JPH06206460A - Four-wheel drive vehicle - Google Patents

Abstract

PURPOSE:To prevent the occurrence of unpleasant vibration and noise by easily suspending even only one hydraulic motor in a 4WD car which drives auxiliary wheels by two hydraulic motors. CONSTITUTION:Working oil delivered from a hydraulic pump 12, is divided by a difference control valve 14 having nine (9) parts and capable of changing over seven (7) positions, so that hydraulic motors 16L and 16R are thereby driven. The valve positions indicated in the figure permits pump pressure to be built up in input-output ports 16Li, 16Lo and 16Ri, and also permits tank pressure to be built up in an output port 16Ro. Therefore, this constitution makes the difference in pressure applied to the input-output ports 16 Li and 16 Lo zero at all times, so that the hydraulic motor 16L is suspended, and meanwhile, the hydraulic motor 16R is normally rotated. In this case, when the hydraulic motor 16L acts even as a pump so as to deliver working oil while being subjected to external force, since pump pressure is instantly built up within pipe lines, neither cavitation nor the like is generated, so that unpleasant vibration and noise thereby do not cause. Since pump pressure guarantees a condition where there exist no pressure difference between the input-output ports 16Li and 16Lo, pressure balance is hardly changed even at the time of high revolutions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-wheel drive vehicle in which an engine drives main drive wheels and a hydraulic motor drives auxiliary drive wheels.

[0002]

2. Description of the Related Art In recent years, four-wheel drive vehicles have rapidly increased with the diversification of automobile applications. Of these, the main drive wheels are driven via a power transmission device including a transmission and a differential, and the hydraulic pump is driven by the power generated by the engine,
A four-wheel drive vehicle has been proposed in which a sub-drive wheel is driven by a hydraulic motor that is rotated by hydraulic power supplied from this hydraulic pump.

In the four-wheel drive vehicle as described above, the supply of the pressure fluid is stopped and the drive of the hydraulic motor is stopped when the driving force is not required, for example, when the vehicle is braked. However, since the drive shaft of the hydraulic motor is not fixed, even if the supply of the pressurized liquid is stopped, the hydraulic motor may be rotated by an external force such as a vibration of the vehicle body or a reaction force from the road surface. When the drive shaft of the hydraulic motor is rotated in this way, the hydraulic motor acts as a pump, and the pressurized liquid is delivered upstream or downstream of the hydraulic motor. As a result, on the side where the pressure fluid is discharged, a sudden high pressure is generated and pulsates irregularly, or on the side where the pressure fluid is sucked in, a negative pressure is generated and cavitation occurs. , Occasionally, noise or vibration was generated which was unpleasant for the driver.

The applicant of the present application filed Japanese Patent Application No. 3-3
No. 41241 proposes a four-wheel drive vehicle having a configuration shown in FIG. 8 and solves some of the problems described above. In this four-wheel drive vehicle, the hydraulic pump 100 has a drain tank 102.
Intake hydraulic oil from the
Discharge the hydraulic oil at the flow rate. The discharge port of the hydraulic pump 100 is a 4-port 3-position directional control valve 104 and pressure control valve 10.
The pressure of the hydraulic oil discharged from the hydraulic pump 100 is adjusted by the pressure control valve 106. The hydraulic oil having the adjusted pressure is supplied to drive the hydraulic motors 108L and 108R. Further, the hydraulic oil that has passed through the hydraulic motors 108L and 108R passes through the distribution / collection valve 110 and the direction control valve 104, and then the drain tank 102.
Is discharged to.

In this four-wheel drive vehicle, the hydraulic motor 10
When stopping the driving of 8L and 108R, the directional control valve 1
04 to the position B, and the distribution / collection valve 110
Open up. As a result, the hydraulic pump 100 and the drain tank 102 communicate with each other to release the pump pressure, and the upstream and downstream of the hydraulic motors 108L and 108R communicate with each other.
The pressure difference disappears. As a result, the hydraulic motors 108L, 1
The supply of hydraulic oil to the 08R is stopped, and the hydraulic motor 108
L and 108R are no longer driven.

