JPH05164104A - Flow control signal circuit for hydraulic pump - Google Patents

Abstract

PURPOSE:To provide a flow control signal circuit for a hydraulic pump which solves problems that shocks in the start of an actuator are large when an operating lever is operated with a full stroke in conventional hydraulic circuits so that the hydraulic pump is liable to cause a cavitation phenomenon. CONSTITUTION:A slow return valve 19 composed in parallel combination of a small throttle 6 and a check valve 7 having the direction from a control valve 2 to a hydraulic pump as free flow is inserted and provided in a pilot flow path 10 branching from the upstream of a large throttle 5 in the control valve 2 generating a negative a negative control signal pressure so as to prevent troubles caused by the fast drop of negative control pressure of the pump.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow control signal circuit applied to a hydraulic pump of a hydraulic excavator.

[0002]

2. Description of the Related Art FIGS. 3 and 4 show techniques relating to a hydraulic pump flow rate control signal circuit of a conventional hydraulic excavator. In FIG. 3, when the directional control valve 3 is in the position where the actuators (not shown) are not driven, that is, in the neutral position N, the variable displacement hydraulic pump 1 is in the unload state, and its discharge oil is the center bypass passage of the control valve 2. 9 and then through the large throttle 5 via the flow path 18 back to the tank 8. When the operating lever 15 shown in FIG. 4 is operated by a full stroke to move an actuator (not shown), the signal pressure A is transmitted to the control valve 2 via the signal oil passages 16 and 13 to shift the directional control valve 3 to the D position. At this time, the center bypass passage 9 is closed, and the discharge oil of the variable displacement hydraulic pump 1 passes through the directional control valve 3 to an actuator (not shown).
The variable displacement hydraulic pump 1 is turned on because the discharge pressure is directed to the flow path to the variable pressure hydraulic pump 1 according to the load of the actuator.

From the above, in the unloading state of the variable displacement hydraulic pump 1, the resistance due to the discharge oil passing through the large throttle 5 upstream of the large throttle 5 provided at the end of the center bypass passage 9 in the control valve 2 A pressure is generated and guided as a signal pressure to the negative control unit 11 of the variable displacement hydraulic pump 1 through the pilot flow path 10, whereby the discharge oil amount of the variable displacement hydraulic pump 1 is suppressed to the minimum, and the discharge pressure is It becomes a low level such that the flow resistance of the center bypass passage 9 in the control valve 2 of the discharged oil is added to the signal pressure at the throttle 5 having a large load state.

Further, when the variable displacement hydraulic pump 1 is in the on-load state, the flow rate of the center bypass passage 9 in the control valve 2 becomes zero, so that the pressure on the upstream side of the large throttle 5 becomes zero. The signal pressure acting on the negative control unit 11 of No. 1 is the pilot flow path 1
0, through the large throttle 5, and the flow path 18 to the tank 8. As a result, the variable displacement hydraulic pump 1 changes from the negative control to the horsepower control state, the discharge pressure of the variable displacement hydraulic pump 1 becomes a level according to the load pressure of the actuator (not shown), and the discharge flow rate Q with respect to the discharge pressure P. Changes according to the set flow rate to pressure characteristic (PQ characteristic).

[0005]

The operating lever 15 shown in FIG. 4 is used to move either actuator (not shown).
When full stroke operation is performed, the variable displacement hydraulic pump 1 shifts from negative control to horsepower control as described above. The state of changes in the negative control pressure and the pump flow rate of the hydraulic pump 1 at that time is as shown in (1) of FIG. That is, in the conventional circuit, changes in the negative control pressure and the pump flow rate with the passage of time of lever operation are both fast,
Rapid rise in the direction of increasing pump flow rate. Therefore, the actuator has a large shock at the time of starting, and the hydraulic pump is apt to cause a cavitation phenomenon in the vicinity of the suction port. It is an object of the present invention to provide a flow control signal circuit that solves these problems.

[0006]

[Means for Solving the Problem] (First Means)

A flow rate control signal circuit of a hydraulic pump according to the present invention is a hydraulic circuit comprising a hydraulic pump 1, a control valve 2 and a tank 8. The hydraulic pump 1 includes a negative control section 11 and a horsepower control section 12. The negative control unit 11 inputs the negative control pressure from the small throttle 6 of the slow return valve 19 through the pilot flow passage 10, and the horsepower control unit 12 inputs the control signal from the discharge unit of the hydraulic pump 1 to control the control valve 2 Is provided with a directional control valve 3, a large throttle 5 and a slow return valve 19, and the directional control valve 3 is controlled by signals (A, B) from the operating lever 15,
The oil input from the hydraulic pump 1 is input to the actuator or the center bypass passage 9, and the large throttle 5 guides the oil from the center bypass passage 9 of the control valve 2 to the tank 8 and the upstream side of the large throttle 5 in the control valve 2. The slow return valve 19 inserted in the pilot flow path 10 branched from is composed of a small throttle 6 and a check valve 7 arranged in parallel, and the check valve 7 is free-flowing in the direction from the control valve 2 to the hydraulic pump 1. The small throttle 6 is characterized in that the negative control pressure on the upstream side of the large throttle 5 is applied to the negative control section 11 of the hydraulic pump 1 via the pilot passage 10. (Second means)

