JP2880481B2 - Control device for variable displacement pump - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for controlling the flow rate of hydraulic oil from a variable displacement pump such as a variable displacement swash plate type axial piston pump.

[0002]

2. Description of the Related Art A control device for a variable displacement pump is used, for example, in an injection molding machine or in a hydraulic press for plastically deforming a metal plate or the like. For example, in an injection molding machine, the hydraulic piston drives the hydraulic piston in accordance with the flow rate of the synthetic resin while maintaining the melted synthetic resin at a predetermined pressure in a short time of, for example, 0.2 seconds. High precision
High response control characteristics are required.

[0003] A typical prior art is Japanese Utility Model Laid-Open No. 1-6648.
In this prior art, a swash plate, which is a variable element in a variable displacement swash plate type axial piston pump, is driven by a hydraulic cylinder to control the tilt angle, thereby corresponding to the tilt angle. The hydraulic oil discharge flow rate is controlled, and the hydraulic oil discharge pressure is controlled. In the injection process of the injection molding machine, it is necessary to follow the injection flow rate according to the flow of the synthetic resin while keeping the injection pressure constant, as described above, depending on the shape of the mold and the synthetic resin material. In the prior art, it is extremely difficult to stably control the inclination angle of the swash plate at a sufficient speed to satisfy the requirements of such an injection molding machine, and there is a limit in responsiveness.

In order to solve this problem, a configuration is considered in which the discharge flow rate of hydraulic oil from the pump is kept constant, and the pressure of hydraulic oil is controlled to be constant using an electromagnetic relief valve for pressure control. Thereby, high-speed response can be ensured. In such a configuration, there is a problem that the relief flow rate of the hydraulic oil bleed off from the electromagnetic relief valve is large, and thus power is wasted.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to make it possible to accurately control the relief flow rate from an electromagnetic relief valve and to minimize the waste of discharged hydraulic oil. To provide a control device for a variable displacement pump.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a variable hydraulic pressure control system for controlling the pressure of hydraulic oil from a variable displacement pump which can change the discharge flow rate of hydraulic oil by changing a variable element. In the control device for a positive displacement pump, a first negative feedback circuit for controlling the pressure of the hydraulic oil from the variable displacement pump, wherein the first negative feedback circuit detects an operating pressure from the variable displacement pump. Pressure detecting means, second pressure detecting means for detecting a pilot pressure of the electromagnetic relief valve, a differential pressure calculating circuit for calculating a differential pressure between the detected pressures of the first and second pressure detecting means,
A target pressure setting means for setting a target pressure of the hydraulic oil from the variable displacement pump; and a first pressure between a signal of the detected pressure from the first pressure detection means and a target pressure set by the target pressure setting means. A first subtraction circuit for determining a deviation,
A first compensation circuit responsive to an output of the first subtraction circuit for controlling the electromagnetic relief valve by obtaining a pressure correction signal so that the first deviation becomes zero. A flow rate detecting means for detecting a flow rate of the hydraulic oil from the variable displacement pump, and a second negative feedback circuit, the second negative feedback circuit comprising:
A second subtraction circuit for calculating the deviation of the variable element, and a second element for changing the variable element in response to the output of the second subtraction circuit so that the second deviation obtained by the second subtraction circuit becomes zero. A second negative feedback circuit having a compensation circuit, target flow rate setting means for setting a target flow rate of hydraulic oil supplied from the variable displacement pump, and a detection pressure of the first pressure detection means, When the pressure is greater than the target pressure of the target pressure setting means, the differential pressure signal from the differential pressure calculation circuit and the signal of the detected flow rate from the flow rate detecting means are calculated, and the second pressure signal is reduced so that the relief flow rate of the working oil is reduced. 2 to the subtraction circuit,
On the other hand, when the detected pressure of the first pressure detecting means is smaller than the target pressure of the target pressure setting means, switching control means for giving a signal of the target flow rate from the target flow rate setting means to the second subtraction circuit, A control device for a variable displacement pump, comprising: According to the invention, the hydraulic oil from the variable displacement pump is controlled by an electromagnetic relief valve, which is controlled by a first negative feedback circuit, so that the discharge pressure of the variable displacement pump is independent of the flow rate It is kept constant. Further, in the pressure control state, when the detected pressure of the hydraulic oil from the variable displacement pump detected by the first pressure detecting means exceeds the target pressure set by the target pressure setting means, the variable displacement pump is activated. A part of the hydraulic oil is relieved via the electromagnetic relief valve. At this time, when the relief flow rate is large, there is a feature that the differential pressure signal becomes large due to the override characteristic of the electromagnetic relief valve. That is, the relief flow rate can be detected based on the level of the differential pressure signal without directly detecting the relief flow rate. The pump flow rate is reduced so that the differential pressure signal has a small specified value, and the relief flow rate is controlled to a minimum value. The pressure difference between the pressure detected by the first pressure detecting means, that is, the pressure of the working oil from the variable displacement pump, and the pressure detected by the second pressure detecting means, that is, the pilot pressure of the electromagnetic relief valve, has hysteresis. And the pressure is substantially proportional to the relief flow rate via the electromagnetic relief valve. Therefore, by utilizing the pressure difference between the first pressure detecting means and the second pressure detecting means, the electromagnetic pressure is reduced. The amount of relief from the relief valve can be controlled with high accuracy. When the detection pressure of the first detection pressure means is smaller than the detection pressure of the second pressure detection means, the target flow rate setting state is set by the target flow rate setting means by the operation of the switching control means in order to enter the flow control state. The signal of the flow rate is provided as an input signal to the second subtraction circuit, and the second negative feedback circuit is operated so as to reach the target flow rate.

