Transmission

Abstract

A transmission (21) is provided with an input shaft (22), an output shaft (23), a planetary continuously variable transmission mechanism (24), a multistage transmission mechanism (26), and a controller (25). The multistage transmission mechanism (26) is provided with a forward rotation mode in which a first forward speed clutch (69) is engaged, and a reverse rotation mode in which a first reverse speed clutch (70) is engaged. When switching from the forward rotation mode to the reverse rotation mode, the controller (25) starts switching from an engaged state to a released state of the first forward speed clutch (69) and starts switching from the released state to the engaged state of the first reverse speed clutch (70), with the rotation of the output shaft (23) in a forward rotation state (forward state).

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 technology described in Patent Document 1 may not be able to smoothly switch between forward and reverse rotation of the output shaft (and thus switch between forward and reverse movement of the vehicle).

[0005] One object of the present invention is to provide a transmission that can smoothly switch between forward and reverse rotation of the output shaft (and thus between forward and reverse movement of the vehicle).

[0006] The present invention preferably provides a transmission comprising an input shaft rotated by a power source mounted on a vehicle, an output shaft outputting 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 on the input shaft side and transmitting it to the output shaft side, and a multi-stage transmission mechanism for changing the speed of the rotation on the output side of the planetary continuously variable transmission mechanism in stages by switching the transmission path of meshing gears, wherein 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 serving as an output side, and a third member serving as an output side separate from the second member, a first variator connected to the second member of the planetary mechanism, and a second variator capable of transmitting power between the first variator and the multi-stage transmission mechanism, a first output clutch provided in a first output transmission path in which the number of engagements of the gears between the output side of the planetary continuously variable transmission mechanism and the output shaft is an odd number, and switching between transmission and release of power of the first output transmission path; and a second output clutch provided in a second output transmission path in which the number of engagements of the gears between the output side of the planetary continuously variable transmission mechanism and the output shaft is zero or an even number, and switching between transmission and release of power of the second output transmission path. The transmission also includes a controller that controls engagement and release of the first output clutch and engagement and release of the second output clutch, and the controller is capable of reversing the traveling direction of the vehicle by switching between a forward rotation mode in which the first output clutch is engaged and the second output clutch is released, and a reverse mode in which the first output clutch is released and the second output clutch is engaged. When switching from the forward rotation mode to the reverse rotation mode, the controller initiates switching of the first output clutch from an engaged state to a released state and also initiates switching of the second output clutch from a released state to an engaged state while the rotation of the output shaft is in the forward rotation state, and reverses the rotation direction of the third member by changing the rotational speed of the first variator.Alternatively, when switching from the reverse rotation mode to the forward rotation mode, the controller initiates switching of the second output clutch from an engaged state to a released state and the first output clutch from a released state to an engaged state while the rotation of the output shaft is in a reverse state, and reverses the rotation direction of the third member by changing the rotational speed of the first variator.

[0007] According to the present invention, the output shaft can be smoothly switched between normal and reverse rotation (and hence between forward and reverse movement of the vehicle).

[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). 20 is a configuration diagram similar to FIG. 3 , showing a first modified example (a configuration in which internal lockup is performed by a brake). 21 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). 22 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). 23 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). 24 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). 25 is a characteristic line diagram showing an example of time changes in various state quantities when switching from a forward rotation mode (forward mode) to a reverse mode (reverse mode). 26 is a characteristic line diagram showing an example of time changes in various state quantities when switching from a reverse mode (reverse mode) to a forward rotation mode (forward mode). 27 is a configuration diagram similar to FIG. 4 , showing a second embodiment. 28 is an enlarged view of portion (C) in FIG. 20 . Fig. 21 is an explanatory diagram of the planetary mechanism in Fig. 20 as seen from the power source side. Fig. 22 is a characteristic diagram showing the relationship between the rotational speeds of the three members of the planetary mechanism in Fig. 20. Fig. 23 is a configuration diagram similar to Fig. 20, 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. 21 is a diagram similar to FIG. 20 but 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 modified example 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 a case where an internal combustion engine is used as the power source for a vehicle. In this case, it is difficult to reverse the rotation of the engine's rotating shaft. Therefore, to enable the vehicle to travel forward and backward, the transmission needs to have a mechanism that switches the rotation of the input shaft between forward and reverse. Because wheel loaders frequently travel both forward and backward, it is desirable to provide a function within the transmission that reverses the rotation direction.

[0105] One way to reverse the direction of rotation is to use a clutch to switch between a forward and reverse power transmission path. However, when switching the output shaft of a transmission between forward and reverse rotation, there is always a point where the output shaft reaches zero rotation, and it is difficult to switch between the forward and reverse power transmission paths by engaging and disengaging the clutch at the moment when the output shaft reaches zero rotation.

[0106] Therefore, in this embodiment, a transmission using a planetary continuously variable transmission mechanism is made to be able to smoothly switch between a forward rotation power transmission path and a reverse rotation power transmission path. That is, in this embodiment, it is made possible to smoothly switch between forward and reverse rotation of the output shaft 23 of the speed change device 21 (transmission), and by extension to smoothly switch between forward and reverse movement of the wheel loader 1 (vehicle). 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] 3 and 4, when the transmission 21 is switched from the forward rotation mode (forward mode) to the reverse mode (reverse mode), the controller 25 switches the forward first-speed clutch 69, which is the first output clutch, from an engaged state to a released state, and switches the reverse first-speed clutch 70, which is the second output clutch, from a released state to an engaged state. At this time, the controller 25 starts switching the forward first-speed clutch 69 and the reverse first-speed clutch 70 while the output shaft 23 is rotating in the forward direction (forward direction). That is, while the output shaft 23 is rotating in the forward direction, the controller 25 starts switching the forward first-speed clutch 69 from an engaged state to a released state, and starts switching the reverse first-speed clutch 70 from a released state to an engaged state.

[0118] Furthermore, when the transmission 21 is switched from the reverse mode (reverse mode) to the forward mode (forward mode), the controller 25 switches the reverse first-speed clutch 70 from an engaged state to a released state, and switches the forward first-speed clutch 69 from a released state to an engaged state. At this time, the controller 25 starts switching the reverse first-speed clutch 70 and the forward first-speed clutch 69 while the rotation of the output shaft 23 is in the reverse direction, i.e., while the output shaft 23 is rotating in the reverse direction (reverse direction). That is, while the rotation of the output shaft 23 is in the reverse direction, the controller 25 starts switching the reverse first-speed clutch 70 from an engaged state to a released state, and starts switching the forward first-speed clutch 69 from a released state to an engaged state.

[0119] When switching from the forward rotation mode to the reverse rotation mode, or from the reverse rotation mode to the forward rotation mode, the rotation of the output side (second sun gear 29C, which serves as the third member, and third connecting member 32) of planetary type continuously variable transmission mechanism 24 is temporarily reversed. Switching from the forward rotation mode to the reverse rotation mode and from the reverse rotation mode to the forward rotation mode will be described below.

