JP2022188378A - work vehicle - Google Patents

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

BACKGROUND OF THE INVENTION 1. Field of the Invention 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 travel.

A work vehicle is known that is provided in a power transmission system of a conventional vehicle and is provided with a hydraulic forward/reverse clutch for switching forward/reverse, an oil passage switching valve for switching forward/reverse, and a proportional solenoid valve for controlling pressure. There is (Patent Document 1).

JP 2007-285313 A

In the above technology, when the forward/reverse clutch is set to neutral when the vehicle is stopped, the elastic force of the internal spring returns to neutral when the hydraulic oil pressure is released. The oil in the clutch and the oil passage between the valve and the clutch sometimes ran out. As a result, the time required to engage the clutch when the vehicle starts moving becomes longer, and the predetermined timing of pressure rise at the time of clutch engagement may be shifted, resulting in a shock.

SUMMARY OF THE INVENTION An object of the present invention is to provide a work vehicle capable of preventing the occurrence of a shock when a clutch is engaged.

In order to solve the above problems, the present invention has taken the following technical means.

According to the first aspect of the invention, a forward hydraulic multi-plate clutch C1 and a reverse hydraulic multi-plate clutch C2 are arranged, and pressure oil supplied from the pump 46s is received to transfer the forward multi-plate clutch C1 or the reverse multi-plate clutch C2. Equipped with a forward/reverse switching valve 50a for switching to the output oil passages 64a and 64b, the supply oil passage 60 to the forward/reverse clutch control valve 50 including the forward/reverse switching valve 50a is branched, and the branched oil passage is interposed with a first throttle 62. 63 is connected, and supplementary oil passages 65a and 65b are provided which are further branched from the branch oil passage 63 and lead to the output oil passages 64a and 64b.

The invention according to claim 2 is the invention according to claim 1, further comprising an oil passage 66 that branches off from the branched portion to the supplementary oil passages 65a and 65b and returns part of the pressure oil to the tank. The path 66 has a second throttle 67 interposed therebetween.

According to a third aspect of the invention, in the second aspect of the invention, shuttle valves 68a and 68b are interposed in the replenishment oil passages 65a and 65b, respectively, and the output port of the forward/reverse switching valve 50a is connected to the forward multi-directional valve. Pilot oil passages 69a and 69b are provided to supply part of the pressure oil to the plate clutch C1 or the reverse multi-plate clutch C2 to the shuttle valve 68a or 68b.

According to the first or second aspect of the invention, since the replenishment oil passages 65a and 65b are configured, oil is supplied from the output side of the forward/reverse switching valve 50a to the forward multi-disc clutch C1 and the reverse multi-disc clutch C2. Since the oil passages 64a, 64b and the like can be replenished with pressurized oil, oil leakage can be prevented even when the vehicle is stopped.

According to the third aspect of the invention, in addition to the effect of the second aspect, the shuttle valves 68a and 68b are switched simultaneously to the forward or reverse movement in which pressure oil is supplied from the output port of the forward/reverse switching valve 50a. , the oil passage 66 returning to the tank can be cut off, and unexpected pressure loss can be prevented.

1 is a schematic diagram of a tractor according to an embodiment of the invention; FIG. FIG. 2 is a view in the direction of arrow B in FIG. 1 (a view of the rear portion of the fuselage); It is a diagram showing a transmission mechanism of a transmission of a tractor according to an embodiment of the present invention. 1 is a hydraulic circuit diagram of a tractor according to an embodiment of the present invention; FIG. (A) is a time-current relationship graph of the tractor according to the embodiment of the present invention, and (B) is a time-pressure relationship graph of the tractor according to the embodiment of the present invention. FIG. 2 is a control block diagram of the forward/reverse switching mechanism of the tractor according to the embodiment of the present invention; (A) and (B) are hydraulic circuit diagrams of different forward and backward clutch control valves of the tractor according to the embodiment of the present invention.

EMBODIMENT OF THE INVENTION Below, embodiment which concerns on this invention is described in detail based on drawing.

