied in one direction and not in the opposite direction) or a state in which rotation is stopped in both directions (a state in which torque is applied in both directions). This completes the gear change (switching).

[0188] Although not shown, the pressure of the non-target clutches (i.e., clutches other than the primary clutch and secondary clutch) of the multi-speed transmission mechanism 26 is always reduced to zero (the non-target clutches are disengaged) before and after the gear shift (switching). In this way, when the planetary continuously variable transmission mechanism 24 is switched from "external lockup" to "internal lockup" and the multi-speed transmission mechanism 26 is also changed (switched), the gear shift (switching) of the multi-speed transmission mechanism 26 begins before the planetary continuously variable transmission mechanism 24 is switched from "external lockup" to "internal lockup." In other words, before the pressure reduction (release) of the first clutch 27C begins, the pressure reduction (release) of the primary clutch and the pressure increase (engagement) of the secondary clutch begin.

[0189] On the other hand, a case where, as in the first modified example shown in FIG. 13 , an internal lockup is performed by the brake mechanism 55, the power transmission state of the planetary continuously variable transmission mechanism 24 is switched from “external lockup” to “internal lockup”, and the multi-speed transmission mechanism 26 is also shifted (switched) will be described with reference to FIG. 30 .

[0190] In the external lockup state from time A to time B in Figure 30, the controller 25 engages the first clutch 27C, disengages the second clutch 36, disengages the brake mechanism 55, engages the primary clutch, and disengages the secondary clutch. The controller 25 also controls the first hydraulic pump / motor 33 to either a "state in which it can rotate freely in one direction and is stopped from rotating in the opposite direction (a state in which torque is not applied in one direction and torque is applied in the opposite direction)" or a "state in which it can rotate freely in both directions (a state in which torque is not applied in both directions)." In the external lockup state, the second clutch 36 and the third clutch 37 may be either disengaged or engaged, but are preferably disengaged to reduce power loss.

[0191] To switch from external lockup to internal lockup, the controller 25 sets the control state of the first hydraulic pump / motor 33 to a state in which rotation in one direction is stopped and rotation in the opposite direction is allowed (a state in which torque is applied in one direction and torque is not applied in the opposite direction) from time B to time I in Figure 30. The controller 25 completes the engagement of the second clutch 36 between time B and time C. This causes the second connecting member 31 to rotate integrally with the first hydraulic pump / motor 33. Note that time B in Figure 30 may be immediately before switching from external lockup to internal lockup, or the second clutch 36 may remain engaged at all times without being present between time A and time C.

[0192] Meanwhile, the controller 25 reduces the pressure of the primary clutch from time D to time F in FIG. 30 to disengage the primary clutch. The controller 25 also increases the pressure of the secondary clutch from time E to time H in FIG. 30 to engage the secondary clutch. The first clutch 27C begins to disengage from time G in FIG. 30 and completes the disengagement at time I. This stops the rotation of the second connecting member 31. From time I in FIG. 30, the controller 25 changes the control state of the first hydraulic pump / motor 33 to a "state in which rotation in one direction is stopped and rotation in the opposite direction is free (a state in which torque is applied in one direction and not in the opposite direction)" or a "state in which rotation in both directions is stopped (a state in which torque is applied in both directions)." This completes the gear shift (switching). Thereafter, the controller 25 increases the pressure of the brake mechanism 55 from time J to time K in FIG. 30 to engage the brake mechanism 55. After time K in Figure 30, the control state of the first hydraulic pump motor 33 may be either "a state in which rotation in both directions is stopped (a state in which torque is applied in both directions)" or "a state in which rotation can be freely performed in both directions (a state in which torque is not applied in both directions)."

[0193] Although not shown, the pressure of the non-target clutches (i.e., clutches other than the primary clutch and secondary clutch) of the multi-speed transmission mechanism 26 is always reduced to zero (the non-target clutches are disengaged) before and after the gear shift (switching). In this way, when the planetary continuously variable transmission mechanism 24 is switched from "external lockup" to "internal lockup" and the multi-speed transmission mechanism 26 is also changed (switched), the gear shift (switching) of the multi-speed transmission mechanism 26 begins before the planetary continuously variable transmission mechanism 24 is switched from "external lockup" to "internal lockup." In other words, before the pressure reduction (release) of the first clutch 27C begins, the pressure reduction (release) of the primary clutch and the pressure increase (engagement) of the secondary clutch begin.

[0194] Next, with reference to FIG. 31 , the reason why the switching of the planetary continuously variable transmission mechanism 24 is initiated prior to the shifting (switching) of the multi-stage transmission mechanism 26 when the planetary continuously variable transmission mechanism 24 is switched from “internal lockup” to “external lockup” and the multi-stage transmission mechanism 26 is also changed (switched) will be described.

[0195] The vertical axis in Figure 31 corresponds to the reduction ratio from the engine 9, which serves as the power source, to the output shaft 23, and the horizontal axis corresponds to time. Furthermore, characteristic lines A, B, C, and D in Figure 31 represent four types of gear ratio transitions, each with different timings for switching from internal lockup to external lockup and for shifting (switching) the multi-speed transmission mechanism 26. Characteristic line A in Figure 31 represents a case in which the multi-speed transmission mechanism 26 is downshifted in an internal lockup state and then switched from internal lockup to external lockup. In this case, the reduction ratio increases once and then decreases. This type of shift is inappropriate because it is likely to significantly disrupt the power transmission from the engine 9, which serves as the power source, to the output shaft 23.

[0196] Characteristic line B in FIG. 31 shows the case where the multi-speed transmission mechanism 26 is downshifted after switching from internal lockup to external lockup. In this case, the reduction ratio decreases once and then increases. This type of shift is appropriate because it reduces the disruption of power transmission from the engine 9, which serves as the power source, to the output shaft 23. In other words, although characteristic line A and characteristic line B ultimately result in the same reduction ratio, the degree of power disruption is significantly different. For this reason, when switching from internal lockup to external lockup and simultaneously shifting (switching) the multi-speed transmission mechanism 26, it is important to start the switch from internal lockup to external lockup before the shift (switching) of the multi-speed transmission mechanism 26.

[0197] Characteristic line C in FIG. 31 shows a case where the multi-speed transmission mechanism 26 is switched from internal lockup to external lockup and then upshifted. In this case, the reduction ratio continuously decreases. This type of shift is appropriate because it minimizes the disruption of power transmission from the engine 9, which serves as the power source, to the output shaft 23. Characteristic line D in FIG. 31 shows a case where the multi-speed transmission mechanism 26 is upshifted in an internal lockup state and then switched from internal lockup to external lockup. In this case, too, the reduction ratio continuously decreases. This type of shift is appropriate because it minimizes the disruption of power transmission from the engine 9, which serves as the power source, to the output shaft 23. Note that either characteristic line C or characteristic line D may be selected because the final shift results in the same reduction ratio.

[0198] Next, when the planetary continuously variable transmission mechanism 24 is switched from "external lockup" to "internal lockup" and the multi-speed change mechanism 26 is also changed (switched), the reason why the speed change (switching) of the multi-speed change mechanism 26 is started prior to the switching of the planetary continuously variable transmission mechanism 24 will be explained with reference to FIG. 32 .

[0199] The vertical axis in Figure 32 corresponds to the reduction ratio from the engine 9, which serves as the power source, to the output shaft 23, and the horizontal axis corresponds to time. Furthermore, characteristic lines A, B, C, and D in Figure 32 represent four transitions in the gear ratio, each with different timings for switching from external lockup to internal lockup and for shifting (switching) the multi-speed transmission mechanism 26. Characteristic line A in Figure 32 represents a case in which the multi-speed transmission mechanism 26 is downshifted in an external lockup state and then switched from external lockup to internal lockup. In this case, the reduction ratio increases in stages. Although this type of shifting is likely to significantly disrupt the power transmission from the engine 9, which serves as the power source, to the output shaft 23, it is appropriate because there is no way to avoid this.

[0200] Characteristic line B in FIG. 32 shows a case where the lockup is switched from external to internal and then the multi-speed transmission mechanism 26 is downshifted. In this case, the reduction ratio increases in stages. Although this type of shifting is likely to cause a significant interruption in the power transmission from the engine 9 (the power source) to the output shaft 23, it is appropriate because there is no way to avoid this. Note that either characteristic line A or characteristic line B can be selected because the final shift to the same reduction ratio is achieved. Characteristic line C in FIG. 32 shows a case where the lockup is switched from external to internal and then the multi-speed transmission mechanism 26 is upshifted. In this case, the reduction ratio increases once and then decreases. This type of shifting is inappropriate because it is likely to cause a significant interruption in the power transmission from the engine 9 (the power source) to the output shaft 23.

[0201] Characteristic line D in FIG. 32 shows the case where the multi-speed transmission mechanism 26 is upshifted in an external lockup state and then switched from external lockup to internal lockup. In this case, the reduction ratio decreases and then increases. This type of shift is appropriate because it causes little disruption to the power transmission from the engine 9, which serves as the power source, to the output shaft 23. In other words, although characteristic line C and characteristic line D ultimately result in the same reduction ratio, the degree of power disruption is significantly different. For this reason, when switching from external lockup to internal lockup and upshifting the multi-speed transmission mechanism 26, it is important to start the shift (switching) of the multi-speed transmission mechanism 26 before switching from internal lockup to external lockup.

[0202] Next, a case where the planetary continuously variable transmission mechanism 24 is switched from "continuously variable transmission" to "external lockup" and the multi-speed transmission mechanism 26 is also changed (switched) will be described with reference to FIG.

[0203] This shift (switching) can be, for example, from forward third infinitely variable speed to forward second external lockup, from forward third infinitely variable speed to forward first external lockup, or from forward second infinitely variable speed to forward first external lockup, according to the configuration of Table 2. Figure 33 is a characteristic diagram (time chart) showing an example of the time changes in the reduction ratio from engine 9, which serves as the power source, to output shaft 23, the pressure of first clutch 27C (lockup clutch) of planetary continuously variable transmission mechanism 24, the pressure of second clutch 36, the pressure of the primary clutch (clutch that switches from engagement to release) of multi-stage transmission mechanism 26, and the pressure of the secondary clutch (clutch that switches from release to engagement) of multi-stage transmission mechanism 26, during this shift.

