Power transmission device for vehicle

Abstract

A transmission device (21) as a power transmission device for a vehicle has an input shaft (22), an output shaft (23), a planetary continuously variable transmission mechanism (31), a direct coupling mechanism (27), and an idle gear (29). The direct coupling mechanism (27) has a direct coupling clutch (30). The planetary continuously variable transmission mechanism (31) has a planetary gear mechanism (32), a pump side clutch (33), a hydraulic pump (36), a hydraulic motor (38), and a motor side clutch (40). The hydraulic pump (36) and the hydraulic motor (38) are connected by a pair of main pipes (37A, 37B). An electromagnetic on-off valve (41) capable of switching the pair of main pipes (37A, 37B) between a communication state and a cutoff state is provided between the pair of main pipes (37A, 37B).

Description

TECHNICAL FIELD

[0001] The present application relates to a vehicle power transmission device, for example, mounted on a wheel loader, which can obtain optimum travel speed and driving force for various work states. BACKGROUND

[0002] The wheel loader repeats a "V-cycle" motion, which is mainly composed of a loading work to a dump truck, or a "loading and unloading" motion, which is mainly composed of a work of feeding to a hopper. The "V-cycle" is a mode of motion in which earth and sand, etc. are excavated and then loaded to a dump truck. The "loading and unloading" is a mode of motion in which, after the earth and sand, etc. are excavated, a carrying (load travel), an unloading to a hopper, and a return (no-load travel) are performed. When various works such as the excavation, the carrying, the loading, the return, etc. are performed, the wheel loader frequently switches a transmission mechanism in order to obtain optimum travel speed and driving force.

[0003] The driving system of the wheel loader is roughly classified into three types as representative examples, i.e., a "transmission with a torque converter", a "hydrostatic type continuously variable transmission (HST)", and a "hydraulic-mechanical type continuously variable transmission (HMT)". In a vehicle with a torque converter (hereinafter referred to as a torque converter vehicle), in order to become high efficiency, there is a lock-up type torque converter vehicle which can be mechanically coupled.

[0004] The torque converter vehicle performs torque amplification based on the torque converter in a low speed region, and exerts the effect of torque amplification in the case of a work requiring torque such as start of the vehicle body, excavation, etc. However, when the torque amplification is performed, slip of the torque converter occurs, resulting in reduction of efficiency. Specifically, as the speed ratio rises, the efficiency also rises, but at a certain speed ratio, the efficiency is maximum, and then starts to decrease. Therefore, the torque converter vehicle has a tendency to reduce the efficiency in a high speed region. However, the torque converter vehicle can improve the power transmission efficiency by adopting a lock-up mechanism which mechanically links the output shaft of the engine and the output shaft of the transmission.

[0005] In the hydrostatic type continuously variable transmission mounted vehicle, both or either of the hydraulic pump and the hydraulic motor in the hydrostatic type continuously variable transmission is of a variable capacity type. The hydrostatic type continuously variable transmission mounted vehicle can control the vehicle speed and the tractive force by controlling the tilt of the hydraulic pump or the hydraulic motor of the variable capacity type to change the volume. The efficiency is obtained by the product of the mechanical efficiency and the volumetric efficiency of the hydrostatic type continuously variable transmission. The hydrostatic type continuously variable transmission mounted vehicle can operate at a high efficiency of about 70 to 80% in a high speed region, and can also exert high efficiency in a low speed region compared with the torque converter.

[0006] The hydraulic-mechanical continuously variable transmission is a configuration in which a hydraulic power transmission mechanism realized based on a hydrostatic continuously variable transmission and a mechanical power transmission mechanism realized based on a gear are combined (Patent Literature 1). The power input from the engine to the hydraulic-mechanical continuously variable transmission is divided into hydraulic power transmission and mechanical power transmission, and then combined and output. The mechanism that takes the role of dividing and combining the power is a planetary gear mechanism. The hydraulic-mechanical continuously variable transmission vehicle, by the action of the planetary gear mechanism, makes the proportion of the mechanical power transmission, which has high transmission efficiency, greater than the proportion of the hydraulic power transmission, which has low transmission efficiency, as the vehicle speed becomes faster. With this configuration, the hydraulic-mechanical continuously variable transmission vehicle improves the low efficiency caused by the torque converter slip in the low speed region, which is one of the disadvantages of the torque converter vehicle, and is able to achieve higher transmission efficiency than the hydrostatic continuously variable transmission vehicle in the high speed region. In addition, the hydraulic-mechanical continuously variable transmission vehicle is able to perform control of the vehicle speed and the tractive force by the volume change by the tilt control based on the hydraulic power transmission mechanism. Therefore, the hydraulic-mechanical continuously variable transmission vehicle is able to perform distribution control of the power input from the engine between the work machine and the drive system.

[0007] Prior Art Documents

[0008] Patent Literature

[0009] Patent Literature 1: Japanese Patent Application Laid-Open No. 2010-540866 (Japanese Patent No. 5190513) SUMMARY

[0010] The hydraulic-mechanical continuously variable transmission vehicle is able to achieve high efficiency by the continuously variable transmission in the case of carrying cargo at low speed (5 to 10 km / h). However, the hydraulic-mechanical continuously variable transmission vehicle also distributes the power to the hydraulic in the case of carrying at high speed (10 to 20 km / h), and thus has the possibility of reducing the transmission efficiency compared to the torque converter vehicle that adopts a lockup mechanism. In addition, the hydraulic-mechanical continuously variable transmission vehicle also distributes the power to the hydraulic in the case of returning (10 to 40 km / h), and thus has the possibility of reducing the transmission efficiency compared to the torque converter vehicle that adopts a lockup mechanism. For example, in 0 to 5 km / h, the difference in efficiency between the hydraulic-mechanical continuously variable transmission vehicle and the torque converter vehicle is close to 0. In contrast, in 5 to 10 km / h, the hydraulic-mechanical continuously variable transmission vehicle becomes high efficiency compared to the torque converter vehicle. On the other hand, in 10 to 40 km / h, the torque converter vehicle that adopts a lockup mechanism becomes high efficiency compared to the hydraulic-mechanical continuously variable transmission vehicle.

[0011] Therefore, in order to achieve higher efficiency, a transmission is considered that, at low speed travel, allows power to pass through a hydraulic mechanical continuously variable transmission that has high transmission efficiency and excellent operability, and at high speed travel such as return and transport, switches the power path to a direct coupling mechanism that has high transmission efficiency at high speed travel. Specifically, a vehicle power transmission device is considered that has an input shaft that rotates by a prime mover mounted on a vehicle, an output shaft that outputs rotation to a travel device of the vehicle; a planetary continuously variable transmission provided between the input shaft and the output shaft and that steps up rotation on the input shaft side and transmits it to the output shaft side; a direct coupling mechanism that transmits rotation on the input shaft side to the output shaft side in a manner that bypasses the planetary continuously variable transmission; and an inert element that mechanically couples the output gear side of the planetary continuously variable transmission and the output shaft side of the direct coupling mechanism, the direct coupling mechanism having an input side gear connected to the input shaft, an output side gear engaged with the input side gear, and a first clutch provided between the output side gear and the inert element, the planetary continuously variable transmission having a planetary gear mechanism connected to the input shaft side, a second clutch provided on the output shaft side of the planetary gear mechanism, a hydraulic pump connected to the output side of the planetary gear mechanism via the second clutch, a hydraulic motor connected to the hydraulic pump via a pair of main pipelines, and a third clutch provided between the hydraulic motor and the inert element or the output shaft.

[0012] In addition, in this configuration, the second clutch and the third clutch are considered to be synchronous engagement mechanism clutches. That is, among the clutches, there are a friction disc clutch and a synchronous engagement mechanism clutch. The synchronous engagement mechanism clutch is an engagement clutch that has synchronization performance. The friction disc clutch is excellent in terms of synchronization performance. However, in order to increase the transmission torque of the friction disc clutch, a large diameter friction disc needs to be used, or the number of friction disc pieces needs to be increased. As a result, there is a possibility that the power transmission device will be upsized and will be subject to space constraints when mounted on a work vehicle. In addition, the area of the sliding portion of the friction disc clutch becomes larger, and when the clutch is released, there is a possibility that the heat generation of the friction surface (sliding surface) of the friction disc will increase. In order to suppress the heat generation of the friction disc clutch, it is considered to cool the friction disc clutch with a liquid. However, in this case, there is a possibility that the loss based on the stirring of the liquid between the friction surfaces and the loss based on the ejection of the liquid to the outside in the rotation direction due to centrifugal force by the rotation of the friction disc will increase.

[0013] In contrast, the synchronous engagement mechanism clutch is small in the friction sliding surface when the clutch is released, and thus can reduce heat generation based on friction (sliding). Thus, the amount of coolant can be reduced, and loss can be reduced. Therefore, the synchronous engagement mechanism clutch is considered to be adopted in order to reduce loss. However, in the case where the synchronous engagement mechanism clutch is adopted in the planetary continuously variable transmission mechanism, if power transmission achieved by the hydraulic pressure in the hydraulic circuit based on the planetary continuously variable transmission mechanism is not cut off in a short time and becomes no load, it is difficult to stably perform connection and release of the clutch.

[0014] An object of the present application is to provide a vehicle power transmission device that can stably perform connection and release of a clutch by cutting off power transmission achieved by a hydraulic pressure in a hydraulic circuit based on a planetary continuously variable transmission mechanism in a short time.

[0015] The vehicle power transmission device of the present application includes an input shaft that rotates by a prime mover mounted on a vehicle; an output shaft that outputs rotation to a traveling device of the vehicle; a planetary continuously variable transmission mechanism that is provided between the input shaft and the output shaft, that changes the rotation on the input shaft side, and that transmits the rotation to the output shaft side; a direct coupling mechanism that transmits the rotation on the input shaft side to the output shaft side in a manner that bypasses the planetary continuously variable transmission mechanism; and an inert element that mechanically couples an output side of the planetary continuously variable transmission mechanism and an output side of the direct coupling mechanism, the direct coupling mechanism including a first clutch provided between the input shaft and the inert element, the planetary continuously variable transmission mechanism including a planetary gear mechanism connected to the input shaft side; a second clutch provided on an output side of the planetary gear mechanism; a hydraulic pump connected to the output side of the planetary gear mechanism via the second clutch; a hydraulic motor connected to the hydraulic pump via a pair of main pipelines; a third clutch provided between the hydraulic motor and the inert element or the output shaft; and a communication valve that can switch between a communication state and a cutoff state between the pair of main pipelines.

[0016] According to the present application, by cutting off power transmission achieved by a hydraulic pressure in a hydraulic circuit based on a planetary continuously variable transmission mechanism in a short time, connection and release of a clutch can be stably performed. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a left side view of a wheel loader on which a vehicle power transmission device of an embodiment is mounted.

[0018] Figure 2 is a side view of a partial cut of a transmission device (vehicle power transmission device) in Figure 1

[0019] ​Figure 3 is a configuration diagram showing a power transmission path of a wheel loader together with a controller.

[0020] Figure 4 is a block diagram of the controller in Figure 3 together with a communication valve (solenoid on-off valve) and the like.

[0021] Figure 5 is a flowchart showing controller-based processing at the time of switching from the planetary continuously variable transmission mechanism to the direct coupling mechanism.

[0022] Figure 6 is a flowchart showing controller-based processing at the time of switching from the direct coupling mechanism to the planetary continuously variable transmission mechanism.

[0023] Figure 7 is an explanatory diagram (torque vs. vehicle speed characteristic line diagram) showing a region Q in which power is transmitted by the planetary continuously variable transmission mechanism and a region P in which power is transmitted by the direct coupling mechanism.

[0024] Figure 8 is a timing chart showing the time of switching from the planetary continuously variable transmission mechanism to the direct coupling mechanism.