Further, the present invention provides a method for calculating a target pressure signal from the target pressure setting means, a pressure correction signal from the first compensation circuit, and a differential pressure signal from the differential pressure calculation circuit. 3 is further provided. According to the present invention, the pressure of the hydraulic oil from the variable displacement pump is equal to the signal of the target pressure from the target pressure setting means,
Is controlled using the pressure correction signal from the correction circuit and the differential pressure signal from the differential pressure arithmetic circuit. In particular, the differential pressure signal from the differential pressure arithmetic circuit is used when the displacement of the variable displacement pump changes. Since the generated surge pressure can also be detected,
Surge pressure can be suppressed.

Further, the present invention provides a hydraulic oil control device for controlling the pressure of hydraulic oil by an electromagnetic relief valve, wherein the first pressure detecting means for detecting the pressure of hydraulic oil, and the pilot pressure of the electromagnetic relief valve are detected. And a differential pressure calculating circuit for calculating a differential pressure between the detected pressures of the first and second pressure detecting means, wherein the current supplied to the electromagnetic relief valve is the differential pressure. The hydraulic oil control device is characterized in that the differential pressure of the pressure detected by the arithmetic circuit is controlled as one parameter, whereby the relief pressure of the electromagnetic relief valve is controlled. According to the present invention, the pressure detected by the first pressure detecting means, that is, the pressure of the hydraulic oil, the pressure detected by the second pressure detecting means,
In other words, the pressure difference from the pilot pressure of the solenoid relief valve has no hysteresis and can detect the surge pressure generated when the capacity of a variable displacement pump changes, etc. And the surge pressure can be suppressed.

[0009]

FIG. 1 is a block diagram showing an electric configuration of an embodiment of a control device for a variable displacement pump according to the present invention. With this electrical configuration, the pressure and flow rate of the hydraulic oil discharged from the variable displacement swash plate type axial piston pump 1 as one of the variable displacement pumps shown in FIG. 2 are controlled. In FIG. 2, the flow rate of the injection according to the flow of the synthetic resin into the mold while the synthetic resin melted in the injection molding machine is kept at a constant pressure in the mold by the hydraulic oil from the pump 1. Therefore, the flow rate of the hydraulic oil can be made to follow. The pump main body 2 and the auxiliary pump 3 have their rotating shafts connected to each other, and are driven to rotate at a constant speed by a drive source. Hydraulic oil from the pump body 2 is supplied from a pipe 4 to an actuator such as a cylinder. An electromagnetic relief valve 6 is connected to the pipe 4 via a pipe 5, and a part of the hydraulic oil is returned to the tank via a pipe 7. In the configuration of the pump 1 shown in FIG. 2, the hydraulic proportional control valve 15 and the electromagnetic proportional control valve 1
9 has an advantage that the configuration is relatively simple.

