JPS61142377A - Capacity controller for variable capacity pump - Google Patents

Abstract

PURPOSE:To achieve practical delivery pressure, in capacity controller suitable for high pressure fuel pump in Diesel engine, by constructing such that the delivery pressure approximately proportional to the rotating speed of external engine can be produced and said delivery pressure can be maintained under specific rotating speed. CONSTITUTION:Upon driving of variable capacity pump 101 and feed pump 102 through an external engine, the delivery oil from the pump 102 will go through a regulate valve 103 to the pump 101 while through control line 108 to a balance piston 104. The delivery oil from the pump 101 is fed through a pressure line 107' in downstream of differential pressure regulator 109 to a load unit. Upon increase of the rotating speed of external engine, for example, the control pressure Pc in control line 108 will increase to move a spool 106 through a piston 104. Consequently, relatively high delivery pressure P1 is led to incremental piston 118 to increment the eccentricity of eccentric ring 113 of pump 101 thus to increase the delivery capacity of pump 101.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a capacity control device for a variable displacement pump, and is applicable to, for example, an ultra-high pressure fuel pump for a diesel engine or an industrial hydraulic pump.

In recent years, a need has arisen to provide new high pressure fuel pumps for diesel engines. This is a fuel supply pump for the so-called common rail injection system (a system that supplies fuel from a single common fuel pipe to the fuel injection valves installed in each cylinder), and this type of pump is powered by a diesel engine. A discharge pressure corresponding to the rotational speed of the engine is required, that is, a relatively low pressure is required at low speeds, and a high pressure is required at high speeds. This means that at low speeds, it is better to inject fuel slowly at -a to achieve slow combustion in terms of noise and emissions, and at high speeds, it is better to inject a large amount of fuel at high pressure in a short period of time to improve thermal efficiency. This is because it is advantageous in terms of To this end, proposals have been made from the perspective of diesel engines, such as making the cross-sectional area of the fuel injector's nozzle variable variable, and multiple injections (injecting fuel little by little at low speeds) at low speeds. There are many difficulties. Therefore, the present invention proposes a fuel supply pump to meet the above-mentioned needs.

(Prior Art) A conventional capacity control device for a variable displacement pump, as disclosed in, for example, Japanese Patent Application Laid-open No. 58-18582, introduces pump discharge pressure to a control piston (26) and controls a spring (3).
1) to control the amount of eccentricity of the cam ring (5). For this reason, there was a problem in that the discharge pressure could not be increased in response to an increase in the rotational speed of an external engine or the like.

(Problems to be Solved by the Invention) The problems to be solved by the present invention are made in view of the above-mentioned points. An object of the present invention is to provide a capacity control device for a variable capacity pump that controls the discharge pressure to be maintained at a predetermined rotation speed.

(Means for Solving the Problems) Therefore, as a means for solving the problems, the present invention provides a variable capacity pump that performs a pumping action by receiving the rotational force of an external engine, and a capacity that controls the discharge capacity of this pump. a control device, a switching valve that controls the discharge capacity by switching the fluid supplied to the capacity control device, a rotation speed proportional pressure generation means that generates a control pressure according to an increase in the rotation speed of the external engine, and the rotation speed of the external engine. a force generating means that converts the control pressure of the proportional pressure generating means into force and acts on one end of the switching valve; a pressure line leading from the discharge port of the variable displacement pump to the load device; It is characterized by having a pilot line leading to the other end of the valve.

(Function) According to the above means, when the rotational speed of the external engine increases,
Correspondingly, the control pressure of the rotational speed proportional pressure generating means increases, and this control pressure is applied to one end of the switching valve by the force generating means. When the switching valve moves, the fluid supplied to the capacity control device is switched, and the discharge capacity of the variable displacement pump is increased.