[0120] First, switching from forward rotation mode to reverse mode will be described with reference to Figure 18. Figure 18 shows an example of changes over time in the pressure (clutch pressure) of the forward first-speed clutch 69 and the reverse first-speed clutch 70, the rotational speed of the first hydraulic pump motor 33 (first variator), the second hydraulic pump motor 34 (second variator), and the output shaft 23, the pressure of the main lines 35A, 35B and the set pressures of the variable relief valves 38A, 38B, the flow rates of the first hydraulic pump motor 33 and the second hydraulic pump motor 34, the torque (output torque) of the output shaft 23, and the volumetric capacity of the first hydraulic pump motor 33 and the second hydraulic pump motor 34 when switching from forward rotation mode to reverse mode. At time A in Figure 18, the wheel loader 1, which is a vehicle, is traveling in forward first-speed infinitely variable transmission. The controller 25 is also attempting to switch from forward first-speed infinitely variable transmission to reverse first-speed infinitely variable transmission. Between time A and time B in Figure 18, power is transmitted from the output shaft 23 to the engine 9, which serves as the power source, in order to reduce the speed of the wheel loader 1. At this time, the controller 25 engages the first forward speed clutch 69.

[0121] The controller 25 also controls the volume of the second hydraulic pump motor 34, which serves as a fluid pressure motor (hydraulic motor), to its maximum, and controls the volume of the first hydraulic pump motor 33, which serves as a fluid pressure pump (hydraulic pump), so that the flow rate of the first hydraulic pump motor 33 is slightly less than the discharge flow rate of the second hydraulic pump motor 34. This allows power to flow from the second hydraulic pump motor 34 to the first hydraulic pump motor 33. In other words, the fluid (hydraulic oil) discharged from the second hydraulic pump motor 34 flows through the second main line 35B toward the first hydraulic pump motor 33 and returns to the second hydraulic pump motor 34 through the first main line 35A. At this time, the pressure in the second main line 35B is higher than the pressure in the first main line 35A.

[0122] From time B to time G, the controller 25 reduces the relief pressure (set relief pressure) of the first adjustable relief valve 38A from a pressure of approximately 30 to 45 MPa to a pressure of approximately 2.5 to 15 MPa. This completes preparations to suppress the generation of surge pressure in the first main line 35A even if the rotation directions of the first hydraulic pump-motor 33 and the second hydraulic pump-motor 34 are reversed.

[0123] From time C to time G, the controller 25 reduces the relief pressure of the second variable relief valve 38B from a pressure of approximately 10 to 35 MPa to a pressure of approximately 2.5 to 15 MPa. This limits the torque of the first hydraulic pump / motor 33, and begins to limit the torque capacity that can transmit power from the idler element 28 to the engine 9. At this time, the controller 25 reduces the pressure of the forward first-speed clutch 69 from time D to time F. This reduces the torque capacity that can be transmitted by the forward first-speed clutch 69. If the torque capacity that can be transmitted by the forward first-speed clutch 69 exceeds the torque capacity that can be transmitted by the idler element 28 to the engine 9, the second variable relief valve 38B performs a relief operation (between C1 and C2 in FIG. 18 ).

[0124] The relief pressure of the second variable relief valve 38B is reduced to prevent surge pressure and sudden fluctuations in transmission torque. The pressure of the forward first-speed clutch 69 begins to decrease from time D and decreases to zero at time F. After time F, the forward first-speed clutch 69 is completely disengaged. In contrast, the pressure of the reverse first-speed clutch 70 is increased from time E to time I. At time G, midway between time E and time I, the rotation direction of the second hydraulic pump / motor 34 is reversed. Meanwhile, the rotation speed of the output shaft 23 remains in the forward direction. In other words, from time G to time H, the reverse first-speed clutch 70 transmits power while slipping occurs between the input side (reverse first-speed gear 67) and the output side (low range shaft 65) of the reverse first-speed clutch 70, with the rotation directions differing.

[0125] This slippage decreases as the pressure in the reverse first-speed clutch 70 increases, and at time H, the slippage disappears. At time G, when the rotational direction of the output side of the planetary continuously variable transmission mechanism 24 (the second sun gear 29C, which serves as the third member, the third connecting member 32, and the second hydraulic pump / motor 34) reverses, surge pressure is likely to occur in the first main line 35A. Because the variable relief valves 38A and 38B respond slowly to sudden surge pressure, the surge pressure can be suppressed by lowering the relief pressure of the first variable relief valve 38A in advance. In FIG. 18 , an example of surge pressure is indicated by a two-dot chain line 101. At time G, the relief pressure of the first variable relief valve 38A is lowered, thereby suppressing the surge pressure. Then, from time G to time H, the relief pressure of the first variable relief valve 38A is gradually increased. As a result, the torque transmitted in the direction in which the rotation direction of the planetary continuously variable transmission mechanism 24 changes from reverse to forward rotation increases, making it possible to decelerate the wheel loader 1 traveling in the forward direction. Between time G and time K, the first variable relief valve 38A performs a relief operation. As a result, the hydrostatic continuously variable transmission mechanism 41 absorbs power, making it possible to decelerate the wheel loader 1 traveling in the forward direction.

[0126] Between time G and time J, the rotation direction of the planetary continuously variable transmission mechanism 24 is reversed. In the first embodiment, this corresponds to a state in which the planetary continuously variable transmission mechanism 24 operates along line Y1 in the lower right quadrant (fourth quadrant) or the upper left quadrant (second quadrant) of the four quadrants in FIG. 9 . Similarly, in the second embodiment, this corresponds to a state in which the planetary continuously variable transmission mechanism 24 operates along line Y2 in the lower right quadrant (fourth quadrant) or the upper left quadrant (second quadrant) of the four quadrants in FIG. 23 . That is, between time G and time J, the output of the planetary continuously variable transmission mechanism 24 is reversed, so that the output shaft 23 rotates in the forward direction despite the reverse first-speed clutch 70 being engaged. After time J, the rotation direction of the planetary continuously variable transmission mechanism 24 returns to forward rotation, and the output shaft 23 begins to rotate in the reverse direction.

[0127] Between time G and time L, torque fluctuations in the output shaft 23 are likely to occur, and shaking of the wheel loader 1 is likely to increase, so it is preferable to maintain the relief pressure of the second variable relief valve 38B at a low pressure of approximately 2.5 to 15 MPa. The relief pressure of the second variable relief valve 38B is maintained at a high pressure of approximately 10 to 50 MPa from time L onwards after the gear shift is completed. In other words, the relief pressure of the second variable relief valve 38B is increased to a pressure of approximately 40 to 50 MPa from time L to time M. This completes the gear shift from forward rotation mode to reverse mode.

