Work vehicle

Abstract

To suppress fluctuation in a time required for switching operation, in a work vehicle that operates a speed switching unit according to an oil supply / discharge state of pilot hydraulic oil, the speed switching unit performing switching operation for switching a hydraulic motor between a high-speed state and a low-speed state.SOLUTION: A work vehicle comprises an operation oil path 53 connected across an operation port of a speed switching unit 51 and a pilot operation valve 52, and a return oil path 58 that is connected to the operation oil path 53 and returns pilot hydraulic oil in the operation oil path 53 to a tank 23. The return oil path 58 is provided with a resistance unit 59 that resists the flow of the pilot hydraulic oil from the operation oil path 53 to the tank 23 so that excess pilot hydraulic oil exceeding pilot hydraulic oil necessary for operating a hydraulic motor 14 to a high speed state H by the speed switching unit 51 is returned to the tank 23 from the operation oil path 53 via the return oil path 58 in a state where the pilot operation valve 52 is operated to a supply position 52a.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a work vehicle equipped with a variable displacement hydraulic motor that drives a driven part. [Background technology]

[0002] Patent document 1 discloses a backhoe equipped with a hydraulic motor 11 that drives a crawler-type traveling device (driven part), a hydraulic actuator 13 that switches the hydraulic motor 11 between a high-speed state and a low-speed state, a pilot-operated valve device V that operates the hydraulic actuator 13 by switching the supply / discharge state of hydraulic oil to the hydraulic actuator 13, and a speed selection valve 37 that operates the valve device V by switching the supply / discharge state of pilot hydraulic oil to the valve device V (the symbols shown in Patent document 1 are used above). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-214562 Summary of the Invention [Problem to be solved by the invention]

[0004] However, with the technology of Patent Document 1, the speed at which the high speed state and the low speed state are switched may fluctuate due to changes in the viscosity of the pilot hydraulic oil caused by changes in the outside air temperature or the like.

[0005] For example, when the speed selection valve 37 is operated to switch from a state in which pilot hydraulic oil is supplied to the operation port of the valve device V to a state in which the pilot hydraulic oil that was being supplied to the operation port of the valve device V is discharged to the hydraulic oil tank, if the outside air temperature is low and the viscosity of the pilot hydraulic oil increases, reducing the fluidity of the pilot hydraulic oil, the discharge of the pilot hydraulic oil will be delayed, causing the switching between the high-speed state and the low-speed state to be slower than usual. Also, if the viscosity of the pilot hydraulic oil decreases and the fluidity of the pilot hydraulic oil increases compared to usual, the discharge of the pilot hydraulic oil will be faster, causing the switching between the high-speed state and the low-speed state to be faster than usual (the symbols used above are those shown in Patent Document 1).

[0006] The present invention aims to suppress fluctuations in the time required for a speed switching operation in a work vehicle in which a speed switching unit that performs a switching operation to switch a hydraulic motor between a high-speed state and a low-speed state is operated according to the supply / discharge state of pilot hydraulic oil. [Means for solving the problem]

[0007] The work vehicle of the present invention is provided with a variable displacement hydraulic motor that drives a driven part, a hydraulic pump that operates the hydraulic motor by supplying hydraulic oil to the hydraulic motor, a speed switching unit that performs a switching operation to switch the hydraulic motor between a high speed state and a low speed state, a pilot operated valve that controls the supply / discharge state of pilot hydraulic oil to the speed switching unit to cause the speed switching unit to perform its switching operation, a tank that stores the pilot hydraulic oil, a hydraulic oil pump that supplies the pilot hydraulic oil from the tank to the pilot operated valve, and an operating oil passage that connects an operating port of the speed switching unit and the pilot operated valve, and the pilot operated valve supplies pilot hydraulic oil supplied from the hydraulic oil pump to the operating port of the speed switching unit via the operating oil passage, thereby controlling the hydraulic pressure by the speed switching unit. The hydraulic motor has a supply position for operating the motor in one of the high-speed state and the low-speed state, and a discharge position for operating the hydraulic motor in the other of the high-speed state and the low-speed state by the speed switching unit by discharging pilot hydraulic oil in the operating oil line into the tank, and is provided with a return oil line that is connected to the operating oil line and returns the pilot hydraulic oil in the operating oil line to the tank, and a resistance unit that provides resistance to the flow of pilot hydraulic oil from the operating oil line to the tank so that, when the pilot operating valve is operated to the supply position, excess pilot hydraulic oil that exceeds the pilot hydraulic oil required to operate the hydraulic motor in one of the high-speed state and the low-speed state by the speed switching unit is returned from the operating oil line to the tank via the return oil line.

[0008] According to the present invention, when the pilot operated valve is operated to the supply position, pilot hydraulic oil in the tank is supplied from the hydraulic oil pump through the pilot operated valve (supply position) and the operating oil passage to the operating port of the speed switching unit, and the hydraulic motor is operated to a high speed state (low speed state) by the speed switching unit. In addition, by operating the pilot operating valve to the discharge position, the pilot hydraulic oil in the operating port of the speed switching unit is efficiently discharged to the tank via a route that passes through the operating oil passage and the pilot operating valve (discharge position) and a route that passes through the operating oil passage and the return oil passage, and the speed switching unit operates the hydraulic motor to a low speed state (high speed state).

