Power transmission device

Abstract

To inhibit power loss of a torque converter when a lock-up device is in an engagement state.SOLUTION: A power transmission device 15 includes: an input shaft 25 which is driven by an engine 10; a transmission 20 which changes a speed of rotation of the input shaft 25; a torque converter 21 which transmits rotation of the input shaft 25 to the transmission through a hydraulic oil; and a lock-up device 35 which is provided at the torque converter 21 and switched between an engagement state where the lock-up device directly transmits rotation of the input shaft 25 to the transmission 20 and a release state where rotation of the input shaft 25 is transmitted to the transmission 20 through the torque converter 21. A pump oil passage 47 for supplying the hydraulic oil to the torque converter 21 includes a fluid control valve 59 which allows flow of the hydraulic oil in the pump oil passage 47 when the lock-up device 35 is in the release state and blocks the pump oil passage 47 when the lock-up device 35 is in the engagement state.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a power transmission device that is mounted on a work vehicle such as a wheel loader and transmits rotation of a power source to an axle. [Background technology]

[0002] Wheeled work vehicles, such as wheel loaders, generally have a power transmission equipped with a torque converter and a gearbox between the prime mover and the axle. The torque converter has a pump impeller, a turbine runner, and a stator, and transmits the rotation of the prime mover to the transmission via a working fluid. The transmission changes the speed of the rotation of the prime mover and transmits it to the axle, driving the wheels. This allows the work vehicle to travel on roads, etc., and the forward / reverse travel, travel speed, etc. of the work vehicle are switched by the power transmission.

[0003] Torque converters are generally equipped with a lockup device. The lockup device has a lockup clutch and a piston, and switches between an engaged state in which the lockup clutch is engaged by the piston and a disengaged state in which the lockup clutch is disengaged by the piston. For example, when the vehicle speed is below a predetermined value, the lockup device is in a disengaged state and transmits the rotation of the prime mover to the transmission via a working fluid. On the other hand, when the vehicle speed exceeds a predetermined value, the lockup device is in an engaged state and transmits the rotation of the prime mover directly to the transmission without using a working fluid (Patent Document 1). Also, a power transmission device has been proposed in which the lockup device is switched between an engaged state and a disengaged state based on the temperature of the working fluid supplied to the torque converter (Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Publication No. 2022-153862 [Patent Document 2] Publication No. 2009-121561 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the lockup devices of Patent Documents 1 and 2, working fluid is still supplied to the interior of the torque converter even when the lockup clutch is engaged. As a result, the working fluid flows together with the pump impeller and turbine runner, which are integrated by the lockup clutch. In this case, the stator fixed inside the torque converter obstructs the smooth flow of working fluid, causing power loss in the torque converter. As a result, there is a problem in that fuel economy (fuel consumption rate) does not necessarily improve when the lockup device is engaged.

[0006] The present invention has been made in consideration of the above-mentioned problems of the conventional technology, and has as its object to provide a power transmission device that can suppress power loss in a torque converter when a lockup device is engaged. [Means for solving the problem]

[0007] The present invention is a power transmission device comprising: a rotating body driven by a prime mover; a transmission that changes the speed of the rotation of the rotating body; a torque converter that transmits the rotation of the rotating body to the transmission via a working fluid; and a lock-up device that is provided in the torque converter and switches between an engaged state in which the rotation of the rotating body is transmitted directly to the transmission and a disengaged state in which the rotation of the rotating body is transmitted to the transmission via the torque converter, wherein a fluid passage that supplies the working fluid to the torque converter is provided with a fluid control valve that connects the fluid passage when the lock-up device is in the disengaged state and that blocks the fluid passage when the lock-up device is in the engaged state. [Effects of the Invention]

[0008] According to the present invention, it is possible to suppress power loss in the torque converter when the lockup device is in the engaged state. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a left side view showing a wheel loader equipped with a power transmission device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a perspective view showing a power transmission device. [Figure 3] FIG. 2 is a cross-sectional view showing a torque converter, a lockup device, etc. of a power transmission device. [Figure 4] FIG. 2 is a hydraulic circuit diagram showing the supply paths of hydraulic oil to a torque converter, a lockup device, etc., with the lockup device in a disengaged state. [Figure 5] FIG. 2 is a hydraulic circuit diagram showing the supply paths of hydraulic oil to a torque converter, a lockup device, etc., with the lockup device in an engaged state. [Figure 6] 4 is an enlarged cross-sectional view of a main part of a pump oil passage, a fluid control valve, etc. in FIG. 3, showing the pump oil passage in a communicated state. [Figure 7] 3 is an enlarged cross-sectional view of a main portion of a pump oil passage, a fluid control valve, etc., showing the pump oil passage in a blocked state. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of a power transmission device according to the present invention will be described in detail with reference to the accompanying drawings, taking as an example an example a case where the power transmission device is mounted on a wheel loader. Note that in the embodiment, the traveling direction of the wheel loader is defined as the front-rear direction, and the direction perpendicular to the traveling direction is defined as the left-right direction.

