JPH08338405A - Capacity control device for variable displacement hydraulic pump - Google Patents

Abstract

PURPOSE: To markedly decrease a delivery flow amount when rotated at a low speed, by changing differential pressure set force of a control valve by an engine speed. CONSTITUTION: A throttle 18 is provided in a delivery path 16 of a fixed oil hydraulic pump 3 driven by the same engine 1 of driving a variable displacement oil hydraulic pump 2. A differential pressure between before and after this throttle 18 is applied to act in a control valve 26 for controlling a capacity, with differential pressure set force made variable, to decrease it at the time of low engine speed, and a delivery flow amount of the variable displacement oil hydraulic pump 2 is markedly decreased, so as to improve fine controllability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for controlling the displacement of a variable displacement hydraulic pump used in a hydraulic circuit that supplies pressure oil to an actuator of a construction machine or the like.

[0002]

2. Description of the Related Art As a hydraulic circuit for supplying pressure oil to an actuator of a construction machine or the like, there is known a hydraulic circuit for supplying pressure oil discharged from a hydraulic pump to an actuator by an operation valve. With a closed center type operation valve that shuts off the oil, when the operation valve is in the neutral position, the discharge pressure oil of the hydraulic pump becomes a dead end and becomes high pressure, so the driving horsepower consumption of the engine that drives the hydraulic pump is large. Become.

As a hydraulic circuit for solving this, for example, as shown in Japanese Utility Model Laid-Open No. 5-86003, the hydraulic pump is a variable displacement hydraulic pump (hereinafter referred to as variable hydraulic pump), and the capacity of the variable hydraulic pump ( The discharge amount per one rotation is set to a small capacity when the differential pressure between the inlet side pressure (pump discharge pressure) and the outlet side pressure (load pressure) of the operating valve is large, and a large volume when the differential pressure is small to keep the differential pressure constant. It is known that the discharge flow rate (capacity × rotation number per unit time) of the variable hydraulic pump is set to a value commensurate with the opening degree of the operation valve (communication area of the pump port and the actuator port).

In the above-mentioned hydraulic circuit, the discharge flow rate of the variable hydraulic pump is small when the engine speed is low and increases when the engine speed is high even if the displacement is the same. Since the pressure difference with the outlet side pressure is different, even if the opening of the operating valve is the same, when the engine speed is low, the capacity of the variable hydraulic pump is large and the discharge flow rate is set to a value commensurate with the opening. The discharge flow rate is set to a value commensurate with the degree of opening by setting the capacity of the valve to be small.

For this reason, even if the engine rotational speed is lowered when it is desired to perform a minute operation in which the actuator is slightly operated by reducing the flow rate supplied to the actuator, the above-mentioned operation increases the capacity of the variable hydraulic pump, and the variable hydraulic pump has a large capacity. Since the discharge flow rate increases, the above-mentioned minute operation cannot be performed.

From the above, the above-mentioned actual Kaihei 5-8
In the hydraulic circuit shown in Japanese Patent No. 6003, a fixed displacement hydraulic pump (hereinafter referred to as a fixed hydraulic pump) is driven by an engine that drives a variable hydraulic pump, and a drain and a relief valve are provided in a discharge passage of the fixed hydraulic pump. Connect the circuit,
The pressure closer to the fixed hydraulic pump than the connecting portion in the discharge passage is detected, and the displacement of the variable hydraulic pump is also controlled by the detected pressure.

With this configuration, the detected pressure has a value commensurate with the engine speed, so that the differential pressure between the pump discharge pressure and the load pressure has a value commensurate with the engine speed, and the displacement of the variable hydraulic pump is changed to the engine speed. Can be added to control.

[0008]

However, with the above-mentioned configuration, a part of the discharge pressure oil of the fixed hydraulic pump is throttled,
Since the pressure oil is discharged from the relief valve to the tank, the discharged pressure oil cannot be used effectively, and when the discharged pressure oil is supplied to other hydraulic equipment, the flow rate to the tank decreases and the differential pressure before and after the throttle is reduced. Changes, the detected pressure differs and the displacement control characteristic of the variable hydraulic pump changes. Also, when the engine speed is extremely low, the discharge flow rate of the fixed hydraulic pump is small and the pressure may not rise to the set pressure of the relief valve. In that case, the capacity of the variable hydraulic pump cannot be controlled in consideration of the engine speed. .