[0025] Figure 9 is a timing chart showing the time of switching from the direct coupling mechanism to the planetary continuously variable transmission mechanism.

[0026] Figure 10 is a configuration diagram showing a power transmission path of a wheel loader together with a controller of a vehicle power transmission device according to a first modification example.

[0027] Figure 11 is a timing chart showing the time of switching from the planetary continuously variable transmission mechanism to the direct coupling mechanism according to the first modification example.

[0028] Figure 12 is a timing chart showing the time of switching from the direct coupling mechanism to the planetary continuously variable transmission mechanism according to the first modification example.

[0029] Figure 13 is a configuration diagram showing a power transmission path of a wheel loader together with a controller of a vehicle power transmission device according to a second modification example. DETAILED DESCRIPTION

[0030] A vehicle power transmission device according to an embodiment of the present application will be described in detail below with reference to the drawings, taking the case of being applied to a wheel loader as an example. Furthermore, in the following description, the same reference numerals are used for the same components, and repeated description thereof will be omitted. Figure 5 and Figure 6 Each step of the flowcharts shown in Figs. 1 to 4 is denoted by "S" (for example, step 1 = "S1").

[0031] Figures 1 to 9 Embodiments are described. Figure 1 In the embodiment, a wheel loader 1 is a representative example of a vehicle (work vehicle). The wheel loader 1 is configured as a hinged work vehicle in which a front body 3 provided with left and right front wheels 2 and a rear body 5 provided with left and right rear wheels 4 are connected so as to be foldable in the left-right direction. That is, the front body 3 and the rear body 5 constitute the body of the wheel loader 1. A central pin 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 are folded in the left-right direction about the central pin 6 by elongating or shortening the steering cylinder. Thus, the wheel loader 1 is capable of steering while traveling.

[0032] In the front body 3 of the wheel loader 1, a work device 7, also referred to as a loading and unloading work machine, is provided so as to be capable of performing a luffing action. The work device 7 has a loading bucket 7A. On the other hand, in the rear body 5 of the wheel loader 1, a cabin 8, which is an interior of a cab, an engine 9, a hydraulic pump 10, a transmission device 21 as a transmission case, and the like are provided. The engine 9 is a power source (prime mover) of the wheel loader 1. The power source (prime mover) can be configured of, for example, only the engine 9 as an internal combustion engine, or an engine and an electric motor, or only an electric motor. The hydraulic pump 10 is connected to the engine 9. The hydraulic pump 10 is a hydraulic source for actuating the work device 7.

[0033] A front accelerator 12 extending in the left-right direction is provided on the lower side of the front body 3. Left and right front wheels 2 are attached to both end sides of the front accelerator 12. On the other hand, a rear accelerator 13 extending in the left-right direction is provided on the lower side of the rear body 5. Left and right rear wheels 4 are attached to both end sides of the rear accelerator 13.

[0034] The front accelerator 12 is connected to the transmission device 21 via a front propeller shaft 14. The rear accelerator 13 is connected to the transmission device 21 via a rear propeller shaft 15. The transmission device 21 reduces 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 device 21 combined with the engine 9.

[0035] The power from the engine 9 is transmitted to the front accelerator 12 and the rear accelerator 13 from the front and rear output shafts 23A, 23B of the transmission device 21 via the front propeller shaft 14 and the rear propeller shaft 15 after the rotation speed and the rotation direction are adjusted by the transmission device 21. That is, as shown in FIG. 1, the power from the engine 9 is transmitted to the front accelerator 12 and the rear accelerator 13 via the front propeller shaft 14 and the rear propeller shaft 15. Figure 2As shown, the transmission 21 has an input shaft 22 connected to the engine 9, a front-side output shaft 23A connected to the front axle 14, and a rear-side output shaft 23B connected to the rear axle 15. The transmission 21 performs a shift between the input shaft 22 and the output shafts 23A, 23B and a switching of forward or reverse rotation by switching a power transmission path in the transmission 21.

[0036] Next, the transmission 21 of the embodiment will be described on the basis of Figure 1 and Figure 2 with reference to Figures 3 to 9 . Further, in Figure 3 , the output shaft 23 of the transmission 21 is schematically shown as a common output shaft 23 (= output shafts 23A, 23B) that transmits power to both the front accelerator 12 and the rear accelerator 13 in order to avoid complication of the drawing. That is, Figure 3 , a configuration for dividing power to the front-side output shaft 23A and the rear-side output shaft 23B, for example, via an inter-axle differential mechanism or the like is omitted.

[0037] The transmission 21 as a vehicle power transmission device has an input shaft 22, an output shaft 23, a planetary continuously variable mechanism 31, a transmission mechanism 25 as a stepped transmission mechanism, a direct coupling mechanism 27, a transmission shaft 28, an inert gear 29 as an inert element. In addition, the transmission 21 has a controller 43, a first pressure detector 46, a second pressure detector 47, a third pressure detector 48, a first speed detector 44, and a second speed detector 45.

[0038] The input shaft 22 is rotated by the engine 9 as a prime mover mounted on the vehicle. That is, the engine 9 (a drive shaft thereof) is connected to the input shaft 22. In contrast, the output shaft 23 outputs rotation to the front accelerator 12 and / or the rear accelerator 13 as a traveling device of the vehicle. That is, power of the engine 9 is output from the output shaft 23 via the transmission 21 as a transmission case. The output shaft 23 outputs rotation to the front wheels 2 and / or the rear wheels 4 via the front accelerator 12 and / or the rear accelerator 13 of the wheel loader 1.

[0039] Power input from the input shaft 22 to the transmission 21 is transmitted to the inert gear 29 via the planetary continuously variable mechanism 31 or the direct coupling mechanism 27. The power transmitted to the inert gear 29 is output from the output shaft 23 by the transmission mechanism 25. The planetary continuously variable mechanism 31 is provided between the input shaft 22 and the output shaft 23. The planetary continuously variable mechanism 31 steps up rotation on the input shaft 22 side and transmits it to the output shaft 23 side. The input side of the planetary continuously variable mechanism 31 is connected to the input shaft 22 provided with the input-side gear 27A of the direct coupling mechanism 27. The output side of the planetary continuously variable mechanism 31 is connected to the transmission shaft 28 provided with the inert gear 29.

[0040] The transmission mechanism 25 is provided in line with the planetary continuously variable transmission mechanism 31 and the direct coupling mechanism 27 between the input shaft 22 and the output shaft 23. The transmission mechanism 25 also steps up the rotation on the input shaft 22 side and transmits it to the output shaft 23 side. In this case, the transmission mechanism 25 is provided between the intermediate gear 26 engaged with the idler gear 29 and the output shaft 23. That is, the input side of the transmission mechanism 25 is connected to the intermediate gear 26. The output side of the transmission mechanism 25 is connected to the output shaft 23. The transmission mechanism 25 is configured, for example, as a stepped transmission mechanism of multiple stages. The configuration of the transmission mechanism 25 includes, for example, a plurality of transmission shafts, a plurality of gears, and a plurality of clutches. In this case, the transmission mechanism 25 can be configured, for example, as a transmission mechanism (DCT: Dual Clutch Transmission) having a forward clutch (not shown) connected when the wheel loader 1 is made to advance and a reverse clutch (not shown) connected when the wheel loader 1 is made to retreat. In addition, the transmission mechanism 25 can be omitted. That is, the intermediate gear 26 and the output shaft 23 can be directly connected without passing through the transmission mechanism 25.

[0041] The direct coupling mechanism 27 transmits the rotation on the input shaft 22 side to the output shaft 23 in a manner that bypasses the planetary continuously variable transmission mechanism 31. That is, the direct coupling mechanism 27 directly transmits the rotation of the input shaft 22 to the transmission mechanism 25 without passing through the planetary continuously variable transmission mechanism 31. The direct coupling mechanism 27 has an input side gear 27A connected to the input shaft 22, an output side gear 27B engaged with the input side gear 27A, a rotation shaft 27B1 coaxially arranged with the transmission shaft 28, and a direct coupling clutch 30 as a first clutch. The rotation of the output side gear 27B is transmitted to the transmission shaft 28 via the direct coupling clutch 30. In the embodiment, the input side gear 27A is provided to the input shaft 22. The output side gear 27B is provided to the rotation shaft 27B1 coaxially arranged with the transmission shaft 28. The direct coupling clutch 30 is provided between the rotation shaft 27B1 and the transmission shaft 28.

[0042] The transmission shaft 28 corresponds to the output shaft of the direct coupling mechanism 27, and corresponds to the output shaft of the planetary continuously variable speed mechanism 31. In this case, the transmission shaft 28 is coaxially arranged with the rotation shaft 27B1 of the direct coupling mechanism 27, and is coaxially arranged with the motor shaft 39 of the planetary continuously variable speed mechanism 31. The transmission shaft 28 is connected to the rotation shaft 27B1 of the direct coupling mechanism 27 via the direct coupling clutch 30. When the direct coupling clutch 30 is connected, the rotation of the output side gear 27B of the direct coupling mechanism 27 is transmitted to the transmission shaft 28. The transmission shaft 28 is connected to the hydraulic motor 38 of the planetary continuously variable speed mechanism 31 via the motor side clutch 40. When the motor side clutch 40 is connected, the rotation of the hydraulic motor 38 of the planetary continuously variable speed mechanism 31 is transmitted to the transmission shaft 28. In addition, the transmission shaft 28 is connected to the planetary output gear 32B of the planetary continuously variable speed mechanism 31 via the idler gear 29.

[0043] The idler gear 29, which is an idler element, is provided to the transmission shaft 28. The idler gear 29 mechanically connects the output side of the planetary continuously variable speed mechanism 31 and the output side of the direct coupling mechanism 27. The idler gear 29 engages with the planetary output gear 32B of the planetary gear mechanism 32, which constitutes the planetary continuously variable speed mechanism 31. The idler gear 29 engages with the intermediate gear 26. The rotation of the idler gear 29 is transmitted to the speed change mechanism 25 via the intermediate gear 26. That is, the power input from the input shaft 22 of the transmission 21 is transmitted to the idler gear 29 via the planetary continuously variable speed mechanism 31 or the direct coupling mechanism 27. The power transmitted to the idler gear 29 is output from the output shaft 23 through the speed change mechanism 25.

[0044] The direct coupling clutch 30 is provided in the direct coupling mechanism 27 provided between the input shaft 22 and the idler gear 29. That is, the direct coupling clutch 30 is provided between the rotation shaft 27B1 of the output side gear 27B in the direct coupling mechanism 27 and the transmission shaft 28 in which the idler gear 29 is provided. The direct coupling clutch 30 can be switched to a "connected state (engaged state)" in which the rotation (torque, rotational force, power) is transmitted between the direct coupling mechanism 27 (rotation shaft 27B1) and the idler gear 29 (transmission shaft 28), and a "cut-off state (released state)" in which the transmission of the rotation is cut off. When the direct coupling clutch 30 is in the connected state, the rotation of the output side gear 27B (rotation shaft 27B1) of the direct coupling mechanism 27 is transmitted to the idler gear 29 via the transmission shaft 28. When the direct coupling clutch 30 is in the released state, the rotation of the output side gear 27B (rotation shaft 27B1) is not transmitted to the transmission shaft 28. The connection and release of the direct coupling clutch 30 are controlled based on an instruction (instruction signal Cl) from the controller 43.

[0045] Next, the planetary continuously variable speed mechanism 31 will be described.

[0046] The planetary continuously variable transmission mechanism 31 has a planetary gear mechanism 32, a pump side clutch 33 as a second clutch, a hydrostatic continuously variable transmission mechanism 34, and a motor side clutch 40 as a third clutch. The hydrostatic continuously variable transmission mechanism 34 has a pump shaft 35, a hydraulic pump 36, a pair of main pipes 37A, 37B, a hydraulic motor 38, a motor shaft 39, an electromagnetic on-off valve 41, and a connection pipe 42.