FIG. 3 is a simplified sectional view showing an example of the electromagnetic relief valve 6. A first valve seat 9a is formed in the valve housing 8, and a spring force is applied in a direction in which the first valve body 10a is seated by the spring force of the first spring 11a.
The valve housing 8 is also provided with a second valve seat 9b, and a spring force is applied in a direction in which the second valve body 10b is seated by the spring force of the second spring 11b. Second valve body 10
A plunger 211 is attached to b, and when the electromagnetic coil 12 is excited, the plunger 211 moves in the direction of the second valve body 10b to act thereon. Pipeline 5 and 1st
The pilot valve 112 communicates with the back side of the valve body 10a via a pilot flow path 112. The pressure acting on the pilot flow path 112 acts in a direction in which the first valve body 10a is seated. A throttle member 114 for regulating the flow path of the hydraulic oil flowing therethrough is provided in the pilot flow path 112. Therefore, the pressure of the pipe 5 acting on the first valve body 10a is reduced by the pilot flow path 11
When the second pilot pressure and the spring force of the first spring 11a are overcome, the first valve body 10a separates from the valve seat 9a, and a part of the hydraulic oil flows from the pipe 5 to the pipe 7. Also, the second valve body 1
The back side of Ob is connected to an oil tank 215 via a flow path 214. Therefore, when the pressure on the back side of the first valve body 10a acting on the second valve body 10b overcomes the electromagnetic force of the electromagnetic coil 12 and the spring force of the second spring 11b, the second valve body 10b is moved to the valve seat 9b. And a part of the hydraulic oil on the back side of the first valve body 10a is
Flow to 15.

In the present embodiment, the first pressure detecting means 13 is provided in the pipe 5, and the second pressure detecting means 114 is provided in the flow path 113 communicating with the choke flow path 112. . The first and second pressure detecting means 13 and 114 can be constituted by pressure gauges for detecting the pressure of the fluid,
The first pressure detecting means 13 detects the pressure of the hydraulic oil in the pipe 5, in other words, the pressure of the hydraulic oil fed from the pump body 2 through the pipe 4, and also detects the second pressure detecting means 114.
Detects the pressure of the choke flow path 112, in other words, the pressure of the hydraulic oil acting on the back side of the valve element 10 via the throttle member 114.

In order to change the inclination angle of the variable element, which is the swash plate of the pump 1, the hydraulic oil from the auxiliary pump 3 passes through the pipe 14 and passes through the small cylinder chamber 1 for the small piston 115.
The large piston 16 is supplied to the large cylinder chamber 17 for the large piston 16 via the hydraulic proportional control valve 15. The displacement position of the swash plate, and thus the piston 16, is determined by a position detecting means 18 realized by a potentiometer or the like.
The inclination angle of the swash plate, that is, the flow rate of the hydraulic oil discharged from the pipeline 4 is detected. Therefore, this position detecting means 18 will be referred to as a flow rate detecting means in the following description. Pipe line 1
Hydraulic oil from 4 is supplied from the electromagnetic proportional control valve 19 to the cylinder chamber 21 of the hydraulic proportional control valve 15 via the pipe 20, and from the hydraulic proportional control valve 15 to the cylinder chamber 17 via the pipe 22. The situation of the oil can be changed continuously.

In this embodiment, when the biasing force of the biasing spring 15a of the hydraulic proportional control valve 15 and the pressure of the hydraulic oil acting on the cylinder chamber 21 are balanced, the hydraulic proportional control valve 15 is shown in FIG. The pump 1 is held at the neutral position and the swash plate of the pump 1 is held at that angular position. On the other hand, the pressure of the hydraulic oil rises (or falls), and the pressure rises.
When the biasing force becomes larger (or smaller) than the biasing force of 5a, the proportional control valve 15 moves to the left (or right) in FIG. The hydraulic oil in the large cylinder chamber 17 is returned through the pipes 22 and 117 (or the pipe 14).
Is supplied to the large cylinder chamber 17 through the conduit 22). Therefore, the large piston 16 is moved rightward (or leftward) in FIG. 2, the inclination angle of the swash plate becomes large (or low), and the discharge amount from the pump body 2 decreases (or increases).

