WO1998046883A1

WO1998046883A1 - Capacity control apparatus for variable displacement hydraulic pump

Info

Publication number: WO1998046883A1
Application number: PCT/JP1998/001556
Authority: WO
Inventors: Kenji Morino; Yousuke Oda; Nobumi Yoshida; Naoki Ishizaki; Mutsumi Ono; Takashi Hori
Original assignee: Komatsu Ltd.
Priority date: 1997-04-11
Filing date: 1998-04-03
Publication date: 1998-10-22
Also published as: JPH10281102A; JP3685287B2

Abstract

The responsiveness of a variable displacement hydraulic pump is improved by controlling the increase and decrease of the capacity thereof in a short period of time. A servo cylinder (5) for tilt-turning a capacity control member (4) of a variable displacement hydraulic pump (1), and an LS valve (8) allowing communication of a larger-diameter chamber (7) of this servo cylinder (5) with a pump discharge passage and a tank are provided, whereby a capacity control operation is carried out so that an actual difference between a pump discharge pressure and a load pressure always corresponds to a set differential pressure. The LS valve (8) is operated by a pump discharge pressure in a capacity decreasing direction and by a dummy load pressure in a capacity increasing direction. The pump discharge pressure is reduced by an accumulator (37), a restriction (35) and a pressure reducing valve (31) so as to set the dummy load pressure equal to, lower than and higher than a load pressure, whereby the LS valve (8) is operated excessively in the capacity increasing direction and capacity decreasing direction as compared with a normal case so that the capacity increases and decreases in a shorter period of time.

Description

Description Capacity control device for variable displacement hydraulic pump

The present invention relates to a hydraulically operated, variable pressure sensing system used to supply hydraulic oil to a hydraulic pump of a hydraulic pump. The present invention relates to a device for controlling the displacement of a displacement hydraulic pump. Background art

As shown in FIG. 1, the discharge pressure oil of a variable displacement hydraulic pump (hereinafter referred to as a variable hydraulic pump) 1 is supplied to a hydraulic actuator 3 by an operation valve 2. In the hydraulic system in which the working machine is operated by the hydraulic actuator 3, the capacity of the variable hydraulic pump 1 is reduced by its own discharge pressure (hereinafter referred to as the pump discharge pressure). P0) and the pressure (P0-PLS) of the hydraulic actuator 3 (hereinafter referred to as the load pressure PLS) is controlled to be constant. .

For example, the small-diameter pressure receiving chamber 6 of the servo cylinder 5 that tilts the capacity control member 4 such as the swash plate of the variable hydraulic pump 1 is connected to the discharge path 1a of the variable hydraulic pump 1, and the pump discharge pressure is changed. P 0 is supplied, and the large-diameter pressure receiving chamber 7 of the servo cylinder 5 is passed through the first circuit 9 by the LS (load sensing) valve 8 to the tanks 10 and 2. Discharge of variable hydraulic pump 1 via circuit 11 The connection is controlled to one side of the path la, and the differential pressure between the pump discharge pressure P 0 and the load pressure PLS is controlled by the LS valve 8 so as to be always constant as a set differential pressure. Review

The S valve 8 is pushed to the supply position A by the pump discharge pressure P0 acting on the first pressure receiving portion 12 and the negative pressure P from the operation valve 2 acting on the second pressure receiving portion 13 is applied. The pressure is pushed to the drain position B by LS, and the pressure difference between the pump discharge pressure P 0 and the load pressure P LS always becomes the set pressure difference.

Specifically, when the actual differential pressure becomes smaller than the set differential pressure, the LS valve 8 is in the drain position B, and the large-diameter pressure receiving chamber 7 of the servo piston 5 is tanked. 10, the displacement control member 4 tilts in the direction of larger displacement, the capacity of the variable hydraulic pump 1 increases, the pump discharge pressure P 0 increases, and the differential pressure increases. .

On the other hand, when the actual differential pressure becomes larger than the set differential pressure, L

The S valve 8 is in the supply position A, and the pump discharge pressure is supplied to the large-diameter pressure receiving chamber 7 of the servo piston 5, and the displacement control member 4 is tilted in the small displacement direction to change the variable hydraulic pump. As the capacity of 1 decreases, the pump discharge pressure P0 decreases, and the differential pressure decreases.

By this action, the LS valve 8 controls the capacity of the variable hydraulic pump 1 so that the differential pressure between the pump discharge pressure P 0 and the load pressure P LS becomes the set differential pressure.

As a result, the differential pressure Δ between the pump discharge pressure P 0 and the load pressure P LS becomes AP = C 1 X (QZA) 2 and the hydraulic pressure Irrespective of the load pressure of the cutout 3, the discharge flow rate of the variable hydraulic pump 1 will be a flow rate that matches the opening area of the control valve 2 (the required flow rate of the control valve). Is controlled by

Here, C 1 is a flow rate coefficient, A is an opening area of the operation valve 2, and Q is a flow rate flowing to the hydraulic actuator.

The opening area of the operating valve 2 is determined by the communication between the pump port 14 and the first actuator port 15 or between the pump port 14 and the second actuator 16. Area. The opening area is determined by the stroke of operating the solenoid valve 17 from the neutral position C to the first position D or the second position E by operating the solenoid 17. Is

In FIG. 1, the first circuit 9 is connected to one of the tank 10 and one of the discharge passages 1 a by a PC (Pressure Control) valve 18. The PC valve 18 is pushed to the drain position F by the spring 19 and is pushed to the supply position G by the pump discharge pressure P0 acting on the pressure receiving portion 18a. The pressing force of the spring 19 is changed by the tilting position (capacity) of the displacement control member 4 of the variable hydraulic pump 1, and the maximum absorption torque (capacity X port) of the variable hydraulic pump 1 is changed. The pump discharge pressure P 0) is limited to reduce the pressure.