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a displacement control device for a variable displacement hydraulic pump that can solve the above-mentioned problems.

[0010]

A first invention is a cylinder 21 for controlling the displacement of a variable displacement hydraulic pump 2, and a control valve 26 for controlling the pump discharge pressure to the cylinder 21.
A fixed displacement hydraulic pump 3 driven by the same engine 1 as the variable displacement hydraulic pump 2 and its discharge passage 16
The control valve 26 is switched by the magnitude relationship between the differential pressure between the pump discharge pressure and the load pressure and the differential pressure setting force to adjust the differential pressure to a constant value corresponding to the differential pressure setting force. The capacity control device for the variable displacement hydraulic pump is such that the differential pressure setting force is large when the differential pressure before and after the throttle 18 is large, and is small when the differential pressure is small. A second aspect of the invention is a cylinder 21 that controls the displacement of the variable displacement hydraulic pump 2, a control valve 26 that controls the supply of pump discharge pressure to the cylinder 21, and an engine 1 that is the same as the variable displacement hydraulic pump 2. A fixed displacement hydraulic pump 3 to be driven and a throttle 18 provided in the discharge passage 16 are provided, and when the pressure oil is supplied to the large diameter pressure receiving chamber 23, the cylinder 21 moves in the small capacity direction, and the large diameter It is assumed that when the pressure receiving chamber 23 communicates with the drain, it moves in the large capacity direction, and the control valve 26 is moved to the drain position where the large diameter pressure receiving chamber 23 communicates with the drain by the pressure of the first pressure receiving portion 30 and the first auxiliary pressure receiving portion 31. A, and the supply position B for supplying the pump discharge pressure to the large-diameter pressure receiving chamber 23 by the pressure oil of the second pressure receiving portion 32 and the second auxiliary pressure receiving portion 33, and supplying the load pressure to the first pressure receiving portion 30. The second pressure receiving portion 32 The discharge pressure is supplied, the upstream pressure of the throttle 18 is supplied to the first auxiliary pressure receiving portion 31, and the second auxiliary pressure receiving portion 33 is provided with an intermediate pressure between the first throttle and the second throttle in the drain path connected to the downstream side of the throttle 18. It is a displacement control device for a variable displacement hydraulic pump that supplies pressure.

[0011]

[Operation] According to the first aspect of the invention, when the rotational speed of the engine 1 is low, the discharge flow rate of the fixed displacement hydraulic pump 3 is small and the differential pressure before and after the throttle 18 becomes small, so that the differential pressure setting force of the control valve 26 is reduced. Becomes smaller and the rotational speed of the engine 1 is high, the fixed displacement hydraulic pump has a large discharge flow rate and the throttle 1
The differential pressure before and after 8 increases, and the differential pressure setting force of the control valve 26 increases. As a result, the discharge flow rate of the variable displacement hydraulic pump 2 is significantly reduced when the engine 1 is rotating at a low speed. According to the second invention, the pressure P ₄ acting on the second auxiliary pressure receiving portion 33 of the control valve 26 is the fixed displacement hydraulic pump 3
Is a value obtained by reducing the downstream side pressure P ₃ of the throttle 18 provided in the discharge passage 16 at a constant ratio, and the discharge flow rate due to the efficiency change due to the discharge pressure of the fixed displacement hydraulic pump 3 with the engine 1 being at a constant rotation speed. Even if there is a change, the pressure difference between the first auxiliary pressure receiving portion 31 and the second auxiliary pressure receiving portion 33 of the control valve 26 becomes substantially the same, so the rotational speed of the fixed displacement hydraulic pump 3 is the same, and the discharge pressure thereof is high. , Control valve 2 when changing to low pressure
The differential pressure setting force of 6 becomes almost the same, and the discharge flow rate of the variable displacement hydraulic pump 2 becomes almost the same.