The work vehicle of the present embodiment shown in FIGS. 1 and 2 is an agricultural tractor that works in a field or the like while self-propelled by power. An agricultural tractor 1 includes front wheels 2 , rear wheels 3 , an engine 4 as a power source, and a transmission 5 . Rotational power generated by an engine 4 mounted in a bonnet 6 at the front of the fuselage can be transmitted to the rear wheels 3 after being appropriately reduced by a transmission 5. Rotational power generated by the engine 4 can also be transmitted to the front wheels 2 as needed. That is, the transmission 5 is capable of switching between two-wheel drive and four-wheel drive. Of these, the front wheels 2 are provided as steering wheels.

Further, the tractor 1 is provided with a coupling device 7 to which a working machine (not shown) such as a rotary can be attached at the rear part of the body. The coupling device 7 is a three-point link consisting of a top link 7a in the upper center and lower left and right lower links 7b, 7b. It is a configuration for lifting and lowering the working machine via.

The tractor 1 is covered with a cabin 9 around an operator's seat 8 on the fuselage. Inside the cabin 9, a steering handle 11 is erected from a dashboard 10 in front of the operator's seat 8, and around the operator's seat 8 various operation pedals such as a clutch pedal, a brake pedal, an accelerator pedal, a forward and backward lever, and a gear shift. Various operation levers such as levers are arranged.

FIG. 3 is a diagram showing the transmission mechanism 13 inside the transmission case 12. As shown in FIG. The transmission 5 includes a transmission case 12 and the transmission mechanism 13 arranged in the transmission case 12 for transmitting rotational power from the engine 4 to the rear wheels 3 and the like. The transmission mechanism 13 transmits rotational power from the engine 4 to the front wheels 2, the rear wheels 3, and the working machine mounted on the machine body to drive the machine.

Specifically, the transmission mechanism 13 transmits the rotational power generated by the engine 4 through the input shaft 14, the forward/reverse switching mechanism 15, the Hi-Lo transmission mechanism 16, the main transmission mechanism 17, and the auxiliary transmission mechanism 18 in order. It is configured to transmit to the wheel 3 . Further, the transmission mechanism 13 can transmit the rotational power generated by the engine 4 from the auxiliary transmission mechanism 18 to the front wheels 2 via the 2WD/4WD switching mechanism 19 . Furthermore, the transmission mechanism 13 can transmit the rotational power generated by the engine 4 to the working machine through the input shaft 14 and the PTO drive mechanism 20 in that order.

The forward/reverse switching mechanism 15 can switch the rotational power transmitted from the engine 4 between forward rotation and reverse rotation. The forward/reverse switching mechanism 15 includes 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. Configured. The forward/reverse hydraulic multi-plate clutches C1 and C2 can switch the power transmission path in the forward/reverse switching mechanism 15 by switching between the engaged/released 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 and C2.

When the forward hydraulic multi-plate clutch C1 is in the engaged state and the reverse hydraulic multi-plate clutch C2 is in the disengaged state, the forward/reverse switching mechanism 15 transfers the rotational power transmitted to the input shaft 14 to the forward gear stage 15a and the forward gear stage 15a. It is configured to transmit forward rotation to the counter shaft 21 via the hydraulic multi-plate clutch C1. Rotational power transmitted to the shaft 14 is transmitted to the counter shaft 21 in the reverse direction through the reverse gear stage 15b, the reverse gear 15c, and the reverse hydraulic multi-plate clutch C2. As a result, the forward/rearward travel switching mechanism 15 can switch the forward/rearward travel of the tractor 1 . The forward/reverse switching mechanism 15 can switch between forward, reverse, and neutral by hydraulic control, for example, when a forward/reverse switching lever is operated by an operator. By depressing the clutch pedal, both the forward and reverse hydraulic multi-plate clutches C1 and C2 can be released. The configuration of a forward/reverse clutch control valve that controls supply and discharge of pressure oil to/from the forward/reverse multi-plate clutches C1 and C2 of the forward/reverse switching mechanism 15 will be described later.

