Work vehicles

Abstract

To provide a work vehicle capable of preventing occurrence of a shock when forward / rearward multiple disc clutches are engaged.SOLUTION: In a work vehicle: a forward hydraulic multiple disc clutch C1 and a reverse hydraulic multiple disc clutch C2 are disposed; a forward / reverse selector valve 50a is provided, which receives pressure oil supplied from a pump 46s and switches to output oil passages 64a, 64b to the forward hydraulic multiple disc clutch C1 or a reverse hydraulic multiple disc clutch C2; a supply oil passage 60 to a forward / reverse clutch control valve 50 including the forward / reverse selector valve 50a is branched to connect a branch oil passage 63 with a first throttle 62 interposed therein; and supplementary oil passages 65a, 65b are provided, which are further branched from the branch oil passage 63 and lead to the output oil passages 64a, 64b. Also, an oil passage 66 is provided, which is further branched at a branch portion to the supplementary oil passages 65a, 65b and return a part of the pressure oil to a tank, and a second throttle 67 is interposed in the return oil passage 66.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a work vehicle such as an agricultural tractor, and more particularly to a work vehicle equipped with a hydraulic forward / reverse clutch for switching between forward and reverse motion. [Background technology]

[0002] A work vehicle is known that is equipped with a hydraulic forward / reverse clutch that switches between forward and reverse travel and is provided within the power transmission system of a conventional vehicle, with an oil path switching valve that switches between forward and reverse travel and a proportional solenoid valve that controls the pressure (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-285313 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the above technology, when the forward / reverse clutch is put into neutral when the vehicle is stopped, the hydraulic oil pressure is released and the clutch returns to neutral due to the elastic force of the internal spring, but if the vehicle is stopped for a long time, the oil inside the forward / reverse clutch and in the oil passage between the valve and the clutch can be completely drained. This lengthens the time until the clutch is engaged when starting, and the timing of the pressure rise when the clutch is engaged is shifted, causing a shock.

[0005] An object of the present invention is to provide a work vehicle that can prevent the occurrence of shocks when the clutch is engaged. [Means for solving the problem]

[0006] In order to solve the above problems, the present invention provides the following technical solutions.

[0007] The first present invention is a work vehicle characterized in that it comprises a forward hydraulic multi-plate clutch (C1) and a reverse hydraulic multi-plate clutch (C2), a forward / reverse switch valve (50a) that receives pressure oil supplied from a pump (46s) and switches between an output oil passage (64a) to the forward multi-plate clutch (C1) or an output oil passage (64b) to the reverse multi-plate clutch (C2), a supply oil passage (60) to a forward / reverse clutch control valve (50) including the forward / reverse switch valve (50a) is branched and connected to a branch oil passage (63) having a first throttle (62) interposed therebetween, and a replenishment oil passage (65a) that is further branched from the branch oil passage (63) and leads to the output oil passage (64a) and a replenishment oil passage (65b) that leads to the output oil passage (64b). The second invention is the work vehicle of the first invention, which is provided with a branching path to the replenishment oil path (65a), a branching portion to the replenishment oil path (65b), and an oil path (66) which further branches off from the branching path to the replenishment oil path (65a) or the branching portion to the replenishment oil path (65b) and returns a portion of the pressurized oil to a tank, and a second throttle (67) is interposed in the return oil path (66). A third aspect of the present invention is the work vehicle of the second aspect of the present invention, wherein a shuttle valve (68a) is interposed in the replenishment oil passage (65a), a shuttle valve (68b) is interposed in the replenishment oil passage (65b), and an output port of the forward / reverse changeover valve (50a) is provided with a pilot oil passage (69a) capable of supplying a portion of the pressurized oil to the forward multi-plate clutch (C1) to the shuttle valve (68a), and a pilot oil passage (69b) capable of supplying a portion of the pressurized oil to the reverse multi-plate clutch (C2) to the shuttle valve (68b). The first invention related to the present invention The hydraulic multi-plate clutch C1 and the hydraulic multi-plate clutch C2 are arranged, and a forward / reverse switch valve 50a is provided which receives pressure oil supplied from a pump 46s and switches between output oil passages 64a, 64b to the forward multi-plate clutch C1 or the reverse multi-plate clutch C2. A supply oil passage 60 to the forward / reverse clutch control valve 50 including the forward / reverse switch valve 50a is branched off to connect a branch oil passage 63 with a first throttle 62 interposed therebetween, and supplementary oil passages 65a, 65b are provided which are further branched off from the branch oil passage 63 and lead to the output oil passages 64a, 64b.