[0012]

[Examples] As shown in FIG. 1, an engine 1 includes a variable displacement hydraulic pump 2 (hereinafter referred to as variable hydraulic pump 2) and a fixed displacement hydraulic pump 3 (hereinafter referred to as fixed hydraulic pump 3).
And the discharge passage 4 of the variable hydraulic pump 2 drives the operation valve 5
Of the operating valve 5 connected to the pump port 6 of the
The actuator ports 7 and 8 are the first and second circuits 9 and 10.
Is connected to the first chamber 12 and the second chamber 13 of the actuator 11, and the tank port 14 is connected to the tank 15.

The discharge passage 16 of the fixed hydraulic pump 3 is connected to the inlet side of the hydraulic pilot valve 17, and the hydraulic pilot valve 17 is operated to supply the discharge flow rate of the fixed hydraulic pump 3 to other hydraulic equipment. A diaphragm 18 is provided in the discharge passage 16.
Is provided.

The swash plate 20 for controlling the displacement of the variable hydraulic pump 2 is tilt-controlled by a piston 22 of a cylinder 21,
The piston 22 of the cylinder 21 moves in the small capacity direction by the pressure oil in the large diameter pressure receiving chamber 23, and moves in the large capacity direction by the pressure oil in the small diameter pressure receiving chamber 24 and the spring 25.

The large-diameter pressure receiving chamber 23 is connected and controlled by the control valve 26 to the tank 15 and the discharge passage 4, and the small-diameter pressure receiving chamber 24 is connected to the discharge passage 4.

The control valve 26 is a first valve connected to the discharge passage 4.
Second port 28 connected to port 27 and large diameter pressure receiving chamber 23
A drain position A in which the first port 27 is shut off by the pressure oil of the first pressure receiving portion 30 and the pressure oil of the first auxiliary pressure receiving portion 31 and the second port 28 communicates with the tank port 29. Is pushed by the pressure oil of the second pressure receiving portion 32 and the second pressure receiving portion 32.
The pressure oil of the auxiliary pressure receiving portion 33 pushes the supply port B to connect the first port 27 and the second port 28 and to block the tank port 29.

The first pressure receiving portion 30 is connected to the outlet side of the shuttle valve 34 for detecting the higher pressure of the first circuit 9 and the second circuit 10, and the outlet side pressure (load pressure) of the operating valve 5 is supplied. Then, the second pressure receiving portion 32 is connected to the discharge passage 4 and the inlet side pressure (pump discharge pressure) of the operation valve 5 is supplied, and the first auxiliary pressure receiving portion 31 is connected to the upstream side of the throttle 18, and the second auxiliary pressure receiving portion 31 is connected. Pressure receiving part 33
Is connected to the downstream side of the diaphragm 18.

The rotation speed of the engine 1 is controlled by sending a rotation speed command from an operating member 34 such as an accelerator pedal to a control governor 35. For example, when the operating member 34 is at the low speed position a, it rotates at low speed, when it is at the medium speed position b, it rotates at medium speed, and when it is at the high speed position c, it rotates at high speed.

Next, the operation will be described. When the differential pressure between the inlet side pressure (pump discharge pressure) and the outlet side pressure (load pressure) of the operating valve 5 is larger than the differential pressure setting force, the control valve 26 switches to the supply position B to tilt the swash plate 4 at a tilt angle. When the differential pressure is tilted in a small direction and the differential pressure is smaller than the differential pressure setting force, it is switched to the drain position A and the swash plate 4 is tilted in the large tilt angle direction so that the inlet side pressure and the outlet side pressure of the operation valve 5 are changed. Of the control valve 26, the discharge flow rate of the variable hydraulic pump 2 is set to a value commensurate with the opening degree of the operation valve 5 (the communication area between the pump port 6 and the first or second actuator port 7, 8). The pressure setting force is variable depending on the differential pressure before and after the throttle 18, and the differential pressure before and after the throttle 18 is 2 times the discharge flow rate (engine speed) of the fixed hydraulic pump 3.
Proportional to the square.

Because of this, the differential pressure setting force of the control valve 26 is small when the engine speed is low and is large when the engine speed is high, and the discharge flow rate of the variable hydraulic pump 2 is small when the engine speed is low and the operation is minute. However, it is less than at high speed, and the micro operability is improved.