The Hi-Lo transmission mechanism 16 can shift the rotational power transmitted from the engine 4 to a high speed stage or a low speed stage. It includes a plate clutch (Hi (high speed) side clutch) C3 and a hydraulic multi-plate clutch (Lo (low speed) side clutch) C4. The rotational power transmitted to the counter shaft 21 is transmitted to the transmission shaft 22 by changing the transmission path according to the engagement/release state of the hydraulic multi-plate clutches C3 and C4. When the hydraulic multi-plate clutch C4 is in the disengaged state, the rotational power transmitted to the counter shaft 21 is shifted via the hydraulic multi-plate clutch C3 and the Hi-side gear stage 16a and transmitted to the transmission shaft 22. . Further, 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 transmitted through the hydraulic multi-plate clutch C4 and the Lo-side gear stage 16b. The speed is changed and transmitted to the speed change shaft 22 .

The main transmission mechanism 17 is a synchromesh type transmission mechanism, and is capable of changing the rotation 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 has a plurality of gear stages such as 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. It comprises a step 17f. The main transmission mechanism 17 converts the rotational power transmitted to the transmission shaft 22 from the first gear stage 17a to the sixth gear stage 17a to the transmission shaft 22 according to the coupling state of the first gear stage 17a to the sixth gear stage 17f with the transmission shaft 22. The gear is shifted through one of the sixth gears 17f and transmitted to the transmission shaft 23. As a result, the main transmission mechanism 17 can shift the rotational power from the engine 4 at any gear ratio of the first gear stage 17a to the sixth gear stage 17f and transmit it to the rear stage. The main transmission mechanism 17 can select and switch one of a plurality of gear stages, for example, by operating a main transmission operating lever by an operator.

The subtransmission mechanism 18 includes a first subtransmission 24, a second subtransmission 25, etc., and transmits the rotational power transmitted to the transmission shaft 23 to the first subtransmission 24 and the second subtransmission 25. etc., and transmitted to the transmission shaft 26 . The first sub-transmission 24 is capable of transmitting rotational power transmitted from the engine 4 and shifted by the main transmission mechanism 17 or the like to the rear wheels 3, which are driving wheels, by shifting the speed at a high speed stage or a low speed stage. It comprises 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. Power is transmitted from the first gear 2a to the transmission shaft 26, and when the clutch claw 26a and the clutch claw 24dc are simultaneously engaged, power is transmitted from the fourth gear 24d to the transmission shaft 26. The second sub-transmission 25 shifts rotational power transmitted from the engine 4 and shifted by the main transmission mechanism 17 and the like to an ultra-low speed stage that is lower than the speed of the first sub-transmission 24, and transmits the power to the rear wheels 3, which are the driving wheels. It is possible to transmit to the side. The second sub-transmission 25 includes a first gear 25a, a second gear 25b, a third gear 25c, a fourth gear 25d, and a shifter 25e. When engaged, power is transmitted from the first gear 2a to the transmission shaft 26, and when the clutch pawls 26a and 24dc are simultaneously engaged, power is transmitted from the fourth gear 24d to the transmission shaft 26. Therefore, the sub-transmission mechanism 18 combines the rotational power transmitted to the transmission shaft 23 with the first sub-transmission 24 and the second sub-transmission 25 to convert it into one of the three stages of high speed, low speed, and ultra-low speed. Either of them can be used to shift the speed and transmit it to the speed change shaft 26 .

The transmission mechanism 13 of the transmission 5 transmits the rotational power transmitted to the transmission shaft 26 to the rear wheels 3 via the rear wheel differential 27, the rear axle 28, the planetary gear reduction mechanism 29 for reduction, and the like. As a result, the tractor 1 rotates the rear wheels 3 as drive wheels by the rotational power from the engine 4 .

