Work vehicles

Abstract

A work vehicle is provided in which the progression of wear on the sliding parts of a clutch that transmits the output rotation of an engine to drive wheels is suppressed. [Solution] A clutch (42) is provided between the transmission path of the engine (E) and the front wheels (2) or rear wheels (3) to transmit the output rotation of the engine (E) to the front wheels (2) or rear wheels (3). The hydraulic oil pressure of the oil supplied to the clutch (42) is increased or decreased depending on the amount of depression of the brake pedal. When the amount of depression is less than a first depression amount, the hydraulic oil pressure is increased to high pressure to connect the clutch (42) and transmit the output rotation of the engine (E) to the front wheels (2) or rear wheels (3). When the amount of depression is equal to or greater than a second depression amount, the hydraulic oil pressure is decreased to low pressure to disengage the clutch (42) and cut off the transmission of the output rotation of the engine (E) to the front wheels (2) or rear wheels (3). When the amount of depression is equal to or greater than the first depression amount but less than the second depression amount, the hydraulic oil pressure is increased to an intermediate pressure between high pressure and low pressure to enter a no-clutch state.

Description

[Technical Field]

[0001] The present invention relates to a work vehicle having a clutch provided in a transmission path between the engine and the drive wheels for transmitting the output rotation of the engine to the drive wheels. [Background technology]

[0002] A conventional technology is known that applies brakes to the drive wheels in accordance with the amount of depression of the brake pedal, and reduces the hydraulic oil pressure of the clutch, thereby linking depression of the brake pedal with engagement and disengagement of the clutch, resulting in a no-clutch state (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-4439 Summary of the Invention [Problem to be solved by the invention]

[0004] However, if the no-clutch state is maintained for a long period of time, there is a problem in that the wear of the clutch plates, which are the sliding parts of the clutch, progresses rapidly.

[0005] SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a work vehicle that suppresses the progression of wear on the sliding parts of the clutch that transmits the output rotation of the engine to the drive wheels. [Means for solving the problem]

[0006] The present invention, which has solved the above problems, is as follows. That is, the invention described in claim 1 is a work vehicle in which a pair of front wheels (2) and a pair of rear wheels (3) are provided below a body frame (1) on which an engine (E) is mounted, and a control section (5) on which a worker rides is provided above the body frame (1), A clutch (42) for transmitting the output rotation of the engine (E) to the front wheels (2) or rear wheels (3) is provided between the engine (E) and the front wheels (2) or rear wheels (3), and a brake pedal (15) for braking the front wheels (2) and rear wheels (3) is provided in the steering unit (5). The hydraulic oil pressure of the oil supplied to the clutch (42) is increased or decreased according to the depression amount of the brake pedal (15). When the depression amount is less than a first depression amount, the hydraulic oil pressure is increased to the high level to brake the clutch (42). (42) is connected to transmit the output rotation of the engine (E) to the front wheels (2) or the rear wheels (3), and when the depression amount is equal to or greater than the second depression amount, the hydraulic oil pressure is made low to disengage the clutch (42) and cut off the transmission of the output rotation of the engine (E) to the front wheels (2) or the rear wheels (3), and when the depression amount is equal to or greater than the first depression amount and less than the second depression amount, the hydraulic oil pressure is made intermediate between high pressure and low pressure to put the vehicle in a no-clutch state.

[0007] The invention described in claim 2 is a work vehicle described in claim 1, in which when the depression amount changes from a second depression amount or more to a first depression amount or more but less than the second depression amount, the hydraulic oil pressure is set to an initial pressure between high pressure and intermediate pressure.

[0008] The invention described in claim 3 is the work vehicle described in claim 2, wherein when the depression amount is equal to or greater than a first depression amount and is less than a second depression amount, and then becomes less than the first depression amount, the hydraulic oil pressure is increased from an intermediate pressure to a high pressure in a ramp or stepwise manner.