[0009] In the above-described configuration, according to the present invention, there are provided a return oil passage connected to the operation oil passage, and a resistance portion provided in the return oil passage. When the pilot operating valve is operated to the supply position, the pilot hydraulic oil required to operate the hydraulic motor at high speed (low speed) by the speed switching unit is secured at the operation port of the speed switching unit by the resistance unit, while excess pilot hydraulic oil is returned to the tank from the return oil line, and the pilot hydraulic oil circulates through the tank, hydraulic oil pump, pilot operating valve (supply position), operation oil line, and return oil line. This allows the pilot hydraulic oil in the operating oil passage to circulate and be replaced, thereby suppressing fluctuations in the temperature of the pilot hydraulic oil in the operating oil passage and suppressing fluctuations in the time required to switch the hydraulic motor between high-speed and low-speed states.

[0010] According to the present invention, it is possible to prevent a drop in the temperature of the pilot hydraulic oil in the operating oil passage, so that when the pilot operating valve is operated from the supply position to the discharge position, the pilot hydraulic oil in the operating port of the speed switching unit is quickly discharged through the operating oil passage and the pilot operating valve (discharge position), and the hydraulic motor is operated to a low speed state (high speed state) without delay by the speed switching unit.

[0011] In the present invention, it is preferable that the speed switching unit includes a hydraulic actuator that switches the hydraulic motor between the high-speed state and the low-speed state, and an actuator operating unit that operates the hydraulic actuator in accordance with the supply / discharge state of the pilot hydraulic oil from the pilot operating valve, and switches the hydraulic motor between the high-speed state and the low-speed state.

[0012] According to the present invention, the speed switching unit is provided with a hydraulic actuator and an actuator operating unit, thereby making it possible to reduce the size of the speed switching unit.

[0013] In the present invention, it is preferable that the resistance portion is a throttle portion.

[0014] According to the present invention, the throttle section ensures that the pilot hydraulic oil required to operate the speed changer to a high speed state (low speed state) is available in the operating port of the speed changer, which is advantageous in terms of simplifying the structure.

[0015] In the present invention, it is preferable that the resistance portion is a constant flow valve that allows pilot hydraulic oil to flow at a constant flow rate downstream relative to the upstream side.

[0016] According to the present invention, the constant flow valve can ensure that the pilot hydraulic oil required to operate the speed switching unit to a high speed state (low speed state) is available at the operating port of the speed switching unit, which is advantageous in terms of simplifying the structure.

[0017] In the present invention, it is preferable that the resistance portion is a relief valve.

[0018] According to the present invention, the relief valve can ensure that the pilot hydraulic oil required to operate the speed changer to a high speed state (low speed state) is available at the operating port of the speed changer, which is advantageous in terms of simplifying the structure.

[0019] In the present invention, it is preferable that the hydraulic oil pump supplies pilot hydraulic oil to the pilot operation valve, and also supplies the pilot hydraulic oil as hydraulic oil to a hydraulic oil passage connecting the hydraulic pump and the hydraulic motor.

[0020] According to the present invention, the hydraulic oil pump functions as both a pilot pump that supplies pilot hydraulic oil to the pilot operated valve and a charge pump that supplies hydraulic oil to the hydraulic oil passage. This allows the hydraulic oil pump to be used as both a pilot pump and a charge pump, which is advantageous in terms of simplifying the structure.

[0021] In the present invention, it is preferable that the driven part includes a traveling device, and when the pilot operated valve is operated to the supply position, the speed switching part is operated to the high speed state, and when the pilot operated valve is operated to the discharge position, the speed switching part is operated to the low speed state.

[0022] Some work vehicles are configured to drive their travel gear with a hydraulic pump and a hydraulic motor. In such work vehicles, the hydraulic motor is operated at high speed during normal work conditions to perform work travel, and the hydraulic motor is operated at low speed when a heavy load is placed on the travel gear, for example, on a slope or in a muddy area of ​​the work site. In this case, the normal work conditions are considered to be relatively long, and the conditions under which a heavy load is placed on the travel gear are considered to be relatively short.

[0023] According to the present invention, when the pilot operating valve is operated to the supply position, the speed switching unit is configured to operate to a high-speed state, so that the pilot operating oil in the operating oil passage can be maintained in a circulating and replaced state for a relatively long period of time, which is advantageous in terms of suppressing fluctuations in the temperature of the pilot operating oil in the operating oil passage.

[0024] In the present invention, the driven parts include a left traveling device and a right traveling device, the hydraulic motors include a left traveling hydraulic motor that drives the left traveling device and a right traveling hydraulic motor that drives the right traveling device, the speed switching parts include a left speed switching part that switches the left traveling hydraulic motor between the high speed state and the low speed state, and a right speed switching part that switches the right traveling hydraulic motor between the high speed state and the low speed state, and the operating oil path includes an operating oil path for operating the left speed switching part. It is preferable that the hydraulic control system has a left operating oil passage connecting the operating port of the right speed switching unit to the pilot operating valve, and a right operating oil passage connecting the operating port of the right speed switching unit to the pilot operating valve, and that the return oil passages include a left return oil passage that returns the pilot operating oil of the left operating oil passage to the tank, and a right return oil passage that returns the pilot operating oil of the right operating oil passage to the tank, and that the resistance portions include a left resistance portion provided in the left return oil passage and a right resistance portion provided in the right return oil passage.

