JP5101440B2 - Work vehicle - Google Patents

Description

  The present invention operates a hydraulic pump and a hydraulic motor in a closed circuit and operates a swash plate of the hydraulic pump with respect to a hydraulic circuit in which a charge circuit for supplying hydraulic fluid from the outside is connected to the closed circuit. The present invention relates to a work vehicle including a hydraulic continuously variable transmission that can perform continuously variable transmission.

  In this type of work vehicle, in order to constitute the hydraulic continuously variable transmission described above, a return side charge circuit is connected to the return side circuit from the hydraulic motor to the hydraulic pump, and the return side charge circuit is connected to the return side circuit. A check valve that prevents the return side charge circuit from flowing into the return side circuit and a relief valve that allows the return side circuit to flow into the return side charge circuit are provided in parallel. A check valve for connecting a supply-side charge circuit to a supply-side circuit from the hydraulic pump to the hydraulic motor and preventing the supply-side charge circuit from flowing from the supply-side circuit to the supply-side charge circuit; A relief valve that allows flow from the side circuit to the supply side charge circuit is interposed (Patent Document 1).

JP 2004-257447 A (FIG. 9)

In the conventional structure shown in Patent Document 1, when a brake operation is performed on a downhill or the like and the brake operation is suddenly released, the hydraulic motor is reversely driven by the traveling body that moves inertial, and a large engine brake acts. In this case, a phenomenon occurs in which the return-side oil passage becomes a high pressure and reverses that during normal traveling in which the supply-side oil passage is at a high pressure.
In this case, the traveling vehicle body is suddenly decelerated by the engine brake, and a large shift shock may occur.

  An object of the present invention is to provide a work vehicle capable of reducing a large shift shock and suppressing negative pressure generation in a closed circuit by adding an effective mechanism to a return side circuit.

〔Constitution〕
According to a first aspect of the present invention, there is provided a hydraulic continuously variable transmission and a sub-transmission device to which a shift output of the hydraulic continuously variable transmission is inputted. A work vehicle configured to be disclosed, wherein a return side charge circuit is connected to a return side circuit from a hydraulic motor to a hydraulic pump in the hydraulic continuously variable transmission, and the return side charge circuit is connected to the return side charge circuit. A check valve that prevents hydraulic fluid from flowing from the return circuit to the return charge circuit, and a relief valve and a throttle valve that allow hydraulic fluid to flow from the return circuit to the return charge circuit. In parallel, the throttle valve is directly connected to the return-side charge circuit, and at least one of the supply-side charge circuit or the supply-side circuit has a circuit pressure that is negative due to a brake operation. Negative to prevent There in that is provided with a valve, the effects thereof are as follows.

[Action]
A relief valve and a throttle valve that allow hydraulic fluid to flow from the return circuit to the return charge circuit are installed in parallel, and the hydraulic fluid is returned from the return circuit to the return charge circuit by the throttle valve. Allow and prevent the return circuit from becoming high voltage.
For high pressure conditions that cannot be handled by the throttle valve, high pressure oil is returned to the return side charge circuit via the relief valve.
With such a configuration, even when the brake is operated and then the brake is released, it is possible to avoid the high pressure in the return side circuit, so that the situation in which the hydraulic motor is reversely driven by the movement of the traveling machine body can be avoided. A sudden shift shock can be avoided.
However, by connecting the relief valve and the throttle valve to the return side circuit, although its return side circuit adopts a configuration which prevents excessively high pressurization, when small set pressure of the relief valve, shift shock However, the closed circuit itself may become negative pressure.
Therefore, in the present invention, the generation of negative pressure is suppressed by providing a negative pressure prevention valve in the supply side circuit or the supply side charge circuit.

〔effect〕
By providing the throttle valve and the relief valve in the return side circuit, it is possible to reduce the shift shock due to the operation of the engine brake, and by providing the throttle valve and the relief valve in the return side circuit, the circuit pressure becomes negative. By providing a negative pressure prevention valve in the supply side circuit or the supply side charge circuit, a work vehicle equipped with a hydraulic continuously variable transmission that can be prevented beforehand can be provided.

