JPH0658413A - Hst hydraulic pressure running driving device - Google Patents

Abstract

PURPOSE:To contrive running with inertia without newly providing a changeover valve for running with inertia. CONSTITUTION:Flow passages 10e, 10f are formed on a first pressure selective valve 10 which is changed over according to a changeover position of a forward/ reverse changeover valve 8, and introduces discharge pressure of a hydraulic pump 2 to a servo cylinder 11 or a changeover valve 12, for outputting the discharge pressure of the hydraulic motor 5. Output pressure of the flow passages 10e, 10f is introduced to a primary side of each of charging check valves 15, 16. When the discharge pressure of the hydraulic motor 5 exceeds intake pressure by releasing operation of an accelerating pedal, the check valves 15, 16 are opened for releasing the discharge pressure of the hydraulic motor 5 to the intake side, and making a vehicle run with inertia.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an HST hydraulic traveling drive system used in a work vehicle such as a wheel loader.

[0002]

2. Description of the Related Art As a hydraulic traveling drive system for a work vehicle such as a wheel loader, for example, as disclosed in Japanese Utility Model Publication No. 3-59552, a variable displacement hydraulic pump driven by a prime mover and a variable displacement by a pair of main pipes. There is known an HST hydraulic traveling drive device including a hydraulic motor that is connected to a variable hydraulic pump in a closed circuit and that is driven by oil discharged from the variable displacement hydraulic pump. In this HST hydraulic traveling drive system, the displacement of the variable displacement hydraulic pump is changed according to the number of revolutions of the prime mover by the depression of the accelerator on the driver's seat, and the number of revolutions of the hydraulic motor is changed according to the amount of pump discharge. Increase or decrease the traveling speed of the work vehicle. Further, in the drive device disclosed in this publication, a pair of main pipes is
Connected to the charge circuit via a position-type electromagnetic switching valve, the discharge side of the hydraulic motor is opened to the tank via the charge relief valve by switching the electromagnetic switching valve when the vehicle is moving forward or backward. It is possible.

In such an HST hydraulic traveling drive system, when the electromagnetic switching valve is switched to the closed position, the flow rate of the variable displacement hydraulic pump is decreased by loosening the accelerator pedal (deceleration operation), A closing pressure is generated on the discharge side of the motor to decelerate the vehicle. On the other hand, when the solenoid switching valve is switched to the open position, the discharge oil of the hydraulic motor flows out to the tank through the charge relief valve by the loosening operation of the accelerator pedal, so a large closing pressure on the discharge side of the hydraulic motor. Does not occur and the vehicle runs inertially.

[0004]

In the device described in the above publication, an electromagnetic switching valve is newly added between the pair of main pipelines and the charge circuit in order to realize inertial traveling, so the number of parts is increased. As a result, the cost is increased, and a space for installing the electromagnetic switching valve is required, which increases the size of the device.
Moreover, since the pressure of the pair of main pipes acts on the solenoid directional control valve, sufficient pressure resistance performance must be given, which further increases the cost, and the size of the solenoid directional control valve is significantly increased to secure the installation space. It can be difficult.

An object of the present invention is to provide an HST hydraulic traveling drive system capable of realizing inertia traveling without newly providing a switching valve for inertia traveling.

[0006]

The present invention will be described with reference to FIG. 1 showing an embodiment. In the present invention, a hydraulic pump 2 driven by a prime mover 1 and a hydraulic pump 2 with a pair of main pipe lines 3 and 4. A variable displacement hydraulic motor 5 which is connected in a closed circuit and is driven by oil discharged from the hydraulic pump 2, and one of the pair of main pipelines 3 and 4 which is one of the main pipelines 3 (4) on the discharge side of the hydraulic pump 2. ) Pressure selection valve 10 for selecting and outputting pressure
And motor capacity control means 11 and 12 that is driven by the discharge pressure of the hydraulic pump 2 output from the pressure selection valve 10 to increase or decrease the discharge capacity of the hydraulic motor 5, and a pair of check valves 15 and 16 for backflow prevention. To a pair of main pipelines 3 and 4 via a charging means 6 for supplying pressure oil when the pressure in the main pipelines 3 and 4 drops below a predetermined value. Applied. The above-mentioned purpose is to provide the pressure selection valve 10 with the flow passage 10e for outputting the pressure of the other main pipeline 4 (3) on the discharge side of the hydraulic motor 5.
(10f) is provided and the discharge pressure of the hydraulic motor 5 output from the flow path 10e (10f) is guided to the primary side of the check valves 15 and 16.