[0204] In the continuously variable transmission state from time A to time B in FIG. 33 , the controller 25 engages the second clutch 36 and the third clutch 37 and disengages the first clutch 27C. In this state, the controller 25 adjusts the rotational speed of the first hydraulic pump / motor 33 and adjusts the rotation of the second connecting member 31 so as to achieve a target reduction ratio. To switch from this continuously variable transmission state, the controller 25 adjusts the reduction ratio from the engine 9 to the output shaft 23 via the planetary continuously variable transmission mechanism 24 by adjusting the rotational speed of the first hydraulic pump / motor 33. In this case, the reduction ratio from the engine 9 to the output shaft 23 via the planetary continuously variable transmission mechanism 24 in the state before the multi-speed transmission mechanism 26 is switched is made to approach the reduction ratio from the engine 9 to the output shaft 23 via the direct-coupled mechanism 27 in the state after the multi-speed transmission mechanism 26 is switched. In this case, the reduction ratios do not need to be exactly the same; they need only be close. Conversely, it is not appropriate for the reduction ratio to exceed the limit. This operation of bringing the reduction ratio closer together is carried out between time B and time C in FIG.

[0205] Note that the solid line S of the reduction ratio in Figure 33 indicates a case where the reduction ratio from the engine 9 to the output shaft 23 via the planetary continuously variable transmission mechanism 24 in a state before the switching of the multi-stage transmission mechanism 26 is smaller than the reduction ratio from the engine 9 to the output shaft 23 via the direct-coupled mechanism 27 in a state after the switching of the multi-stage transmission mechanism 26. Conversely, there are also cases where this relationship of speed change ratios is larger. The dashed line B of the reduction ratio in Figure 33 indicates a case where the reduction ratio from the engine 9 to the output shaft 23 via the planetary continuously variable transmission mechanism 24 in a state before the switching of the multi-stage transmission mechanism 26 is larger than the reduction ratio from the engine 9 to the output shaft 23 via the direct-coupled mechanism 27 in a state after the switching of the multi-stage transmission mechanism 26.

[0206] From time D in FIG. 33 , the controller 25 changes the control state of the first hydraulic pump / motor 33 to a state in which torque is applied in one direction and torque is not applied in the opposite direction. This makes it possible to prepare for switching from continuously variable transmission to external lockup simply by increasing the pressure of the first clutch 27C. The controller 25 increases the pressure of the first clutch 27C from time D in FIG. 33 and completes engagement of the first clutch 27C at time H. The controller 25 reduces the pressure of the primary clutch from time E in FIG. 33 and completes release of the primary clutch at time G. The controller 25 also increases the pressure of the secondary clutch from time F in FIG. 33 and completes engagement of the secondary clutch at time I. After time I in FIG. 33 , the second clutch 36 and the third clutch 37 may be released. In FIG. 33, the pressure of the second clutch 36 (and the third clutch 37) is reduced from time J, and at time K, the release of the second clutch 36 (and the third clutch 37) is completed.

[0207] After time K in Figure 33, the control state of the first hydraulic pump / motor 33 may be either "a state in which it can rotate freely in both directions (a state in which torque is not applied in both directions)" or "a state in which torque is applied in one direction but not in the opposite direction." In this way, when switching the planetary continuously variable transmission mechanism 24 from "continuously variable transmission" to "external lockup" and also changing (switching) the speed of the multi-stage transmission mechanism 26, the gear ratio of the planetary continuously variable transmission mechanism 24 is first changed to approach the reduction ratio after the completion of the gear change of the multi-stage transmission mechanism 26. Thereafter, the switching of the planetary continuously variable transmission mechanism 24 from "continuously variable transmission" to "external lockup" is initiated, and then the gear change (switching) of the multi-stage transmission mechanism 26 is initiated. In other words, the first clutch 27C is started to be increased (engaged), and then the primary clutch is decreased (disengaged) and the secondary clutch is increased (engaged).

[0208] Between time D and time K in Figure 33, the controller 25 sets the control state of the first hydraulic pump / motor 33 to a state in which a torque load is applied in one direction and no torque load is applied in the opposite direction. In other words, the controller 25 performs control based on the direction of torque application, regardless of the rotational direction of the first hydraulic pump / motor 33. As shown in Figure 35, the first hydraulic pump / motor 33 has four states: a state in which it rotates in one direction and transmits torque in one direction, a state in which it rotates in one direction and transmits torque in the opposite direction, a state in which it rotates in the opposite direction and transmits torque in one direction, and a state in which it rotates in the opposite direction and transmits torque in the opposite direction.

[0209] The first hydraulic pump / motor 33 is in a state in which it rotates in one direction and transmits torque in one direction between time D and time K in Figure 33. With this type of speed change, there is only a slight change in the rotational speed of the engine 9, which serves as the power source, while the clutches (first clutch 27C, second clutch 36, primary clutch, and secondary clutch) are being switched, which shortens the time required to switch the clutches and reduces the change in output torque from the output shaft 23. This improves the operability of the wheel loader 1 and improves the ride comfort.

[0210] Next, a case where the planetary continuously variable transmission mechanism 24 is switched from "external lockup" to "continuously variable transmission" and the multi-speed transmission mechanism 26 is also changed (switched) will be described with reference to FIG.

[0211] According to the configuration of Table 2 above, for example, this gear change (switching) can be from forward first gear external lockup to forward second gear infinitely variable, from forward first gear external lockup to forward third gear infinitely variable, from forward first gear external lockup to reverse first gear infinitely variable, from forward second gear external lockup to forward third gear infinitely variable, from forward second gear external lockup to forward first gear infinitely variable, from forward second gear external lockup to reverse first gear infinitely variable, from forward third gear external lockup to forward second gear infinitely variable, from forward third gear external lockup to forward first gear infinitely variable, and from forward third gear external lockup to reverse first gear infinitely variable.

[0212] In the external lockup state from time A to time B in Figure 34, the controller 25 engages the first clutch 27C and disengages the second clutch 36. The controller 25 also sets the control state of the first hydraulic pump / motor 33 to either a "state in which it can rotate freely in both directions (a state in which torque is not applied in both directions)" or a "state in which torque is applied in one direction but not in the opposite direction." In the external lockup state, the second clutch 36 and the third clutch 37 may be engaged or disengaged, but are preferably disengaged to reduce power loss.

[0213] The controller 25 completes the engagement of the second clutch 36 and the third clutch 37 between time B and time C. This causes the second connecting member 31 and the first hydraulic pump / motor 33 to rotate integrally, and power transmission is possible between the second hydraulic pump / motor 34 and the idler element 28 (idler shaft 28A). The controller 25 adjusts the reduction ratio from the engine 9 to the output shaft 23 via the planetary continuously variable transmission mechanism 24 by adjusting the rotational speed of the first hydraulic pump / motor 33. In this case, the reduction ratio from the engine 9 to the output shaft 23 via the planetary continuously variable transmission mechanism 24 after the multi-speed transmission mechanism 26 is switched is adjusted to approach the reduction ratio from the engine 9 to the output shaft 23 via the direct-coupled mechanism 27 before the multi-speed transmission mechanism 26 is switched. In this case, the reduction ratios do not need to be perfectly equal; they only need to be close. Conversely, it is not appropriate for the reduction ratios to exceed each other. This operation of bringing the reduction ratios closer together is carried out between time D and time E in FIG.

[0214] Between time D and time K in Figure 34, the controller 25 sets the control state of the first hydraulic pump / motor 33 to a state in which torque is applied in one direction and torque is not applied in the opposite direction. This makes it possible to prepare for switching from external lockup to continuously variable transmission simply by reducing the pressure of the first clutch 27C. The controller 25 reduces the pressure of the primary clutch from time F in Figure 34, and completes the release of the primary clutch at time I. In addition, the controller 25 increases the pressure of the secondary clutch from time G in Figure 34, and completes the engagement of the secondary clutch at time K.

[0215] The controller 25 reduces the pressure of the first clutch 27C from time H in Figure 34, and completes the release of the first clutch 27C at time J. From time K in Figure 34 onwards, the control state of the first hydraulic pump / motor 33 becomes a state in which the rotational speed is adjusted to adjust the reduction ratio of the planetary continuously variable transmission mechanism 24. In other words, the controller 25 adjusts the rotational speed of the first hydraulic pump / motor 33, and thereby adjusts the rotation of the second connecting member 31 so as to achieve the target reduction ratio.

[0216] In this way, when the planetary continuously variable transmission mechanism 24 is switched from "external lockup" to "continuously variable speed" and the multi-speed transmission mechanism 26 is also changed (switched) in speed, the gear ratio of the planetary continuously variable transmission mechanism 24 is first changed to approach the reduction ratio after the completion of the gear change of the multi-speed transmission mechanism 26. After that, the gear change (switching) of the multi-speed transmission mechanism 26 is started, and then the switching of the planetary continuously variable transmission mechanism 24 from "external lockup" to "continuously variable speed" is started. In other words, the pressure reduction (release) of the primary clutch and the pressure increase (engagement) of the secondary clutch are started, and then the pressure reduction (release) of the first clutch 27C is started.

[0217] With this type of gear change, there is only a slight change in the rotational speed of the engine 9, which serves as the power source, while the clutches (first clutch 27C, second clutch 36, primary clutch, and secondary clutch) are being switched, which shortens the time required to switch the clutches and reduces the change in output torque from the output shaft 23. This improves the operability of the wheel loader 1 and improves the ride comfort.

[0218] Next, the relationship between the communication state and the cut-off state of the adjustable relief valves 38A, 38B and the rotation direction and torque load direction of the first hydraulic pump / motor 33 will be described in more detail with reference to FIG.

[0219] First, a case where the set pressures of both the first and second adjustable relief valves 38A and 38B are high, that is, where both the first and second adjustable relief valves 38A and 38B are in the shut-off state, will be described.