〔Constitution〕
Characterizing feature of the invention according to claim 2, wherein the negative pressure valve, the supply-side charge circuit or tank fluid passage, wherein the connecting the supply circuit and the oil pressure tank, the supply-side charge circuit or said supply side There is a check valve that prevents the hydraulic oil from flowing from the circuit to the hydraulic tank and allows the hydraulic oil to flow from the hydraulic tank to the supply side charge circuit or the supply side circuit. The effect is as follows.

[Function and effect]
The negative pressure prevention valve was composed of a check valve. As a result, if the supply side charge circuit or the supply side circuit is in a negative pressure state, hydraulic fluid flows into the supply side charge circuit or the supply side circuit from the hydraulic tank side maintaining a constant pressure. , Eliminate the negative pressure state.
In this way, the hydraulic continuously variable transmission can be operated smoothly only by adding a simple component called a check valve.
According to a third aspect of the present invention, there is provided a check valve for preventing hydraulic fluid from flowing from the supply side circuit into the supply side charge circuit to the supply side charge circuit, and from the supply side circuit to the supply side charge. A relief valve that allows hydraulic oil to flow into the circuit is installed in parallel, and the relief pressure of the relief valve of the return side charge circuit is set lower than the relief pressure of the relief valve of the supply side charge circuit. It is in a certain point.

  A multipurpose vehicle which is an example of a work vehicle will be described. As shown in FIG. 1, the work vehicle includes a pair of left and right steerable front wheels 1 and a pair of left and right rear wheels 2, an engine 3 between the front and rear wheels, a seat 5 at the front of the traveling machine body 4, and an awning frame 6. The driving unit 7 is provided, and a dump bed 9 that is swung up and down by a hydraulic cylinder 8 is provided at the rear part of the traveling machine body 4.

As shown in FIGS. 1 and 2, a mission case 11 is disposed between the front and rear wheels 1 and 2, and the engine 3 is mounted on the side surface of the front end portion of the mission case 11. A hydrostatic continuously variable transmission 12 is mounted on the side opposite to the mounting surface of the engine 3 in the transmission case 11, receives the engine output, shifts continuously, and outputs the shift output to the auxiliary transmission 13. It is comprised so that it may do. The auxiliary transmission 13 can shift two steps in the forward direction and one step in the reverse direction.
The output from the auxiliary transmission 13 is transmitted to the left and right axles 15 via the rear wheel differential mechanism 14 and used for driving the rear wheels.

  The transmission system to the front wheel 1 and the transmission system to the rear wheel 2 are equipped with multi-plate brakes 45 and 46, respectively. As shown in FIG. 7, the front wheel brake 45 is configured to perform a pressure contact operation of the friction plate group by displacing an internal piston (not shown) by a hydraulic operation. The brake 46 for the rear wheel is configured to perform a pressure contact operation of the friction plate group by swinging the brake operation lever 40 with an operation cylinder 41 and rotating an internal cam (not shown). . The brake 45 for the front wheel and the operation cylinder 41 are connected by piping to a master cylinder 43 operated by a brake pedal 42 provided at the foot of the operation unit 7, and pressure oil is supplied from the master cylinder 43 by depressing the brake pedal 42. As a result, the front wheel brake 45 is braked according to the operating oil pressure, the operating cylinder 41 is retracted, and the rear wheel brake 46 is braked according to the operating oil pressure. By releasing the depression, the operating oil pressure disappears and the brakes 45 and 46 return to the brake release state.

  The brake operating lever 40 is connected to a parking lever 44 provided in the driving unit 7 by wire, and only the brake 46 of the left and right rear wheels 2 is operated by holding the parking lever 44 in the “parking” position. Parking is done by braking.