[0025] According to the present invention, the difference between the time required to switch the left traveling device between a high speed state and a low speed state and the time required to switch the right traveling device between a high speed state and a low speed state can be reduced, thereby improving straight-line traveling ability.

[0026] In the present invention, it is preferable that at least a part of the return oil passage and the resistance portion are provided inside a case of the hydraulic motor.

[0027] According to the present invention, the return oil passage and the resistance portion can be realized in a compact configuration. [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 2 is a left side view of the compact track loader. [Figure 2] FIG. 2 is a longitudinal sectional front view of the hydraulic motor. [Figure 3] FIG. 2 is a vertical cross-sectional side view of the vicinity of a first case of the hydraulic motor. [Figure 4]FIG. 10 is a hydraulic circuit diagram in a state where the second operating valve is operated to a supply position and the first operating valve is operated to a high-speed position. [Figure 5] FIG. 4 is a hydraulic circuit diagram in a state where the second operating valve is operated to a discharge position and the first operating valve is operated to a low speed position. [Figure 6] FIG. 10 is a hydraulic circuit diagram in a state in which the second operating valve is operated to a supply position and the first operating valve is operated to a high-speed position in the first alternative embodiment of the invention. [Figure 7] FIG. 10 is a hydraulic circuit diagram in a second alternative embodiment of the invention, in which the second operating valve is operated to a supply position and the first operating valve is operated to a high-speed position. [Figure 8] FIG. 10 is a hydraulic circuit diagram in a state where the second operating valve is operated to a supply position and the first operating valve is operated to a high-speed position in a third alternative embodiment of the invention. [Figure 9] FIG. 10 is a hydraulic circuit diagram according to a fourth modified embodiment of the invention. [Figure 10] FIG. 10 is a hydraulic circuit diagram according to a fifth modified embodiment of the invention. [Figure 11] FIG. 10 is a hydraulic circuit diagram according to a sixth modified embodiment of the invention. [Figure 12] FIG. 13 is a hydraulic circuit diagram according to a seventh modified embodiment of the invention. [Figure 13] FIG. 13 is a hydraulic circuit diagram showing a constant flow valve according to an eighth modified embodiment of the invention. [Figure 14] FIG. 13 is a hydraulic circuit diagram showing a relief valve in a ninth modified embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION

[0029] A compact track loader (CTL) is an example of a work vehicle, and is shown in Figures 1 to 14. F indicates the forward direction, B indicates the rearward direction, U indicates the upward direction, and D indicates the downward direction.

[0030] (Compact track loader overall configuration) As shown in Fig. 1, a machine body 1 is supported by right and left crawler-type traveling devices 2 (corresponding to driven parts), and a driving part 3 is provided on the machine body 1. Right and left booms 4 are supported at the rear of the machine body 1 so as to be swingable up and down and extend forward, and a boom cylinder 6 is provided for swinging the booms 4 up and down. A bucket 5 is supported at the front end of the boom 4 so as to be swingable up and down, and a bucket cylinder 7 is provided for swinging the bucket 5.

[0031] The running device 2 has drive wheels 8, idler wheels 10 supported at the front and rear of the track frame 9, rollers 11 supported on the track frame 9, and crawler belts 12 attached across the drive wheels 8, idler wheels 10, and rollers 11.

[0032] In the right and left traveling devices 2, the crawler belts 12 are rotationally driven by the drive wheels 8, and by independently driving the right and left traveling devices 2 forward and backward, it is possible to perform forward and backward movement, gentle turns to the right and left, right and left pivot turns, and right and left super pivot turns.

[0033] (Configuration of hydrostatic continuously variable transmission that drives the traveling device) A right hydrostatic continuously variable transmission 13 is provided to drive the drive wheels 8 of the right traveling device 2, and a left hydrostatic continuously variable transmission 13 is provided to drive the drive wheels 8 of the left traveling device 2, and the right and left traveling devices 2 are driven forward and backward independently by the right and left continuously variable transmissions 13. The right and left continuously variable transmissions 13 have the same structure, and therefore will be described below without distinguishing between the right and left continuously variable transmissions 13.

[0034] As shown in FIG. 4, the continuously variable transmission 13 is provided with a variable displacement hydraulic motor 14 (corresponding to a traveling hydraulic motor) that drives the drive wheels 8, a hydraulic pump 15 and a charge pump 16 that are driven by an engine (not shown) mounted on the machine body 1, and a pair of hydraulic oil passages 17 that are connected between the hydraulic pump 15 and the hydraulic motor 14.

[0035] The hydraulic pump 15 is configured as a variable displacement type and is configured so that the speed can be changed continuously from the neutral position to the forward and reverse sides. The hydraulic oil of the hydraulic pump 15 is supplied to the hydraulic motor 14 via the hydraulic oil passage 17, causing the hydraulic motor 14 to operate continuously to the forward and reverse sides.