[0011] In the figure, the wheel loader 1 is configured as an articulated work vehicle in which a front body 3 equipped with left and right front wheels 2 and a rear body 5 equipped with left and right rear wheels 4 are connected via a connecting mechanism 6 so that they can bend left and right. A steering cylinder 7 is provided between the front body 3 and the rear body 5, and by extending and contracting this steering cylinder 7, the front body 3 and the rear body 5 bend left and right, allowing the wheel loader 1 to be steered when traveling.

[0012] A work implement 8 equipped with a loader bucket 8A is mounted on the front body 3 of the wheel loader 1 so that it can be raised and lowered. The rear body 5 of the wheel loader 1 is provided with a cab 9 that defines the operator's compartment, an engine 10 as a prime mover, a power transmission device 15 (described later), and the like.

[0013] Furthermore, a front axle 11 extending in the left-right direction is provided below the front vehicle body 3, and front wheels 2 are attached to the left and right sides of the front axle 11. A rear axle 12 extending in the left-right direction is provided below the rear vehicle body 5, and rear wheels 4 are attached to the left and right sides of the rear axle 12. The front axle 11 is connected to an output shaft 17 of a power transmission device 15 via a propeller shaft 13, and the rear axle 12 is connected to the output shaft 17 of the power transmission device 15 via a propeller shaft 14.

[0014] Next, the power transmission according to this embodiment will be described.

[0015] The power transmission device 15 is mounted on the rear body 5 of the wheel loader 1, and transmits the output of the engine 10 at a variable speed to the front axle 11 and the rear axle 12. The power transmission device 15 is configured to include a casing 16, a transmission 20, a torque converter 21, a lockup device 35, etc., which will be described later.

[0016] The power transmission device 15 has a casing 16 that forms an outer shell, and the casing 16 houses a transmission 20, a torque converter 21, etc. An output shaft 17 is disposed below the casing 16, and the output shaft 17 is connected to the propeller shafts 13, 14. The power transmission device 15 changes the speed of the rotation of the engine 10 and transmits it to the output shaft 17. The rotation of the output shaft 17 is transmitted to the front axle 11 via the propeller shaft 13, and is also transmitted to the rear axle 12 via the propeller shaft 14. This causes the front wheels 2 and rear wheels 4 to rotate simultaneously, and the wheel loader 1 can travel forward or backward at the desired gear.

[0017] A hydraulic pump 18, a control valve 19, etc. are arranged on the upper side of the casing 16. The hydraulic pump 18 is driven by the engine 10 to discharge hydraulic oil as a working fluid, and the hydraulic oil (pressurized oil) discharged from the hydraulic pump 18 is selectively supplied to various clutch mechanisms that constitute a transmission 20 and a torque converter 21 under the control of the control valve 19.

[0018] The transmission 20 is provided in the casing 16 together with the torque converter 21. The transmission 20 includes a forward shaft, a reverse shaft, a speed-change shaft, various clutch mechanisms, brake mechanisms, etc. (none of which are shown). The transmission 20 changes the speed of the rotation of the engine 10 transmitted via the torque converter 21 or a lockup device 35, and outputs the rotation to the propeller shafts 13, 14.

[0019] The torque converter 21 is provided in the casing 16 together with the transmission 20. The torque converter 21 transmits the rotation of the engine 10 to the transmission 20 via a working fluid. As shown in Fig. 3, the torque converter 21 includes a stator shaft 22, a converter housing 23, a transmission shaft 28, a pump impeller 31, a turbine runner 32, a stator 33, etc., which will be described later.

[0020] The stator shaft 22 is fixed to the casing 16 of the power transmission device 15. The stator shaft 22 has a disk-shaped flange 22A and a cylindrical portion 22B that protrudes axially from the center of the flange 22A. The flange 22A is fixed to the casing 16 using bolts, surrounding the shaft insertion hole 16A of the casing 16. The cylindrical portion 22B rotatably supports the converter housing 23. A cylindrical stator boss 22C is attached to the outer periphery of the cylindrical portion 22B. The stator shaft 22 is formed with a supply oil passage 21A for supplying hydraulic oil to the torque converter 21 and a discharge oil passage 21B for discharging hydraulic oil from the torque converter 21.

[0021] The converter housing 23 is rotatably supported by the cylindrical portion 22B of the stator shaft 22 via a bearing 24. The converter housing 23 is formed in a hollow ring shape (doughnut shape) as a whole, with one axial side being an open end 23A. The open end 23A of the converter housing 23 is covered with a housing cover 23B. A pump impeller 31, a turbine runner 32, and a stator 33 (described later) are provided inside the converter housing 23, and hydraulic oil is supplied as a working fluid for power transmission.

[0022] An annular flange plate 23C is provided on the inner peripheral surface of the converter housing 23 on the open end 23A side, and the flange plate 23C faces the housing cover 23B with an axial gap between them. A shaft fitting hole 23D is formed in the center of the housing cover 23B, and a fitting portion 25A of the input shaft 25, which will be described later, is fitted into the shaft fitting hole 23D. An annular piston fitting groove 23E is formed on the inner surface of the housing cover 23B that faces the converter housing 23. A piston 37, which will be described later, is fitted into the piston fitting groove 23E.