[0008] The second invention related to the present invention teeth, The first invention related to the present invention an oil passage 66 which branches off from the branched portion to the replenishment oil passages 65a, 65b and returns a portion of the pressure oil to a tank, and a second throttle 67 is interposed in the return oil passage 66.

[0009] The third invention related to the present invention teeth, The second invention related to the present invention In the above, a shuttle valve 68a, 68b is interposed in the replenishment oil passage 65a, 65b, and a pilot oil passage 69a, 69b is provided in the output port of the forward / reverse changeover valve 50a, which can supply a portion of the pressurized oil for the forward multi-plate clutch C1 or the reverse multi-plate clutch C2 to the shuttle valve 68a or 68b. Effect of the Invention

[0010] According to the invention described in claim 1 or claim 2, since replenishment oil passages 65a, 65b are configured, pressurized oil can be replenished from the output side of the forward / reverse changeover valve 50a to the forward multi-plate clutch C1 and the reverse multi-plate clutch C2, etc., thereby preventing oil leakage even when the vehicle is stopped.

[0011] According to the invention described in claim 3, in addition to the effect described in claim 2, when pressure oil is supplied from the output port of forward / reverse switching valve 50a, shuttle valves 68a, 68b switch at the same time, so that oil passage 66 returning to the tank can be blocked, thereby preventing unexpected loss of pressure. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic diagram of a tractor according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a view taken along arrow B in FIG. 1 (looking toward the rear of the aircraft). [Diagram 3] 1 is a diagram showing a transmission mechanism of a transmission device of a tractor according to an embodiment of the present invention. [Figure 4] 1 is a hydraulic circuit diagram of a tractor according to an embodiment of the present invention. [Diagram 5] 1A is a graph showing the time-current relationship of a tractor according to an embodiment of the present invention, and FIG. 1B is a graph showing the time-pressure relationship of a tractor according to an embodiment of the present invention. [Figure 6] 1 is a control block diagram of a forward / reverse switching mechanism of a tractor according to an embodiment of the present invention. [Figure 7] 4A and 4B are hydraulic circuit diagrams of different forward / reverse clutch control valves of a tractor according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0014] The work vehicle of this embodiment shown in Figs. 1 and 2 is an agricultural tractor that works in a field or the like while propelled by power. The agricultural tractor 1 has front wheels 2, rear wheels 3, an engine 4 as a power source, and a transmission 5. The transmission 5 can transmit the rotational power generated by the engine 4 mounted inside a bonnet 6 at the front of the vehicle body to the rear wheels 3 after appropriately reducing the speed, and this transmission 5 can also transmit the rotational power generated by the engine 4 to the front wheels 2 as necessary. In other words, the transmission 5 can switch between two-wheel drive and four-wheel drive. Of these, the front wheels 2 are provided as steered wheels.

[0015] The tractor 1 is also provided with a coupling device 7 at the rear of the body to which a work machine such as a rotary (not shown) can be attached. The coupling device 7 is a three-point link consisting of a top link 7a at the top center and lower links 7b, 7b at the bottom left and right, and is configured to raise and lower the work machine via the lift rod and the lower links 7b by hydraulically rotating the left and right lift arms.

[0016] In the tractor 1, a cockpit 8 on the body is surrounded by a cabin 9. Inside the cabin 9, a steering wheel 11 stands on a dashboard 10 in front of the cockpit 8, and various operation pedals such as a clutch pedal, a brake pedal, an accelerator pedal, etc., and various operation levers such as a forward / reverse lever, a gear shift lever, etc. are arranged around the cockpit 8.