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 in the engaged state and the hydraulic multi-plate clutch C7 is in the disengaged state, the rotational power transmitted to the transmission shaft 19a is shifted through the Lo-side gear stage 19c and the hydraulic multi-plate clutch C6. The front wheels and the rear wheels are driven at substantially the same speed. When the hydraulic multi-plate clutch C7 is in the engaged state and the hydraulic multi-plate clutch C6 is in the disengaged state, transmission is performed to the transmission shaft 19d via the Hi-side gear stage 19b. Can drive fast. It is a four-wheel drive configuration in which the rotational power transmitted to the transmission shaft 19d is transmitted to the front wheels 2 via the front wheel differential 34, the front axle 35, the vertical shaft 36, the planetary gear reduction mechanism 37, and the like.

In addition, the 2WD/4WD switching mechanism 19 is configured such that the rotational power transmitted to the transmission shaft 19a is transferred to the transmission shaft 19d side by releasing both the hydraulic multi-plate clutches C6 and C7. Power transmission is interrupted. As a result, the tractor 1 can travel in two-wheel drive. The transmission shaft 19a receives (inputs) the rotational power from the transmission shaft 26 via the gears 30, 31, the transmission shaft 32, the coupling 33, and the like. A transmission shaft 19a is inserted into the Hi-side gear stage 19b as the first gear, and is assembled so as to be relatively rotatable with respect to the transmission shaft 19a.

The PTO drive mechanism 20 changes the speed of rotational power transmitted from the engine 4 and outputs it from the PTO shaft 40 at the rear part of the machine body to the working machine (not shown), thereby driving the working machine with the power from the engine 4. be. The PTO drive mechanism 20 includes a PTO clutch mechanism 38, a PTO transmission mechanism 39, a PTO shaft 40, and the like.

The PTO clutch mechanism 38 switches between transmission and interruption of 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 meshes with a gear 41 coupled to the input shaft 14 so as to rotate integrally therewith. The hydraulic multi-plate clutch C5 switches the power transmission state between the gear 38a and the transmission shaft 38b by switching between the engagement and release states, and the PTO shaft 40 is engaged by the hydraulic multi-plate clutch C5 being engaged. A PTO drive state is established in which power is transmitted to the 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. The PTO non-driving state (neutral state) is established by disengaging the hydraulic multi-plate clutch C5.

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, and the like. The gear pump 46 applies hydraulic pressure to the hydraulic system such as the transmission mechanism 13 .

The PTO speed change mechanism 39 performs speed change when power is transmitted to the PTO shaft 40 side. The PTO transmission 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 transmission mechanism 39 changes the speed of the rotational power transmitted to the transmission shaft 38b through the Hi-side gear stage 39a or the Lo-side gear stage 39b according to the position of the shifter 39d, and transmits it to the transmission shaft 39c. do.

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 is offset from the center of the machine body, the PTO shaft 40 is arranged at the center of the machine body so that it can be transmitted through the first gear 43, the second gear 44, and the like.

As shown in the hydraulic circuit diagram of FIG. 4, the hydraulic pump 46 includes a main pump 46m and a sub-pump 46s. An oil passage 47a is formed to detour to the load state, and pressurized oil is supplied to the working machine lifting control valve 69 via this oil passage, and is supplied to and discharged from the working machine lifting cylinder mechanism LC.

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.

The forward/reverse clutch control valve 50 that controls the supply and discharge of pressure oil to/from 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 switching 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. The forward/reverse switching valve 50a is provided with a forward solenoid 50af and a reverse solenoid 50ar. When the forward solenoid 50af is energized, pressurized oil is supplied to the forward multi-disc clutch C1, and when the reverse solenoid 50ar is energized, pressure is applied to the reverse multi-disc clutch C2. Can supply oil. On the upstream side of the forward/reverse switching valve 50a, a clutch pedal valve 50b that switches between two positions to switch 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 blocked, and a variable relief valve 50c. and a proportional pressure control valve 50d for adjusting the relief pressure of the variable relief valve 50c.