At this time, the hydraulic motor 108 is driven by an external force.
Even if the drive shafts of L and 108R are rotated, the hydraulic oil on the discharge side is discharged to the drain tank 102, and the hydraulic oil on the suction side is replenished by the pressure in the drain tank 102. As a result, the pressure in the pipe immediately becomes the same as that of the drain tank 102, and the above-mentioned unpleasant noise and vibration are unlikely to occur.

On the other hand, in the above-described four-wheel drive vehicle, control is also performed to stop the driving of only one of the hydraulic motors 108L and 108R. For example, the left hydraulic motor 108L
Is higher than the rotation speed of the right hydraulic motor 108R (when the left wheel is in a slip state, etc.), the load of the left hydraulic motor 108L with respect to the hydraulic pump 100 is the load of the right hydraulic motor 108R. The hydraulic oil discharged from the hydraulic pump 100 flows through the left hydraulic motor 108L. Then, hydraulic oil is not supplied to the right hydraulic motor 108R, and it becomes impossible to drive the right wheel. Therefore, in this prior application, the distribution / collection valve 110 is operated to narrow the flow passage on the left wheel side to increase the load. As a result, the driving force of the left hydraulic motor 108L is reduced and the hydraulic oil can be supplied to the right hydraulic motor 108R, so that the left and right wheels can be rotationally driven with an appropriate driving force.

[0008]

However, when the left hydraulic motor 108L is rotated by an external force when the distribution / collection valve 110 is throttled in this way, the distribution / collection of the left hydraulic motor 108L is performed. The pressure with the valve 110 varies. However, in response to this pressure fluctuation, the hydraulic oil is not immediately supplied or discharged, and thus the unpleasant noise and vibration described above may occur. In order to prevent this pressure fluctuation, the pressure control valve 106 that determines the upstream pressure of the left hydraulic motor 108L and the distribution / collection valve 11 that determines the downstream pressure.
A method of controlling 0 and an appropriate pressure can be considered, but
Two valves had to be adjusted by complicated feedback control, which was not realistic.

Further, for example, the hydraulic motor 1 may be operated during high-speed traveling.
When the driving of the 08L and 108R is stopped, the left and right wheels rotate at high speed to increase the amount of hydraulic oil that the hydraulic motors 108L and 108R send out like a pump, so that the hydraulic oil is sent out and decreases due to flow path resistance. There is also a risk that unpleasant noise and vibration due to the above-mentioned cavitation may occur because the hydraulic oil on the side cannot be replenished.

In view of the above, the present invention aims at enabling a hydraulic motor to be stopped in a four-wheel drive vehicle having drive wheels driven by two hydraulic motors, without causing unpleasant vibration or noise even with only one of them. A second object is to make it possible to stop the hydraulic motor without generating unpleasant vibration or noise even when the hydraulic motor is in a high rotation state.

[0011]

The present invention has the following means for solving the problems in order to achieve the above-mentioned first object. That is, as described in claim 1,
A power transmission device that is rotationally driven by the power of the engine, a main drive wheel that is rotationally driven by the power transmission device, a hydraulic pump that discharges pressure liquid by the power of the engine, and a supply of the pressure liquid that is discharged. Two hydraulic motors that are rotationally driven, a direction control valve that switches the hydraulic liquid supply direction to the hydraulic motors according to the valve position, and rotates the hydraulic motors forward, reverse, and stop, and the two hydraulic liquids. In a four-wheel drive vehicle including sub-drive wheels whose left and right are driven to rotate by a pressure motor, the directional control valve makes a pressure difference between an upstream side and a downstream side of the hydraulic motor zero, and the pressure difference zero. In order to ensure the above condition, the hydraulic motor is stopped by switching to a valve position that forms a flow path capable of supplying and discharging the hydraulic liquid both upstream and downstream of the hydraulic motor. , Especially one liquid Construction of a four-wheel drive vehicle, characterized in that also have only a one wheel stop valve stopping position the motor is it.