[0017] 3 is a diagram showing the power transmission mechanism 13 in the transmission case 12. The speed change device (transmission) 5 is configured to include the transmission case 12 and the power transmission mechanism 13 that is disposed in the transmission case 12 and transmits rotational power from the engine 4 to the rear wheels 3, etc. The power transmission mechanism 13 transmits the rotational power from the engine 4 to the front wheels 2, the rear wheels 3, and the working machine attached to the vehicle body to drive them.

[0018] Specifically, the power transmission mechanism 13 is configured to transmit the rotational power generated by the engine 4 to the rear wheels 3 via the input shaft 14, the forward / reverse switching mechanism 15, the Hi-Lo transmission mechanism 16, the main transmission mechanism 17, and the sub-transmission mechanism 18 in this order. The power transmission mechanism 13 can also transmit the rotational power generated by the engine 4 from the sub-transmission mechanism 18 to the front wheels 2 via a 2WD / 4WD switching mechanism 19. The power transmission mechanism 13 can also transmit the rotational power generated by the engine 4 to the working machine via the input shaft 14 and the PTO drive mechanism 20 in this order.

[0019] The forward / reverse switching mechanism 15 is capable of switching the rotational power transmitted from the engine 4 between forward rotation and reverse rotation. The forward / reverse switching mechanism 15 is configured to include a forward gear stage 15a, a reverse gear stage 15b, a reverse counter gear (reverse gear) 15c, a forward hydraulic multi-plate clutch C1 in the form of a hydraulic multi-plate clutch, and a reverse hydraulic multi-plate clutch C2. The forward / reverse hydraulic multi-plate clutches C1, C2 can switch the power transmission path in the forward / reverse switching mechanism 15 by switching between engaged / disengaged states. The forward / reverse switching mechanism 15 transmits the rotational power transmitted to the input shaft 14 to the counter shaft 21 by changing the transmission path according to the engaged / disengaged states of the forward / reverse hydraulic multi-plate clutches C1, C2.

[0020] The forward / reverse switching mechanism 15 is configured to transmit the rotational power transmitted to the input shaft 14 to the counter shaft 21 in a forward direction rotation via the forward gear stage 15a and the forward hydraulic multi-plate clutch C1 when the forward hydraulic multi-plate clutch C1 is engaged and the reverse hydraulic multi-plate clutch C2 is disengaged, and transmit the rotational power transmitted to the input shaft 14 to the counter shaft 21 in a reverse direction rotation via the reverse gear stage 15b, the reverse gear 15c and the reverse hydraulic multi-plate clutch C2 when the forward hydraulic multi-plate clutch C1 is disengaged and the reverse hydraulic multi-plate clutch C2 is engaged. In this way, the forward / reverse switching mechanism 15 can switch between forward and reverse of the tractor 1. The forward / reverse switching mechanism 15 can switch between forward, reverse and neutral by hydraulic control, for example, when the forward / reverse switching lever is operated by an operator. Note that both the forward and reverse hydraulic multi-plate clutches C1 and C2 can be released by depressing the clutch pedal. The configuration of a forward / reverse clutch control valve that controls the supply and discharge of pressure oil to the forward / reverse multi-plate clutches C1, C2 of the forward / reverse switching mechanism 15 will be described later.