A branch oil passage is provided in the oil passage connecting the hydraulic pump 46 and the forward/reverse switching valve 50a, and the variable relief valve 50c is interposed. The spool of the variable relief valve 50c is biased by a spring and the hydraulic pressure of the pilot port, and the combined pressure of the spring pressure and the pilot pressure controls the hydraulic pressure on the inlet side. When the pilot pressure at the pilot port is low, the spool of the variable relief valve 50c is easily opened, and a large amount of oil returns to the tank. The hydraulic pressure flowing to 50a becomes low pressure. On the other hand, as the pilot pressure at the pilot port increases, the spool of the variable relief valve 50c becomes more difficult to open, and the hydraulic pressure on the inlet side of the variable relief valve 50c, that is, the hydraulic pressure flowing to the forward/reverse switching valve 50a, becomes high. becomes. Thus, by increasing or decreasing the pilot pressure of the variable relief valve 50c, the supply pressure to the forward/reverse switching valve 50a can be controlled. A solenoid type 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 varying the pressure output from the proportional pressure control valve 50d by increasing or decreasing the control current Is to the proportional solenoid 50ds according to a signal from the controller. is. A relational graph is set in advance in which the control current Is gradually increases with the lapse of time.

More specifically, when a switching actuation signal for the forward/reverse switching valve 50a is received, and a forward command or reverse command signal is received, the proportional solenoid 50ds is supplied with the maximum current Imax as the control current Is until the clutch is engaged, and then once decreases. After that, the value of the control current Is gradually rises and is set to reach the maximum current Imax again (FIG. 5(A)). Such a change in the control current Is changes the level of the pilot pressure, and controls the hydraulic pressure to the forward/reverse switching valve 50a, the forward hydraulic multi-plate clutch C1 or the reverse hydraulic multi-plate clutch C2 (Fig. (B)).

As shown in the block diagram of FIG. 6, the switching operation of the forward/reverse switching valve 50a to the forward/reverse is performed by a forward/reverse switching lever 51 disposed near the steering handle 11. As shown in FIG. By switching the forward/reverse switching lever 51 to each operating position of forward F-neutral N-reverse R, the forward/reverse switching valve 50a is switched from neutral N 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 are provided corresponding to the above-described operating positions of the forward/reverse switching lever 51, and the forward/reverse switching valve 50a advances based on the ON operation of each of the switches 51f, 51r, and 51n. It is configured to excite the solenoid 50af or the reverse solenoid 50ar.

It also has a clutch pedal 53 that operates to switch both the forward and reverse sides of a forward/reverse switching valve 50a of the forward/reverse clutch control valve 50. The switching clutch pedal 53 has two clutch sensors, that is, a limit sensor 52a. and a potentiometer 52b, and when the limit sensor 52a is ON and the potentiometer 52b detects a predetermined angle or less, and it is determined that the clutch is disengaged by depressing the clutch pedal 53, the clutch pedal valve 50b is switched to supply pressure oil to the forward/reverse switching valve 50a. The supply is interrupted to create a clutch disengaged state in which hydraulic oil is not supplied to any of the clutches C1 and C2. When the potentiometer 52b detects the clutch engagement state of the clutch pedal, the clutch pedal valve 50b enters the pressure oil supply state, and the control current Is to the proportional solenoid 50ds can be controlled based on the detected value of the potentiometer 52b. Engagement control of the clutch C1 or C2 is performed according to the depression of the pedal.

Next, another example of the forward/reverse clutch control valve 50 will be described with reference to FIG. The forward/reverse clutch control valve 50A in FIG. 10 eliminates the variable relief valve 50c and directly connects the proportional pressure control valve 50e to the input port of the forward/reverse switching valve 50a to perform pressure change control (FIG. 7(A)). . In FIG. 7, members common to the forward/reverse clutch control valve 50 are denoted by the same reference numerals.