[0220] First, a case will be described in which, facing the direction from the engine 9 (power source) to the output shaft 23 (axle), the engine 9 rotates clockwise, applying a clockwise torque to the first connecting member 30, and the second connecting member 31 rotates clockwise (in one direction). In this case, a clockwise torque acts on the second connecting member 31, and a clockwise (in one direction) torque load is generated on the first hydraulic pump / motor 33. At this time, the hydraulic fluid flows from the first hydraulic pump / motor 33 through the first main line 35A, the second hydraulic pump / motor 34, and the second main line 35B in this order, and attempts to return to the first hydraulic pump / motor 33. In this case, the discharge volume per rotation of the first hydraulic pump / motor 33 and the second hydraulic pump / motor 34 is adjusted to make the discharge flow rate of the second hydraulic pump / motor 34 smaller than the discharge flow rate of the first hydraulic pump / motor 33. As a result, the first main line 35A becomes higher in pressure than the second main line 35B, and it becomes possible to apply a unidirectional torque load to the first hydraulic pump / motor 33. In other words, the first hydraulic pump / motor 33 can be rotated in one direction, and a unidirectional torque load can be applied.

[0221] A case will be described in which, facing the direction from the engine 9 (power source) to the output shaft 23 (axle), the engine 9 rotates clockwise, applying a counterclockwise torque to the first connecting member 30, and the second connecting member 31 rotates clockwise (in one direction). In this case, a counterclockwise torque acts on the second connecting member 31, and a counterclockwise (opposite direction) torque load is generated on the first hydraulic pump / motor 33. At this time, the hydraulic fluid flows from the first hydraulic pump / motor 33 through the first main line 35A, the second hydraulic pump / motor 34, and the second main line 35B in this order, and attempts to return to the first hydraulic pump / motor 33. In this case, the discharge volume per rotation of the first hydraulic pump / motor 33 and the second hydraulic pump / motor 34 is adjusted to make the discharge flow rate of the first hydraulic pump / motor 33 smaller than the discharge flow rate of the second hydraulic pump / motor 34. As a result, the second main line 35B becomes higher in pressure than the first main line 35A, and it becomes possible to apply a torque load in the opposite direction to the first hydraulic pump / motor 33. In other words, the first hydraulic pump / motor 33 can be placed in a state where it rotates in one direction and applies a torque load in the opposite direction.

[0222] A case will be described in which, facing the direction from the engine 9 (power source) to the output shaft 23 (axle), the engine 9 rotates clockwise, applying a clockwise torque to the first connecting member 30, and the second connecting member 31 rotates counterclockwise (in the opposite direction). In this case, a clockwise torque acts on the second connecting member 31, and a clockwise (unidirectional) torque load is generated on the first hydraulic pump / motor 33. At this time, the hydraulic fluid flows from the first hydraulic pump / motor 33 through the second main line 35B, the second hydraulic pump / motor 34, and the first main line 35A in this order, and attempts to return to the first hydraulic pump / motor 33. In this case, by adjusting the discharge volumes per rotation of the first hydraulic pump / motor 33 and the second hydraulic pump / motor 34, the discharge flow rate of the second hydraulic pump / motor 34 is made smaller than the discharge flow rate of the first hydraulic pump / motor 33. As a result, the first main line 35A becomes higher in pressure than the second main line 35B, and it becomes possible to apply a unidirectional torque load to the first hydraulic pump / motor 33. In other words, the first hydraulic pump / motor 33 rotates in the opposite direction, and a unidirectional torque load can be applied.

[0223] A case will be described in which, facing the direction from the engine 9 (power source) to the output shaft 23 (axle), the engine 9 rotates clockwise, applying a counterclockwise torque to the first connecting member 30, and the second connecting member 31 rotates counterclockwise (in the opposite direction). In this case, a counterclockwise torque acts on the second connecting member 31, and a counterclockwise (in the opposite direction) torque load is generated on the first hydraulic pump / motor 33. At this time, the hydraulic fluid flows from the first hydraulic pump / motor 33 through the second main line 35B, the second hydraulic pump / motor 34, and the first main line 35A in this order, and attempts to return to the first hydraulic pump / motor 33. In this case, the discharge volume per rotation of the first hydraulic pump / motor 33 and the second hydraulic pump / motor 34 is adjusted to make the discharge flow rate of the first hydraulic pump / motor 33 smaller than the discharge flow rate of the second hydraulic pump / motor 34. As a result, the second main line 35B becomes higher in pressure than the first main line 35A, and it becomes possible to apply a torque load in the opposite direction to the first hydraulic pump / motor 33. In other words, the first hydraulic pump / motor 33 rotates in the opposite direction, and a torque load can be applied in the opposite direction.

[0224] Next, a case where the set pressure of the first adjustable relief valve 38A is low and the set pressure of the second adjustable relief valve 38B is high, i.e., the first adjustable relief valve 38A is in the open state and the second adjustable relief valve 38B is in the closed state, will be described.

[0225] First, a case will be described in which, facing the direction from the engine 9 (power source) to the output shaft 23 (axle), the engine 9 rotates clockwise, applying a clockwise torque to the first connecting member 30, and the second connecting member 31 rotates clockwise (in one direction). In this case, a clockwise torque acts on the second connecting member 31, and a clockwise (in one direction) torque load is generated on the first hydraulic pump / motor 33. At this time, the hydraulic fluid flows from the first hydraulic pump / motor 33 through the first main line 35A, the second hydraulic pump / motor 34, and the second main line 35B in this order, and attempts to return to the first hydraulic pump / motor 33. In this case, the discharge volume per rotation of the first hydraulic pump / motor 33 and the second hydraulic pump / motor 34 is adjusted to make the discharge flow rate of the second hydraulic pump / motor 34 smaller than the discharge flow rate of the first hydraulic pump / motor 33. As a result, the first main line 35A becomes higher in pressure than the second main line 35B, causing a unidirectional torque load to act on the first hydraulic pump / motor 33. However, because the first adjustable relief valve 38A is in a communicating state, the hydraulic fluid flows to the second main line 35B in the following order: first main line 35A, connecting line 44, first bypass line 45, first adjustable relief valve 38A, and second check valve 48. For this reason, the first main line 35A does not become higher in pressure than the second main line 35B. In other words, the first hydraulic pump / motor 33 rotates in one direction, preventing a unidirectional torque load from acting on the first hydraulic pump / motor 33.

[0226] A case will be described in which, facing the direction from the engine 9 (power source) to the output shaft 23 (axle), the engine 9 rotates clockwise, applying a counterclockwise torque to the first connecting member 30, and the second connecting member 31 rotates clockwise (in one direction). In this case, a counterclockwise torque acts on the second connecting member 31, and a counterclockwise (opposite direction) torque load is generated on the first hydraulic pump / motor 33. At this time, the hydraulic fluid flows from the first hydraulic pump / motor 33 through the first main line 35A, the second hydraulic pump / motor 34, and the second main line 35B in this order, and attempts to return to the first hydraulic pump / motor 33. In this case, the discharge volume per rotation of the first hydraulic pump / motor 33 and the second hydraulic pump / motor 34 is adjusted to make the discharge flow rate of the first hydraulic pump / motor 33 smaller than the discharge flow rate of the second hydraulic pump / motor 34. As a result, the second main line 35B becomes higher in pressure than the first main line 35A, and it becomes possible to apply a torque load in the opposite direction to the first hydraulic pump / motor 33. In other words, the first hydraulic pump / motor 33 can be placed in a state where it rotates in one direction and applies a torque load in the opposite direction.

[0227] A case will be described in which, facing the direction from the engine 9 (power source) to the output shaft 23 (axle), the engine 9 rotates clockwise, applying a clockwise torque to the first connecting member 30, and the second connecting member 31 rotates counterclockwise (in the opposite direction). In this case, a clockwise torque acts on the second connecting member 31, and a clockwise (unidirectional) torque load is generated on the first hydraulic pump / motor 33. At this time, the hydraulic fluid flows from the first hydraulic pump / motor 33 through the second main line 35B, the second hydraulic pump / motor 34, and the first main line 35A in this order, and attempts to return to the first hydraulic pump / motor 33. In this case, by adjusting the discharge volumes per rotation of the first hydraulic pump / motor 33 and the second hydraulic pump / motor 34, the discharge flow rate of the second hydraulic pump / motor 34 is made smaller than the discharge flow rate of the first hydraulic pump / motor 33. As a result, the first main line 35A becomes higher in pressure than the second main line 35B, causing a unidirectional torque load to act on the first hydraulic pump / motor 33. However, because the first adjustable relief valve 38A is in a communicating state, the hydraulic fluid flows to the second main line 35B in the following order: first main line 35A, connecting line 44, first bypass line 45, first adjustable relief valve 38A, and second check valve 48. For this reason, the first main line 35A does not become higher in pressure than the second main line 35B. In other words, the first hydraulic pump / motor 33 rotates in the opposite direction, preventing a unidirectional torque load from acting on the first hydraulic pump / motor 33.

[0228] A case will be described in which, facing the direction from the engine 9 (power source) to the output shaft 23 (axle), the engine 9 rotates clockwise, applying a counterclockwise torque to the first connecting member 30, and the second connecting member 31 rotates counterclockwise (in the opposite direction). In this case, a counterclockwise torque acts on the second connecting member 31, and a counterclockwise (in the opposite direction) torque load is generated on the first hydraulic pump / motor 33. At this time, the hydraulic fluid flows from the first hydraulic pump / motor 33 through the second main line 35B, the second hydraulic pump / motor 34, and the first main line 35A in this order, and attempts to return to the first hydraulic pump / motor 33. In this case, the discharge volume per rotation of the first hydraulic pump / motor 33 and the second hydraulic pump / motor 34 is adjusted to make the discharge flow rate of the first hydraulic pump / motor 33 smaller than the discharge flow rate of the second hydraulic pump / motor 34. As a result, the second main line 35B becomes higher in pressure than the first main line 35A, and it becomes possible to apply a torque load in the opposite direction to the first hydraulic pump / motor 33. In other words, the first hydraulic pump / motor 33 rotates in the opposite direction, and a torque load can be applied in the opposite direction.

[0229] Next, a case where the set pressure of the first adjustable relief valve 38A is high and the set pressure of the second adjustable relief valve 38B is low, i.e., the first adjustable relief valve 38A is in a closed state and the second adjustable relief valve 38B is in a connected state, will be described.

