JPH11257489A - Controller for variable displacement piston pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove dispersion in a pump discharge quantity and control the pump discharge quantity without reducing the engine rotational speed by providing a variable restrictor parallel to a fixed restrictor installed in a second flow passage and regulating an opening of a variable displacement hydraulic pump according to the pressure difference between the front/rear of the fixed restrictor. SOLUTION: An engine 20 is started so that a variable displacement hydraulic main pump 1 and a fixed displacement charge pump 2 interlocked therewith are driven. The main pump 1 drives a hydraulic motor 9 via first flow passages 12, 13. The working fluid from the charge pump 2 passes through the fixed restrictor 6 and the variable restrictor 7 of the second flow passage 19 in parallel, its one part flows through a pressure reducing valve 5 to a pilot pressure circuit 17 via a directional switch valve 4, and another part flows to main circuits 12, 13 via a chuck valve 11. The opening of the variable restrictor 7 is so regulated as to be a prescribed pressure difference so that the dispersion in the pressure difference generated by passing through the fixed restrictor 6 is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for a variable displacement axial piston pump used for a wheel loader of a construction vehicle, for example.

[0002]

2. Description of the Related Art An example of a control device for a variable displacement piston pump is disclosed in Japanese Patent Publication No. 3-7829. FIG. 6 is a circuit diagram showing the configuration of a conventional variable displacement piston pump control device. As shown in the figure,
The engine (80) that drives the variable-type hydraulic pump is started as the main pump (61), and the constant-displacement-type hydraulic pump is driven together with the main pump (61) as the charge pump (62) interlocked therewith. The main pump (61) drives the fluid pressure motor (69) by the generated working fluid via the main circuits (72) and (73) as the first flow path.

The main pump (61) is configured to adjust the angle of the swash plate angle by a pump discharge amount adjusting piston (63) which returns to a neutral state by a spring. This adjustment is as follows.

[0004] A constant displacement type charge pump (62) discharges a discharge amount proportional to the engine speed. The working fluid discharged from the charge pump passes through the fixed throttle (66) of the sub-circuit (79) as a second flow path, and a part of the working fluid is reduced by the pressure reducing valve (65).
Through a directional control valve (64) to a pilot pressure circuit (77) leading to a pump discharge amount adjustment piston, and another part is provided when the pressure in the main circuits (72) and (73) is low. , Check valve
It is sent to the main circuits (72) and (73) via (71). Further, the outlet pressure of the fixed throttle (66) is regulated by a predetermined upper limit value by a relief valve (68). The throttles (74), (75), (76) are provided to adjust the responsiveness of the pump discharge amount adjusting piston.

In such a circuit, in the sub-circuit (79) in which the discharge amount proportional to the engine speed flows as the engine speed increases, the amount of working fluid passing through the fixed throttle (66) increases, and the fixed throttle (66) ) Increase the pressure difference before and after. When the engine speed rises and a pressure differential pressure equal to or greater than the initial spring force of the pressure reducing valve (65) occurs before and after the fixed throttle (66), the pressure reducing valve (65) starts to operate gradually. The reduced pressure is led to the pilot pressure circuit (77).

The pilot pressure guided to the pilot pressure circuit (77) is guided into one cylinder chamber of the pump discharge amount adjusting piston (63) by switching the electromagnetic switching valve (64), and the pilot pressure is supplied to the main pump (61). Is adjusted according to the pilot pressure. The working fluid in the other cylinder chamber of the pump discharge amount adjusting piston (63) is pushed out and discharged to the tank line.

[0007]

However, in the control device shown in FIG. 6, the pump discharge amount adjusting piston (6) is controlled according to the pressure difference generated when oil flows through the fixed throttle (66).
Although 3) is deviated, there is a problem in that the pressure difference generated varies due to the shape and processing error of the fixed aperture, and it is difficult to make the shape and processing accuracy of the fixed aperture constant.

When a traveling system and a bucket working system are driven by one engine and a plurality of fluid pressure pumps as in a wheel loader, for example, when the bucket is used to scoop up earth and sand, the engine speed must be reduced. It is necessary to control the running speed to be low while maximizing the output of the bucket working system while providing high output. Therefore, a mechanism for controlling at least the hydraulic pump of the traveling system without reducing the engine speed is required.