[0128] During this shift from forward rotation mode to reverse rotation mode, the displacement of the second hydraulic pump / motor 34 is always controlled to its maximum, while the displacement of the first hydraulic pump / motor 33 needs to be changed. That is, from time A to time G, the displacement of the first hydraulic pump / motor 33 is controlled so that the first hydraulic pump / motor 33 discharges a flow rate slightly less than the discharge flow rate of the second hydraulic pump / motor 34. As a result, power flows from the second hydraulic pump / motor 34 to the first hydraulic pump / motor 33. That is, the fluid discharged by the forward rotation of the first hydraulic pump / motor 33 flows through the first main line 35A to the second hydraulic pump / motor 34, rotates the second hydraulic pump / motor 34 forward, and then returns to the first hydraulic pump / motor 33 through the second main line 35B. At this time, the second main line 35B is under higher pressure than the first main line 35A.

[0129] From time G to time J, the first hydraulic pump / motor 33 is controlled between 0 and 10% of the maximum discharge volume. The second hydraulic pump / motor 34 rotates in the reverse direction and sends fluid (hydraulic oil) to the first main line 35A. The first hydraulic pump / motor 33 rotates in the forward direction and sends fluid (hydraulic oil) to the first main line 35A. The fluid sent to the first main line 35A flows 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 is supplied to the first hydraulic pump / motor 33 and the second hydraulic pump / motor 34. At this time, the flow rate flowing through the second check valve 48 is the sum of the flow rate of the first hydraulic pump / motor 33 (first variator) and the flow rate of the second hydraulic pump / motor 34 (second variator) shown in FIG. 18 . In addition, the flow rate in FIG. 18 is positive (+) when the first hydraulic pump motor 33 and the second hydraulic pump motor 34 are rotating forward, and negative (-) when they are rotating reversely.

[0130] From time J onwards, the volume of the first hydraulic pump motor 33 is controlled so that the first hydraulic pump motor 33 discharges a flow rate slightly greater than the discharge flow rate of the second hydraulic pump motor 34. As a result, power flows from the first hydraulic pump motor 33 to the second hydraulic pump motor 34. In other words, the fluid discharged by the forward rotation of the first hydraulic pump motor 33 flows through the first main line 35A to the second hydraulic pump motor 34, rotates the second hydraulic pump motor 34 forward, and then returns to the first hydraulic pump motor 33 through the second main line 35B. At this time, the first main line 35A is under higher pressure than the second main line 35B.

[0131] Next, Figure 19 shows an example of changes over time in the pressure (clutch pressure) of the reverse first-speed clutch 70 and the forward first-speed clutch 69, the rotational speed of the first hydraulic pump motor 33 (first variator), the second hydraulic pump motor 34 (second variator), and the output shaft 23, the pressure in the main lines 35A, 35B and the set pressures of the variable relief valves 38A, 38B, the flow rates of the first hydraulic pump motor 33 and the second hydraulic pump motor 34, the torque (output torque) of the output shaft 23, and the volumetric capacity of the first hydraulic pump motor 33 and the second hydraulic pump motor 34 when switching from reverse mode to forward mode. At time A in Figure 19, the wheel loader 1, which is a vehicle, is traveling in reverse first-speed infinitely variable speed mode. The controller 25 is also attempting to switch from reverse first-speed infinitely variable speed mode to forward first-speed infinitely variable speed mode. Between time A and time B in Figure 19, power is transmitted from the output shaft 23 to the engine 9, which is the power source, in order to reduce the speed of the wheel loader 1. At this time, the controller 25 engages the reverse first-speed clutch 70 .

[0132] The controller 25 also controls the volume of the second hydraulic pump motor 34, which serves as a fluid pressure motor (hydraulic motor), to its maximum, and controls the volume of the first hydraulic pump motor 33, which serves as a fluid pressure pump (hydraulic pump), so that the flow rate of the first hydraulic pump motor 33 is slightly less than the discharge flow rate of the second hydraulic pump motor 34. This allows power to flow from the second hydraulic pump motor 34 to the first hydraulic pump motor 33. In other words, the fluid (hydraulic oil) discharged from the second hydraulic pump motor 34 flows through the second main line 35B toward the first hydraulic pump motor 33 and returns to the second hydraulic pump motor 34 through the first main line 35A. At this time, the pressure in the second main line 35B is higher than the pressure in the first main line 35A.

[0133] From time B to time G, the controller 25 reduces the relief pressure (set relief pressure) of the first adjustable relief valve 38A from a pressure of approximately 30 to 45 MPa to a pressure of approximately 2.5 to 15 MPa. This completes preparations to suppress the generation of surge pressure in the first main line 35A even if the rotation directions of the first hydraulic pump-motor 33 and the second hydraulic pump-motor 34 are reversed.

[0134] From time C to time G, the controller 25 reduces the relief pressure of the second variable relief valve 38B from a pressure of approximately 10 to 35 MPa to a pressure of approximately 2.5 to 15 MPa. This limits the torque of the first hydraulic pump / motor 33, and begins to limit the torque capacity that can transmit power from the idler element 28 to the engine 9. At this time, the controller 25 reduces the pressure of the reverse first-speed clutch 70 from time D to time F. This reduces the torque capacity that can be transmitted by the reverse first-speed clutch 70. If the torque capacity that can be transmitted by the reverse first-speed clutch 70 exceeds the torque capacity that can be transmitted by the idler element 28 to the engine 9, the second variable relief valve 38B performs a relief operation (between C1 and C2 in FIG. 19 ).

[0135] The relief pressure of the second variable relief valve 38B is reduced to prevent surge pressure and sudden fluctuations in transmission torque. The pressure of the reverse first-speed clutch 70 begins to decrease from time D and decreases to zero at time F. After time F, the reverse first-speed clutch 70 is completely disengaged. In contrast, the pressure of the forward first-speed clutch 69 is increased from time E to time I. At time G, midway between time E and time I, the rotation direction of the second hydraulic pump / motor 34 is reversed. Meanwhile, the rotation speed of the output shaft 23 remains in the reverse direction. That is, from time G to time H, the forward first-speed clutch 69 transmits power while slipping occurs between the input side (forward first-speed gear 66) and the output side (low range shaft 65) of the forward first-speed clutch 69, with the rotation directions differing.

[0136] This slippage decreases as the pressure in the first forward clutch 69 increases, and at time H, the slippage disappears. At time G, when the rotational direction of the output side of the planetary continuously variable transmission mechanism 24 (the second sun gear 29C, which serves as the third member, the third connecting member 32, and the second hydraulic pump / motor 34) reverses, surge pressure is likely to occur in the first main line 35A. Because the variable relief valves 38A and 38B respond slowly to sudden surge pressure, the surge pressure can be suppressed by lowering the relief pressure of the first variable relief valve 38A in advance. In FIG. 19 , an example of surge pressure is indicated by a two-dot chain line 101. At time G, the relief pressure of the first variable relief valve 38A is lowered, thereby suppressing the surge pressure. Then, from time G to time H, the relief pressure of the first variable relief valve 38A is gradually increased. As a result, the torque transmitted in the direction in which the rotation direction of the planetary continuously variable transmission mechanism 24 changes from reverse to forward rotation increases, making it possible to decelerate the wheel loader 1 traveling in the reverse direction. Between time G and time K, the first variable relief valve 38A performs a relief operation. As a result, the hydrostatic continuously variable transmission mechanism 41 absorbs power, making it possible to decelerate the wheel loader 1 traveling in the reverse direction.