That is, the differential pressure before and after the throttle 18 is proportional to the square of the engine speed (the discharge flow rate of the fixed hydraulic pump) as shown in FIG. 2A, and the differential pressure setting force of the control valve 26 is shown in FIG. (B), it is linearly proportional to the differential pressure before and after the throttle 18,
Since the capacity of the variable hydraulic pump is proportional to the square of the differential pressure setting force as shown in FIG. 2 (c), the discharge flow rate of the variable hydraulic pump is linearly proportional to the engine speed as shown in FIG. 2 (d). To do.

Next, the specific structure of the control valve 26 will be described. As shown in FIG. 3, the sleeve 42 is fitted and inserted into the sleeve hole 41 of the valve body 40 such as the housing of the variable hydraulic pump 2,
A first port 43, a second port 44, a third port 45, a fourth port 46, and a fifth port 47 are formed in the sleeve 42, and the spool fitting hole 42a of the sleeve 42 is provided in the sleeve 42. The spool 48 is fitted and the spring 49 is inserted in the spring insertion hole 42b.

The spool 48 has a first small diameter portion 50 and a second small diameter portion 50.
The small diameter portion 51 has a small diameter portion 51 and a third small diameter portion 52, and the small diameter portion 54 of the fixed piston 53 fitted into the spool fitting hole 42a is fitted to the shaft center of the one end portion to form the first pressure receiving chamber 55 and the second pressure receiving chamber 55. 56, the first pressure receiving chamber 55 is opened in the second small diameter portion 51 by an oil hole 57 formed in the spool 48, and the third small diameter portion 5 is formed.
2 protrudes into the spring insertion hole 42a and the third pressure receiving chamber 58
Is formed.

The spring insertion hole 42 of the sleeve 42
The tip cylindrical portion 60 of the screw rod 59 is fitted in b to form a fourth pressure receiving chamber 61, the screw rod 59 is screwed into the sleeve 42 and fixed by a lock nut 62, and the other end of the screw rod 59 is fixed. A hole 64 opening from the pipe joint portion 63 to the fourth pressure receiving chamber 61 is formed.

The first port 43 communicates with the second pressure receiving chamber 56 and the first inflow port 65, and the first inflow port 65 thereof.
Is connected to the downstream side of the throttle 18 in FIG.
Is connected to the outflow port 66, the outflow port 66 communicates with the tank, the third port 45 is connected to the control port 67, the fourth port 46 is connected to the pump pressure supply port 68, and the fifth port. 47 is connected to the second inflow port 69,
The second inflow port 69 is connected to the upstream side of the throttle 18 in FIG. 1, and a hose is connected to the other end pipe joint portion 63 to supply the operating valve outlet side pressure (load pressure) to the fourth pressure receiving chamber 61. To be done.

Next, the operation will be described. The pump discharge pressure P ₁ of the variable hydraulic pump 2 is supplied to the fourth port 46 from the pump pressure supply port 68 and to the first pressure receiving chamber 55 through the second small diameter portion 51 and the oil hole 57, and the spool 48 is moved to the right. The control valve output side pressure (load pressure) P _LS is supplied to the fourth pressure receiving chamber 61 and pushes the spool 48 to the left.

Here, when the differential pressure between the pump discharge pressure P ₁ and the load pressure P _LS is zero (P ₁ = P _LS ), that is, when the operation valve opening is large, the pressure receiving diameter d ₁ of the first pressure receiving chamber 55 becomes Fourth pressure receiving chamber 61
Since the pressure receiving diameters d ₂ are equal to each other, the spool 48 is pushed leftward in FIG. 3 by the spring 49.

As a result, the first small diameter portion 5 of the spool 48 is
At 0, the second port 44 and the third port 45 communicate with each other, the control port 67 communicates with the tank through the outflow port 66, and the control valve 26 in FIG. The capacity of the pump 2 increases.

