JPS61182478A - Control circuit of pump delivery quantity - Google Patents

Abstract

PURPOSE:To reduce the power loss of a variable pump, by connecting a main flow line with a divided flow line through a switching means and decreasing a delivery quantity of the variable pump to almost zero by a delivery quantity control part, in the standby condition of a return end or the like where almost no power is required for a reciprocating actuator. CONSTITUTION:A variable pump 1 additionally provides the first delivery quantity control part 8, controlling a delivery quantity in a range reaching an intermediate flow from a large flow, and the second delivery quantity control part 9 controlling a delivery quantity to its range decreasing to almost zero. When an actuator 7 is in forward operation, a rise of the pressure in a main flow line 2 first connects the first control part 8 with the main flow line 2 through the first pressure control valve 10 and the following rise of the pressure connects the second control part 9 with the main flow line 2 through the second pressure control valve 20, respectively. On the contrary, when the actuator is in return operation, a control circuit, switching a switching means 38 to connect the main flow line 2 with a divided flow line 35 and enabling the main flow line 2 to be connected with the second control part 9 through the third pressure control valve 30, decreases a delivery quantity of the variable pump 1 to almost zero.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a pump discharge amount control circuit, and in particular to a pump discharge amount control circuit that can reduce power loss when an actuator is in a standby state. It is related to.

(Prior Art) In a hydraulic device used in a press molding machine, etc., when the actuator 7 is in a low load state as shown in FIGS. 4(a) to 4(C) during forward movement before starting molding, A low-pressure, high-flow working fluid is supplied to the
When the actuator 7 is in a high load state as shown in e) during molding, a high pressure and low flow rate working fluid is supplied,
Furthermore, it is necessary to control the pump discharge amount according to the state of the actuator 7, such as supplying low-pressure, high-flow fluid again during the return movement shown in FIG. 4 (tll to (gl).

A conventional example of a control circuit for controlling the pump discharge amount as described above will be explained based on FIG. 2. In the figure, 1 is a variable pump, and the main line 2 of this variable pump 1 is It is connected to the pump port P of the directional control valve 3. The tank port T of this directional control valve 3 is connected to the tank 4, and the two secondary ports A and B are each connected to the line 5.6.
The forward moving side 7a and the backward moving side 7b of the actuator 7
and is connected to. The variable pump 1 has first and second discharge rate control sections 8.9 for controlling its discharge rate in two stages, high and low. The second discharge amount control section 9 has a function of controlling the discharge amount between the maximum flow rate and zero flow rate. Specifically, as shown in the figure, the double ridge discharge amount control unit 8.9 consists of first and second control cylinders, and when both control cylinders 8.9 are in the non-operating position, the discharge amount is At maximum flow rate, the first
The angle of the swash plate 1a is controlled so that when the control cylinder 8 is in the operating state, the discharge amount is an intermediate flow rate, and when the second control cylinder 9 is in the operating state, the discharge amount is zero. be. That is, the first control cylinder 8 is tilted i
The swash plate 1a is not provided with a stroke sufficient to move it to the neutral position (the position where the pump discharge amount becomes zero), and the movement of the swash plate 1a to the neutral position is performed by the second control cylinder 9.

10 is a first pressure control valve; this first pressure control valve 1
0 is a spring offset type pilot type two-position switching valve having three ports: pump port P1, tank port T1, and control port A1, and a spring 12 is arranged in its spring chamber 11. Along with the spring chamber 11
The pilot chamber 13 is arranged in a position opposite to the 11.13, and the neutral position S1 and the switching position S
It has a structure that allows the position to be switched between 2 and 2. In the first pressure control valve 10, the control port A
1 is connected to the first discharge rate control section 8 via line 14, pump port PI is connected to main line 2 via first branch line 15, tank port T1 is connected to tank 16, and its pilot chamber 13 is connected to The fluid pressure of the main line 2 is introduced to the main line 2 via a pilot line 17.

