JPH0614113Y2 - Hydraulic control device for vehicle hydraulic transmission - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] This invention is for controlling the hydraulic pressure of a closed circuit of a hydraulic transmission in a work vehicle such as a tractor equipped with a hydraulic transmission that continuously changes and controls the vehicle speed. The present invention relates to a hydraulic control device.

[Prior Art] A variable displacement hydraulic pump and a constant displacement hydraulic motor
In a work vehicle including a hydraulic power transmission device that is connected by a pair of oil supply / discharge circuits that form a closed circuit together with these pumps and motors, the hydraulic motor of the hydraulic motor is started when the vehicle is started by tilting the pump swash plate from the neutral position. Until rotation starts, hydraulic pressure is trapped in the oil supply / discharge circuit (high pressure side circuit) on the discharge side of the hydraulic pump, abnormally high pressure is generated, and the pump swash plate is returned to the neutral position and the vehicle is stopped. Occasionally, while the hydraulic motor continues to rotate due to inertia, the pumping action of the hydraulic motor due to the inertial rotation causes the hydraulic pressure to be trapped in the oil supply / exhaust circuit that was on the low pressure side, resulting in abnormally high pressure.

Therefore, as already disclosed in, for example, Japanese Utility Model Publication No. Sho 49-12541, a pair of relief valves connecting between a pair of oil supply / discharge circuits of a hydraulic transmission are set to a high pressure from a state of relief operation at low hydraulic pressure. It is known that a relief relief valve that gradually increases the relief pressure to hydraulic pressure is used to eliminate the abnormal high pressure (surge pressure) as described above. With such a hydraulic control mechanism, when a vehicle starts, a relief relief valve that operates to relieve pressure from the high-pressure side circuit to the low-pressure side circuit gradually increases the hydraulic pressure in the high-pressure side circuit, thereby increasing surge pressure in the circuit. The surge relief pressure that prevents the occurrence of a surge pressure in the low-pressure side circuit is generated by a modular relief valve that operates from the low-pressure side circuit to the high-pressure side circuit when the vehicle is stopped. Surge pressure is prevented by pulling out toward the supply / discharge circuit.
These module relief valves, like ordinary relief valves, also operate so that surge pressure that may occur in the high pressure side circuit while the vehicle is traveling is also released into the low pressure side circuit.

The module relief valve disclosed in the above publication is configured as a balance piston type by separately providing a pilot relief valve for controlling the relief pressure, and the base end of the valve spring of the pilot relief valve is provided through a throttle. It is received by the control piston that gradually moves by the action of hydraulic pressure to increase the valve spring force.

[Problems to be solved by the invention]

In the above publication, the hydraulic pressure is applied to the control piston by a hydraulic responsive switching valve that switches the circuit in response to the hydraulic pressure of the oil supply / exhaust circuit on the high pressure side. At the neutral position of the valve, oil is drained from the hydraulic action passage for the control piston by the switching valve.

Such a switching valve does not necessarily require the control piston of the module relief valve when the swash plate of the hydraulic pump is tilted from the neutral position and the vehicle is started, so that the valve spring force of the pilot relief valve is minimized. By starting the movement from the above, the hydraulic pressure set by the module relief valve is inevitably gradually increased from the desired low hydraulic pressure, so that abrupt start of the hydraulic motor is avoided and the vehicle start is buffered. Let them do it.

On the other hand, on the other hand, according to the present publication in which a switching valve for guiding the hydraulic pressure from a pair of oil supply / discharge circuits of the hydraulic transmission and switching the circuit in response to the hydraulic pressure is separately provided, a valve structure of a hydraulic control mechanism is provided. The oil passage structure becomes complicated and the manufacturing cost is increased.

Therefore, the present invention is intended to provide a hydraulic control device which has the same advantages as the above-mentioned conventional example and has a simple valve structure and oil passage structure.

