JPH06307540A - Pump control device for hydrostatic power transmitting mechanism - Google Patents

Abstract

PURPOSE:To compensate for a minimum deliver flow rate of a pump so that a vehicle is escaped from the recessed part of a road. CONSTITUTION:A pump control device for a hydrostatic power transmitting mechanism comprises springs 15A and 15B to energize a regular piston 10 to an initial position from the opposite side of oil pressure chambers 12A and 12B; main spool 13A and 13B positioned opposite to a regular piston through the force of the main springs; pressure chambers 17A and 17B to slidably contain the respective main spools; an oil pressure switching valve 18 to feed the delivery pressure of a charge pump 2, interlocked with a main pump, to a pressure chamber as occasion demands; passages 21A and 21B to guide the oil pressure of a pressure chamber to an oil pressure chamber through orifices 20A and 10B according to the position of the main spool; and a free piston 16 slidably extending through the regulator piston and brought into contact with the main spool. Further, stoppers 30A and 30B to regulate a stroke, by which the main spool is pushed back to an initial position by a free piston by means of the pressure of the oil pressure chamber, in the middle of the stroke are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for controlling a pump discharge amount of a hydraulic transmission mechanism.

[0002]

2. Description of the Related Art A hydraulic transmission mechanism (HST) used in a construction machine or the like is composed of a hydraulic pump driven by an engine, a hydraulic motor rotating by receiving the pump discharge pressure, and the like. Then, as a device for performing torque control for suppressing the pump driving horsepower to a constant value, the control pressure and spring force acting on the main spool, and the change in the tilting moment due to the load of the pump are detected as the holding pressure of the regulator piston, A method in which it is fed back to the main spool via a free piston is proposed by the present applicant in Japanese Patent Application No. 3-194049.

In this case, a swash plate for controlling the discharge amount of the main pump, a regulator piston for changing the tilt angle of the swash plate, a hydraulic chamber for slidably accommodating the regulator piston, and a hydraulic chamber for the regulator piston are provided. , A main spool that opposes the regulator piston via the spring, a pressure chamber that slidably accommodates the main spool, and a charge pump that interlocks with the main pump in the pressure chamber. Pressure switching valve that supplies the discharge pressure of the main spool as needed, a passage that guides the hydraulic pressure of the pressure chamber to the hydraulic chamber via an orifice according to the position of the main spool, and a main spool that freely slides through the regulator piston. Is provided with a free piston.

When the discharge pressure of the charge pump, which changes in proportion to the engine speed, is introduced into the pressure chamber through the hydraulic pressure switching valve, the main spool is displaced while compressing the spring. In response to this, the holding pressure of the hydraulic chamber is generated, the regulator piston is displaced against the main spool, and the pump discharge amount is increased. At steady (or maximum) engine speed, the pump reaches maximum discharge.

When the pump load increases at a discharge amount according to the engine speed, a reaction force that pushes the regulator piston back to the initial position works, and the holding pressure of the hydraulic chamber rises.
This holding pressure causes the free piston to push back the main spool, so that the holding pressure of the hydraulic chamber decreases according to the position of the main spool. As a result, the regulator piston is displaced toward the initial position, and the discharge amount of the main pump is reduced according to the pump load.

[0006]

However, in such a conventional example, when a large pump load increases and acts, the regulator piston is returned to the initial position as the holding pressure decreases. In other words, the pump discharge amount may be zero. Therefore, there is a concern that the vehicle may be unable to escape when the vehicle gets stuck in a recess (e.g., a rut) on the road surface and requires a considerably large driving force.

An object of the present invention is to provide an effective solution to such problems.

[0008]

Therefore, a swash plate for controlling the discharge amount of the main pump, a regulator piston for changing the tilt angle of the swash plate, and a hydraulic chamber for slidably accommodating the regulator piston, A spring that urges the regulator piston from the opposite side of the hydraulic chamber to the initial position, a main spool that opposes the regulator piston via the spring, a pressure chamber that slidably accommodates the main spool, and a main pump in the pressure chamber. A hydraulic switching valve that supplies the discharge pressure of the charge pump that interlocks with the valve as needed, a passage that guides the hydraulic pressure of the pressure chamber to the hydraulic chamber via an orifice according to the position of the main spool, and the regulator piston can slide freely. In a pump control device of a hydraulic transmission mechanism that includes a free piston that penetrates and abuts the main spool,
A stopper is provided to restrict the stroke of the free piston that pushes the main spool back to the initial position by the pressure in the hydraulic chamber.

[0009]

[Operation] When the holding pressure of the hydraulic chamber rises as the pump load increases, the free piston pushes back the main spool accordingly. However, since the stroke is restricted by the stopper, push the main spool back to the initial position. There is no. That is, it is possible to prevent the holding pressure of the regulator piston from dropping below a predetermined value by the main spool at the stopper restricting position, so that the minimum discharge flow rate of the main pump can be compensated.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, 1 is a main pump driven by an engine, 2 is a charge pump which works in conjunction with the main pump 1, 3 is a hydraulic motor which is reversibly driven by receiving oil discharged from the main pump 1, Reference numerals 4 and 5 are hydraulic circuits that connect the main pump 1 and the hydraulic motor 3 to each other, and constitute a hydraulic transmission mechanism.