On the other hand, 20 is a second pressure control valve, and like the first pressure control valve 10, this second pressure control valve 20 has three ports: a pump port P2, a tank port T2, and a control port A2. A spring offset type pilot type two-position switching valve has a spring chamber 21 in which a spring 22 is arranged, a pilot chamber 23 in a position opposite to the spring chamber 21, and both chambers 21 and 21. It has a structure in which the position is switched between the neutral position S3 and the switching position S4 by a pressure difference of .23. In the second pressure control valve 20, the control port A2 is connected to the second discharge amount control section 9 via the line 24, the pump port P2 is connected to the main line 2 via the second branch line 25, and the tank port T2 are each connected to a tank 26, and the fluid pressure of the main line 2 is introduced to the viroft chamber 23 via a pilot line 27. Note that in the first pressure control valve 10 and the second pressure control valve 20, the first
The spring force of the spring 12 of the pressure control valve 10 is set to be smaller than the spring force of the spring 22 of the second pressure control valve 20.

Next, the operating state of the flow rate control circuit will be explained. First, immediately after the directional control valve 3 is positioned at the switching position S5, that is, when the load acting on the actuator tough is small as shown in FIGS. 4(a) to (C), the fluid pressure in the main flow line 2 is is also low, and the first and second pressure control valves 10.2
0 are both in the neutral position S1, by the force of springs 12 and 22.
S3, each control port At, A2 communicates with the tank 16.26 via tank ports Tl, T2, and therefore the first and second discharge amount control sections 8.9 both control the maximum discharge amount. The discharge amount of the variable pump 1 is located at the third side.
As shown in point b in the figure, the discharge amount is on the maximum discharge amount side. Next, Figure 4 (
In the state shown in C), the load on the actuator 7 gradually increases, and the fluid pressure in the main line 2 gradually increases accordingly. When the fluid pressure in the main flow line 2 becomes higher than the fluid pressure PB corresponding to the spring force of the spring 12 of the first pressure control valve 10, the first pressure control valve 10
is switched to the switching position S2 by the fluid pressure in the main line 2, and the fluid in the main line 2 is transferred to the pump port P1,
Through the control port A1, the line 14 is led to the first discharge rate control section 8, whereby the discharge rate of the variable pump 1 is
This becomes the intermediate flow port 2 as shown at point d in FIG. Next, when the actuator 7 reaches the forward end as shown in FIG. 4(e), the fluid pressure in the main flow line 2 further increases, and finally the second
The fluid pressure pc corresponding to the spring force of the spring 22 of the pressure control valve 20 is about to be exceeded, but at this time, the fluid pressure in the main line 2 switches the second pressure control valve 20 to the switching position S4, and the main flow line 2 The fluid at pump port P2,
Through the control port A2, the line 24 is led to the second discharge rate control section 9, whereby the discharge rate of the variable pump 1 is
It becomes approximately zero as at point e in FIG. At this point e, the discharge amount should theoretically be zero, but in reality there is fluid leakage in the circuit, and therefore the variable pump 1 has enough fluid to compensate for the leakage amount. A flow rate will be discharged. Hereinafter, the discharge amount in this state will be referred to as approximately zero.

Next, the directional control valve 3 is switched to the switching position S6, and the fourth direction control valve 3 is switched to the switching position S6.
As shown in Figure (f), the actuator 7 is returned to its original position, but in this case, the load acting on the actuator 7 becomes extremely small, so the fluid pressure in the main line 2 is sufficient to cause the actuator 7 to move back. The pressure suddenly decreases to the required minimum pressure, which causes the second and first pressure control valves 2
0.10 successively moves to neutral position S3 by the force of spring 22.12
, Sl, and each control boat A2, A1 will both communicate with tank 26.16. Therefore, the re-discharge amount control section 9.8 returns to the maximum discharge amount position, and the maximum flow rate Ql is supplied to the main flow line 2 as shown at point f in FIG.