An example of the electromagnetic relief valve 6 shown in FIG.
Is a control circuit 3 having a transfer function of Gp2 in FIG.
2 is equivalently replaced. Further, the pump 1 shown in FIG. 2 is equivalently replaced as a control circuit 32a having a transfer function Gq2 as shown by a reference numeral 32a in FIG. The control circuit 32 of this transfer function Gq2
a is a pump body 2, an auxiliary pump 3, a hydraulic proportional control valve 1
5, equivalently includes a swash plate, a piston 16 for driving the swash plate, an electromagnetic proportional control valve 19, and the like. Line 11 in FIG.
The control amount derived to 8 is a line from which the signal of the detected pressure of the hydraulic oil by the second pressure detecting means 114 is derived. The control amount led out to the line 119 is a line from which the signal of the detected pressure of the hydraulic oil by the first pressure detecting means 13 is derived. Further, the signal derived from the control circuit 32a via the line 118a is a line from which the signal of the detected flow rate of the hydraulic oil from the pipeline 4 represented by the flow rate detection means 18 for detecting the displacement position of the swash plate is derived. The first negative feedback circuit 24 for controlling the pressure and the second negative feedback circuit 24a for controlling the flow rate of the hydraulic oil have a similar configuration, and the corresponding parts are denoted by the same reference numerals but with the suffix a. Shown.

The target pressure for the pressure of the hydraulic oil supplied from the pump body 2 to the pipeline 4 is set by target pressure setting means 25. The signal of the target pressure is transferred from a line 26 to a transfer function Gp1 for performing feedforward control.
And an open control circuit 31 having
The signal is supplied to one input of a first subtraction circuit 34. The output from the first pressure detecting means 13 is supplied to the first
To the other input of the subtraction circuit 34. The first subtraction circuit 34 derives a signal representing a first deviation obtained by subtracting the signal of the detected pressure Pa from the signal of the target pressure on a line 28 and supplies the signal to a first compensation circuit 29. Open control circuit 3
The output of 1 and the pressure correction signal derived from the first compensation circuit 29 to the line 77 are added in the first arithmetic circuit 75. The signal derived from the first arithmetic circuit 75 to the line 78 is sent to the arithmetic circuit 120, processed by the arithmetic circuit 120, and applied to the electromagnetic coil 12 of the electromagnetic relief valve 6 from the line 121. Furthermore, a phase lead compensation circuit 79 is provided. First compensation circuit 29
In response to the output of the first subtraction circuit 34, a pressure correction signal for causing the first deviation to be zero is obtained and is derived to a line 77.

In the present embodiment, a signal of the detected pressure Pd of the first pressure detecting means 13 is led out to a line 119, and then sent to a differential pressure calculating circuit 122 through a line 123. After the signal of the detected pressure Pc of the pressure detecting means 114 is led out to a line 124, the differential pressure calculating circuit 12
Sent to 2. The differential pressure calculation circuit 122 subtracts the signal of the detected pressure Pc of the second pressure detecting means 114 from the signal of the detected signal Pd of the first pressure detecting means 13 and calculates the differential pressure (Pd-Pc) of the detected pressure. Generate. Differential pressure calculation circuit 122
The signal of the differential pressure (Pd−Pc) is output to a control circuit 126 having a transfer function HP5 through a line 125, and then sent to an arithmetic circuit 120 through a line 127. The signal from the line 127 is subtracted from the signal from the first arithmetic circuit 75 and applied to the electromagnetic coil 12.

The discharge flow rate of the hydraulic oil discharged from the pipeline 4 of the pump 1 is set by target flow rate setting means 25a. The output is supplied to a changeover switch means 8 via a line 26a.
0 is provided to one individual contact 82 of the changeover switch 81. The changeover switch 81 has another individual contact 83
Having. The common contact 84 can be switched to the individual contact 82 or 83 to conduct. The output from the common contact 84 is supplied from a line 85 to an open control circuit 31a having a transfer function Gq1. This open control circuit 3
The output of 1a is supplied to a second operation circuit 75a, and is added to the flow rate correction signal derived from the second compensation circuit 29a to the line 77a to be operated. The output of the second arithmetic circuit 75a is supplied to the electromagnetic proportional control valve 1 of the pump 1 via a line 78a.
9 whereby the piston 16 and thus the swash plate are driven angularly displaced and the discharge flow rate is varied.