[0007]

When the vehicle is traveling, the discharge pressure of the hydraulic motor 5 is output from the flow passage 10e (10f) of the pressure selection valve 10 and guided to the primary side of the check valves 15 and 16. When the accelerator pedal is loosened in this state and the discharge pressure of the hydraulic pump 2 falls below a predetermined value, the check valve 15 (16) opens and the primary side of the main line 3 becomes the suction side of the hydraulic motor 5.
Communicate with (4). As a result, the discharge pressure of the hydraulic motor 5 is guided to the suction side, and the vehicle runs inertially.

Incidentally, in the section of means and action for solving the above-mentioned problems for explaining the constitution of the present invention, the drawings of the embodiments are used to make the present invention easy to understand. It is not limited to.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, reference numeral 1 is a prime mover (for example, a diesel engine) of a wheel loader according to the present embodiment, and a variable displacement hydraulic pump 2 driven by the prime mover 1 includes a hydraulic motor 5 with a pair of main pipes 3 and 4. Are connected in a closed circuit. The discharge capacity of the variable displacement hydraulic pump 2 is controlled by a fixed displacement charge pump 6 that discharges pressure oil at a flow rate according to the rotation speed of the prime mover 1.
That is, a part of the oil discharged from the charge pump 6 is guided to the forward / reverse switching valve 8 via the throttle 7, while the rest is directly guided to the forward / reverse switching valve 8 without passing through the throttle 7, and These discharged oils are guided to the oil chambers 9a and 9b of the tilt cylinder 9 according to the switching position of the forward / reverse switching valve 8.
The pressure difference between the upstream side and the downstream side of the throttle 7 changes according to the discharge flow rate of the charge pump 6, the tilt cylinder 9 is driven by this pressure difference, and the tilt angle of the hydraulic pump 2 changes. The discharge capacity increases or decreases. When the forward / reverse switching valve 8 is in the F position, pressure oil is discharged to the main pipe line 3 to move the vehicle forward,
When the forward / reverse switching valve 8 is at the R position, pressure oil is discharged to the main pipe line 4 and the vehicle moves backward. When the forward / reverse switching valve 8 is at the neutral position, the oil chambers 9a and 9b have the same pressure, the piston 9c is returned to the neutral position by the spring 9d, and the discharge capacity of the hydraulic pump 2 becomes zero.

The pressure before and after the throttle 7 is supplied to the pilot line 10 of the three-position type pressure selection valve 10 via the forward / reverse switching valve 8.
The pressure selection valve 10 is also switched and controlled according to the pressure difference between the pressure a and the pressure a. When the forward / reverse switching valve 8 is in the F position, the pressure selection valve 10 is switched to the A position, and the discharge pressure of the hydraulic pump 2 is guided from the main pipe line 3 to the servo cylinder 11 and the switching valve 12 via the pressure selection valve 10. . on the other hand,
The oil discharged from the hydraulic motor 5 flows out from the main pipe 4 to the tank via the pressure selection valve 10 and a charge relief valve 14 described later, whereby so-called flushing is performed. When the forward / reverse switching valve 8 is at the R position, the pressure selection valve 10 is switched to the B position, and the discharge pressure of the hydraulic pump 2 is guided from the main pipe line 4 to the servo cylinder 11 and the switching valve 12 via the pressure selection valve 10. . Further, the oil discharged from the hydraulic motor 5 flows out from the main pipe 3 to the tank via the pressure selection valve 10 and the charge relief valve 14 described later.