When the actuator 7 reaches the backward movement end as shown in FIG. .20 is sequentially switched to the switching positions s2 and s4, and the flow rate in the main line 2 is again brought to a state of approximately zero due to the high pressure PC as shown at point g in Fig. 3.This state is similar to that described above. This will be maintained even if the direction control valve 3 is switched to the neutral position S7.Hereafter, the above-described operations are repeated to sequentially perform the pressing operation.

(Problems to be Solved by the Invention) The conventional pump discharge amount control circuit described above has the following drawbacks. This is because, as mentioned above, when the actuator 7 is at the end of the backward movement, it is usually in a state where the workpiece is being replaced, that is, in a standby state where no force is required on the actuator tough. As mentioned above, the main line 2 is maintained at a high pressure, which causes power loss. That is, in the above state, although the discharge amount of the variable pump 1 is theoretically zero, in reality there is fluid leakage outside the circuit, so the variable pump 1 has no way to compensate for this leakage amount. The amount of fluid necessary for This results in a large power loss.

This invention was made in order to solve the above-mentioned conventional drawbacks, and its purpose is to control the pump discharge amount by reducing power loss in a standby state such as when the actuator is located at the end of backward motion. The purpose is to provide circuits.

(Means for Solving the Problems) Therefore, in the pump discharge rate control circuit of the present invention, a first discharge rate control section 8 that controls the discharge rate within a range from a large flow rate to an intermediate flow rate; Variable pump 1 having a second discharge amount control section 9 that controls the discharge amount until it becomes approximately zero
Connect the reciprocating actuator 7 to the main line 2 of the pump port P1, tank port 1-Tl and control port).
Control port 81 of the first pressure control valve 1o containing Al is connected to the first discharge amount control section 8, its pump port P1 is connected to the main stream line 1, and its tank port 1-TI is connected to the tank 16.
At the same time, the fluid pressure of the main flow line 1 is introduced into the pilot chamber 13 facing opposite to the spring chamber 11 to switch the first discharge amount control section 8 into communication between the main flow line 1 and the tank 16. The control port A2 of the second pressure control valve 20, which has a pump port P2, a tank port T2, and a control port A2, is connected to the second discharge amount control section 9, and the pump port P2 is connected to the main stream line. 1, and the fluid pressure of the main flow line 1 is introduced into the pilot chamber 23 facing opposite to the spring chamber 21, thereby switching the second discharge amount control section 9 between the main flow line 1 and the tank port T2. In addition, the control port ^3 of the third pressure control valve 3o, which has a pump port P3, a tank port T3, and a control boat A3, is connected to the tank port T2 of the second pressure control valve 20, and the tank port T3 is connected to the tank 36. At the same time, a branch line 35 is connected to the pump port P3, and this branch line 35 is connected to the main line 2 by a switching means 38.
In addition, the fluid pressure acting on the pump port P3 is introduced into the pilot chamber 33 opposite to the spring chamber 31 of the third pressure control valve 30, and on the other hand, the double-motion state of the actuator 7 is controlled. A detecting means 39 is provided for detecting the double-motion state, and the switching means 38 is switched to connect the branch line 35 to the main line 2 when the detecting means 39 detects the double-acting state, and the third pressure control valve 30 The force of the spring 32 is set smaller than the force of the spring 22 of the second pressure control valve 20.

(Function) In the above-described discharge amount control circuit, the actuator 7
When the fluid pressure in the main stream line 2 increases during forward movement, first the first pressure control valve 1o controls the first discharge amount control section 8
communicates with the mainstream line 2 and the pump discharge rate is controlled to an intermediate flow rate. When the fluid pressure in the mainstream line 2 further increases, the second pressure control valve 20 then controls the pump discharge rate to an intermediate flow rate.
communicates with the main stream line 2, the pump discharge amount is reduced to approximately zero, and the inside of the main stream line 2 is regulated by the pressure when the pressure control valve 20 is switched.