[0047] The planetary gear mechanism 32 is connected to the input shaft 22 side. Specifically, the planetary gear mechanism 32 is connected to the input shaft 22. The planetary gear mechanism 32 is constituted by a single stage or multiple stages of a planetary gear device (not shown), a planetary output shaft 32A, and a planetary output gear 32B. The planetary gear device has, for example, a sun gear, a ring gear, and a carrier that supports a planetary gear that meshes with the sun gear and the ring gear. For example, the input shaft 22 is connected to any one of the sun gear, the ring gear, and the carrier. The planetary output shaft 32A is connected to a component other than the component to which the input shaft 22 is connected, among the sun gear, the ring gear, and the carrier. The planetary output gear 32B is connected to the remaining component among the sun gear, the ring gear, and the carrier. The planetary output shaft 32A is connected to the pump shaft 35 (the hydraulic pump 36) of the hydrostatic continuously variable transmission mechanism 34 via the pump side clutch 33. Rotation of the planetary output shaft 32A is transmitted to the pump shaft 35 (the hydraulic pump 36) of the hydrostatic continuously variable transmission mechanism 34 via the pump side clutch 33. The planetary output gear 32B meshes with the idler gear 29. Rotation of the planetary output gear 32B is transmitted to the idler gear 29.

[0048] The pump side clutch 33 is provided on the output side of the planetary gear mechanism 32. That is, the pump side clutch 33 is provided between the planetary output shaft 32A of the planetary gear mechanism 32 and the pump shaft 35 (the hydraulic pump 36) of the hydrostatic continuously variable transmission mechanism 34. The pump side clutch 33 can be switched to a "connected state (engaged state)" in which rotation is transmitted between the planetary gear mechanism 32 (the planetary output shaft 32A) and the hydraulic pump 36 (the pump shaft 35) of the hydrostatic continuously variable transmission mechanism 34, and a "cut-off state (released state)" in which transmission of rotation is cut off. When the pump side clutch 33 is in the connected state, rotation of the planetary output shaft 32A of the planetary gear mechanism 32 is transmitted to the hydraulic pump 36 via the pump shaft 35 of the hydrostatic continuously variable transmission mechanism 34. When the pump side clutch 33 is in the released state, rotation of the planetary output shaft 32A is not transmitted to the pump shaft 35. The connection and release of the pump side clutch 33 are controlled on the basis of an instruction (an instruction signal C2) from the controller 43.

[0049] The pump shaft 35 of the hydrostatic continuously variable transmission mechanism 34 corresponds to the input shaft of the hydrostatic continuously variable transmission mechanism 34. The pump shaft 35 is connected to the rotational shaft (input shaft) of the hydraulic pump 36. Alternatively, the pump shaft 35 corresponds to the rotational shaft (input shaft) of the hydraulic pump 36. The hydraulic pump 36 is connected to the output side of the planetary gear mechanism 32, i.e., to the planetary output shaft 32A of the planetary gear mechanism 32, via the pump-side clutch 33. The hydraulic pump 36 circulates hydraulic oil into a pair of main pipes 37A, 37B by driving the pump shaft 35 to rotate. The hydraulic pump 36 is constituted by, for example, a hydraulic pump of a variable displacement type and a swash plate type. The hydraulic pump 36 has a regulator 36A for adjusting the pump displacement. The regulator 36A of the hydraulic pump 36 is variably controlled on the basis of an instruction (instruction signal W P ) from the controller 43. The pair of main pipes 37A, 37B connects a pair of supply and discharge ports of the hydraulic pump 36 and a pair of supply and discharge ports of the hydraulic motor 38.

[0050] The hydraulic motor 38 is connected to the hydraulic pump 36 via the pair of main pipes 37A, 37B. The hydraulic motor 38 rotates by the hydraulic oil supplied from the hydraulic pump 36. The hydraulic motor 38 is constituted by, for example, a hydraulic motor of a variable displacement type and a swash plate type. The hydraulic motor 38 has a regulator 38A for adjusting the motor displacement. The regulator 38A of the hydraulic motor 38 is variably controlled on the basis of an instruction (instruction signal W M ) from the controller 43. The motor shaft 39 of the hydrostatic continuously variable transmission mechanism 34 corresponds to the output shaft of the hydrostatic continuously variable transmission mechanism 34. The motor shaft 39 is connected to the rotational shaft (output shaft) of the hydraulic motor 38. Alternatively, the motor shaft 39 corresponds to the rotational shaft (output shaft) of the hydraulic motor 38.

[0051] The motor-side clutch 40 is provided between the hydraulic motor 38 and the inert gear 29. Thus, the hydraulic motor 38 is connected to the inert gear 29 via the motor-side clutch 40. That is, the motor-side clutch 40 is provided between the motor shaft 39 of the hydrostatic continuously variable transmission mechanism 34 and the transmission shaft 28 on which the inert gear 29 is provided. The motor-side clutch 40 can be switched to a "connected state (engaged state)" in which rotation is transmitted between the inert gear 29 (transmission shaft 28) and the hydraulic motor 38 (motor shaft 39) of the hydrostatic continuously variable transmission mechanism 34, and a "cut-off state (released state)" in which the transmission of rotation is cut off. When the motor-side clutch 40 is in the connected state, the rotation of the motor shaft 39 of the hydrostatic continuously variable transmission mechanism 34 (= the rotation of the hydraulic motor 38) is transmitted to the inert gear 29 via the transmission shaft 28. When the motor-side clutch 40 is in the released state, the rotation of the motor shaft 39 is not transmitted to the transmission shaft 28. The connection and release of the motor-side clutch 40 are controlled on the basis of an instruction (instruction signal C3) from the controller 43.

[0052] In the embodiment, it is arbitrarily selected whether the power input from the input shaft 22 of the transmission 21 is transmitted to the transmission mechanism 25 via the planetary continuously variable transmission mechanism 31 or via the direct coupling mechanism 27. Thereby, in a condition suitable for the operation of the planetary continuously variable transmission mechanism 31, the planetary continuously variable transmission mechanism 31 can be utilized. On the other hand, in a condition suitable for the transmission based on the direct coupling mechanism 27, the power can be transmitted via the direct coupling mechanism 27.

[0053] In the case where the power is transmitted to the transmission mechanism 25 via the planetary continuously variable transmission mechanism 31, the direct coupling clutch 30 is released, and the pump-side clutch 33 and the motor-side clutch 40 are each connected. In this case, there are a case where the power is distributed to the transmission mechanism 25 side via the planetary gear mechanism 32 and the hydrostatic continuously variable transmission mechanism 34 as the flow of the power, and a case where the power is transmitted to the transmission mechanism 25 side without transmitting the power to the hydrostatic continuously variable transmission mechanism 34 by setting the rotational speed of the hydraulic pump 36 to 0.

[0054] The state where the direct coupling clutch 30 is released, the pump-side clutch 33 and the motor-side clutch 40 are each connected, the power is transmitted to the hydrostatic continuously variable transmission mechanism 34, and the power is transmitted to the transmission mechanism 25 side is referred to as a continuously variable transmission state. The state where the direct coupling clutch 30 is released, the pump-side clutch 33 and the motor-side clutch 40 are each connected, the power is not transmitted to the hydrostatic continuously variable transmission mechanism 34, and the power is transmitted to the transmission mechanism 25 side is referred to as an internal direct coupling. When this internal direct coupling, the inclination (discharge capacity) of the hydraulic pump 36 is increased up to a predetermined value, the inclination of the hydraulic motor 38 is set to neutral, whereby a braking action is applied to the inside of the hydrostatic continuously variable transmission mechanism 34, and the rotational speed of the hydraulic pump 36 is set to 0. Thereby, the power from the engine 9 is transmitted to the transmission mechanism 25. In practice, since there is a leakage of oil from the hydraulic pump 36 and the hydraulic motor 38, the rotational speed of the hydraulic pump 36 is not set to 0, but most of the power from the engine 9 can be distributed to the transmission mechanism 25. On the other hand, in the case where the power is transmitted to the transmission mechanism 25 via the direct coupling mechanism 27, the direct coupling clutch 30 is connected, and the pump-side clutch 33 and the motor-side clutch 40 are each released.

[0055] Here, the direct coupling clutch 30, the pump-side clutch 33, and the motor-side clutch 40 can employ a wet-type multiple-plate clutch or a synchronous meshing mechanism clutch. The wet-type multiple-plate clutch transmits torque by pressing friction plates. The synchronous meshing mechanism clutch transmits torque by causing small teeth fixed to shaft head end surfaces of shafts to mesh with each other. Therefore, the synchronous meshing mechanism clutch is small in size and large in torque transmission capacity, as compared with the friction plate clutch. Also, the synchronous meshing mechanism clutch is small in drag torque when the meshing is released, and therefore, heat generation due to the link rotation is smaller than that of the wet-type multiple-plate clutch.

[0056] Therefore, in the embodiment, in order to reduce the loss, the pump-side clutch 33 and the motor-side clutch 40 are provided as meshing clutches, i.e., synchronous meshing mechanism clutches, which transmit rotation by engagement (meshing) of pawls. The direct coupling clutch 30 is provided as a wet-type multiple-plate clutch. However, in the case where the pump-side clutch 33 and the motor-side clutch 40 are provided as synchronous meshing mechanism clutches as such, if the loads of the hydraulic pump 36 and the hydraulic motor 38 of the hydrostatic continuously variable transmission mechanism 34 are not reduced, the connection and release of the pump-side clutch 33 and the motor-side clutch 40 become difficult.

[0057] Therefore, in the embodiment, the hydrostatic continuously variable transmission mechanism 34 has an electromagnetic on-off valve 41 as a communication valve. That is, the pair of main pipes 37A, 37B of the hydrostatic continuously variable transmission mechanism 34 are connected by a connection pipe 42. Also, the electromagnetic on-off valve 41 is provided midway in the connection pipe 42. Thus, between the pair of main pipes 37A, 37B, the electromagnetic on-off valve 41 is provided, which can switch the pair of main pipes 37A, 37B between a communication state and a cutoff state. The electromagnetic on-off valve 41 can be switched to an open position (A) corresponding to the communication state and a closed position (B) corresponding to the cutoff state. The switching of the electromagnetic on-off valve 41 is controlled based on an instruction (instruction signal W) from a controller 43. The electromagnetic on-off valve 41 is in the closed position (B) that cuts off the pair of main pipes 37A, 37B when the power is transmitted via the planetary continuously variable transmission mechanism 31. On the other hand, the electromagnetic on-off valve 41 is switched to the open position (A) that communicates the pair of main pipes 37A, 37B when the switching of the power transmission path of the planetary continuously variable transmission mechanism 31 and the direct coupling mechanism 27 is performed. At this time, by communicating the pair of main pipes 37A, 37B, the connection and release of the pump-side clutch 33 and the motor-side clutch 40 are performed in a state where the power transmission based on the hydraulic pressure in the hydraulic circuit of the planetary continuously variable transmission mechanism 31 is cut off for a short time. Thus, the switching from the planetary continuously variable transmission mechanism 31 to the direct coupling mechanism 27 and the switching from the direct coupling mechanism 27 to the planetary continuously variable transmission mechanism 31 can be performed.

[0058] Next, the operation of the power transmission device 1 will be described with reference to FIG. 2. Figure 3and Figure 4 The controller 43 will be described to perform the switching control of the power transmission path of the transmission 21. Here, Figure 4 is a block diagram showing the controller 43 in detail.