A signal of the detected flow rate of the hydraulic oil discharged from the pump body 2 to the line 4 detected by the flow rate detecting means 18 is supplied from a line 27a to one input of a second subtraction circuit 34a. The input signal from the line 85 is given to the other input to the subtraction circuit 34a. The second subtraction circuit 34a subtracts the signal of the detected flow rate on the line 27a from the input signal from the line 85, derives a signal representing the second deviation to the line 28a, and
Give to a. The second compensating circuit 29a responds to the output of the second subtracting circuit 34a and applies a flow correction signal to change the swash plate, and thus the piston 16, so that the second deviation is zero, as described above. 77a. The output of the flow rate detecting means 18 is also supplied to a phase lead compensation circuit 79a, and the output of the phase lead compensation circuit 79a is supplied to a calculation circuit 75a to be subtracted, and a signal derived from the calculation circuit 75a to a line 78a. Thus, the electromagnetic proportional control valve 19 is controlled as described above.

FIG. 4 is a graph showing a pressure override characteristic of the electromagnetic relief valve 6. In the pressure control operation state of the hydraulic oil in the pipe line 4 to make the target pressure set by the target pressure setting means 25, the relief flow rate Q of the electromagnetic relief valve 6 is zero at the cracking pressure, but the relief flow rate Q is lower than the cracking pressure. When it becomes slightly higher, the electromagnetic relief valve 6 is opened, and the line 7 is released with a small relief flow rate.
A part of the hydraulic oil flows out of the pump. When the target pressure is set to a pressure slightly higher than the cracking pressure above the target pressure, a part of the hydraulic oil is relieved through the line 7 at a small relief flow rate at the target pressure. As shown by the line L1 in FIG. 4, the relief flow rate and the pressure difference (Pd-Pc) between the detection pressures of the first and second pressure detection means 13 and 114 are substantially proportional in a range exceeding the target flow rate. Has properties that increase in relationship. When the relief flow rate increases, the pressure tends to be higher than the target pressure due to the pressure override characteristic. Therefore, the pressure correction signal derived from the first compensation circuit 29 to the line 77 is a deviation signal for lowering the detected pressure detected by the first pressure detecting means 13, and the level of this pressure correction signal is There is a relationship between an unnecessary relief flow rate exceeding the relief flow rate and a linear function, for example, a proportional relation.

In this embodiment, the signal of the detected flow rate of the hydraulic oil detected by the flow rate detecting means 18 includes a first pressure detecting means 13 and a second pressure detecting means which have substantially the same relationship as the pressure rise in the override characteristic. The signal of the differential pressure (Pd-Pc) from the detected pressure of 114 is added, and this value is given as an input signal that becomes the target flow rate of the second negative feedback circuit 24a during the pressure control operation. That is, in the case of the relief flow rate Q1 in FIG.
When the differential pressure (Pd-Pc) of the detected pressures 3, 114 increases to the pressure difference P1 indicated by reference numeral 87, the pressure correction signal derived from the first compensation circuit 29 to the line 77 is: The target flow rate of the second compensation circuit 29a is a deviation signal for decreasing the pressure by the pressure difference ΔP1, so that the relief flow rate Q1 at this time becomes a small relief flow rate (relief flow rate at the target pressure) close to zero. An input signal is provided on line 85 as described below.
Thus, it is possible to prevent the wasteful large relief flow rate Q1 from being generated, and to reduce the wasteful flow rate as much as possible.

In this embodiment, a switching control means 88 is provided. The second arithmetic circuit 89 in the switching control means 88 includes a comparison circuit 91 for deriving the differential pressure signal to the line 90 only when the differential pressure signal from the differential pressure arithmetic circuit 122 is positive, and a line 90. Pressure difference (Pd-Pc)
And a control circuit 92 having a transfer function Hp4 in response to the The positive differential pressure of the differential pressure calculating circuit 122 means that the detected pressure detected by the first pressure detecting means 13 exceeds the detected pressure detected by the second pressure detecting means 114, The signal of the pressure difference at that time is supplied to the arithmetic circuit 93 as described above. The arithmetic circuit 93 calculates the control circuit 9 in the first arithmetic circuit 89 from the signal of the detected flow rate via the line 27 a of the flow rate detecting means 18.
The signal representing the flow rate obtained by subtracting the difference from the output from the second flow rate and the difference from the detected flow rate is led out to a line 94 and given to the individual contact 83 of the changeover switch 81. Differential pressure calculation circuit 12
Since the signal of the pressure difference from No. 2 has no hysteresis characteristic and does not include a signal for correction, the error is small, and therefore, by using this signal, the hydraulic oil Flow rate control can be performed with high accuracy.