Further, during the backward movement, the detection means 39 detects the backward movement state, and the switching means 38 switches so that the main flow line 2 communicates with the branch line 35. and the third
The force of the spring 33 of the pressure control valve 30 is transferred to the second pressure control valve 20.
Since the force of the spring 23 is set to be smaller than the force of the spring 23, when the actuator 7 reaches the backward movement end, etc., the fluid pressure in the main line 2 becomes the fluid pressure corresponding to the spring force of the third pressure control valve 30. If the flow rate exceeds the flow rate, the main flow line 2 communicates with the second discharge amount control unit 9 via the branch line 35 through the following route, and the discharge amount of the variable pump 1 becomes approximately zero.
The pressure inside the main stream line 2 is regulated at that time. That is, in this case, the main flow line 2 is the branch line 3
5. The second discharge amount control unit 9 via the pump port P3 and control boat ^3 of the third pressure control valve 30, the tank port T2 of the second pressure control valve 20, and the control port 82, respectively.
This will lead to communication.

Since the spring force of the third pressure control valve 3o is set smaller than the spring force of the second pressure control valve 20, the fluid pressure in the main line 2 is higher during backward movement than during forward movement. will be regulated to a low pressure.

(Example) Next, a specific example of the pump discharge amount control circuit of the present invention will be described in detail with reference to the drawings.

In FIG. 1, I is a variable pump, and the main line 2 of this variable pump 1 is the pump port P of the directional control valve 3.
It is connected to the. Tank boat T of this directional control valve 3
is connected to the tank 4, and the two secondary ports A and B are connected to the forward movement of the actuator 7 (!I
It is connected to J7a and the double-acting side 7b. The variable pump 1 has a first pump for controlling its discharge amount in two stages, high and low.
and a second discharge amount control section 8.9.
The discharge rate control section 8 has a function of controlling the discharge rate between the maximum flow rate and the intermediate flow rate, and the second discharge rate control section 9 has a function of controlling the discharge rate between the maximum flow rate and zero flow rate. be. Specifically, as shown in the figure, the re-discharge amount control section 8
．． Reference numeral 9 consists of a first and second control cylinder, and when both re-control cylinders 8 and 9 are in the non-operating position, the discharge amount is at the maximum flow rate, and when the first control cylinder 8 is in the operating state where fluid is introduced. The angle of the swash plate 1a, etc. is controlled so that when the second control cylinder 9 is in the operating state where fluid is introduced, the discharge amount is zero. . That is, the first control cylinder 8 does not have enough stroke to move the swash plate 1a to the neutral position (the position where the pump discharge amount becomes zero), and the swash plate 1a
The movement to the neutral position is performed by the second control cylinder 9.

10 is a first pressure control valve; this first pressure control valve 1
0 is a spring offset type pilot operated two-position switching valve having three ports: a pump port P1, a tank port Tl, and a control port 81, and a spring 12 is arranged in its spring chamber 11. At the same time, the spring chamber 11
The pilot chamber 13 is arranged at a position opposite to the 11.
It has a structure that allows the position to be switched between 2 and 2. In the first pressure control valve 10, the control boat A
1 is connected to the first discharge rate control section 8 via a line 14, the pump port PI is connected to the main flow line 2 via a first branch line 15, and the tank boat T1 is connected to the tank 16. The fluid pressure of the main flow line 2 is introduced to the main flow line 2 via a viroft line 17.

On the other hand, 20 is a second pressure control valve, and like the first pressure control valve 1o, this second pressure control valve 20 has three ports: pump port P2, tank port 1-T2, and control boat A2. This is a spring offset type pilot type two-position switching valve having a port, in which a spring 22 is arranged in a spring chamber 21, a pilot chamber 23 is arranged in a position opposite to the spring chamber 21, and both chambers are arranged. It has a structure in which the position is switched between the neutral position S3 and the switching position S4 by a pressure difference of 21.23. In the second pressure control valve 20, the control boat A2 is connected to the line 24.
The pump port P2 is connected to the second discharge amount control section 9 via the pump port P2.
are respectively connected to the main line 2 via a second branch line 25, and the fluid pressure of the main line 2 is introduced to the pilot chamber 23 via a pilot line 27.