Specifically, when the variable hydraulic pump 1 has a certain capacity, the pump discharge pressure P0 is set to a value within the range of the set maximum absorption torque (capacity at that time X pump discharge pressure P0). If the pressure is PC pressure, the PC valve 18 will be at the drain position F at the spring 19, and the pump discharge pressure P0 will be (capacity at that time X pump discharge pressure P0 )> When the pressure reaches the set maximum absorption torque, the PC valve 18 becomes the supply position G at the pump discharge pressure P 0, and the large-diameter pressure receiving chamber of the servo piston 5 7 is supplied with the pump discharge pressure Po, and the capacity of the variable hydraulic pump 1 is reduced.

With the capacity control device for the variable hydraulic pump, if the opening area is changed by operating the operation valve 2, the capacity control of the variable hydraulic pump 1 is delayed, resulting in an Ching etc. occur. This is remarkable when the opening area is rapidly changed by suddenly operating the operation valve 2.

Specifically, when the operating valve 2 has a small opening area and the pump discharge flow rate is small, the operator operates the levers 17 to open the operating valve 2 in a state of (small capacity). When the valve is operated in the opposite direction. The opening area of the control valve 2 increases.

For this reason, when the required flow rate of the operation valve becomes larger than the pump discharge flow rate, the pump discharge pressure P0 decreases, and the actual differential pressure

(P0-PLS) becomes smaller, and becomes smaller than the set differential pressure. As a result, the LS valve 8 is actuated to the 8 force S drain position B to increase the capacity of the variable hydraulic pump 1 and increase the pump discharge flow rate as described above.

However, as a mechanism of the pump mechanism with a variable pump capacity of a swash plate and a swash axis, the change of the tilt angle is controlled by a hydraulic cylinder type actuator (servo piston 5). ), It takes a certain amount of time to reach the specified discharge flow rate (capacity). Therefore, as the pump discharge flow rate approaches the predetermined discharge flow rate (the actual differential pressure approaches the set differential pressure). As a result, the opening area of the LS valve 8 is started to be reduced (when the actual differential pressure reaches the set differential pressure, the opening of the LS valve 8 is almost closed).

If the opening area of the LS valve 8 is reduced, the rate of change of the pump discharge flow rate (capacity) becomes slow. That is, as the target discharge flow rate approaches, the increase in the pump discharge flow rate gradually approaches the target value (the approach speed up to the target flow rate becomes slower).

If the amount of change in the opening area of the LS valve 8 (LS valve opening gain) due to the difference between the actual differential pressure and the set differential pressure is increased, the approach speed up to the target flow rate is reduced. The lower part can be suppressed (the force S that can keep the LS differential pressure drop state within a small time range), but the control loop gainer S The control system becomes unstable, causing problems such as hunting.

Therefore, it is inevitable for the control system to allow the actual differential pressure drop state within a stable range.

In addition, when the operating valve 2 has a large opening area and the pump discharge flow rate is large (large capacity), the operator operates the lever 17 to open the operating valve 2 with a small opening area. When operated in the direction, the opening area force S of the control valve 2 decreases.

For this reason, the required flow rate of the operating valve becomes smaller than the pump discharge flow rate, the pump discharge pressure P0 increases, the actual differential pressure (PO-PLS) increases, and the set differential pressure increases. As a result, the LS valve 8 is operated to the supply position A and An attempt is made to reduce the capacity of the variable hydraulic pump 1 and increase the pump discharge flow rate as described above.

However, as described above, it takes a certain amount of time to reach the specified pump discharge flow rate (capacity). As a result, the actual differential pressure increases until the pump discharge flow rate reaches the predetermined discharge flow rate, but as the pump discharge flow rate decreases and approaches the required flow rate of the operation valve (actual differential pressure). pressure Re twofold rather closer to the set pressure differential), if squeezed open port area of _c LS valve 8 the apertures area Ru Ri start down the LS valve 8, it slow rate of change of the port down flop discharge flow rate . That is, as the target discharge flow rate approaches, the pump discharge flow rate decreases asymptotically to the target value (the approach speed up to the target flow rate decreases.) _C As described above. Thus, regardless of whether the operating valve 2 is operated in the direction of large opening area or in the direction of small opening area, the actual differential pressure is reduced (increased) within a stable range as a control system. During the time, there is a difference between the time it takes to reach the target discharge flow rate (capacity) because it has to be forgiven, and the time up to the target discharge flow rate (capacity) is given priority. In some cases, even a hunting situation has to be compromised.

Also, the pressure signals of the pump discharge pressure P 0 and the load pressure PLS are particularly affected by the pressure loss due to the leakage of the piping in the piping 20 and the piping 21, the inertia of the hydraulic oil, etc. If the pressure change is sudden (for example, sudden operation), the first and second pressure receiving sections 12 and 13 of the LS valve 8 are not transmitted as scheduled differential pressure signals. The operation of the initially set pump tilt angle is delayed, The tilt angle operation may be excessive.