[0230] First, a case will be described in which, facing the direction from the engine 9 (power source) to the output shaft 23 (axle), the engine 9 rotates clockwise, applying a clockwise torque to the first connecting member 30, and the second connecting member 31 rotates clockwise (in one direction). In this case, a clockwise torque acts on the second connecting member 31, and a clockwise (in one direction) torque load is generated on the first hydraulic pump / motor 33. At this time, the hydraulic fluid flows from the first hydraulic pump / motor 33 through the first main line 35A, the second hydraulic pump / motor 34, and the second main line 35B in this order, and attempts to return to the first hydraulic pump / motor 33. In this case, the discharge volume per rotation of the first hydraulic pump / motor 33 and the second hydraulic pump / motor 34 is adjusted to make the discharge flow rate of the second hydraulic pump / motor 34 smaller than the discharge flow rate of the first hydraulic pump / motor 33. As a result, the first main line 35A becomes higher in pressure than the second main line 35B, and it becomes possible to apply a unidirectional torque load to the first hydraulic pump / motor 33. In other words, the first hydraulic pump / motor 33 can be rotated in one direction, and a unidirectional torque load can be applied.

[0231] A case will be described in which, facing the direction from the engine 9 (power source) to the output shaft 23 (axle), the engine 9 rotates clockwise, applying a counterclockwise torque to the first connecting member 30, and the second connecting member 31 rotates clockwise (in one direction). In this case, a counterclockwise torque acts on the second connecting member 31, and a counterclockwise (opposite direction) torque load is generated on the first hydraulic pump / motor 33. At this time, the hydraulic fluid flows from the first hydraulic pump / motor 33 through the first main line 35A, the second hydraulic pump / motor 34, and the second main line 35B in this order, and attempts to return to the first hydraulic pump / motor 33. In this case, the discharge volume per rotation of the first hydraulic pump / motor 33 and the second hydraulic pump / motor 34 is adjusted to make the discharge flow rate of the first hydraulic pump / motor 33 smaller than the discharge flow rate of the second hydraulic pump / motor 34. As a result, the second main line 35B becomes higher in pressure than the first main line 35A, and a torque load in the opposite direction is intended to be applied to the first hydraulic pump / motor 33. However, because the second adjustable relief valve 38B is in a communicating state, the hydraulic fluid flows to the first main line 35A in the following order: the second main line 35B, the connecting line 44, the second bypass line 46, the second adjustable relief valve 38B, and the first check valve 47. For this reason, the second main line 35B does not become higher in pressure than the first main line 35A. In other words, the first hydraulic pump / motor 33 can be rotated in one direction, without applying a torque load in the opposite direction.

[0232] A case will be described in which, facing the direction from the engine 9 (power source) to the output shaft 23 (axle), the engine 9 rotates clockwise, applying a clockwise torque to the first connecting member 30, and the second connecting member 31 rotates counterclockwise (in the opposite direction). In this case, a clockwise torque acts on the second connecting member 31, and a clockwise (unidirectional) torque load is generated on the first hydraulic pump / motor 33. At this time, the hydraulic fluid flows from the first hydraulic pump / motor 33 through the second main line 35B, the second hydraulic pump / motor 34, and the first main line 35A in this order, and attempts to return to the first hydraulic pump / motor 33. In this case, by adjusting the discharge volumes per rotation of the first hydraulic pump / motor 33 and the second hydraulic pump / motor 34, the discharge flow rate of the second hydraulic pump / motor 34 is made smaller than the discharge flow rate of the first hydraulic pump / motor 33. As a result, the first main line 35A becomes higher in pressure than the second main line 35B, and it becomes possible to apply a unidirectional torque load to the first hydraulic pump / motor 33. In other words, the first hydraulic pump / motor 33 rotates in the opposite direction, and a unidirectional torque load can be applied.

[0233] A case will be described in which, facing the direction from the engine 9 (power source) to the output shaft 23 (axle), the engine 9 rotates clockwise, applying a counterclockwise torque to the first connecting member 30, and the second connecting member 31 rotates counterclockwise (in the opposite direction). In this case, a counterclockwise torque acts on the second connecting member 31, and a counterclockwise (in the opposite direction) torque load is generated on the first hydraulic pump / motor 33. At this time, the hydraulic fluid flows from the first hydraulic pump / motor 33 through the second main line 35B, the second hydraulic pump / motor 34, and the first main line 35A in this order, and attempts to return to the first hydraulic pump / motor 33. In this case, the discharge volume per rotation of the first hydraulic pump / motor 33 and the second hydraulic pump / motor 34 is adjusted to make the discharge flow rate of the first hydraulic pump / motor 33 smaller than the discharge flow rate of the second hydraulic pump / motor 34. As a result, the second main line 35B becomes higher in pressure than the first main line 35A, and a torque load in the opposite direction is intended to be applied to the first hydraulic pump-motor 33. However, because the second adjustable relief valve 38B is in a communicating state, the hydraulic fluid flows to the first main line 35A in the following order: the second main line 35B, the connecting line 44, the second bypass line 46, the second adjustable relief valve 38B, and the first check valve 47. For this reason, the second main line 35B does not become higher in pressure than the first main line 35A. In other words, the first hydraulic pump-motor 33 rotates in the opposite direction, and a state in which a torque load in the opposite direction is not applied can be achieved.

[0234] Next, a case where the set pressures of both the first and second adjustable relief valves 38A and 38B are low, that is, where both the first and second adjustable relief valves 38A and 38B are in a communication state, will be described.

[0235] First, a case will be described in which, facing the direction from the engine 9 (power source) to the output shaft 23 (axle), the engine 9 rotates clockwise, applying a clockwise torque to the first connecting member 30, and the second connecting member 31 rotates clockwise (in one direction). In this case, a clockwise torque acts on the second connecting member 31, and a clockwise (in one direction) torque load is generated on the first hydraulic pump / motor 33. At this time, the hydraulic fluid flows from the first hydraulic pump / motor 33 through the first main line 35A, the second hydraulic pump / motor 34, and the second main line 35B in this order, and attempts to return to the first hydraulic pump / motor 33. In this case, the discharge volume per rotation of the first hydraulic pump / motor 33 and the second hydraulic pump / motor 34 is adjusted to make the discharge flow rate of the second hydraulic pump / motor 34 smaller than the discharge flow rate of the first hydraulic pump / motor 33. As a result, the first main line 35A becomes higher in pressure than the second main line 35B, causing a unidirectional torque load to act on the first hydraulic pump / motor 33. However, because the first adjustable relief valve 38A is in a communicating state, the hydraulic fluid flows to the second main line 35B in the following order: first main line 35A, connecting line 44, first bypass line 45, first adjustable relief valve 38A, and second check valve 48. For this reason, the first main line 35A does not become higher in pressure than the second main line 35B. In other words, the first hydraulic pump / motor 33 rotates in one direction, preventing a unidirectional torque load from acting on the first hydraulic pump / motor 33.

[0236] A case will be described in which, facing the direction from the engine 9 (power source) to the output shaft 23 (axle), the engine 9 rotates clockwise, applying a counterclockwise torque to the first connecting member 30, and the second connecting member 31 rotates clockwise (in one direction). In this case, a counterclockwise torque acts on the second connecting member 31, and a counterclockwise (opposite direction) torque load is generated on the first hydraulic pump / motor 33. At this time, the hydraulic fluid flows from the first hydraulic pump / motor 33 through the first main line 35A, the second hydraulic pump / motor 34, and the second main line 35B in this order, and attempts to return to the first hydraulic pump / motor 33. In this case, the discharge volume per rotation of the first hydraulic pump / motor 33 and the second hydraulic pump / motor 34 is adjusted to make the discharge flow rate of the first hydraulic pump / motor 33 smaller than the discharge flow rate of the second hydraulic pump / motor 34. As a result, the second main line 35B becomes higher in pressure than the first main line 35A, and a torque load in the opposite direction is intended to be applied to the first hydraulic pump / motor 33. However, because the second adjustable relief valve 38B is in a communicating state, the hydraulic fluid flows to the first main line 35A in the following order: the second main line 35B, the connecting line 44, the second bypass line 46, the second adjustable relief valve 38B, and the first check valve 47. For this reason, the second main line 35B does not become higher in pressure than the first main line 35A. In other words, the first hydraulic pump / motor 33 can be rotated in one direction, without applying a torque load in the opposite direction.

[0237] A case will be described in which, facing the direction from the engine 9 (power source) to the output shaft 23 (axle), the engine 9 rotates clockwise, applying a clockwise torque to the first connecting member 30, and the second connecting member 31 rotates counterclockwise (in the opposite direction). In this case, a clockwise torque acts on the second connecting member 31, and a clockwise (unidirectional) torque load is generated on the first hydraulic pump / motor 33. At this time, the hydraulic fluid flows from the first hydraulic pump / motor 33 through the second main line 35B, the second hydraulic pump / motor 34, and the first main line 35A in this order, and attempts to return to the first hydraulic pump / motor 33. In this case, by adjusting the discharge volumes per rotation of the first hydraulic pump / motor 33 and the second hydraulic pump / motor 34, the discharge flow rate of the second hydraulic pump / motor 34 is made smaller than the discharge flow rate of the first hydraulic pump / motor 33. As a result, the first main line 35A becomes higher in pressure than the second main line 35B, causing a unidirectional torque load to act on the first hydraulic pump / motor 33. However, because the first adjustable relief valve 38A is in a communicating state, the hydraulic fluid flows to the second main line 35B in the following order: first main line 35A, connecting line 44, first bypass line 45, first adjustable relief valve 38A, and second check valve 48. For this reason, the first main line 35A does not become higher in pressure than the second main line 35B. In other words, the first hydraulic pump / motor 33 rotates in the opposite direction, preventing a unidirectional torque load from acting on the first hydraulic pump / motor 33.