[0021] The Hi-Lo transmission mechanism 16 is capable of shifting the rotational power transmitted from the engine 4 between high and low speed stages, and is configured to include a Hi (high speed) side gear stage 16a, a Lo (low speed) side gear stage 16b, a hydraulic multi-plate clutch (Hi (high speed) side clutch) C3, and a hydraulic multi-plate clutch (Lo (low speed) side clutch) C4. Depending on the engagement / release state of the hydraulic multi-plate clutches C3 and C4, the rotational power transmitted to the countershaft 21 is transmitted to the transmission shaft 22 by changing the transmission path. When the hydraulic multi-plate clutch C3 is in an engaged state and the hydraulic multi-plate clutch C4 is in a released state, the rotational power transmitted to the countershaft 21 is shifted and transmitted to the transmission shaft 22 via the hydraulic multi-plate clutch C3 and the Hi side gear stage 16a. In addition, when the hydraulic multi-plate clutch C3 is in the released state and the hydraulic multi-plate clutch C4 is in the engaged state, the rotational power transmitted to the counter shaft 21 is shifted via the hydraulic multi-plate clutch C4 and the Lo side gear stage 16b and transmitted to the transmission shaft 22.

[0022] The main transmission mechanism 17 is a synchromesh type transmission mechanism, and is capable of changing the speed of the rotational power transmitted from the engine 4 via the forward / reverse switching mechanism 15 and the Hi-Lo transmission mechanism 16. The main transmission mechanism 17 is configured to include a first gear stage 17a, a second gear stage 17b, a third gear stage 17c, a fourth gear stage 17d, a fifth gear stage 17e, and a sixth gear stage 17f as a plurality of gear stages. The main transmission mechanism 17 changes the speed of the rotational power transmitted to the transmission shaft 22 via any one of the first gear stage 17a to the sixth gear stage 17f depending on the coupling state of the first gear stage 17a to the sixth gear stage 17f with the transmission shaft 22, and transmits the rotational power to the transmission shaft 23. As a result, the main transmission mechanism 17 can transmit the rotational power from the engine 4 to a subsequent stage by changing the speed at any one of the first gear ratio 17a to sixth gear ratio 17f. The main transmission mechanism 17 can select and switch to one of a plurality of gear ratios by, for example, an operator operating a main transmission operation lever.

[0023] The auxiliary transmission mechanism 18 is configured to include a first auxiliary transmission 24, a second auxiliary transmission 25, etc., and changes the speed of the rotational power transmitted to the transmission shaft 23 via the first auxiliary transmission 24, the second auxiliary transmission 25, etc., and transmits it to the transmission shaft 26. The first auxiliary transmission 24 can change the speed of the rotational power transmitted from the engine 4 and changed in speed by the main transmission mechanism 17, etc., to a high speed or low speed, and transmit it to the rear wheels 3, which are the drive wheels. The second auxiliary transmission 25 is configured to include a first gear 24a, a second gear 24b, a third gear 24c, a fourth gear 24d, a shifter 24e, and clutch pawls 24ac and 24dc, and when the shifter 24e engages the clutch pawl 26a and the clutch pawl 24ac simultaneously, power is transmitted from the first gear 2a to the transmission shaft 26, and when the clutch pawl 26a and the clutch pawl 24dc simultaneously engage, power is transmitted from the fourth gear 24d to the transmission shaft 26. The second auxiliary transmission 25 is capable of changing the speed of the rotational power transmitted from the engine 4 and changed in speed by the main transmission mechanism 17 and the like to an ultra-low speed stage that is even slower than that of the first auxiliary transmission 24, and transmitting the rotational power to the rear wheels 3, which are the drive wheels. The second auxiliary transmission 25 includes a first gear 25a, a second gear 25b, a third gear 25c, a fourth gear 25d, and a shifter 25e, and is configured such that when the shifter 24e simultaneously engages the clutch pawl 26a and the clutch pawl 24ac, power is transmitted from the first gear 2a to the transmission shaft 26, and when the clutch pawl 26a and the clutch pawl 24dc are simultaneously engaged, power is transmitted from the fourth gear 24d to the transmission shaft 26. Therefore, by combining the first auxiliary transmission 24 and the second auxiliary transmission 25, the auxiliary transmission mechanism 18 can shift the rotational power transmitted to the transmission shaft 23 to any one of three speeds, high speed, low speed, and very low speed, and transmit the rotational power to the transmission shaft 26.