According to the four-wheel drive vehicle of the present invention having the above structure, when the valve position of the directional control valve is switched, the pressure difference between the upstream side and the downstream side of the hydraulic motor becomes zero and the driving of the hydraulic motor is stopped. To be done. Further, at this time, even if the drive shaft of the hydraulic motor is rotated by an external force, by discharging the pressure liquid from the pressure liquid increasing side pipe and by supplying the pressure liquid to the pressure liquid decreasing side pipe, Since the state in which the pressure difference is zero is guaranteed, the pressure inside the pipe does not fluctuate greatly in part. In particular, since it also has a one-wheel stop valve position, even when only one hydraulic motor is stopped, the same supply / discharge of the pressure liquid is performed, and it is possible to stop without changing the pressure.

In order to achieve the above-mentioned second object,
Configured as follows. That is, as described in claim 2, a power transmission device that is rotationally driven by the power of the engine, a main drive wheel that is rotationally driven by the power transmission device, and a hydraulic pump that discharges pressure liquid by the power of the engine. , Two hydraulic motors that are rotationally driven by the supply of the discharged hydraulic fluid, and the direction in which the hydraulic fluid is supplied to the hydraulic motors is switched depending on the valve position, and the hydraulic motors are normally rotated, reversed, and stopped. In a four-wheel drive vehicle that includes a directional control valve and a sub-drive wheel whose left and right are driven to rotate by the two hydraulic motors, the directional control valve includes a pressure difference between an upstream side and a downstream side of the hydraulic motor. And a valve position forming a flow path through which the discharge pressure from the hydraulic pump is simultaneously guided to both the upstream side and the downstream side of the hydraulic motor so that the state where the pressure difference is zero is ensured. Switched to Construction of a four-wheel drive vehicle, characterized in that it is configured to stop the hydraulic motor is therewith.

According to the four-wheel drive vehicle of the present invention having the above-described structure, the discharge pressure from the hydraulic pump is introduced upstream and downstream of the hydraulic motor, so that the drive shaft of the hydraulic motor is driven by an external force. Thus, even in the high rotation state, the pressure liquid is more quickly supplied to the pipe on the pressure liquid reducing side, and the pressure difference between the upstream and the downstream can be kept zero without changing the pressure.

[0015]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is an overall schematic diagram showing the configuration of the present invention.
In this four-wheel drive vehicle, the rear wheels are main drive wheels driven by a conventionally known power transmission device, and the front wheels are auxiliary drive wheels driven by a hydraulic circuit.

In FIG. 1, the engine 1 is connected to the left and right rear wheels 5RL, 5RR via a power transmission mechanism 3, and mechanically transmits the power of the engine 1 to drive the left and right rear wheels 5RL, 5RR. . The power transmission mechanism 3 is a well-known one including a clutch, a transmission, a propulsion shaft, a differential gear, a drive shaft, and the like.

The engine 1 is also connected to a hydraulic pump 12 via a pulley belt 10. The hydraulic pump 12 sends hydraulic oil to the directional control valve 14, and the directional control valve 14 distributes the hydraulic oil to the hydraulic motors 16L and 16R, and switches the flow paths to control the hydraulic motors 16L and 16R.
Change the rotation direction of. The hydraulic motors 16L and 16R are
The left and right front wheels 5FL and 5FR connected to each other are driven.

Further, each wheel 5FL, 5FR, 5RL, 5
The RR includes wheel speed sensors 20 and 2 for detecting the rotation speed.
0, 20, 20, a steering sensor 24 that detects the steering angle of the steering wheel 22, and an electronic control unit 26 (hereinafter referred to as ECU 26) that controls the directional control valve 14 based on detection signals from these sensors. It is provided.

Next, regarding the hydraulic circuit for driving the front wheels,
This will be described in detail with reference to FIG. A pressure control valve 30 is arranged in parallel with the hydraulic pump 12. Pressure control valve 30
Is an electromagnetic proportional pressure control valve in which the opening degree of the valve is adjusted by the ECU 26, and a part of the hydraulic oil delivered by the hydraulic pump 12 is returned to the drain tank 32 according to the opening degree to adjust the hydraulic pressure. There is.