Therefore, an object of the present invention is to provide a displacement control device for a variable displacement hydraulic pump which can solve the above-mentioned problem. Disclosure of the invention

The first invention operates by the actual differential pressure between the pump discharge pressure of the variable displacement hydraulic pump 1 and the load pressure of the hydraulic actuator 3, and the actual differential pressure is used. LS valve 8 for controlling the capacity of the variable displacement hydraulic pump 1 so that the pressure becomes the set differential pressure, and the difference between the actual differential pressure and the set differential pressure and the time of the actual differential pressure. Means for generating a pseudo load pressure according to the change in pressure, and reducing the pump discharge pressure with the load pressure and the pseudo load pressure, and applying the reduced output pressure to the LS valve 8 as the load pressure. And a pressure reducing valve 31 acting as a pressure difference, wherein when the actual differential pressure and the set differential pressure are equal, the pseudo load pressure is equal to the load pressure, and the actual differential pressure is equal to the set differential pressure. Is smaller than the load pressure, the pseudo load pressure is set lower than the load pressure in accordance with the degree of change in the actual differential pressure. When the pressure is larger than the set differential pressure, the pseudo load pressure is set to be higher than the negative load pressure according to the degree of change of the actual differential pressure, and the pressure reducing valve 31 supplies the pseudo load pressure to the load. When the pressure is equal to the output pressure, the output pressure is the load pressure.When the pseudo load pressure is lower than the load pressure, the output pressure is higher than the load pressure, and the pseudo load pressure is higher than the load pressure. When high pressure, the output pressure is lower than the load pressure. This is a displacement control device for variable displacement hydraulic pumps.

According to the first invention, the pump pressure and the load pressure act on the LS valve 8 at the time of a delay, and the variable pressure hydraulic pump is balanced. The capacity of the pump 1 is controlled so as to become the set differential pressure.

When the actual differential pressure is smaller than the set differential pressure, a pressure higher than the load pressure acts on the LS valve 8, and a differential pressure greater than the actual differential pressure acts on the LS valve 8. The LS valve 8 controls to increase the capacity of the variable displacement hydraulic pump 1 more than based on the actual differential pressure. As a result, the capacity of the variable displacement hydraulic pump 1 is increased in a short time, and the responsiveness is improved.

Since the actual differential pressure is larger than the set differential pressure, sometimes a pressure lower than the load pressure acts on the LS valve 8, and a differential pressure greater than the actual differential pressure acts on the LS valve 8. The LS valve 8 controls the capacity of the variable displacement hydraulic pump 1 to decrease more than based on the actual differential pressure. As a result, the capacity of the variable displacement hydraulic pump 1 is reduced in a short time, and the response is improved.

Further, when the pseudo load pressure has a high degree of change in the actual differential pressure, the pseudo load pressure is set to be lower and higher than the load pressure, so that the capacity of the variable displacement hydraulic pump 1 is increased. The decreasing speed is in accordance with the operating speed of the operating valve 2. Thereby, the responsiveness is further improved.

In the second invention, the pressure reducing valve 31 in the first invention is pushed toward the drain position by the pressure of the first pressure receiving chamber 32 and the second pressure receiving chamber 33. , Communicating position by the pressure of the third pressure receiving chamber 34 , The accumulator 37 is provided with an accumulator 37 and a throttle 35, and the accumulator 37 is provided in the accumulator chamber 38 of the accumulator 37. When the discharge pressure is supplied, the back pressure chamber 41 of the accumulator 37 is connected to the load pressure detection circuit 36 via the throttle 35, and the throttle 35 and the back pressure chamber are connected. The first pressure receiving chamber 3 2 of the pressure reducing valve 3 1 is connected to the output side, and the third pressure receiving chamber 3 2 of the pressure reducing valve 3 1 is connected to the output side. The pressure receiving chamber 34 is a displacement control device for the variable displacement hydraulic pump connected to the load pressure detection circuit 36.

According to the second invention, the piston 3 is provided by the pressure difference between the pump discharge pressure and the load pressure acting on the accumulator chamber 38 and the back pressure chamber 41 of the accumulator 37. 9 moves and load pressure flows into and out of the back pressure chamber 41. As a result, a differential pressure is generated before and after the throttle 35, so that a pseudo load pressure lower or higher than the load pressure is generated.

Also, since the differential pressure around the throttle 35 differs depending on the flow velocity of the load pressure flowing into and out of the back pressure chamber 41, the pseudo load pressure is lower than the load pressure according to the operating speed of the operating valve. As a result of the high pressure, the capacity of the variable displacement hydraulic pump increases and decreases more quickly when the operating valve is suddenly operated, so that the responsiveness is further improved.

The third invention operates by the actual differential pressure between the pump discharge pressure of the variable displacement hydraulic pump 1 and the load pressure of the hydraulic actuator 3, and the actual pressure difference LS valve 8 that controls the capacity of variable displacement hydraulic pump 1 so that the differential pressure becomes the set differential pressure. And a means for generating a control pressure based on a difference between the actual differential pressure and the set differential pressure and a change in the actual differential pressure per unit time, wherein the means includes an actual differential pressure and a set differential pressure. When the pressures are equal, the control pressure is equal to the load pressure.When the actual differential pressure is smaller than the set differential pressure, the control pressure is set to the load pressure according to the degree of change of the actual differential pressure. When the actual differential pressure is larger than the set differential pressure, the control pressure is set higher than the negative pressure according to the degree of change of the actual differential pressure. When the control pressure is equal to the load pressure, the capacity is controlled so that it becomes the set differential pressure, and when the control pressure is lower than the load pressure, the capacity is increased so that it becomes higher than the set differential pressure. When the control pressure is higher than the load pressure, the capacity is reduced so that it becomes lower than the set differential pressure. DOO Ru displacement controller der of the variable displacement hydraulic port down-flop, wherein.

According to the third invention, when the actual differential pressure and the set differential pressure are equal, the control pressure equal to the pump discharge pressure and the load pressure acts on the LS valve 8, and the LS valve 8 balances. Then, the displacement of the variable displacement hydraulic pump 1 is controlled so as to become the set differential pressure.