Therefore, the discharge flow rate from the pump increases. Therefore, if the consumption of the load device is constant, the discharge pressure in the pressure line will increase. On the other hand, at a predetermined rotation speed, that is, a predetermined discharge pressure, when the flow rate of the pressure line from the pump to the load device, that is, the discharge pressure changes, that pressure change is applied to the other end of the switching valve via the pilot line. Ru. Therefore, the switching valve controls the discharge capacity of the variable displacement pump by switching the fluid supplied to the capacity control device, and maintains the pressure in the pressure line at a predetermined discharge pressure.

(Example) A first embodiment of the present invention will be described below based on the drawings.

FIG. 1 is a schematic hydraulic circuit diagram showing a displacement control device for a variable displacement pump according to a first embodiment. The capacity control device of this variable displacement pump consists of an eccentric ring 113 (13) serving as a variable displacement pump 101° capacity control device, and a volume increasing piston 117 (17).
), a reduction piston 118 (18), a fixed capacity feed pump 102 and a regulation valve 103 that serve as rotational speed proportional pressure generation means, and a spool valve 10 that serves as a switching valve.
5. It basically consists of a balance piston 104 serving as a force generating means, a differential pressure regulator 109, etc.

First, the variable displacement pump 101 will be specifically explained based on FIGS. 2 and 3. 2 and 3 show the structure of a radial rotary piston type variable displacement pump.

A shaft 1 is rotatably supported in a housing 2 by a bearing 3. The right end of the shaft 1 is connected by a joint 4 to a pump shaft 6 at the left end of the rotor 5.

Seven pistons 7 are slidably fitted in the rotor 5 in a radial manner, and rotate around a pintle 8 that is integrally fixed to the housing 2 . The pistons 7 are urged toward the outside of the rotor 5 by respective springs 9, and each tip of the pistons 7 is always in contact with the cam ring 11 via a shoe IO. The inner and outer circumferences of the cam ring 11 have cylindrical surfaces, and the outer circumference is rotatably fitted into the eccentric ring 13 via a number of rollers 12 .

The upper part of the eccentric ring 13 is pivotally supported so as to be swingable about a pin 14 which is fixed to the housing 2 and serves as a fulcrum. A plate 15, which is a protrusion, is integrally provided at the lower part of the eccentric ring 13, that is, at a position facing the bin I4, and the plate 15 is slidably engaged with a groove or slit 16' provided in the slider 16. ing.

The slider 16 is slidably disposed within the housing 2 substantially parallel to the rotation axis of the rotor 5 and the axis of the bottle 8. Further, the slit 16' and the plate 15 have a shallow predetermined angle with respect to the sliding direction of the slider 16.

The nfft pistol 17 is in contact with the right side of the slider 16, and the increase piston 18 is in contact with the left side thereof. The increase piston 18 and the slider 16 are connected by a spring 19 with a weak biasing force.
is constantly biased to the right. Further, the decrease/increase pistons 17 and 18 are slidable coaxially with the slider 16, and the slider 16 is moved by both.

The liquid pressure on the back side of the decrease/increase pistons 17, 18 is switched and controlled by a spool valve 105, which will be described later.

The housing 2 is formed with an inflow boat 20 into which liquid sent from a feed pump 102 (described later) flows, and a discharge port 21 through which liquid pressurized by the pump action is discharged. Further, the rotor 5 is provided with a communication port 23 that communicates the inflow port 20 with a space 22 within the housing 2 . The space 22 communicates with the tank via a relief port 24 formed in the housing 2.

Next, the operation will be explained based on the above configuration. When the rotor 5 rotates around the bottle 8, the shoe 1
The cam ring 11 in contact with the rotor 5 rotates in the same direction as the rotor 5 due to the frictional force. At this time, if the rotation center of the cam ring 11 is eccentric with respect to the axis of the bottle 8, the piston 7 reciprocates with respect to the rotor 5 by twice the amount of eccentricity due to the action of the spring 9 and the cam ring 11.