[0009] The invention of claim 4 is the work vehicle of any one of claims 1 to 3, wherein a continuously variable transmission (40) that increases or decreases the output rotation of the engine (E) and a combined output device (41) that combines the output rotation of a first output shaft (40B) and a second output shaft (40C) of the continuously variable transmission (40) are provided between a transmission path of the engine (E) and the clutch (42), and when the depression amount is equal to or greater than the first depression amount and less than the second depression amount, the output rotation of the output shaft (41C) of the combined output device (41) that is transmitted to the clutch (42) is slowed down.

[0010] The invention described in claim 5 is the work vehicle described in claim 4, wherein the control section (5) is provided with a forward / reverse lever (22) for switching the direction of travel of the work vehicle, the clutch (42) is formed of a forward clutch (42A) for causing the work vehicle to travel in the forward direction and a reverse clutch (42B) for causing the work vehicle to travel in the reverse direction, and when the forward / reverse lever (22) is operated to the forward position, oil is supplied to the forward clutch (42A), and when the forward / reverse lever (22) is operated to the reverse position, oil is supplied to the reverse clutch (42B). [Effects of the Invention]

[0011] According to the invention of claim 1, a clutch (42) for transmitting the output rotation of the engine (E) to the front wheels (2) or the rear wheels (3) is provided between the transmission path of the engine (E) and the front wheels (2) or the rear wheels (3), a brake pedal (15) for braking the front wheels (2) and the rear wheels (3) is provided in the steering unit (5), and the hydraulic oil pressure of the oil supplied to the clutch (42) is increased or decreased according to the depression amount of the brake pedal (15), and when the depression amount is less than a first depression amount, the hydraulic oil pressure is increased to connect the clutch (42). The output rotation of the engine (E) is transmitted to the front wheels (2) or the rear wheels (3), and when the depression amount is equal to or greater than the second depression amount, the hydraulic oil pressure is reduced to low pressure to disengage the clutch (42) and cut off the transmission of the output rotation of the engine (E) to the front wheels (2) or the rear wheels (3), and when the depression amount is equal to or greater than the first depression amount but less than the second depression amount, the hydraulic oil pressure is reduced to an intermediate pressure between high pressure and low pressure to put the clutch in a no-clutch state, thereby suppressing the progress of wear on the clutch plates and other sliding parts of the clutch (42).

[0012] According to the invention of claim 2, in addition to the effect of the invention of claim 1, when the depression amount changes from the second depression amount or more to the first depression amount or more but less than the second depression amount, the hydraulic oil pressure is set to an initial pressure between the high pressure and the intermediate pressure, so that the sliding parts of the clutch (42) can move smoothly and enter a no-clutch state.

[0013] According to the invention described in claim 3, in addition to the effect of the invention described in claim 2, when the depression amount is equal to or greater than the first depression amount and less than the second depression amount, and then becomes less than the first depression amount, the hydraulic oil pressure is increased from intermediate pressure to high pressure in a ramp or step-like manner, allowing the work vehicle to be restarted smoothly.

[0014] According to the invention of claim 4, in addition to the effects of the invention of any one of claims 1 to 3, a continuously variable transmission (40) that increases or decreases the output rotation of the engine (E) and a combining output device (41) that combines the output rotation of the first output shaft (40B) and the second output shaft (40C) of the continuously variable transmission (40) are provided between the transmission path of the engine (E) and the clutch (42), and when the depression amount is equal to or greater than the first depression amount and less than the second depression amount, the output rotation of the output shaft (41C) of the combining output device (41) that is transmitted to the clutch (42) is slowed down, thereby making it possible to further suppress the progress of wear on the clutch plates and the like that are sliding parts of the clutch (42).