[0238] A case will be described in which, facing the direction from the engine 9 (power source) to the output shaft 23 (axle), the engine 9 rotates clockwise, applying a counterclockwise torque to the first connecting member 30, and the second connecting member 31 rotates counterclockwise (in the opposite direction). In this case, a counterclockwise torque acts on the second connecting member 31, and a counterclockwise (in the opposite direction) torque load is generated on the first hydraulic pump / motor 33. At this time, the hydraulic fluid flows from the first hydraulic pump / motor 33 through the second main line 35B, the second hydraulic pump / motor 34, and the first main line 35A in this order, and attempts to return to the first hydraulic pump / motor 33. In this case, the discharge volume per rotation of the first hydraulic pump / motor 33 and the second hydraulic pump / motor 34 is adjusted to make the discharge flow rate of the first hydraulic pump / motor 33 smaller than the discharge flow rate of the second hydraulic pump / motor 34. As a result, the second main line 35B becomes higher in pressure than the first main line 35A, and a torque load in the opposite direction is intended to be applied to the first hydraulic pump-motor 33. However, because the second adjustable relief valve 38B is in a communicating state, the hydraulic fluid flows to the first main line 35A in the following order: the second main line 35B, the connecting line 44, the second bypass line 46, the second adjustable relief valve 38B, and the first check valve 47. For this reason, the second main line 35B does not become higher in pressure than the first main line 35A. In other words, the first hydraulic pump-motor 33 rotates in the opposite direction, and a state in which a torque load in the opposite direction is not applied can be achieved.

[0239] As described above, according to the first embodiment, the transmission 21 includes the input shaft 22 (input member), the output shaft 23 (output member), the planetary continuously variable transmission mechanism 24, the direct-coupled mechanism 27, the idler element 28, and the multi-speed transmission mechanism 26. The input shaft 22 is rotated by a power source (engine 9) mounted on the vehicle (wheel loader 1). The output shaft 23 outputs rotation to the vehicle's travel device (front axle 12 and / or rear axle 13). The planetary continuously variable transmission mechanism 24 is provided between the input shaft 22 and the output shaft 23. The planetary continuously variable transmission mechanism 24 changes the speed of the rotation on the input shaft 22 side and transmits it to the output shaft 23 side. The direct-coupled mechanism 27 transmits the rotation on the input shaft 22 side to the output shaft 23 side, bypassing the planetary continuously variable transmission mechanism 24. Idler element 28 mechanically couples the output side of planetary continuously variable transmission mechanism 24 and the output side of direct-coupled mechanism 27. Multi-speed mechanism 26 changes the speed of the rotation on the output side of planetary continuously variable transmission mechanism 24 in stages by switching the transmission path of meshing gears.

[0240] The direct-coupled mechanism 27 includes a first clutch 27C (direct-coupled clutch) provided between the input shaft 22 and the idler element 28. The planetary continuously variable transmission mechanism 24 includes a planetary gear mechanism 29 (planetary mechanism), a first variator 33 (first hydraulic pump / motor 33), and a second variator 34 (second hydraulic pump / motor 34). As shown in FIGS. 4 and 5 , the planetary gear mechanism 29 includes three members: a carrier 29A (first member) connected to the input shaft 22, a first sun gear 29B (second member) serving as an output side, and a second sun gear 29C (third member) connected to the idler element 28 and serving as an output side separate from the first sun gear 29B. In this case, the carrier 29A (first member) is connected to the input shaft 22 via a first connecting member 30. The first sun gear 29B (second member) is connected to the first variator 33 via the second connecting member 31 and the second clutch 36. The second sun gear 29C (third member) is connected to the idler element 28 (first idler gear 28B) via the third connecting member 32.

[0241] The first variator 33 is connected to the first sun gear 29B of the planetary gear mechanism 29. In this case, as shown in FIG. 7 , the first variator 33 is configured as a pump motor serving as a hydraulic rotating machine (hydraulic rotating machine) that performs pumping or motoring. A first rotating shaft 42 of the first variator 33 is connected to the first sun gear 29B of the planetary gear mechanism 29. The second variator 34 is capable of transmitting power to the first variator 33. In this case, the second variator 34 is configured as a pump motor serving as a hydraulic rotating machine (hydraulic rotating machine) that performs pumping or motoring. The second variator 34 is capable of transmitting power to the first variator 33 via a pair of main lines 35A, 35B through which a fluid (hydraulic oil) flows. The transmission 21 also includes a controller 25. The controller 25 controls the rotational speed of the first variator 33 and the engagement and disengagement of the first clutch 27C.

[0242] The controller 25 can switch the transmission 21 between three power transmission states: a first power transmission state, a second power transmission state, and a third power transmission state. In the first power transmission state, the first clutch 27C is disengaged and the rotational speed of the first variator 33 is changed to change the rotational speed of the first sun gear 29B. In this first power transmission state, two-degree-of-freedom rotational motion occurs between the carrier 29A, the first sun gear 29B, and the second sun gear 29C, and power transmitted from the engine 9 to the planetary continuously variable transmission mechanism 24 is transmitted to the multi-stage transmission mechanism 26 (continuously variable transmission).

[0243] In the second power transmission state, first clutch 27C is disengaged and rotation of first variator 33 is stopped, thereby stopping rotation of first sun gear 29B. In this second power transmission state, one degree of freedom of rotational motion occurs between carrier 29A, first sun gear 29B, and second sun gear 29C, and power transmitted from engine 9 to planetary continuously variable transmission mechanism 24 is transmitted to multi-stage transmission mechanism 26 (internal lockup). In the third power transmission state, first clutch 27C is engaged. In this third power transmission state, power transmitted from engine 9 to direct-coupled mechanism 27 is transmitted to multi-stage transmission mechanism 26, bypassing planetary continuously variable transmission mechanism 24 (external lockup).

[0244] The controller 25 switches between the second power transmission state (internal lockup) and the third power transmission state (external lockup) in accordance with the rotational speed of the output shaft 23. That is, the controller 25 is connected to a second speed detector 50 that detects the rotational speed (output rotational speed Vout) and rotation direction of the output shaft 23. The rotational speed of the output shaft 23 (output rotational speed Vout) corresponds to the vehicle speed of the wheel loader 1. As shown in FIG. 11 and Table 1 or FIG. 12 and Table 2, the controller 25 can switch between the second power transmission state (internal lockup) and the third power transmission state (external lockup) in accordance with the rotational speed of the output shaft 23 (output rotational speed Vout). This allows for smooth switching between the second power transmission state (internal lockup) and the third power transmission state (external lockup). Furthermore, because it is possible to switch between the second power transmission state (internal lockup) and the third power transmission state (external lockup), the number of speed stages (number of gears) of the multi-speed transmission mechanism 26 can be reduced compared to a configuration that does not allow this switching (for example, a configuration with only internal lockup). This allows the multi-speed transmission mechanism 26 to be made smaller and less expensive. Furthermore, because power loss in the multi-speed transmission mechanism 26 can be reduced, the transmission efficiency of the transmission device 21 as a whole can be improved.

[0245] According to the first embodiment, a first check valve 47 and a second adjustable relief valve 38B are provided in series between the pair of main lines 35A, 35B. The first check valve 47 is a check valve that allows pressure oil to flow from the second main line 35B as one main line toward the first main line 35A as the other main line and prevents pressure oil from flowing in the opposite direction. The second adjustable relief valve 38B is a communication valve that switches the pair of main lines 35A, 35B between a communication state and a cut-off state. The controller 25 lowers the set pressure of the second adjustable relief valve 38B to bring the state of the second adjustable relief valve 38B into a communication state, i.e., a communication state that communicates between the pair of main lines 35A, 35B. As a result, the controller 25 can open the second variable relief valve 38B, thereby allowing communication between the pair of main lines 35A, 35B in one direction while blocking communication in the opposite direction by the first check valve 47.

[0246] That is, by bringing the first variable relief valve 38A into a shutoff state and the second variable relief valve 38B into a connected state, the controller 25 can enable the flow of pressure oil from the second main line 35B to the first main line 35A, and can block the flow of pressure oil from the first main line 35A to the second main line 35B by the first check valve 47. Therefore, when switching the power transmission state of the planetary continuously variable transmission mechanism 24 and / or when switching the speed stages of the multi-speed transmission mechanism 26, the controller 25 can enable the flow of pressure oil from the second main line 35B to the first main line 35A, and can block the flow of pressure oil from the first main line 35A to the second main line 35B.

[0247] This allows smooth switching of the power transmission state of the planetary continuously variable transmission mechanism 24 and / or smooth switching of the speed stages of the multi-speed transmission mechanism 26. Depending on the setting of the rotational direction (forward direction) of the input shaft 22, the second variable relief valve 38B may be shut off and the first variable relief valve 38A may be connected, thereby allowing the flow of pressure oil from the first main line 35A, which serves as one main line, to the second main line 35B, which serves as the other main line, and the second check valve 48 may block the flow of pressure oil from the second main line 35B to the first main line 35A. In the case of the fifth modified example shown in FIG. 17 , instead of connecting the first variable relief valve 38A or the second variable relief valve 38B (reducing the set pressure), the first on-off valve 81A or the second on-off valve 81B may be connected (open position).

[0248] According to the first embodiment, by bringing the second variable relief valve 38B into a communicating state, the controller 25 can simultaneously realize a state in which power generated by the rotation of the first variator 33 in one direction of the planetary continuously variable transmission mechanism 24 is transmitted to the second variator 34, and a state in which power generated by the rotation of the first variator 33 in the opposite direction of the first variator 33 is blocked from being transmitted to the second variator 34. That is, by bringing the first variable relief valve 38A into a blocked state and the second variable relief valve 38B into a communicating state, the controller 25 can change the operating state of the first variator 33 to a state in which torque (load) acts in one direction and torque (load) does not act in the opposite direction. In other words, by bringing the first variable relief valve 38A into a blocked state and the second variable relief valve 38B into a communicating state, the controller 25 can restrict the rotation of the first variator 33 in one direction and allow it to rotate freely in the opposite direction. Therefore, when switching the power transmission state of the planetary continuously variable transmission mechanism 24 and / or when switching the speed stages of the multi-stage transmission mechanism 26, the controller 25 can restrict rotation of the first variator 33 in one direction and allow rotation in the opposite direction by opening the second variable relief valve 38B. This makes it possible to smoothly switch the power transmission state of the planetary continuously variable transmission mechanism 24 and / or switch the speed stages of the multi-stage transmission mechanism 26.