FIG. 7B shows an improved configuration of the forward/reverse clutch control valve 50A. The supply oil passage for 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 form a branched oil passage 63 with a first throttle 62 interposed therebetween. The supplementary oil is further branched from this branch oil passage 63 and communicates with output oil passages (supply oil passages) 64a and 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. The passages 65a and 65b are connected so that part of the pressure oil flow rate can always be supplied to the forward multi-plate clutch C1 and the reverse multi-plate clutch C2. An oil passage 66 is further provided at the branched portion to the supplementary oil passages 65a and 65b to return part of the pressurized oil to the tank.

Shuttle valves 68a and 68b are interposed in the supplementary oil passages 65a and 65b, respectively, and pressure is applied to output oil passages 64a and 64b from the output port of the forward/reverse switching valve 50a to the forward multiple disc clutch C1 or the reverse multiple disc clutch C2. The replenishment oil passage 65a or 65b is configured to be blocked during forward or reverse travel in which oil is supplied. That is, the output port of the forward/reverse switching valve 50a is provided with pilot oil passages 69a and 69b for supplying part of the pressure oil to the forward multi-plate clutch C1 or the reverse multi-plate clutch C2 to the shuttle valve 68a or 68b. .

In the case of the configuration of FIG. 7(A), when the stop time becomes long, the forward multi-plate clutch C1 and the reverse multi-plate clutch C2 are connected. Since the pressure oil in the oil passages 61a, 61b, etc. from the output side of the switching valve 50a to the forward multi-plate clutch C1 and the reverse multi-plate clutch C2 is exhausted, it takes an unnecessarily long time to connect the clutches when starting the next vehicle. However, if supplementary oil passages 65a and 65b are constructed as shown in FIG. can be filled with pressure oil to eliminate the above drawbacks.

In addition, by interposing the second throttle 67 in the oil passage 66 for returning part of the replenishment pressure oil to the tank, resistance is applied to the extent that the operating pressure to the forward multi-plate clutch C1 and the reverse multi-plate clutch C2 is not generated. be able to.

Further, by constructing the pilot oil passages 69a and 69b with the intervening shuttle valves 68a and 68b, the shuttle valves 68a and 68b are simultaneously switched to the forward or reverse movement in which pressure oil is supplied from the output port of the forward/reverse switching valve 50a. 68a, 68b can be switched to block the oil line 66 returning to the tank.

The configuration of the supplementary oil passages 65a, 65b, the configuration of the shuttle valves 68a, 68b, etc. shown in FIG. 7B can also be employed in the hydraulic circuit shown in FIG.

46s Pump 50 Forward/reverse clutch control valve 50a Forward/reverse switching valve 60 Supply oil passage 62 First throttle 63 Branch oil passage 64a Output oil passage 64b Output oil passage 65a Refill oil passage 65b Refill oil passage 66 Return oil passage 67 Second throttle 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 (3)

A forward hydraulic multi-plate clutch (C1) and a reverse hydraulic multi-plate clutch (C2) are arranged, and receive pressure oil supplied from a pump (46s) to shift to the forward multi-plate clutch (C1) or the reverse multi-plate clutch (C2). and a forward/reverse switching valve (50a) for switching to the output oil passages (64a, 64b) of the forward/rearward movement switching valve (50a). , supplementary oil passages (65a, 65b) connecting a branch oil passage (63) with a first throttle (62) interposed therebetween, further branching from the branch oil passage (63), and communicating with the output oil passages (64a, 64b). A work vehicle characterized by providing a An oil passage (66) is further provided at the branched portion to the supplementary oil passages (65a, 65b) to return part of the pressurized oil to the tank, and a second throttle (67) is interposed in the return oil passage (66). The work vehicle according to claim 1. A shuttle valve (68a, 68b) is interposed in each of the supplementary oil passages (65a, 65b), and a forward multi-plate clutch (C1) or a reverse multi-plate clutch (C2) is connected to the output port of the forward/reverse switching valve (50a). ) is provided with a pilot oil passage (69a, 69b) capable of supplying part of the pressure oil to the shuttle valve (68a or 68b).

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