  A transmission structure from the engine 3 to the hydrostatic continuously variable transmission 12 will be described. As shown in FIGS. 2 and 3, a flywheel 3B is attached to the first output shaft 3A of the engine 3, and the second output shaft 3C is extended from the flywheel 3B. The second output shaft 3C and the hydrostatic continuously variable A first gear transmission mechanism 17 is provided between the input shaft 12 </ b> A of the transmission 12. The flywheel 3B, the first and second output shafts 3A, 3C are located in an output case 11A that connects the engine 3, and a protruding portion that protrudes toward the hydrostatic continuously variable transmission 12 of the output case 11A. An output gear 17A of the first gear transmission mechanism 17 is arranged at 11a.

  That is, as shown in FIG. 2, the output gear 17 </ b> A is attached to the second output shaft 3 </ b> C and is rotatably supported in the protruding portion 11 a via the bearing. An outward boss portion 11b is formed adjacent to the protruding portion 11a of the output case 11A, and the input gear 17B of the first gear transmission mechanism 17 is supported by a bearing on the outward boss portion 11b. The input gear 17B is externally fitted to an input shaft 12A extending from the hydrostatic continuously variable transmission 12, and is configured to transmit engine power to the hydrostatic continuously variable transmission 12.

  The configuration of the hydrostatic continuously variable transmission 12 will be described. As shown in FIG. 2, the hydrostatic continuously variable transmission 12 includes a main hydraulic motor M, a sub hydraulic motor SM, and a hydraulic pump P that supplies pressure oil to them. The main hydraulic motor M is housed in a boss portion 11 </ b> B that protrudes outward from one side surface of the mission case 11. The sub hydraulic motor SM is housed in a motor case 19 that is mounted and fixed via a hydraulic port block 18 that is mounted so as to close the open end of the boss portion 11B that houses the main hydraulic motor M. The hydraulic pump P is attached and fixed to a pump case 20 that is attached and fixed to the hydraulic port block 18 together with the motor case 19.

  The hydraulic pump P is an axial plunger variable displacement pump, the main hydraulic motor M is an axial plunger fixed motor, and the auxiliary hydraulic motor SM is an axial plunger variable displacement motor. The hydraulic pump P is attached to the input shaft 12A passing through the hydraulic port block 18 and reaching the output case 11A, and the main and auxiliary hydraulic motors M and SM are attached to the common output shaft 16 to the auxiliary transmission 13. is there.

The auxiliary transmission 13 will be described. As shown in FIGS. 2 and 3, the input shaft 31 of the auxiliary transmission device 13 is installed in the transmission case 11, and the input shaft 31 is arranged at a concentric position with the common output shaft 16. The shaft end is fitted into the shaft end of the input shaft 31 and is spline-engaged so that power is supplied to the input shaft 31 from the hydrostatic continuously variable transmission 12.
The input shaft 31 is integrally formed with a large-diameter gear portion 31A for high speed, a small-diameter gear portion 31B for low speed, and a reverse gear portion 31C.

A first transmission shaft 32 is installed in parallel with the input shaft 31. The first transmission shaft 32 includes a large-diameter gear portion 31A formed on the input shaft 31, a small-diameter input gear 32A that normally bites, a small-diameter gear portion 31B formed on the input shaft 31, a large-diameter input gear 32B that normally bites, and a reverse gear. The input gear 32C is attached in an idle state. Between the small-diameter input gear 32A and the large-diameter input gear 32B, and between the large-diameter input gear 32B and the reverse input gear 32C, there are provided first and second clutch sleeves 32D and 32E that are switched in a synchromesh manner. By engaging the first clutch sleeve 32D with the small diameter input gear 32A, the forward second speed power can be introduced from the large diameter gear portion 31A for the forward second speed. By bite the first clutch sleeve 32D to the large diameter input gear portion 32 B, can be introduced first forward speed power from the small diameter gear portion 3 1B for the first forward speed. Reverse power can be taken out by engaging the second clutch sleeve 32E with the reverse input gear 32C.

  As shown in FIGS. 2, 3, and 5, a reverse shaft 33 is installed in the transmission case 11 in parallel with the first transmission shaft 32, and a reverse gear 33 </ b> A is supported by a bearing on the reverse shaft 33. The reversing gear 33A is engaged with the reverse input gear 32C and the reverse gear 31C of the input shaft 31 to transmit a reverse output.