[0015] According to the invention of claim 5, in addition to the effect of the invention of claim 5, a forward / reverse lever (22) for switching the traveling direction of the work vehicle is provided on the operating section (5), and the clutch (42) is formed of a forward clutch (42A) for moving the work vehicle in the forward direction and a reverse clutch (42B) for moving the work vehicle in the reverse direction, and when the forward / reverse lever (22) is operated to the forward position, oil is supplied to the forward clutch (42A), and when the forward / reverse lever (22) is operated to the reverse position, oil is supplied to the reverse clutch (42B), so that the forward direction and reverse method of the work vehicle can be easily switched. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. [Figure 2] FIG. [Figure 3] FIG. [Figure 4] 1 is a transmission diagram of the engine output rotation. [Figure 5] FIG. [Figure 6] FIG. 2 is a connection diagram of a controller. [Figure 7] This is a no-clutch operation method that involves stepping on the brake pedal. [Figure 8] This is a no-clutch operation method that involves stepping on the brake pedal. [Figure 9] FIG. 4 is an explanatory diagram of clutch oil pressure, etc. DETAILED DESCRIPTION OF THE INVENTION

[0017] As shown in FIG. 1, a work vehicle such as a tractor has a pair of left and right front wheels 2 provided at the front lower part of a body frame 1, and a pair of left and right rear wheels 3 provided at the rear lower part of the body frame 1.

[0018] A bonnet 4 that houses the engine E is provided at the front upper part of the body frame 1, and a control section 5 on which an operator sits is provided behind the bonnet 4. A PTO shaft 6 that extends in the fore-and-aft direction and to which the output rotation of the engine E is transmitted is provided below and behind the control section 5, and a work machine 7 such as a manure spreader that spreads compost on a field can be connected to the rear of the PTO shaft 6.

[0019] A steering wheel 12 is provided in front of a driver's seat 11 in the control section 5, and the steering wheel 12 is supported by a steering column 13 via a steering shaft. A clutch pedal 14 is provided on the left side of the steering column 13, a pair of brake pedals 15 for forward and reverse travel are provided on the right side, and a fender 16 covering the rear wheels 3 is provided above the rear wheels 3. The depression position of the clutch pedal 14 is measured by an angle sensor 20A such as a potentiometer attached to the base of the clutch pedal 14, and the depression position of the brake pedal 15 is measured by an angle sensor 35, which will be described later.

[0020] 2, a main speed change lever 20 that rotates a trunnion shaft (not shown) of a continuously variable transmission 40 that increases or decreases the output rotation of the engine E is provided in the front of the fender 16 located on the right side of the cockpit 11, an auxiliary speed change lever 21 that switches the gear of a transmission gearbox 43 that increases or decreases the output rotation of the continuously variable transmission 40 is provided in the front of the fender 16 located on the left side of the cockpit 11, and a forward / reverse lever 22 that switches a forward / reverse clutch 42 (described later) is provided behind the auxiliary speed change lever 21. The operating position of the main speed change lever 20 is measured by an angle sensor 20A such as a potentiometer attached to the base of the main speed change lever 20, the shift position of the auxiliary speed change lever 21 is measured by an angle sensor 21A such as a potentiometer attached to the base of the auxiliary speed change lever 21, and the operating position of the forward / reverse lever 22 is measured by an angle sensor 22A such as a potentiometer attached to the base of the forward / reverse lever 22.

[0021] 3, the brake pedal 15 is rotatably supported on a support shaft 30 extending in the left-right direction and provided on the right side of the steering column 13. A pedal 32 that is operated by an operator by stepping on it with their foot is provided at the bottom of an arm 31 extending in the up-down direction of the brake pedal 15, and a pin 33 extending in the left-right direction is provided at the top of the arm 31.

[0022] The amount of depression by the operator is measured by an angle sensor 35 such as a potentiometer disposed above the brake pedal 15. A detection terminal 35A of the angle sensor 35 is engaged with the pin 33.