[0059] The input side of the controller 43 is connected to the first speed detector 44, the second speed detector 45, the first pressure detector 46, the second pressure detector 47, and the third pressure detector 48. The output side of the controller 43 is connected to the electromagnetic on-off valve 41, the direct connection clutch 30, the pump-side clutch 33, the motor-side clutch 40, the regulator 36A of the hydraulic pump 36 of the planetary continuously variable mechanism 31, and the regulator 38A of the hydraulic motor 38 of the planetary continuously variable mechanism 31. The configuration of the controller 43 includes, for example, a microcomputer having an arithmetic circuit (CPU), a memory, and the like, and a processing program for performing the processing flow shown in the processing flowchart of FIG. 8, that is, a processing program for the switching control processing of the power transmission path of the transmission 21, and the like is stored in the memory. Figure 5 and Figure 6 The processing program for performing the processing flow shown in the processing flowchart of FIG. 8, that is, the processing program for the switching control processing of the power transmission path of the transmission 21, and the like is stored in the memory.

[0060] The first speed detector 44 is provided at the input shaft 22 of the transmission 21. The first speed detector 44 is a rotation detection sensor that detects the rotational speed and the rotational direction of the input shaft 22. The rotational speed of the input shaft 22 corresponds to the rotational speed of the engine 9 (hereinafter referred to as engine rotational speed Vin). The first speed detector 44 outputs a detection signal corresponding to the engine rotational speed Vin to the controller 43. The second speed detector 45 is provided at the output shaft 23 of the transmission 21. The second speed detector 45 is a rotation detection sensor that detects the rotational speed (hereinafter referred to as output rotational speed Vout) and the rotational direction of the output shaft 23. The output rotational speed Vout corresponds to the vehicle speed. The second speed detector 45 outputs a detection signal corresponding to the output rotational speed Vout and the rotational direction to the controller 43.

[0061] The first pressure detector 46 is provided at the one-side main pipe 37A. The first pressure detector 46 is a pressure sensor that detects the hydraulic pressure (pressure) of the one-side main pipe 37A. The first pressure detector 46 outputs a detection signal corresponding to the hydraulic pressure P A of the one-side main pipe 37A to the controller 43. The second pressure detector 47 is provided at the other-side main pipe 37B. The second pressure detector 47 is a pressure sensor that detects the hydraulic pressure (pressure) of the other-side main pipe 37B. The second pressure detector 47 outputs a detection signal corresponding to the hydraulic pressure P Bcorresponding detection signal. The 3rd pressure detector 48 is provided at the direct coupling clutch 30. The 3rd pressure detector 48 is a pressure sensor that detects the clutch pressure (pressure) of the direct coupling clutch 30. The 3rd pressure detector 48 outputs a signal corresponding to the clutch pressure P of the direct coupling clutch 30 to the controller 43. C corresponding detection signal.

[0062] The controller 43 controls the adjustment of the pump capacity, the motor capacity, the communication or the shut-off of the electromagnetic on-off valve 41, and the connection or the release of the direct coupling clutch 30, the pump-side clutch 33, and the motor-side clutch 40. Here, a state in which the rotation of the input shaft 22 is transmitted to the output shaft 23 via the planetary stepless speed change mechanism 31 by releasing the direct coupling clutch 30 and connecting the pump-side clutch 33 and the motor-side clutch 40 each other is set as a 1st state (planetary transmission state). In contrast to this, a state in which the rotation of the input shaft 22 is transmitted to the output shaft 23 via the direct coupling mechanism 27 by connecting the direct coupling clutch 30 and releasing the pump-side clutch 33 and the motor-side clutch 40 each other is set as a 2nd state (direct coupling transmission state). The 2nd state is a state in which the rotation of the input shaft 22 is transmitted to the output shaft 23 by bypassing the planetary stepless speed change mechanism 31.

[0063] In this case, the controller 43 connects the direct coupling clutch 30, switches the electromagnetic on-off valve 41 from the closed position (B) to the open position (A), and then releases the pump-side clutch 33 and the motor-side clutch 40 when switching from the 1st state to the 2nd state. At this time, that is, when switching from the 1st state to the 2nd state, the controller 43 is set to a state in which the three clutches of the direct coupling clutch 30, the pump-side clutch 33, and the motor-side clutch 40 are connected each other. On the other hand, the controller 43 switches the electromagnetic on-off valve 41 from the open position (A) to the closed position (B) after connecting the pump-side clutch 33 and the motor-side clutch 40 when switching from the 2nd state to the 1st state, and releases the direct coupling clutch 30. At this time, that is, when switching from the 2nd state to the 1st state, the controller 43 is set to a state in which the three clutches of the direct coupling clutch 30, the pump-side clutch 33, and the motor-side clutch 40 are connected each other.

[0064] Additionally, the controller 43 switches the solenoid valve 41 based on the detection values ​​of the first pressure detector 46 and the second pressure detector 47. The first pressure detector 46 and the second pressure detector 47 correspond to pressure detectors that detect the pressure difference between a pair of main pipelines 37A and 37B. The controller 43 switches the solenoid valve 41 from the closed position (B) to the open position (A) when the detection values ​​of the first pressure detector 46 and the second pressure detector 47 are below a threshold. More specifically, the controller 43 switches the solenoid valve 41 from the closed position (B) to the open position (A) when the difference between the detection values ​​of the first pressure detector 46 and the second pressure detector 47, i.e., the pressure difference (differential pressure) between the pair of main pipelines 37A and 37B, is below a threshold (the first pressure threshold described later). Furthermore, for the detection of the differential pressure, a differential pressure gauge (differential pressure detector) that directly detects the differential pressure can be used. In addition, the pressure difference threshold can be set, for example, as a value to suppress pressure fluctuations when the solenoid valve 41 is switched from the closed position (B) to the open position (A).

[0065] like Figure 4 As shown, the controller 43 includes an engine rotation speed detection unit 43A, a vehicle speed determination unit 43B, a pressure detection unit 43C, a command calculation unit 43D, a connecting valve command unit 43E, a clutch command unit 43F, and a tilt control command unit 43G. For the engine rotation speed detection unit 43A, the engine rotation speed Vin is input from the first speed detector 44. The engine rotation speed detection unit 43A outputs the engine rotation speed Vin to the command calculation unit 43D. For the vehicle speed determination unit 43B, the output rotation speed Vout is input from the second speed detector 45. The vehicle speed determination unit 43B outputs the output rotation speed Vout corresponding to the vehicle speed to the command calculation unit 43D. For the pressure detection unit 43C, hydraulic pressure P is input from the first pressure detector 46, the second pressure detector 47, and the third pressure detector 48. A P B and clutch pressure P C The pressure detection unit 43C outputs hydraulic pressure P to the command processing unit 43D. A With hydraulic P B The pressure difference (= the pressure difference between a pair of main lines 37A and 37B) and the clutch pressure P C .

[0066] The instruction calculation unit 43D calculates the gearbox output torque, which is the output torque of the transmission device 21. Specifically, in the first state, the gearbox output torque is calculated based on the torque of the idler gear 29 and the gear ratio of the transmission mechanism 25. The torque of the idler gear 29 can be calculated based on the output torque of the engine 9, the gear ratio of the planetary gear mechanism 32, the rotational speed of the hydraulic pump 36, the rotational speed of the hydraulic motor 38, and the hydraulic P of the pair of main pipelines 37A and 37B. A PB And is calculated, where the output torque of the engine 9 is calculated in accordance with the release time of the injector that delivers fuel to the combustion chamber of the engine 9 that is to be the power source and the rotational speed of the engine 9. On the other hand, in the case of the 2nd state, the torque of the input shaft 22 is estimated in accordance with the output torque of the engine 9 and the load torque of the hydraulic pump 10 that actuates the work implement 7, and multiplied by the gear ratio from the input shaft 22 via the direct coupling clutch 30 up to the output shaft 23 to calculate the transmission output torque.

[0067] The command operation section 43D operates a command to the electromagnetic on-off valve 41 (solenoid valve command), a command to the clutches 30, 33, 40 (clutch command), a command to the regulator 36A of the hydraulic pump 36 (pump command), and a command to the regulator 38A of the hydraulic motor 38 (motor command) based on the inputs from the engine rotational speed detection section 43A, the vehicle speed determination section 43B, and the pressure detection section 43C and the value of the transmission output torque. The command operation section 43D outputs the solenoid valve command to the communication valve command section 43E, the clutch command to the clutch command section 43F, and the pump command and the motor command to the tilt control command section 43G.

[0068] To the communication valve command section 43E, the solenoid valve command is input from the command operation section 43D. The communication valve command section 43E outputs a control command related to the opening and closing operation of the electromagnetic on-off valve 41 to the electromagnetic on-off valve 41 in accordance with the solenoid valve command from the command operation section 43D. That is, the communication valve command section 43E outputs an ON (communication) / OFF (shutoff) signal W with respect to the electromagnetic on-off valve 41. In this case, ON (communication) corresponds to the open position (A) of the electromagnetic on-off valve 41, and OFF (shutoff) corresponds to the closed position (B) of the electromagnetic on-off valve 41. To the clutch command section 43F, the clutch command is input from the command operation section 43D. The clutch command section 43F outputs a control command related to the connection and release operation of the clutches 30, 33, 40 to the clutches 30, 33, 40 based on the clutch command from the command operation section 43D. That is, the clutch command section 43F outputs an ON (connection) / OFF (release) signal Cl, C2, C3 with respect to the clutches 30, 33, 40. In this case, the signal Cl is output with respect to the direct coupling clutch 30, the signal C2 is output with respect to the pump side clutch 33, and the signal C3 is output with respect to the motor side clutch 40.

[0069] For the tilt control command unit 43G, pump commands and motor commands are input from the command processing unit 43D. Based on the pump commands and motor commands from the command processing unit 43D, the tilt control command unit 43G outputs control commands related to the tilting action of the hydraulic pump 36 and the hydraulic motor 38 to the regulator 36A of the hydraulic pump 36 and the regulator 38A of the hydraulic motor 38. That is, the tilt control command unit 43G outputs a tilt command signal W for the swashplate or swashplate to the regulator 36A of the hydraulic pump 36 and the regulator 38A of the hydraulic motor 38. P W M In this case, the regulator 36A of the hydraulic pump 36 outputs a tilt command signal W. P The regulator 38A outputs a tilt command signal W for the hydraulic motor 38. M The hydraulic pump 36 and hydraulic motor 38 within the hydrostatic continuously variable transmission (CVT) 34 are variable capacity types. The discharge capacity of the hydraulic pump 36 and hydraulic motor 38 is changed by altering the tilt angle of the swashplate or swashplate. The hydraulic pump 36 and hydraulic motor 38 can be either single-tilt or double-tilt types.

[0070] Next, the specific control processes of clutches 30, 33, 40 and electromagnetic opening and closing valve 41 performed by controller 43 will be explained.

[0071] Here, Figure 7 This is a characteristic curve diagram showing the relationship between torque and vehicle speed (“torque-vehicle speed” characteristic curve diagram). The region P for switching from the planetary continuously variable transmission (CVT) 31 to the direct coupling mechanism 27 and the region Q for switching from the direct coupling mechanism 27 to the planetary CVT 31 are predetermined. Region P corresponds to the region where power is transmitted through the direct coupling mechanism 27. Region Q corresponds to the region where power is transmitted through the planetary CVT 31. Figure 7 The "direct connection mechanism ON line" in the text is the boundary line of region P. Figure 7 The "direct coupling mechanism OFF line" is the boundary line of region Q. The side of the boundary line with the diagonal line represents the region. Vehicle speed V1 (= first speed threshold V1) is the vehicle speed at the lowest engine speed at which the vehicle can travel through the direct coupling mechanism 27, for example, it can be set to about 6 km / h. Vehicle speed V2 (= second speed threshold V2) is the vehicle speed at the maximum engine speed of the planetary continuously variable transmission 31 when switching to the direct coupling mechanism 27, for example, it can be set to about 9 km / h. Vehicle speed V3 (= third speed threshold V3) is the lowest vehicle speed on the direct coupling mechanism ON line, for example, it can be set to about 7 km / h. Vehicle speed V4 (= fourth speed threshold V4) is the maximum vehicle speed on the direct coupling mechanism OFF line, for example, it can be set to about 7.5 km / h.