  A second transmission shaft 34 is installed in parallel between the first transmission shaft 32 and the axle 15, and a large-diameter transmission gear 34A is loosely fitted to the second transmission shaft 34, adjacent to the transmission gear 34A, A small-diameter output gear portion 34B is formed constant. An output gear 32F is externally fitted to the first transmission shaft 32 by a spline, and the output gear 32F and the transmission gear 34A of the second transmission shaft 34 are engaged with each other in a normal bite state, whereby the second transmission shaft 32 is engaged with the second transmission shaft 32. Power transmission to the transmission shaft 34 is possible.

  A rear wheel differential mechanism 14 is provided at the abutting position with the left and right axles 15, 15. The second transmission shaft 34 is configured to transmit power from the second transmission shaft 34 to the axle 15 by engaging the portion 34B in a normal manner. In FIG. 2, 51 is a differential lock operation tool.

  Next, the shift operation structure of the auxiliary transmission 13 will be described. As shown in FIGS. 3 and 5, a rotation operation shaft 35 is installed in parallel with the first transmission shaft 32, and a drum operation shaft 36 is installed in parallel with the rotation operation shaft 35, and this drum operation shaft 36 is operated. An interlocking operation shaft 37 is provided. A first shifter 35A and a second shifter 35B that engage with the first clutch sleeve 32D and the second clutch sleeve 32E are attached to the rotation operation shaft 35.

  The drum operating shaft 36 is provided with two spiral grooves 36a in the axial direction on the outer peripheral surface, and the two spiral grooves 36a are engaged with the first shifter 35A and the second shifter 35B, respectively. On the other hand, the first shifter 35A and the second shifter 35B are slidable in the axial direction of the drum operation shaft 36 and are attached so as not to rotate.

  The interlocking operation shaft 37 is linked to the auxiliary transmission operating tool. As shown in FIGS. 4 and 5, a fan-shaped drive gear 37 </ b> A is attached and fixed to the interlocking operation shaft 37. On the other hand, a passive gear 36A meshing with the sector drive gear 37A is attached to the drum operation shaft 36 so as to be integrally rotatable. When the interlocking operation shaft 37 is driven and rotated around its own axis, the sector drive gear 37A is Then, the passive gear 36A rotates and the drum operation shaft 36 rotates. When the drum operation shaft 36 rotates, the first shifter 35A and the second shifter 35B engaged with the spiral groove 36a are driven and moved along the axial direction of the rotation operation shaft 35.

When the first shifter 35A and the second shifter 35B are driven and moved, the clutch sleeves 32D and 32E engaged with the shifters 35A and 35B mesh with the large diameter input gear 32A, the small diameter input gear 32B, and the reverse input gear 32C. The state is created, and the speed change operation of the auxiliary transmission 13 is enabled.
Specifically, it is as follows. As shown in FIGS. 4 and 5, when the output arm 37B attached and fixed to the interlocking operation shaft 37 is set to the reverse operation position approaching the engine 3, the second shifter 35B slides to move the second clutch sleeve 32E. Is engaged with the reverse input gear 32C to reveal the reverse state.
Each time the output arm 37B is operated away from the engine 3, the output arm 37B can be switched between neutral, high speed, and low speed.

  A mechanism for positioning the shift operation position of the auxiliary transmission 13 will be described. As shown in FIGS. 4 and 5, a star-shaped positioning gear 38 is attached and fixed to the drum operation shaft 36 so as to be integrally rotatable, and a swing arm 39 is attached to the rotation operation shaft 35. A cam follower 39a is attached to the tip of the positioning gear 38, and the gear change operation position is positioned by engaging the cam follower 39a with a recess 38a formed on the outer peripheral surface of the positioning gear 38. The swing arm 39 is biased in the engagement direction by a torsion spring 39b.

  The hydraulic circuit of the hydrostatic continuously variable transmission 12 will be described. As shown in FIG. 6, the swash plate 52 of the hydraulic pump P is linked to a speed change operation tool 53 via a hydraulic servo mechanism 54. When the operation on the speed change operation tool 53 is released, the swash plate 52 is maintained back to neutral (swash plate angle 0 °), the supply of pressure oil is stopped, and a travel stop state is brought about. On the contrary, as the shift operation tool 53 is operated largely, the inclination angle of the swash plate 52 increases and the supply amount increases, and the common output shaft 16 of the main hydraulic motor M enters a high-speed rotation state.