In the flow rate control signal circuit of the hydraulic pump according to the present invention, in the first means, the slow return valve 19 is
A small throttle 6 and a check valve 7 are arranged in parallel, the check valve 7 is a free flow in the direction from the control valve 2 to the hydraulic pump 1, and the small throttle 6 is a negative control upstream of the large throttle 5. The pressure is applied to the negative control unit 11 of the hydraulic pump 1 through the pilot flow path 10 together with the check valve 7, and the directional control valve 3 on the upstream side is switched to close the center bypass passage 9 and the upstream side of the large throttle 5. When the discharge oil of the hydraulic pump 1 is no longer supplied to the branch point 20, the small throttle 6 prevents the pressure in the pilot flow passage 10 from rapidly dropping.

[0009]

When the directional control valve 3 is shifted from the neutral position N to the C or D position to drive the actuator, the flow rate in the bypass passage 9 of the control valve 2 is blocked, so that the negative control pressure on the upstream side of the large throttle 5 is increased. The hydraulic pump 1 goes down to zero and shifts from negative control to horsepower control.

The slow return valve 19 in the circuit of the present invention is used when the hydraulic pump 1 shifts from negative control to horsepower control, that is, when the hydraulic pump 1 is on-load, and the negative control pressure is suddenly increased as shown in (1) of FIG. It works to suppress the change to zero. That is, the negative control pressure of the hydraulic pump 1 causes the compressed oil in the pilot flow passage 10 to flow through the slow return valve 1
The negative control pressure gradually decreases as compared with the conventional circuit because the control flow function of 9 causes the small throttle 6 to gradually release.

When the hydraulic pump 1 is unloaded, the center bypass passage 9 of the control valve 2 opens, and negative control pressure is generated upstream of the large throttle 5, but the check valve 7 of the slow return valve 19 has a large throttle 5. There is a free flow from the upstream side to the negative control direction, and the negative control pressure acts on the hydraulic pump 1 at a quick rise as in the conventional case.

As a result, in the present invention, as shown in FIG. 2 (2), the negative control pressure gradually drops when the hydraulic pump 1 shifts from unload to on-load, and the hydraulic pump discharge flow rate gradually increases. .. On the contrary, when the hydraulic pump 1 shifts from on-load to unload, the negative control pressure rises as fast as the conventional one, and the hydraulic pump also falls quickly to the negative flow rate (minimum flow rate) level.

[0013]

Embodiments of the hydraulic excavator according to the present invention will be described with reference to FIGS. As shown in FIG. 1, a slow return valve 19 is newly provided in the present invention as compared with the conventional circuit of FIG.
Is added as follows.

A slow return valve 19 is inserted in the pilot passage 10 downstream of the branch point 20 of the pilot passage 10 upstream of the large throttle 5 in the control valve 2. The slow return valve 19 is composed of a small throttle 6 and a check valve 7. The check valve 7 has a free flow in the direction from the control valve 2 to the hydraulic pump 1 and is configured by combining the small throttle 6 in parallel.

In the unloading state of the variable displacement hydraulic pump 1, the negative control pressure upstream of the large throttle 5 acts on the negative control section 11 of the variable displacement hydraulic pump 1 through the slow return valve 19 and the pilot passage 10. Minimize the flow rate.

The operating lever 15 is fully stroked to drive an actuator (not shown), and the directional control valve 3
Is shifted from the neutral position N to the position C or D, the flow rate in the center bypass passage 9 of the control valve 2 becomes zero. As a result, the signal pressure at the upstream branch point 20 of the large throttle 5 rapidly drops to zero. Variable capacity hydraulic pump 1 at this time
Since the negative control pressure of a certain specified pressure acting on the negative control unit 11 is blocked by the check valve 7 of the slow return valve 19, the flow passes through the small throttle 6,
From the branch point 20 through the large throttle 5 and the flow path 18 to the tank 8
Therefore, the squeeze effect of the small iris 6 causes the gradual decrease to zero. As a result, the swash plate of the variable displacement hydraulic pump 1 also gently rises to increase the discharge flow rate. Then, the discharge oil of the variable displacement hydraulic pump 1 flows to an actuator (not shown) through the directional control valve 3,
In the case of the present invention, as shown in (2) of FIG.
Even if full stroke (100%) is operated, the negative control pressure acting on the negative control unit 11 of the variable displacement hydraulic pump 1 gradually changes from the specified pressure to zero. As a result, the shift from the negative control of the variable displacement hydraulic pump 1 to the horsepower control, that is, the increase in the discharge flow rate also changes gradually with the passage of time.