The left hydraulic motor 16L has an input port 16Li into which hydraulic oil flows when the drive shaft of the hydraulic motor rotates in the forward direction of the vehicle, and an output port 16Lo from which hydraulic oil flows out. When moving backward, hydraulic oil flows in through the output port 16Lo and flows out through the input port 16Li. This left hydraulic motor 16L is used for the left front wheel 5F.
It is joined to L by a constant velocity ball joint or the like, and is arranged to transmit the rotational force to the wheels. The right hydraulic motor 16R has the same input port 16Ri and output port 16Ro and drives the right front wheel 5FR.

The directional control valve 14 is a 7-position switching valve having 9 ports, and an actuator such as a step motor (not shown) controlled by the ECU 26 causes the cylindrical rotary valve to move to seven positions shown in FIG. It can be switched. The directional control valve 14 is formed with nine ports 14a to 14i.
b and 14c are connected to the hydraulic oil discharge side of the hydraulic pump 12, and the ports 14d, 14e and 14f are connected to the drain tank 32. The port 14g is connected to the input ports 16Li and 16Ri of the hydraulic motors 16L and 16R by a bifurcated pipe.
h and 14i are connected to the output ports 16Lo and 16Ro of the hydraulic motors 16L and 16R, respectively.

Inside the directional control valve 14, by switching the valve position, one of the ports 14a and 14d is connected to the port 14g, one of the ports 14b and 14e is connected to the port 14h, and further, the ports 14c and 14f are connected. Either one communicates with the port 14i. Of these ports 14a to 14f, the ports that do not communicate with the ports 14g to 14i are in a closed state.

Next, the seven valve positions of the directional control valve 14 will be described. In the following description, for the sake of convenience, the hydraulic pressure adjusted by the hydraulic pump 12 and the pressure control valve 30 will be referred to as pump pressure, and the pressure in the drain tank 32 will be referred to as tank pressure. First, FIG. 2 shows the valve position when both wheels are stopped. This valve position is used when the vehicle is being braked or when it is desired to switch from four-wheel drive to rear-wheel drive.

In FIG. 2, port 1 of the directional control valve 14
4a communicates with 14g, and the pump pressure is applied to the input ports 16Li and 16Ri of the hydraulic motors 16L and 16R. Also,
The port 14b communicates with 14h and the port 14c communicates with 14i, and the output port 1 of the hydraulic motors 16L and 16R is connected.
6Lo and 16Ro also become pump pressure. Therefore, the upstream and downstream pressures of both the hydraulic motors 16L and 16R become equal, and the hydraulic motors 16L and 16R stop.

At this time, the input / output ports 16Li, 16R
Pump pressure is applied to i, 16Lo, 16Ro, and this hydraulic circuit is kept at a constant pressure by the pressure control valve 30. When the drive shafts of the hydraulic motors 16L and 16R are moved by external force, the pressure is immediately guaranteed by the discharge pressure from the pump on the side where the hydraulic oil is reduced by the pump action of the hydraulic motors 16L and 16R.
On the side where the hydraulic oil increases, the increased hydraulic oil overflows from the pressure control valve 30 and both become pump pressure.

As a result, both sides maintain the state of pump pressure, the pressure balance in the pipe is maintained, cavitation is not generated, and unnecessary vibration and noise from the hydraulic motors 16L and 16R are not generated. . Next, FIG. 4 shows the valve position during forward movement.

In FIG. 4, port 1 of the directional control valve 14
4a communicates with the port 14g, and hydraulic motors 16L, 16
The pump pressure is applied to the R input ports 16Li and 16Ri.
Further, the port 14h communicates with 14e and the port 14i communicates with 14f, and the output port 1 of the hydraulic motors 16L and 16R is connected.
6Lo and 16Ro are tank pressure. Therefore, the hydraulic motors 16L and 16R are connected from the input port 16Li to the output port 16Lo and from the input port 16Ri to the output port 16L.
The hydraulic oil flows to Ro to generate torque. Generally, the torque generated by the hydraulic motor is roughly proportional to the pressure applied to the hydraulic motor, and therefore, as shown in FIG.
When L and 16R are arranged in parallel, the left and right hydraulic motors 16L and 16R generate substantially equal torque, and the left and right wheels also generate substantially equal driving force.