Therefore, when the rotor 5 rotates in the clockwise direction in FIG.
Discharge fluid. In other words, the fluid entering from the inlet 20 is
It is sent to the port 25, the pump chamber 27, the boat 26, and the discharge port 21, and is sent to a load device (not shown) via the pressure line 107. Further, of the fluid that entered from the inlet 20, surplus fluid that is not sucked into the pump chamber 27 cools each sliding part in the housing 2 and connects it to the communication hole 23. Space 22.
It flows out to the tank side through the relief flow 24. The discharge capacity per rotation of the rotor 5 is determined according to the amount of change in volume of the pump chamber 27, that is, the amount of reciprocating motion of the piston 7, that is, the amount of eccentricity between the cam ring 11 and the rotor 5. The positions of the cam ring 11 and the eccentric ring 13 are determined by the slider I6 with which the plate 15 engages.

At normal B (when stopped), the slider 16 is positioned to the right due to the action of the springs 19. (However, in FIGS. 1 and 2, the plate 15 is shown in an intermediate position.) Therefore, the plate 15 has a slit 16
As a result, the eccentric ring 13 is given the maximum amount of eccentricity with respect to the rotor 5. In this state, the pump discharge capacity is at its maximum.

Next, when the rotor 5 rotates and starts pumping, the discharge pressure in the pressure line 107 increases. Here, a spool valve 105, which will be described later, switches the fluid supplied to the back surfaces of the reducing piston 17 and the increasing piston 18 to control the volume.

When the supply fluid is switched by the spool valve 105 so that the leftward force of the decreasing histone 17 is increased by the rightward force of the increasing piston 18 and the spring 19, the slider 16 is moved to the left. At this time, the plate 15 is movable in the direction perpendicular to the axis, but is restrained in the axial direction, so the holding position of the plate 15 moves relative to the right of the slit 16. At this time slit 1
Since 6' has a predetermined shallow angle with respect to the axial direction, the plate 15 is moved to the right in FIG. As a result, the eccentric ring 13 integrated with the plate 15 swings counterclockwise, and the rotor 5 and the eccentric ring 13
The amount of eccentricity decreases, and therefore the pump discharge capacity decreases.

On the other hand, when the supply fluid is switched so that the rightward force of the increase piston 18 and the spring 19 becomes greater than the leftward force of the decrease piston 17, the slider 16 moves to the right, contrary to the above. At this time, the eccentric ring 13 swings clockwise in FIG. 3, the amount of eccentricity between the rotor 5 and the eccentric ring 13 increases, and therefore the pump discharge capacity increases.

Next, referring to FIG. 1, a variable displacement pump capacity control device using the variable displacement pump 101 described above will be explained.

The variable displacement pump 101 described above is shown schematically for ease of understanding. That is, the rotor 2, piston 7, etc. in FIG. 2 are the same as the pump section 100 in FIG.
Similarly, the eccentric ring 13 is 113, and the Kl piston 17 is 1
17. The increase piston 18 is 118. The springs 19 correspond to 119, respectively.

Next, another configuration of the displacement control device for a variable displacement pump will be explained.

The feed pump 102 is provided coaxially with the variable displacement pump 101, and is driven to rotate along with the shaft 1 by the rotational force of an external engine such as a diesel engine.

The foot pump 102 is preferably a vane-type pump provided inside the housing 2 of the variable displacement pump 101, but may also be a gear-type, piston-type, etc. pump. The pump 102 discharges a discharge flow rate proportional to the rotational speed of the external engine, and its discharge pressure is lower than that of the above-mentioned pump 101, and its discharge flow rate is set to be higher than the suction flow rate of the above-mentioned pump 101. .

The regulator valve 103 is a pressure control device that has the function of generating a pressure Pc (hereinafter referred to as control pressure PC) that is approximately proportional to the flow rate of liquid passing through it, and is used for timer control of the VE type fuel pump. It is similar to the regulator valve used. The liquid discharged from the feed pump 102 is passed from the inlet 3-1 to the regulation valve 1.
03, the piston 3-2 is pushed to the right against the spring 3-4, and the opening area of the outlet 3-3 is changed.

