JPH10103248A - Flow control device of variable displacement pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To set the maximum flow rate of a variable displacement pump in stages by means of a pilot hydraulic circuit with simple constitution. SOLUTION: A spool 36 is fittingly inserted into the sleeve 35 connected to a servo piston 30 for setting the slant angle in rotation for a variable displacement pump through a feedback lever 44, and a spring 37 is arranged in one end of this spool 36, and the small diameter section 47 of a pilot piston 38 is made to abut on the other end. By using a second hydraulic pressure chamber as a pressure source with pilot pressure working to a second hydraulic pressure chamber 54, the spool 36 is made to displace much resisting the spring force of the spring 37 to set the slant angle in rotation large corresponding to a first maximum flow rate Qmax1, and pilot pressure is led to a first hydraulic pressure chamber 50 to return a pilot piston 46 by means of an auxiliary piston 49 to make the spool 36 displace by spring force for changing the inclination angle in rotation for setting the flow rate to a second maximum flow rate Qmax2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow control device for a variable displacement pump which can be advantageously implemented on construction machines and other general industrial machines.

[0002]

2. Description of the Related Art A typical prior art is disclosed in Japanese Utility Model Laid-Open No. 62-16 / 1987.
9285, the configuration of which is shown in FIGS. 4, a servo piston 3 connected to a pump tilting member 2 of a variable displacement pump 1 is constantly pressed to the right in FIG. Another hydraulic chamber 5 facing the hydraulic chamber 4 is connected to the tank 7 by the switching valve 6 or to the pump 1.
Is connected to the pipeline 8 to which the pressure oil is supplied.
In the switching valve 6, one end of the spool 9 is provided with a spring 1.
0 contacts, and the pilot piston 11 contacts the other end. The pilot piston 11 pushes the spool 9 by the hydraulic pressure Pi supplied from the pipeline 17 to the hydraulic chamber 16.

When the pressing force of the spring 10 against the spool 9 exceeds the pressing force of the pilot piston 11, the hydraulic chamber 5 communicates with the tank 7 and the servo piston 3 is
To the right, whereby the tilt angle α of the pump 1 decreases. The sleeve 12 is connected to one end of a feedback lever 13, the intermediate portion of which is a fulcrum 14, and the other end is connected to the servo piston 3. Therefore, the sleeve 12 follows the spool 9 in conjunction with the servo piston 3 by the feedback lever 13, and when the sleeve 12 moves by the moving amount of the spool 9, the hydraulic chamber 5 is shut off from the tank. Therefore, the servo piston 3 stops moving.

Conversely, when the pressing force of the pilot piston 11 against the spool 9 overcomes the spring force of the spring 10, the spool 9 is displaced rightward, and the pump oil pressure is guided to the hydraulic chamber 5. Therefore, the pilot piston 11 moves to the left in FIG. 4, and the pump tilt angle α increases. The sleeve 12 follows the spool 9 by the action of the feedback lever 13, and the hydraulic chamber 5 is cut off from the pump hydraulic pressure. When the servo piston 3 is displaced leftward in FIG. 4 and comes into contact with the stopper 15, the maximum flow rate Qmax is reached.

FIG. 5 is a hydraulic circuit diagram for guiding the pilot pressure Pi to the hydraulic chamber 16 in the flow control device shown in FIG. Remote control valve 19 from pilot pump 18
, The pilot pressure P through the two-position electromagnetic switching valve 20
i is derived.

FIG. 6 is a diagram showing the characteristics of the prior art shown in FIGS. 4 and 5. The maximum flow rate Qmax of the variable displacement hydraulic pump 1 is uniquely determined when the servo piston 3 is in contact with the stopper 15. Then the maximum flow rate Qma
In order to be able to set x in a stepwise manner, a two-position electromagnetic switching valve 20 is used as shown in FIG. 5 and a pressure reducing valve 21 is further provided. Needs to be set wider.

Therefore, it is desired that the hydraulic circuit for the pilot pressure Pi can be further simplified so that the maximum flow rate Qmax of the variable displacement pump 1 can be set stepwise.