The changeover switch control means 95, which constitutes the changeover switch means 80 together with the changeover switch 81, sets the target pressure when the pressure correction signal of the first compensating circuit 29 is negative, that is, the detected pressure of the first pressure detecting means 13 When the pressure exceeds the target pressure set by the pressure setting means 25, the common contact 84 of the changeover switch 81 is conducted to the individual contact 83, whereby the output of the arithmetic circuit 93 is output via the line 85 to the target of the second compensation circuit 29a. Give as pressure input signal. The changeover switch control means 95 responds to the pressure correction signal of the first compensation circuit 29, and
When the detected pressure of No. 3 is equal to or lower than the target pressure, the common contact 84 of the changeover switch 81 is conducted to the individual contact 82, whereby the signal of the target flow rate from the target flow rate setting means 25a is given from the line 26a to the line 85. As a result, the pressure of the hydraulic oil can be raised to and reached the target pressure.

The specific configuration of the first compensation circuit 29 will be described again with reference to FIG. First subtraction circuit 34
Is applied to a compensation circuit 51 having a transfer function Hp1, the output of which is applied to a limiter 50. As shown in FIG. 5, the limiter 50 receives signals from the compensation circuit 51 from M1 to M1.
If it exceeds M2, the output is limited to M1 and M2. First
The output of the limiter 50 is added in the arithmetic circuit 65. The output of the first subtraction circuit 34 via line 28 is also provided via a switch 76 to a compensation circuit 62 having a transfer function Hp2. The output of the compensating circuit 62 is provided to the integral compensating circuit 61 to perform an integrating operation. The output of the integration compensation circuit 61 is supplied to the second limiter 60, and the same limiter operation as in FIG. 5 is performed. Arithmetic circuit 65
Adds the output of the limiter 60 together with the output of the limiter 50 described above and derives it as a pressure correction signal on line 77.

The level discriminating means 96 in the first compensation circuit 29 turns off the switch 76 when the absolute value of the first deviation derived from the first subtraction circuit 34 to the line 28 exceeds a predetermined value. , Thereby compensating circuit 6
2. The functions of the integral compensation circuit 61 and the second limiter 60 are stopped. When the level discriminating means 96 discriminates that the absolute value of the first deviation is equal to or smaller than the predetermined value, the level discriminating means 96 conducts the switch 76 to allow the integration operation by the integration compensating circuit 61.

FIG. 6 is a waveform chart for explaining the operation of the first compensation circuit 29. The signal derived from the target pressure setting means 25 to the line 26 has a staircase waveform shown in FIG. At this time, the first subtraction circuit 34
FIG. 6 shows the waveform of the first deviation derived from
This is as shown in (2). Each absolute value of the discrimination levels Hε1 and Lε1 shown in FIG. 6 (2) may be equally selected. The compensating circuit 51 derives a signal having a waveform indicated by reference numeral 97 in FIG.
Is the compensation circuit 51 as shown by the solid line in FIG.
Is limited as shown by reference numeral 98 and applied to the adding circuit 65.

The level discriminating means 96 includes a first subtracting circuit 3
4 is discriminated by upper and lower discrimination levels Hε1 and Lε1 to obtain a range Hε.
When it is out of the range of 1 to Lε1, the switch 76 is turned off. Since the first deviation is within the above-mentioned upper and lower discrimination levels Hε1 to Lε1 after time t1, the switch 76
Is conducted, so that the integral compensating circuit 61
An integrated signal having a waveform indicated by reference numeral 99 in (4) is obtained. The second limiter 60 includes an integral compensating circuit 61
Is limited as indicated by reference numeral 100, and a signal having a waveform indicated by a solid line in FIG. Thus, a signal for pressure control by the electromagnetic relief valve 6 shown in FIG. 6 (5) is obtained on the line 78 by the operations of the first compensation circuit 29, the open control circuit 31, and the phase advance compensation circuit 79.

The second compensating circuit 29a relating to the flow rate of the working oil of the pump 1 has the same configuration as the above-described first compensating circuit 29, and the same numerals are given the suffix a to indicate the corresponding parts. . In the second compensating circuit 29, instead of reading the pressure related to the description of the first compensating circuit 29 as a flow rate, and instead of controlling the electromagnetic relief valve 6, an electromagnetic force for displacing the piston 16 and thus the swash plate is used. What is necessary is just to read as what operates the proportional control valve 19.