[0023] The input shaft 25, which serves as a rotating body, is attached to the output shaft of the engine 10. The input shaft 25 has a cylindrical fitting portion 25A, a disk-shaped flange portion 25B, and a cylindrical portion 25C. The fitting portion 25A is fitted into a shaft fitting hole 23D of a housing cover 23B that constitutes the converter housing 23. The flange portion 25B is fixed to the end face of the housing cover 23B using bolts 26. The cylindrical portion 25C protrudes axially from the center of the flange portion 25B, and a bearing 27 is fitted to its outer circumferential surface. The cylindrical portion 25C of the input shaft 25 is rotatably supported by the casing 16 of the power transmission device 15 via the bearing 27. An input shaft internal oil passage 54B, which will be described later, is formed in the fitting portion 25A of the input shaft 25, and an annular groove 25D is formed around the entire outer circumferential surface of the fitting portion 25A.

[0024] The transmission shaft 28 is formed as a hollow cylinder, and transmits the rotation of the input shaft 25 to the transmission 20. An axially intermediate portion of the transmission shaft 28 is inserted into the inner periphery of the stator shaft 22, and the transmission shaft 28 is rotatably supported by the casing 16 via a bearing 29 or the like. A connection flange 30 is spline-coupled to one end 28A (the input shaft 25 side) of the transmission shaft 28. A transmission gear (not shown) is spline-coupled to the other end 28B of the transmission shaft 28, and the rotation of the transmission shaft 28 is transmitted to the transmission 20 via this transmission gear. In addition, a hydraulic oil inlet 28C is formed on the other end 28B of the transmission shaft 28, through which hydraulic oil for lockup is introduced into the inner periphery of the transmission shaft 28.

[0025] The connection flange 30 is provided on one axial side of the transmission shaft 28. The connection flange 30 is made of an annular plate, and has a cylindrical boss portion 30A at its center. The boss portion 30A is spline-connected to one end 28A of the transmission shaft 28, so that the connection flange 30 rotates integrally with the transmission shaft 28. The boss portion 30A is rotatably supported by a housing cover 23B of the converter housing 23 via a bearing 30B. This allows the transmission shaft 28 to rotate relative to the input shaft 25. A turbine runner 32, described later, is fixed to a radially intermediate portion of the connection flange 30. A spline-shaped disk engagement portion 30C is formed on the outer peripheral edge of the connection flange 30, and a disk 39 of a lockup device 35, described later, engages with the disk engagement portion 30C.

[0026] A pump impeller 31, a turbine runner 32, and a stator 33 are provided inside the converter housing 23. The pump impeller 31 is an impeller having a large number of blades arranged continuously in the circumferential direction around the input shaft 25, and is attached to the inside of the converter housing 23. The pump impeller 31 is connected to the input shaft 25 via the converter housing 23 and rotates integrally with the input shaft 25.

[0027] The turbine runner 32 is attached to a radially intermediate portion of the connection flange 30. The turbine runner 32 is an impeller having many blades, and faces the pump impeller 31 in the axial direction. The rotation of the pump impeller 31, i.e., the rotation of the engine 10, is transmitted to the turbine runner 32 via the hydraulic oil (working fluid) supplied into the converter housing 23. The rotation of the turbine runner 32 is transmitted to the transmission 20 via the connection flange 30 and the transmission shaft 28.

[0028] The stator 33 is attached to the stator boss 22C of the stator shaft 22. The stator 33 is disposed between the pump impeller 31 and the turbine runner 32, and is fixed to the casing 16 via the stator shaft 22. The stator 33 is a non-rotating impeller having a large number of blades, and increases the output torque of the transmission shaft 28 by guiding the flow of hydraulic oil from the turbine runner 32 in the rotational direction of the pump impeller 31.

[0029] The rotation of the engine 10 is transmitted from the input shaft 25 to the converter housing 23, and the converter housing 23 rotates together with the pump impeller 31. At this time, a flow of hydraulic oil is generated inside the converter housing 23, causing the turbine runner 32 to rotate, and the rotation of the turbine runner 32 is transmitted to the transmission shaft 28 via the connection flange 30. As a result, the rotation of the engine 10 is transmitted to the transmission 20 via a transmission gear (not shown) or the like splined to the transmission shaft 28.

[0030] The shaft body 34 is disposed coaxially with the transmission shaft 28 on the inner peripheral side of the transmission shaft 28. One axial end of the shaft body 34 (the input shaft 25 side) is spline-connected to the inner peripheral side of the input shaft 25. The other axial end of the shaft body 34 protrudes from the other end 28B of the transmission shaft 28 and is configured to be connected to an external device (not shown) attached to the outside of the casing 16. Here, the axial middle portion of the shaft body 34 is formed with a smaller diameter than both axial end portions. As a result, a cylindrical gap extending in the axial direction is formed between the transmission shaft 28 and the shaft body 34, and this gap serves as a transmission shaft internal oil passage 54A, which will be described later.