Another prior art is disclosed in Japanese Patent Application Laid-Open No. 62-288378.
Is disclosed. In this prior art, a shim is used to adjust the rightward displacement position of the pilot piston 11 against the spring force of the spring 10 in the prior art described in connection with FIGS. The shim is configured to set the maximum flow rate. Therefore, in this prior art, the flow control device is disassembled and the shim is mounted /
There is a problem that it has to be replaced and it takes time to set the maximum flow rate.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to make it possible to change the maximum flow rate Qmax of a variable displacement pump by a pilot hydraulic circuit having a simple structure, and to easily set the maximum flow rate. An object of the present invention is to provide a flow control device for a variable displacement pump which can be adjusted.

[0010]

According to the present invention, there is provided a switching valve in which a spring is in contact with one end of a spool fitted in a sleeve and a pilot piston is in contact with the other end, and a hydraulic switching of the switching valve. A servo piston that operates to change the tilt angle of the variable displacement pump, and a feedback lever that interlocks the servo piston with the sleeve of the switching valve, wherein the pilot piston displaces the spool against the spring force of the spring. In the variable displacement pump flow control device in which the discharge flow rate of the variable displacement pump changes greatly, the pilot piston has a large-diameter portion and a smaller diameter than the large-diameter portion and the other end of the spool. A small-diameter portion capable of abutting on the casing, and defining a first hydraulic chamber housed in the casing and the casing, and the small-diameter portions are inserted so as to be mutually displaceable. An auxiliary piston, which is displaceably accommodated in the casing, and a large-diameter portion of the pilot piston is accommodated in a displaceable manner to define a second hydraulic chamber. A hydraulic pressure area including a stopper for restricting and a pilot hydraulic circuit for selectively supplying and shutting off the pressure oil to the first hydraulic chamber and the second hydraulic chamber. Is larger than the hydraulic area S2 on the side of the second hydraulic chamber, and the forces P1 and S1 acting on the auxiliary piston by the pressure oil in the first hydraulic chamber.
And the spring force of the spring is configured to be greater than the force Pi · S2 acting on the pilot piston due to the pressure oil in the second hydraulic chamber, and acts on the pilot piston due to the pressure oil in the second hydraulic chamber. A flow control device for a variable displacement pump, wherein a force Pi · S2 is configured to be larger than a spring force F of the spring. Also, in the present invention, the pilot hydraulic circuit may include a pilot pressure pump, a first on-off valve for guiding hydraulic pressure from the pilot pressure pump to the first hydraulic chamber, and a second on / off valve for guiding hydraulic pressure from the pilot pressure pump to the second hydraulic chamber. And an on-off valve. Further, the present invention is characterized in that it includes an adjusting bolt screwed into the casing, one end of which can be operated from the outside of the casing, and the other end of which can be brought into contact with the stopper.
Further, the invention is characterized in that a drain oil passage communicating with the tank is formed in the casing at a contact position between the auxiliary piston and the stopper.

According to the present invention, the hydraulic pressure P of the first hydraulic chamber 50
1 is set to zero as the tank pressure, and the hydraulic pressure Pi is stored in the second hydraulic chamber 54.
, The force Pi · S2 acting on the large-diameter portion 46 of the pilot piston 38 exceeds the spring force F of the spring 37, and the pilot piston 38 has the large-diameter portion 46 and the small-diameter portion 4
7, the auxiliary piston 49 is displaced rightward in FIG. 1, and the small diameter portion 47 displaces the spool 36 against the spring force, whereby the displacement of the spool is maximized. Accordingly, the servo piston 30 is displaced to the left in FIG. 1, and the tilt angle α of the variable displacement pump becomes the maximum, and the first maximum flow rate Qmax1 is obtained. This first
The maximum flow rate Qmax1 can be set by the stopper 31.

When, for example, the same hydraulic pressure is introduced into the first hydraulic chamber 50 and the second hydraulic chamber 54, the first
The hydraulic area S1 on the hydraulic chamber side is larger than the hydraulic area S2 on the second hydraulic chamber side of the large-diameter portion 46, and the forces P1 and S1 acting on the auxiliary piston 49 by the hydraulic oil in the first hydraulic chamber 50 and the spring 37 Is larger than the force Pi · S2 acting on the large-diameter portion 46 of the pilot piston 38 due to the pressure oil in the second hydraulic chamber 54, so that the auxiliary piston 49 The auxiliary piston 49 pulls the pilot piston 38 back to the left in FIG. 1 by contacting the step 48 between the large-diameter portion and the small-diameter portion of the piston 38, and accordingly, the spool 36 is moved by the spring force of the spring 37 to the left in FIG. In the direction corresponding to the position of the pilot piston 38,
In response, the servo piston 30 changes the tilt angle α of the variable displacement pump to a small value. Therefore, the variable displacement pump is set to another second maximum flow rate Qmax2 that is lower than the first maximum flow rate Qmax1.