[0023] As shown in Figure 4, the output rotation of the engine E is transmitted to an input shaft 40A of the continuously variable transmission 40. The output rotation transmitted to the input shaft 40A is increased or decreased by the continuously variable transmission 40 and is output from a first output shaft 40B and a second output shaft 40C. The continuously variable transmission 40 is formed of a pump chamber 40D having a hydraulic pump and a swash plate, and a motor chamber 40E having a hydraulic motor and a swash plate.

[0024] The output rotation of the first output shaft 40B is transmitted to a first input shaft 41A of a combiner output device 41, such as a strain wave gear device, and the output rotation of the second output shaft 40C is transmitted via gears to a second input shaft 41B of the combiner output device 41. The output rotations transmitted to the first input shaft 41A and the second input shaft 41B are combined within the combiner output device 41 and output from the output shaft 41C. As shown in FIG. 9, the phase (horizontal position in FIG. 9) of the output rotation of the second output shaft 40C of the continuously variable transmission 40 and the output rotation of the output shaft 41C of the combiner output device 41 are the same, and the intensity (vertical height in FIG. 9) of the output rotation is high.

[0025] The output rotation of the output shaft 41C is transmitted to the input shaft 43A of the speed change gear box 43 via the forward / reverse clutch 42. The clutch 42 is switched between engagement and disengagement by depressing the clutch pedal 14. The output rotation transmitted to the input shaft 43A is increased or decreased by the speed change gear box 43 and is output from the output shaft 43B.

[0026] The output rotation of the output shaft 43B is transmitted to the input shaft of a differential gear 45 for the rear wheels via a bevel gear 44. The output rotation transmitted to the input shaft is given an output rotation difference by the differential gear 45 and is output to left and right drive shafts 46 extending in the left-right direction. This gives a constant output rotation difference to the output rotation of the left and right rear wheels 3, allowing the work vehicle to turn smoothly.

[0027] The output rotation of the left drive shaft 46 is transmitted to the left rear wheel 3 via the left wheel, and the output rotation of the right drive shaft 46 is transmitted to the right rear wheel 3 via the right wheel.

[0028] The output rotation of output shaft 43B is transmitted to output shaft 51 via gear 50, and the output rotation of output shaft 51 is transmitted to bevel gear 53 via four-wheel drive clutch 52. The clutch 47 is switched between engagement and disengagement by operating a four-wheel drive lever (not shown) provided on the control unit 5.

[0029] The output rotation of the bevel gear 53 is transmitted to the input shaft of a differential gear 54 for the front wheels. The output rotation transmitted to the input shaft is given an output rotation difference by the differential gear 54 and is output to left and right drive shafts 55 extending in the left-right direction. This gives a constant output rotation difference to the output rotation of the left and right front wheels 2, allowing the work vehicle to turn smoothly.

[0030] The output rotation of the left drive shaft 55 is transmitted to the left front wheel 2 via the left wheel, and the output rotation of the right drive shaft 55 is transmitted to the right front wheel 2 via the right wheel.

[0031] The second output shaft 40C of the continuously variable transmission 40 is transmitted to a clutch 61 for the PTO via a gear 60, and the output rotation of the clutch 61 is transmitted to an input shaft 62A of a PTO transmission gearbox 62. The clutch 42 is switched between engagement and disengagement by operating a clutch lever (not shown) provided on the operating unit 5.

[0032] The output rotation of the input shaft 62A is transmitted to the output shaft 62B after being increased or decreased in speed and the direction of output rotation is switched by the PTO speed change gear box 62. The output rotation of the output shaft 62B is transmitted to the PTO shaft 6 via a gear 63.

[0033] 5, the clutch 42 is made up of a forward clutch 42A and a reverse clutch 42B. The forward clutch 42A and the reverse clutch 42B are formed to be symmetrical and have the same shape, so the following will only describe the forward clutch 42A, and a description of the reverse clutch 42B will be omitted.

[0034] The forward clutch 42A has a forward clutch shaft 71A attached to a forward gear 70A. The forward clutch shaft 71A is rotatably supported on an output shaft 73 by a bearing 72. A pressing plate 71B is attached to the front of the forward clutch shaft 71A, and a clutch case 71C is attached to the rear. Reference numeral 70B denotes a reverse gear.