[0031] Next, the lockup device 35 provided in the torque converter 21 will be described.

[0032] The lockup device 35 is provided inside the converter housing 23. The lockup device 35 is switched between an engaged state and a disengaged state depending on, for example, the traveling speed of the wheel loader 1. When the lockup device 35 is in the engaged state, the rotation of the converter housing 23 is transmitted directly to the transmission 20 without passing through hydraulic oil. When the lockup device 35 is in the disengaged state, the rotation of the converter housing 23 is transmitted to the transmission 20 via hydraulic oil supplied to the torque converter 21. The lockup device 35 is configured to include a lockup clutch 36, which will be described later, and a lockup control valve 55.

[0033] The lock-up clutch 36 is provided between the converter housing 23 and a connection flange 30 splined to the transmission shaft 28. The lock-up clutch 36 includes a piston 37, a plate 38, a disc 39, and a return spring 40.

[0034] The piston 37 is formed of an annular plate and is fitted into the piston fitting groove 23E of the housing cover 23B so as to be slidable in the axial direction. An annular oil chamber 41 is formed between the inner surface of the housing cover 23B and the piston 37, and an in-cover oil passage 54C (described later) formed in the housing cover 23B opens into the oil chamber 41. An outer peripheral O-ring 42 is provided on the outer peripheral surface of the piston 37, and an inner peripheral O-ring 43 provided on the housing cover 23B abuts against the inner peripheral surface of the piston 37. The outer peripheral O-ring 42 and the inner peripheral O-ring 43 provide a seal between the inner surface of the housing cover 23B and the piston 37.

[0035] The plate 38 is formed of an annular plate. The plate 38 is disposed on the inner peripheral side of the converter housing 23 with a gap formed between the plate 38 and the piston 37. The plate 38 abuts against the flange plate 23C of the converter housing 23, thereby restricting its axial movement.

[0036] The disk 39 is formed of an annular plate. The disk 39 is attached to the connection flange 30 while being sandwiched between the piston 37 and the plate 38. The inner peripheral edge of the disk 39 engages with a spline-shaped disk engaging portion 30C formed on the outer peripheral edge of the connection flange 30. This prevents the disk 39 from moving (rotating) in the circumferential direction relative to the connection flange 30, and allows it to move only in the axial direction.

[0037] The return spring 40 is provided between the piston 37 and the plate 38. The return spring 40 is, for example, a wave spring, and biases the piston 37 in a direction away from the plate 38.

[0038] A lockup oil passage 54, which will be described later, is connected to the oil chamber 41 of the lockup clutch 36. When hydraulic oil from the hydraulic pump 18 is supplied to the oil chamber 41 through the lockup oil passage 54, the disc 39 is pressed against the plate 38 by the piston 37 and engages with the plate 38, thereby engaging the lockup device 35. As a result, the converter housing 23 and the transmission shaft 28 are integrated via the disc 39 and the connecting flange 30, and the rotation of the converter housing 23 is transmitted directly to the transmission shaft 28. In this way, with the lockup device 35 engaged, the rotation of the converter housing 23 is transmitted directly to the transmission 20 without passing through hydraulic oil.

[0039] On the other hand, when the supply of hydraulic oil to the oil chamber 41 is stopped, the biasing force of the return spring 40 causes the disc 39 to separate from the plate 38, and the lock-up device 35 is released. This separates the converter housing 23 from the transmission shaft 28, and the rotation of the converter housing 23 is transmitted to the transmission shaft 28 via the hydraulic oil supplied to the torque converter 21.

[0040] Next, a hydraulic circuit for supplying hydraulic oil to the torque converter 21, the lockup device 35, etc. will be described with reference to FIG.

[0041] In the figure, hydraulic pump 18 constitutes a hydraulic pressure source together with tank 45. A filter 46 is attached to the suction port of hydraulic pump 18, and one end of a pump oil passage 47 is connected to the discharge port of hydraulic pump 18. Pump oil passage 47 constitutes a fluid passage connecting hydraulic pump 18, which discharges hydraulic oil as a working fluid, with torque converter 21. The other end of pump oil passage 47 is connected to supply oil passage 21A formed in stator shaft 22 to supply hydraulic oil to torque converter 21 (see FIG. 6).

[0042] One end of a return oil passage 48 is connected to a discharge oil passage 21B formed in the stator shaft 22 for discharging hydraulic oil from the torque converter 21. The other end of the return oil passage 48 is connected to a tank 45. When the lockup device 35 is in the disengaged state, hydraulic oil discharged from the hydraulic pump 18 is supplied to the torque converter 21 (converter housing 23) from the pump oil passage 47 through the supply oil passage 21A, and then flows back to the tank 45 from the discharge oil passage 21B through the return oil passage 48.