By setting the second hydraulic chamber 54 to the tank pressure, the spool 36 further displaces the pilot piston 38 leftward in FIG. 1 by the spring force of the spring 37, and displaces the servo piston 30 rightward in FIG. Then, the tilt angle α of the variable displacement pump becomes the minimum, whereby the minimum flow rate Qmin is set. At this time, the hydraulic pressure P1 may be led to the first hydraulic chamber, or may be the tank pressure. Minimum flow rate Q
min can be adjusted by the stopper 32.

Thus, the two maximum flow rates Qmax1 and Qmax2 of the variable displacement pump are set to the tank pressure without guiding the hydraulic pressure P1 to the first hydraulic chamber while maintaining the hydraulic pressure Pi to the second hydraulic chamber. By deriving P1, it becomes possible to set in a stepwise manner, thereby simplifying the configuration of the pilot pressure hydraulic circuit.

Further, according to the present invention, the position of the stopper can be set by operating the stopper from outside the casing with the adjusting bolt. As a result, the second maximum flow rate Qmax2 can be adjusted.

Further, according to the present invention, at the contact position between the auxiliary piston and the stopper, the tank pressure is set by the drain oil passage, whereby the contact position at the time of applying a hydraulic pressure to the first hydraulic chamber is set. Compression is prevented, and it is ensured that the auxiliary piston abuts the stopper.

[0017]

FIG. 1 is a sectional view showing the structure of an embodiment of the present invention. The flow control device of the variable displacement hydraulic pump 25 according to the present invention basically includes a servo drive unit 2 for tilting the tilting member 33 of the variable displacement pump 25 such as a swash plate or a cylinder block.
6 and a switching valve 27 connected to the servo driving means 26
And a flow control means 28 for controlling the switching valve 27. In the servo drive means 26, a servo piston 30 is housed in a casing 29. The displacement amount of the servo piston 30 corresponding to the first maximum flow rate Qmax1 is
Stopper 3 which is an adjustment bolt screwed into casing 29
Set by 1. Further, the position of the servo piston 30 corresponding to the minimum flow rate Qmin is set by a stopper 32 which is an adjustment bolt screwed into the casing 29. The hydraulic pressure from the pump 25 via the conduit 61 is constantly guided to the hydraulic chamber 39 on the stopper 31 side of the casing 29. The other hydraulic chamber 40 is connected to the tank 42 via the line 41 by the switching valve 27, or the hydraulic pressure of the pump 25 is guided from the line 43. The tilt member 33 of the variable displacement pump 25 is connected to the servo piston 30, and the tilt angle is changed.

In the switching valve 27, a sleeve 35 is housed in a casing 34 so as to be displaceable, and a spool 36 is fitted into the sleeve 35. Spool 3
A spring 37 is abutted on one end of 6. Spool 36
The other end of the pilot piston 38 can be in contact with one end.

One end of the feedback lever 44 is pin-connected to the servo piston 30. This lever 44
Is angularly displaceable about a fulcrum 45 and the other end is pinned to a sleeve 35.

In the flow control means 28, the pilot piston 38 has a large diameter portion 46 and a small diameter portion 47.
The small diameter portion 47 has a smaller diameter than the large diameter portion 46, and the small diameter portion 47 can contact the other end of the spool 36. The pilot piston 38 has a large diameter portion 46 and a small diameter portion 4.
7 has a step 48.

The auxiliary piston 49 accommodated in the casing 34 defines a first hydraulic chamber 50 on the spool 36 side. The small diameter portion 47 is inserted into the auxiliary piston 49 so as to be mutually displaceable left and right in FIG. The auxiliary piston 49 has a room 51 for accommodating the large diameter portion 46. When the step portion 48 comes into contact with the end surface 52 of the room 51, the forward displacement of the pilot piston 38 toward the spool 36 is limited.