[0035] A plurality of inner clutch plates 71D and a plurality of outer clutch plates 71E are provided in the space formed by the pressing plate 71B and the clutch case 71C, and each outer clutch plate 71E is arranged between the inner clutch plate 71D and the adjacent inner clutch plate 71D. The pressing plate 71B is arranged downstream in the power transmission direction of the inner clutch plate 71D arranged at the forefront.

[0036] An engaging portion formed on the inner periphery of the inner clutch plate 71D engages with the outer periphery of the forward clutch shaft 71A, so that the inner clutch plate 71D and the forward clutch shaft 71A rotate together. An engaging portion formed on the outer periphery of the outer clutch plate 71E engages with the inner periphery of the clutch case 71C, so that the outer clutch plate 71E and the clutch case 71C rotate together.

[0037] A biasing member 71H such as a spring is provided in the space formed by the forward clutch shaft 71A and the clutch case 71C to bias the clutch piston 71F toward the rear cylinder portion 71G to which hydraulic oil is supplied.

[0038] When the pressure of the hydraulic oil supplied to the cylinder portion 71G increases and the pushing force moving the piston 71F becomes greater than the biasing force of the biasing member 71H, the piston 71F moves toward the outer clutch plate 71E, pressing the outer clutch plate 71E against the inner clutch plate 71D, and the output rotation of the inner clutch plate 71D is transmitted to the outer clutch plate 71E by friction. As a result, the output rotation transmitted from the output shaft 41C of the combined output device 41 to the forward gear 70A is transmitted to the clutch case 71C via the inner clutch plate 71D and the outer clutch plate 71E, and the output rotation of the clutch case 71C is transmitted to the output shaft 73 via the spline. The output shaft 73 is connected to the input shaft 43A of the speed change gearbox 43 via a connecting member.

[0039] When the hydraulic oil is discharged from the cylinder portion 71G, the pressure of the hydraulic oil decreases, and the pressing force that moves the piston 71F becomes smaller than the biasing force of the biasing member 71H, the piston 71F moves toward the cylinder portion 71G, and the outer clutch plate 71E and the inner clutch plate 71D are separated from each other. As a result, the output rotation transmitted to the forward gear 70A is no longer transmitted to the clutch case 71C.

[0040] As shown in FIG. 6, the controller 80 is made up of a processing unit 81 consisting of a CPU or the like, a storage unit 82 consisting of a ROM, RAM, hard disk drive, flash memory or the like, and a communication unit 83 for data communication with the outside.

[0041] An angle sensor 14A that measures the depression position of the clutch pedal 14, an angle sensor 20A that measures the operating position of the main shift lever 20, an angle sensor 21A that measures the operating position of the sub-shift lever 21, an angle sensor 22A that measures the operating position of the forward / reverse lever 22, and an angle sensor 35 that measures the depression position of the brake pedal 15 are connected to the input side of the controller 80 via a predetermined input interface circuit.

[0042] The output side of the controller 80 is connected, via a predetermined output interface circuit, to the continuously variable transmission 40 that increases or decreases the output rotation of the engine E, the transmission gearbox 43 that increases or decreases the output rotation of the continuously variable transmission 40, the hydraulic pump 75 that supplies hydraulic oil to the cylinder portion 71G of the forward / reverse clutch 42, and the switching valve 76, such as an electromagnetic valve, that switches the flow path between the hydraulic pump 75 and the cylinder portion 71G.

[0043] <How to operate the no-clutch by depressing the brake pedal> 7 and 8, in step S1, the processing unit 81 of the controller 80 reads the measurement value of the angle sensor 22A and proceeds to step S2. The angle sensor 22A measures the operating position of the forward / reverse lever 22.