At this time, by appropriately determining the cross-sectional shape of the outlet 3-3 of the regulator valve 103 and the spring constant of the spring 3-4,
The control pressure Pc of the control line 10B is determined approximately proportional to the flow rate of the liquid, that is, the rotational speed Np of the pump 102. still,
Outlet 3-3 of legileate valve 103 from pump 102
As explained above, a part of the liquid flowing into the tank is sucked into the variable displacement pump 101, and the excess liquid flows out from the relief port 27 to the tank side.

The control pressure Pc from the rotation speed proportional pressure generating means composed of the foot pump 102 and the regulation valve 103 described above is guided to the left side of the balance piston 104 in FIG. 1 via the control line 108.

The spool valve 105 is a four-way valve with a known structure in which flow path switching is controlled by a four-land spool 106. is received via pilot line 110. Further, the left end surface of the spool 106 is in contact with the balance piston 104. The pressure receiving surface on which the balance piston 104 receives the control pressure Pc is set to have a larger area than the right end surface of the spool 106, and a large force Fs+ is derived from the relatively low control pressure Pc.

The inlet port 6-1 of the spool valve 105 communicates with the pressure line 107 upstream of the differential pressure regulator 109,
Outlet port 6-4 communicates with pressure line 107 downstream of differential pressure regulator 109 via a pilot line. Also, the control port 6-2 of the spool valve 105.
6-3 communicates with an oil chamber on the back side of the increase piston 118 and an oil chamber on the back side of the decrease piston 117, respectively. Also, inside the spool 106, there is an outlet passage 6-6 communicating with a pressure line 107 downstream of the differential pressure regulator 109.
When the pressure in the pressure line 107' rises rapidly and stops above a predetermined pressure plate, a relief passage 6-5 is formed which communicates with the low pressure side. Note that the spool valve 105 shown in FIG.
indicates that the spool 106 is in the neutral position.

A differential pressure regulator 109 is provided midway between the pressure lines 107 and 107'. This is differential pressure regulator 10
Due to the differential pressure between upstream and downstream of 9 and spring 109a,
The pressure line 109 is opened and closed, and the pressure difference therebetween is set to be ΔP.

Hereinafter, the discharge pressure of the pressure line 107 upstream of the differential pressure regulator 109 is assumed to be PI+, and the discharge pressure of the downstream pressure line 107'' is assumed to be P2. explain.

Since the variable displacement pump 101 is held at the maximum discharge capacity by the action of the spring 19 when stopped, when the pumps 101 and 102 are rotationally driven by an external engine, both pumps 101 and 102 perform a pumping action and pump fluid. Discharge.

The fluid discharged from the feed pump 102 reaches the variable displacement pump 101 via the regulation valve 103, and presses the balance piston 104 at the control pressure Pc via the control line 108, causing a rightward force on the piston 104. Generate Fs+. The fluid discharged from the variable displacement pump 101 is supplied to the load device at a discharge pressure P2 from a pressure line 107'' downstream of the differential pressure regulator 109. The spool 106 is guided by the spool 106 to generate a leftward force FSX on the spool 106. Therefore, the spool 106 moves so that the rightward force FSI and the leftward force Fsz are balanced.

Next, when the rotational speed of the external engine increases, the control pressure and Pc increase due to the action of the pump 102 and regulator valve 103 as described above, and the balance piston 104 and spool 106 move as shown in FIG. 4(a). Move to the right. Then, the increase piston 118 is activated by the spool valve 105.
The hydraulic pressure on the back side of the pump is switched to the discharge pressure P1 of the pressure line 107 via the control port 6-2 and the inlet boat 6-1. At the same time, the oil chamber on the back of the piston 117 is
Control port 6-3. The pressure is switched to the discharge pressure P2 of the pressure line 107' through the outlet port 6-4. Here, since the discharge pressure P1 is ΔP higher than the discharge pressure P2, the leftward force F1 acting on the increase piston 118 is
Overcoming the rightward force F2 acting on the piston 117, the eccentricity of the eccentric ring 113 of the variable displacement pump 101 increases as described above, increasing the discharge capacity, and as a result, the pressure line 1
The discharge pressure Pl+ of 07 and P2 of 107° increase.