[0036] A charge oil passage 18 is connected across the hydraulic oil passage 17, and an oil passage 19 from the charge pump 16 is connected to the charge oil passage 18. The charge pump 16 is provided in one of the right or left continuously variable transmissions 13, and an oil passage 20 branching from the oil passage 19 is connected to the charge oil passage 18 of the other continuously variable transmission 13. A tank 23 is provided to store hydraulic oil, and the hydraulic oil in the tank 23 is supplied from the charge pump 16 to the hydraulic oil passage 17 via the oil passages 19, 20 and the charge oil passage 18.

[0037] (Configuration of hydraulic motor mechanical system) As shown in Figures 2 and 3, the hydraulic motor 14 is provided with a first case 21 (corresponding to the case of the hydraulic motor) connected to the machine body 1, a second case 22 connected to the first case 21, a hydraulic motor section 24 arranged in the internal space 22a of the second case 22, and a rotating case 25 supported by the second case 22 so as to be rotatable around an axis P1 along the left-right direction, and the drive wheels 8 are connected to the rotating case 25 (see Figure 1).

[0038] In the hydraulic motor section 24, a drive shaft 26 is rotatably supported at the position of the axis P1, a plunger case 27 is connected to the drive shaft 26, and multiple plungers 28 are supported on the plunger case 27 so as to be able to move back and forth along the axis P1.

[0039] In the hydraulic motor section 24, a swash plate 29 is disposed in the internal space 22a of the second case 22 and is supported so as to be swingable about an axis P2 perpendicular to the axis P1, and an end of a plunger 28 is in contact with the swash plate 29. A piston section 30 (corresponding to a hydraulic actuator) (corresponding to a speed switching section) that can be operated by pressing a part of the swash plate 29 is supported by the second case 22, and the posture of the swash plate 29 can be changed about the axis P2 by the piston section 30.

[0040] Hydraulic oil from the hydraulic pump 15 is supplied to the plunger 28 of the hydraulic motor section 24 via the hydraulic oil passage 17, and the plunger 28 moves circumferentially along the swash plate 29 while protruding from the plunger case 27, thereby rotating the hydraulic motor section 24.

[0041] A drive shaft 31 is disposed at the position of the axis P1 and connected to the drive shaft 26, and a transmission member 32 is disposed between a transmission gear 31a of the drive shaft 31 and a transmission gear 25a on the inner surface of the rotating case 25. The transmission member 32 is configured such that a plurality of transmission gear portions 32b are non-rotatably connected to a disk-shaped support portion 32a, and a transmission gear 32c is rotatably supported by the transmission gear portions 32b.

[0042] A cylindrical transmission gear 33 is rotatably supported on the drive shaft 31. A transmission gear 34 is rotatably supported on a plurality of shaft portions 22b of the second case 22, and the transmission gear 34 meshes with the transmission gear 33 and the transmission gear 25a of the rotating case 25. A transmission gear 32c of the transmission member 32 meshes with the transmission gear 31a of the drive shaft 31 and the transmission gear 25a of the rotating case 25, and a transmission gear portion 32b of the transmission member 32 meshes with the transmission gear 33.

[0043] With the above configuration, when the hydraulic motor unit 24 is rotationally driven, the drive shaft 31 is rotationally driven, and the transmission gear 31a of the drive shaft 31 rotationally drives the transmission gear 32c of the transmission member 32, so that the transmission member 32 is rotationally driven about the axis P1. When the transmission member 32 is rotationally driven, the transmission gear 33 is rotationally driven by the transmission gear unit 32b of the transmission member 32, and the rotating case 25 is rotationally driven via the transmission gear 34.

[0044] A parking brake 35 is provided across the second case 22 and the plunger case 27. A ring-shaped brake operating portion 36 is provided to operate the parking brake 35 to a braking state, and the brake operating portion 36 is biased toward the braking side by a spring 37.

[0045] (Configuration of hydraulic system of hydraulic motor) 4, a relief valve 38 and a pilot-operated switching valve 39 are provided inside the first case 21. An oil passage 40 extending from the pair of hydraulic oil passages 17 is connected to the switching valve 39, and oil passages 41 and 42 extending from the relief valve 38 are connected to the tank 23. An oil passage 45 for discharging hydraulic oil leaked from the hydraulic motor unit 24 is connected to the oil passage 42.

[0046] 4 shows a state in which the switching valve 39 is operated to the neutral position. When one hydraulic oil line 17 becomes high pressure and the other hydraulic oil line 17 becomes low pressure during driving, the pilot hydraulic oil in the high-pressure hydraulic oil line 17 operates the switching valve 39 to a position that connects the low-pressure hydraulic oil line 17 and the relief valve 38.

[0047] 2, 3, and 4, a first operating valve 51 (corresponding to the speed switching unit) (corresponding to the actuator operating unit) is provided inside the first case 21. An oil passage 43 is connected between the hydraulic oil passage 17 and the first operating valve 51, and an oil passage 46 is connected between the oil passage 45 and the first operating valve 51. An oil passage 44 is provided inside the first case 21 and the second case 22 between the first operating valve 51 and the piston portion 30.

[0048] The first operating valve 51 is configured as a pilot-operated type having a high-speed position 51a and a low-speed position 51b, and is biased to the low-speed position 51b by a spring.When pilot hydraulic oil is supplied to the operating port of the first operating valve 51, it is operated to the high-speed position 51a.