[0024] The transmission mechanism 13 of the speed change device 5 transmits the rotational power transmitted to the speed change shaft 26 to the rear wheels 3 via a rear wheel differential 27, a rear axle 28, a planetary gear reduction mechanism 29 for reducing speed, etc. As a result, the rear wheels 3 of the tractor 1 are rotated and driven as drive wheels by the rotational power from the engine 4.

[0025] The 2WD / 4WD switching mechanism 19 includes a transmission shaft 19a, a Hi (high-speed) side gear stage 19b, a Lo (low-speed) side gear stage 19c, a hydraulic multi-plate clutch (Lo (low-speed) side clutch) C6, a hydraulic multi-plate clutch (Hi (high-speed) side clutch) C7, and a transmission shaft 19d. When the hydraulic multi-plate clutch C6 is engaged and the hydraulic multi-plate clutch C7 is released, the rotational power transmitted to the transmission shaft 19a is changed in speed via the Lo-side gear stage 19c and the hydraulic multi-plate clutch C6 and transmitted to the transmission shaft 19d, so that the front and rear wheels are driven at substantially the same speed. When the hydraulic multi-plate clutch C7 is engaged and the hydraulic multi-plate clutch C6 is released, the rotational power is transmitted to the transmission shaft 19d via the Hi-side gear stage 19b, so that the front wheels can be driven at a faster speed than the rear wheels. The rotational power transmitted to the transmission shaft 19d is transmitted to the front wheels 2 via a front wheel differential 34, a front axle 35, a vertical shaft 36, a planetary gear reduction mechanism 37, etc., resulting in a four-wheel drive configuration.

[0026] In addition, in the 2WD / 4WD switching mechanism 19, when both hydraulic multi-plate clutches C6, C7 are in a released state, the transmission of the rotational power transmitted to the transmission shaft 19a to the transmission shaft 19d side is interrupted. As a result, the tractor 1 can travel in two-wheel drive. The rotational power from the speed change shaft 26 is transmitted (input) to the transmission shaft 19a via a gear 30, a gear 31, a transmission shaft 32, a coupling 33, etc. The Hi-side gear stage 19b as the first gear is inserted through the transmission shaft 19a and is assembled so as to be rotatable relative to the transmission shaft 19a.

[0027] The PTO drive mechanism 20 changes the speed of the rotational power transmitted from the engine 4 and outputs it to a work machine (not shown) from a PTO shaft 40 at the rear of the machine body, thereby driving the work machine with the power from the engine 4. The PTO drive mechanism 20 is composed of a PTO clutch mechanism 38, a PTO speed change mechanism 39, a PTO shaft 40, etc.

[0028] The PTO clutch mechanism 38 switches between transmitting and cutting off power to the PTO shaft 40 side. The PTO clutch mechanism 38 includes a gear 38a, a hydraulic multi-plate clutch C5, and a transmission shaft 38b. The gear 38a is engaged with a gear 41 that is connected to the input shaft 14 so as to be rotatable together with the input shaft 14. The hydraulic multi-plate clutch C5 switches the power transmission state between the gear 38a and the transmission shaft 38b by switching between an engaged state and a disengaged state, and when the hydraulic multi-plate clutch C5 is in an engaged state, the PTO is in a PTO driving state in which power is transmitted to the PTO shaft 40 side, and the rotational power transmitted from the input shaft 14 to the gear 38a via the gear 41 is transmitted to the transmission shaft 38b. When the hydraulic multi-plate clutch C5 is in a disengaged state, the PTO is in a non-driving state (neutral state).

[0029] The tractor 1 is provided with a gear pump (hydraulic pump) 46 via a gear 46a meshing with the gear 38a, a gear 46b meshing with the gear 46a, etc. The gear pump 46 applies hydraulic pressure to a hydraulic system such as the transmission mechanism 13.