When the actual differential pressure is smaller than the set differential pressure, a control pressure lower than the load pressure acts on the LS valve 8, and a differential pressure higher than the actual differential pressure acts on the LS valve 8. Therefore, the LS valve 8 controls to increase the capacity of the variable displacement hydraulic pump 1 so as to be equal to or higher than the set differential pressure. As a result, the capacity of the variable displacement hydraulic pump 1 increases in a short time, and the response improves. When the actual differential pressure is larger than the set differential pressure, the LS valve is used. Since a control pressure higher than the load pressure acts on the LS valve 8 and a differential pressure higher than the actual differential pressure acts on the LS valve 8, the LS valve 8 has the capacity of the variable displacement hydraulic pump 1. Is controlled so as to be equal to or less than the set differential pressure. Their in one Reniyo, displacement of the variable displacement hydraulic pump 1 was _c or improved responsiveness decreases in a short time, the control pressure is at the actual fast change degree of the pressure difference Ri by the load pressure Since the pressure is set to be even lower and higher, the speed at which the capacity of the variable displacement hydraulic pump 1 increases and decreases depends on the operation speed of the operation valve 2. Thereby, the responsiveness is further improved.

The fourth invention is that the LS valve 8 according to the third invention is operated in a capacity decreasing direction by a pump discharge pressure and a control pressure, and is operated in a capacity increasing direction by two load pressures. The pump discharge pressure is supplied to the accumulator chamber 38 of the accumulator 37 by using the accumulator 37 and the throttle 35 as a means. Then, the load pressure is supplied to the back pressure chamber 41 via the throttle 35, and the control pressure is detected from the back pressure chamber 41 closer to the back pressure chamber 41 of the variable pressure hydraulic pump. It is a capacity control device.

According to the fourth invention, the piston 3 is provided by the differential pressure between the pump discharge pressure and the load pressure acting on the pressure accumulating chamber 38 and the back pressure chamber 41 of the accumulator 37. 9 moves and load pressure flows into and out of the back pressure chamber 41. As a result, a differential pressure is generated before and after the throttle 35, so that a control pressure lower and higher than the load pressure is generated.

LS valve 8 sets the differential pressure between pump discharge pressure and one load pressure. At the same time, the capacity is controlled by the control pressure and the other load pressure. As a result, when the control pressure is lower than the load pressure, the LS valve 8 operates in the capacity increasing direction at the other load pressure. The capacity of the hydraulic pump 1 increases in a short time, and the response is improved.

Also, when the control pressure is higher than the load pressure, the LS valve 8 operates in the direction of decreasing the capacity by the control pressure. The capacity is reduced in a short time and the response is improved.

Also, since the differential pressure across the throttle 35 differs depending on the flow velocity of the load pressure flowing into and out of the back pressure chamber 41, the control pressure is lower and higher than the load pressure according to the operating speed of the operating valve. It becomes. As a result, the capacity of the variable displacement hydraulic pump increases and decreases more quickly when the operating valve is suddenly operated, so that the responsiveness is further improved. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a hydraulic circuit diagram of a conventional example.

FIG. 2 is a hydraulic circuit diagram showing the first embodiment of the present invention.

FIG. 3 is a hydraulic circuit diagram showing a second embodiment of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION As shown in FIG. 2, a pressure reducing valve 31 is provided in a circuit 30 connecting the discharge passage 1 a of the variable hydraulic pump 1 and the second pressure receiving portion 13 of the LS valve 8. The pressure reducing valve 31 is pushed toward the drain position a by the pressure of the first and second pressure receiving chambers 32 and 33, and is moved toward the communication position b by the pressure of the third pressure receiving chamber 34. _c the pressed Te first pressure receiving chamber 3 2 is connected to the circuitry 3 6 out load pressure via a diaphragm 35, a second pressure receiving chamber 3 3 is connected to the output side of the pressure reducing valve 3 1, 3 The pressure receiving chamber 34 is connected to a load pressure detection circuit 36.

The pressure receiving area of the first pressure receiving chamber 32 and the pressure receiving area of the second pressure receiving chamber 33 are equal, and the pressure receiving area of the third pressure receiving chamber 34 is doubled. Due to such a force, the pressure reducing valve 31 is non-linear at Pl = 2XP31-P2. Here, P 1 is the output pressure, P 2 is the pressure in the first pressure receiving chamber 32, and P 3 is the pressure in the third pressure receiving chamber 34.

The input side of the pressure reducing valve 31 is connected to a pressure accumulating chamber 38 of an accumulator 37, and the accumulator 37 has a piston 39 connected to a spring 4. The pressure of 0 and the back pressure chamber (spring chamber) 4 1 is pushed in the direction of decreasing the pressure in the accumulator chamber. The back pressure chamber 41 is connected to a load pressure detection circuit 36 via the restrictor 35, and is connected.

Next, the operation will be described.

(In the steady state, when the control valve 2 is held at a position with a small opening area).

The actual differential pressure is equal to the set differential pressure. The capacity is small (the pump discharge flow rate is small) corresponding to the opening area of the control valve 2.

At this time, the pump discharge pressure P 0 acts on the accumulator chamber 38 of the accumulator 37, the load pressure PLS acts on the back pressure chamber 41, and the piston Numeral 39 denotes a position where the differential pressure between the pump discharge pressure PO and the load pressure PLS and the force of the spring 40 are no longer in balance, and then stop.