[0049] 2 is a state in which the first operating valve 51 is operated to the low-speed position 51b, and the hydraulic oil in the piston unit 30 is discharged to the tank 23 via the oil passage 44, the first operating valve 51 (low-speed position 51b), and the oil passages 46, 45, and 42. In this state, the piston unit 30 is retracted, and the swash plate 29 is operated to the low-speed state L in which it is inclined with respect to the axis P1, and the hydraulic motor 14 is operated to the low-speed state L.

[0050] 4, when the first operating valve 51 is operated to the high-speed position 51a, the hydraulic oil in the hydraulic oil passage 17 is supplied to the piston 30 via the oil passage 43, the first operating valve 51 (high-speed position 51a), and the oil passage 44. This causes the piston 30 to protrude and push a part of the swash plate 29, causing the swash plate 29 to be operated to the high-speed state H, which is close to a position perpendicular to the axis P1, and the hydraulic motor 14 is operated to the high-speed state H.

[0051] (Configuration of the second operating valve that operates the first operating valve) As shown in FIG. 4, a hydraulic oil pump 47 driven by the engine is provided outside the hydraulic motor 14, and an oil passage 48 is connected between the hydraulic oil pump 47 and the tank 23.

[0052] 2 and 4, a second operating valve 52 (corresponding to a pilot operated valve) is provided. The second operating valve 52 is configured as an electromagnetically operated type having a supply position 52a and a discharge position 52b, and is biased to the discharge position 52b by a spring. Note that the second operating valve 52 is not limited to being an electromagnetically operated type, and may be, for example, a mechanically operated type that is operated via various link mechanisms or the like, or a hydraulically operated type that is operated using hydraulic pressure.

[0053] An oil passage 49 is connected between the hydraulic oil pump 47 and the second operating valve 52, and an oil passage 50 is connected between the second operating valve 52 and the tank 23. An operating oil passage 53 is connected between the operating port of the first operating valve 51 and the second operating valve 52, and the operating oil passage 53 is provided outside the hydraulic motor 14 and inside the first case 21.

[0054] Inside the first case 21, a return oil passage 58 is connected across the operation oil passage 53 and the oil passage 42, and a throttle section 59 (corresponding to a resistance section) is provided in the return oil passage 58. An oil passage 54 is connected across the oil passage 49 and the oil passage 50, and a relief valve 55 is provided in the oil passage 54.

[0055] (Operational state of the first operating valve and the second operating valve) (Part 1) 4, in a normal operating state, the second operating valve 52 is operated to the supply position 52a. The hydraulic oil in the tank 23 is supplied as pilot hydraulic oil to the operation port of the first operating valve 51 via the oil passage 48, the hydraulic oil pump 47, the oil passage 49, the second operating valve 52 (supply position 52a), and the operating oil passage 53, and the first operating valve 51 is operated to the high-speed position 51a.

[0056] When the second operating valve 52 is operated to the supply position 52a, the pilot operating oil required to operate the first operating valve 51 to the high-speed position 51a is secured in the operating port of the first operating valve 51 by the throttle section 59 so that the pilot operating oil required to operate the first operating valve 51 to the high-speed position 51a is not discharged to the return oil passage 58.

[0057] Excess pilot hydraulic oil exceeding the pilot hydraulic oil required to operate the first operating valve 51 to the high-speed position 51a is discharged from the operating oil passage 53 through the throttle section 59 to the return oil passage 58, and then discharged to the tank 23 via the oil passage 42.

[0058] As a result, the hydraulic oil in the tank 23 circulates as pilot hydraulic oil through the oil passage 48, hydraulic oil pump 47, oil passage 49, second operating valve 52 (supply position 52a), operating oil passage 53, return oil passage 58, and oil passage 42, and the pilot hydraulic oil in the operating oil passage 53 is replaced with pilot hydraulic oil newly supplied from the tank 23, thereby suppressing fluctuations in the temperature of the pilot hydraulic oil in the operating oil passage 53.

[0059] In a low-temperature environment such as a cold region, the hydraulic oil that is warmed by the hydraulic oil pump 47, hydraulic pump 15, charge pump 16, hydraulic motor 14, etc. and returned to the tank 23 is circulated as pilot hydraulic oil, thereby suppressing temperature fluctuations of the pilot hydraulic oil in the operation oil passage 53. In a high-temperature environment, the hydraulic oil that is cooled in an oil cooler (not shown) and returned to the tank 23 is circulated as pilot hydraulic oil, thereby suppressing temperature fluctuations of the pilot hydraulic oil in the operation oil passage 53.

[0060] For example, in a low-temperature environment such as a cold region, as described above, the first case 21 is also heated by circulating warm pilot hydraulic oil in the tank 23, and the temperature of the first case 21 is maintained constant regardless of changes in the outside air temperature. This suppresses temperature changes in the relief valve 38, the switching valve 39, and the first operating valve 51, and suppresses expansion and contraction of the relief valve 38, the switching valve 39, and the first operating valve 51 due to temperature changes.