In order to control the tilt angle of the swash plate for adjusting the discharge amount of the main pump 1, a regulator piston 10 is provided as shown in FIG. The regulator piston 10 connected to the swash plate arm is slidably arranged inside the pump case 11, and hydraulic chambers 12A and 12B for introducing the holding pressure of the regulator piston 10 are formed on the left and right sides thereof. Further, the pump case 11 accommodates main spools 13A and 13B which are slidable coaxially on both sides of the regulator piston 10, respectively.

These main spools 13A and 13B are
Spring seats 14A, 14B and spring 15
The regulator piston 10 is contacted via A and 15B. Further, a free piston 16 penetrating the center of the regulator piston 10 in a slidable manner is provided, and the piston 16 has a spring seat 15 by a holding pressure of a hydraulic chamber.
It contacts the main spools 13A and 13B via A and 15B.

The free piston 16 has hydraulic chambers 12A and 12A.
To prevent the main spools 13A and 13B from being returned to the initial position by the holding pressure of B during the stroke,
In this example, both ends of the free piston 16 are flanged stoppers 30 </ b> A, 30 that abut the regulator piston 10.
B is formed.

A control pressure corresponding to the discharge pressure of the charge pump 2 is selectively introduced into the pressure chambers 17A and 17B accommodating the main spools 13A and 13B via a hydraulic pressure switching valve 18 (solenoid valve). The hydraulic chambers 12A, 12B of the regulator piston 10 communicate with annular ports 19B, 19A formed around the main spools 13B, 13A on opposite sides via passages 21A, 21B with orifices 20A, 20B interposed therebetween. To do.

A through hole 21 for opening the pressure chambers 17A, 17B and an annular groove 24 for draining to the tank side on the outer circumference of the spool are formed in the main spools 13A, 13B so as to sandwich the annular ports 19A, 19B, respectively. Annular port 19 depending on the positions of the spools 13A and 13B
Controls the pressure acting on A and 19B.

That is, the main spools 13A and 13B are in the retracted position where the control pressure is small, and the annular ports 19A and 19B are in the retracted position.
Is communicated with the low pressure annular groove 24 to lower the pressure, the annular ports 19A and 19B are communicated with the high pressure through hole 21 at the forward position where the control pressure is large, and the pressure is increased. The pressure is adjusted according to the degree of communication with 21.

Reference numerals 31A and 31B denote adjusters that regulate the retracted positions of the main spools 13A and 13B in order to adjust the neutral position of the regulator piston 10.

The hydraulic switching valve 18 selectively connects the passages 22A and 22B to the pressure chambers 17A and 17B with the control passage 23, and the discharge pressure from the charge pump 2 is supplied to the control passage 23. An inching spool 25 is provided in the middle of the control passage 23.
Return passage 2 for releasing control pressure to the low pressure side by rotating
Open 6 That is, the pump discharge amount is reduced toward zero according to the opening degree of the inching spool 25.

A choke 27 for temperature-compensating the control pressure is provided upstream of the inching spool 25. Further, 28 is a variable orifice for adjusting the inclination characteristics of the rotation speed and the flow rate, and 29 is a variable orifice for adjusting the starting rotation speed. These are installed in the middle of the passage branched from the control passage 23 to the return passage 26. Then, the control pressure to the control passage 23 is adjusted to the reference value.

Explaining the operation based on such a configuration, the discharge pressure of the charge pump 2 rises almost in proportion to the engine speed. This discharged oil is sent to the control passage 23, and the variable orifices 28 and 29 adjust the flow rate characteristics when the control pressure is started and the rotation speed. This control pressure is transmitted via the inching spool 25 to the hydraulic switching valve 1
With the switching of No. 8, the pressure is supplied selectively to the pressure chambers 17A, 17B of the main spools 13A, 13B.

The switching of the hydraulic switching valve 18 is artificially selected by the operator's judgment whether to move the vehicle forward or backward. Now, when the control pressure is introduced into one pressure chamber 17A, the other pressure chamber 17B is drained to the tank side. Then, the main spool 13A has the spring 15
A is displaced while being compressed, and accordingly pressure is guided from the through hole 21 to the annular port 19A, and this is supplied to the hydraulic chamber 12B on the opposite side as the holding pressure of the regulator piston 10 via the passage 21A.

Therefore, the regulator piston 10 moves to the left side in the figure while compressing the spring 15A.
However, since the main spool 13A pushes against the spring 15A by the control pressure, the free piston 16 moves leftward until it comes into contact with the spring seat 14A by the holding pressure of the hydraulic chamber 12B, and exerts a counter force against the displacement of the main spool 13A. The regulator piston 10 stops at the position where these are balanced.