On the other hand, when the rotational speed decreases, the control pressure Pc decreases, contrary to the above, and as shown in FIG. 4 (bl), the balance piston 104.
Spool 106 moves to the left. Then, the oil chamber on the back side of the increase piston 118 is switched to the discharge pressure P2 of the pressure line 107° via the control port 6-2 and the outlet port 6-4. At the same time, the oil chamber on the back side of the weight loss piston 117 is switched to the discharge pressure P of the pressure line 107 via the control port 6-3 and the inlet boat 6-1. Here, since the spring 119 has a weak biasing force, the rightward force F2 acting on the weight loss piston 117 due to the discharge pressure P1 is applied to the spring 119.
The leftward force F acting on the volume increaser piston 118 due to the discharge pressure P2 and the discharge pressure P2 is greater than, and contrary to the above, the variable displacement pump 1
The eccentricity of the eccentric ring 113 of 01 decreases and the discharge capacity decreases, resulting in the discharge pressures P, , P, of the pressure line 107.
decreases.

As described above, when the rotational speed of the external engine changes, the control pressure Pc changes, and the pressure line 10
The discharge pressure P2 of No. 7 is controlled. Furthermore, since the control pressure Pc is approximately proportional to the rotational speed of the feed pump 102 driven by an external engine, the discharge pressure P2 of the pressure line 107 is equal to the pressure receiving area of the balance piston 104, as shown in FIG. It is controlled approximately in proportion to its rotational speed, with the ratio to the pressure-receiving area of the spool 106 as a proportionality constant.

Next, as mentioned above, when the rotational speed of the external engine is constant and the discharge pressures P+ and Pz of the pressure lines 107 and 107' are the predetermined discharge pressures, if the liquid consumption of the load device (not shown) changes, the change will be This results in a change in the discharge pressure P2 of the pressure line 107'. This change in the discharge pressure P2 acts on the spool as a change in the left force F32 acting on the spool 106, causing the spool to move. If the liquid consumption of the load device increases and the discharge pressure P2 decreases, the spool 106
moves to the right as shown in FIG. 4(a), the ports communicate with each other as described above, the discharge capacity of the variable displacement pump 101 increases, and the discharge pressure P of the pressure line 107 increases.

The decrease in P is suppressed and maintained at a predetermined discharge pressure. Conversely, when the liquid consumption of the load device decreases and the discharge pressure P7 increases, the spool 106 moves to the left as shown in FIG. The discharge capacity of the variable displacement pump 101 decreases, suppressing increases in the discharge pressures P+ and Pz of the pressure line 107 and maintaining them at predetermined discharge pressures.

In addition, when the liquid consumption of a load device (not shown) rapidly becomes 0 (for example, when rapid fuel injection is performed in a common rail injection system), the pressure line 107 is in the same state as a blockage, and the discharge Pressure P2 is about to rise rapidly.

If the discharge capacity of the pump 101 is not controlled to decrease promptly in response to the rate of increase in the discharge pressure P2, the discharge pressure P2 will become abnormally high, and the high-pressure piping system of the pump 101 and the pressure line! 07 may be destroyed. This phenomenon occurs when the discharge pressure P increases and the spool 1
06 is generated because the liquid in the oil chamber on the back of the increase piston 118 has no place to escape even if it is in the state shown in FIG. This is because the spool 106 cannot be moved to the right by the force F2 (that is, the discharge capacity of the pump 101 cannot be reduced). When the discharge pressure P2 becomes equal to or higher than the predetermined pressure, the fourth (C)
The relief port 6-5 opens to the low pressure chamber 4-1.