[0061] By suppressing the expansion and contraction of the relief valve 38, the switching valve 39, and the first operating valve 51 due to temperature changes, the tolerances (clearances) of the relief valve 38, the switching valve 39, and the first operating valve 51 can be set to small values, and there is no need to set them to large values ​​in anticipation of expansion and contraction. By setting the tolerances (clearances) of the relief valve 38, the switching valve 39, and the first operating valve 51 to small values, leakage of hydraulic oil (pilot hydraulic oil) can be reduced, thereby improving the performance of the hydraulic motor 14.

[0062] (Operational state of the first operating valve and the second operating valve) (Part 2) In contrast to the normal working conditions described above in (Operating conditions of the first operating valve and the second operating valve) (Part 1), when a large load is placed on the traveling device 2, such as on a slope or a muddy part of the work area, the second operating valve 52 is automatically operated to the discharge position 52b based on the detection of the load on the traveling device 2.

[0063] As shown in Figure 5, when the second operating valve 52 is operated to the discharge position 52b, the pilot hydraulic oil at the operating port of the first operating valve 51 is discharged to the tank 23 through the operating oil passage 53, the second operating valve 52 (discharge position 52b), and the oil passage 50.

[0064] In this case, as described above in (Operating State of First Operating Valve and Second Operating Valve) (Part 1), the pilot hydraulic oil in the operating oil passage 53 is replaced with warm pilot hydraulic oil, and a drop in the temperature of the pilot hydraulic oil in the operating oil passage 53 is prevented. Therefore, the pilot hydraulic oil in the operating port of the first operating valve 51 is quickly discharged to the tank 23 through a route that passes through the operating oil passage 53 and the second operating valve 52 (discharge position 52b) and a route that passes through the operating oil passage 53 and the return oil passage 58, and the first operating valve 51 is operated to the low-speed position 51b without delay, and the swash plate 29 (hydraulic motor 14) is quickly operated to the low-speed state L.

[0065] In the right and left continuously variable transmissions 13, as described above, the swash plate 29 (hydraulic motor 14) is quickly operated to the low speed state L, thereby reducing the difference between the time required for the right traveling device 13 to be switched to the low speed state L and the time required for the left traveling device 13 to be switched to the low speed state L, thereby improving straight-line traveling ability.

[0066] When the load on the traveling device 2 decreases as the work site passes through slopes or muddy areas, the second operating valve 52 is automatically operated to the supply position 52a based on the detection of the load on the traveling device 2, as shown in Figure 4, and returns to the state described in (Operating state of the first operating valve and the second operating valve) (Part 1) above.

[0067] (Configuration regarding parking brake operation) 4, an oil passage 56 branches off from the oil passage 49 and is connected to the brake operating unit 36, and a brake operating valve 57 is provided in the oil passage 56. The brake operating valve 57 is configured as an electromagnetically operated type having a braking position 57a ​​and a release position 57b, and is biased to the braking position 57a ​​by a spring.

[0068] The state shown in Figure 4 is a state in which the brake operation valve 57 is operated to the braking position 57a, hydraulic oil is discharged from the brake operation unit 36, and the brake operation unit 36 ​​(parking brake 35) is operated to a braking state by the spring 37.

[0069] A release switch (not shown) is provided in the driving unit 3 (see FIG. 1), and when the release switch is operated, the brake operation valve 57 is operated to the release position 57b. As a result, hydraulic oil from the hydraulic oil pump 47 is supplied to the brake operation unit 36 ​​via the oil passage 56 and the brake operation valve 57 (release position 57b), and the brake operation unit 36 ​​(parking brake 35) is operated to the released state.

[0070] (First Alternative Embodiment of the Invention) In the configurations shown in FIGS. 4 and 5, the charge pump 16 may be eliminated. 6, oil passage 60 branches off from oil passage 49 and is connected to charge oil passage 18, and oil passage 20 branched off from oil passage 60 is connected to charge oil passage 18 of the other continuously variable transmission 13. As a result, pilot hydraulic oil from hydraulic oil pump 47 branches off and is supplied to charge oil passage 18 as hydraulic oil.

[0071] (Second Alternative Embodiment of the Invention) In the configuration shown in FIGS. 4 and 5, the return oil passage 58 may be arranged outside the hydraulic motor 14. 7, the return oil passage 58 is connected across the portion of the operation oil passage 53 outside the hydraulic motor 14 and the oil passage 50. Warm hydraulic oil in the tank 23 circulates as pilot hydraulic oil through the oil passage 48, the hydraulic oil pump 47, the oil passage 49, the second operation valve 52 (supply position 52a), the operation oil passage 53, the return oil passage 58, and the oil passage 50.

[0072] (Third Alternative Embodiment of the Invention) In the configuration shown in FIG. 6, the return oil passage 58 may be connected across the portion of the operation oil passage 53 outside the hydraulic motor 14 and the oil passage 50, and may be arranged outside the hydraulic motor 14, as shown in FIG.