When the displacement of the variable hydraulic pump 2 becomes large and the discharge flow rate increases, the flow rate of the flow from the pump port 6 of the operation valve 5 to the first or second actuator port 7, 8 increases, and the opening degree of the operation valve 5 increases. If the above condition remains the same as above, the pressure loss of the operating valve becomes large and the differential pressure between the pump discharge pressure P ₁ and the load pressure P _LS becomes large.

As a result, the force acting on the spool 48 becomes π / 4d ₁ ² × P ₁ −π / 4d ₂ ² × P _LS > 0, and when the force becomes larger than the mounting load of the spring 49, the spool 48 moves to the right. Then, the second port 44 and the third port 45 are shut off, and the control port 67 and the outflow port 66 are shut off.

Further, since d ₁ = d ₂ as described above, if π / 4d ₂ ² × ΔP _LS (differential pressure) and the initial mounting load of the spring 49 are equal, the spool 48 always stops at the position shown in FIG. and are, thus the differential pressure △ P _LS of the discharge pressure P ₁ and the load pressure P _LS pump is always kept constant, the differential pressure (differential pressure set force) is determined by the initial mounting load of the spring 49.

Further, the spool 48 is the second pressure receiving chamber 5
6 is pushed to the right by the pressure on the downstream side of the throttle 18 acting on
Since the pressure on the upstream side of the throttle 18 acting on the pressure receiving chamber 58 is pushed to the left, the spool 48 is pushed to the left due to the differential pressure before and after the throttle 18, and the differential pressure setting force becomes larger than that in the case described above.

That is, the condition for stopping the spool 48 at the position shown in FIG. 3 is π / 4d ₂ ² × ΔP _LS = spring 49
Mounting load of ^{+ π / 4 (D 2 -d} 1 2) × (P 2 -P 3)
Becomes However, D is the diameter of the spool 48, P ₂ is the diaphragm 18
The upstream pressure, P ₃ is the downstream pressure of the throttle 18.

If the desired differential pressure ΔP _LS is set at the set rotation speed under the above-mentioned conditions, the discharge flow rate of the fixed hydraulic pump 3 decreases and the throttle valve before and after the throttle 18 is reduced when the engine rotation speed is low. differential pressure (P ₂ -P ₃₎ is differential pressure set force is reduced smaller, the spool 48 is moved to the right the third port 45 and fourth port 46 communicates with the pump discharge pressure control port 67, the control valve 26 of FIG.
In this state, the swash plate 20 tilts in the small capacity direction, the capacity of the variable hydraulic pump 2 is reduced, and the discharge flow rate is significantly reduced as compared with the high speed state.

FIG. 4 shows a second embodiment, in which the discharge passage 16 of the fixed hydraulic pump 3 is downstream of the throttle 18 and the control valve 26.
The first throttle 71 is provided in the pilot circuit 70 that connects the second auxiliary pressure receiving portion 33, the downstream side of the first throttle 71 is connected to the tank 15 by the drain circuit 72, and the second throttle 73 is connected to the drain circuit 72. It is provided.

The discharge passage 16 of the fixed hydraulic pump 3 is connected to a swing hydraulic motor 76 by an auxiliary operating valve 75, and the swing hydraulic motor 26 is driven with the auxiliary operating valve 75 as a supply position.

Next, the operation will be described. Pilot circuit 70
By providing the first throttle 71 on the downstream side and connecting the downstream side of the first throttle 71 to the tank 15 via the second throttle 73, the pressure P ₄ acting on the second auxiliary pressure receiving portion 33 of the control valve 26 is reduced. Since the pressure drops when passing through the first throttle 71 than the downstream side pressure P _{3 of} 18, P ₃ > P ₄ .

The pressure drop has a constant ratio determined by the flow area of the first throttle 71 and the flow area of the second throttle 73.

When the auxiliary hydraulic valve 75 is used as the supply position to supply the hydraulic fluid discharged from the fixed hydraulic pump 3 to the swing hydraulic motor 76 to drive it, the swing torque of the swing hydraulic motor 76 is large. The discharge pressure of the pump 3 becomes extremely high, and the discharge pressure of the fixed hydraulic pump 3 becomes low during a steady turn.