  The hydraulic pump P and the main / sub hydraulic motors M and SM are connected in communication by closed circuits a and b formed inside the hydraulic port block 18. A part a of the closed circuits a and b is a supply side circuit on the high pressure side in which the pressure oil from the hydraulic pump P is supplied to the main and auxiliary hydraulic motors M and SM, and the other parts b of the closed circuits a and b are the main and auxiliary hydraulic circuits. This is a low-pressure-side return circuit that returns hydraulic oil from the hydraulic motors M and SM to the hydraulic pump P. The closed circuits a and b are connected to a charge oil passage c for replenishing the leakage, and the pressure oil from the charge pump CP driven by the power of the engine 3 is supplied via the supply oil passage e. c is supplied. The oil pressure replenished in the charge oil passage c is maintained at a set value by the relief valve 55.

  As shown in FIG. 6, the return side charge circuit c is connected to the return side circuit b from the hydraulic motor M to the hydraulic pump P in the hydrostatic continuously variable transmission 12. A check valve 65 for preventing the hydraulic fluid from flowing from the return circuit b to the return charge circuit c into the return charge circuit c, and allowing the hydraulic fluid to flow from the return circuit b into the return charge circuit c. The relief valve 48 and the throttle valve 49A are interposed in parallel. On the other hand, a supply side charge circuit c is connected to a supply side circuit a from the hydraulic pump P to the hydraulic motor M. A check valve 21 for preventing hydraulic fluid from flowing from the supply-side circuit a into the supply-side charge circuit c into the supply-side charge circuit c, and allowing hydraulic fluid to flow into the supply-side charge circuit c from the supply-side circuit a The relief valve 22 is interposed.

  The hydraulic servo mechanism 54 will be described. As shown in FIG. 6, the speed change operation tool 53 is mechanically linked to the servo valve 56 and the servo valve 56 is connected to the servo cylinder 57. The servo cylinder 57 is linked to the swash plate operating portion of the hydraulic pump P, and the displacement of the servo cylinder 57 is fed back to the servo valve 56 by the feedback mechanism 58. The swash plate 52 of the hydraulic pump P is operated corresponding to the position. The primary side oil passage f of the hydraulic servo mechanism 54 is connected to the charge oil passage c, and the system pressure of the hydraulic servo mechanism 54 is the same as the charge pressure.

  The swash plate 62 of the sub hydraulic motor SM is supported from the front and rear by the tip of the control piston 59 and the return piston 61 biased forward by the return spring 60. As shown in FIG. When retreating to the forward movement limit, the angle of the swash plate 62 in the sub hydraulic motor SM becomes neutral (swash plate angle 0 °), and as the control piston 59 advances backward against the return spring 60, the angle is increased. The angle of the plate 62 is increased, and the capacity of the sub hydraulic motor SM is increased. The return spring 60 is incorporated with initial compression, and the swash plate 62 is biased toward the neutral side with a preset spring load.

  The control piston 59 is connected to a supply side circuit a on the high pressure side that supplies pressure oil from the hydraulic pump P to the main / sub hydraulic motors M and SM via a control oil passage h, and the pressure of the supply side circuit a When the spring force of the return spring 60 is balanced, the angle of the swash plate 62 is stabilized.

The automatic transmission control operation using the control piston 59 will be described below.
When the transmission operating tool 53 is operated, the angle of the swash plate 52 in the hydraulic pump P is increased, and an amount of pressure oil corresponding to the swash plate angle is supplied to the main hydraulic motor M and the sub hydraulic motor SM. In this case, when the traveling load is in the range below the setting and the pressure in the supply side circuit a and the control oil passage h is below the setting, the return is more than the advance output of the control piston 59 receiving the pressure in the control oil passage h. The initial spring force of the spring 60 becomes larger, the swash plate 62 of the sub hydraulic motor SM is maintained neutral (swash plate angle 0 °), and the entire amount of pressure oil from the hydraulic pump P is supplied to the main hydraulic motor M. The common output shaft 16 is driven only by the main hydraulic motor M.