The servo cylinder 11 and the switching valve 12 control the discharge capacity of the hydraulic motor 5, and the pressure selection valve 1
When the discharge pressure of the hydraulic pump 2 output from 0 and guided to the pilot line 12a of the switching valve 12 is equal to or lower than the pressure set by the spring 12s, the switching valve 12 is held in the H position and the piston 11a of the servo cylinder 11 is operated. The discharge pressure of the hydraulic pump 2 acts only on the end surface on the small diameter side, and the discharge capacity of the hydraulic motor 5 is set to the minimum value. The discharge pressure of the hydraulic pump 2 is the spring 1
When the pressure set by 2 s is exceeded, the switching valve 12 switches to the L position, and the discharge pressure of the hydraulic pump 2 also acts on the large-diameter side end surface of the piston 11a of the servo cylinder 11 to cause the piston 11 to move.
a moves downward, and the discharge capacity of the hydraulic motor 5 is set to the maximum value.

When the forward / reverse switching valve 8 is in the neutral position, the pressure selection valve 10 is held in the neutral position by its springs 10c and 10d, whereby the pressure of the main pipe lines 3 and 4 flows into the servo cylinder 11 side. The pressure acting on the servo cylinder 11 and the switching valve 12 while being blocked is introduced to the primary side of the charge relief valve 14 and the pair of check valves 15 and 16 via the pipe 13. Charge relief valve 1
4 and the check valves 15 and 16 are provided to regulate the minimum pressure of the main pipelines 3 and 4, and the pressure oil discharged from the charge pump 6 is guided to the primary side thereof via the throttle 7. . The pressure on the primary side of the check valves 15 and 16 is kept above the set pressure by the spring 14s of the charge relief valve 14, and if the pressure on the main pipelines 3 and 4 drops below the pressure on the primary side, the check valve 15 , 16 are opened and the discharge oil of the charge pump 6 is replenished to the main pipelines 3, 4.

The spring 14 of the charge relief valve 14
The pressure set by s is made lower than the pressure set by the spring 12s of the switching valve 12, so that when the pressure selection valve 10 is in the neutral position, the switching valve 12 is switched to the H position and the discharge capacity of the hydraulic motor 5 becomes the minimum value. Is set. This is because, when the forward / reverse switching valve 8 is switched to the neutral side during traveling, if the discharge capacity of the hydraulic motor 5 is large, a large braking torque acts on the closing pressure generated on the discharge side of the hydraulic motor 5, and the vehicle is Since the speed is rapidly reduced, the discharge capacity of the hydraulic motor 5 is reduced to reduce the brake torque, and the vehicle is gently decelerated.

Inside the pressure selection valve 10, when the pressure selection valve 10 is at the A position or the B position, a flow for selecting and outputting the pressure of the low pressure side pipe line of the pair of main pipe lines 3 and 4. The passages 10e and 10f are provided, and the pressure output from these passages is guided to the primary side of the check valves 15 and 16 via the pipe 13.

Numerals 17 and 18 are crossover load relief valves for controlling the maximum pressure in the main pipelines 3 and 4.

In the HST hydraulic traveling drive system having the above construction, the accelerator pedal is loosened during the forward movement of the vehicle by switching the forward / reverse switching valve 8 to the F position to lower the rotational speed of the prime mover 1. In this case, while the discharge flow rate of the hydraulic pump 2 decreases, the hydraulic motor 5 continues to rotate due to inertia, so that the discharge flow rate of the hydraulic motor 5 becomes larger than the discharge flow rate of the hydraulic pump 2 and the discharge pressure of the hydraulic motor 5 rises. To do.
At this time, the pressure selection valve 10 is held in the A position because the forward / reverse switching valve 8 is in the F position, which causes the hydraulic motor 5 to move.
Is discharged from the main conduit 4 to the primary side of the check valves 15 and 16 via the conduit 10e of the pressure selection valve 10 and the conduit 13. Then, when the discharge pressure of the hydraulic motor 5 exceeds the discharge pressure of the hydraulic pump 2, the check valve 15 opens and the main pipe line 4 passes through the flow passage 10e of the pressure selection valve 10, the pipe line 13 and the check valve 15 and the main pipe line 3 is opened. The discharge pressure of the hydraulic motor 5 is guided to the main pipe line 3 by communicating with the. As a result, the vehicle inertially travels without generating a closing pressure on the discharge side of the hydraulic motor 5.