The fixed hydraulic pump 3 is a gear pump. When the discharge pressure of the fixed hydraulic pump 3 increases, the internal leakage increases and the efficiency decreases. In the case of high pressure, it decreases more than in the case of low pressure.

When the discharge flow rate of the fixed hydraulic pump 3 decreases, the differential pressure (P ₂ -P ₃ ) before and after the throttle 18 decreases,
The diaphragm 18 of the differential pressure across when starting the hydraulic swing motor 76 (P ₂ -P ₃₎ is small, aperture to steady rotation 18 of the differential pressure across (P ₂ -P ₃₎ is increased.

To this end, the pilot circuit 70 has a first
When the downstream side pressure P ₃ of the throttle 18 is directly applied to the second auxiliary pressure receiving portion 33 of the control valve 26 without the second throttles 71 and 73, the pressure acting on the first auxiliary pressure receiving portion 31 of the control valve 26 and 2 The differential pressure of the pressure acting on the auxiliary pressure receiving portion 33 changes between the time when the swing hydraulic motor 76 is started and the time when it is in steady rotation, and the discharge flow rate of the variable hydraulic pump 2 is different.

However, by providing the pilot circuit 70 with the first and second throttles 71 and 73 as shown in FIG. 4, the pressure P acting on the second auxiliary pressure receiving portion 33 of the control valve 26 is increased.
_{Since the} pressure of ₄ becomes lower than the pressure P ₃ on the downstream side of the throttle 18 at a constant ratio, as described above, even if the discharge flow rate of the fixed hydraulic pump 3 decreases due to a decrease in efficiency due to discharge pressure, the control valve 2
The differential pressure of the pressures acting on the first auxiliary pressure receiving portion 31 and the second auxiliary pressure receiving portion 33 becomes substantially constant, and the discharge flow rate of the variable hydraulic pump 2 does not change between when the swing hydraulic motor 76 is started and when it is steadily rotating. Like

For example, when the swing hydraulic motor 26 is in steady rotation, the discharge pressure of the fixed hydraulic pump 3 is 50 kg / cm ² , the discharge flow rate is 20 l / min, and the pressure P ₃ on the downstream side of the throttle 18 is small.
There 40 kg / cm ^2, the pressure P ₄ of the second auxiliary pressure receiving portion 33 and 39.5kg / cm ^2, the pressure P ₂ and the second auxiliary pressure receiving section 33 that acts on the first auxiliary pressure receiving portion 31 of the control valve 26 differential pressure of the pressure P ₄ acting (P ₂ -P ₄₎ is 10 kg / c
It becomes m ² .

In the above-mentioned state, when the swing hydraulic motor is started, the discharge pressure of the fixed hydraulic pump 3 is 200 kg / cm ²
When the discharge flow rate becomes 18 l / min, the downstream pressure P ₃ of the throttle 18 becomes 192 kg / cm ² , and the pressure P ₄ acting on the second auxiliary pressure receiving portion 33 is approximately 189.5 kg / cm.
Since the ^2, the differential pressure (P ₂ -P ₄₎ is approximately 10k
It becomes g / cm ² .

FIG. 5 shows a third embodiment, in which the control valve 26
The drain port 29 of the switching valve 80 for input torque control
Is connected to one of the tank 15 and the discharge path 4.

The switching valve 80 is pushed to the drain position C by the spring 81, and the supply position D is adjusted by the pump discharge pressure acting on the first pressure receiving portion 82 and the external pressure acting on the second pressure receiving portion 83.
The spring 81 is pushed by the link 84 to the piston 22.
Is associated with.

Therefore, when the pump discharge pressure becomes higher than the pressure commensurate with the mounting load of the spring 81, the switching valve 80 becomes the supply position D and the pump discharge pressure becomes the control valve 26.
Through the large-diameter pressure receiving chamber 23, the piston 22 moves to the right, and the swash plate 20 tilts in the small capacity direction.
The load of the spring 81 increases due to the movement of the switch 81, and the switching valve 80 is pushed to the drain position C.

By repeating such operations, the displacement of the variable hydraulic pump 2 is controlled so that the input torque (pump discharge pressure × capacity) becomes constant.