[0030] The PTO speed change mechanism 39 changes the speed when transmitting power to the PTO shaft 40. The PTO speed change mechanism 39 includes a Hi (high speed) side gear stage 39a, a Lo (low speed) side gear stage 39b, a transmission shaft 39c, and a shifter 39d. The PTO speed change mechanism 39 changes the speed of the rotational power transmitted to the transmission shaft 38b via the Hi side gear stage 39a or the Lo side gear stage 39b according to the position of the shifter 39d, and transmits the rotational power to the transmission shaft 39c.

[0031] The PTO shaft 40 is coupled to a work machine side input shaft (not shown) via a universal joint shaft (not shown) and transmits rotational power from the engine 4 to the work machine. Since the transmission shaft 39c of the PTO shaft 40 is positioned offset from the center of the machine body, the PTO shaft 40 is disposed at the lateral center of the machine body so as to be transmittable via a first gear 43, a second gear 44, etc.

[0032] As shown in the hydraulic circuit diagram of FIG. 4, the hydraulic pump 46 is equipped with a main pump 46m and a sub pump 46s, and pressurized oil from the main pump 46m first enters an external hydraulic control valve 47 and forms an oil passage 47a that bypasses the external hydraulic control valve 47 to an unloaded state, and pressurized oil is supplied to a work machine lifting control valve 69 via this oil passage, and pressurized oil is supplied to and discharged from a work machine lifting cylinder mechanism LC.

[0033] On the other hand, the pressure oil of the sub-pump 46s is configured to be supplied to a power steering control valve 48, a PTO clutch control valve 49, and a forward / reverse clutch control valve 50.

[0034] The forward / reverse clutch control valve 50, which controls the supply and discharge of pressure oil to the forward / reverse multi-plate clutches C1 and C2 of the forward / reverse switching mechanism 15, will be described in detail. It has a three-position forward / reverse switching valve 50a that receives pressure oil supplied from the sub-pump 46s and switches the supply oil path to the forward multi-plate clutch C1 or the reverse multi-plate clutch C2. This forward / reverse switching valve 50a is equipped with a forward solenoid 50af and a reverse solenoid 50ar, and pressure oil is supplied to the forward multi-plate clutch C1 side by energizing the forward solenoid 50af, and pressure oil is supplied to the reverse multi-plate clutch C2 side by energizing the reverse solenoid 50ar. On the upstream side of the forward / reverse switching valve 50a, there are a clutch pedal valve 50b that switches between a state in which pressure oil can be supplied to the forward / reverse switching valve 50a and a state in which the supply is cut off, a variable relief valve 50c, and a proportional pressure control valve 50d for adjusting the relief pressure of the variable relief valve 50c.

[0035] The variable relief valve 50c is interposed in a branch oil passage provided in the oil passage connecting the hydraulic pump 46 and the forward / reverse switching valve 50a. The spool of the variable relief valve 50c is biased by a spring and the hydraulic pressure of the pilot port, and the hydraulic pressure on the inlet side is controlled by the combined pressure of the spring pressure and the pilot pressure. Now, when the pilot pressure of the pilot port is low, the spool of the variable relief valve 50c opens easily and a large amount of oil returns to the tank, so that the hydraulic pressure on the inlet side of the variable relief valve 50c, i.e., the pressure of the hydraulic pressure flowing to the forward / reverse switching valve 50a, becomes low. On the other hand, as the pilot pressure of the pilot port increases, the spool of the variable relief valve 50c becomes difficult to open, and the hydraulic pressure on the inlet side of the variable relief valve 50c, i.e., the pressure of the hydraulic pressure flowing to the forward / reverse switching valve 50a, becomes high. In this way, the supply pressure to the forward / reverse switching valve 50a can be controlled by increasing or decreasing the pilot pressure of the variable relief valve 50c. A solenoid proportional pressure control valve 50d is provided to control the pilot pressure of the variable relief valve 50c. The proportional pressure control valve 50d is configured to control the pilot pressure p by increasing or decreasing a control current Is to a proportional solenoid 50ds in response to a signal from a controller, thereby changing the pressure output from the proportional pressure control valve 50d. A relationship graph showing the gradual increase in the control current Is over time is preset.