The actual load pressure PLS detected by the load pressure detection circuit 36 acts on the first pressure receiving chamber 32 of the pressure reducing valve 31, and the actual load pressure PLS also acts on the third pressure receiving chamber 34 of the pressure reducing valve 31. PLS is than to act, the output pressure of the pressure reducing valve 3 1 is One by the being this _c actual ing negative Ni圧PLS, LS valve 8 of the actual load pressure PLS and Po emissions flop discharge pressure PO The differential pressure balances with the set differential pressure, and the discharge flow rate (capacity) of the variable hydraulic pump 1 becomes the required flow rate of the operation valve.

(When the control valve 2 is operated from the position of the small opening area to the large opening area.)

As described above, since the required flow rate of the operating valve increases and the pump discharge pressure P O decreases, the actual differential pressure decreases below the set differential pressure.

At this time, the pressure in the accumulator chamber 38 of the accumulator 37 decreases, and the piston 39 slides with the spring 40 in the direction of decreasing the volume of the accumulator chamber, causing the back pressure chamber to slide. since 4 1 volume is increased, the actual load pressure PLS is acting on _c this Reniyo one with decompression valve 3 1 of the first pressure receiving portion 3 2 which flows into the back pressure chamber 4 1 through the aperture 35 The pressure is lower than the actual load pressure PLS by the pressure drop corresponding to the flow resistance of the throttle 35.

For this reason, the output pressure of the pressure reducing valve 31 becomes higher than the actual load pressure PLS by the pressure ΔΡ corresponding to the above-mentioned pressure drop, and the second pressure receiving portion 13 of the LS valve 8 has ( P LS + Δ Ρ) acts. Therefore, the differential pressure between the first pressure receiving portion 12 and the second pressure receiving portion 13 of the LS valve 8 becomes PO— (PLS + ΔP), and the actual load pressure p LS and the pump discharge pressure P It is smaller than the differential pressure (PO-PLS) from 0.

Therefore, the force that pushes the LS valve 8 to the drain position B is larger than the force based on the actual differential pressure, and the large-diameter pressure receiving chamber 7 of the servo piston 5 and the first circuit 9 Since the opening area is large, the displacement speed of the displacement control member 4 increases, and the displacement of the variable hydraulic pump 1 increases rapidly.

(When the capacity of the variable hydraulic pump 1 increases and the pump discharge flow rate approaches the required flow rate of the operation valve.)

The pump discharge pressure P O increases, and the actual differential pressure is slightly smaller than the set L S differential pressure.

At this time, the pressure in the accumulator chamber 38 of the accumulator 37 increases (pump discharge pressure PO), the piston 39 is pushed, and the spring 40 once expands. The oil in the back pressure chamber 41 of the accumulator 37 flows back to the load pressure detection circuit 36 because it moves in the direction of contraction from the state, but there is a restriction 35. The pressure in the back pressure chamber 41 of the accumulator 37 is higher than the actual LS pressure (PLS), but the change in differential pressure is small. Changes in pressure and movement are less. Therefore, the pressure in the back pressure chamber 41 of the accumulator 37 is almost equal to the actual LS pressure (PLS), and the pressure is slightly higher.

Acting on the first pressure receiving part 32 of the pressure reducing valve 31, the pressure in the back pressure chamber 41 of the accumulator 37 is equal to the actual load pressure (PLS). The output pressure (P1) of the pressure reducing valve 31 is slightly higher or almost equal to the actual load pressure (PLS) because the pressure is slightly higher and the force is equivalent.

Therefore, the differential pressure between the pressure acting on the first pressure receiving portion 12 and the second pressure receiving portion 13 of the LS valve 8 is slightly smaller than the differential pressure between the actual pump discharge pressure PO and the actual load pressure PLS. High or almost equal.

As a result, the LS valve 8 is operated, and the tilt angle of the displacement control member 4 is reduced (the pump discharge amount is reduced to increase the brake force), or the LS valve 8 is operated. Brake in the direction of opening and closing (increase the pump discharge amount).

(When the capacity of the variable hydraulic pump 1 has become larger than the value corresponding to the set differential pressure, and the pump discharge flow rate has exceeded the required flow rate of the operation valve.)

The pump discharge pressure P 0 increases, and the actual differential pressure is larger than the set differential pressure.

At this time, the pressure in the accumulator chamber 38 of the accumulator 37 increases, and the piston 39 moves at a position corresponding to the set differential pressure more than it is stationary. Then, the spring 40 is contracted. Since the spring 40 moves in the contracting direction, The pressure oil in the back pressure chamber 41 of the heater 37 flows back to the load pressure detection circuit 36. However, since there is a throttle 35, the back pressure chamber 41 of the accumulator 37 The pressure inside is higher than the actual load pressure PLS.

Therefore, the pressure in the back pressure chamber 41 of the accumulator 37 acting on the first pressure receiving portion 32 of the pressure reducing valve 31 is higher than the actual load pressure PLS. Therefore, the output pressure of the pressure reducing valve 31 becomes lower than the actual load pressure PLS.

As a result, the differential pressure between the pressure acting on the first pressure receiving portion 12 and the second pressure receiving portion 13 of the LS valve 8 is equal to the difference between the pump discharge pressure PO and the actual load pressure PLS. When the pressure is greater than the pressure, the LS valve 8 is operated to the supply position A to reduce the capacity of the variable hydraulic pump 1 and reduce the discharge flow rate. Therefore, the pump discharge flow rate matches the required flow rate of the operation valve.

(When the control valve 2 is operated from the large opening area to the small opening area.)

As described above, the pump discharge pressure P O increases, and the actual differential pressure is larger than the set differential pressure (the pump discharge flow rate is higher than the required flow rate of the operation valve).