[0249] According to the first embodiment, the controller 25 switches from the first power transmission state (continuously variable transmission) or the second power transmission state (internal lockup) to the third power transmission state (external lockup) by bringing the second variable relief valve 38B into a communicating state and switching the first clutch 27C from a released state to an engaged state. The first power transmission state (continuously variable transmission) is a power transmission state in which the rotation of the input shaft 22 is transmitted to the multi-stage transmission mechanism 26 via the planetary continuously variable transmission mechanism 24. The second power transmission state (internal lockup) is also a power transmission state in which the rotation of the input shaft 22 is transmitted to the multi-stage transmission mechanism 26 via the planetary continuously variable transmission mechanism 24. The third power transmission state (external lockup) is a power transmission state in which the rotation of the input shaft 22 is transmitted to the multi-stage transmission mechanism 26, bypassing the planetary continuously variable transmission mechanism 24. When the first clutch 27C is switched from released to engaged, the controller 25 places the second variable relief valve 38B in a communicating state, thereby enabling smooth switching from the first power transmission state (continuously variable transmission) or the second power transmission state (internal lockup) to the third power transmission state (external lockup).

[0250] According to the first embodiment, the controller 25 switches from the third power transmission state (external lockup) to the first power transmission state (infinitely variable transmission) or the second power transmission state (internal lockup) by bringing the second variable relief valve 38B into a communicating state and switching the first clutch 27C from an engaged state to a released state. In other words, when switching the first clutch 27C from an engaged state to a released state, the controller 25 brings the second variable relief valve 38B into a communicating state, thereby enabling smooth switching from the third power transmission state (external lockup) to the first power transmission state (infinitely variable transmission) or the second power transmission state (internal lockup).

[0251] According to the first embodiment, the second variable relief valve 38B serving as a communication valve is an electromagnetic relief valve with a variable relief set pressure. The controller 25 sets the second variable relief valve 38B to a closed state by increasing the relief set pressure, and sets the second variable relief valve 38B to a communicating state by decreasing the relief set pressure. Therefore, the controller 25 can set the second variable relief valve 38B to a communicating state when switching the power transmission state of the planetary continuously variable transmission mechanism 24 and / or when switching the speed stages of the multi-speed transmission mechanism 26.

[0252] According to the first embodiment, the multi-speed transmission mechanism 26 is provided with a plurality of power transmission paths with different reduction ratios. For example, the multi-speed transmission mechanism 26 includes a low-range shaft unit 61 that serves as a first output transmission path (forward first-speed power transmission path) and a high-range shaft unit 62 that serves as a second output transmission path (forward second-speed power transmission path) and a third output transmission path (forward third-speed power transmission path). The plurality of transmission paths have different rotational speed ratios at which the rotation of the idler element 28 is transmitted to the output shaft 23. For example, the first output transmission path (forward first speed) of the low-range shaft unit 61, the second output transmission path (forward second speed) of the high-range shaft unit 62, and the third output transmission path (forward third speed) of the high-range shaft unit 62 have different rotational speed ratios.

[0253] Furthermore, when switching the power transmission path of the multi-speed transmission mechanism 26 together with switching from the second power transmission state (internal lockup) to the third power transmission state (external lockup), the controller 25 places the second variable relief valve 38B in a communicating state. This restricts rotation of the first variator 33 in one direction and allows rotation in the opposite direction. That is, the controller 25 places the first variable relief valve 38A in a blocking state, places the second variable relief valve 38B in a communicating state, and switches the first clutch 27C from a released state to an engaged state, thereby switching from the second power transmission state (internal lockup) to the third power transmission state (external lockup) and switching the power transmission path of the multi-speed transmission mechanism 26. Therefore, when switching from the second power transmission state (internal lockup) to the third power transmission state (external lockup) and switching the power transmission path of the multi-speed transmission mechanism 26 together with switching, these switching operations can be performed smoothly.

[0254] According to the first embodiment, when switching the power transmission path of the multi-speed transmission mechanism 26 together with switching from the third power transmission state (external lockup) to the second power transmission state (internal lockup), the controller 25 places the second variable relief valve 38B in a communicating state. This restricts rotation of the first variator 33 in one direction and allows rotation in the opposite direction. That is, the controller 25 places the first variable relief valve 38A in a blocking state, places the second variable relief valve 38B in a communicating state, and switches the first clutch 27C from an engaged state to a released state, thereby switching from the third power transmission state (external lockup) to the second power transmission state (internal lockup) and switching the power transmission path of the multi-speed transmission mechanism 26. Therefore, when switching from the third power transmission state (external lockup) to the second power transmission state (internal lockup) and switching the power transmission path of the multi-speed transmission mechanism 26 together, these switching operations can be performed smoothly.

[0255] According to the first embodiment, when switching from the first power transmission state (continuously variable transmission) to the third power transmission state (external lockup) and switching the power transmission path of the multi-speed transmission mechanism 26, the controller 25 places the second variable relief valve 38B in a communicating state. This restricts rotation of the first variator 33 in one direction and allows rotation in the opposite direction. That is, the controller 25 places the first variable relief valve 38A in a blocking state, places the second variable relief valve 38B in a communicating state, and switches the first clutch 27C from a released state to an engaged state, thereby switching from the first power transmission state (continuously variable transmission) to the third power transmission state (external lockup) and switching the power transmission path of the multi-speed transmission mechanism 26. Therefore, when switching from the first power transmission state (continuously variable speed) to the third power transmission state (external lockup) and switching the power transmission path of the multi-speed transmission mechanism 26, these switching operations can be performed smoothly.

[0256] According to the first embodiment, when switching from the third power transmission state (external lockup) to the first power transmission state (continuously variable transmission) and switching the power transmission path of the multi-speed transmission mechanism 26, the controller 25 places the second variable relief valve 38B in a communicating state. This restricts rotation of the first variator 33 in one direction and allows rotation in the opposite direction. That is, the controller 25 places the first variable relief valve 38A in a blocking state, places the second variable relief valve 38B in a communicating state, and switches the first clutch 27C from an engaged state to a released state, thereby switching from the third power transmission state (external lockup) to the first power transmission state (continuously variable transmission) and switching the power transmission path of the multi-speed transmission mechanism 26. Therefore, when switching from the third power transmission state (external lockup) to the first power transmission state (continuously variable speed) and switching the power transmission path of the multi-speed transmission mechanism 26, these switching operations can be performed smoothly.

[0257] According to the first embodiment, the transmission 21 includes a multi-speed transmission mechanism 26 between a third member of the planetary gear mechanism 29 (planetary mechanism) (i.e., a member connected to the idler element 28 via the third connecting member 32, e.g., the second sun gear 29C) and the output shaft 23 (output member). The multi-speed transmission mechanism 26 includes a forward first-speed power transmission path (low range shaft unit 61) serving as a first output transmission path, a forward second-speed power transmission path (high range shaft unit 62) serving as a second output transmission path, and a forward third-speed power transmission path (high range shaft unit 62) serving as a third output transmission path. These first to third output transmission paths are forward paths in which the number of gear meshings between the idler element 28 and the output shaft 23 is the same (e.g., an odd number). The multi-speed transmission mechanism 26 also includes a reverse first-speed power transmission path (low range shaft unit 61) that is a reverse path in which the number of gear meshings between the idler element 28 and the output shaft 23 is different from the forward rotation path (for example, zero or an even number). When the reverse first-speed clutch 70 couples (connects) the reverse first-speed gear 67 and the low range shaft 65, the first idler gear 28B, counter gear 64, reverse first-speed gear 67, low range shaft 65, low range gear 68, low range output gear 78, and output shaft 77 (output shaft 23) rotate integrally. When the reverse first-speed clutch 70 is connected, the number of gear meshings is even when power transmitted to the idler element 28 by the planetary continuously variable transmission mechanism 24 or the direct-coupled mechanism 27 is transmitted to the output shaft 77 (output shaft 23).

[0258] On the other hand, when the forward first-speed clutch 69 couples (connects) the forward first-speed gear 66 and the low range shaft 65, the second idler gear 28C, forward first-speed gear 66, low range shaft 65, low range gear 68, low range output gear 78, and output shaft 77 (output shaft 23) rotate together. When the forward first-speed clutch 69 is engaged and power transmitted to the idler element 28 by the planetary continuously variable transmission mechanism 24 or the direct-coupled mechanism 27 is transmitted to the output shaft 77 (output shaft 23), the number of meshing of the gears becomes odd. Furthermore, when the forward second-speed gear 72 and the high range shaft 71 are coupled (connected) by the forward second-speed clutch 75, the second idler gear 28C, forward second gear 72, high range shaft 71, high range gear 74, high range output gear 79, and output shaft 77 (output shaft 23) rotate together. When the forward second-speed clutch 75 is engaged, the number of times the gears mesh is odd when the power transmitted to the idler element 28 by the planetary continuously variable transmission mechanism 24 or the direct-coupled mechanism 27 is transmitted to the output shaft 77 (output shaft 23).

[0259] Furthermore, when the forward third-speed gear 73 and high range shaft 71 are coupled (engaged) by the forward third-speed clutch 76, the first idler gear 28B, forward third-speed gear 73, high range shaft 71, high range gear 74, high range output gear 79, and output shaft 77 (output shaft 23) rotate together. When the forward third-speed clutch 76 is engaged, the number of times the gears mesh is odd when power transmitted to the idler element 28 by the planetary continuously variable transmission mechanism 24 or direct-coupled mechanism 27 is transmitted to the output shaft 77 (output shaft 23). In other words, the multi-speed transmission mechanism 26 can reverse the traveling direction of the wheel loader 1 (vehicle) by switching between a reverse mode (reverse mode) in which the reverse first-speed clutch 70 is engaged, and a forward mode (forward mode) in which the forward first-speed clutch 69, forward second-speed clutch 75, or forward third-speed clutch 76 is engaged. Therefore, the transmission 21 can reverse the rotation direction of the load (output shaft 23).