In this way, the regulator piston 1
The position of 0 is controlled, and the tilt angle of the swash plate of the main pump 1 changes accordingly. That is, the tilting angle of the swash plate increases according to the control pressure applied to the main spool 13A, and the discharge amount of the main pump 1 increases as shown in FIG.

When the pump load on the swash plate increases at a constant rotation speed during operation, the reaction force depending on the pump discharge pressure (pump load) tends to restore the swash plate tilt angle. This acts to return the regulator piston 10 to the neutral position as a tilting moment proportional to the length of the swash plate arm.

Since the regulator piston 10 receives the tilting moment to compress the hydraulic chamber 12B, the hydraulic chamber 12B is compressed.
Holding pressure increases. This allows the free piston 1
Since 6 is pushed further to the left and pushes back the main spool 13A, the degree of communication between the annular port 19A and the low-pressure annular groove 24 increases as the main spool 13A moves backward, and while releasing the holding pressure of the hydraulic chamber 12B, The regulator piston 10 is retracted to the neutral position.

The regulator piston 10 is stopped at a position where these are balanced, and since the acting force based on the pump discharge pressure is fed back in this way, when the pump load exceeds a predetermined value, the discharge flow rate of the main pump 1 decreases. To do.

The free piston 16 pushes the main spool 13A back to the retracted position as the pump load increases. Absent.

That is, since the main spool 13A can prevent the holding pressure of the regulator piston 10 from dropping below a predetermined value at the restriction position of the stopper 30B, the minimum discharge flow rate of the main pump can be compensated as shown in FIG.
Therefore, when the vehicle gets stuck in a recess (e.g., a rut) on the road surface, it becomes possible to secure the driving force necessary for the escape of the vehicle.

When the opening of the inching spool 25 is fully closed, all the control pressure is directly supplied to the pressure chamber 17A of the main spool 13A, and the pump discharge flow rate is proportionally controlled according to the engine speed. When the opening degree of the inching spool 25 is increased by operating an inching pedal (not shown), the discharge oil from the charge pump escapes into the return passage 26 to reduce the control pressure.

Due to the decrease in control pressure, the main spool 1
Since the displacement amount of 3 A and the regulator piston 10 becomes small, the pump discharge amount decreases. When the inching spool 25 is fully opened, the control pressure becomes equal to the pressure on the low pressure side of either the main circuit 4 or 5, and the regulator piston 10 returns to the neutral position, so the pump discharge amount decreases to zero.

Therefore, by operating the inching pedal, the rotation of the hydraulic motor 3 (running of the vehicle) can be stopped even though the main pump 1 is rotating.

[0032]

In summary, according to the present invention, since the stopper for restricting the stroke for the free piston to push the main spool back to the initial position by the pressure of the hydraulic chamber is added during the stroke, the regulator is controlled by the main spool at the restriction position of the stopper. Since the holding pressure of the piston can be suppressed from falling below a predetermined value, the minimum discharge flow rate of the main pump can be compensated. Therefore, when the vehicle gets stuck in a recess (e.g., a rut) on the road surface, it is possible to obtain an effect that it is possible to secure the driving force necessary for the vehicle to escape.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram showing an embodiment of the present invention.

FIG. 2 is a sectional view of the regulator piston as a center.

FIG. 3 is a flow rate control characteristic diagram showing the relationship between pump flow rate and rotation speed.

FIG. 4 is a horsepower control characteristic diagram showing the relationship between pump flow rate and pressure.

[Explanation of symbols]

 1 Main Pump 2 Charge Pump 3 Hydraulic Motor 10 Regulator Piston 12A, 12B Hydraulic Chamber 13A, 13B Main Spool 15A, 15B Spring 16 Free Piston 17A, 17B Pressure Chamber 18 Hydraulic Switching Valve 19A, 19B Annular Port 20A, 20B Orifice 21A, 21B Passage 23 Control passage 30A, 30B Stopper

Claims (1)

[Claims] 1. A swash plate for controlling the discharge amount of the main pump, a regulator piston for changing the tilt angle of the swash plate, a hydraulic chamber for slidably accommodating the regulator piston, and a regulator piston for the hydraulic chamber. The spring that urges from the opposite side to the initial position, the main spool that opposes the regulator piston via the spring, the pressure chamber that slidably accommodates the main spool, and the charge pump that interlocks with the main pump in the pressure chamber A hydraulic pressure switching valve that supplies the discharge pressure as needed, a passage that guides the hydraulic pressure of the pressure chamber to the hydraulic chamber via an orifice according to the position of the main spool, and a regulator piston that slides freely through the main spool. In a pump control device of a hydraulic transmission mechanism that has a free piston that abuts, the free piston is driven by the main spool due to the pressure in the hydraulic chamber. A pump control device for a hydraulic transmission mechanism, which is provided with a stopper that restricts a stroke for returning the lever to the initial position in the middle thereof.