Next, FIG. 5 shows the valve positions for stopping the left front wheel while rotating the right front wheel forward. This state is used when it is desired to reduce the turning radius when turning left or when the left front wheel is in a slip state. The ECU 26 receives the detection signals from the wheel speed sensor 20 and the steering sensor 24 to determine that the right wheel and the left wheel have different rotational speeds due to turning or slipping.

In FIG. 5, port 1 of the directional control valve 14
4a communicates with 14g and port 14b communicates with 14h, and pump pressure is applied to the input / output ports 16Li and 16Lo of the left hydraulic motor 16L and the input port 16Ri of the right hydraulic motor 16R. On the other hand, the port 14f communicates with 14i, and the output port 16Ro of the right hydraulic motor 16R becomes the tank pressure. Therefore, the left hydraulic motor 16L stops when the upstream and downstream pressures become equal. On the other hand, the right hydraulic motor 16R
Causes the hydraulic oil to flow from the input port 16Ri to the output port 16Ro to generate torque.

At this time, the left hydraulic motor 16L is in the same state as the two-wheel stop described with reference to FIG.
The pressure balance in the pipe is maintained, cavitation does not occur, and unnecessary vibration or noise from the hydraulic motor 16L does not occur. Next, the valve position when retracting is shown in FIG.
Shown in. In the present embodiment, the hydraulic motor 16 is used to move the vehicle forward and backward.
This is achieved by changing the rotation directions of L and 16R.

In FIG. 6, port 1 of the directional control valve 14
4d communicates with 14g, and the tank pressure is applied to the input ports 16Li and 16Ri of the hydraulic motors 16L and 16R. On the other hand, the port 14b communicates with 14h and 14c communicates with 14i, and the output ports 16L of the hydraulic motors 16L and 16R are connected.
o and 16Ro are pump pressure. Therefore, the hydraulic motor 1
6L and 16R are from the output port 16Lo to the input port 1
6Li, output port 16Ro to input port 16Ri
Hydraulic fluid flows to generate torque. Since the flow of this hydraulic oil is opposite to that in the forward movement, the hydraulic motors 16L, 1
6R rotates in reverse. At this time, the left and right wheels generate substantially the same driving force for the same reason as when moving forward.

Next, FIG. 7 shows valve positions for stopping the left front wheel while rotating the right front wheel backward. This state is used when it is desired to reduce the turning radius of the left turn when the vehicle is moving backward, or when the left front wheel slips. In FIG. 7, the port 14c of the directional control valve 14 communicates with 14i, and the output port 16Ro of the right hydraulic motor 16R becomes the pump pressure. On the other hand, the port 14d communicates with 14g, the port 14e communicates with 14h, and the input / output port 16L of the left hydraulic motor 16L is connected.
i, 16Lo and the input port 16 of the right hydraulic motor 16R
Ri becomes the tank pressure. Therefore, the left hydraulic motor 16L
Stops when the upstream and downstream pressures become equal. On the other hand, in the right hydraulic motor 16R, hydraulic oil flows from the output port 16Ro to the input port 16Ri to generate torque.

At this time, the input / output ports 16Li and 16L
The hydraulic pressure applied to o is kept constant by communicating with the drain tank 32, and the pressure difference is always zero. Even when the drive shaft of the hydraulic motor 16L is moved by an external force, the drain tank 32 and the input / output port 16L are
The increased / decreased amount is supplied / exhausted in the pipe communicating between i and 16Lo to maintain the same pressure as in the drain tank 32. As a result, the pressure balance in the pipe is maintained and cavitation does not occur, so that unnecessary vibration and noise from the hydraulic motor 16L do not occur.

By the way, in the case of right forward and left stop, the pump pressure is introduced to the input / output ports 16Li and 16Lo as shown in FIG. 5 so that the decreasing hydraulic oil is quickly supplied. However, normally, when moving backward, it is not as fast as when moving forward, and it is rare that the drive shaft is rotated at high speed by external force when the supply of hydraulic oil to the hydraulic motor 16L is stopped. Cavitation can be sufficiently prevented by simply supplying and discharging hydraulic oil.