Therefore, the fluid in the pressure line 107' quickly flows out from the outlet port 6-4 into the low pressure chamber 4-1, and is lowered to a predetermined pressure.

In the embodiments described above, the discharge pressure P2 is controlled by controlling the spool valve 106 by balance with the rightward force Fs+ generated in the balance piston 104, but the force FSI is controlled by the force FSI described above. For example, the output from a mechanical governor used in a fuel injection pump or the like may be used as long as the force is from a rotational speed proportional pressure generation circuit that generates a force substantially proportional to the rotational speed of the external engine.

When using a mechanical governor, the force obtained from the control block against the spring force is amplified by the centrifugal force generated in the flyweight depending on the rotational speed of the rotating shaft via a link mechanism, and is converted into the above force FSI. Make use of it.

In addition, the spool 1 of the spool valve 105 of the L stroke 1 embodiment
06 shows the 4-round type, but a 3-round type as shown in FIG. 6 may also be used. In addition, a leap port 6-5 is provided inside the spool 106 to prevent abnormally high pressure in the pressure line 107'', but the 7th port has a similar function.
The structure shown in the figure may be used.

Next, a second embodiment will be explained based on FIG. 8.

The difference between the second embodiment and the first embodiment is that the pressure line 10
The differential pressure regierator 109 provided in the pump 7 is eliminated, the fluid discharged from the pump 101 is directly supplied to the load device, and the spool valve is replaced by a spool three-way valve 111.

That is, the inlet port 2-1 of the spool three-way valve 112 communicates with the pressure line 107 of the discharge pressure P2, the out-left port 2-2 is connected to the tank side, and the control port 2-3 is connected to the oil chamber on the back side of the increase piston 118. Each is connected. Further, the spool 112 is provided with a control passage 2-4. On the other hand, the oil chamber on the back of the heavy piston 117 is connected to the pressure line 1.
07 to receive the discharge pressure P2, the weight loss piston 1
The pressure receiving area of the piston 17 is set smaller than the pressure receiving area of the increase piston 118. Incidentally, the same components as those in the first embodiment are given the same reference numerals, and the explanation thereof will be omitted.

Next, its operation will be explained. Similar to the first embodiment described above,
The spool 112 is moved by the control pressure Pc and the discharge pressure P2 of the pressure line 107, and the same discharge pressure control as described above is performed. That is, the control pressure Pc increases, or the discharge pressure P2
When the amount decreases, the spool 112 moves to the right, and the oil chamber on the back side of the increase piston 118 communicates with the pressure line 107 via the control port 2-3 and the inlet boat 2-1.

Then -$j,? Piston 117 and increase piston 118
Due to the difference in the pressure receiving areas, the increase piston 118 moves to the left, and the discharge pressure P2 increases as described in the first embodiment. On the other hand, the control pressure Pc decreases, or the discharge pressure P
2 rises, the spool 112 moves to the left, and the oil chamber on the back of the increase piston 118 communicates with the tank via the control port 2-3 and the outlet port 2-2. Then, the reduction piston 117 moves to the right due to the discharge pressure, and the discharge pressure P2 decreases as described in the first embodiment.

Therefore, the capacity control of the variable displacement pump is the same as in the first embodiment.

Here, differences between the first embodiment and the second embodiment will be briefly explained.

In the first embodiment, the liquid used for capacity control flows out from the outlet port 6-4 of the spool valve 105 into the pressure line 107 at the discharge pressure P2, whereas the liquid used for volume control flows out into the pressure line 107 at the discharge pressure P2.
In an embodiment, the liquid is supplied to outlet port 2-
1 will leak into the tank. Therefore, in the first embodiment, all the high pressure liquid once pressurized is transferred to the pressure line 107.
Therefore, there is an advantage that the power consumed by the variable displacement pump 101 can be used effectively.