At this time, the pressure in the pressure accumulating chamber 41 of the accumulator 37 increases, and the piston 39 moves at a position corresponding to the set differential pressure more than it is stationary. As a result, the spring 40 is contracted. ₍ This causes the pressure oil in the back pressure chamber 41 of the accumulator 37 to flow back to the load pressure detection circuit 36, The pressure in the back pressure chamber 41 of the accumulator 37 is actually Load pressure PLS.

Therefore, the pressure acting on the first pressure receiving chamber 32 of the pressure reducing valve 31 becomes higher than the actual load pressure PLS only by a pressure increase corresponding to the flow resistance of the throttle 35, and the pressure reducing valve becomes higher. The output pressure of 31 is lower than the actual load pressure PLS only by the pressure P corresponding to the pressure rise.

For this reason, the pressure (PLS−ΔP) acts on the second pressure receiving portion 13 of the LS valve 8. Accordingly, the differential pressure between the pressure acting on the first pressure receiving portion 12 and the second pressure receiving portion 13 of the LS valve 8 is PO-(PLS-ΔΡ), and the difference between the pump discharge pressure PO and the actual Load pressure differential pressure (PO—PLS).

Accordingly, the force for pushing the LS valve 8 to the supply position A is larger than the force based on the actual differential pressure, and the large-diameter pressure receiving chamber 7 of the servo piston 5 and the opening of the second circuit 11 are opened. Since the opening area is large, the displacement speed of the displacement control member 4 increases, and the displacement of the variable hydraulic pump 1 decreases rapidly.

To summarize the above operation, the accumulator 37 and the throttle 35 have the difference between the actual pressure difference between the pump discharge pressure PO and the load pressure PLS, and the actual pressure difference between the pump pressure PLS and the load pressure PLS. the _c concrete to form the means that occurs a pseudo-negative Ni圧in time Tsu by to the person Ri changes in differential pressure, is sometimes not equal the set differential pressure and the actual differential pressure, a queue-time The pseudo load pressure becomes equal to the load pressure because the pin 39 of the rater 37 is settled and the pressurized oil does not flow to the throttle 35. If the actual differential pressure is lower than the set differential pressure, The spring 40 expands and pushes the piston 39 to apply a load pressure to the back pressure chamber 41, and a differential pressure is generated before and after the throttle 35 so that the pseudo load pressure is lower than the load pressure. Become . The actual differential pressure is larger than the set differential pressure, and sometimes, the piston 39 moves in the direction to contract the S-spring 40, causing the load pressure in the back pressure chamber 41 to flow out and restricting. A differential pressure is generated around 35, and the pseudo load pressure becomes higher than the load pressure.

The speed at which the load pressure flows into and out of the back pressure chamber 41 of the accumulator 37 is determined by the pressure change rate of the pump discharge pressure, that is, the time corresponding to the actual load pressure time. The larger the change, the faster the change, and the smaller the change, the slower. Therefore, the above-mentioned pseudo load pressure changes per unit time of the actual load pressure (in other words, the lower the operating speed of the operating valve 2), the lower the pressure. , High pressure.

The pressure reducing valve 31 reduces the pump discharge pressure with the load pressure and the pseudo load pressure to make the output pressure higher and lower than the load pressure. Specifically, when the pseudo differential pressure is equal to the load pressure, the output pressure is equal to the load pressure, and when the pseudo differential pressure is lower than the load pressure, the output pressure is lower than the negative pressure. If the pseudo differential pressure is higher than the load pressure, the output pressure will be lower than the load pressure.

Since the LS valve 8 becomes the communication position A and the drain position B based on the differential pressure between the pump discharge pressure and the output pressure of the pressure reducing valve 31, the actual differential pressure becomes the set differential pressure as described above. When the pressure is smaller than the above, the differential pressure between the pump discharge pressure acting on the LS valve 8 and the output pressure of the pressure reducing valve 31 is larger than the differential pressure between the pump discharge pressure and the load pressure. Become . As a result, the force for pushing the LS valve 8 to the drain position B increases, and the pump discharge pressure is quickly supplied to the large-diameter chamber 7 of the servo piston 5. As a result, the capacity of the variable hydraulic pump 1 increases in a short time.

As the capacity of the variable hydraulic pump 1 increases and the discharge flow rate approaches the required flow rate of the control valve, the difference between the actual differential pressure and the set differential pressure becomes smaller. Since the differential pressure acting on the valve 8 is larger than the actual differential pressure difference, the force for pushing the LS valve 8 to the drain position B is large. As a result, a large amount of pump discharge pressure is continuously supplied to the large-diameter chamber 7 of the servo piston 5, so that the asymptotic increase in the discharge flow rate of the variable hydraulic pump 1 is suppressed. Be done. That is, it prevents a decrease in the change in the approach speed to the target discharge flow rate.

Further, as described above, when the actual differential pressure is larger than the set differential pressure, the differential pressure between the pump discharge pressure acting on the LS valve 8 and the output pressure of the pressure reducing valve 31 becomes the pump pressure. It becomes larger than the differential pressure between the discharge pressure and the load pressure. As a result, the force for pushing the LS valve 8 to the communication position A increases, and the hydraulic oil in the large-diameter chamber of the servo piston 5 flows out to the tank, and the pressure of the variable hydraulic pump 1 increases. The capacity decreases in a short time.

As the capacity of the variable hydraulic pump 1 decreases and the discharge flow rate approaches the required flow rate of the control valve, the difference between the actual differential pressure and the set differential pressure becomes smaller. Since the differential pressure acting on the valve 8 is larger than the actual differential pressure difference, the force for pushing the LS valve 8 to the communication position A is large. By this Since a large amount of pressure oil in the large-diameter chamber 7 of the servo piston 5 continues to flow out to the tank, the decrease in the discharge flow rate of the variable hydraulic pump 1 is suppressed. That is, it prevents the change in the approach speed to the target discharge flow rate.