[0137] Between time G and time J, the rotation direction of the planetary continuously variable transmission mechanism 24 is reversed. In the first embodiment, this corresponds to a state in which the planetary continuously variable transmission mechanism 24 operates along line Y1 in the lower right quadrant (fourth quadrant) or the upper left quadrant (second quadrant) of the four quadrants in FIG. 9 . Similarly, in the second embodiment, this corresponds to a state in which the planetary continuously variable transmission mechanism 24 operates along line Y2 in the lower right quadrant (fourth quadrant) or the upper left quadrant (second quadrant) of the four quadrants in FIG. 23 . That is, between time G and time J, the output of the planetary continuously variable transmission mechanism 24 is reversed, so that the output shaft 23 rotates in the reverse direction despite the forward first-speed clutch 69 being engaged. After time J, the rotation direction of the planetary continuously variable transmission mechanism 24 returns to normal rotation, and the output shaft 23 begins to rotate in the forward direction.

[0138] Between time G and time L, torque fluctuations in the output shaft 23 are likely to occur, and shaking of the wheel loader 1 is likely to increase, so it is preferable to maintain the relief pressure of the second variable relief valve 38B at a low pressure of approximately 2.5 to 15 MPa. The relief pressure of the second variable relief valve 38B is maintained at a high pressure of approximately 10 to 50 MPa from time L onwards after the gear shift is completed. In other words, the relief pressure of the second variable relief valve 38B is increased to a pressure of approximately 40 to 50 MPa from time L to time M. This completes the gear shift from reverse rotation mode to forward rotation mode.

[0139] During this shift from reverse rotation mode to forward rotation mode, the displacement of the second hydraulic pump / motor 34 is always controlled to its maximum, while the displacement of the first hydraulic pump / motor 33 needs to be changed. That is, from time A to time G, the displacement of the first hydraulic pump / motor 33 is controlled so that the first hydraulic pump / motor 33 discharges a flow rate slightly less than the discharge flow rate of the second hydraulic pump / motor 34. As a result, power flows from the second hydraulic pump / motor 34 to the first hydraulic pump / motor 33. That is, the fluid discharged by the forward rotation of the first hydraulic pump / motor 33 flows through the first main line 35A to the second hydraulic pump / motor 34, rotates the second hydraulic pump / motor 34 forward, and then returns to the first hydraulic pump / motor 33 through the second main line 35B. At this time, the second main line 35B is under higher pressure than the first main line 35A.

[0140] From time G to time J, the first hydraulic pump / motor 33 is controlled between 0 and 10% of the maximum discharge volume. The first hydraulic pump / motor 33 rotates forward, sending fluid (hydraulic oil) to the first main line 35A. The second hydraulic pump / motor 34 rotates reversely, sending fluid (hydraulic oil) to the first main line 35A. The fluid sent to the first main line 35A flows 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 is supplied to the first hydraulic pump / motor 33 and the second hydraulic pump / motor 34. At this time, the flow rate flowing through the second check valve 48 is the sum of the flow rate of the first hydraulic pump / motor 33 (first variator) and the flow rate of the second hydraulic pump / motor 34 (second variator) shown in FIG. 19 . In addition, the flow rate in FIG. 19 is positive (+) when the first hydraulic pump motor 33 and the second hydraulic pump motor 34 are rotating forward, and negative (-) when they are rotating reversely.

[0141] From time J onwards, the volume of the first hydraulic pump motor 33 is controlled so that the first hydraulic pump motor 33 discharges a flow rate slightly greater than the discharge flow rate of the second hydraulic pump motor 34. As a result, power flows from the first hydraulic pump motor 33 to the second hydraulic pump motor 34. In other words, the fluid discharged by the forward rotation of the first hydraulic pump motor 33 flows through the first main line 35A to the second hydraulic pump motor 34, rotates the second hydraulic pump motor 34 forward, and then returns to the first hydraulic pump motor 33 through the second main line 35B. At this time, the first main line 35A is under higher pressure than the second main line 35B.

[0142] Next, the reason why it is preferable to switch the forward first-speed clutch 69 and the reverse first-speed clutch 70 before the rotational speed of the output side (second sun gear 29C and third connecting member 32, which are the third members) of the planetary continuously variable transmission mechanism 24 reaches zero will be explained. When switching between the forward rotation mode and the reverse mode, the switching of the forward first-speed clutch 69 and the reverse first-speed clutch 70 can start in the following cases (A), (B), and (C). (A) The rotation of the output side (second sun gear 29C and third connecting member 32, which are the third members) of the planetary continuously variable transmission mechanism 24 starts in a forward rotation state. (B) The switching starts after the rotation of the output side (second sun gear 29C and third connecting member 32, which are the third members) of the planetary continuously variable transmission mechanism 24 changes from forward rotation to reverse rotation. (C) It starts when the rotation of the output side of the planetary type continuously variable transmission mechanism 24 (the second sun gear 29C, which is the third member, and the third connecting member 32) becomes zero.

[0143] The above (C) is not preferable because, unless the responsiveness of the clutch control is sufficiently increased, pulsation occurs in the torque of the output shaft 23 of the transmission 21, causing discomfort to the occupants. For this reason, it is preferable to start switching the forward first-speed clutch 69 and the reverse first-speed clutch 70 when the output side of the planetary continuously variable transmission mechanism 24 (the second sun gear 29C, which is the third member, and the third connecting member 32) is rotating in the forward direction.

[0144] Here, in order to increase the allowable rotational speed of the output side of planetary continuously variable transmission mechanism 24 (second sun gear 29C and third connecting member 32, which are the third members) in the reverse rotation state, it is necessary to increase the allowable rotational speed of first hydraulic pump / motor 33. In this case, it is necessary to change the gear ratio of planetary gear mechanism 29 and review the relationship between the rotational speed ratios of input shaft 22, first hydraulic pump / motor 33, and the output side of planetary continuously variable transmission mechanism 24 (second sun gear 29C and third connecting member 32, which are the third members) so that the rotational speed of first hydraulic pump / motor 33 does not exceed the allowable rotational speed. In other words, the slopes of line Y1 in FIG. 9 and line Y2 in FIG. 23 are changed. When the gear ratio of the planetary gear mechanism 29 is set in a direction that increases the rotational speed of the first hydraulic pump motor 33, more of the torque transmitted from the input shaft 22 to the planetary gear mechanism 29 is transmitted to the output side (second sun gear 29C, which is the third member, and third connecting member 32) of the planetary continuously variable transmission mechanism 24 than to the first hydraulic pump motor 33 (first sun gear 29B, which is the second member). This allows the first hydraulic pump motor 33 to be made smaller.