[0043] A filter 49 is provided in the pump oil passage 47. A relief oil passage 51 is connected to the pump oil passage 47 downstream of the filter 49 via a first connection part 50A. A relief valve 52 is provided in the relief oil passage 51, and a relief pressure is set to relieve surge pressure in order to protect the hydraulic circuit.

[0044] A clutch oil passage 53 is connected to the pump oil passage 47 downstream of the first connection portion 50A via a second connection portion 50B. Hydraulic oil to be supplied to various clutch mechanisms (not shown) mounted on the power transmission device 15 flows through the clutch oil passage 53. A control valve (not shown) is connected to the clutch oil passage 53, located between the third connection portion 50C and the clutch mechanism. The control valve selectively supplies hydraulic oil whose pressure has been adjusted (to adjust the engagement and release of the clutch) by a pressure reducing valve 56 (described later), to the various clutch mechanisms. One end of a lock-up oil passage 54 is connected to the clutch oil passage 53 via the third connection portion 50C, and the other end of the lock-up oil passage 54 is connected to the oil chamber 41 of the lock-up clutch 36.

[0045] Here, lockup oil passage 54 is formed in power transmission device 15, and guides hydraulic oil discharged from hydraulic pump 18 to oil chamber 41 via lockup control valve 55. As shown in Fig. 3, lockup oil passage 54 is configured to include a transmission shaft oil passage 54A, an input shaft oil passage 54B, and a cover oil passage 54C.

[0046] The transmission shaft oil passage 54A is provided on the inner peripheral side of the transmission shaft 28. The transmission shaft oil passage 54A is cylindrically formed between the outer peripheral surface of the shaft body 34, which is arranged on the inner peripheral side of the transmission shaft 28, and the inner peripheral surface of the transmission shaft 28, and extends in the axial direction. One axial end side (the input shaft 25 side) of the transmission shaft oil passage 54A communicates with the input shaft oil passage 54B, and the other axial end side of the transmission shaft oil passage 54A communicates with the hydraulic oil inlet port 28C of the transmission shaft 28. The transmission shaft oil passage 54A is connected to a port of the lockup control valve 55 via an oil passage connected to the hydraulic oil inlet port 28C.

[0047] The input shaft oil passage 54B is formed in the fitting portion 25A of the input shaft 25 so as to extend radially. One end of the input shaft oil passage 54B is connected to the other end of the transmission shaft oil passage 54A. The other end of the input shaft oil passage 54B is connected to the annular groove 25D formed in the fitting portion 25A of the input shaft 25. The cover oil passage 54C is formed in the housing cover 23B so as to extend radially. One end of the cover oil passage 54C is connected to the annular groove 25D of the input shaft 25, and the other end of the cover oil passage 54C is connected to the oil chamber 41.

[0048] The lockup control valve 55 is provided in the lockup oil passage 54 on the upstream side of the transmission shaft internal oil passage 54A. The lockup control valve 55 is configured, for example, by a 3-port 2-position solenoid valve, and is switched between switching position (a) and switching position (b) in response to a control signal supplied from a controller (not shown). For example, the lockup control valve 55 is in switching position (a) when the traveling speed of the wheel loader 1 is equal to or less than a set value, and is switched to switching position (b) when the traveling speed of the wheel loader 1 exceeds the set value. When the lockup control valve 55 is in switching position (a), the lockup oil passage 54 is blocked and the lockup device 35 is in a released state. When the lockup control valve 55 is in switching position (b), the lockup oil passage 54 is connected and the lockup device 35 is in an engaged state.

[0049] A pressure reducing valve (regulator valve) 56 is provided in the pump oil passage 47 downstream of the second connection portion 50B. The pressure reducing valve 56 supplies a constant amount of pressurized oil to a control valve that supplies clutch pressure to various clutch mechanisms. When the pressure in the pump pipe 47 upstream of the pressure reducing valve 56 exceeds a set pressure, the pressure reducing valve 56 releases this pressure downstream (towards the torque converter 21).

[0050] An oil cooler 57 is provided in the return oil passage 48. The oil cooler 57 cools the hydraulic oil that returns to the tank 45 through the return oil passage 48. The hydraulic oil cooled by the oil cooler 57 is guided to a clutch lubrication circuit 58, lubricates various clutches mounted in the power transmission device 15, and then returns to the tank 45.

[0051] A fluid control valve 59 is provided in a portion of pump oil passage 47 upstream of torque converter 21 (a portion between pressure reducing valve 56 and torque converter 21). Fluid control valve 59 opens pump oil passage 47 when lockup device 35 is in a disengaged state, and blocks pump oil passage 47 when lockup device 35 is in an engaged state. As shown in FIG. 6, fluid control valve 59 includes a valve body fitting hole 59A, a valve body 59C, a spring guide 59F, and a spring 59H.