When the forward / reverse switching valve 8 is in the R position, the pressure selection valve 10 is held in the B position, and the pressure in the main conduit 3 on the discharge side of the hydraulic motor 5 is guided from the conduit 10f to the conduit 13. . Then, as the discharge pressure of the hydraulic motor 5 rises due to the loosening operation of the accelerator pedal, the check valve 16 opens and the pressure in the pipeline 13 is guided to the main pipeline 4 on the suction side of the hydraulic motor 5. Similarly, the vehicle runs inertially. When the forward / reverse selector valve 8 is in the neutral position, the main conduits 3, 4 and the conduit 13 are shut off by the pressure selection valve 10 as described above. When switched to, the closing pressure is generated on the discharge side of the hydraulic motor 5 and the vehicle is decelerated.

As is clear from the above, in this embodiment, the pressure selection valve 10 necessary for controlling the discharge capacity of the hydraulic motor 5 is used.
And the check valves 15 and 16 necessary for maintaining the minimum pressure of the main pipelines 3 and 4 at a certain value or more, the inertia traveling is realized, so that a new electromagnetic switching valve is provided for the inertia traveling. Comparing with the circuit configuration when there is no need and inertia traveling is not necessary, when forward or reverse is selected, the pressure to guide the discharge pressure of the hydraulic motor 5 to the primary side of the check valves 15 and 16 is set. The only difference is that the selection valve 10 is provided with channels 10e and 10f. Therefore, the number of parts does not increase,
The increase in cost and the increase in size of the device due to the addition of the inertial traveling function are minimized. Pressure selection valve 10 and check valve 15,
No. 16 requires strength that can withstand the pressure of the main pipelines 3 and 4 regardless of the presence or absence of the inertial traveling function. Therefore, the addition of the inertial traveling function makes them significantly large, and it becomes difficult to secure the installation space. There is no fear.

In this embodiment, the pressure before and after the throttle 7 is adjusted according to the switching position of the forward / reverse switching valve 8 to the pilot line 10.
Although the pressure selection valve 10 is switched by introducing to a and 10b,
The present invention is not limited to such an aspect. For example, the pressure selection valve 10 may be changed from a hydraulic pilot type to an electromagnetic switching type, and switching control may be performed according to the switching state of a switch instructing switching of the forward / reverse switching valve 8. May be switched according to the magnitude relation of the discharge direction of the hydraulic pump 2.

In this embodiment, the charge pump 6 constitutes charging means, and the servo cylinder 11 and the switching valve 12 constitute motor capacity control means.

[0021]

As described above, according to the present invention,
Since inertia traveling can be performed using the pressure selection valve used for displacement control of the hydraulic motor and the pair of check valves used in the charge circuit, there is no need to provide a new switching valve for inertia traveling, which increases costs. It is possible to obtain an excellent effect that it is possible to provide an HST hydraulic traveling drive device capable of inertial traveling while suppressing an increase in the size of the engine and the device.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an HST hydraulic traveling drive system according to an embodiment of the present invention.

[Explanation of symbols]

 1 prime mover 2 hydraulic pump 3,4 main line 5 hydraulic motor 6 charge pump 10 pressure selection valve 11 servo cylinder 12 switching valve 13 line 14 charge relief valve 15,16 check valve

Claims (1)

[Claims] 1. A hydraulic pump driven by a prime mover, and a closed circuit connection with the hydraulic pump by a pair of main pipe lines,
A variable displacement hydraulic motor driven by oil discharged from the hydraulic pump; and a pressure selection valve for selecting and outputting the pressure of one of the main pipelines on the discharge side of the hydraulic pump among the pair of main pipelines. , A motor capacity control unit that is driven by the discharge pressure of the hydraulic pump output from the pressure selection valve to increase or decrease the discharge capacity of the hydraulic motor, and the pair of main pipelines via a pair of check valves for backflow prevention. And a charging means for replenishing the pressure oil when the pressure of these main pipes drops below a predetermined value, in the HST hydraulic traveling drive device, wherein the pressure selection valve is on the discharge side of the hydraulic motor. A HST hydraulic traveling drive device characterized in that a passage for outputting the pressure of the other main pipeline is provided, and the discharge pressure of the hydraulic motor outputted from this passage is led to the primary side of the check valve. Place