[Means for solving problems]

To this end, the present invention, as illustrated in the accompanying drawings, includes a first port 11 connected to an oil supply / discharge circuit between a hydraulic pump 1 and a hydraulic motor 2 of a hydraulic transmission and an oil supply circuit 6 by a charge pump 5 of the hydraulic transmission. The second port 12 and the third port 13, which are connected to each other, respectively, and the second port 12 is arranged at an intermediate position between the first port 11 and the third port 13, and is opened in the valve hole 10 respectively. Having a throttle oil passage 15 penetrating in the direction
A differential piston 14 having a pressure receiving area on one side smaller than a pressure receiving area on the opposite side, the differential piston 14 performing a relief operation to drain oil from the first port 11 to the second port 12, The control piston 16 is provided in the control piston 16 so that the sliding range in the direction away from the differential piston 14 is restricted, and the valve hole 10 between the pistons 14 and 16 communicates with the third port 13. A high pressure actuating pilot relief valve 17 for shutting off the communicating passage from the side of the third port 13 is inserted and installed in series, and the control piston 16 becomes the actuating piston 14 under the bias of the valve spring 17a of the high pressure actuating pilot relief valve 17. The relief operation of the differential piston 14 in the contacting state is performed when a hydraulic pressure higher than the hydraulic pressure of the oil supply circuit 6 by an appropriate amount acts on the first port 11. As constituted the hydraulic control device.

[Action]

FIG. 1 shows a steady operating state of the hydraulic transmission, in which the oil supply / discharge circuit 13A connecting the first port 11 of the valve mechanism on the right side is connected to the high pressure side and the first port 11 of the valve mechanism on the left side. The figure shows a case where the pump swash plate 1a (Figs. 1 and 2) is tilted so that the oil supply / drain circuit 13B is set to the low pressure side, and Fig. 3 (a)-(d). Shows the valve action of the valve mechanism on the right side of FIG. 1 when the pump swash plate 1a is operated from the neutral position.
(a)) to a steady state (Fig. 3 (d)) are shown in order.

In the neutral state shown in FIG. 3 (a), the control piston 16 is connected to the valve spring 17a of the high pressure operation pilot relief valve 17 and the third
The differential piston 14 is energized by the hydraulic pressure (for example, 5 kg / cm ² ) of the oil supply circuit 6 (Figs. 1 and 2) acting from the port 13.
Therefore, the differential piston 14 also receives the same bias and blocks the second port 12.

When the pump swash plate 1a is tilted and the hydraulic pump 1 discharges oil to the oil supply / discharge circuit 3A in FIG. 1, the oil pressure of the oil supply / discharge circuit 3A is confined by the confinement of the hydraulic pressure until the hydraulic motor 2 starts rotating. Is rapidly increased. However, when the control piston 16 is in contact with the differential piston 14 as shown in FIG. 3 (a), the differential piston 14 is, for example, 5 kg / cm ^2, which is an appropriate amount higher than the oil pressure of the oil supply circuit 6. Since the relief operation is performed with a high hydraulic pressure (for example, 10 kg / cm ² ), when the hydraulic pressure of the oil supply circuit 3A is increased to the latter hydraulic pressure, the differential piston 14 as shown in FIG. Moves while pressing the control piston 16 to perform a relief operation, and the hydraulic pressure of the oil supply / exhaust circuit 3A is reduced from the first port 11 to the second port 12. For this reason, abnormal high pressure is prevented from occurring in the high pressure side oil supply / discharge circuit 3A when the vehicle starts.

The hydraulic motor 2 starts to rotate and the load applied to the motor 2 raises the hydraulic pressure of the high-pressure side oil supply / discharge circuit 3A, while the hydraulic oil of the same hydraulic pressure increases the hydraulic oil passage 1 of the differential piston 14.
5 gradually flows between the pistons 14 and 16 via the valve 5.
At this time, the differential piston 14 has a larger pressure receiving area on the control piston 16 side than the pressure receiving area on the first port 11 side.
On the contrary, the control piston 16 resists the force of the valve spring 17a of the high pressure operation pilot relief valve 17 and the oil pressure of the oil supply circuit 6 due to the increase of the oil pressure in the valve hole between the pistons 14 and 16 on the contrary. Then, as shown in FIG. 3 (c), it is separated from the differential piston 14. In the state shown in FIG. 3 (c), the differential piston 14 is controlled by the increase in the hydraulic pressure between the pistons 14 and 16 and the difference in the pressure receiving area of the differential piston 14.
Is slightly different from the position shown in FIG.
It is displaced to the side.