[0072] Reference Figure 5 as well as Figure 8This explains the control processing of the controller 43 and the state changes of each part when switching the power transmission path of the transmission device 21 from the planetary continuously variable transmission mechanism 31 to the direct coupling mechanism 27.

[0073] Figure 5 This indicates the specific processing flow executed by the controller 43, namely, the control processing (judgment processing) when switching the power transmission path from the planetary continuously variable transmission mechanism 31 to the direct coupling mechanism 27. Figure 5 The control processing, for example, is repeatedly executed according to a prescribed control cycle during the period when power is transmitted by the planetary continuously variable transmission 31.

[0074] For example, if through the following Figure 6 The processing of S14 switches the power transmission path of the transmission device 21 to the planetary continuously variable transmission mechanism 31, and then begins... Figure 5 The processing flow. Figure 5 In step S1, it is determined whether the vehicle speed V of the wheel loader 1 is greater than the second speed threshold V2 (also known as the maximum switching speed V2). The vehicle speed V corresponds to the actual speed (actual speed) of the wheel loader 1 detected by the second speed detector 45. The second speed threshold V2 is the vehicle speed judgment value that serves as the reference (threshold) for switching from the planetary continuously variable transmission 31 to the direct coupling mechanism 27. If S1 is "yes", that is, if it is determined that the vehicle speed V is higher than the second speed threshold V2, proceed to step S5. In step S5, the power transmission path is switched from the planetary continuously variable transmission 31 to the direct coupling mechanism 27. That is, the controller 43 switches from the first state where the direct coupling clutch 30 is released and both the pump-side clutch 33 and the motor-side clutch 40 are engaged to the second state where the direct coupling clutch 30 is engaged and both the pump-side clutch 33 and the motor-side clutch 40 are disengaged. Furthermore, the highest switching speed V2, which is the second speed threshold V2, corresponds to the vehicle speed at which the power transmission shifts to the direct coupling mechanism 27 at the maximum engine speed of the planetary continuously variable transmission 31. Thus, when the vehicle speed V is higher than the second speed threshold V2, the power transmission path is switched to the direct coupling mechanism 27, and the process begins. Figure 6 The processing.

[0075] On the other hand, if S1 is "No," meaning the vehicle speed V is determined to be below the second speed threshold V2, then proceed to S2. In S2, it is determined whether the vehicle speed V is greater than the third speed threshold V3 (also known as the switching speed V3). Figure 7As shown, the third speed threshold V3 is smaller than the second speed threshold V2 (V3 < V2). If S2 is "No," meaning the vehicle speed V is determined to be below the third speed threshold V3, proceed to S3. In S3, the power transmission path remains within the planetary continuously variable transmission (CVT) 31. That is, the power transmission path continues to be maintained within the planetary CVT 31. No switching to the direct connection mechanism 27 is performed. Thus, if the vehicle speed V is less than the highest switching speed V2 and less than the switching speed V3, the power transmission path continues to be maintained within the planetary CVT 31 and the vehicle returns.

[0076] In contrast, if S2 is "yes," meaning the vehicle speed V is determined to be greater than the third speed threshold V3, proceed to S4. In S4, it is determined whether the transmission output torque is included in region P. That is, in S4, it is determined whether the relationship between vehicle speed V and output torque is included in region P. Figure 7 Region P. The output torque is calculated by the command processing unit 43D. If S4 is "No", it means that the relationship between vehicle speed V and output torque is not included in the calculation. Figure 7 In the case of region P, proceed to S3. That is, maintain the power transmission path through the planetary continuously variable transmission 31. Thus, when the vehicle speed V is above the switching speed V3 but below the maximum switching speed V2, and is not included in region P where the vehicle switches to the direct coupling mechanism 27, the power transmission path continues to be maintained through the planetary continuously variable transmission 31, and the vehicle returns.

[0077] On the other hand, if S4 is "yes", that is, it is determined that the relationship between vehicle speed V and output torque is included in... Figure 7 In region P, proceeding to S5, the power transmission path is switched from the planetary continuously variable transmission 31 to the direct coupling mechanism 27. Thus, when the vehicle speed V is above the switching speed V3 but below the maximum switching speed V2, and is contained within region P where the switching to the direct coupling mechanism 27 occurs, the power transmission path is switched to the direct coupling mechanism 27, and the process begins. Figure 6 The processing.

[0078] Figure 8 This is a timing diagram showing the switching of the power transmission path from the planetary continuously variable transmission mechanism 31 to the direct coupling mechanism 27. Figure 8 The value in the middle indicates the pressure difference (P) between main pipelines 37A and 37B. B -P A ), clutch pressure P of direct-connection clutch 30 C The tilting amount of hydraulic pump 36, the tilting amount of hydraulic motor 38, the state of electromagnetic on / off valve 41, the state of pump-side clutch 33, the state of motor-side clutch 40, the speed of hydraulic pump 36, and the speed of hydraulic motor 38.

[0079] First, let's explain the situation where the power transmission path is switched from continuously variable transmission (CVT) via planetary CVT 31 to direct coupling mechanism 27. When the power transmission path is via planetary CVT 31, the wheel loader 1 is in a low-speed range. In this case, the controller 43 sets the pump-side clutch 33 and motor-side clutch 40 to "ON (connected)," sets the direct coupling clutch 30 to "OFF (released)," and sets the solenoid valve 41 to "OFF (cut off)." If... Figure 5 If the process proceeds to S5, the controller 43 switches the power transmission path to the direct coupling mechanism 27. At this time, the controller 43 outputs an ON command (at time A) from the clutch command unit 43F to the direct coupling clutch 30. Consequently, the clutch pressure P... C Ascend, directly engage clutch 30 (at point B). Then, controller 43 activates when the pressure difference (P) between main lines 37A and 37B... B -P A When the pressure falls below the first pressure threshold, the connecting valve command unit 43E outputs an ON command to the solenoid valve 41, switching the solenoid valve 41 from the closed position (B) to the open position (A). This connects the main pipes 37A and 37B within the hydrostatic continuously variable transmission 34 (at point C). Then, the controller 43 obtains the pressure difference (P) between the main pipes 37A and 37B from the pressure detection unit 43C. B -P A If the second pressure threshold is below a certain value, a release command is output from the clutch command unit 43F to the pump-side clutch 33 and the motor-side clutch 40. As a result, the pump-side clutch 33 and the motor-side clutch 40 are released (at time D). Consequently, the power transmission path is completely switched from the planetary continuously variable transmission 31 to the direct coupling mechanism 27. Furthermore, the second pressure threshold is set to determine the pressure difference (P) between the main circuits 37A and 37B. B -P A The judgment value is whether the power transmission based on the hydrostatic continuously variable transmission mechanism 34 is cut off (released). This indicates the case where the power transmission path is switched from the continuously variable transmission state of the planetary continuously variable transmission mechanism 31 to the direct connection mechanism 27. The difference in switching the power transmission path from the state of direct connection within the planetary continuously variable transmission mechanism 31 to the direct connection mechanism 27 lies in the point where the motor-side clutch 40 becomes OFF before time point A, the tilt of the hydraulic motor 38 becomes neutral, and the pump speed is 0 (or close to 0).

[0080] Next, refer to Figure 6 as well as Figure 9This explains the control processing of the controller 43 and the state changes of each part when switching the power transmission path of the transmission device 21 from the direct coupling mechanism 27 to the planetary continuously variable transmission mechanism 31.

[0081] Figure 6 This indicates the specific processing flow executed by the controller 43, namely, the control processing (judgment processing) when switching the power transmission path from the direct coupling mechanism 27 to the planetary continuously variable transmission mechanism 31. Figure 9 For example, the control processing is repeatedly executed according to a prescribed control cycle during the period when power is transmitted through the direct coupling mechanism 27.

[0082] For example, when through Figure 5 When the S5 process switches the power transmission path of the transmission device 21 to the direct coupling mechanism 27, it begins... Figure 6 The processing flow. Figure 6 In step S11, it is determined whether the vehicle speed V is less than the fourth speed threshold V4 (also known as the switching speed V4). The fourth speed threshold V4 is the vehicle speed judgment value that serves as the reference (threshold) for switching from the direct coupling mechanism 27 to the planetary continuously variable transmission (CVT) 31. If S11 is "No", that is, if it is determined that the vehicle speed V is above the fourth speed threshold V4, the process proceeds to S12. In S12, the power transmission path remains in the direct coupling mechanism 27. That is, the power transmission path continues to be maintained in the direct coupling mechanism 27. Switching to the planetary CVT 31 is not performed. Thus, if the vehicle speed V is above the switching speed V4, the power transmission path continues to be maintained in the direct coupling mechanism 27, and the process returns.

[0083] On the other hand, if S11 is "yes," meaning it's determined that the vehicle speed V is less than the fourth speed threshold V4, then proceed to S13. In S13, it's determined whether the vehicle speed V is less than the first speed threshold V1 (also known as the minimum switching speed V1). For example... Figure 7 As shown, the first speed threshold V1 is smaller than the fourth speed threshold V4 (V1 < V4). When S13 is "yes," meaning it's determined that the vehicle speed V is less than the first speed threshold V1, the process proceeds to S14. In S14, the power transmission path is switched from the direct coupling mechanism 27 to the planetary continuously variable transmission (CVT) 31. That is, the controller 43 switches from the second state where the direct coupling clutch 30 is engaged and both the pump-side clutch 33 and the motor-side clutch 40 are disengaged, to the first state where the direct coupling clutch 30 is disengaged and both the pump-side clutch 33 and the motor-side clutch 40 are engaged. Furthermore, the minimum switching speed V1, which is the first speed threshold V1, corresponds to the vehicle speed at the minimum engine speed of the direct coupling mechanism 27 when switching to the planetary CVT 31. Thus, when the vehicle speed V is lower than the first speed threshold V1, the power transmission path is switched to the planetary CVT 31, and the process begins.Figure 5 the process.

[0084] In contrast, in the case where S13 is "NO", that is, in the case where it is determined that the vehicle speed V is the first speed threshold value VI or more, the process proceeds to S15. In S15, it is determined whether the transmission output torque is included in the region Q. That is, in S15, it is determined whether the relationship between the vehicle speed V and the output torque is included in the region Q. In the case where S15 is "NO", that is, in the case where it is determined that the relationship between the vehicle speed V and the output torque is not included in the region Q, the process proceeds to S12. That is, the power transmission path is maintained in the direct coupling mechanism 27. In this way, in the case where the vehicle speed V is the switching speed VI or more and less than the maximum switching speed V4, and is not included in the region Q in which the switching to the planetary continuously variable transmission mechanism 31 is performed, the power transmission path is continuously maintained in the direct coupling mechanism 27, and the process returns. Figure 7 Figure 7 In contrast, in the case where S13 is "NO", that is, in the case where it is determined that the vehicle speed V is the first speed threshold value VI or more, the process proceeds to S15. In S15, it is determined whether the transmission output torque is included in the region Q. That is, in S15, it is determined whether the relationship between the vehicle speed V and the output torque is included in the region Q. In the case where S15 is "NO", that is, in the case where it is determined that the relationship between the vehicle speed V and the output torque is not included in the region Q, the process proceeds to S12. That is, the power transmission path is maintained in the direct coupling mechanism 27. In this way, in the case where the vehicle speed V is the switching speed VI or more and less than the maximum switching speed V4, and is not included in the region Q in which the switching to the planetary continuously variable transmission mechanism 31 is performed, the power transmission path is continuously maintained in the direct coupling mechanism 27, and the process returns.