Further, the directional control valve 14 shown in FIGS.
Valve position, or the directional control valve 14 shown in FIGS. 6 and 7.
By alternately switching the valve positions of 1 and 2, the driving force distribution of the left and right wheels can be controlled without completely stopping the left front wheel. Note that stopping only the right front wheel while rotating the left front wheel forward or backward means switching only the left front wheel by switching to the valve positions shown in FIGS. 3 (D) and 3 (G), respectively. Can be done in the same way.

As described above, in this four-wheel drive vehicle, all of the two-wheel stop, the two-wheel forward, the one-wheel forward one-wheel stop, the two-wheel backward, and the one-wheel reverse one-wheel stop can be realized only by switching the directional control valve. Therefore, the control of driving force distribution and the like is simplified, and the load on the ECU 26 is reduced.

Further, the input / output ports 16Li, 16Lo or 16Ri, 16 of the hydraulic motor 16L or 16R to be stopped are stopped in both cases of stopping both wheels and one wheel.
Since the same pressure is stably applied to Ro, a state in which no pressure difference is generated is always maintained. Particularly, in this embodiment, since the hydraulic oil discharge side and the suction side pipe of the hydraulic motor 16L or 16R are in communication with each other, the hydraulic motor 16L can be operated without complicated control for eliminating the pressure difference.
Alternatively, the driving of 16R can be stopped.

Further, when the hydraulic motor 16L or 16R is in a stopped state, even if the drive shaft is rotated by an external force, the side where the hydraulic oil is discharged discharges the hydraulic oil through the pipe and sucks the hydraulic oil. On the other hand, since hydraulic oil is supplied through the pipe, pressure fluctuation due to the hydraulic motor 16L or 16R does not occur. As a result, cavitation or the like does not occur, and unpleasant vibration or noise does not occur. Particularly, in the present embodiment, the hydraulic oil from the hydraulic pump 12 or the drain tank 32 is always in a state in which it can sufficiently flow into and out of the pipe, so that the discharge pressure of the hydraulic pump 12 is controlled by the pressure control valve 30. No control is required regarding the supply and discharge of hydraulic fluid other than the adjustment by.

Although the embodiment of the present invention has been described above, the present invention is not limited to this, and various embodiments can be adopted without departing from the scope of the present invention. For example, although the four-wheel drive vehicle in which the front wheels are hydraulically driven has been shown in the embodiment, the driving means for the front wheels and the rear wheels may be exchanged, and the rear wheels may be hydraulically driven.

Further, in the embodiment, when both wheels are stopped, the input / output ports 16Li, 16Ri of the hydraulic motors 16L, 16R,
Although the pump pressure from the hydraulic pump 12 is guided to all of the 16Lo and 16Ro, since sufficient hydraulic oil flows in and out of the drain tank 32, cavitation does not occur even during high speed forward movement. If so, all of them may be connected to the drain tank 32 to maintain the pressure balance by the tank pressure.

Alternatively, the hydraulic pump 12 and the drain tank 32 can be simply connected to the input / output ports of each hydraulic motor.
It may not be connected to the flow path between and. Even this
The amount of hydraulic oil discharged from the hydraulic motors 16L and 16R and the amount of hydraulic oil sucked in are equal, and the pressure does not rise or fall as a whole.
In addition, since the pressure difference does not occur due to the communication, the same function can be achieved as long as the hydraulic oil sufficiently flows through the connected pipes.

Further, when the supply of the hydraulic oil to the hydraulic motors 16L and 16R is stopped, the wheels 5FL and 5FR are in a state in which the brakes are applied to some extent due to the resistance of the hydraulic oil. If a clutch is provided between 16R and the wheels 5FL and 5FR, the wheels 5
It is also easy to spin the FL and 5FR and switch to two-wheel drive mode. Alternatively, the wheels 5FL and 5FR may be driven to the extent that the directional control valve 14 is controlled to cancel the braking action without providing the clutch. Of course, if the hydraulic motors 16L and 16R can rotate at a sufficiently high speed, the braking action can be sufficiently canceled without the clutch.

In addition, the hydraulic pump 1 when both wheels are stopped
Since the discharge pressure of 2 does not have to be as high as the pressure required during traveling, the pressure control valve 30 is controlled to reduce the load on the hydraulic pump 12 and to reduce the power loss when the vehicle is stopped. Good.