[0044] In step S2, if the forward / reverse lever 22 is operated to the forward position, the processing unit 81 connects the forward clutch 42A of the clutch 42 and disengages the reverse clutch 42B, and then proceeds to step S3. This allows communication between the cylinder portion 71G of the forward clutch 42A and the hydraulic pump 75. On the other hand, if the forward / reverse lever 22 is operated to the reverse position, the processing unit 81 connects the reverse clutch 42B of the clutch 42 and disengages the forward clutch 42A, and then proceeds to step S13. This allows communication between the cylinder portion 71G of the reverse clutch 42B and the hydraulic pump 75.

[0045] In step S3, the processing unit 81 reads the measurement value of the angle sensor 35, and if it determines that the depression amount of the brake pedal 15 is less than the first depression amount, it proceeds to step S4, if it determines that the depression amount of the brake pedal 15 is equal to or greater than the first depression amount but less than the second depression amount, it proceeds to step S5, and if it determines that the depression amount of the brake pedal 15 is equal to or greater than the second depression amount, it proceeds to step S8. The angle sensor 35 measures the depression amount of the brake pedal 15.

[0046] In step S4, the processing unit 81 drives the hydraulic pump 75 to increase the pressure of the hydraulic oil supplied from the hydraulic pump 75 to the cylinder unit 71G, and then returns to step S1. This allows the output rotation transmitted to the forward gear 70A of the clutch 42 to be transmitted to the clutch case 71C. Note that, as shown in Fig. 9, the high pressure is set higher than the intermediate pressure and low pressure, which will be described later, and the intermediate pressure is set higher than the low pressure.

[0047] In step S5, the processing unit 81 drives the hydraulic pump 75 to reduce the pressure of the hydraulic oil supplied from the hydraulic pump 75 to the cylinder unit 71G from high to intermediate pressure, and then proceeds to step S6. This allows for a no-clutch state, i.e., a state in which depression of the brake pedal 15 and engagement and release of the forward clutch 42A are linked.

[0048] In step S6, the processing unit 81 reads the measurement value of the angle sensor 35, and if it determines that the depression amount of the brake pedal 15 is equal to or greater than the second depression amount, it proceeds to step S7, if it determines that the depression amount of the brake pedal 15 is equal to or greater than the first depression amount but less than the second depression amount, it repeats step S6, and if it determines that the depression amount of the brake pedal 15 is less than the first depression amount, it returns to step S1.

[0049] In step S7, the processing unit 81 drives the hydraulic pump 75 to reduce the pressure of the hydraulic oil supplied from the hydraulic pump 75 to the cylinder unit 71G from the intermediate pressure to the low pressure, and then returns to step S1. This makes it possible to block the transmission of the output rotation transmitted to the forward gear 70A of the clutch 42 to the clutch case 71C.

[0050] In step S8, the processing unit 81 drives the hydraulic pump 75 to reduce the pressure of the hydraulic oil supplied from the hydraulic pump 75 to the cylinder unit 71G from high to low, and then proceeds to step S9, whereby the output rotation transmitted to the forward gear 70A of the clutch 42 can be blocked from being transmitted to the clutch case 71C.

[0051] In step S9, the processing unit 81 reads the measurement value of the angle sensor 35, and if it determines that the depression amount of the brake pedal 15 is equal to or greater than the first depression amount and less than the second depression amount, it proceeds to step S10, and if it determines that the depression amount of the brake pedal 15 is equal to or greater than the second depression amount, it repeats step S9.

[0052] In step S10, the processing unit 81 drives the hydraulic pump 75 to increase the pressure of the hydraulic oil supplied from the hydraulic pump 75 to the cylinder unit 71G from low pressure to initial pressure for a predetermined time, and then reduces the pressure from the initial pressure to intermediate pressure, and proceeds to step S11. This allows the piston 71F of the forward clutch 42A to move smoothly toward the outer clutch plate 71E, and then the clutch can be released.