Further, the control piston 16 goes away from the differential piston 14, and the differential piston 14 moves toward the first port 11
By displacing to the side, as shown in FIG. 3 (d), the control piston 16 is held in the restricting position where it is maximally separated from the differential piston 14, and the differential piston 14 is moved to the second port 12. The steady operation state shown in FIG. 3 (d) is obtained. In this state, the differential piston 14
On the basis of the pressure receiving area difference, the oil pressure leakage from the high pressure side oil supply / discharge circuit 13A is reliably prevented, and the valve spring 17a of the high pressure operation pilot relief valve 17 is compressed to the maximum.

The hydraulic pressure of the high pressure side oil supply / discharge circuit 3A in the state shown in FIG. 3 (d) is determined by the load applied to the hydraulic motor 2, but when the load is abnormally high, the circuit 3A has an abnormally high pressure. Can occur. In such a case, the high pressure operation pilot relief valve 17, which is assumed to be operated by a hydraulic pressure higher than the circuit pressure during steady operation by relief, operates as shown in FIG. The hydraulic pressure is released from the valve hole between 16 to the third port 13 to reduce the back pressure applied to the differential piston 14. For this reason, the differential piston 14 performs a relief operation as shown in FIG.
By removing the hydraulic pressure from the port 11 to the second port 12, it is possible to prevent abnormal high pressure from occurring in the high pressure side oil supply / discharge circuit 13A.

FIG. 4 schematically illustrates the operation described above. When the pump swash plate 1a is tilted at time t = 0, the high pressure side oil supply / discharge circuit tries to rise sharply as indicated by a curve C _1. 3A
The hydraulic pressure P is cut by the relief operation of the differential piston 14 at a low hydraulic pressure P _{1 of} , for example, 10 kg / cm ^2, and then the hydraulic pressure P is gradually increased until time t ₁ and the steady operating pressure P is increased.
reach a. The hydraulic pressure P, which tends to rise sharply as shown by the curve C ₂ due to the sudden increase in load during steady operation, is also cut to a proper value P ₂ by the differential piston 14 which is in relief operation by the pilot of the high pressure pilot relief valve 17. The hydraulic pressure that can be established in the first port 11 in the neutral state shown in FIG. 3 (a) is increased even if the hydraulic pressure P ₀ of the oil supply circuit 6 or the inclination of the pump swash plate 1a is increased. Hydraulic pressure P ₁ shown in
The differential piston 14 is inevitable when the vehicle starts.
Since the hydraulic pressure P is gradually increased after performing the relief operation, the vehicle is started in a buffer manner.

The operation when the vehicle is stopped will be described. When the pump swash plate 1a is returned to the neutral position from the state shown in FIG. 1, the hydraulic motor 2 that continues to rotate due to inertia even after the driving of the hydraulic pump 1 is stopped acts as a pump. Then, the oil is trapped in the oil supply / discharge circuit 3B, which has been on the low pressure side until then, and the hydraulic pressure of the circuit 3B rapidly increases. At that time, the differential piston 14 of the valve mechanism having the first port 11 connected to the same circuit 3B is shown in FIG. 3 (b) when the vehicle starts and is exactly the same as that described above, for example, 10 kg / cm ² And because it operates relief with hydraulic pressure,
There will be no situation where an abnormally high pressure is generated in the oil supply / discharge circuit 3B which was on the low pressure side.

〔Example〕

As shown in FIG. 2, the hydraulic power transmission device includes a pair of oil supply / discharge circuits 3A and 3B that connect the pair of suction and discharge ports of the hydraulic pump 1 and the hydraulic motor 2 to each other. A charge pump 5 that is driven by an engine (not shown) along with the hydraulic pump 1 to replenish oil from the oil tank 4 to the oil supply / discharge circuits 3A and 3B via check valves 8A and 8B, respectively, is provided in the discharge circuit. The oil pressure of the oil supply circuit 6 is, for example, 5 kg / cm ²
The setting is made by the relief valve 7 which operates in relief by hydraulic pressure. Instead of the relief valve 7, a pressure reducing valve for reducing the discharge pressure of the charge pump 5 may be directly inserted into the pump discharge circuit, and the secondary side thereof may be configured as an oil supply circuit.