[0052] The valve element fitting hole 59A is formed in the casing 16 so as to be perpendicular to the pump oil passage 47. One end of the valve element fitting hole 59A is closed by a sealing plug 59B, and a spring guide 59F (described later) is attached to the other end of the valve element fitting hole 59A. The sealing plug 59B has a small hole (not shown) that discharges hydraulic oil from the valve element fitting hole 59A when the valve element 59C moves from a blocking position (described later) to a communicating position. A small-diameter pilot oil passage 60 is formed in the casing 16 parallel to the pump oil passage 47 and connected to one end of the valve element fitting hole 59A (the sealing plug 59B side). The pilot oil passage 60 connects the lockup oil passage 54 and the valve element fitting hole 59A, and introduces a portion of the hydraulic oil flowing through the lockup oil passage 54 into the valve element fitting hole 59A as pilot pressure.

[0053] The valve element 59C is slidably disposed within the valve element fitting hole 59A. The valve element 59C is formed in a cylindrical shape, and an O-ring 59D is attached to its outer surface. The O-ring 59D seals the gap between the valve element 59C and the valve element fitting hole 59A. The valve element 59C is switched between a communicating position (position in FIG. 6 ) that communicates with the pump oil passage 47 and a blocking position (position in FIG. 7 ) that blocks the pump oil passage 47, depending on the pilot pressure supplied into the valve element fitting hole 59A through the pilot oil passage 60. A retaining ring (snap ring) 59E for the hole is provided on the inner peripheral surface of the valve element fitting hole 59A adjacent to the connection between the valve element fitting hole 59A and the pilot oil passage 60. When the valve element 59C moves to the communicating position, it abuts against the retaining ring 59E, thereby restricting further movement.

[0054] The spring guide 59F is provided on the other end side of the valve element fitting hole 59A. The spring guide 59F has a guide shaft 59G extending toward the valve element 59C, and a spring 59H is disposed on the outer periphery of the guide shaft 59G. The spring 59H is a compression coil spring and biases the valve element 59C toward the communicating position. As a result, when pilot pressure is not supplied to one end side of the valve element fitting hole 59A, the valve element 59C is held in the communicating position by the spring 59H, and the pump oil passage 47 is communicated. On the other hand, when pilot pressure is supplied to one end side of the valve element fitting hole 59A, the valve element 59C moves against the spring 59H to the blocking position and blocks the pump oil passage 47. The spring guide 59F is formed with a minute hole (not shown) for discharging hydraulic oil accumulated between the valve body 59C and the spring guide 59F when the valve body 59C moves from the communicating position to the blocking position.

[0055] One end of a bypass oil passage 61 is connected via a fourth connection 50D to a portion of the pump oil passage 47 upstream of the fluid control valve 59 (a portion between the pressure reducing valve 56 and the fluid control valve 59). The other end of the bypass oil passage 61 bypasses the fluid control valve 59 and the torque converter 21, and is connected to the return oil passage 48 at a fifth connection 50E. A pressure regulating valve 62 is provided in the bypass oil passage 61. The pressure regulating valve 62 regulates the pressure in the pump oil passage 47 by opening the bypass oil passage 61 when the fluid control valve 59 is in the shutoff position and the pressure in the pump oil passage 47 increases.

[0056] 6, the pressure regulating valve 62 is a check valve having a setting spring 62A, and opens when the pressure in the pump oil passage 47 exceeds the pressure set by the setting spring 62A. As a result, the hydraulic oil flowing through the pump oil passage 47 is guided to the return oil passage 48 via the bypass oil passage 61.

[0057] A fluid injection device 63 is provided in a portion of the bypass oil passage 61 downstream of the pressure regulation valve 62 (a portion between the pressure regulation valve 62 and the fifth connection part 50E). The fluid injection device 63 has, for example, a throttle (not shown) connected to the bypass oil passage 61, and injects a portion of the hydraulic oil flowing through the bypass oil passage 61 to the return oil passage 48 toward the torque converter 21 and the lockup device 35. This allows the torque converter 21 and the lockup device 35 to be cooled from the outside.

[0058] The power transmission device 15 according to this embodiment has the above-described configuration, and its operation will be described below.

[0059] For example, when the wheel loader 1 is caused to travel forward, the rotation of the engine 10 is transmitted to the transmission 20 of the power transmission device 15 via the torque converter 21. The rotation, the speed of which has been changed by the transmission 20, is output to the output shaft 17 of the power transmission device 15. The rotation of the output shaft 17 is transmitted to the front axle 11 via the propeller shaft 13, and is also transmitted to the rear axle 12 via the propeller shaft 14. This causes the front wheels 2 and rear wheels 4 to rotate simultaneously, allowing the wheel loader 1 to travel forward at the desired gear position.

[0060] Here, while the travel speed of the wheel loader 1 is equal to or less than the set value, the lockup control valve 55 holds the switched position (a). As a result, the lockup oil passage 54 is blocked, and the supply of hydraulic oil to the oil chamber 41 of the lockup device 35 is stopped. As a result, the lockup clutch 36 is disengaged by the return spring 40, and the lockup device 35 is in a released state. In addition, the supply of pilot pressure from the pilot oil passage 60 to the valve disc fitting hole 59A of the fluid control valve 59 is stopped. As a result, the valve disc 59C of the fluid control valve 59 is held in a position in contact with the retaining ring 59E by the spring 59H, and the pump oil passage 47 is opened (see FIG. 6).