[0050]

According to the first aspect of the present invention, when the rotational speed of the engine 1 is low, the discharge flow rate of the fixed displacement hydraulic pump 3 is small and the differential pressure before and after the throttle 18 is small, so that the differential pressure set by the control valve 26 is set. When the force becomes small and the rotation speed of the engine 1 is high, the discharge flow rate of the fixed displacement hydraulic pump 3 is large, the differential pressure before and after the throttle 18 is large, and the differential pressure setting force of the control valve 26 is large. Therefore, the discharge flow rate of the variable displacement hydraulic pump 2 is remarkably reduced when the engine 1 is operating at a low speed, and the operability is improved.

The discharge passage 1 of the fixed displacement hydraulic pump 3
Since the differential pressure setting force of the control valve 26 is changed by the differential pressure across the throttle 18 provided at 6, the discharge pressure oil of the fixed displacement hydraulic pump 3 can be effectively used without flowing out to the tank, and the discharge pressure Throttling 1 even if oil is supplied to other hydraulic equipment
8 The displacement control characteristic of the variable displacement hydraulic pump can be made constant without changing the front-rear differential pressure, and even when the engine 1 is at an extremely low speed, the throttle 18 front-rear differential pressure is generated to change the displacement of the variable displacement hydraulic pump 2. It can be controlled by considering the engine speed.

According to the second invention, the pressure P ₄ acting on the second auxiliary pressure receiving portion 33 of the control valve 26 is the pressure P ₃ on the downstream side of the throttle 18 provided in the discharge passage 16 of the fixed displacement hydraulic pump _3.
Is a value reduced by a constant ratio, and even when the rotation speed of the engine 1 is constant and the discharge flow rate changes due to a change in efficiency due to the discharge pressure of the fixed displacement hydraulic pump 3,
The pressure difference between the auxiliary pressure receiving portion 31 and the second auxiliary pressure receiving portion 33 becomes substantially the same. Therefore, when the rotation speed of the fixed displacement hydraulic pump 3 is the same and the discharge pressure thereof changes to high pressure and low pressure, the differential pressure setting force of the control valve 26 becomes substantially the same, and the discharge flow rate of the variable displacement hydraulic pump 2 becomes It will be almost the same.

[Brief description of drawings]

FIG. 1 is a schematic configuration explanatory view showing a first embodiment of the present invention.

FIG. 2 is a chart showing the relationship between engine speed and discharge flow rate.

FIG. 3 is a sectional view showing a specific structure of a control valve.

FIG. 4 is a schematic configuration explanatory view showing a second embodiment of the present invention.

FIG. 5 is a schematic configuration explanatory view showing a third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Engine 2 ... Variable displacement hydraulic pump 3 ... Fixed displacement hydraulic pump 4 ... Discharge passage 5 ... Operation valve 16 ... Discharge passage 18 ... Restrictor 21 ... Cylinder 23 ... Large diameter pressure receiving chamber 24 ... Small diameter pressure receiving chamber 26 ... Control valve 27 ... 1st port 28 ... 2nd port 29 ... Drain port 30 ... 1st pressure receiving part 31 ... 1st auxiliary pressure receiving part 32 ... 2nd pressure receiving part 33 ... 2nd auxiliary pressure receiving part 40 ... Valve main body 41 ... Sleeve hole 42 ... Sleeve 48 ... Spool 49 ... Spring 55 ... First pressure receiving chamber 56 ... Second pressure receiving chamber 58 ... Third pressure receiving chamber 61 ... Fourth pressure receiving chamber 66 ... Outflow port 67 ... Control port 68 ... Pump pressure supply port 70 ... Pilot circuit 71 ... first throttle 72 ... drain circuit 73 ... second throttle 80 ... switching valve 81 ... spring 84 ... link.