In the casing 34, a stopper 53 is provided.
Are accommodated so as to be displaceable in the axial direction. This stopper 53
Accommodates the large-diameter portion 46 of the pilot piston 38 so as to be mutually displaceable along the axis thereof, and defines the second hydraulic chamber 54. End 55 of stopper 53 on auxiliary piston 49 side
Is opposite to the spool 36 of the auxiliary piston 49 (FIG. 1).
Of the auxiliary piston 49 is restricted in this contact state.

An adjusting bolt 57 is screwed into the casing 34. One end 58 of the adjustment bolt 57 is rotatable from outside the casing 34. Adjustment bolt 57
Is in contact with the end face of the stopper 53 on the side opposite to the auxiliary piston 49. Thus, the position of the stopper 53 can be set outside the casing 34 by rotating the adjustment bolt 57. A lock nut 60 is screwed into the adjustment bolt 57. The sleeve 35, the spool 36, the spring 37, the pilot piston 38, the auxiliary piston 49, the stopper 53, and the adjustment bolt 57 have respective axes on a straight line.

The auxiliary piston 49 has a small-diameter stepped portion 62a on the stopper 53 side, and an oil passage 62 is formed between the small-diameter stepped portion 62a and the casing 34. The stopper 53 is formed with a groove 63 extending in the radial direction at the end portion 55 abutting on the auxiliary piston 49. A drain oil passage 64 communicating with the oil passage 62 and the groove 63 is formed in the casing 34. The oil passage 64 is connected to the tank 42. Thus, the auxiliary piston 49 and the stopper 53
The oil passage 64 communicates with the tank 42 at the position where the auxiliary piston 49 comes into contact with the tank 42, so that pressurization is prevented, and the auxiliary piston 49 reliably contacts the stopper 53, so that the retracted position of the auxiliary piston 49 by the stopper 53 can be accurately determined. It can be set.

The hydraulic area S1 of the hydraulic surface 71 of the auxiliary piston 49 facing the first hydraulic chamber 50 is larger than the hydraulic area S2 of the auxiliary pressure surface 72 of the large diameter portion 46 facing the second hydraulic chamber 54 (S1> S2). .

The force Pi · S2 acting on the pressure receiving surface 72 having the pressure receiving area S2 of the large diameter portion 46 of the pilot piston 38 due to the pressure oil in the second hydraulic chamber 54 is larger than the spring force F of the spring 37. It is configured as follows.

Pi · S2> F (1) Forces P1 · S1 acting on the pressure receiving surface 71 having the pressure receiving area S1 of the auxiliary piston 49 by the pressure oil in the first hydraulic chamber 50;
The sum of the spring 37 and the spring force F to the left in FIG. 1 is greater than the force Pi · S2 that acts on the pressure receiving surface 72 of the large-diameter portion 46 of the pilot piston 38 due to the pressure oil in the second hydraulic chamber 54. It is configured as follows.

P1 · S1 + F> Pi · S2 (2) FIG. 2 is a diagram showing a pilot hydraulic circuit related to the first and second hydraulic chambers 50 and 54 of the embodiment of the present invention shown in FIG. It is. The pressure oil from the pilot pressure pump 65 is guided to the first hydraulic chamber 50 as the first pilot pressure P1 via the two-position solenoid valve 66. An on-off valve 68 manually and remotely operated by the handle 67 guides the second pilot pressure Pi to the second hydraulic chamber 54. Pump 2
5, 65 are rotationally driven by a drive source such as a common diesel engine. Pilot pressures P1 and Pi are equal (P1 = Pi).

FIG. 3 is a graph showing the flow rate control characteristics of the variable displacement pump shown in FIGS. In setting the first maximum flow rate Qmax1 of the variable displacement pump 25, the hydraulic pressure P of the first hydraulic chamber 50 is set by the first on-off valve 66.
1 is set to the tank pressure to zero, and the second hydraulic chamber 54
, A pilot pressure Pi is applied by the second on-off valve 68.