Next, a second embodiment of the present invention will be described.

As shown in FIG. 3, the LS valve 8 is provided with a third pressure receiving portion 50 and a fourth pressure receiving portion 51. The load pressure detection circuit 36 is squeezed and the squeeze 3 5 is squeezed to communicate with the back pressure chamber 41 of the accumulator 37, and the circuit 30 is stored in the accumulator 37. Access to rooms 3-8.

The third pressure receiving portion 50 is connected to the back pressure chamber 41 closer to the throttle 35 than to the throttle 35, and the fourth pressure receiving portion 51 is connected to the load pressure detection circuit 36.

Next, the operation will be described.

The LS valve 8 has a differential pressure between a pump discharge pressure PO acting on the first pressure receiving portion 12 and a load pressure PLS acting on the second pressure receiving portion 13, and a control pressure acting on the third pressure receiving portion 50. It is pushed to the communication position A and the drain position B by the pressure difference between the pressure and the load pressure acting on the fourth pressure receiving portion 51.

The piston 39 of the accumulator 37 is settled when the actual differential pressure between the pump discharge pressure and the load pressure is equal to the set differential pressure. Load pressure does not flow to Thereby, the control pressure acting on the third pressure receiving portion 50 of the LS valve 8 is equal to the load pressure.

The piston 39 of the accumulator 37 is pump discharge. When the actual pressure difference between the pressure and the load pressure is smaller than the set pressure difference, the spring moves by the spring 40 and the load pressure flows into the back pressure chamber 41. As a result, a differential pressure is generated before and after the throttle 35, and the control pressure acting on the third pressure receiving portion 50 of the LS valve 8 becomes lower than the load pressure.

The piston 39 of the accumulator 37 has a spring 40 at the pump discharge pressure when the actual differential pressure between the pump discharge pressure and the load pressure is larger than the set differential pressure. , And the load pressure in the back pressure chamber 41 flows out. As a result, a differential pressure is generated before and after the restrictor 35, and the control pressure acting on the third pressure receiving portion 50 of the LS valve 8 becomes higher than the load pressure.

In other words, the accumulator 37 and the throttle 35 reduce and increase the load pressure according to the difference between the actual differential pressure between the pump discharge pressure and the load pressure and the differential pressure between the set differential pressure. Thus, a means for controlling the pressure is formed.

When the discharge flow rate of the variable hydraulic pump 1 is equal to the required flow rate of the operation valve 2 and the actual differential pressure is equal to the set differential pressure, the third pressure receiving section 50 of the S valve 8 is operated as described above. The control pressure acting on the LS valve 8 becomes the load pressure, the load pressure S acts on the fourth pressure receiving portion 51 of the LS valve 8, and the LS valve 8 acts on the first pressure receiving portion 12. Balancing at a position corresponding to the pump discharge pressure and the load pressure acting on the second pressure receiving portion 13, the variable hydraulic pump 1 maintains its capacity.

Operate the valve 17 to increase the opening area of the control valve 2 so that the required flow rate of the control valve is less than the discharge flow rate of the variable hydraulic pump 1. When the pressure increases, the pump discharge pressure decreases as described above, and the actual differential pressure between the pump discharge pressure and the load pressure decreases.

As a result, as described above, the accumulator 37 is actuated, and the third pressure receiving portion 50 of the LS valve 8 is actuated by a pressure lower than the load pressure. The LS valve 8 is pushed toward the drain position B by the load pressure acting on the fourth pressure receiving portion 51.

On the other hand, the LS valve 8 moves toward the drain position B due to the differential pressure between the pump discharge pressure acting on the first pressure receiving part 12 and the negative pressure acting on the second pressure receiving part 13. It is pushed. In other words, the L S valve 8 is the same as when the set differential pressure is increased.

Therefore, the opening area for communicating the first circuit 9 with the large-diameter chamber 7 of the servopiston 5 by the LS valve 8 is larger than that of a normal LS valve. Since a large amount of pressure oil in the large-diameter chamber 7 flows out to the tank, the capacity of the variable hydraulic pump 1 increases quickly.

When the discharge flow rate of the variable hydraulic pump 1 approaches the required flow rate of the operation valve, the actual differential pressure is slightly smaller than the set differential pressure. The piston 39 of the accumulator 37 slightly moves in the direction of contracting the spring 40, and approaches the above-mentioned settled position. The load pressure in the back pressure chamber 41 flows out, and a differential pressure is generated around the throttle 35.However, since the outflow is small, the pressure difference around the throttle 35 is small. There is little change in movement. Therefore, the control pressure is slightly higher than the load pressure, or equivalently, the pressure of the third pressure receiving portion 50 of the S valve 8 is slightly higher than or equal to the load pressure. As a result, the LS valve 8 is pushed toward the communicating position A to reduce the capacity of the variable hydraulic pump 1 (brake the capacity boost B).

When the opening area of the control valve 2 is reduced by operating the lever 17 and the required flow rate of the control valve is lower than the discharge flow rate of the variable hydraulic pump 1, as described above, The pump discharge pressure increases, and the actual pressure difference between the pump discharge pressure and the load pressure increases.

As a result, the accumulator 37 is actuated as described above, and the third pressure receiving portion 50 of the LS valve 8 receives a force higher than the load pressure on the third pressure receiving portion 50. The LS valve 8 is pushed toward the communication position A by the pressure difference between the LS valve 8 and the load pressure acting on the fourth pressure receiving portion 51.