Further, 30 is a third pressure control valve, and like the first and second pressure control valves 10 and 20, this third pressure control valve 30 has a pump port P3, a tank port T3, and a control boat A3. This is a spring offset type pilot type two-position switching valve having three boats, in which a spring 32 is arranged in a spring chamber 31, and a pilot chamber 33 is arranged in a position opposite to the spring chamber 31. The pressure difference between the two chambers 31 and 33 causes the neutral position S8 and the switching position s9 to be
It has a structure that allows the position to be switched between. In the third pressure control valve 30, its control port ^3
is connected to the tank port T2 of the second pressure control valve 20 through the line 34, and the tank port T3 is connected to the tank 3.
6, respectively. The pump port P3 of the third pressure control valve 30 is connected to a third branch line 35 that communicates with the tank 41 in the state shown in the figure, while the pyloft chamber 33 receives fluid pressure acting on the pump port P3. It is led via a pilot line 37.

An electromagnetic switching valve 38 as a switching means is interposed between the second branch line 25 and the third branch line 35.
5 or 35 is connected to the main line 2, the other branch line 35 or 25 is connected to the tank 41.

On the other hand, a limit switch 39 as a detection means for detecting when the actuator 7 has reached a position near the end of backward movement is arranged near the actuator unit. When the limit switch 39 is reached, the output of the limit switch 39 can be transmitted to the electromagnetic switching valve 38 through a signal circuit 40. That is, when the actuator 7 reaches the vicinity of the backward movement end, the above-mentioned disconnection occurs.

The switching valve 38 is switched to the switching position Sll, and the third branch line 35 is communicated with the main line 2, and the second branch line 25 is opened to the tank 41. Otherwise, the switching valve 38 is set to the neutral position. Positioned at position S10 to communicate the second branch line 25 with the main flow line 2,
The third branch line 35 is left open to the tank 41.

Note that in the third pressure control valve 30, the spring force of the spring 32 is applied to the first pressure control valve 10.
The spring force of the spring 12 and the spring 22 of the second pressure control valve 20
The reason for this will be explained in the course of the description of the operating state below.

Next, the operating state of the above flow control circuit will be explained.
During the forward movement of the actuator 7 and the backward movement until the actuator 7 reaches the vicinity of the return end and the limit switch 39 is activated, the electromagnetic switching valve 38 is located at the neutral position SIO. 35 is opened to the tank 41, and the third pressure control valve 30 is located at the neutral position S8, so that it is substantially the same as the conventional example as described below. First, immediately after positioning the directional control valve 3 to the switching position S5,
In other words, when the load acting on the actuator tough is small as shown in FIG. 4(a) to (C), the main line 2
The fluid pressure inside is also low, and the first pressure control valve 10 is located at the neutral position S1 by the force of the spring 12, and the control port A
I communicates with tank 16. Further, the second pressure control valve 20 is also located at the neutral position S3 by the force of the spring 22, and the control port A2 communicates with the tank port T2. 30 control port) A3 and its tank port T3 to the tank 36. Therefore, the first and second discharge rate control sections 8.9 are both located on the maximum discharge rate side, and the discharge rate of the variable pump 1 becomes the maximum discharge rate Q1 as shown at point b in FIG. Next, Fig. 4 (+1.
), the load on the actuator 7 gradually increases, and the fluid pressure in the main stream line 2 gradually increases accordingly. And the fluid pressure in the main stream line 2 is
When the fluid pressure becomes higher than the fluid pressure PB corresponding to the spring force of the spring 12 of the first pressure control valve 10, the first pressure control valve 10 is switched to the switching position S2 by the fluid pressure of the main flow line 2, and the first pressure control valve 10 is switched to the switching position S2 by the fluid pressure of the main flow line 2. The fluid is guided from the ' line 14 to the first discharge rate control section 8 via the pump port P1 and the control port A1, whereby the discharge rate of the variable pump 1 is
The flow rate becomes an intermediate flow rate Q2 as shown at point d in FIG. Next, when the actuator 7 reaches the forward end as shown in FIG.
The pressure control valve 20 attempts to exceed the fluid pressure PC corresponding to the spring force of the spring 22, but at this time, the fluid pressure in the main stream line 2 switches the second pressure control valve 20 to the switching position S4, and the main line 2 The fluid at pump port P2,
Through the control port A2, the line 24 is led to the second discharge rate control section 9, whereby the discharge rate of the variable pump 1 is
It becomes approximately zero, like the 0 point in FIG.