Then, when the operating lever 15 is returned from the full stroke (100%) to zero, the directional control valve 3 shifts from the C or D position to the neutral position N. As a result, the center bypass passage 9 of the control valve 2 is opened, the discharge flow rate of the variable displacement hydraulic pump 1 flows through the center bypass passage 9, and a signal pressure is generated on the upstream side of the large throttle 5 as described above. The check valve 7 of the slow return valve 19 is from the control valve 2 to the negative control section 11 of the pump 1.
Since there is free flow in the direction of, the signal pressure is transmitted to the negative controller 11 without resistance. Therefore, in the case of the present invention, as shown in (2) of FIG. 2, the negative control pressure rapidly rises from zero to the specified pressure with respect to the return of the operating lever 15 from the full stroke (100%) to zero. Therefore, the variable displacement hydraulic pump 1 is also quickly lowered from the horsepower control to the negative control state, that is, from the state where the discharge flow rate is large to the state where the discharge flow rate is the minimum flow rate. As shown in (2) and (1) of FIG. 2, the change of the operation lever 15 from the full stroke to zero is completely the same as that of the present invention and the conventional one.

In the present invention, the function of the slow return valve 19 is used to cause the signal pressure (negative control pressure) generated upstream of the large throttle 5 to act on the negative control section 11 of the variable displacement hydraulic pump 1 through the pilot passage 10. The flow in the direction from the hydraulic pump 1 to the control valve 2 is a control flow having a throttling effect, and the flow in the opposite direction is a free flow.

[0019]

Since the present invention is constructed as described above, it has the following effects.

(1) As shown in (2) of FIG. 2, when the operating lever is turned from OFF to ON with full stroke (100%) operation, the negative control pressure of the hydraulic pump changes from the specified pressure to zero. Will be alleviated.

(2) Therefore, the change over time in the hydraulic pump flow rate from the minimum flow rate during unloading to the large flow rate during on-loading is greatly alleviated as compared with the prior art, that is, (1) in FIG. (3) As a result, the shock at the time of starting the actuator is alleviated, and cavitation is less likely to occur at the suction port of the hydraulic pump.

[Brief description of drawings]

FIG. 1 is a diagram showing a hydraulic pump flow rate control signal circuit in a hydraulic excavator according to an embodiment of the present invention.

FIG. 2 is a diagram showing changes in control pressure and flow rate of the hydraulic pump with respect to lever operation (comparison between prior art and the present invention).

FIG. 3 is a diagram showing a hydraulic pump flow rate control signal circuit in a conventional hydraulic excavator.

FIG. 4 is a partial view of an operation lever.

[Explanation of symbols]

1 ... Variable displacement hydraulic pump, 2 ... Control valve, 3 ... Directional control valve, 4 ... Relief valve, 5 ... Large throttle, 6 ... Small throttle, 7 ... Check valve, 8 ... Tank, 9 ... Center bypass passage, 10 ... Pilot channel, 11 ... Negative control section, 12 ... Horsepower control section, 13 ... Signal channel, 14 ... Signal channel, 15 ... Operating lever, 16 ... Signal channel, 17 ... Signal channel, 18 ... Channel, 19 ... Slow return valve.

Claims (2)

[Claims] 1. A hydraulic circuit comprising a hydraulic pump (1), a control valve (2) and a tank (8), wherein the hydraulic pump (1) comprises a negative control section (11) and a horsepower control section (12). The negative control unit (11) inputs the negative control pressure from the small throttle (6) of the slow return valve (19) and the check valve (7) through the pilot flow path (10), and the horsepower control unit (12) controls the hydraulic pressure. A control signal is inputted from the discharge part of the pump (1), the control valve (2) comprises a directional control valve (3), a large throttle (5) and a slow return valve (19), and the directional control valve (3) Is controlled by the signals (A, B) from the operating lever (15) to output the oil input from the hydraulic pump (1) to the actuator or the center bypass passage (9), and the large throttle (5) to the control valve ( A slow return valve that introduces oil from the center bypass passage (9) of 2) to the tank (8) and inserts it into the pilot flow passage (10) branched from the upstream side of the large throttle (5) in the control valve (2). (1
9) is configured by arranging a small throttle (6) and a check valve (7) in parallel, and the check valve (7) is a free flow in the direction from the control valve (2) to the hydraulic pump (1), The small aperture (6) is the large aperture (5)
The negative control pressure on the upstream side of the hydraulic pump (1) through the pilot flow path (10) together with the check valve (7).
A flow control signal circuit for a hydraulic pump, characterized in that the negative control unit (11) is operated. 2. The slow return valve (19) is configured by arranging a small throttle (6) and a check valve (7) in parallel, and the check valve (7) includes a control valve (2) to a hydraulic pump (1). ) As a free flow, and the small throttle (6) passes the negative control pressure on the upstream side of the large throttle (5) together with the check valve (7) through the pilot flow passage (10) to the hydraulic pump (1). Of the hydraulic pump (20) to the upstream branch point (20) of the large throttle (5) by closing the center bypass passage (9) by switching the directional control valve (3) on the upstream side. When the discharge oil of 1) is no longer supplied, the small throttle (6) prevents the pressure in the pilot passage (10) from rapidly dropping.
Flow control signal circuit of the hydraulic pump described.