[0044]

As described above, according to the four-wheel drive vehicle of the first aspect, control such as one-wheel stop, two-wheel stop, or switching between them can be easily performed, and further, it is uncomfortable while the hydraulic motor is stopped. No vibration or noise is generated.

According to the four-wheel drive vehicle of the second aspect,
Even when the hydraulic motor is in a high rotation state due to the rotation of the wheels while the hydraulic motor is stopped, the pressure difference between the upstream and downstream of the hydraulic motor is zero due to the discharge pressure of the hydraulic pump. Since this is ensured, the pressure balance in the pipe is less likely to be disturbed and the generation of unpleasant vibrations and noises can be suppressed more accurately than in the case of simply communicating via a drain tank.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a configuration as an embodiment.

FIG. 2 is a schematic configuration diagram showing a hydraulic circuit set to stop both wheels in the embodiment.

FIG. 3 is an explanatory diagram showing a switching position of the directional control valve in the embodiment.

FIG. 4 is a schematic configuration diagram showing a hydraulic circuit set for two-wheel forward movement in an embodiment.

FIG. 5 is a schematic configuration diagram showing a hydraulic circuit set to forward right wheel stop and left wheel stop in the embodiment.

FIG. 6 is a schematic configuration diagram showing a hydraulic circuit set to reverse both wheels in an embodiment.

FIG. 7 is a schematic configuration diagram showing a hydraulic circuit that is set to right wheel reverse and left wheel stop in the embodiment.

FIG. 8 is a schematic configuration diagram showing a conventional hydraulic circuit.

[Explanation of symbols]

1 ... Engine, 3 ... Power transmission device, 5FL, 5
FR, 5RL, 5RR ... Wheels, 10 ... Pulley belt, 12 ... Hydraulic pump, 14 ... Direction control valve,
16L, 16R ... Hydraulic motor, 20 ... Wheel speed sensor, 22 ... Steering, 24 ... Steering sensor, 26 ... Electronic control device, 30 ... Pressure control valve, 32 ... Drain tank.

Claims (2)

[Claims] 1. A power transmission device that is rotationally driven by the power of an engine, a main drive wheel that is rotationally driven by the power transmission device, a hydraulic pump that discharges pressure liquid by the power of the engine, and the discharge. Two hydraulic motors that are rotationally driven by the supply of the hydraulic liquid, and a directional control valve that switches the supply direction of the hydraulic liquid to the hydraulic motors according to the valve position to rotate the hydraulic motors forward, reverse, and stop. In a four-wheel drive vehicle including left and right auxiliary drive wheels that are rotationally driven by the two hydraulic motors, the directional control valve reduces a pressure difference between an upstream side and a downstream side of the hydraulic motor to zero. , The hydraulic motor is stopped by switching to a valve position that configures a flow path that allows the supply and discharge of the hydraulic fluid both upstream and downstream of the hydraulic motor so that the state of the pressure difference of zero is guaranteed. Configured to let In particular, a four-wheel drive vehicle also having a one-wheel stop valve position for stopping only one hydraulic motor. 2. A power transmission device that is rotationally driven by the power of the engine, a main drive wheel that is rotationally driven by the power transmission device, a hydraulic pump that discharges pressure liquid by the power of the engine, and the discharge. Two hydraulic motors that are rotationally driven by the supply of the hydraulic liquid, and a directional control valve that switches the supply direction of the hydraulic liquid to the hydraulic motors according to the valve position to rotate the hydraulic motors forward, reverse, and stop. In a four-wheel drive vehicle including left and right auxiliary drive wheels that are rotationally driven by the two hydraulic motors, the directional control valve reduces a pressure difference between an upstream side and a downstream side of the hydraulic motor to zero. , So that the state in which the pressure difference is zero is ensured, the liquid is switched to a valve position that constitutes a flow path through which the discharge pressure from the hydraulic pump is simultaneously guided both upstream and downstream of the hydraulic motor. Pressure motor A four-wheel drive vehicle configured to stop the vehicle.