Next, the directional control valve 3 is switched to the switching position S6, and the fourth direction control valve 3 is switched to the switching position S6.
As shown in Figure (f), the actuator 7 is returned to its original position, but in this case, the load acting on the actuator 7 becomes extremely small, so the fluid pressure in the main flow line 2 also drops rapidly, which causes the 2 and the first pressure control valve 20
．． 10 successively move to neutral position S3 by the force of spring 22.12,
Return to Sl. Then, in the second pressure control valve 20, the control port A2 communicates with the tank port T2, and this tank port T2 further communicates with the line 34 and the third
Control port A3 and tank port T3 of pressure control valve 30
The control port ^1 of the first pressure control valve 10 communicates with the tank 16 via the first pressure control valve 10. Therefore, the both ridges amount control section 9.8 returns to the maximum discharge amount position by the force of the spring 9a, and the maximum flow rate Q1 is supplied to the main flow line 2 as shown at point f in FIG. Become.

When the actuator 7 reaches the vicinity of the reciprocating end, the solenoid switching valve 3 is activated by the limit switch 39.
8 is switched to the switching position Sll, and the third branch line 3 is switched to the switching position Sll.
5 to the main flow line 2, and the second branch line 25 is opened to the tank 41. Then, the fluid pressure in the main stream line 2 is applied to the spring 3 of the third pressure control valve 30.
When a fluid pressure PD corresponding to a spring force of 4 is reached, this fluid pressure causes the third pressure control valve 30 to switch to the switching position S9. As a result, the main line 2 is
Diversion line 35, pump port P of third pressure control valve 30
3 and control port A3, line 34, second pressure control valve 2
0 tank port T2 and control port A2, line 24
are connected to the first discharge rate control section 9 through the respective pumps, and thereby the first discharge rate control section 9 operates to make the discharge rate of the variable pump 1 substantially zero. In other words, in this case, since the force of the spring 32 of the third pressure control valve 30 is set to be smaller than the force of the spring 12 of the first pressure control valve 10, when the actuator 7 moves back, the force of the spring 32 of the third pressure control valve 30 is 10, the third pressure control valve 30 switches to a pressure PD that is even lower than the regulated pressure PR by the first pressure control valve 10.
This means that the pressure in the main line 2 is regulated.

As described above, in the above-described discharge amount control circuit, at the forward end where a high load is required on the actuator unit, the main line 2 is maintained at a high pressure PC as in the past, while almost no force is applied to the actuator unit. At the non-required reciprocating end, the fluid pressure in the main line 2 is regulated to a low pressure PD, so the actuator 7
It is possible to reduce power loss in the standby state where the rotor is located at the reciprocating end.

In the above description, the force of the spring 33 of the third pressure control valve 30 is applied to both the springs 13 of the first and second pressure control valves 10.20.
．． The force of the spring 13 of the first pressure control valve 10 is set to be smaller than the force of the spring 13 of the first pressure control valve 10.
The force of the spring 23 may be set to be smaller than the force of the spring 23. Further, in the above, the second branch line 25 is opened to the tank 41 when the switching valve 38 is switched, but the point is that it is sufficient if the third branch line 35 can be switched and connected to the main line 2; In some cases, line 25 is not switched.