[0073] (Fourth Alternative Embodiment of the Invention) FIG. 9 shows a configuration in which a right continuously variable transmission 13 and a left continuously variable transmission 13 are provided in the configuration shown in FIGS. As shown in FIG. 9, the right continuously variable transmission 13 is provided with a right hydraulic motor (corresponding to the right traveling hydraulic motor) that drives the right hydraulic pump 15 and the right traveling device 2, a right piston section 30 (corresponding to the right speed switching section) (corresponding to the right hydraulic actuator), a right first operating valve 51 (corresponding to the right speed switching section) (corresponding to the right actuator operating section), a right operating oil passage 53, a right return oil passage 58, and a right throttling section 59.

[0074] The left continuously variable transmission 13 is provided with a left hydraulic motor (corresponding to the left traveling hydraulic motor) that drives the left hydraulic pump 15 and the left traveling device 2, a left piston section 30 (corresponding to the left speed switching section) (corresponding to the left hydraulic actuator), a left first operating valve 51 (corresponding to the left speed switching section) (corresponding to the left actuator operating section), a left operating oil passage 53, a left return oil passage 58, and a left throttling section 59.

[0075] One hydraulic oil pump 47 and one second operating valve 52 are provided for each of the right and left first operating valves 51, and right and left operating oil passages 53 branching off from the second operating valve 52 are connected to the operating ports of the right and left first operating valves 51.

[0076] (Fifth Alternative Embodiment of the Invention) FIG. 10 shows a configuration in which a right continuously variable transmission 13 and a left continuously variable transmission 13 are provided in the configuration described above (first alternative embodiment of the invention) and shown in FIG. The configuration of the right and left continuously variable transmissions 13 is the same as that described above (fourth alternative embodiment of the invention).

[0077] (Sixth Alternative Embodiment of the Invention) FIG. 11 shows a configuration in which a right continuously variable transmission 13 and a left continuously variable transmission 13 are provided in the configuration described above (second alternative embodiment of the invention) and shown in FIG. The configuration of the right and left continuously variable transmissions 13 is the same as that described above (fourth alternative embodiment of the invention).

[0078] (Seventh Alternative Embodiment of the Invention) FIG. 12 shows a configuration in which a right continuously variable transmission 13 and a left continuously variable transmission 13 are provided in the configuration described above (third alternative embodiment of the invention) and shown in FIG. The configuration of the right and left continuously variable transmissions 13 is the same as that described above (fourth alternative embodiment of the invention).

[0079] (Eighth Alternative Embodiment of the Invention) As shown in FIG. 13, instead of the throttle portion 59, a constant flow valve 61 that allows pilot hydraulic oil to flow at a constant flow rate downstream relative to the upstream side may be provided in the return oil passage 58 as a resistance portion. Regardless of changes in the pressure and flow rate of the pilot hydraulic oil in the portion (upstream side) of the return oil passage 58 connected to the operating oil passage 53, a constant amount of pilot hydraulic oil is discharged from the constant flow valve 61 to the portion (downstream side) of the return oil passage 58 connected to the oil passages 42, 50.

[0080] (Ninth Alternative Embodiment of the Invention) As shown in FIG. 14, instead of the throttle portion 59, a relief valve 62 that opens when the pressure in the operation oil passage 53 exceeds a set value may be provided in the return oil passage 58 as a resistance portion. When the pressure of the pilot hydraulic oil in the portion (upstream side) of the return oil passage 58 connected to the operation oil passage 53 exceeds a set value, the relief valve 62 opens and the pilot hydraulic oil is discharged from the relief valve 62 to the portion (downstream side) of the return oil passage 58 connected to the oil passages 42, 50. In this case, the set value may be set to the pressure of the pilot hydraulic oil required to operate the first operation valve 51 to the high speed position 51a.

[0081] (Tenth Alternative Embodiment of the Invention) In the case of a work vehicle in which the hydraulic motor 14 is operated to the low speed state L for work travel and is operated to the high speed state H when moving over a long distance to the work site, the first operating valve 51 can be configured to be operated to the low speed position 51b when the second operating valve 52 is operated to the supply position 52a, and to be operated to the high speed position 51a when the second operating valve 52 is operated to the discharge position 52b.

[0082] (Eleventh Alternative Embodiment of the Invention) Instead of providing right and left continuously variable transmissions 13, it is also possible to provide one continuously variable transmission 13 and transmit the power of the hydraulic motor 14 to a gear transmission (not shown) and then from the gear transmission to the right and left traveling devices 2. The traveling device 2 is not limited to a crawler type traveling device 2, but may be wheels for traveling such as front wheels and rear wheels (not shown).

[0083] (Twelfth Alternative Embodiment of the Invention) For example, in a backhoe, which is an example of a construction vehicle, a hydraulic motor 14 may be configured to drive a swivel base (corresponding to a driven part) (not shown) to rotate. In this case, the hydraulic pump 15 may be configured as a fixed displacement type instead of a variable displacement type, so that the hydraulic pump 15 does not perform stepless speed change of the hydraulic motor 14 .