By the pressure oil guided to the second hydraulic chamber 54,
The pilot piston 38 contacts the contact portion 52 of the auxiliary piston 49 at the step 48 and pushes it to the right in FIG. 1 so that the contact surface 71 of the auxiliary piston 49 contacts the contact surface 73 of the casing 34 in the first hydraulic chamber 50. Abut As shown in Expression 1, the spool 36 is displaced against the spring force F of the spring 37. As a result, in the switching valve 27, the pipe 43 is connected to the pipe 41, the hydraulic chamber 40 of the servo drive unit 26 becomes pump pressure, and the servo piston 30 is displaced until it comes into contact with the stopper 31. Therefore, in conjunction with the servo piston 30, the tilting member 33 of the variable displacement pump 25 has the maximum tilt angle α.
And the first maximum flow rate Qmax1 is obtained. The displacement of the servo piston 30 causes the field back lever 4
4 displaces the sleeve 35 rightward in FIG. 1 following the spool 36, thereby closing the conduit 41 from the conduit 43 and the tank 42.

In setting the variable displacement pump 25 to the second maximum flow rate Qmax2 lower than the first maximum flow rate Qmax1, the first opening / closing valve 66 is opened and the first hydraulic chamber 5 is opened.
The hydraulic pressure P1 of 0 is set as the pump pressure, and the second on-off valve 68 is opened to set the hydraulic pressure Pi of the second hydraulic chamber 54 as the pump pressure. As a result, as shown in Expression 2, the auxiliary piston 49 is connected to the stopper 5
3 is displaced to the left in FIG.
7, and the step 48 of the pilot piston 38 is pushed by the contact surface 52 to be displaced to the left in FIG. 1 to set the retracted position of the pilot piston 38. The force Pi · S2 of the pilot piston 38 due to the oil pressure Pi of the second oil pressure chamber 54 is larger than the spring force F of the spring 37 in the spool 36 as shown in Expression 1. Thus spool 3
The position 6 is a position on the left side of FIG. 1 from the position at the first maximum flow rate Qmax1 described above. Accordingly, the hydraulic pressure in the hydraulic chamber 40 of the servo drive means 26 decreases in accordance with the position of the spool 36 to the left, and the servo piston 30 separates from the stopper 31. Accordingly, the variable displacement pump 2
5 is changed to be smaller than that at the time of the first maximum flow rate Qmax1. The sleeve 35 is displaced in a direction following the spool 36 in accordance with the displacement of the servo piston 30, and the hydraulic chamber 40 is closed. Thus, the tilt angle α of the variable displacement pump 25 is set so that the second maximum flow rate Qmax2 is obtained.

In order to adjust the second maximum flow rate Qmax2, the adjusting bolt 57 is operated from outside the casing 34 to adjust the position of the stopper 53 in the left-right direction in FIG. For example, the adjusting bolt 57 is rotated and its end 59 causes the stopper 53 and thus the auxiliary piston 4 to rotate.
9 is displaced rightward in FIG. 1, the pilot piston 38 is displaced rightward, and accordingly, the spool 36 is displaced rightward against the spring force of the spring 37, and the servo valve 26 The hydraulic pressure in the hydraulic chamber 40 rises, and the servo piston 30
Is set to be displaced leftward in FIG. 1 and the tilt angle α becomes large. Conversely, when the adjustment bolt 57 is adjusted and displaced to the left in FIG.
5, the second maximum flow rate Qmax2 can be set small.

The variable displacement pump 25 is set to the minimum flow rate Qmin.
, The second on-off valve 68 is operated to set the second hydraulic chamber 54 to the tank pressure. At this time, the hydraulic pressure P1 of the first hydraulic chamber 50 may be the pump pressure or the tank pressure by the on-off valve 66. Therefore, the spool 36
Is displaced to the left in FIG. 1 by the spring force of the spring 37, whereby the pipeline 41 and the hydraulic chamber 4 of the servo drive means 26 are moved.
0 is connected to the tank 42. Therefore, the servo piston 30 is displaced rightward in FIG. Thus, the tilt angle α of the variable displacement pump 25 is minimized. The servo piston 30 displaces the sleeve 35 to the left by the feedback lever 44 to move the hydraulic chamber 4
0 is shut off from the tank 42 and the line 43. The left position of the spool 36 is when the servo piston 30 is
It is determined by the position of contact with 2.

[0034]

As described above, according to the present invention, the position of the spool of the switching valve is set to the two first and second maximum flow rates Qm.
ax1 and Qmax2, the second
In a state where the pilot pressure Pi is led to the hydraulic chamber 54, the pilot pressure P1 is not led to the first hydraulic chamber 50, and the tank pressure is used.
Alternatively, it can be achieved by introducing the pilot pressure P1, so that the configuration of the pilot hydraulic circuit can be simplified and the cost can be reduced.