[0085] On the other hand, in the case where S15 is "YES", that is, in the case where it is determined that the relationship between the vehicle speed V and the output torque is included in the region Q, the process proceeds to S14, and the power transmission path is switched from the direct coupling mechanism 27 to the planetary continuously variable transmission mechanism 31. In this way, in the case where the vehicle speed V is the switching speed VI or more and less than the maximum switching speed V4, and is included in the region Q in which the switching to the planetary continuously variable transmission mechanism 31 is performed, the power transmission path is switched to the planetary continuously variable transmission mechanism 31, and the process of Figure 7 Figure 5

[0086] Figure 9 is a time chart indicating the case where the power transmission path is switched from the direct coupling mechanism 27 to the planetary continuously variable transmission mechanism 31. Figure 9 In the time chart of FIG. 8, the pressure difference (P B -P A ) of the main hydraulic lines 37A, 37B, the clutch pressure P C of the direct coupling clutch 30, the tilt amount of the hydraulic pump 36, the tilt amount of the hydraulic motor 38, the state of the electromagnetic on-off valve 41, the state of the pump-side clutch 33, the state of the motor-side clutch 40, the rotational speed of the hydraulic pump 36, and the rotational speed of the hydraulic motor 38 are indicated.

[0087] First, the case where the state of the power transmission path is switched from the direct coupling mechanism 27 to the planetary continuously variable transmission mechanism 31 in which the continuously variable transmission is performed will be described. In the case where the power transmission path is the direct coupling mechanism 27, the wheel loader 1 is in the high speed region. In this case, the controller 43 sets the pump-side clutch 33 and the motor-side clutch 40 to "OFF (released)", sets the direct coupling clutch 30 to "ON (connected)", and sets the electromagnetic on-off valve 41 to "ON (communicated)". If the vehicle speed V is the switching speed VI or more and less than the maximum switching speed V4, the controller 43 switches the power transmission path from the direct coupling mechanism 27 to the planetary continuously variable transmission mechanism 31. Figure 6 ​​​the controller 43 advances to S14, the controller 43 acquires the pressure difference (P B - P A ) of the main pipes 37A, 37B from the pressure detecting section 43C, and outputs a connection command to the pump-side clutch 33 and the motor-side clutch 40 from the clutch command section 43F if the information is below the second pressure threshold value. Thus, the pump-side clutch 33 and the motor-side clutch 40 are connected (point A). By this connection, the hydraulic pump 36 and the hydraulic motor 38 start rotating and rise to a predetermined rotational speed. After the pump-side clutch 33 and the motor-side clutch 40 are completely connected, the controller 43 outputs a command of OFF to the electromagnetic on-off valve 41 from the communication valve command section 43E and switches the electromagnetic on-off valve 41 from the open position (A) to the closed position (B) (point B). Then, the tilt of the hydraulic pump 36 is increased, the discharge amount of the hydraulic pump 36 is increased, and the pressure difference (P B - P A ) of the main pipes 37A, 37B is increased. Thus, power transmission based on hydraulic pressure in the planetary continuously variable transmission mechanism 31 becomes possible (point C). At the same time, a command of OFF is output to the direct coupling clutch 30, and the direct coupling clutch 30 is released. Thus, the power transmission path is completely switched from the direct coupling mechanism 27 to the planetary continuously variable transmission mechanism 31. Thus far, a case in which the state of the power transmission path is switched from the direct coupling mechanism 27 to the planetary continuously variable transmission mechanism 31 for continuously variable transmission has been described. In a case in which the state of the power transmission path is switched from the direct coupling mechanism 27 to the planetary continuously variable transmission mechanism 31 for internal direct coupling, the points at which the motor-side clutch 40 becomes OFF before point A, the point at which the tilt of the hydraulic motor 38 is neutral, and the point at which the pump rotational speed is 0 (or a value close to 0) are different.

[0088] With the above arrangement, according to the embodiment, the clutches 30, 33, 40 are provided between the direct coupling mechanism 27 and the idler gear 29, between the planetary gear mechanism 32 and the hydraulic pump 36, and between the hydraulic motor 38 and the idler gear 29, respectively, and the power transmission path is switched by engagement and release of the clutches 30, 33, 40. Therefore, it is possible to reduce loss and to achieve high efficiency. In addition, the hydraulic pump 36 and the hydraulic motor 38 rotate only in the case where power is transmitted via the planetary continuously variable transmission mechanism 31. Therefore, in the case where power is transmitted via the direct coupling mechanism 27, it is possible to reduce loss based on rotation of the hydraulic pump 36 and the hydraulic motor 38 and to achieve high efficiency. Further, the electromagnetic on-off valve 41 as a communication valve is provided between the pair of main lines 37A, 37B to which the hydraulic pump 36 and the hydraulic motor 38 are connected. Therefore, by making the electromagnetic on-off valve 41 communicate, it is possible to stably engage and release the clutches 30, 33, 40 in a state where power transmission based on hydraulic pressure in the hydraulic circuit of the planetary continuously variable transmission mechanism 31 (the hydrostatic continuously variable transmission mechanism 34) is cut off in a short time. Thus, it is possible to stably switch the power transmission path.

[0089] According to the embodiment, the pump-side clutch 33 (2nd clutch) and the motor-side clutch 40 (3rd clutch) are provided as synchronous meshing mechanism clutches. Therefore, by making the hydraulic pump 36 and the hydraulic motor 38 communicate via the electromagnetic on-off valve 41, it is possible to stably engage and release the synchronous meshing mechanism clutches in a state where power based on rotation of the hydraulic pump 36 and the hydraulic motor 38 is cut off in a short time. As a result, it is possible to provide the transmission 21 (transmission) that uses the synchronous meshing mechanism clutches having small drag torque when the pump-side clutch 33 and the motor-side clutch 40 are released, that reduces power loss of the vehicle, and that has high transmission efficiency.

[0090] According to the embodiment, the controller 43 switches the electromagnetic on-off valve 41 from the closed position (B) in which it is in a cut-off state to the open position (A) in which it is in a communication state, and then releases the pump-side clutch 33 and the motor-side clutch 40, when switching from a 1st state in which the power transmission path is the planetary continuously variable transmission mechanism 31 to a 2nd state in which the power transmission path is the direct coupling mechanism 27. Therefore, it is possible to smoothly release the pump-side clutch 33 and the motor-side clutch 40 in a state where power transmission based on hydraulic pressure in the hydraulic circuit of the planetary continuously variable transmission mechanism 31 (the hydrostatic continuously variable transmission mechanism 34) is cut off in a short time by switching the electromagnetic on-off valve 41 from the closed position (B) to the open position (A).

[0091] According to the embodiment, the controller 43 switches the electromagnetic on-off valve 41 from the open position (A) in which the communication state is established to the closed position (B) in which the cutoff state is established after connecting the pump-side clutch 33 and the motor-side clutch 40 when switching from the second state in which the power transmission path is the planetary type continuously variable transmission mechanism 31 to the first state in which the power transmission path is the direct coupling mechanism 27. Therefore, the pressure fluctuation can be reduced when the pump-side clutch 33 and the motor-side clutch 40 are connected, and the pump-side clutch 33 and the motor-side clutch 40 can be smoothly connected.

[0092] According to the embodiment, the controller 43 sets a state in which the three clutches 30, 33, 40 of the direct coupling clutch 30 (first clutch), the pump-side clutch 33, and the motor-side clutch 40 are each connected when switching from the first state to the second state. Therefore, the variation in the output torque when switching from the first state to the second state can be reduced.

[0093] According to the embodiment, the controller 43 sets a state in which the three clutches 30, 33, 40 of the direct coupling clutch 30, the pump-side clutch 33, and the motor-side clutch 40 are each connected when switching from the second state to the first state. Therefore, the variation in the output torque when switching from the second state to the first state can be reduced.

[0094] According to the embodiment, the controller 43 switches the electromagnetic on-off valve 41 from the closed position (B) to the open position (A) when the pressure difference between the pair of main pipes 37A, 37B detected by the pressure detectors 46, 47 becomes equal to or lower than a threshold value (first pressure threshold value). Therefore, the pressure fluctuation when the pair of main pipes 37A, 37B are connected can be suppressed by switching the electromagnetic on-off valve 41 from the closed position (B) to the open position (A).

[0095] According to the embodiment, the communication valve that communicates or cuts off the pair of main pipes 37A, 37B is set as the electromagnetic on-off valve 41. Therefore, the pair of main pipes 37A, 37B can be set from the cutoff state to the communication state by setting the electromagnetic on-off valve 41 from the closed position (B) in which the cutoff position is established to the open position (A) in which the communication position is established. On the other hand, the pair of main pipes 37A, 37B can be set from the communication state to the cutoff state by setting the electromagnetic on-off valve 41 from the open position (A) to the closed position (B).

[0096] Further, in the embodiment, a case in which the pump-side clutch 33 and the motor-side clutch 40 are set as the synchronous engagement mechanism clutches is described. However, this is not limiting, and for example, the pump-side clutch (second clutch) and the motor-side clutch (third clutch) can be set as a ratchet clutch and a wet-type multi-plate clutch.

[0097] In this embodiment, the example described is that the connecting valve for connecting or disconnecting a pair of main pipelines 37A and 37B is an electromagnetic on / off valve 41. However, it is not limited to this; for example, it could be, as... Figure 10 As shown in the first variation, the connecting valves capable of switching the pair of main pipelines 37A and 37B between an open state and a closed state are provided as electromagnetic relief valves 51A and 51B capable of changing the set pressure (overflow set pressure, overflow start pressure). Here, check valves 52 and 53, which are also check valves, are provided on the connecting pipe 42 connecting the pair of main pipelines 37A and 37B. One check valve 52 allows hydraulic oil to flow from one main pipeline 37A to the other main pipeline 37B, preventing hydraulic oil from flowing in the opposite direction. The other check valve 53 allows hydraulic oil to flow from the other main pipeline 37B to one main pipeline 37A, preventing hydraulic oil from flowing in the opposite direction. Bypass pipes 54 and 55 are connected to the connecting pipe 42, respectively bypassing check valves 52 and 53. Electromagnetic relief valves 51A and 51B are located midway through the bypass pipes 54 and 55.

[0098] Electromagnetic relief valves 51A and 51B are electrically operated variable relief valves whose opening pressure (relief pressure) changes based on a command signal (command signal W) from the controller 43. The change of the set pressure (relief set pressure, relief start pressure) of the electromagnetic relief valves 51A and 51B is controlled based on the command signal (command signal W) from the controller 43. The electromagnetic relief valves 51A and 51B are set to an open state, connecting a pair of main pipelines 37A and 37B, by lowering the set pressure, and to an closed state, cutting off the connection between the pair of main pipelines 37A and 37B, by increasing the set pressure.

[0099] In this first modification, electromagnetic relief valves 51A and 51B, which are variable relief valves, are used as a means to cut off the power transmission based on the hydraulic pressure within the hydrostatic continuously variable transmission 34. The electromagnetic relief valves 51A and 51B typically set the relief pressure to a specified value on the high-pressure side (e.g., 35 MPa to 50 MPa). Furthermore, when switching the power transmission path of the transmission device 21 from the planetary continuously variable transmission 31 to the direct coupling mechanism 27, the relief pressure of the electromagnetic relief valves 51A and 51B is changed to a specified value on the low-pressure side (e.g., the minimum value). That is, pressure is relieved between a pair of main lines 37A and 37B via the electromagnetic relief valves 51A and 51B. Therefore, it is possible to connect or release the pump-side clutch 33 and the motor-side clutch 40 while the power transmission based on the hydraulic pressure within the hydrostatic continuously variable transmission 34 is cut off. Thus, switching from the planetary continuously variable transmission 31 to the direct coupling mechanism 27 is possible. Alternatively, it can be configured such that both electromagnetic on / off valve 41 and electromagnetic relief valves 51A and 51B are provided as connecting valves. In this case, electromagnetic on / off valve 41 and electromagnetic relief valves 51A and 51B can be arranged side by side.