[0084] (13th Alternative Embodiment of the Invention) As the hydraulic actuator that operates the swash plate 29 of the hydraulic motor 14, another hydraulic actuator may be provided instead of the piston portion 30. Furthermore, the hydraulic actuator is not limited to a configuration in which the first operation valve 51 is operated by pilot hydraulic oil supplied / discharged from the second operation valve 52 (pilot operation valve) and the hydraulic actuator is operated by switching the supply / discharge state of the hydraulic oil from the first operation valve 51 to the hydraulic actuator, but the hydraulic actuator may be directly operated by the pilot hydraulic oil supplied / discharged from the second operation valve 52 to the hydraulic actuator. [Industrial Applicability]

[0085] The present invention can be applied not only to compact track loaders, but also to various other work vehicles, such as construction or civil engineering work vehicles such as skid steer loaders (SSL), wheel shovels, wheel loaders, and backhoes, and agricultural work vehicles such as combine harvesters, tractors, rice transplanters, crawler carriers, and mowers.The present invention is also suitable for work vehicles equipped with a pump / motor separated HST (HydroStatic Transmission) in which the pump and motor are separated. [Explanation of symbols]

[0086] 2. Running gear (driven part) 14 Hydraulic motor (travel hydraulic motor) 15 Hydraulic pump 17 Hydraulic oil passage 21 Case 1 (Case) 23 Tank 30 Piston section (speed switching section) (hydraulic actuator) 47 Hydraulic oil pump 51 First operating valve (speed switching unit) (actuator operating unit) 52 Second operating valve (pilot operated valve) 52a Supply position 52b Ejection position 53 Operation oil path 58 Return oil passage 59 Throttle section (resistance section) 61 Constant flow valve (resistance part) 62 Relief valve (resistance part) H High speed state L Low speed state

Claims

1. a variable displacement hydraulic motor that drives the driven part; a hydraulic pump that supplies hydraulic oil to the hydraulic motor to operate the hydraulic motor; a speed switching unit that performs a switching operation to switch the hydraulic motor between a high speed state and a low speed state; a pilot operation valve that controls a supply / discharge state of pilot hydraulic oil to the speed change unit to cause the speed change unit to perform a changeover operation; a tank for storing the pilot hydraulic oil; a hydraulic oil pump that supplies pilot hydraulic oil from the tank to the pilot operated valve; an operating oil passage connecting an operating port of the speed switching unit and the pilot operated valve; the pilot operation valve has a supply position at which the speed switching unit operates the hydraulic motor to one of the high-speed state and the low-speed state by supplying pilot hydraulic oil supplied from the hydraulic oil pump to an operation port of the speed switching unit through the operation oil passage, and a discharge position at which the speed switching unit operates the hydraulic motor to the other of the high-speed state and the low-speed state by discharging pilot hydraulic oil from the operation oil passage to the tank, a return oil passage connected to the operation oil passage and returning the pilot hydraulic oil in the operation oil passage to the tank; A work vehicle having a resistance section in the return oil line that provides resistance to the flow of pilot hydraulic oil from the operating oil line to the tank, so that when the pilot operating valve is operated to the supply position, excess pilot hydraulic oil that exceeds the pilot hydraulic oil required to operate the hydraulic motor to one of the high speed state and the low speed state by the speed switching section is returned from the operating oil line to the tank via the return oil line.

2. The speed switching unit a hydraulic actuator that switches the hydraulic motor between the high speed state and the low speed state; 2. The work vehicle according to claim 1, further comprising an actuator operating unit that operates the hydraulic actuator in accordance with a supply / discharge state of the pilot hydraulic oil from the pilot operating valve, and switches the hydraulic motor between the high speed state and the low speed state.

3. 3. A work vehicle according to claim 1, wherein the resistance portion is a throttle portion.

4. 3. A work vehicle according to claim 1, wherein the resistance portion is a constant flow valve that allows pilot hydraulic oil to flow at a constant flow rate downstream relative to the upstream side.

5. 3. The work vehicle according to claim 1, wherein the resistance portion is a relief valve.

6. The work vehicle according to any one of claims 1 to 5, wherein the hydraulic oil pump supplies pilot hydraulic oil to the pilot operation valve, and also supplies pilot hydraulic oil as hydraulic oil to a hydraulic oil line connecting the hydraulic pump and the hydraulic motor.

7. The driven part includes a traveling device, A work vehicle as described in any one of claims 1 to 6, wherein when the pilot-operated valve is operated to the supply position, the speed switching unit is operated to the high-speed state, and when the pilot-operated valve is operated to the discharge position, the speed switching unit is operated to the low-speed state.

8. The driven parts include a left traveling device and a right traveling device, The hydraulic motors include a left traveling hydraulic motor that drives the left traveling device and a right traveling hydraulic motor that drives the right traveling device, the speed switching units include a left speed switching unit that switches the left traveling hydraulic motor between the high speed state and the low speed state, and a right speed switching unit that switches the right traveling hydraulic motor between the high speed state and the low speed state, the operating oil passages include a left operating oil passage connecting an operating port of the left speed changer and the pilot operating valve, and a right operating oil passage connecting an operating port of the right speed changer and the pilot operating valve, The return oil passages include a left return oil passage that returns the pilot hydraulic oil of the left operation oil passage to the tank, and a right return oil passage that returns the pilot hydraulic oil of the right operation oil passage to the tank, A work vehicle as described in any one of claims 1 to 7, wherein the resistance portions include a left resistance portion provided in the left return oil passage and a right resistance portion provided in the right return oil passage.

9. 9. The work vehicle according to claim 1, wherein at least a portion of the return oil passage and the resistance portion are provided within a case of the hydraulic motor.

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