The present invention is a control device for a variable displacement piston pump capable of smoothly controlling the pump discharge amount in response to a change in the engine speed, and can eliminate variations in the pump discharge amount. It is an object of the present invention to obtain a control device for a variable displacement piston pump, and further to obtain a control device for a variable displacement piston pump added with a function of controlling the pump discharge amount without lowering the engine speed. .

[0010]

According to a first aspect of the present invention, there is provided a control apparatus for a variable displacement piston pump according to the present invention, wherein the variable hydraulic pump is driven by a prime mover, and is generated by the variable hydraulic pump. A first flow path through which the first working fluid flows, a constant displacement fluid pressure pump driven by the prime mover to generate a second working fluid having a discharge amount proportional to a driving speed of the prime mover, and the constant displacement fluid pressure A second flow path through which a second working fluid generated by the pump flows; and a discharge amount of the first working fluid generated by the variable fluid pressure pump when the second working fluid reaches a predetermined pressure. A control device for a variable displacement piston pump, comprising: a discharge amount changing means for changing a discharge amount of the second working fluid; Variable according to the difference And adjusts the opening degree of the fluid pressure pump, is provided with a variable throttle in parallel to the fixed throttle.

According to a second aspect of the present invention, there is provided a control apparatus for a variable displacement piston pump, wherein the variable throttle according to the first aspect is interlocked with an inching pedal of a wheel loader.

According to a third aspect of the present invention, there is provided a control device for a variable displacement piston pump, wherein a variable hydraulic pump driven by a prime mover and a first working fluid generated from the variable hydraulic pump are provided. A first flow path, a constant displacement fluid pressure pump driven by the prime mover to generate a second working fluid having a discharge amount proportional to the driving speed of the prime mover, and a second displacement fluid generated from the constant displacement fluid pressure pump. A second flow path through which the working fluid flows, and a discharge amount changing means for changing a discharge amount of the first working fluid generated by the variable fluid pressure pump when the second working fluid reaches a predetermined pressure. A control device for a variable displacement type piston pump, wherein the discharge amount changing means includes a pilot pressure corresponding to a pressure difference between before and after a fixed throttle provided in the second flow path. Can be The operation amount is adjusted by introducing the pilot pressure into a pump discharge amount adjusting piston for adjusting the discharge amount of the hydraulic fluid pump. And a take-out port for taking the part out of the flow path.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the discharge amount changing means is provided for the second working fluid generated from the constant displacement type hydraulic pump before joining with the first working fluid generated from the variable type hydraulic pump. The discharge amount of the variable fluid pressure pump is adjusted according to the pressure difference before and after the fixed throttle provided in the two flow paths, and a variable throttle is provided in parallel with the fixed throttle. As a result, even if there is no special ingenuity in the shape of the fixed throttle, and even if the processing of the shape of the fixed throttle is not performed with particularly high precision, it is possible to eliminate the variation in the generated pressure difference by adjusting the variable throttle. Can be.

That is, when the pump discharge amount is controlled only by the fixed throttle, the differential pressure generated by the flow rate of the working fluid passing through the throttle tends to vary. For this reason, processing of the fixed drawing was performed with high accuracy, or a device with a shape with less variation was required. By arranging the variable aperture in parallel with this fixed aperture and adjusting the variable aperture,
Variations in the differential pressure generated in each device can be eliminated, and variations in the discharge amount of the working fluid in each device can be suppressed.

Further, by opening the variable throttle in conjunction with the inching pedal of the wheel loader, it is possible to adjust the opening in accordance with the amount of depression of the inching pedal. For example, when the engine speed is increased, the opening of the variable throttle is reduced. By adjusting, the pump discharge amount can be adjusted without lowering the engine speed.

Further, as another discharge amount changing means for adjusting the discharge amount of the pump without lowering the engine speed, there is provided one of the working fluids in a flow passage for introducing a pilot pressure from a takeout port to a piston for adjusting the discharge amount of the pump. When the section is bleed off out of the flow path, the circuit pressure of the pilot pressure circuit is reduced, thereby reducing the pump discharge amount. For example, when cleaning the road or mowing the grass while keeping the speed of the wheel loader at a low speed, the speed can be controlled by adjusting the opening of the throttle valve. At this time, the operator is released from speed control by the inching pedal, and workability is improved.