On the other hand, the LS valve 8 is pushed toward the communication position A by the differential pressure between the pump discharge pressure acting on the first pressure receiving part 12 and the negative load pressure acting on the second pressure receiving part 13. Is That is, the L S valve 8 is the same as when the set differential pressure is reduced.

Therefore, the opening area for communicating the second circuit 11 with the large-diameter chamber 7 of the servopiston 5 by the LS valve 8 is larger than that of a normal LS valve. However, since a large amount of the pump discharge pressure flows into the large-diameter chamber 7, the capacity of the variable hydraulic pump 1 decreases quickly.

The discharge flow rate of the variable hydraulic pump 1 is close to the required flow rate of the operation valve. The actual differential pressure is slightly larger than the set differential pressure. The piston 39 of the accumulator 37 is slightly moved by the spring 40 to approach the above-mentioned settled position. Back pressure chamber

4 1 The internal load pressure flows in, and a differential pressure is generated around the throttle 35.However, since the flow rate is small, the differential pressure around the throttle 35 is small. changes in-out fine movement is Tsu by less Do have _c, control or pressure is slightly lower Ri by load pressure, a third pressure receiving portion 5 0 S valve 8 because equivalent was of little Ri by the load pressure Low power, equivalent. As a result, the LS valve 8 is pushed toward the drain position C to increase the capacity of the variable hydraulic pump 1 Π (force the brake for decreasing the capacity). .

Claims

The scope of the claims

1. Operated by the actual differential pressure between the pump discharge pressure of the variable displacement hydraulic pump 1 and the load pressure of the hydraulic actuator 3, and the actual differential pressure is set. An LS valve 8 for controlling the capacity of the variable displacement hydraulic pump 1 so as to be a differential pressure, a difference between the actual differential pressure and the set differential pressure, and a time of the actual differential pressure. Means for generating a pseudo load pressure by a hit change;

A pressure reducing valve 31 for reducing the pump discharge pressure with the load pressure and the pseudo load pressure and operating the reduced pressure as the load pressure on the LS valve 8. When the actual differential pressure is equal to the set differential pressure, the pseudo load pressure is equal to the load pressure, and when the actual differential pressure is smaller than the set differential pressure, it depends on the degree of change of the actual differential pressure. The pseudo load pressure is lower than the load pressure, and when the actual differential pressure is higher than the set differential pressure, the pseudo load pressure is higher than the load pressure according to the degree of change in the actual differential pressure. The pressure reducing valve 31 sets the output pressure to the load pressure when the pseudo load pressure is equal to the load pressure, and sets the output pressure to the load pressure when the pseudo load pressure is lower than the load pressure. When the pseudo load pressure is higher than the load pressure, the output pressure is lower than the load pressure. Variable displacement hydraulic port down-flop of the displacement control device comprising a call to.

2. The pressure reducing valve 31 is pushed toward the drain position by the pressure of the first pressure receiving chamber 32 and the second pressure receiving chamber 33, and is directed to the communicating position by the pressure of the third pressure receiving chamber 34. Shall be pushed, The above means is provided with an accumulator 37 and a throttle 35. A pump discharge pressure is supplied to a pressure accumulating chamber 38 of the accumulator 37, and the accumulator is operated. The back pressure chamber 41 of the muffler 37 is connected to the load pressure detection circuit 36 via the throttle 35, and the space between the throttle 35 and the back pressure chamber 41 is the first pressure reducing valve 31. 1 The second pressure receiving chamber 3 of the pressure reducing valve 3 1 is connected to the pressure receiving chamber 3 2.

The displacement control device for a variable displacement hydraulic pump according to claim 1, wherein 3 is connected to the output side, and the third pressure receiving chamber 34 is connected to a load pressure detection circuit 36.

3. Operated by the actual differential pressure between the pump discharge pressure of the variable displacement hydraulic pump 1 and the load pressure of the hydraulic actuator 3, and the actual differential pressure is set. An LS valve 8 for controlling the capacity of the variable displacement hydraulic pump 1 so as to be a differential pressure, a difference between the actual differential pressure and the set differential pressure, and a time for the actual differential pressure. Means for generating a control pressure according to the change is provided. When the actual differential pressure and the set differential pressure are equal, the control means sets the control pressure equal to the load pressure and sets the actual differential pressure to When the differential pressure is smaller than the set differential pressure, the control pressure is set lower than the load pressure according to the degree of change of the actual differential pressure, and when the actual differential pressure is larger than the set differential pressure. The control pressure is set higher than the load pressure in accordance with the degree of change in the actual differential pressure, and the LS valve 8 controls the control pressure to be equal to the load pressure. When the pressures are equal, the capacity is controlled so as to be the set differential pressure, and when the control pressure is lower than the load pressure, the capacity is increased so as to be higher than the set differential pressure. When the control pressure is higher than the load pressure, it is lower than the set differential pressure. A displacement control device for a variable displacement hydraulic pump, characterized in that the displacement is controlled so that the displacement becomes as follows.

4. The LS valve 8 is operated in the direction of decreasing the capacity by the pump discharge pressure and the control pressure, and is operated in the direction of increasing the capacity by the load pressure. And a throttle 35 as means for generating the control pressure. A pump discharge pressure is supplied to a pressure accumulating chamber 38 of the accumulator 37, and a throttle 3 is supplied to the back pressure chamber 41. 5. The capacity control of the variable displacement hydraulic pump according to claim 3, wherein the control pressure is supplied from a position near the back pressure chamber 41 of the throttle 3 5 by supplying the load pressure via the pressure pump 5. apparatus.