[0100] Figure 11 This diagram illustrates the timing of the power transmission path switching from continuously variable transmission (CVT) 31 to direct coupling mechanism 27 in the first variation. When the power transmission path is the CVT 31, the wheel loader 1 is in a low-speed range. The controller 43 sets the pump-side clutch 33 and motor-side clutch 40 to "ON" (connected), sets the direct coupling clutch 30 to "OFF" (released), and maintains the overflow initiation pressure of the electromagnetic overflow valves 51A and 51B at a high state. If... Figure 5 During the processing, moving towards S5, the controller 43 outputs an ON command (connection command) from the clutch command unit 43F to the direct engagement clutch 30. Simultaneously, the controller 43, from the electromagnetic relief valve command unit (not shown) that outputs control commands to the electromagnetic relief valves 51A and 51B regarding the relief start pressure, outputs a command to the electromagnetic relief valve 51A to reduce the relief start pressure (timing point A). As a result, the relief start pressure of the electromagnetic relief valve 51A decreases (timing point A). Then, the clutch pressure P... C As it rises, the direct-connect clutch 30 begins to engage (at point B). Then, when the pressure difference (P) between main line 37A and main line 37B... B -P A When the pressure drops below the first pressure threshold, controller 43 outputs a command from the solenoid relief valve command unit to the solenoid relief valve 51B to cause the relief pressure to decrease (time point C). Then, controller 43 obtains the pressure difference (P) between main pipe 37A and main pipe 37B from pressure detection unit 43C. B -PA If the information indicates that the second pressure threshold is below a certain value, the clutch command unit 43F outputs an OFF command (release command) to the pump-side clutch 33 and the motor-side clutch 40. As a result, the pump-side clutch 33 and the motor-side clutch 40 are released (at time D). As a result, the power transmission path is completely switched from the planetary continuously variable transmission mechanism 31 to the direct coupling mechanism 27.

[0101] exist Figure 11 During the period from time point 0 to time point A, the pressure remains high at the beginning of the overflow from electromagnetic relief valves 51A and 51B. Therefore, the flow of working fluid from main pipeline 37A to main pipeline 37B via connecting pipe 42, and the flow of working fluid from main pipeline 37B to main pipeline 37A, are both cut off. Thus, power transmission is possible in both directions between hydraulic pump 36 and hydraulic motor 38. On the other hand, during the period from time point A to time point C, the pressure remains low at the beginning of the overflow from electromagnetic relief valve 51A, and high at the beginning of the overflow from electromagnetic relief valve 51B. That is, the flow of working fluid from main pipeline 37A to main pipeline 37B via connecting pipe 42 is continuous, while the flow of working fluid from main pipeline 37B to main pipeline 37A is cut off. Therefore, although power transmission is possible from hydraulic pump 36 to hydraulic motor 38, power transmission from hydraulic motor 38 to hydraulic pump 36 is cut off. On the other hand, after point C, the overflow pressure of both electromagnetic relief valve 51A and electromagnetic relief valve 51B remains low. Therefore, the flow of working fluid from main pipe 37A to main pipe 37B through connecting pipe 42, and the flow of working fluid from main pipe 37B to main pipe 37A, are both connected. Therefore, power transmission in both directions between hydraulic pump 36 and hydraulic motor 38 is interrupted.

[0102] By such control, during the period from time point 0 to time point A, power transmission in both directions of the hydraulic pump 36 and the hydraulic motor 38 is possible, whereby power transmission in both directions between the input shaft 22 and the output shaft 23 through the planetary continuously variable transmission mechanism 31 and the idler gear 29 is possible. Thereby, power transmitted from the engine 9 to the input shaft 22 is transmitted to the front wheels 2 and the rear wheels 4 via the output shaft 23, the front accelerator 12, and the rear accelerator 13. Also, force input from the front wheels 2 and the rear wheels 4 is transmitted from the input shaft 22 to the engine 9 via the front accelerator 12 and the rear accelerator 13, the output shaft 23. That is, in both cases of the case where power output from the engine 9 is transmitted to the front wheels 2 and the rear wheels 4 in order to accelerate the wheel loader 1, and the case where force transmitted from the front wheels 2 and the rear wheels 4 is transmitted to the engine 9 and the engine 9 absorbs the power in order to decelerate the wheel loader 1 (engine brake), the transmission 21 can perform power transmission. Therefore, the engine 9 can not only accelerate the wheel loader 1, but also decelerate it (engine brake), and the load of the brake device (not shown) provided in the front accelerator 12 and the rear accelerator 13 can be reduced.

[0103] On the other hand, although power transmission from the hydraulic pump 36 to the hydraulic motor 38 is possible during the period from time point A to time point C, power transmission from the hydraulic motor 38 to the hydraulic pump 36 is cut off. Therefore, although power transmitted from the input shaft 22 to the planetary continuously variable transmission mechanism 3 can be transmitted to the idler gear 29, power cannot be transmitted from the idler gear 29 to the input shaft 22 through the planetary continuously variable transmission mechanism 31. After time point A, the direct coupling clutch 30 is given the clutch pressure P C Thereby, power transmitted to the input shaft 22 can be transmitted to the idler gear 29 via the direct coupling mechanism 27. Thereby, it is possible to be in the state where "power transmitted to the input shaft 22 can be transmitted to the idler gear 29 via the direct coupling mechanism 27", the state where "power transmitted to the input shaft 22 can be transmitted to the idler gear 29 via the planetary continuously variable transmission mechanism 31", and the state where "power transmitted to the input shaft 22 is cut off from being transmitted to the idler gear 29 via the direct coupling mechanism 27 and being transmitted to the input shaft 22 through the planetary continuously variable transmission mechanism 31" at the same time. Therefore, it is not the "power circulation state where power transmitted to the input shaft 22 is transmitted to the idler gear 29 via the direct coupling mechanism 27 and is transmitted to the input shaft 22 through the planetary continuously variable transmission mechanism 31", and thereby, it is possible to easily switch the power transmission path from the planetary continuously variable transmission mechanism 31 to the direct coupling mechanism 27.

[0104] After the point C, the main line 37A and the main line 37B are in communication in both directions through the connection line 42, whereby the power transmission in both directions of the hydraulic pump 36 and the hydraulic motor 38 is cut off. Therefore, the pump side clutch 33 and the motor side clutch 40 can be stably released in the state where the power transmission from the hydraulic circuit in the planetary continuously variable transmission mechanism 31 (hydrostatic continuously variable transmission mechanism 34) is cut off.

[0105] By the control of the spill start pressure of the electromagnetic spill valves 51A and 51B during the period from the point 0 to the point D, the power transmission path from the planetary continuously variable transmission mechanism 31 to the direct coupling mechanism 27 can be easily switched, and the switching can be performed while reducing the torque variation.

[0106] Further, up to now, the case where the power transmission path from the state where the power is continuously transmitted by the planetary continuously variable transmission mechanism 31 is switched to the direct coupling mechanism 27 has been described. The control of the spill start pressure of the electromagnetic spill valves 51A and 51B in the case where the power transmission path from the state where the power is internally directly coupled by the planetary continuously variable transmission mechanism 31 is switched to the direct coupling mechanism 27 is also the same. The difference is the point where the motor side clutch 40 becomes OFF from the point 0, the point where the tilt of the hydraulic motor 38 becomes neutral, and the point where the rotation speed of the hydraulic pump 36 becomes 0 (or a value close to 0).

[0107] Figure 12 A timing chart at the time of switching the power transmission path from the state where the power is continuously transmitted by the direct coupling mechanism 27 to the planetary continuously variable transmission mechanism 31 in the first modified example is shown. In the case where the power transmission path is the direct coupling mechanism 27, the wheel loader 1 is in the high speed region. The controller 43 sets the pump side clutch 33 and the motor side clutch 40 to "OFF (release)", sets the direct coupling clutch 30 to "ON (connection)", and maintains the state where the spill start pressure of the electromagnetic spill valves 51A and 51B is low. When the process of S14 is advanced to S15 in the process of Figure 6 When the process of S14 is advanced to S15 in the process of S14, the controller 43 outputs an ON command (connection command) from the clutch command section 43F to the pump side clutch 33 and the motor side clutch 40. Thereby, the connection of the pump side clutch 33 and the motor side clutch 40 is started (point A). If the connection of the pump side clutch 33 and the motor side clutch 40 is completed, an OFF command (release command) is output from the clutch command section 43F to the direct coupling clutch 30, and a command (point B) to raise the spill start pressure of the electromagnetic spill valve 51B is output from the electromagnetic spill valve command section (not shown) which outputs the control command of the spill start pressure of the electromagnetic spill valves 51A and 51B to the electromagnetic spill valve 51B. Thereby, the spill start pressure of the electromagnetic spill valve 51B is raised (point B). Then, the clutch pressure PC The pressure difference (P B -P A ) of the main line 37A and the main line 37B rises. Then, the controller 43 outputs a command to the electromagnetic spill valve 51A from the electromagnetic spill valve command section to raise the spill start pressure when the pressure difference (P B -P A ) of the main line 37A and the main line 37B becomes the third pressure threshold or more (time point C). Thereby, the power transmission path is completely switched from the direct coupling mechanism 27 to the planetary continuously variable transmission mechanism 31.

[0108] Figure 12 During the period from time point 0 to time point B, the spill start pressure of the electromagnetic spill valve 51A and the electromagnetic spill valve 51B is kept low, and thus the flow of the working fluid from the main line 37A toward the main line 37B through the connection line 42 and the flow of the working fluid from the main line 37B toward the main line 37A are in a communication state in both directions. Therefore, the power transmission is cut off in both directions of the hydraulic pump 36 and the hydraulic motor 38. On the other hand, during the period from time point B to time point C, the spill start pressure of the electromagnetic spill valve 51A is kept low, and the spill start pressure of the electromagnetic spill valve 51B is kept high. That is, the flow of the working fluid from the main line 37A toward the main line 37B through the connection line 42 is in a communication state, and, in contrast, the flow of the working fluid from the main line 37B toward the main line 37A is in a cut-off state. Therefore, the power transmission from the hydraulic pump 36 to the hydraulic motor 38 is possible, but the power transmission from the hydraulic motor 38 to the hydraulic pump 36 is cut off. On the other hand, after time point C, the spill start pressure of the electromagnetic spill valve 51A and the electromagnetic spill valve 51B is kept high, and thus the flow of the working fluid from the main line 37A toward the main line 37B through the connection line 42 and the flow of the working fluid from the main line 37B toward the main line 37A are in a cut-off state. Therefore, the power transmission in both directions of the hydraulic pump 36 and the hydraulic motor 38 is possible.

[0109] By such control, during the period from time point 0 to time point B, the main line 37A and the main line 37B are in a communication state in both directions through the connection line 42, and thus in a state in which the power transmission in both directions of the hydraulic pump 36 and the hydraulic motor 38 is cut off. Therefore, it is possible to stably engage the pump-side clutch 33 and the motor-side clutch 40 in a state in which the power transmission based on the hydraulic pressure in the hydraulic circuit of the planetary continuously variable transmission mechanism 31 (hydrostatic continuously variable transmission mechanism 34) is cut off.