[0145] Furthermore, the transmission efficiency between the first hydraulic pump-motor 33 and the second hydraulic pump-motor 34 is poorer than the transmission efficiency from the output side of the planetary continuously variable transmission mechanism 24 (the second sun gear 29C and the third connecting member 32, which serve as the third member) to the output shaft 23 of the transmission device 21, where power is transmitted via gears. In order to improve the transmission efficiency of the planetary continuously variable transmission mechanism 24, the gear ratio of the planetary gear mechanism 29 is set in a direction that increases the rotational speed of the first hydraulic pump-motor 33 as long as the rotational speed of the first hydraulic pump-motor 33 is allowable. For this reason, there is a trade-off in that the transmission efficiency on the forward rotation side must be sacrificed in order to increase the allowable rotational speed in the reverse rotation state of the output side of the planetary continuously variable transmission mechanism 24 (the second sun gear 29C and the third connecting member 32, which serve as the third member).

[0146] Consider a case where switching between the forward first-speed clutch 69 and the reverse first-speed clutch 70 is initiated after the rotation of the output side (second sun gear 29C, third connecting member 32, which constitutes the third member) of the planetary continuously variable transmission mechanism 24 changes from forward to reverse. In this case, the allowable rotational speed in the reverse state must be increased compared to when switching is initiated while the rotation of the output side (second sun gear 29C, third connecting member 32, which constitutes the third member) of the planetary continuously variable transmission mechanism 24 is in the forward rotation state. For this reason, it is preferable to initiate switching between the forward first-speed clutch 69 and the reverse first-speed clutch 70 while the rotation of the output side (second sun gear 29C, third connecting member 32, which constitutes the third member) of the planetary continuously variable transmission mechanism 24 is in the forward rotation state.

[0147] The first hydraulic pump / motor 33 serving as the first variator and the second hydraulic pump / motor 34 serving as the second variator may be configured with an electric motor or a generator (power-generating motor) instead of a hydraulic pump / motor (hydraulic pump, hydraulic motor) that is a hydraulic rotating machine. That is, the first variator 33 and the second variator 34 may be configured with electric devices instead of hydraulic devices. Even when the first variator 33 and the second variator 34 are configured with electric devices, it is preferable to start switching between the forward rotation mode and the reverse rotation mode by switching the forward first-speed clutch 69 and the reverse first-speed clutch 70 when the rotation of the output side (the second sun gear 29C and the third connecting member 32 that serve as the third member) of the planetary continuously variable transmission mechanism 24 is in the forward rotation state.

[0148] 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, and the multi-speed transmission mechanism 26. The transmission 21 also includes an idler element 28. 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 multi-speed transmission mechanism 26 changes the speed of the rotation on the output side of the planetary continuously variable transmission mechanism 24 in stages by switching the transmission path of the meshing gears. The idler element 28 connects the output side of the planetary continuously variable transmission mechanism 24 to the multi-speed transmission mechanism 26 .

[0149] 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; and a second sun gear 29C (third member) serving as an output 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 a second connecting member 31 and a second clutch 36. The second sun gear 29C (third member) is connected to the idler element 28. That is, the second sun gear 29C (third member) is connected to the idler element 28 (first idler gear 28B) via the third connecting member 32. 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.

[0150] The multi-speed transmission mechanism 26 includes a forward first-speed transmission path (forward transmission path, forward rotation transmission path) as a first output transmission path, and a reverse first-speed transmission path (reverse transmission path, reverse rotation transmission path) as a second output transmission path. The multi-speed transmission mechanism 26 also includes a forward first-speed clutch 69 as a first output clutch, and a reverse first-speed clutch 70 as a second output clutch. The forward first-speed transmission path is an output transmission path in which the number of gear engagements between the idler element 28 (second idler gear 28C) and the output shaft 23 is odd. Specifically, the forward first-speed transmission path corresponds to the low range shaft unit 61 in a state in which the forward first-speed clutch 69 is engaged. 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 connected, 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).

[0151] The reverse first-speed transmission path is an output transmission path in which the number of gear meshings between the idler element 28 (first idler gear 28B) and the output shaft 23 is zero or an even number. Specifically, the reverse first-speed transmission path corresponds to the low-range shaft unit 61 in a state in which the reverse first-speed clutch 70 is engaged. 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 engaged, 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).

[0152] That is, since the reverse first-speed transmission path includes the counter gear 64, the number of times the gears mesh is "odd number" or "zero or even number" differs from that of the forward first-speed transmission path. As a result, the rotation directions of the output shaft 23 are opposite between the forward first-speed transmission path and the reverse first-speed transmission path. Note that the relationship between "odd number" and "zero or even number" may be reversed between the forward first-speed transmission path and the reverse first-speed transmission path. That is, the first output transmission path, in which the number of times the gears mesh is "odd number," may be the reverse first-speed transmission path (reverse transmission path, reverse transmission path), and the second output transmission path, in which the number of times the gears mesh is "zero or even number," may be the forward first-speed transmission path (forward transmission path, forward transmission path).

[0153] The forward first-speed clutch 69 is provided in the forward first-speed transmission path (low range shaft unit 61). The forward first-speed clutch 69 switches between power transmission and release of the forward first-speed transmission path. That is, the forward first-speed clutch 69 switches between engagement (connection) and release of the forward first-speed gear 66 and the low range shaft 65. The reverse first-speed clutch 70 is provided in the reverse first-speed transmission path (low range shaft unit 61). The reverse first-speed clutch 70 switches between power transmission and release of the reverse first-speed transmission path. That is, the reverse first-speed clutch 70 switches between engagement (connection) and release of the reverse first-speed gear 67 and the low range shaft 65.

[0154] The transmission 21 also includes a controller 25. The controller 25 controls the engagement and disengagement of the forward first-speed clutch 69. The controller 25 also controls the engagement and disengagement of the reverse first-speed clutch 70. The controller 25 is able to reverse the direction of travel of the wheel loader 1, which is a vehicle, by switching between a forward rotation mode (a state in which forward first-speed infinitely variable speed is achieved) and a reverse mode (a state in which reverse first-speed infinitely variable speed is achieved). The controller 25 establishes the forward rotation mode (a state in which forward first-speed infinitely variable speed is achieved) by engaging the forward first-speed clutch 69 and disengaging the reverse first-speed clutch 70. The controller 25 establishes the reverse mode (a state in which reverse first-speed infinitely variable speed is achieved) by disengaging the forward first-speed clutch 69 and engaging the reverse first-speed clutch 70.