[0036] More specifically, when the forward / reverse switching valve 50a receives a switching operation signal and a forward command or reverse command signal, the proportional solenoid 50ds flows a maximum current Imax as a control current Is until the clutch meets state, and after a temporary drop, the value of the control current Is gradually increases and is set to reach the maximum current Imax again (FIG. 5(A)). Such a change in the control current Is changes the pilot pressure and controls the hydraulic pressure to the forward / reverse switching valve 50a and thus to the forward hydraulic multi-plate clutch C1 or reverse hydraulic multi-plate clutch C2 (FIG. 5(B)).

[0037] As shown in the block diagram of Fig. 6, the forward / reverse switching valve 50a is switched to the forward side or the reverse side by a forward / reverse switching lever 51 disposed near the steering wheel 11. By switching the forward / reverse switching lever 51 to each of the operation positions of forward F-neutral N-reverse R, the forward / reverse switching valve 50a is switched from the neutral N shown in the figure to the forward F side or the reverse R side. That is, a forward switch 51f, a reverse switch 51r, and a neutral switch 51n corresponding to the above operation positions of the forward / reverse switching lever 51 are disposed, and the forward solenoid 50af or the reverse solenoid 50ar of the forward / reverse switching valve 50a is excited based on the ON operation of each switch 51f, 51r, 51n.

[0038] In addition, the clutch pedal 53 is provided with two clutch sensors, namely, a limit sensor 52a and a potentiometer 52b, and when it is determined that the clutch pedal 53 is disengaged by depression by detecting that the limit sensor 52a is ON and the potentiometer 52b is equal to or less than a predetermined angle, the clutch pedal valve 50b is switched to cut off the supply of pressure oil to the forward / reverse switching valve 50a, and a clutch disengagement state is established in which no hydraulic oil is supplied to either of the clutches C1 or C2. When the potentiometer 52b detects that the clutch pedal is engaged, the clutch pedal valve 50b is in a pressure oil supply state, and the control current Is to the proportional solenoid 50ds is controlled based on the detection value of the potentiometer 52b, and the engagement control of the clutch C1 or C2 is performed according to the pedal depression.

[0039] Next, a different example of the forward / reverse clutch control valve 50 will be described with reference to Fig. 7. The forward / reverse clutch control valve 50A in Fig. 10 is configured to eliminate the variable relief valve 50c and directly connect a proportional pressure control valve 50e to the input port of the forward / reverse switching valve 50a to perform pressure change control (Fig. 7(A)). Note that in Fig. 7, the same reference numerals are used to designate the same members as those in the forward / reverse clutch control valve 50.

[0040] 7(B) shows an improved configuration of the forward / reverse clutch control valve 50A. The supply oil passage of the forward / reverse clutch control valve 50A, specifically, the supply oil passage 60 to the forward / reverse clutch control valve 50 (clutch pedal valve 50b) is branched to connect a branch oil passage 63 with a first throttle 62 interposed therein, and this branch oil passage 63 is further branched to connect refill oil passages 65a, 65b leading to output oil passages (supply oil passages) 64a, 64b from the output side of the forward / reverse switching valve 50a to the forward multi-plate clutch C1 and the reverse multi-plate clutch C2, so that a part of the pressure oil flow rate can be constantly supplied to the forward multi-plate clutch C1 and the reverse multi-plate clutch C2. An oil passage 66 is further branched at the branch to the refill oil passages 65a, 65b to return a part of the pressure oil to a tank, and a second throttle 67 is interposed in this return oil passage 66.

[0041] The replenishment oil passages 65a, 65b are provided with shuttle valves 68a, 68b, respectively, and the replenishment oil passages 65a or 65b are cut off during forward or reverse travel when pressure oil is supplied from the output port of the forward / reverse changeover valve 50a to the output oil passages 64a, 64b to the forward multi-plate clutch C1 or reverse multi-plate clutch C2. In other words, the output port of the forward / reverse changeover valve 50a is provided with pilot oil passages 69a, 69b that can supply a portion of the pressure oil to the forward multi-plate clutch C1 or reverse multi-plate clutch C2 to the shuttle valves 68a or 68b.

