JP2811200B2 - Closed loop control method for variable displacement pump and control device therefor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a closed-loop control method for controlling the flow rate and pressure of a variable displacement pump with a single electromagnetic proportional control valve, and a control device therefor.

2. Description of the Related Art Conventionally, a closed-loop control method and a control device for controlling the flow rate and pressure of a variable displacement pump with one electromagnetic proportional control valve have been described. Were controlled using an electromagnetic proportional control valve and a solenoid from these four signals.

With respect to the closed loop control of a variable displacement pump, for example, Japanese Patent Application Laid-Open No. 62-225788 or Japanese Patent Application Laid-Open No. 63-109289 is known. They used the following scheme to control flow and pressure.

That is, the former is a limiter that amplifies the difference between the pressure setting signal and the detected pressure and sets a constant output when the difference exceeds a certain value. Similarly, the difference between the flow rate setting and the detected flow rate is calculated by putting the difference between the flow rate setting and the detected flow rate into a multiplier. Was. As a result, the proportional solenoid is controlled with the output depending on the calculated value, the flow rate and pressure of the variable displacement pump are controlled, and a means for detecting the rate of change in the flow rate from the flow rate detector is added. It was input to an adder / subtractor that adds and subtracts the pressure difference.

In Japanese Patent Application Laid-Open No. 63-109289, the following method is used to control the flow rate and pressure. That is, the difference between the pressure set value and the detected pressure and the difference between the flow set value and the detected flow rate are both compared, and pressure control or flow control is selected. In this method, a so-called binary control decision is made and one of the deviation signals is output.

However, first, when pressure control is performed on a general variable displacement pump using these control methods, there is a large difference between the maximum discharge flow rate and the suction flow rate of the pump. Therefore, the maximum speed at which the hydraulic fluid flows into a certain load volume when the pressure is increased from the set pressure value is much faster than the maximum speed at which the hydraulic fluid flows out from the certain load volume when the pressure is reduced. For this reason,
If the step-up and step-down were controlled by the same transfer function, it was extremely difficult to optimally adjust the step-up and step-down characteristics at the same time.

Second, in pressure control, feedback compensation of a detected pressure is generally used in a pressure control loop in order to suppress so-called overshoot or undershoot. The differential value of the detected pressure is calculated, and the calculated value is subtracted in the pressure loop to suppress overshoot and undershoot. FIG. 2 shows this example, specifically showing a circuit configuration and a pump system of the closed loop control device of the variable displacement pump. As a whole, the circuit configuration of the control device detects the detected pressure and flow rate of the pump with a pressure sensor 1 for detecting the pressure of the variable displacement pump and a flow rate sensor 2 for detecting the pump discharge flow rate. The adder / subtractor 3 for calculating the difference between the two and detecting the pressure deviation is connected to the pressure setting signal input terminal 16. Further, an adder / subtractor 4 for calculating a difference between a pump flow command and a detected flow and outputting a flow deviation is connected to a flow setting signal input terminal 17. Further, the pressure sensor amplifier 14 is a pressure sensor 1
The flow sensor amplifier 15 is an amplifier of the flow sensor 2.

The output of the result of addition / subtraction of the adder / subtractor 3 is input to the pressure control amplifier 5, but at the same time, a feedback compensation circuit is provided.
Through the adder / subtractor included in 10, compensation depending on the transfer function is performed. The outputs of the pressure control amplifier 5 and the adder / subtractor 4 are amplified by the flow rate control amplifier 6, and both outputs are input to the minimum value selection circuit 7.

The minimum value selection circuit 7 is connected to a proportional solenoid 12 via a power amplifier 11. Further, the variable displacement pump 13 is controlled by the proportional solenoid 12. In this control method, the differential value of the detected pressure is calculated and subtracted in the feedback compensation circuit 10 to suppress overshoot and undershoot. However, in this feedback compensation, when the flow rate command is increased stepwise in the flow rate control, the load pressure increases as the flow rate increases. The step shape has a steep rising edge, but is not limited to an accurate vertical rising edge, a rectangular waveform, or the like.

As a result, feedback compensation is generated for the increase in the load pressure, and the calculation is performed as if the load pressure is large. This is not a problem if the pressure command is sufficiently large with respect to the value obtained by adding feedback compensation to the load pressure, but both values are reversed, that is, the pressure command becomes smaller than the value obtained by adding feedback compensation to the load pressure. Switches to pressure control. As a result, the pump discharge flow rate is reduced so as not to overshoot the pressure. This has the disadvantage that the flow rate once decreases even though the load pressure has not reached the pressure command, causing the phenomenon that the load speed drops momentarily.