According to the present invention, the pilot hydraulic circuit is realized by a pilot pressure pump and first and second opening / closing valves, and is provided in the prior art described with reference to FIGS. Thus, the pressure reducing valve 21 can be omitted, and the pressure can be simplified.

According to the present invention, the excellent effect that the second maximum flow rate Qmax2 can be adjusted without using the adjusting bolt 57 without disassembling is also achieved.

Further, according to the present invention, the contact position between the auxiliary piston and the stopper is set to the tank pressure by the drain oil passage. Therefore, in order to achieve the second maximum flow rate Qmax2, for example, when hydraulic pressure is guided to the first hydraulic chamber, there is no pressure build-up, and the auxiliary piston and the stopper can surely abut.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing a pilot hydraulic circuit according to the embodiment of the present invention shown in FIG. 1;

FIG. 3 is a diagram showing a flow rate characteristic of the embodiment of the present invention shown in FIGS. 1 and 2;

FIG. 4 is a cross-sectional view showing the configuration of the prior art.

FIG. 5 is a diagram showing a pilot hydraulic circuit in the prior art shown in FIG. 4;

FIG. 6 is a diagram showing flow characteristics of the prior art shown in FIGS. 4 and 5;

[Explanation of symbols]

 25 Variable displacement pump 26 Servo drive means 27 Switching valve 28 Flow control means 30 Servo piston 34 Casing 35 Sleeve 36 Spool 37 Spring 38 Pilot piston 44 Feedback lever 46 Pilot piston 48 Step 49 Auxiliary piston 50 First hydraulic chamber 53 Stopper 54 First 2 hydraulic chamber 57 adjustment bolt 64 drain oil passage 66 first on-off valve 68 second on-off valve

Claims (4)

[Claims] 1. A switching valve in which a spring is in contact with one end of a spool inserted in a sleeve and a pilot piston is in contact with the other end, and a variable displacement pump which is operated by switching the hydraulic pressure of the switching valve. A variable displacement pump including a servo piston for changing the tilt angle of the piston and a feedback lever interlocking the servo piston and the sleeve of the switching valve, wherein the pilot piston displaces the spool against the spring force of the spring. In the flow control device for a variable displacement pump in which the discharge flow rate of the pilot piston varies greatly, the pilot piston has a large-diameter portion and a small-diameter portion having a smaller diameter than the large-diameter portion and capable of contacting the other end of the spool. A casing, and an auxiliary piston housed in the casing to define a first hydraulic chamber and through which the small-diameter portion is displaceably inserted. A stopper that is displaceably housed in the casing, accommodates a large-diameter portion of the pilot piston in a mutually displaceable manner, defines a second hydraulic chamber, and abuts on the auxiliary piston to limit a retreat position of the auxiliary piston; A pilot hydraulic circuit for selectively supplying and shutting off the pressure oil to the first hydraulic chamber and the second hydraulic chamber; a hydraulic area S1 of the auxiliary piston on the first hydraulic chamber side is a large-diameter second hydraulic chamber; Is larger than the hydraulic area S2 on the side, and the force P1 acting on the auxiliary piston by the pressure oil in the first hydraulic chamber
The sum of S1 and the spring force of the spring is configured to be greater than the force Pi · S2 acting on the pilot piston due to the pressure oil in the second hydraulic chamber; The flow control device for a variable displacement pump, wherein an acting force Pi · S2 is configured to be larger than a spring force F of the spring. 2. The pilot hydraulic circuit includes a pilot pressure pump, a first on-off valve for guiding hydraulic pressure from the pilot pressure pump to a first hydraulic chamber, and a second on-off valve for guiding hydraulic pressure from the pilot pressure pump to a second hydraulic chamber. The flow control device for a variable displacement pump according to claim 1, further comprising an on-off valve. 3. An adjusting bolt screwed into the casing, one end of which is operable from outside of the casing, and the other end of which includes an adjusting bolt which can abut against a stopper. A flow control device for the variable displacement pump according to the above. 4. The flow control device for a variable displacement pump according to claim 1, wherein a drain oil passage communicating with the tank is formed in the casing at a contact position between the auxiliary piston and the stopper.