In the phase lead compensation circuit 79, line 2
3, the output of the first pressure detecting means 13 is supplied to a compensating circuit 73 having a transfer function Hp3, and the output of the compensating circuit 73 is supplied to a phase lead circuit 74. Is subtracted in the arithmetic circuit 75. As a result, the signal derived from the line 78 can suppress the overshoot of the hydraulic oil pressure caused by the electromagnetic relief valve 6 and accelerate the subsequent attenuation. This is the same for the other phase lead compensation circuit 79a for the flow rate of the hydraulic oil, and it is possible to suppress the overshoot of the flow rate due to the displacement of the piston 16 and the swash plate and to accelerate the subsequent damping. I have to.

In this embodiment, the arithmetic circuit 75
Is further supplied to the arithmetic circuit 120, and the arithmetic circuit 120 converts the signal from the arithmetic circuit 75 into the signal of the differential pressure (Pd-Pc) from the differential pressure arithmetic circuit 122 (the transfer function HP5). (The signal after passing through the control circuit 126). By using the differential pressure signal of the differential pressure calculation circuit 122 in this manner, a surge pressure generated when an actuator such as a cylinder is operated can also be detected. By controlling this pressure, it is possible to perform a control for reducing the surge pressure, and it is possible to significantly reduce the surge pressure, which tends to be a problem in high-precision pressure control.

[0030]

According to the control apparatus for a variable displacement pump according to the first aspect of the present invention, the hydraulic oil from the variable displacement pump is controlled by an electromagnetic relief valve, and the electromagnetic relief valve is provided with a first negative feedback circuit. Therefore, the discharge pressure of the variable displacement pump is kept constant regardless of the flow rate. Further, in the pressure control state, when the detected pressure of the hydraulic oil from the variable displacement pump detected by the first pressure detecting means exceeds the target pressure set by the target pressure setting means, the variable displacement pump is activated. A part of the hydraulic oil is relieved via the electromagnetic relief valve. At this time, when the relief flow rate is large, there is a feature that the differential pressure signal becomes large due to the override characteristic of the electromagnetic relief valve. That is, the relief flow rate can be detected based on the level of the differential pressure signal without directly detecting the relief flow rate. The pump flow rate is reduced so that this differential pressure signal has a small specified value,
Control the relief flow rate to the minimum value. The pressure difference between the pressure detected by the first pressure detecting means, that is, the pressure of the working oil from the variable displacement pump, and the pressure detected by the second pressure detecting means, that is, the pilot pressure of the electromagnetic relief valve, has hysteresis. And the pressure is substantially proportional to the relief flow rate via the electromagnetic relief valve. Therefore, by utilizing the pressure difference between the first pressure detecting means and the second pressure detecting means, the electromagnetic pressure is reduced. The amount of relief from the relief valve can be controlled with high accuracy. When the detection pressure of the first detection pressure means is smaller than the detection pressure of the second pressure detection means, the target flow rate setting state is set by the target flow rate setting means by the operation of the switching control means in order to enter the flow control state. The flow signal is the second input signal.
, And the second negative feedback circuit is operated so as to achieve the target flow rate.

According to the control apparatus for a variable displacement pump of the second aspect of the present invention, the pressure of the hydraulic oil from the variable displacement pump is determined by the signal of the target pressure from the target pressure setting means, the first
Is controlled using the pressure correction signal from the correction circuit and the differential pressure signal from the differential pressure arithmetic circuit. In particular, the differential pressure signal from the differential pressure arithmetic circuit is used when the displacement of the variable displacement pump changes. Since the generated surge pressure can also be detected,
Surge pressure can be suppressed.

Further, according to the hydraulic oil control device of the third aspect of the present invention, the current supplied to the electromagnetic relief valve is controlled using the differential pressure of the pressure detected by the differential pressure calculating circuit as one parameter. The relief pressure of the relief valve is controlled. The pressure difference between the pressure detected by the first pressure detecting means, that is, the pressure of the hydraulic oil, and the pressure detected by the second pressure detecting means, that is, the pilot pressure of the electromagnetic relief valve has no hysteresis and is of a variable displacement type. Since the surge pressure generated when the capacity of the pump changes or the like can also be detected, the pressure of the hydraulic oil can be kept constant with high accuracy, and the surge pressure can be suppressed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an overall configuration of an embodiment of a variable displacement pump control device according to the present invention.

FIG. 2 is a diagram showing a specific configuration of a hydraulic circuit indicated by a control circuit in the control device of FIG.