In order to clarify this point in detail, FIG. 3 illustrates the above-mentioned problem based on the time course of the pressure and the flow rate in the conventional method. The vertical axis indicates the pressure in FIG. A, the flow rate in FIG. B, and the horizontal axis indicates the elapsed time. In this figure, at # 1, feedback compensation is performed on the flow rate command and the pressure control state is established, so that the detected flow rate decreases.

That is, when the pressure command and the flow command are simultaneously increased stepwise, the load pressure also increases as the detected flow rate increases. At this time, the pressure deviation is given by the following equation.

Pressure deviation = pressure command− (detected pressure + feedback compensation) (I) However, despite the fact that the pressure command is larger than the detected pressure, due to the dynamic change of the detected pressure, the pressure command becomes as follows: .

Pressure command <(detected pressure + feedback compensation) ... (II) In addition, ... flow rate deviation> pressure deviation ... (III). During the above period, the output of the minimum value selection circuit 7 becomes a pressure deviation. Since the calculation result of the formula (I) is negative, the control current to the proportional solenoid 12 changes in the direction of decreasing the flow rate. This point can be solved by the present invention described later.

(Problems to be Solved by the Invention) Therefore, conventionally, in the closed-loop control of the variable displacement pump, constant pressure feedback compensation is always provided regardless of the control state. The difference existing between them could not be optimally compensated in each case of the step-up and step-down. In addition, feedback compensation for the purpose of suppressing pressure overshoot also acts during flow rate control.Therefore, there is a possibility that pressure control will be performed once when the flow rate command is increased, and the pump discharge flow rate will decrease so as not to overshoot the pressure. This has the disadvantage that the load speed decreases momentarily.

The present invention solves these problems, and provides a closed-loop control method for a variable displacement pump and a control device therefor, which can add optimal feedback compensation to any dynamic changes in pressure control and flow rate control. With the goal.

B. Effects of the Invention (Means for Solving the Problems) In order to achieve the above object, a closed loop control method for a variable displacement pump according to the present invention calculates a pressure deviation between a pressure detection output of the pump and a pressure command. Calculate the flow deviation between the flow detection output and the flow command, compare the pressure deviation and the flow deviation, select a smaller one of them, and perform simultaneous pressure / flow control of the variable displacement pump. In performing this, a plurality of feedback compensations for compensating the pressure deviation amount are selectively provided, and when a stepwise increase in the flow rate command is detected by the speed-up switching circuit, the flow rate is changed for a certain period of time. Switching to feedback compensation during acceleration, and when the step-down switching circuit detects a step-down in the pressure command, feedback for the change during the step-down control for a certain period of time. When the step-up of the flow rate command is simultaneously performed by the switching circuit at the time of acceleration and the step-like decrease of the pressure command is generated by the switching circuit at the time of step-down, the priority determination circuit determines the flow rate. The method is provided by a closed-loop control method for a variable displacement pump, wherein the method is switched to feedback compensation during speed-up or feedback compensation during step-down control.

Further, in order to achieve the above method, means for calculating a pressure deviation between a pressure detection output of the pump and the pressure command, and means for calculating a flow deviation between the flow detection output and the flow command, Means for comparing the pressure deviation amount and the flow amount deviation amount and selecting a smaller one thereof; a plurality of feedback compensations; and a means for selecting the plurality of feedback compensations to compensate for the pressure deviation amount. Means for detecting that the flow command has increased in a step-like manner, for a fixed time with respect to a flow rate change, means for switching to feedback compensation at the time of flow rate increase, and detecting that the pressure command has decreased in a step-like manner with respect to a pressure change. A certain time for the pressure change,
Means for switching to feedback compensation at the time of step-down control; feedback compensation means depending on a step-like change of a flow command by the switching circuit at the time of acceleration and a step-like change of a pressure command by the circuit at the time of step-down; When a step-like increase in the flow rate command by the switching circuit and a step-like decrease in the pressure command by the step-down switching circuit occur simultaneously, the priority order determination circuit causes the feedback compensation during the flow rate increase or the step-down control. Means for switching to time feedback compensation.

(Operation) The operation of the present invention configured as described above is as follows.

First, the closed loop control of the variable displacement pump can be understood by dividing a static state into the following three states in the pressure control and the flow rate control.