  When the traveling load exceeds the set range and the pressure in the supply side circuit a and the control oil passage h exceeds the set value, the advance output of the control piston 59 that receives the pressure in the control oil passage h is the initial spring of the return spring 60. As the force increases, the angle of the swash plate 62 of the sub hydraulic motor SM increases, generating a motor capacity in the sub hydraulic motor SM, and the pressure oil from the hydraulic pump P is transferred to the main hydraulic motor M and the sub hydraulic motor SM. Supplied. That is, when the traveling load increases beyond the set range, the total capacity on the motor side is automatically increased, the output shaft 32 is driven to decelerate, and the output torque is increased.

  When the traveling load further increases after the swash plate angle of the sub hydraulic motor SM becomes maximum with the increase in traveling load, the pressure in the supply side circuit a becomes higher. Here, the pressure of the part a acts as a reaction force that pushes the swash plate 52 of the hydraulic pump P back to the neutral side, and this reaction force is supported by the servo cylinder 57 in the hydraulic servo mechanism 54 during normal load. However, when the pressure of the supply side circuit a becomes particularly high as described above and the hydraulic reaction force applied to the swash plate 52 increases, the servo cylinder 57 operating at the same low system pressure as the charge pressure is inclined. The plate angle can no longer be maintained, and the swash plate 52 is automatically displaced in the direction in which the swash plate angle is automatically reduced by the hydraulic reaction force, that is, the deceleration side, and the pressure of the supply side circuit a is increased and output. Torque is increased.

  The shift operation tool 53 for operating the hydrostatic continuously variable transmission 12 is also linked to a speed adjusting mechanism (not shown) that changes the rotational speed of the engine 3 and has a function as an accelerator lever. The engine 3 is at an idling rotational speed in a stopped state where the speed change operation tool 53 is not operated, and the engine speed is increased as the travel speed is increased by operating the speed change operation tool 53.

A configuration for suppressing the generation of negative pressure during engine brake operation will be described. As shown in FIG. 6, the relief pressure of the relief valve 48 provided in the return side charge circuit c to the return side circuit b is applied to the relief valve relief provided in the supply side charge circuit c to the supply side circuit a. A bypass passage 49 is provided that bypasses the check valve 65 that prevents the hydraulic fluid from flowing from the return side circuit b to the return side charge circuit c, and has a pressure of about 60 percent compared to the pressure. 49 can be provided with an orifice 49A as a throttle valve to relieve the engine braking force of the hydrostatic continuously variable transmission 12 and achieve smooth deceleration without shock.

  More specifically, by providing the relief valve 48 and the orifice 49A, the engine brake works smoothly. That is, during normal travel, the supply circuit a is a high voltage circuit, and the return circuit b is a low voltage circuit (same as the charge circuit pressure). Here, when the brake pedal 42 is depressed and then the brake pedal 42 is returned, the hydraulic motor M or the like is reversely driven by the traveling machine body 4 so that the return side circuit b is on the high pressure side and the supply side circuit a is on the low pressure side. The reverse phenomenon occurs. Then, an abrupt engine braking force acts on the traveling machine body 4 and a shift shock is generated.

Therefore, as described above, the relief valve 48 and the orifice 49A are provided, and the pressure generated in the return side circuit b is always discharged by the orifice 49A to suppress the high pressure. The relief valve 48 copes with a high pressure that cannot be easily discharged by the orifice 49A.
With such a configuration, it is possible to suppress a sudden pressure increase in the return side circuit b and to prevent the engine brake from acting suddenly.
The reason why the relief pressure of the return side circuit b can be set lower than that of the supply side circuit a is that the hydrostatic continuously variable transmission 12 is used only in the normal rotation state. 13 is configured to appear.