[0155] When switching from forward rotation mode to reverse mode, the controller 25 initiates switching of the forward first-speed clutch 69 from an engaged state to a released state and also initiates switching of the reverse first-speed clutch 70 from a released state to an engaged state while the output shaft 23 is rotating in the forward rotation state (forward state). In other words, when switching from forward rotation mode to reverse mode, the controller 25 switches the forward first-speed clutch 69 from an engaged state to a released state and switches the reverse first-speed clutch 70 from a released state to an engaged state while the output shaft 23 is rotating in the forward rotation state (forward state). At this time, the controller 25 initiates disengagement (pressure reduction) of the forward first-speed clutch 69 and then initiates engagement (pressure increase) of the reverse first-speed clutch 70. As a result, when switching from forward rotation mode to reverse mode, the output shaft 23 can be switched from forward to reverse, and the wheel loader 1 can be switched from forward to reverse smoothly.

[0156] Furthermore, when switching from reverse mode to forward mode, the controller 25 initiates switching of the reverse first-speed clutch 70 from an engaged state to a released state and initiates switching of the forward first-speed clutch 69 from a released state to an engaged state while the rotation of the output shaft 23 is in the reverse state (reverse state). In other words, when switching from reverse mode to forward mode, the controller 25 switches the reverse first-speed clutch 70 from an engaged state to a released state and switches the forward first-speed clutch 69 from a released state to an engaged state while the rotation of the output shaft 23 is in the reverse state (reverse state). At this time, the controller 25 initiates disengagement (pressure reduction) of the reverse first-speed clutch 70 and then initiates engagement (pressure increase) of the forward first-speed clutch 69. As a result, when switching from reverse mode to forward mode, the output shaft 23 can be switched from reverse to forward, and therefore the wheel loader 1 can be switched from reverse to forward.

[0157] As shown in FIG. 18 , when switching from the forward rotation mode to the reverse rotation mode, the controller 25 changes the rotational speed of the first variator 33 (first hydraulic pump motor 33) to reverse the rotation direction of the output side of the planetary continuously variable transmission mechanism 24, i.e., the second sun gear 29C serving as the third member, and therefore the third connecting member 32. This allows the output side of the planetary continuously variable transmission mechanism 24 to be smoothly reversed when switching from the forward rotation mode to the reverse mode. Also, as shown in FIG. 19 , when switching from the reverse rotation mode to the forward rotation mode, the controller 25 changes the rotational speed of the first variator 33 (first hydraulic pump motor 33) to reverse the rotation direction of the output side of the planetary continuously variable transmission mechanism 24, i.e., the second sun gear 29C serving as the third member, and therefore the third connecting member 32. This allows the output side of the planetary continuously variable transmission mechanism 24 to be smoothly reversed when switching from the reverse rotation mode to the forward rotation mode.

[0158] As shown in FIG. 7 , according to the first embodiment, the first variator 33 is configured as a pump motor serving as a hydraulic rotating machine (hydraulic rotating machine) that performs pumping or motoring. That is, the first variator 33 is the first hydraulic pump / motor 33 that functions as a hydraulic pump (hydraulic pump). The second variator 34 is configured as a pump motor serving as a hydraulic rotating machine (hydraulic rotating machine) that performs pumping or motoring. That is, the second variator 34 is the second hydraulic pump / motor 34 that functions as a hydraulic motor (hydraulic motor). The first hydraulic pump / motor 33 and the second hydraulic pump / motor 34 are connected by a pair of main lines 35A, 35B. A liquid (hydraulic oil) flows through the pair of main lines 35A, 35B. The pair of main lines 35A, 35B enables power transmission between the first hydraulic pump / motor 33 and the second hydraulic pump / motor 34. A first variable relief valve 38A and a second variable relief valve 38B are provided between the pair of main lines 35A, 35B as relief valves for controlling the main lines 35A, 35B between a communication state and a cut-off state. The controller 25 is capable of changing the communication start pressures (relief pressures) of the first variable relief valve 38A and the second variable relief valve 38B.

[0159] Furthermore, when switching from forward rotation mode to reverse mode, the controller 25 reduces the set value of the communication start pressure of the first variable relief valve 38A prior to the start of switching of the forward first-speed clutch 69 and the reverse first-speed clutch 70. In other words, the controller 25 reduces the relief pressure of the first variable relief valve 38A prior to the start of switching of the forward first-speed clutch 69 from the engaged state to the disengaged state. That is, as shown in FIG. 18 , the controller 25 reduces the relief pressure of the first variable relief valve 38A for time B. This makes it possible to suppress the generation of surge pressure in the first main line 35A. This also contributes to a smooth switching from forward rotation mode to reverse mode.

[0160] Furthermore, when switching from reverse mode to forward mode, the controller 25 reduces the set value of the communication start pressure of the first variable relief valve 38A prior to the start of switching of the reverse first-speed clutch 70 and the forward first-speed clutch 69. In other words, the controller 25 reduces the relief pressure of the first variable relief valve 38A prior to the start of switching of the reverse first-speed clutch 70 from the engaged state to the disengaged state. That is, as shown in FIG. 19 , the controller 25 reduces the relief pressure of the first variable relief valve 38A for time B. This makes it possible to suppress the generation of surge pressure in the first main line 35A. This also contributes to a smooth switching from reverse mode to forward mode.

[0161] Furthermore, when switching from forward rotation mode to reverse mode, the controller 25 increases the set value of the communication start pressure of the first variable relief valve 38A while the forward first-speed clutch 69 is being switched from its engaged state to its released state and while the reverse first-speed clutch 70 is being switched from its released state to its engaged state. In other words, after starting to switch the forward first-speed clutch 69 from its engaged state to its released state, the controller 25 increases the relief pressure of the first variable relief valve 38A before the reverse first-speed clutch 70 has completely switched from its released state to its engaged state. That is, as shown in FIG. 18 , the controller 25 increases the relief pressure of the first variable relief valve 38A between time G and time H. This increases the torque transmitted in the direction in which the rotational direction of the planetary continuously variable transmission mechanism 24 changes from reverse to forward rotation, making it possible to decelerate the wheel loader 1 traveling in the forward direction.

[0162] Furthermore, when switching from reverse mode to forward mode, the controller 25 increases the set value of the communication start pressure of the first variable relief valve 38A while the reverse first-speed clutch 70 is being switched from its engaged state to its released state and while the forward first-speed clutch 69 is being switched from its released state to its engaged state. In other words, after starting to switch the reverse first-speed clutch 70 from its engaged state to its released state, the controller 25 increases the relief pressure of the first variable relief valve 38A before the forward first-speed clutch 69 has completely switched from its released state to its engaged state. That is, as shown in FIG. 19 , the controller 25 increases the relief pressure of the first variable relief valve 38A between time G and time H. This increases the torque transmitted in the direction in which the rotational direction of the planetary continuously variable transmission mechanism 24 changes from reverse to forward, making it possible to decelerate the wheel loader 1 traveling in the reverse direction.