[0110] On the other hand, during the period from time point B to time point C, although power transmission from the hydraulic pump 36 to the hydraulic motor 38 is possible, power transmission from the hydraulic motor 38 to the hydraulic pump 36 is cut off. Therefore, power transmitted from the input shaft 22 to the planetary continuously variable transmission mechanism 31 can be transmitted to the idler gear 29, but power from the idler gear 29 cannot be transmitted to the input shaft 22 through the planetary continuously variable transmission mechanism 31. Before time point C, the direct coupling clutch 30 is given the clutch pressure P C Thereby, power transmitted to the input shaft 22 can be transmitted to the idler gear 29 via the direct coupling mechanism 27. Thereby, the "state in which power transmitted to the input shaft 22 can be transmitted to the idler gear 29 via the direct coupling mechanism 27", the "state in which power transmitted to the input shaft 22 can be transmitted to the idler gear 29 via the planetary continuously variable transmission mechanism 31", and the "state in which power transmitted to the input shaft 22 is cut off from being transmitted to the idler gear 29 via the direct coupling mechanism 27 and transmitted to the input shaft 22 through the planetary continuously variable transmission mechanism 31" can be satisfied at the same time. Therefore, the "power circulation state in which power transmitted to the input shaft 22 is transmitted to the idler gear 29 via the direct coupling mechanism 27 and transmitted to the input shaft 22 through the planetary continuously variable transmission mechanism 31" is not established, and thereby, the switching of the power transmission path from the direct coupling mechanism 27 to the planetary continuously variable transmission mechanism 31 can be easily performed.

[0111] After time point C, power transmission in both directions of the hydraulic pump 36 and the hydraulic motor 38 is possible, and thereby, power transmission in both directions between the input shaft 22 and the output shaft 23 through the planetary continuously variable transmission mechanism 31 and the idler gear 29 is possible. Thereby, power transmitted from the engine 9 to the input shaft 22 is transmitted to the front wheels 2 and the rear wheels 4 via the output shaft 23, the front accelerator 12, and the rear accelerator 13. In addition, force input from the front wheels 2 and the rear wheels 4 can be transmitted from the input shaft 22 to the engine 9 via the front accelerator 12 and the rear accelerator 13, and the output shaft 23. That is, the transmission 21 can perform power transmission in both cases of the case in which power output from the engine 9 is transmitted to the front wheels 2 and the rear wheels 4 in order to accelerate the wheel loader 1 and the case in which force transmitted from the front wheels 2 and the rear wheels 4 is transmitted to the engine 9 and the engine 9 absorbs the power in order to decelerate the wheel loader 1 (engine brake). Therefore, the engine 9 can not only accelerate the wheel loader 1 but also decelerate the wheel loader 1 (engine brake), and the load of the brake device (not shown) provided in the front accelerator 12 and the rear accelerator 13 can be reduced.

[0112] By the control of the spill start pressure of the electromagnetic spill valves 51A and 51B during the period from time point 0 to time point C, the power transmission path can be easily switched from the direct coupling mechanism 27 to the planetary continuously variable transmission mechanism 31, and the switching can be performed while reducing the torque variation.

[0113] Further, up to now, the case where the state of continuously varying the power transmission path from the direct coupling mechanism 27 to the planetary continuously variable transmission mechanism 31 is switched has been described. The control of the spill start pressure of the electromagnetic spill valves 51A and 51B in the case where the state of the power transmission path from the direct coupling mechanism 27 to the inside of the planetary continuously variable transmission mechanism 31 is switched is also the same. The difference is the point at which the motor-side clutch 40 becomes OFF from time point 0, the point at which the tilt of the hydraulic motor 38 becomes neutral, and the point at which the rotational speed of the hydraulic pump 36 is 0 (or a value close to 0).

[0114] Further, in the above-described embodiment, the case where the motor-side clutch 40 as the third clutch is provided between the hydraulic motor 38 of the planetary continuously variable transmission mechanism 31 and the idler gear 29 has been described. However, it is not limited thereto, and for example, as in the second modified example shown in Figure 13 the motor-side clutch 40 can be provided between the hydraulic motor 38 of the planetary continuously variable transmission mechanism 31 and the output shaft 23. That is, the output shaft gear 61 can be provided on the output shaft 23 connected to the output side of the transmission mechanism 25. On the output shaft-side transmission shaft 62, the transmission gear 63 that directly or via a plurality of gears (not shown) engages with the output shaft gear 61 of the output shaft 23 is provided.

[0115] The motor-side clutch 40 is provided between the motor shaft 39 of the hydrostatic continuously variable transmission mechanism 34 and the output shaft-side transmission shaft 62. The motor-side clutch 40 can be switched to a "connected state (engaged state)" in which rotation is transmitted between the output shaft 23 and the hydrostatic continuously variable transmission mechanism 34 (the motor shaft 39 of the hydraulic motor 38) and a "cut-off state (released state)" in which the transmission of rotation is cut off. When the motor-side clutch 40 is in the connected state, the rotation of the motor shaft 39 of the hydrostatic continuously variable transmission mechanism 34 (= the rotation of the hydraulic motor 38) is transmitted to the output shaft 23 via the output shaft-side transmission shaft 62, the transmission gear 63, and the output shaft gear 61. When the motor-side clutch 40 is in the released state, the rotation of the motor shaft 39 is not transmitted to the output shaft-side transmission shaft 62. According to such a second modified example, the transmission mechanism 25 can be made compact.

[0116] In the embodiment, the case where the transmission device 21 as a power transmission device for a vehicle is mounted on the wheel loader 1 as a working vehicle is described as an example. However, it is not limited thereto, and can be widely applied as a power transmission device for various vehicles such as an engineering vehicle such as a wheel excavator, a transport vehicle such as a crane truck, an agricultural vehicle such as a tractor, and the like.

[0117] BRIEF DESCRIPTION OF DRAWINGS

[0118] 1 Wheel loader (vehicle)

[0119] 9 Engine (prime mover)

[0120] 12 Front accelerator (travel device)

[0121] 13 Rear accelerator (travel device)

[0122] 21 Transmission device (power transmission device for vehicle)

[0123] 22 Input shaft

[0124] 23, 23A, 23B Output shaft

[0125] 27 Direct coupling mechanism

[0126] 29 Inertia gear (inertial element)

[0127] 30 Direct coupling clutch (1st clutch)

[0128] 31 Planetary continuously variable transmission mechanism

[0129] 32 Planetary gear mechanism

[0130] 33 Pump side clutch (2nd clutch)

[0131] 36 Hydraulic pump

[0132] 37A, 37B Main pipe line

[0133] 38 Hydraulic motor

[0134] 40 Motor side clutch (3rd clutch)

[0135] 41 Electromagnetic on-off valve (communication valve)

[0136] 43 Controller

[0137] 46 1st pressure detector (pressure detector)

[0138] 47 2nd pressure detector (pressure detector)

[0139] 51 Electromagnetic overflow valve (communication valve)

Claims

1. A power transmitting apparatus for a vehicle, characterized by comprising: has: an input shaft that rotates by a prime mover mounted on a vehicle; an output shaft that outputs rotation to a traveling device of the vehicle; a planetary continuously variable transmission mechanism that is provided between the input shaft and the output shaft, that changes the rotation on the input shaft side, and that transmits the changed rotation to the output shaft side; a direct coupling mechanism that transmits the rotation on the input shaft side to the output shaft side in a manner that bypasses the planetary continuously variable transmission mechanism; and an inert element that mechanically combines an output side of the planetary continuously variable transmission mechanism and an output side of the direct coupling mechanism, the direct coupling mechanism has a first clutch provided between the input shaft and the inert element, the planetary continuously variable transmission mechanism has: a planetary gear mechanism connected to the input shaft; a second clutch provided on an output side of the planetary gear mechanism; a hydraulic pump connected to the output side of the planetary gear mechanism via the second clutch; a hydraulic motor connected to the hydraulic pump via a pair of main lines; a third clutch provided between the hydraulic motor and the inert element or the output shaft; and a communication valve that can switch between a communication state and a cutoff state between the pair of main lines, the communication valve is an electromagnetic overflow valve that can change a set pressure, that is set to the cutoff state by increasing the set pressure, and that is set to the communication state by decreasing the set pressure, has a controller that controls the change of the set pressure of the electromagnetic overflow valve and the connection or release of the first clutch, the second clutch, and the third clutch, the controller sets the pair of main lines to a state in which communication is established in one direction and cutoff is established in the opposite direction when switching from a first state to a second state, wherein the first state is a state in which the rotation of the input shaft is transmitted to the output shaft via the planetary continuously variable transmission mechanism by releasing the first clutch and connecting both the second clutch and the third clutch, and the second state is a state in which the rotation of the input shaft is transmitted to the output shaft bypassing the planetary continuously variable transmission mechanism by connecting the first clutch and releasing both the second clutch and the third clutch.

2. The vehicle power transmission device according to claim 1, wherein the second clutch and the third clutch are synchronous meshing mechanism clutches.

3. The vehicle power transmission device according to claim 1, wherein the controller switches via a third state in which all of the first clutch, the second clutch, and the third clutch are connected when switching from the first state to the second state.

4. The vehicle power transmission device according to claim 1, wherein the controller switches via a third state in which all of the first clutch, the second clutch, and the third clutch are connected when switching from the second state to the first state.

5. The vehicle power transmission device according to claim 1, wherein has a pressure detector that detects a pressure difference of the pair of main pipes, and a controller that switches the communication valve based on a detection value of the pressure detector, the controller switches the communication valve from a cutoff state to a communication state when the detection value of the pressure detector is below a threshold value.

6. A power transmitting apparatus for a vehicle, characterized by comprising: has: an input shaft that rotates by a prime mover mounted on a vehicle; an output shaft that outputs rotation to a traveling device of the vehicle; a planetary continuously variable transmission mechanism that is provided between the input shaft and the output shaft, that steps up rotation on the input shaft side, and that transmits the stepped-up rotation to the output shaft side; a direct coupling mechanism that transmits rotation on the input shaft side to the output shaft side in a manner that bypasses the planetary continuously variable transmission mechanism; and an inert element that mechanically couples an output side of the planetary continuously variable transmission mechanism and an output side of the direct coupling mechanism, the direct coupling mechanism has a first clutch provided between the input shaft and the inert element, the planetary continuously variable transmission mechanism has: a planetary gear mechanism connected to the input shaft; a second clutch provided on an output side of the planetary gear mechanism; a hydraulic pump connected to the output side of the planetary gear mechanism via the second clutch; a hydraulic motor connected to the hydraulic pump via a pair of main pipes; a third clutch provided between the hydraulic motor and the inert element or the output shaft; and a communication valve that can switch the pair of main pipes between a communication state and a cutoff state, the communication valve is an electromagnetic overflow valve that can change a set pressure, that is set to the cutoff state by increasing the set pressure, and that is set to the communication state by decreasing the set pressure, has a controller that controls the change of the set pressure of the electromagnetic overflow valve and the connection or release of the first clutch, the second clutch, and the third clutch, the controller sets the pair of main pipes to a state in which communication is established in one direction and cutoff is established in the opposite direction when switching from a second state to a first state, wherein the first state is a state in which rotation of the input shaft is transmitted to the output shaft via the planetary continuously variable transmission mechanism by releasing the first clutch and connecting both the second clutch and the third clutch, and the second state is a state in which rotation of the input shaft is transmitted to the output shaft by bypassing the planetary continuously variable transmission mechanism by connecting the first clutch and releasing both the second clutch and the third clutch.

7. The vehicle power transmission device according to claim 6, wherein the second clutch and the third clutch are synchronous meshing mechanism clutches.

8. The vehicle power transmission device according to claim 6, wherein the controller switches via a third state in which all of the first clutch, the second clutch, and the third clutch are connected when switching from the first state to the second state.

9. The vehicle power transmission device according to claim 6, wherein The controller switches from the second state to the first state via a third state that is a state in which the first clutch, the second clutch, and the third clutch are each connected.

10. The power transmission apparatus for vehicle according to claim 6, characterized in that, a pressure detector that detects a pressure difference of the pair of main lines, and a controller that switches the communication valve based on a detection value of the pressure detector, the controller switches the communication valve from a cutoff state to a communication state when the detection value of the pressure detector is below a threshold value.

Images