[0017]

FIG. 1 is a hydraulic circuit diagram showing an embodiment of a control device for a variable displacement axial piston pump according to the present invention. As shown in the figure, the engine (20) that drives the variable-type hydraulic pump is started as the main pump (1), and
A constant displacement type fluid pressure pump is driven as a charge pump (2) in conjunction with (1). The main pump (1) drives the fluid pressure motor (9) through the main circuits (12) and (13) as the first flow path by the generated working fluid.

The swash plate angle of the main pump (1) is adjusted by a pump discharge amount adjusting piston (3) that returns to neutral by a spring. This adjustment is as follows.

The constant displacement type charge pump (2) discharges a discharge amount proportional to the engine speed. The working fluid discharged from the charge pump passes in parallel through the fixed throttle (6) and the variable throttle (7) of the sub-circuit (19) as the second flow path, and a part of the fluid flows through the pressure reducing valve (5). Through the directional control valve (4) to the pilot pressure circuit (17) leading to the pump discharge amount adjustment piston, and the other part is used when the pressure in the main circuits (12) and (13) is low. , Main circuit (12) (13) via check valve (11)
Sent to

The outlet pressure of the fixed throttle (6) is regulated to a predetermined upper limit by a relief valve (8). Aperture (14)
(15) and (16) are provided for adjusting the responsiveness of the pump discharge amount control piston. The throttle (14) is provided to prevent the pressure of the sub-circuit (19) from suddenly dropping when the bleed-off from the take-out port (18) to the tank side by a throttle valve or the like.

In such a circuit, when the engine speed increases, the sub-circuit (19) in which the discharge amount flows in proportion to the engine speed, the operation of passing through the fixed throttle (6) and the variable throttle (7) in parallel. The amount of fluid increases, and the pressure difference before and after throttling increases. FIG. 2 is an explanatory diagram showing the relationship between the engine speed and the pilot pressure. As shown in FIG. 2, when the engine speed exceeds idling and a pressure difference greater than or equal to the initial spring force of the pressure reducing valve (5) occurs before and after the fixed throttle (6), the pressure reducing valve (5) Starts operating gradually, and the reduced pressure is led to the pilot pressure circuit (17).

The pilot pressure guided to the pilot pressure circuit (17) is guided into one cylinder chamber of the pump discharge amount adjusting piston (3) by switching of the electromagnetic switching valve (4). FIG. 3 is an explanatory diagram showing the relationship between the pump discharge amount and the pilot pressure. Due to the pilot pressure acting on the pump discharge amount adjusting piston (3), the pump discharge amount of the variable displacement type piston pump increases as the pilot pressure increases up to 100% discharge amount as shown in FIG.

FIG. 4 is an explanatory diagram showing the relationship between the engine speed, the pilot pressure and the pump discharge amount. FIG. 4 shows the relationship between the engine speed, the pilot pressure and the pump discharge amount.

The pressure difference generated by passing through the fixed throttle (6) varies depending on the shape of the fixed throttle, processing errors and the like. Variations in the pressure difference cause variations in characteristics of the engine speed and the pump discharge amount. In the present invention, in order to eliminate the variation of the pressure difference,
The opening degree of the variable throttles (7) connected in parallel is adjusted so that a predetermined pressure difference is obtained. Opening adjustment
This is usually done at the highest engine speed.

A variable throttle adjusted to have a predetermined pressure difference
In (7), when the opening is further opened, the pressure difference between before and after the throttles (6) and (7) decreases, and the pressure reducing valve (5) operates in the closing direction, so that the pilot pressure decreases. This means that the pilot pressure is reduced by opening the opening of the variable throttle (7) with the engine speed kept constant, and as a result, the pump discharge amount is reduced.

For example, when the present pump system is applied to a wheel loader, a traveling system is mainly used in combination with a fluid pressure motor. When scooping up sediment with a bucket, the engine speed must be maximized and the running speed must be very slow. In this case, by opening the opening of the variable throttle (7), it is possible to control the pump discharge amount to be reduced and the traveling speed to be reduced. Thereby, the engine output can be used to the maximum extent on the work implement side for the bucket operation.