As shown in FIG. 1, the valve hole 10 has a valve housing 9
The valve hole 10 has a smaller inner diameter than the upper side thereof. The first port 11 is from the lower side with respect to the valve hole 10, and the second and third ports 12,
13 are opened from the side crossing the valve hole 10. The second port 12 is communicated with an oil passage that is formed in the valve housing 19 and forms the end portion of the oil supply circuit 6 through a communication passage 21 in the valve housing 9, and the third port 13 is By providing the communication passage 22 in the valve housing 9 for communicating it with the communication passage 21, it is similarly connected to the oil supply circuit 6.

The differential piston 14 is fitted into the valve hole 10 in which the diameter of the lower half portion is smaller than the diameter of the upper half portion and the inner diameter is set as described above, and the pressure receiving area S ₁ on the lower surface side It is made smaller than the pressure receiving area S ₂ by an appropriate amount. The differential piston 14 is seated on an annular valve seat 23 on the inner peripheral surface of the valve hole 10 slightly below the second port 12. The throttle oil passage 15 is provided in the throttle forming hardware screwed to the differential piston 14.

The control piston 16 is formed in a cylindrical shape having a bottom wall, and a circular hole 16a formed in the center of the bottom wall and an appropriate number of circular holes 16b formed in the peripheral wall allow the control piston 16 to be in the valve hole 10 between the pistons 14, 16. Is connected to the third port 13. The upper end of the valve hole 10 has a screw plug 25.
The control piston 15 is closed by the screw plug 2
5, the sliding range in the direction away from the differential piston 14 is restricted.

The high pressure operation pilot relief valve 17 is formed in a poppet having the upper end surface of the circular hole 16a in the bottom wall of the control piston as a valve seat, and its valve spring 17a receives the upper end by the screw plug 25 and moves to the relief valve 17 at the lower end. It is made to act. The relief pressure P ₂ of the relief valve 17 shown in FIG.
The maximum compression of the valve spring 17a and the hydraulic pressure of the oil supply circuit 6 acting as a back pressure from the third port 13 in the state shown in FIG.
This is ensured by making 6a relatively small and setting the pressure receiving area of the relief valve 17 small.

As shown in FIG. 1, the pair of check valves 8A and 8B described above with reference to FIG. 2 are arranged side by side in the valve housing 9. The primary side port 27 of each check valve 8A, 8B is connected to the oil supply circuit 6, and the secondary side port 28 is the first port 1 described above.
1 is connected to each oil supply / discharge circuit 3A, 3B. As shown in the check valve 8B in FIG. 1, oil is supplied to the low pressure side oil supply / discharge circuit (circuit 13B in the state of FIG. 1) by opening the check valve. In case the work vehicle equipped with the illustrated hydraulic transmission is towed by another vehicle, hydraulic pressure is confined in the oil supply / exhaust circuit 3A or 3B by the pumping action of the hydraulic motor 2 driven from the wheel side at that time. In order to avoid this, an opening operation rod 29 that allows the check valves 8A and 8B to be opened from the outside is provided. Each opening operation rod 29 is held by a screw plug 30 that closes the upper end of the check valve installation hole through an O-ring.

[Effect of device]

As is clear from the above as the function of the invention,
The hydraulic control device of the present invention has the same advantages as the above-mentioned conventional example disclosed in Japanese Utility Model Publication No. Sho 49-12541, but the structure is simpler than that of the conventional example.