Claims (4)

[Claims] 1. A cylinder 21 that controls the displacement of a variable displacement hydraulic pump 2, a control valve 26 that controls the supply of pump discharge pressure to the cylinder 21, and an engine 1 that is the same as the variable displacement hydraulic pump 2. A fixed displacement hydraulic pump 3 and a throttle 18 provided in the discharge passage 16 of the fixed displacement hydraulic pump 3, and the control valve 26 is switched and operated depending on the magnitude relation between the pump discharge pressure, the load pressure differential pressure, and the differential pressure setting force. The differential pressure to a constant value corresponding to the differential pressure setting force, and the throttle 18
A displacement control device for a variable displacement hydraulic pump, which sets a large differential pressure setting force when the front-rear differential pressure is large, and reduces the differential pressure setting force when it is small. 2. The cylinder 21 moves in a small capacity direction when pressure oil is supplied to the large diameter pressure receiving chamber 23, and moves in the large capacity direction when the large diameter pressure receiving chamber 23 communicates with a drain, The control valve 26 is connected to the first pressure receiving portion 30 and the first auxiliary pressure receiving portion 3
With the pressure of 1, it becomes the drain position A where the large diameter pressure receiving chamber 23 communicates with the drain, and the second pressure receiving portion 32 and the second auxiliary pressure receiving portion 33 are provided.
It is assumed that the supply position B for supplying the pump discharge pressure to the large diameter pressure receiving chamber 23 with the above pressure oil is applied, the load pressure is supplied to the first pressure receiving portion 30, and the second pressure receiving portion 32 is supplied.
Pump discharge pressure to the first auxiliary pressure receiving portion 31
8 upstream side pressure is supplied, and the second auxiliary pressure receiving portion 33 is throttled 18
The displacement control device for a variable displacement hydraulic pump according to claim 1, wherein a downstream pressure is supplied. 3. A cylinder 21 that controls the displacement of the variable displacement hydraulic pump 2, a control valve 26 that controls the supply of pump discharge pressure to the cylinder 21, and an engine 1 that is the same as the variable displacement hydraulic pump 2. Is provided with a fixed displacement hydraulic pump 3 and a throttle 18 provided in the discharge passage 16, and when the pressure oil is supplied to the large diameter pressure receiving chamber 23, the cylinder 21 moves in the small capacity direction to receive the large diameter pressure reception. It is assumed that when the chamber 23 communicates with the drain, the chamber 23 moves in the large capacity direction, and the control valve 26 is connected to the first pressure receiving portion 30 and the first auxiliary pressure receiving portion 3.
With the pressure of 1, it becomes the drain position A where the large diameter pressure receiving chamber 23 communicates with the drain, and the second pressure receiving portion 32 and the second auxiliary pressure receiving portion 33 are provided.
It is assumed that the supply position B for supplying the pump discharge pressure to the large diameter pressure receiving chamber 23 with the above pressure oil is applied, the load pressure is supplied to the first pressure receiving portion 30, and the second pressure receiving portion 32 is supplied.
Pump discharge pressure to the first auxiliary pressure receiving portion 31
8 upstream side pressure is supplied, and the second auxiliary pressure receiving portion 33 is throttled 18
A displacement control device for a variable displacement hydraulic pump that supplies an intermediate pressure between a first throttle and a second throttle in a drain path connected to a downstream side. 4. A first pressure receiving chamber 55 and a fourth pressure receiving chamber 61 having the same pressure receiving diameter by inserting a sleeve 42 into a sleeve hole 41 of a valve body 40 and inserting a spool 48 into the sleeve 42.
The second pressure receiving chamber 56 and the third pressure receiving chamber 58 having the same pressure receiving diameter are formed, and the spool 48 is supplied by the pressure difference between the pressure of the first pressure receiving chamber 55 and the pressure of the fourth pressure receiving chamber 61 and the spring 49 to the spool 48. The port 68, the control port 67, and the outflow port 66 are moved to a position where they communicate / block, and the differential pressure between the pressure in the second pressure receiving chamber 56 and the pressure in the third pressure receiving chamber 58 pushes the spool 48 against the spring 49. In this way, the control valve 26 is provided, the pump discharge pressure is supplied to the first pressure receiving chamber 55, the load pressure is supplied to the fourth pressure receiving chamber 61, and the throttle 18 downstream side pressure is supplied to the second pressure receiving chamber 56. The displacement control device for a variable displacement hydraulic pump according to claim 1, 2 or 3, wherein the pressure receiving chamber 58 is supplied with the upstream pressure of the throttle 18.