The variable aperture (7) has a mechanism in which the opening of the variable aperture (7) opens when the inching pedal is depressed, in conjunction with an inching pedal attached to the wheel loader.
FIG. 5 is an explanatory diagram showing the relationship between the pump discharge amount and the engine speed when the opening degree of the variable throttle is changed. As shown in FIG. 5, when the opening of the variable throttle (7) is changed, by increasing the opening of the throttle, the discharge amount corresponding to the engine speed decreases as compared with the initial state.

When bleed off from the take-out port (18) to the tank side by a throttle valve or the like, the circuit pressure of the pilot pressure circuit (17) decreases, the pump discharge rate decreases, and the traveling speed of the wheel loader decreases. You can control in the direction you want it to be. For example, cleaning the road while keeping the speed of the wheel loader constant,
When mowing, the speed can be controlled by adjusting the opening of the throttle valve. At this time, the operator is released from speed control by the inching pedal, and workability is improved.

[0029]

As described above, the present invention provides a control device for a variable displacement piston pump which can eliminate the variation in the pump discharge amount and further has a function of controlling the engine speed without lowering the engine speed. There is an effect that it can be obtained.

[Brief description of the drawings]

FIG. 1 is a hydraulic circuit diagram showing an embodiment of a control device for a variable displacement axial piston pump of the present invention.

FIG. 2 is an explanatory diagram showing a relationship between an engine speed and a pilot pressure.

FIG. 3 is an explanatory diagram showing a relationship between a pump discharge amount and a pilot pressure.

FIG. 4 is an explanatory diagram showing a relationship among an engine speed, a pilot pressure, and a pump discharge amount.

FIG. 5 is an explanatory diagram showing a relationship between a pump discharge amount and an engine speed when an opening degree of a variable throttle is changed.

FIG. 6 is a circuit diagram showing a configuration of a conventional variable displacement piston pump control device.

[Explanation of symbols]

(1)… Main pump (variable fluid pressure pump), (2)… Charge pump (constant displacement fluid pressure pump), (3)… Pump for adjusting pump discharge amount, (4)… Directional switching valve, (5) ) ... pressure reducing valve, (6) ... fixed throttle, (7) ... variable throttle, (8) ... relief valve, (9) ... fluid pressure motor, (10) ... relief valve, (11) ... check valve, (12) ) (13)… Main circuit (first flow path), (14) (15) (16)… Fixed throttle, (17)… Pilot pressure circuit, (18)… Extraction port, (19)… Sub circuit (No. (2 channels), (20)… engine,

Claims (3)

[Claims] 1. A variable hydraulic pump driven by a prime mover, a first flow path through which a first working fluid generated from the variable hydraulic pump flows, and a first flow path driven by the prime mover and proportional to a driving speed of the prime mover A constant displacement type fluid pressure pump that generates a second working fluid having a predetermined discharge amount, a second flow path through which the second working fluid generated from the constant displacement type fluid pressure pump flows, and the second working fluid is predetermined. And a discharge amount changing means for changing a discharge amount of the first working fluid generated by the variable hydraulic pressure pump when the pressure reaches the predetermined pressure. The changing means adjusts an opening degree of the variable-type fluid pressure pump according to a pressure difference before and after a fixed throttle provided in the second flow path with the second working fluid. Variable aperture in parallel DOO variable displacement piston pump control apparatus according to claim. 2. The control device for a variable displacement piston pump according to claim 1, wherein the variable throttle is interlocked with an inching pedal of a wheel loader. 3. A variable fluid pressure pump driven by a prime mover, a first flow path through which a first working fluid generated from the variable fluid pressure pump flows, and proportional to a drive speed of the prime mover driven by the prime mover. A constant displacement type fluid pressure pump that generates a second working fluid having a predetermined discharge amount, a second flow path through which the second working fluid generated from the constant displacement type fluid pressure pump flows, and the second working fluid is predetermined. And a discharge amount changing means for changing a discharge amount of the first working fluid generated by the variable hydraulic pressure pump when the pressure reaches the predetermined pressure. The changing means is configured to adjust a pilot pressure according to a pressure difference between before and after a fixed throttle provided in the second flow path with the second working fluid, and to adjust a pump discharge amount for adjusting a discharge amount of the variable fluid pressure pump. Introduced into the piston A variable amount characterized by having an extraction port for extracting a part of the working fluid in the flow path for introducing the pilot pressure into the pump discharge amount adjustment piston to the outside of the flow path. Control device for displacement piston pump.