FIG. 3 is a cross-sectional view showing a specific configuration of an example of an electromagnetic relief valve in the hydraulic circuit of FIG.

FIG. 4 is a diagram for explaining a relationship between a relief flow rate of an electromagnetic relief valve and a differential pressure between pressures detected by first and second pressure detecting means.

FIG. 5 is a diagram showing input / output characteristics of a limiter in the control device of FIG. 1;

FIG. 6 is a diagram for explaining the operation of the control device of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Variable displacement swash plate type axial piston pump 6 Electromagnetic relief valve 13 First pressure detecting means 16 Piston 18 Position detecting means (flow rate detecting means) 24 First negative feedback circuit 24a Second negative feedback circuit 25 Target pressure setting means 25a Target flow rate setting means 29 First compensation circuit 29a Second compensation circuit 31, 31a Open control circuit 34 First subtraction circuit 34a Second subtraction circuit 75, 75a Second operation circuit 79, 79a Phase lead compensation circuit 80, 95 changeover switch means 81 changeover switch 88 changeover control means 89 first arithmetic circuit 96 level discriminating means 114 second pressure detecting means 120 arithmetic circuit 122 differential pressure arithmetic circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-64-32082 (JP, A) JP-A-5-99121 (JP, A) JP-A-2-161185 (JP, A) 176771 (JP, U) JP-A 1-66483 (JP, U) JP-A 62-41883 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) F04B 49/06 321 F04B 49/00 341 F04B 49/08 321

Claims (3)

(57) [Claims] 1. A variable displacement pump control device that controls the pressure of hydraulic fluid from a variable displacement pump capable of changing a discharge flow rate of hydraulic fluid by changing a variable element by an electromagnetic relief valve. A first negative feedback circuit for controlling a pressure of hydraulic oil from the variable displacement pump, a first pressure detection means for detecting a pressure of operation from the variable displacement pump; Second pressure detecting means for detecting a pilot pressure of the valve, a differential pressure calculating circuit for calculating a differential pressure between the detected pressures of the first and second pressure detecting means, and a target of hydraulic oil from the variable displacement pump A target pressure setting means for setting a pressure, and a first reduction for obtaining a first deviation between a signal of the detected pressure from the first pressure detecting means and a target pressure set by the target pressure setting means. A first compensation circuit responsive to an output of the first subtraction circuit and for controlling the electromagnetic relief valve by obtaining a pressure correction signal so that the first deviation becomes zero. A negative feedback circuit, a second negative feedback circuit, a flow rate detecting means for detecting a flow rate of the hydraulic oil from the variable displacement pump, and a second signal of the detected flow rate signal and the input signal from the flow rate detecting means. A second subtraction circuit for determining the deviation of 2 and a second element for changing the variable element in response to an output of the second subtraction circuit so that the second deviation obtained by the second subtraction circuit becomes zero. A second negative feedback circuit having a second compensation circuit, a target flow rate setting means for setting a target flow rate of hydraulic oil supplied from the variable displacement pump, and a detection pressure of the first pressure detection means. When greater than the target pressure of the target pressure setting means, the The differential pressure signal from the differential pressure calculating circuit and the signal of the detected flow rate from the flow rate detecting means are calculated and given to the second subtraction circuit so as to reduce the relief flow rate of the hydraulic oil. Switching control means for providing a signal of the target flow rate from the target flow rate setting means to the second subtraction circuit when the pressure detected by the pressure detection means is smaller than the target pressure of the target pressure setting means. Control device for a variable displacement pump. 2. An arithmetic circuit for calculating a target pressure signal from the target pressure setting means, a pressure correction signal from the first compensation circuit, and a differential pressure signal from the differential pressure arithmetic circuit. The control device for a variable displacement pump according to claim 1, further comprising: 3. A hydraulic oil control device for controlling the pressure of hydraulic oil by an electromagnetic relief valve, wherein the first pressure detecting means detects the pressure of the hydraulic oil, and the second pressure detecting means detects the pilot pressure of the electromagnetic relief valve. And a differential pressure calculating circuit for calculating a differential pressure between the pressures detected by the first and second pressure detecting means. The current supplied to the electromagnetic relief valve is determined by the differential pressure calculating circuit. A control device for hydraulic oil, wherein the differential pressure of the detected pressure is controlled as one parameter, whereby the relief pressure of the electromagnetic relief valve is controlled.