[0061] As described above, when the lockup device 35 is in the disengaged state, the hydraulic oil discharged from the hydraulic pump 18 is guided through the pump oil passage 47 to the supply oil passage 21A of the torque converter 21 (stator shaft 22), and is then supplied from the supply oil passage 21A into the converter housing 23. The rotation of the engine 10 is transmitted from the input shaft 25 to the converter housing 23, which rotates together with the pump impeller 31. The flow of hydraulic oil generated within the converter housing 23 at this time rotates the turbine runner 32, and the rotation of the turbine runner 32 is transmitted to the transmission shaft 28 via the connecting flange 30. In this way, the rotation of the engine 10 is transmitted to the transmission shaft 28 via the working fluid of the torque converter 21, and is then transmitted to the transmission 20 via a transmission gear (not shown) or the like splined to the transmission shaft 28.

[0062] Next, when the traveling speed of the wheel loader 1 exceeds a set value, a control signal is output from a controller (not shown) to the lockup control valve 55, and the lockup control valve 55 switches to the switching position (b). This opens the lockup oil passage 54, and hydraulic oil is supplied to the oil chamber 41 of the lockup device 35. This causes the piston 37 to press the disc 39 against the plate 38, engaging the lockup clutch 36 and placing the lockup device 35 in an engaged state. In addition, pilot pressure is supplied to the valve disc fitting hole 59A of the fluid control valve 59 through the pilot oil passage 60, and the valve disc 59C of the fluid control valve 59 moves to the shut-off position against the spring 59H, shutting off the pump oil passage 47 (see FIG. 7).

[0063] In this way, when the lockup device 35 is engaged, the converter housing 23 and the transmission shaft 28 are integrated via the lockup clutch 36, and the rotation of the engine 10 is transmitted directly to the transmission 20 without passing through the torque converter 21. At this time, the pump oil passage 47 is blocked by the fluid control valve 59, so the supply of hydraulic oil to the torque converter 21 is stopped. This prevents hydraulic oil from flowing inside the converter housing 23, thereby suppressing power loss in the torque converter 21 that would be caused by the flow of hydraulic oil being obstructed by the stator 33. As a result, when the lockup device 35 is engaged and the rotation of the engine 10 is transmitted directly to the transmission 20, it is possible to avoid a decrease in fuel economy that would be caused by the supply of hydraulic oil to the torque converter 21.

[0064] On the other hand, when the fluid control valve 59 blocks the pump oil passage 47 and the pressure in the pump oil passage 47 exceeds the pressure set by the setting spring 62A of the pressure regulating valve 62, the pressure regulating valve 62 opens. As a result, the hydraulic oil discharged from the hydraulic pump 18 is guided to the return oil passage 48 through the bypass oil passage 61 without being supplied to the torque converter 21. The hydraulic oil guided to the return oil passage 48 is cooled by the oil cooler 57 and then supplied to the clutch lubrication circuit 58, where it lubricates the various clutches mounted in the power transmission device 15 and then returns to the tank 45.

[0065] Here, a portion of the hydraulic oil flowing through the bypass oil passage 61 to the return oil passage 48 is injected toward the torque converter 21 and the lockup device 35 by a fluid injection device 63 provided in the bypass oil passage 61. Therefore, even if the supply of hydraulic oil to the torque converter 21 is stopped and the temperatures of the torque converter 21 and the lockup device 35 rise, the hydraulic oil injected from the fluid injection device 63 can appropriately cool the torque converter 21 and the like from the outside.

[0066] On the other hand, when the wheel loader 1 is traveling and digging by driving the loader bucket 8A into piles of earth and sand, for example, when the engine 10 (input rotational speed) is high and the wheel loader 1 operates in a low speed ratio range where the traveling speed is zero or close to zero, the lockup device 35 is disengaged, reducing the power transmission efficiency of the torque converter 21. This causes the torque converter 21 to generate a large amount of heat and increase its internal pressure. When the pressure in the torque converter 21 increases and the pressure in the pump oil passage 47 exceeds the pressure set by the setting spring 62A of the pressure regulating valve 62, the pressure regulating valve 62 opens. As a result, much of the hydraulic oil discharged from the hydraulic pump 18 flows to the return oil passage 48 via the bypass oil passage 61. As a result, it may not be possible to supply enough hydraulic oil to the interior of the torque converter 21 (converter housing 23) to properly cool it.

[0067] In contrast, since the bypass oil passage 61 is provided with the fluid injection device 63, a portion of the hydraulic oil flowing through the bypass oil passage 61 can be injected by the fluid injection device 63 to the outside of the torque converter 21. As a result, even if the hydraulic oil supplied to the inside of the torque converter 21 cannot sufficiently cool the torque converter 21, the hydraulic oil can be sprayed to the outside of the torque converter 21 by the fluid injection device 63, thereby cooling the torque converter 21 from the outside.