(Effects of the Invention) In the pump discharge amount control circuit of the present invention, as described above, at the forward end where the load on the actuator is high, the pressure in the main flow line is maintained at a high pressure as in the past, while almost no force is applied to the actuator. In a standby state such as at the reciprocating end where the actuator is not required, the fluid pressure in the main line is regulated to a lower pressure than the above, reducing the power loss of the variable pump when the actuator is in the standby state. is possible. That is, in the above standby state,
Although the discharge amount of a variable pump is theoretically zero, in reality there is fluid leakage outside the circuit, so the variable pump discharges the amount of fluid necessary to compensate for this. In this discharge amount control circuit, the leakage pressure is lower than that of the conventional one, and in this respect, power loss can be reduced and the amount of heat generated by the working fluid can be suppressed.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the pump discharge amount control circuit of the present invention, FIG. 2 is a circuit diagram of a conventional example, FIG. 3 is a graph showing the relationship between fluid discharge pressure and flow rate, and T4 diagram (al ~(g
1 is an explanatory diagram of the operation of the actuator. ■...Variable pump, 2...Main line, 7...Actuator, 8...First discharge amount control section, 9...Second discharge amount control section, 10...First pressure control Valve, 11...
・Spring chamber, 12... Spring, 13... Pilot chamber,
16...Tank, Pl...Pump port, T1...
・Tank port, AI...control port, 20...second pressure control valve, 21...spring chamber, 22...spring, 2
3...Pilot chamber, P2...Pump port, T
2... Tank boat, A2... Control boat, 30.
...Third pressure control valve, 31...Spring chamber, 32...Bane, 33...Pilot chamber, 35...Third branch line, 36...Tank, P3...Pump port, T3
...Tank boat, A3...Control boat, 38...
・Switching valve, 39...Limit switch.

Claims (1)

[Claims] 1. A first discharge rate control unit (8) that controls the discharge rate within a range from a large flow rate to an intermediate flow rate, and a first discharge rate control unit (8) that controls the discharge rate until the discharge rate becomes approximately zero. A reciprocating actuator (7) is connected to the main line (2) of a variable pump (1) having two discharge rate control units (9), a pump port (P1), a tank port (T1) and a control port (A1). The control port (A1) of the first pressure control valve (10) having the above is connected to the first discharge rate control section (8), its pump port (P1) is connected to the main stream line (1), and its tank port (T1) are communicated with the tank (16), and the fluid pressure of the main flow line (1) is guided to the pilot chamber (13) opposite to the spring chamber (11) to control the first discharge amount control section (8). A second pressure control valve (having a pump port (P2), a tank port (T2), and a control port (A2)) The control port (A2) of 20) is communicated with the second discharge amount control section (9), and the pump port (P2) thereof is communicated with the main stream line (1), and the spring chamber (21) is opposite to the second discharge rate control section (9). The fluid pressure of the mainstream line (1) is introduced into the pilot chamber (23) to control the second discharge amount control section (9).
1) and the tank port (T2), and the control port (A3) of the third pressure control valve (30) has a pump port (P3), a tank port (T3), and a control port (A3). is communicated with the tank port (T2) of the second pressure control valve (20), and its tank port (T3) is communicated with the tank (36), and the diversion line (35) is connected to the pump port (P3). This branch line (35) can be switched and connected to the main line (2) by a switching means (38), and this third pressure control valve (
The pilot chamber (30) is opposite to the spring chamber (31).
33) is provided with a detection means (39) for guiding the fluid pressure acting on the pump port (P3) and detecting the backward movement state of the actuator (7), and also for detecting the backward movement state by this detection means (39). The switching means (38) is configured to connect the branch line (35) to the main line (2) by switching the switching means (38) upon detection of the state, and furthermore, the force of the spring (32) of the third pressure control valve (30) is A pump discharge amount control circuit characterized in that the force of a spring (22) of a second pressure control valve (20) is set to be smaller.