[0053] In step S11, the processing unit 81 reads the measurement value of the angle sensor 35, and if it determines that the depression amount of the brake pedal 15 is less than the first depression amount, it proceeds to step S12, and if it determines that the depression amount of the brake pedal 15 is equal to or greater than the second depression amount, it repeats step S11.

[0054] In step S12, processing unit 81 drives hydraulic pump 75 to increase the pressure of the hydraulic oil supplied from hydraulic pump 75 to cylinder unit 71G from intermediate pressure to high pressure, and then returns to step S1. This allows the output rotation transmitted to forward gear 70A of clutch 42 to be transmitted to clutch case 71C. When increasing the pressure from intermediate pressure to high pressure, it is preferable to increase the pressure gradually, like a ramp or in steps, in order to restart the work vehicle smoothly.

[0055] In step S13, the processing unit 81 reads the measurement value of the angle sensor 35, and if it determines that the depression amount of the brake pedal 15 is less than the first depression amount, it proceeds to step S14; if it determines that the depression amount of the brake pedal 15 is equal to or greater than the first depression amount but less than the second depression amount, it proceeds to step S15; and if it determines that the depression amount of the brake pedal 15 is equal to or greater than the second depression amount, it proceeds to step S18.

[0056] In step S14, the processing unit 81 drives the hydraulic pump 75 to increase the pressure of the hydraulic oil supplied from the hydraulic pump 75 to the cylinder unit 71G, and then returns to step S1. As a result, the output rotation transmitted to the reverse gear 70B of the clutch 42 can be transmitted to the clutch case 71C.

[0057] In step S15, the processing unit 81 drives the hydraulic pump 75 to reduce the pressure of the hydraulic oil supplied from the hydraulic pump 75 to the cylinder unit 71G from high to intermediate pressure, and then proceeds to step S16. This allows for a no-clutch state, that is, a state in which depression of the brake pedal 15 and engagement and disengagement of the forward clutch 42A are linked.

[0058] In step S16, the processing unit 81 reads the measurement value of the angle sensor 35, and if it determines that the depression amount of the brake pedal 15 is equal to or greater than the second depression amount, it proceeds to step S17, if it determines that the depression amount of the brake pedal 15 is equal to or greater than the first depression amount but less than the second depression amount, it repeats step S16, and if it determines that the depression amount of the brake pedal 15 is less than the first depression amount, it returns to step S1.

[0059] In step S17, the processing unit 81 drives the hydraulic pump 75 to reduce the pressure of the hydraulic oil supplied from the hydraulic pump 75 to the cylinder unit 71G from the intermediate pressure to the low pressure, and then returns to step S1. This makes it possible to block the transmission of the output rotation transmitted to the reverse gear 70B of the clutch 42 to the clutch case 71C.

[0060] In step S18, the processing unit 81 drives the hydraulic pump 75 to reduce the pressure of the hydraulic oil supplied from the hydraulic pump 75 to the cylinder unit 71G from high to low, and then proceeds to step S19. This makes it possible to block the output rotation transmitted to the reverse gear 70B of the clutch 42 from being transmitted to the clutch case 71C.

[0061] In step S19, the processing unit 81 reads the measurement value of the angle sensor 35, and if it determines that the depression amount of the brake pedal 15 is equal to or greater than the first depression amount and less than the second depression amount, it proceeds to step S20, and if it determines that the depression amount of the brake pedal 15 is equal to or greater than the second depression amount, it repeats step S19.

[0062] In step S20, processing unit 81 drives hydraulic pump 75 to increase the pressure of the hydraulic oil supplied from hydraulic pump 75 to cylinder unit 71G from low pressure to initial pressure for a predetermined time, and then reduces the pressure from the initial pressure to intermediate pressure, and proceeds to step S21. This allows piston 71F of reverse clutch 42B to move smoothly toward outer clutch plate 71E, and then the clutch can be released.