[0260] 13 , a brake mechanism 55 (brake) is provided on the second connecting member 31 connected to the first variator 33. As a result, in the first modified example, the brake mechanism 55 (brake) is connected to the second member of the planetary gear mechanism 29 (planetary mechanism) (i.e., a member connected to the first variator 33 via the second connecting member 31, for example, the first sun gear 29B). The controller 25 maintains the second power transmission state (internal lockup) by engaging the brake mechanism 55 (brake). Therefore, even if the first variator 33 does not maintain the rotational speed of the second connecting member 31 (and therefore the second member of the planetary gear mechanism 29) at zero, the brake mechanism 55 can maintain the rotational speed of the second connecting member 31 (and therefore the second member of the planetary gear mechanism 29) at zero. As a result, for example, when the first variator 33 is an electric motor, the rotation speed can be maintained at 0 without continuously supplying power to the first variator 33. As a result, loss during the second power transmission state (internal lockup) can be reduced.

[0261] 36 to 39 show a second embodiment. The second embodiment is characterized in that the planetary gear mechanism is composed of a carrier, a sun gear, and a ring gear. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and their description will be omitted.

[0262] In the first embodiment, the planetary gear mechanism 29 of the planetary continuously variable transmission mechanism 24 is configured with a carrier and two sun gears. In contrast, in the second embodiment, the planetary gear mechanism 91 of the planetary continuously variable transmission mechanism 24 is configured with a carrier 91A, a sun gear 91B, and a ring gear 91C. Table 5 below shows combinations of the components (carrier, sun gear, ring gear) of the planetary gear mechanism 91. Power transmission is possible in either case. "No. 2-A" in Table 5 is most suitable in terms of improving the transmission efficiency of the planetary continuously variable transmission mechanism 24, reducing the maximum absorption torque of the first variator 33, and making the entire planetary continuously variable transmission mechanism 24 small and lightweight.

[0263]

[0264] 36 and 37 , in the second embodiment (i.e., No. 2-A in Table 5), the planetary gear mechanism 91 includes a carrier 91A corresponding to the first member, a sun gear 91B corresponding to the second member, and a ring gear 91C and planet gears 91D corresponding to the third member. Note that the sun gear 91B, ring gear 91C, and planet gears 91D do not necessarily need to transmit power through meshing of gears, and may instead transmit power through friction between rollers (outer circumferential surfaces), for example.

[0265] The engine 9 (input shaft 22) is coupled to the carrier 91A via a first connecting member 30. The sun gear 91B is connected to a first variator 33 via a second connecting member 31. The ring gear 91C is connected to an idler element 28 (first idler gear 28B) via a third connecting member 32. The sun gear 91B meshes with a planet gear 91D. The planet gear 91D also meshes with the ring gear 91C. The rotation axis Sp (Figure 38) of the planet gear 91D is supported by the carrier 91A. Therefore, the planet gear 91D rotates while revolving around the central axis S (Figure 38) of the planetary gear mechanism 91.

[0266] Next, the operation of the planetary gear mechanism 91, which is composed of the carrier 91A, the sun gear 91B, and the ring gear 91C, will be described. The following holds true under all conditions of "No. 2-A," "No. 2-B," "No. 2-C," "No. 2-D," "No. 2-E," and "No. 2-F" in Table 5.

[0267] First, the distribution of torque among the three members of the planetary gear mechanism 91 (carrier 91A, sun gear 91B, and ring gear 91C) will be described. FIG. 38 is a cross-sectional view of the planetary gear mechanism 91 as seen from the power source side. The carrier 91A, sun gear 91B, and ring gear 91C are arranged concentrically. That is, the central axes S (rotational centers) of the carrier 91A, sun gear 91B, and ring gear 91C are aligned. The planet gear 91D is arranged to be in contact with the outer periphery of the sun gear 91B and the inner periphery of the ring gear 91C. The planet gear 91D meshes with the sun gear 91B and the ring gear 91C. The carrier 91A, sun gear 91B, and ring gear 91C are supported by the casing of the planetary continuously variable transmission mechanism 24 so that they can rotate about the central axis S but cannot move in any other direction, allowing the respective gears to mesh with each other. The planet gear 91D is supported by the carrier 91A so as to be rotatable about a rotation axis Sp, which is the central axis of the planet gear 91D, but not to be able to move in other directions. The planet gear 91D rotates about the central axis Sp of the planet gear 91D while revolving around the central axis S of the carrier 91A.

[0268] The constraint of the planetary gear mechanism 91 is that the sun gear 91B, ring gear 91C, and planet gear 91D must mesh together, as shown in FIG. 38 . Furthermore, to ensure the strength of the gears, the diameter of the planet gear 91D must be large. That is, the constraint of the planetary gear mechanism 91 is that the meshing radius rs of the sun gear 91B must be significantly smaller than the meshing radius rr of the ring gear 91C. In the configuration of "No. 2-A" in Table 5, the carrier 91A is connected to the first connecting member 30 connected to the engine 9 (power source). Therefore, the torque Tc of the carrier 91A is the torque that the engine 9 can generate. The sun gear 91B is connected to the second connecting member 31 connected to the first variator 33. Therefore, the torque Ts of the sun gear 91B is the torque that the first variator 33 can generate. The ring gear 91C is connected to the third connecting member 32 connected to the idler element 28. Therefore, the torque Tr of the ring gear 91C is a torque reaction force received from the first idler gear 28B.

[0269] The ratio between the torque Ts of the sun gear 91B, the torque Tr of the ring gear 91C, and the torque Tc of the carrier 91A remains constant while the planetary continuously variable transmission mechanism 24 is transmitting power. Based on this law, the controller 25 outputs a signal to control the first variator 33, thereby controlling the torque of the second connecting member 31 (e.g., sun gear 91B) connected to the first variator 33. That is, the controller 25 controls the torque of the second connecting member 31 (e.g., sun gear 91B) by controlling the first variator 33. In this way, the controller 25 indirectly controls the torque of the first connecting member 30 (e.g., carrier 91A) connected to the engine 9 and the torque of the third connecting member 32 (e.g., ring gear 91C) connected to the idler element 28. As a result, the torque transmitted between the first connecting member 30 (e.g., carrier 91A) connected to the engine 9 and the third connecting member 32 (e.g., ring gear 91C) connected to the idler element 28 can be controlled.

[0270] FIG. 39 shows the relationship between the rotational speeds of the planetary gear mechanism 91. Assume that the rotational speed of the carrier 91A is constant. In this case, increasing the rotational speed of the ring gear 91C decreases the rotational speed of the sun gear 91B. Conversely, decreasing the rotational speed of the ring gear 91C increases the rotational speed of the sun gear 91B. Based on this law, the controller 25 outputs a signal to control the first variator 33 and controls the rotational speed of the second connecting member 31 (e.g., sun gear 91B) connected to the first variator 33. That is, the controller 25 controls the rotational speed of the second connecting member 31 (e.g., sun gear 91B) by controlling the first variator 33. In this way, the controller 25 indirectly controls the rotational speed of the first connecting member 30 (e.g., carrier 91A) connected to the engine 9 and the rotational speed of the third connecting member 32 (e.g., ring gear 91C) connected to the idler element 28. As a result, the gear ratio can be controlled between the first connecting member 30 (e.g., carrier 91A) connected to the engine 9 and the third connecting member 32 (e.g., ring gear 91C) connected to the idler element 28.

[0271] 40 (No. 2-B in Table 5), the planetary gear mechanism 91 may have the ring gear 91C connected to the first connecting member 30 that is a member connected to the engine 9, the carrier 91A connected to the second connecting member 31 that is a member connected to the first variator 33, and the sun gear 91B connected to the third connecting member 32 that is a member connected to the idler element 28. Also, as in a seventh modified example shown in FIG. 41 (No. 2-C in Table 5), the planetary gear mechanism 91 may have the carrier 91A connected to the first connecting member 30, the ring gear 91C connected to the second connecting member 31, and the sun gear 91B connected to the third connecting member 32. Furthermore, although not shown in the figures, the planetary gear mechanism 91 may connect the carrier 91A, the sun gear 91B, and the ring gear 91C to the first connecting member 30, the second connecting member 31, and the third connecting member 32 as in "No. 2-D," "No. 2-E," or "No. 2-F" in Table 5.

[0272] The second embodiment is equipped with the planetary gear mechanism 91 as described above, and its basic operation is not particularly different from that of the first embodiment. That is, like the first embodiment, the second embodiment also switches between the second power transmission state (internal lockup) and the third power transmission state (external lockup) in accordance with the rotational speed of the output shaft 23. This allows smooth switching between the second power transmission state (internal lockup) and the third power transmission state (external lockup).

[0273] In the first embodiment, the second variator 34 is connected to an idler element 28 (specifically, an idler shaft 28A serving as a rotating element) provided between the planetary gear mechanism 29 and the multi-speed transmission 26. In contrast, although not shown, the second variator 34 may be connected to a rotating element provided between the input shaft 22 (input member) and the power source (engine 9), a rotating element constituting the multi-speed transmission 26, a rotating element provided between the multi-speed transmission 26 and the output shaft 23 (output member), the output shaft 23 (output member), or a rotating element provided between the output shaft 23 and the traveling device (front axle 12, rear axle 13).

[0274] That is, in the first embodiment, the second variator 34 is connected closer to the output shaft 23 (output member) than the planetary gear mechanism 29, in other words, the second variator 34 is connected between the planetary gear mechanism 29 and the output shaft 23. However, for example, the second variator 34 may be connected to the input gear 27A of the direct-coupled mechanism 27 provided on the input shaft 22 (input member). That is, the second variator 34 may be connected between the planetary gear mechanism 29 and the input shaft 22 (input member). In this way, the second variator 34 may be connected closer to the engine 9 (power source) than the planetary gear mechanism 29. Also, for example, the second variator 34 may be connected to the lockup gear 27B of the direct-coupled mechanism 27. For example, the second variator 34 may be connected to the third connecting member 32. For example, the second variator 34 may be connected to the first idler gear 28B of the idler element 28. The second variator 34 may be connected to the second idler gear 28C of the idler element 28.

[0275] For example, the second variator 34 may be connected to the high-range gear 74 of the multi-speed transmission mechanism 26. For example, the second variator 34 may be connected to the low-range gear 68 of the multi-speed transmission mechanism 26. For example, the second variator 34 may be connected to the high-range output gear 79 of the multi-speed transmission mechanism 26. For example, the second variator 34 may be connected to the low-range output gear 78 of the multi-speed transmission mechanism 26. For example, the second variator 34 may be connected to the output shaft 77 of the multi-speed transmission mechanism 26 (the output shaft 23 of the transmission 21). For example, the second variator 34 may be connected to the load side (the front axle 12 side or the rear axle 13 side) of the output shaft 23 of the transmission 21. For example, the second variator 34 may be connected to the front axle 12, the rear axle 13, the front propeller shaft 14, or the rear propeller shaft 15. The same applies to the second embodiment and each of the modified examples.