[0163] When switching from forward rotation mode to reverse rotation mode, the controller 25 provides a time period during which the first variable relief valve 38A remains open while the rotation direction of the output side (third member) of the planetary continuously variable transmission mechanism 24 is reversed by changing the rotation speed of the first variator 33 (first hydraulic pump / motor 33). That is, as shown in FIG. 18 , from time G to time J, the pressure in the first main line 35A (dashed line) is higher than the set pressure of the first variable relief valve 38A (solid line), and the first variable relief valve 38A performs a relief operation. This allows the hydrostatic continuously variable transmission mechanism 41 to absorb power. This also contributes to a smooth switching from forward rotation mode to reverse rotation mode.

[0164] When switching from reverse rotation mode to forward rotation mode, the controller 25 sets a time during which the first variable relief valve 38A remains open while the rotation direction of the output side (third member) of the planetary continuously variable transmission mechanism 24 is reversed by changing the rotation speed of the first variator 33 (first hydraulic pump / motor 33). That is, as shown in FIG. 19 , from time G to time J, the pressure in the first main line 35A (dashed line) is higher than the set pressure of the first variable relief valve 38A (solid line), and the first variable relief valve 38A performs a relief operation. This allows the hydrostatic continuously variable transmission mechanism 41 to absorb power. This also contributes to a smooth switching from reverse rotation mode to forward rotation mode.

[0165] In the first embodiment, the first variator is configured by a first hydraulic pump / motor 33, and the second variator is configured by a second hydraulic pump / motor 34, and they are connected by a pair of main lines 35A, 35B. Alternatively, the first variator and the second variator may each be configured by an electric motor (electric motor / generator, electric motor, electric generator). In this case, the first variator and the second variator are connected by an electric circuit. An electric motor control device is provided on the electric circuit. The electric motor control device controls, for example, the power of the electric circuit. This enables power transmission between the first variator and the second variator via the electric circuit. In this case, too, when switching from the forward rotation mode to the reverse rotation mode, switching of the forward first-speed clutch 69 (first output clutch) and the reverse first-speed clutch 70 (second output clutch) is started while the output shaft 23 is in the forward rotation state (forward state). Furthermore, when switching from reverse rotation mode to forward rotation mode, switching of the reverse first-speed clutch 70 (second output clutch) and the forward first-speed clutch 69 (first output clutch) begins with the output shaft 23 rotating in the reverse direction (reverse state). This allows the output shaft 23 to be smoothly switched between forward and reverse rotation, and ultimately the wheel loader 1 to be smoothly switched between forward and reverse rotation.

[0166] In the first embodiment, both when switching from the forward rotation mode to the reverse rotation mode and when switching from the reverse rotation mode to the forward rotation mode, the forward first-speed clutch 69 and the reverse first-speed clutch 70 are switched before the rotation of the output side of the planetary continuously variable transmission mechanism 24 (and therefore the rotation of the output shaft 23) is reversed. However, this does not necessarily have to be done both when switching from the forward rotation mode to the reverse rotation mode and when switching from the reverse mode to the forward rotation mode. That is, the forward first-speed clutch 69 and the reverse first-speed clutch 70 may be switched before the rotation of the output side of the planetary continuously variable transmission mechanism 24 (and therefore the rotation of the output shaft 23) is reversed either when switching from the forward rotation mode to the reverse rotation mode or when switching from the reverse mode to the forward rotation mode.

[0167] 20 to 23 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.

[0168] 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.

[0169]

[0170] 20 and 21 , 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.

[0171] 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 the first variator 33 via a second connecting member 31. The ring gear 91C is connected to the idler element 28 (first idler gear 28B) via a third connecting member 32. The sun gear 91B meshes with the planet gear 91D. The planet gear 91D also meshes with the ring gear 91C. The rotation axis Sp (FIG. 22) of the planet gear 91D is supported by the carrier 91A. Therefore, the planet gear 91D rotates while revolving around the central axis S (FIG. 22) of the planetary gear mechanism 91.

[0172] 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.

[0173] 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. 22 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 (central axes of rotation) 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 the 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.

[0174] 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. 22 . 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.

[0175] 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.

[0176] FIG. 23 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.

[0177] 24 (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. Furthermore, as in a seventh modified example shown in FIG. 25 (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.

[0178] 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, in the second embodiment, as in the first embodiment, when switching from forward rotation mode to reverse mode, switching of the forward first-speed clutch 69 (first output clutch) and the reverse first-speed clutch 70 (second output clutch) begins with the output shaft 23 rotating in the forward direction (forward direction). Furthermore, when switching from reverse rotation mode to forward mode, switching of the reverse first-speed clutch 70 (second output clutch) and the forward first-speed clutch 69 (first output clutch) begins with the output shaft 23 rotating in the reverse direction (reverse direction). This allows smooth switching between forward and reverse rotation of the output shaft 23, and therefore between forward and reverse movement of the wheel loader 1.

[0179] 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).

[0180] 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.

[0181] 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.

[0182] 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.

[0183] In the first embodiment, the transmission device 21 including the multi-speed change mechanism 26 and the direct-drive mechanism 27 has been described as an example. However, this is not limiting, and the transmission device 21 may omit the multi-speed change mechanism 26 and / or the direct-drive mechanism 27 as necessary. Furthermore, in the first embodiment, the idler element 28 is provided on the output side of the planetary continuously variable transmission mechanism 24, i.e., the output side of the planetary continuously variable transmission mechanism 24 includes the idler element 28. However, the idler element 28 may be omitted. That is, the output side of the planetary continuously variable transmission mechanism (e.g., the third member or third connecting member of the planetary mechanism) may be connected to the multi-speed change mechanism without an idler element. In either case, the multi-speed change mechanism is connected to the output side of the planetary continuously variable transmission mechanism (e.g., the third member, third connecting member, or idler element of the planetary mechanism). The first output clutch of the multi-speed transmission mechanism is provided in a first output transmission path in which the number of meshing of the gears between the output side of the planetary continuously variable transmission mechanism and the output shaft (output shaft of the multi-speed transmission mechanism) is odd. The second output clutch of the multi-speed transmission mechanism is provided in a second output transmission path in which the number of meshing of the gears between the output side of the planetary continuously variable transmission mechanism and the output shaft (output shaft of the multi-speed transmission mechanism) is zero or an even number. These are the same for the second embodiment and each of the modified examples.

[0184] 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.

[0185] 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.