[0068] Thus, the power transmission device 15 according to the embodiment includes an input shaft 25 driven by the engine 10, a transmission 20 that changes the speed of the rotation of the input shaft 25, a torque converter 21 that transmits the rotation of the input shaft 25 to the transmission 20 via hydraulic fluid, and a lockup device 35 that is provided in the torque converter 21 and switches between an engaged state in which the rotation of the input shaft 25 is directly transmitted to the transmission 20 and a disengaged state in which the rotation of the input shaft 25 is transmitted to the transmission 20 via the torque converter 21. A pump oil passage 47 that supplies hydraulic fluid to the torque converter 21 is provided with a fluid control valve 59 that connects the pump oil passage 47 when the lockup device 35 is in the disengaged state and that blocks the pump oil passage 47 when the lockup device 35 is in the engaged state.

[0069] According to this configuration, when the lockup device 35 is in the engaged state, the fluid control valve 59 blocks the pump oil passage 47. This stops the supply of hydraulic oil to the torque converter 21, and prevents hydraulic oil from flowing inside the converter housing 23. As a result, power loss in the torque converter 21 caused by the stator 33 blocking the flow of hydraulic oil can be suppressed.

[0070] In the embodiment, the pump oil passage 47 connects the torque converter 21 with the hydraulic pump 18, which discharges hydraulic oil to be supplied to the torque converter 21, the fluid control valve 59 is disposed in the pump oil passage 47 upstream of the torque converter 21, and a pressure adjustment valve 62 is provided in the pump oil passage 47 upstream of the fluid control valve 59, which adjusts the pressure in the pump oil passage 47 when the fluid control valve 59 blocks the pump oil passage 47. According to this configuration, when the fluid control valve 59 blocks the pump oil passage 47 and the pressure in the pump oil passage 47 increases, the pressure adjustment valve 62 opens, thereby enabling the pressure in the pump oil passage 47 to be stably adjusted.

[0071] In this embodiment, pressure regulating valve 62 is configured to open when the pressure in pump oil passage 47 exceeds a set value, and to return the hydraulic oil flowing through pump oil passage 47 to tank 45 via bypass oil passage 61, and bypass oil passage 61 is provided with a fluid injection device 63 that injects the hydraulic oil flowing through bypass oil passage 61 toward torque converter 21 and lockup device 35. With this configuration, even if the supply of hydraulic oil to torque converter 21 is stopped and the temperatures of torque converter 21 and lockup device 35 rise, the hydraulic oil injected from fluid injection device 63 can appropriately cool torque converter 21 and the like from the outside.

[0072] In the embodiment, the engine 10 is exemplified as the prime mover, but the present invention is not limited to this, and for example, an electric motor or the like may be used as the prime mover.

[0073] In addition, in the embodiment, the outer circumferential O-ring 42, the inner circumferential O-ring 43, and the O-ring 59D are exemplified as seals, but instead of these O-rings, a seal ring or a D-ring may be used, for example.

[0074] In addition, in the embodiment, a wheel loader 1 is exemplified as a work vehicle on which the power transmission device 15 is mounted. However, the present invention is not limited to this, and can be widely applied to work vehicles such as dump trucks, bulldozers, forklifts, etc. [Explanation of symbols]

[0075] 10 Engine (prime mover) 18 Hydraulic pump (pump) 20 Transmission 21 Torque converter 25 Input shaft (rotating body) 35 Lock-up device 45 Tank 47 Pump oil passage (fluid passage) 59 Fluid Control Valve 61 Bypass oil passage (bypass passage) 62 Pressure Regulating Valve 63 Fluid injection device

Claims

1. a rotating body driven by a prime mover; a transmission that changes the speed of rotation of the rotating body; a torque converter that transmits the rotation of the rotating body to the transmission via a working fluid; a lock-up device provided in the torque converter and switchable between an engaged state in which rotation of the rotating body is directly transmitted to the transmission and a disengaged state in which rotation of the rotating body is transmitted to the transmission via the torque converter, a fluid passageway for supplying the hydraulic fluid to the torque converter, the fluid control valve opening the fluid passageway when the lock-up device is in the released state, and blocking the fluid passageway when the lock-up device is in the engaged state.

2. the fluid passage connects the torque converter to a pump that discharges the hydraulic fluid to be supplied to the torque converter; the fluid control valve is disposed in the fluid passage upstream of the torque converter, 2. The power transmission device according to claim 1, wherein a pressure regulating valve is provided in the fluid passage upstream of the fluid control valve, to adjust the pressure in the fluid passage when the fluid control valve blocks the fluid passage.

3. the pressure regulating valve is configured to open when the pressure in the fluid passage exceeds a set value, and to return the working fluid flowing through the fluid passage to a tank via a bypass passage; 3. The power transmission device according to claim 2, wherein the bypass passage is provided with a fluid injection device that injects the working fluid flowing through the bypass passage toward the torque converter and the lockup device.

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