[0276] In the first embodiment, the planetary gear mechanism 29 has been described as an example of the planetary mechanism that constitutes the planetary continuously variable transmission mechanism 24. That is, in the first embodiment, the planetary members of the planetary mechanism have been described as planetary gears. However, this is not limiting, and the planetary members of the planetary mechanism may be composed of members other than gears, such as planetary rollers. This also applies to the second embodiment and each of the modified examples.

[0277] In the first embodiment, the transmission 21 is described as including the multi-speed change mechanism 26 and the direct-coupled mechanism 27. However, the present invention is not limited to this, and the transmission 21 may omit the multi-speed change mechanism 26 and / or the direct-coupled mechanism 27 as necessary. This also applies to the second embodiment and each of the modified examples.

[0278] In the first embodiment, an example has been described in which the transmission 21 is mounted on a wheel loader 1. However, the present invention is not limited to this, and the transmission 21 may be mounted on work vehicles (construction machinery) other than wheel loaders, such as hydraulic excavators, hydraulic cranes, dump trucks, and forklifts. Furthermore, the transmission 21 is not limited to work vehicles, and can be widely applied as a transmission incorporated in various vehicles such as automobiles and railway vehicles, or various industrial and general machinery. The same applies to the second embodiment and each of the modified examples.

[0279] Furthermore, the above-described embodiments and modifications are merely examples, and it goes without saying that partial substitution or combination of the configurations shown in different embodiments and modifications is possible.

[0280] DESCRIPTION OF SYMBOLS 1 Wheel loader (vehicle) 9 Engine (power source) 12 Front axle (traveling device) 13 Rear axle (traveling device) 21 Transmission 22 Input shaft (input member) 23, 23A, 23B, 77 Output shaft (output member) 24 Planetary continuously variable transmission mechanism 25 Controller 26 Multi-speed change mechanism (auxiliary transmission mechanism) 27 Direct-coupled mechanism (external lock-up mechanism) 27C First clutch (direct-coupled clutch) 28 Idler element 29 Planetary gear mechanism (planetary mechanism) 29A Carrier (first member, second member, or third member) 29B First sun gear (first member, second member, or third member) 29C Second sun gear (first member, second member, or third member) 33 First hydraulic pump motor (first variator) 34 Second hydraulic pump motor (second variator) 35A First main line (main line) 35B Second main line (main line) 36 Second clutch 37 Third clutch 38B Second variable relief valve (communicating valve) 47 First check valve (check valve) 61 Low range shaft unit (first output transmission path, transmission path) 62 High range shaft unit (second output transmission path, third output transmission path, transmission path) 81B Second opening / closing valve (communicating valve) 91 Planetary gear mechanism (planetary mechanism) 91A Carrier (first member, second member or third member) 91B Sun gear (first member, second member or third member) 91C Ring gear (first member, second member or third member)

Claims

1. A vehicle comprising: an input shaft rotated by a power source mounted on a vehicle; an output shaft which outputs rotation to a running device of the vehicle; a planetary continuously variable transmission mechanism provided between the input shaft and the output shaft for changing the speed of the rotation of the input shaft side and transmitting it to the output shaft side; a direct drive mechanism which transmits the rotation of the input shaft side to the output shaft side, bypassing the planetary continuously variable transmission mechanism; an idler element which mechanically couples the output side of the planetary continuously variable transmission mechanism and the output side of the direct drive mechanism; and a multi-stage transmission mechanism which changes the speed of the rotation of the output side of the planetary continuously variable transmission mechanism in stages by switching the transmission path of the meshing of gears, wherein the direct drive mechanism comprises a direct drive clutch provided between the input shaft and the idler element, and the planetary continuously variable transmission mechanism comprises: a planetary mechanism having three members: a first member connected to the input shaft side, a second member which serves as an output side, and a third member which is connected to the idler element and serves as an output side separate from the second member; a first variator configured with a hydraulic rotating machine performing a pumping operation or a motoring operation, the rotating shaft of which is connected to the second member of the planetary mechanism, and a second variator configured with a hydraulic rotating machine performing a pumping operation or a motoring operation, the second variator being capable of transmitting power to the first variator via a pair of main pipes through which a liquid flows, the transmission comprising: a controller that controls the rotational speed of the first variator and engagement and disengagement of the direct-coupled clutch, the controller being configured to: disengage the direct-coupled clutch and change the rotational speed of the first variator, thereby changing the rotational speed of the second member, perform a two-degree-of-freedom rotational motion between the first member, the second member, and the third member, and transmit the power transmitted from the power source to the planetary continuously variable transmission mechanism to the multi-stage transmission mechanism; a second power transmission state in which the direct-coupled clutch is released and the rotation of the first variator is stopped, thereby stopping the rotation of the second member, and a rotational motion with one degree of freedom is performed between the first member, the second member, and the third member, so that the power transmitted from the power source to the planetary continuously variable transmission mechanism is transmitted to the multi-stage transmission mechanism;and a third power transmission state in which the power transmitted from the power source to the direct-drive mechanism is transmitted to the multi-stage transmission mechanism, bypassing the planetary-type continuously variable transmission mechanism, by engaging the direct-drive clutch, and the controller switches between the second power transmission state and the third power transmission state in accordance with the rotational speed of the output shaft.

2. A transmission as claimed in claim 1, wherein a check valve which allows pressure oil to flow from one main line to the other main line and prevents pressure oil from flowing in the opposite direction, and a communication valve which switches the pair of main lines between a communicating state and a blocked state are provided in series between the pair of main lines, and the controller sets the communicating valve in a communicating state, thereby communicating the pair of main lines in one direction and blocking the flow in the opposite direction by the check valve.

3. A transmission as claimed in claim 2, characterized in that the controller, by bringing the communication valve into a communicating state, simultaneously realises a state in which power resulting from the rotation of the first variator in one direction of the planetary continuously variable transmission mechanism is transmitted to the second variator, and a state in which the transmission of power resulting from the rotation of the first variator in the opposite direction in the second variator is blocked, thereby restricting the rotation of the first variator in one direction and allowing it to rotate in the opposite direction.

4. A transmission as claimed in claim 2, characterized in that the controller switches from the first power transmission state or the second power transmission state, in which the rotation of the input shaft is transmitted to the multi-stage variable transmission mechanism via the planetary type continuously variable transmission mechanism, to the third power transmission state, in which the rotation of the input shaft is transmitted to the multi-stage variable transmission mechanism, bypassing the planetary type continuously variable transmission mechanism, by bringing the communication valve into a communicating state and switching the direct-coupled clutch from a released state to an engaged state.

5. A transmission as claimed in claim 2, characterized in that the controller switches from the third power transmission state, in which the rotation of the input shaft is transmitted to the multi-stage variable transmission mechanism by bypassing the planetary type continuously variable transmission mechanism, to the first power transmission state or the second power transmission state, in which the rotation of the input shaft is transmitted to the multi-stage variable transmission mechanism via the planetary type continuously variable transmission mechanism, by bringing the communication valve into a communicating state and switching the direct-coupled clutch from an engaged state to a released state.

6. A transmission as claimed in claim 2, wherein the communication valve is an electromagnetic relief valve whose relief set pressure can be changed, and the controller brings the communication valve into the blocked state by increasing the relief set pressure, and brings the communication valve into the communicating state by decreasing the relief set pressure.

7. A transmission as claimed in claim 2, wherein the multi-speed mechanism is provided with a plurality of power transmission paths with different reduction ratios, and the controller, when switching the power transmission paths of the multi-speed mechanism together with switching from the second power transmission state to the third power transmission state, places the communication valve in a communicating state, thereby restricting rotation of the first variator in one direction and allowing rotation in the opposite direction freely.

8. A transmission as claimed in claim 2, characterized in that the multi-speed mechanism is provided with a plurality of power transmission paths with different reduction ratios, and when switching from the third power transmission state to the second power transmission state and switching the power transmission path of the multi-speed mechanism, the controller places the communication valve in a communicating state, thereby restricting rotation of the first variator in one direction and allowing rotation in the opposite direction freely.

9. A transmission as claimed in claim 7, characterized in that the controller switches from the second power transmission state to the third power transmission state and switches the power transmission path of the multi-speed mechanism by bringing the communication valve into a communicating state and switching the direct-coupled clutch from a released state to an engaged state.

10. A transmission as claimed in claim 8, characterized in that the controller switches from the third power transmission state to the second power transmission state and switches the power transmission path of the multi-stage transmission mechanism by bringing the communication valve into a communicating state and switching the direct-coupled clutch from an engaged state to a released state.

11. A transmission as described in claim 2, wherein the multi-speed transmission mechanism is provided with a plurality of power transmission paths with different reduction ratios, and the controller, when switching the power transmission path of the multi-speed transmission mechanism together with switching from the first power transmission state to the third power transmission state, places the communication valve in a communicating state, thereby restricting rotation of the first variator in one direction and allowing rotation in the opposite direction freely.

12. A transmission as described in claim 2, wherein the multi-speed mechanism is provided with a plurality of power transmission paths with different reduction ratios, and the controller, when switching the power transmission paths of the multi-speed mechanism together with switching from the third power transmission state to the first power transmission state, places the communication valve in a communicating state, thereby restricting rotation of the first variator in one direction and allowing rotation in the opposite direction freely.

13. A transmission as claimed in claim 11, characterized in that the controller switches from the first power transmission state to the third power transmission state and switches the power transmission path of the multi-stage transmission mechanism by bringing the communication valve into a communicating state and switching the direct-coupled clutch from a released state to an engaged state.

14. A transmission as claimed in claim 12, characterized in that the controller switches from the third power transmission state to the first power transmission state and switches the power transmission path of the multi-stage transmission mechanism by bringing the communication valve into a communicating state and switching the direct-coupled clutch from an engaged state to a released state.

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