[0186] 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 transmission mechanism (auxiliary transmission mechanism) 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) 38A First variable relief valve (relief valve) 69 Forward first speed clutch (first output clutch) 70 Reverse first speed clutch (second output clutch) 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 having 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, which changes the speed of the rotation of the input shaft side and transmits it to the output shaft side; 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 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 serves as an output side different from the second member; a first variator connected to the second member of the planetary mechanism; and a second variator capable of transmitting power between the first variator and the multi-stage transmission mechanism. a first output clutch provided in a first output transmission path in which the number of meshing of gears between the output side of the planetary type continuously variable transmission mechanism and the output shaft is an odd number, switching between transmission and release of power of the first output transmission path; and a second output clutch provided in a second output transmission path in which the number of meshing of gears between the output side of the planetary type continuously variable transmission mechanism and the output shaft is zero or an even number, switching between transmission and release of power of the second output transmission path, the transmission device further comprises a controller that controls engagement and release of the first output clutch and engagement and release of the second output clutch, the controller being capable of reversing a traveling direction of the vehicle by switching between a forward rotation mode in which the first output clutch is engaged and the second output clutch is released, and a reverse mode in which the first output clutch is released and the second output clutch is engaged, and the controller, when switching from the forward rotation mode to the reverse mode, a transmission comprising: a first output clutch that is initiating a change from an engaged state to a released state and a second output clutch that is initiating a change from a released state to an engaged state while the output shaft is in a forward rotation state; and a rotational speed of the first variator that is changed to reverse the rotational direction of the third member.

2. 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 type continuously variable transmission mechanism provided between the input shaft and the output shaft which changes the speed of the rotation of the input shaft side and transmits it to the output shaft side; and a multi-stage transmission mechanism which changes the speed of the rotation of the output side of the planetary type continuously variable transmission mechanism in stages by switching the transmission path of the meshing of gears, wherein the planetary type 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 serves as an output side different from the second member; a first variator connected to the second member of the planetary mechanism; and a second variator capable of transmitting power between the first variator, and the multi-stage transmission mechanism comprises: a first output clutch provided in a first output transmission path in which the number of meshing of gears between the output side of the planetary type continuously variable transmission mechanism and the output shaft is an odd number, switching between transmission and release of power of the first output transmission path; and a second output clutch provided in a second output transmission path in which the number of meshing of gears between the output side of the planetary type continuously variable transmission mechanism and the output shaft is zero or an even number, switching between transmission and release of power of the second output transmission path, the transmission device further comprises a controller that controls engagement and release of the first output clutch and engagement and release of the second output clutch, the controller being capable of reversing a traveling direction of the vehicle by switching between a forward rotation mode in which the first output clutch is engaged and the second output clutch is released, and a reverse mode in which the first output clutch is released and the second output clutch is engaged, and the controller, when switching from the reverse rotation mode to the forward rotation mode, a transmission comprising: a first output clutch that is connected to a first variator and a second output clutch that is connected to a first variator; a first output clutch that is connected to a first variator; a second output clutch that is connected to a first variator; 3. A transmission as claimed in claim 1, wherein the first variator is a hydraulic pump, and the second variator is a hydraulic motor, the hydraulic pump and the hydraulic motor are connected by a pair of main lines, and the pair of main lines enable power transmission between the hydraulic pump and the hydraulic motor, and a relief valve is provided between the pair of main lines for controlling the main lines to be in a connected state or a cut-off state, the controller is capable of changing the communication start pressure of the relief valve, and when switching from the forward rotation mode to the reverse rotation mode, the controller reduces the set value of the communication start pressure of the relief valve prior to the start of switching of the first output clutch and the start of switching of the second output clutch.

4. A transmission as claimed in claim 2, wherein the first variator is a hydraulic pump, and the second variator is a hydraulic motor, the hydraulic pump and the hydraulic motor are connected by a pair of main lines, and the pair of main lines enable power transmission between the hydraulic pump and the hydraulic motor, and a relief valve is provided between the pair of main lines for controlling the main lines to be in a connected state or a cut-off state, the controller is capable of changing the communication start pressure of the relief valve, and when switching from the reverse mode to the forward mode, the controller reduces the set value of the communication start pressure of the relief valve prior to the start of switching of the second output clutch and the start of switching of the first output clutch.

5. A transmission as claimed in claim 1, wherein the first variator is a hydraulic pump, and the second variator is a hydraulic motor, the hydraulic pump and the hydraulic motor are connected by a pair of main lines, and the pair of main lines enable power transmission between the hydraulic pump and the hydraulic motor, and a relief valve is provided between the pair of main lines for controlling the main lines to be in a connected state or a cut-off state, the controller is capable of changing the communication start pressure of the relief valve, and when switching from the forward rotation mode to the reverse rotation mode, the controller increases the set value of the communication start pressure of the relief valve while switching the first output clutch from an engaged state to a released state and switching the second output clutch from a released state to an engaged state.

6. A transmission as claimed in claim 2, wherein the first variator is a hydraulic pump, and the second variator is a hydraulic motor, the hydraulic pump and the hydraulic motor are connected by a pair of main lines, and the pair of main lines enable power transmission between the hydraulic pump and the hydraulic motor, and a relief valve is provided between the pair of main lines for controlling the main lines to be in a connected state or a cut-off state, the controller is capable of changing the communication start pressure of the relief valve, and when switching from the reverse mode to the forward mode, the controller increases the set value of the communication start pressure of the relief valve while switching the second output clutch from an engaged state to a released state and switching the first output clutch from a released state to an engaged state.

7. A transmission as claimed in claim 1, wherein the first variator is a hydraulic pump, and the second variator is a hydraulic motor, the hydraulic pump and the hydraulic motor are connected by a pair of main lines, and the pair of main lines enable power transmission between the hydraulic pump and the hydraulic motor, and a relief valve is provided between the pair of main lines for controlling the main lines to be in a connected state or a cut-off state, the controller is capable of changing the communication start pressure of the relief valve, and when switching from the forward rotation mode to the reverse mode, the controller sets a time for which the relief valve is connected while the rotational direction of the third member is being reversed by changing the rotational speed of the first variator.

8. A transmission as claimed in claim 2, wherein the first variator is a hydraulic pump, and the second variator is a hydraulic motor, the hydraulic pump and the hydraulic motor are connected by a pair of main lines, and the pair of main lines enable power transmission between the hydraulic pump and the hydraulic motor, and a relief valve is provided between the pair of main lines for controlling the main lines to be in a connected state or a cut-off state, the controller is capable of changing the communication start pressure of the relief valve, and when switching from the reverse mode to the forward mode, the controller sets a time for which the relief valve is connected while the rotational direction of the third member is being reversed by changing the rotational speed of the first variator.

9. A transmission as described in claim 1, characterized in that the first variator and the second variator are each an electric motor, the first variator and the second variator are connected by an electric circuit, an electric motor control device is provided on the electric circuit, and the first variator and the second variator are capable of transmitting power via the electric circuit.

10. A transmission as described in claim 2, characterized in that the first variator and the second variator are each an electric motor, the first variator and the second variator are connected by an electric circuit, an electric motor control device is provided on the electric circuit, and the first variator and the second variator are capable of transmitting power via the electric circuit.

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