[0063] In step S21, the processing unit 81 reads the measurement value of the angle sensor 35, and if it determines that the depression amount of the brake pedal 15 is less than the first depression amount, it proceeds to step S22, and if it determines that the depression amount of the brake pedal 15 is equal to or greater than the second depression amount, it repeats step S21.

[0064] In step S22, processing unit 81 drives hydraulic pump 75 to increase the pressure of the hydraulic oil supplied from hydraulic pump 75 to cylinder unit 71G from intermediate pressure to high pressure, and then returns to step S1. This allows the output rotation transmitted to reverse gear 70B of clutch 42 to be transmitted to clutch case 71C. When increasing the pressure from intermediate pressure to high pressure, it is preferable to increase the pressure gradually, like a ramp or in steps, in order to restart the work vehicle smoothly. [Explanation of symbols]

[0065] 1 Aircraft frame 2 front wheels 3 rear wheels 5 Control Unit 15 Brake pedal 22 Forward / reverse lever 40 Continuously variable transmission 40B 1st output shaft 40C Second output shaft 41 Synthetic Output Device 41C output shaft 42 Clutch 42A forward clutch 42B reverse clutch E-Engine

Claims

1. A work vehicle has a pair of left and right front wheels (2) and rear wheels (3) mounted below a body frame (1) on which an engine (E) is mounted, and a control section (5) on which a worker rides is mounted above the body frame (1), a clutch (42) for transmitting the output rotation of the engine (E) to the front wheels (2) or the rear wheels (3) is provided between the engine (E) and the transmission path of the front wheels (2) or the rear wheels (3); The steering unit (5) is provided with a brake pedal (15) for braking the front wheels (2) and the rear wheels (3), The hydraulic oil pressure of the oil supplied to the clutch (42) is increased or decreased according to the depression amount of the brake pedal (15), When the depression amount is less than a first depression amount, the hydraulic oil pressure is increased to a high pressure to connect the clutch (42), and the output rotation of the engine (E) is transmitted to the front wheels (2) or the rear wheels (3); When the depression amount is equal to or greater than a second depression amount, the hydraulic oil pressure is reduced to disengage the clutch (42), and transmission of the output rotation of the engine (E) to the front wheels (2) or the rear wheels (3) is interrupted; When the depression amount is equal to or greater than a first depression amount and less than a second depression amount, the hydraulic oil pressure is set to an intermediate pressure between high pressure and low pressure, resulting in a no-clutch state.

2. 2. The work vehicle according to claim 1, wherein when the depression amount changes from a second depression amount or more to a first depression amount or more but less than the second depression amount, the hydraulic oil pressure is set to an initial pressure between the high pressure and the intermediate pressure.

3. 3. The work vehicle according to claim 2, wherein when the depression amount is equal to or greater than a first depression amount and less than a second depression amount, the hydraulic oil pressure is increased from an intermediate pressure to a high pressure in a ramp or stepwise manner.

4. A continuously variable transmission (40) for increasing or decreasing the output rotation of the engine (E) and a combining output device (41) for combining the output rotation of a first output shaft (40B) and a second output shaft (40C) of the continuously variable transmission (40) are provided between a transmission path of the engine (E) and the clutch (42), The work vehicle according to any one of claims 1 to 3, wherein when the depression amount is equal to or greater than a first depression amount and less than a second depression amount, the output rotation of the output shaft (41C) of the combined output device (41) transmitted to the clutch (42) is slowed down.

5. The operation unit (5) is provided with a forward / reverse lever (22) for switching the direction of travel of the work vehicle, The clutch (42) is formed of a forward clutch (42A) for driving the work vehicle in a forward direction and a reverse clutch (42B) for driving the work vehicle in a reverse direction, When the forward / reverse lever (22) is operated to a forward position, oil is supplied to the forward clutch (42A), 5. A work vehicle according to claim 4, wherein oil is supplied to the reverse clutch when the forward / reverse lever is operated to the reverse position.

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