[0042] In the case of the configuration in FIG. 7(A), if the vehicle is stopped for a long time, the forward multi-plate clutch C1 and reverse multi-plate clutch C2 and the pressurized oil in the forward multi-plate clutch C1, reverse multi-plate clutch C2, and oil passages 61a, 61b from the output side of forward / reverse switch valve 50a to the forward multi-plate clutch C1 and reverse multi-plate clutch C2 will all drain out, which has the disadvantage that it will take an unnecessary long time until the next clutch engagement at start-up; however, if replenishment oil passages 65a, 65b are configured as in FIG. 7(B), pressurized oil will be replenished from the output side of forward / reverse switch valve 50a to the supply oil passages 64a, 64b to the forward multi-plate clutch C1 and reverse multi-plate clutch C2, eliminating the above disadvantage.

[0043] In addition, by providing a second throttle 67 in the oil passage 66 that returns a portion of the replenishment pressure oil to the tank, resistance can be applied to the extent that no operating pressure is generated in the forward multi-plate clutch C1 and the reverse multi-plate clutch C2.

[0044] Furthermore, by providing shuttle valves 68a, 68b and configuring pilot oil passages 69a, 69b, the shuttle valves 68a, 68b can be switched at the same time as switching to forward or reverse when pressurized oil is supplied from the output port of forward / reverse changeover valve 50a, thereby blocking the oil passage 66 returning to the tank.

[0045] The configuration of the refill oil passages 65a, 65b and the configuration of the shuttle valves 68a, 68b in FIG. 7B can also be adopted in the hydraulic circuit in FIG. [Explanation of symbols]

[0046] 46s Pump 50 Forward / reverse clutch control valve 50a Forward / reverse switching valve 60 Oil supply line 62 First squeeze 63 Branch oil passage 64a Output oil passage 64b Output oil path 65a Refill oil path 65b Refill oil path 66 Return oil passage 67 Second squeeze 68a Shuttle valve 68b Shuttle valve 69a Pilot oil passage 69b Pilot oil passage C1 forward hydraulic multi-plate clutch C2 Reverse hydraulic multi-plate clutch

Claims

1. A work vehicle comprising a forward hydraulic multi-plate clutch (C1) and a reverse hydraulic multi-plate clutch (C2), a forward / reverse changeover valve (50a) which receives pressurized oil supplied from a pump (46s) and switches between an output oil passage (64a) to the forward multi-plate clutch (C1) or an output oil passage (64b) to the reverse multi-plate clutch (C2), a supply oil passage (60) to a forward / reverse clutch control valve (50) which includes the forward / reverse changeover valve (50a) is branched and connected to a branch oil passage (63) which has a first throttle (62) interposed therebetween, and a refill oil passage (65a) which is further branched from the branch oil passage (63) and leads to the output oil passage (64a) and a refill oil passage (65b) which leads to the output oil passage (64b).

2. A work vehicle as described in claim 1, comprising a branch path to the replenishment oil passage (65a), a branch portion to the replenishment oil passage (65b), and an oil passage (66) which further branches off from the branch path to the replenishment oil passage (65a) or the branch portion to the replenishment oil passage (65b) and returns a portion of the pressurized oil to a tank, and a second throttle (67) is interposed in the return oil passage (66).

3. A work vehicle as described in claim 2, wherein a shuttle valve (68a) is interposed in the replenishment oil passage (65a), a shuttle valve (68b) is interposed in the replenishment oil passage (65b), and the output port of the forward / reverse switching valve (50a) is provided with a pilot oil passage (69a) capable of supplying a portion of the pressurized oil to the forward multi-plate clutch (C1) to the shuttle valve (68a), and a pilot oil passage (69b) capable of supplying a portion of the pressurized oil to the reverse multi-plate clutch (C2) to the shuttle valve (68b).

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