In particular, when the discharge pressure P2 is high, the first embodiment described above is
Power consumption can be reduced compared to the embodiment.
-Although the variable displacement pump 101 in the above embodiment is a radial rotary piston type pump, it may also be a vane type pump. Further, the balance piston 104 may be integrated with the spool valve.

(Effects of the Invention) As described above, when the rotational speed of the external engine increases, the control pressure of the rotational speed proportional pressure generation means increases accordingly, and this control pressure is applied to one end of the switching valve by the force generation means. be done. When the switching valve moves, the fluid supplied to the capacity control device is switched, and the discharge capacity of the variable displacement pump is increased. Therefore, the discharge flow rate from the pump increases. Therefore, if the consumption of the load device is constant, the discharge pressure in the pressure line will increase. On the other hand, at a predetermined rotation speed, that is, a predetermined discharge pressure, when the flow rate of the pressure line from the pump to the load device, that is, the discharge pressure changes, that pressure change is applied to the other end of the switching valve via the pilot line. Ru. Therefore, the switching valve controls the discharge capacity of the variable displacement pump by switching the fluid supplied to the capacity control device, and maintains the pressure in the pressure line at a predetermined discharge pressure. Therefore, when the rotational speed of the external engine changes from low to high speed, the discharge capacity of the variable displacement pump changes accordingly, changing from low pressure to high pressure to a predetermined discharge pressure, and at that predetermined discharge pressure. It becomes possible to stably maintain the predetermined discharge pressure regardless of the magnitude of the discharge capacity of the variable displacement pump.

[Brief explanation of drawings]

1 is a schematic hydraulic circuit diagram showing a first embodiment of the present invention, FIG. 2 is a cross section of the variable displacement pump 101 shown in FIG. 1, FIG. 2(a) is a longitudinal sectional view, and FIG. is a sectional view taken along line 1-1 of the pump shown in Fig. 2 (al), and Fig.
), FIG. 4 is a diagram for explaining the operation of the spool valve 105, FIG. 5 is a characteristic diagram showing the relationship between pump rotational speed Np and discharge pressure P, 6 and 7 are sectional views of essential parts showing other examples of the spool valve of the first embodiment, and FIG. 8 is a schematic hydraulic circuit diagram showing a second embodiment of the present invention. 101... Variable displacement pump, 102... Foot pump, 103... Regulate valve, lO4...
Balance piston, 105... Spool valve, 106...
...Spool, 107...Pressure line, 108...
Control unit, 109... Differential pressure regulator, 110.
... Pilot line, 113 (13) ... Eccentric ring, 117 (17) ... Reduction piston, 118 (18
)... Increased piston.

Claims (3)

[Claims] 1. A variable displacement pump that performs a pumping action in response to the rotational force of an external engine, a displacement control device that controls the discharge capacity of this pump, and a switching valve that controls the discharge capacity by switching the fluid supplied to the capacity control device. rotational speed proportional pressure generation means for generating control pressure in accordance with an increase in the rotational speed of the external engine;
A force generating means that converts the control pressure of the rotation speed proportional pressure generating means into force and acts on one end of the switching valve, a pressure line leading from the discharge port of the variable displacement pump to the load device, and the pressure of this pressure line. and a pilot line leading the switching valve to the other end of the switching valve. 2. The rotational speed proportional pressure generation means includes a fixed capacity pump that performs a pumping action in response to the rotational force of an external engine, and a pressure control device that generates a substantially proportional control pressure according to the discharge capacity of the fixed capacity pump. A capacity control device for a variable capacity pump according to claim 1. 3. Claim 1, wherein the force generating means is a balance piston that receives the control pressure of the rotational speed proportional pressure generating means, and the pressure receiving area thereof is larger than the pressure receiving area of the other end of the switching valve. Or the capacity control device for a variable capacity pump according to item 2.