However, as described above, the relief pressure of the relief valve 49A is set to 60% of the relief pressure of the supply side circuit a in order to alleviate the rapid increase in circuit pressure of the return side oil passage b by the orifice 49A and the relief valve 48. It is.
Then, since the relief pressure is low, the circuit pressures in the closed circuits a and b and the charge circuit c may be excessively reduced.
Therefore, by providing a tank oil passage 63 that communicates with the hydraulic tank T for the supply side circuit a that may become negative pressure when the engine brake is operated, and providing a negative pressure prevention valve 64 in the tank oil passage 63. The hydraulic oil in the hydraulic tank T can be sucked into the tank oil passage 63 to prevent a negative pressure state.

  As the negative pressure prevention valve 64, a check valve is used to prevent the hydraulic oil from flowing from the supply side circuit a to the hydraulic tank T, and to allow the flow from the hydraulic tank T to the supply side circuit a. A configuration is adopted in which the pivot is biased by the biasing spring 64A.

[Another embodiment]
(1) Although not shown, the supply side charge circuit c connected to the supply side circuit a may be selected as a target for providing the negative pressure prevention valve 64. That is, a tank oil passage may be provided from the supply side charge circuit c toward the hydraulic tank T, and the negative pressure prevention valve 64 may be provided in the tank oil passage.
(2) The throttle valve provided in the return side charge circuit c may be a narrow-diameter throttle path other than the orifice.
(3) The supply side charge circuit c may not be provided, and the charge circuit c may be connected only to the return side circuit b.
(4) As the hydraulic motor, only one of the fixed capacity type hydraulic motor M and the variable capacity type hydraulic motor SM may be employed.
(5) The brake operating tool 42 may be an operating lever type other than the pedal type.
(6) Although the multi-purpose work vehicle has been described as the work vehicle, it may be another work vehicle such as an agricultural tractor.

Overall side view of work vehicle Longitudinal rear view showing mission structure Longitudinal rear view showing auxiliary transmission Side view showing positioning mechanism of auxiliary transmission Cross-sectional plan view showing the shift operation structure of the auxiliary transmission Hydraulic circuit diagram of hydrostatic continuously variable transmission Configuration diagram showing brake operation structure

12 Hydrostatic continuously variable transmission 48 Relief valve 49A Orifice (throttle valve)
63 Tank oil passage 64 Check valve (Negative pressure check valve)
65 Check valve M Main hydraulic motor SM Sub hydraulic motor P Hydraulic pump T Hydraulic tank a Supply side circuit b Return side circuit c Supply side charge circuit, Return side charge circuit

Claims (3)

An operation comprising a hydraulic continuously variable transmission and a sub-transmission device to which a shift output of the hydraulic continuously variable transmission is input, and a reverse reverse state is generated by the auxiliary transmission. A car,
A return side charge circuit is connected to a return side circuit from the hydraulic motor to the hydraulic pump in the hydraulic continuously variable transmission, and hydraulic fluid flows into the return side charge circuit from the return side circuit to the return side charge circuit. A check valve that prevents the hydraulic oil from flowing from the return side circuit to the return side charge circuit, and a throttle valve in parallel, and the throttle valve in the return side charge circuit. A work vehicle that is directly connected and provided with a negative pressure prevention valve in at least one of a supply side charge circuit or a supply side circuit to prevent the circuit pressure from becoming negative due to a brake operation. Wherein a negative pressure valve, the tank oil passage for connecting the supply-side charge circuit or said supply side circuit and the oil pressure tank, flows from said supply-side charge circuit or said supply side circuit of the hydraulic oil to the hydraulic tank The work vehicle according to claim 1, further comprising a check valve that prevents hydraulic oil from flowing into the supply side charge circuit or the supply side circuit from the hydraulic tank. A check valve for preventing hydraulic fluid from flowing from the supply circuit to the supply charge circuit to the supply charge circuit, and allowing hydraulic fluid to flow from the supply circuit to the supply charge circuit. 3. The relief valve according to claim 1, wherein a relief valve is provided in parallel, and a relief pressure of the relief valve of the return side charge circuit is set lower than a relief pressure of the relief valve of the supply side charge circuit. Work vehicle.

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