That is, the invention is directed to a differential piston 1 which eliminates an abnormally high pressure that may occur in the oil supply / discharge circuit 3A or 3B when the vehicle starts and stops by a relief operation at a low hydraulic pressure.
4, the pressure receiving area on the first port 11 side from which oil is to be relieved therefrom is set smaller than the pressure receiving area on the opposite side, contrary to the case of a normal differential relief valve. It is assumed that oil gradually flows from the side of the first port 11 having a small pressure receiving area to the side having a large pressure receiving area by the throttle oil passage 15 provided at 14, and the differential piston 24 is relieved to the relief operation position due to the pressure receiving area difference. To gradually return to the non-relief position to obtain a buffering hydraulic pressure increase similar to the case of using the modular relief valve. Then, the valve spring 17a of the high pressure operation pilot relief valve 17 is compressed by the control piston 16 which separates from the differential piston 14 during the increase of the oil pressure, and the high pressure side in the steady operation state of the hydraulic transmission device. The pilot relief valve 17 for detecting an abnormally high pressure that may occur in the oil supply / drain circuit is operated to perform a relief operation with the valve spring 17a compressed to the maximum extent, and the valve spring 17a is moved to the differential piston 14 It is possible to design the pilot relief valve 17 to operate in a high pressure pilot relief mode without difficulty despite being involved in the low pressure relief operation. Abnormal pressure sensing of the pilot relief valve 17 in a steady operation state is slightly delayed due to the restriction of the flow passage by the throttle oil passage 15 of the differential piston 14, but the differential piston 14 relief operation immediately after the relief valve 17 operates in the pilot relief operation. Therefore, there is practically no inconvenience in preventing the occurrence of abnormally high pressure. The oil that is relieved from the high pressure side oil supply / exhaust circuit is returned to the oil supply circuit 6 that is supplying oil to the low pressure side oil supply / exhaust circuit. There is no such thing as a call.

As described above, the present invention is designed to prevent inconveniences in operation and design, and the differential piston, the control piston, the high pressure actuated pilot relief valve, and a few other components are arranged in series in a simple arrangement for hydraulic control. This is a structure of a valve mechanism, and has the effect of greatly reducing the cost of the hydraulic control device by simplifying the valve structure and the oil passage structure.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention together with a part of a hydraulic circuit, FIG. 2 is a circuit diagram of a hydraulic circuit including the embodiment, and FIG.
(a), (b), (c), (d) and (e) are respectively for explaining the operation in the longitudinal sectional view showing the valve mechanism shown on the right side of FIG. 1, and FIG. It is a schematic graph illustrating the operation. DESCRIPTION OF SYMBOLS 1 ... Hydraulic pump, 2 ... Hydraulic motor, 3A, 3B ... Oil supply / discharge circuit, 5 ... Charge pump, 6 ... Oil supply circuit, 9 ... Valve housing, 10 ... Valve hole, 11 ... First port, 12 ...
2nd port, 13 ... 3rd port, 14 ... Differential piston,
15 ... Throttle oil passage, 16 ... Control piston, 16a ... Circular hole, 17 ... High pressure operation pilot relief valve, 17a ... Valve spring, 23 ... Valve seat, 25 ... Screw plug.

Claims (1)

[Scope of utility model registration request] 1. A first port 11 connected to an oil supply / discharge circuit between a hydraulic pump 1 and a hydraulic motor 2 of a hydraulic transmission, and a second port connected to an oil supply circuit 6 by a charge pump 5 of a hydraulic transmission. 12 and third port 13
The second port 12 to the first port 11 and the third port 13
Valve holes 10 arranged at intermediate positions between
A differential piston 14 having a throttle oil passage 15 penetrating in the axial direction therein and having a pressure receiving area on the first port 11 side smaller than a pressure receiving area on the opposite side, that is, the first port 11 to the second port 12, a differential piston 14 that performs a relief operation so as to drain oil, and the differential piston 1
4 is provided in the control piston 16 so that the sliding range in the direction away from the control piston 16 is regulated, and the valve hole 10 between the pistons 14 and 16 communicates with the third port 13. A high pressure operated pilot relief valve 17 for shutting off the passage from the side of the third port 13 is inserted and installed in series, and a valve spring 17 of the high pressure operated pilot relief valve 17 is installed.
The relief operation of the differential piston 14 in the state where the control piston 16 is in contact with the working piston 14 under the energization of a is such that the oil pressure in the first port 11 is higher than the oil pressure in the oil supply circuit 6 by an appropriate amount. A hydraulic control device for a hydraulic transmission for a vehicle, characterized in that it is configured to be performed when it is actuated.