A: The state where the load pressure is equal to or less than the pressure command and only the flow control is executed (flow control state).

B: When the load pressure is less than the pressure command and the flow exists,
A state in which pressure control is being performed (a so-called override state).

C: A state in which there is almost no flow and only pressure control is performed (pressure control state).

There are three states.

In the closed-loop control method and the control device for the variable displacement pump according to the present invention, in the state A, that is, in the state where the load pressure is equal to or less than the pressure command and only the flow rate control is executed, the operation is performed by the adder / subtractor 3. The pressure deviation signal becomes very large and places no restrictions on the flow deviation signal passing through the minimum selection circuit. Therefore, the power amplifier 11
The only signal input to is the flow deviation signal.

Further, in the states B and C, that is, when the load pressure is equal to or less than the pressure command and the flow is present, the pressure control is being performed, and the case corresponds to a so-called override region or there is almost no flow, In a state where only the pressure control is executed, the following operation is performed.

The pressure deviation signal calculated from the difference between the pump pressure command and the detected pressure is smaller than the flow deviation signal, and therefore the signal input to the power amplifier 11 is only the pressure deviation signal.

The above control method is an example of simultaneous control of pressure and flow rate in a variable displacement pump.However, in order to suppress overshoot and undershoot with respect to a step-like change of a pressure command in a pressure control state, a pressure deviation signal is generally used. Add feedback compensation. When the value of the feedback compensation is added to the extent that the overshoot is suppressed, the step-down response time may be longer than necessary due to the difference between the discharge capacity and the suction capacity of the variable displacement pump. Here, an optimal step-down response is realized by detecting that the pressure command has decreased stepwise, and switching to pressure feedback compensation by the step-down switching circuit 9 for a certain period in response to the change.

Here, the fixed time is not limited to an exactly determined time. It includes the switching time for the target optimal feedback compensation and the time required to suppress overshoot.

Also, during flow control, when the flow command increases stepwise, the load pressure generally also increases. In this case, when the normal feedback compensation is added, it is attempted to switch to the pressure control earlier by the negative amount of the pressure feedback compensation before the load pressure reaches the pressure command.

Regarding this point, as described above, the above problem was pointed out in FIG. 3 based on the time history of the pressure and the flow rate in the conventional method. That is, when the pressure command and the flow command are simultaneously increased stepwise, the load pressure also increases as the detected flow rate increases. At this time, a state where pressure command <(detected pressure + feedback compensation) occurs due to the dynamic change of the detected pressure, and further, the flow rate deviation> the pressure deviation. During the above period, the output of the minimum value selection circuit 7 becomes a pressure deviation, and the control current to the proportional solenoid 12 changes in the direction of decreasing the flow rate.

In the present invention, the speed-increasing switching circuit 8 detects that the flow rate command has increased in a step-like manner, and switches to a feedback compensation dedicated to the speed-increasing control for a certain time in response to the change, thereby increasing the normal boosting. The amount of feedback compensation can be adjusted independently of time.

Therefore, in the closed-loop control method for controlling the flow rate and the pressure of the variable displacement pump with one electromagnetic proportional control valve, as described above, four signal processings of the pressure command, the flow rate command, the detected pressure and the flow rate are performed. Controlling. Therefore, when the pressure command and the flow rate command are simultaneously increased from the state where the pressure command, the flow rate command, the detected pressure and the flow rate are all 0, it is determined whether the load state is the flow control state or the pressure control state. You need a way to do that.

Here, “simultaneously” is not limited to a case where the two coincide exactly.
It should be recognized that the width is substantially capable of responding to the response time in the loop for switching the feedback compensation.

Further, when an increase in the flow rate command is detected and no pressure feedback compensation is performed for a certain period of time, and when the load is in a pressure control state, an extremely large pressure overshoot may occur. Therefore, switching to the feedback compensation dedicated to the speed-up control was carried out, and the pressure overshoot was kept below the allowable value to solve this point.

(Embodiment) An embodiment will be described with reference to the drawings. FIG. 1 specifically shows a closed-loop control method for a variable displacement pump and a control device thereof according to the present invention, specifically showing a circuit configuration of the control device and a pump system. is there.

As a whole, the circuit configuration of the control device is such that the pressure sensor 1 for detecting the pressure of the variable displacement pump 13 and the output thereof are amplified by the pressure sensor amplifier 14 (output P _MON ) and input to the adder / subtractor 3. A flow sensor 2 for detecting a pump discharge flow rate,
The output is amplified by the flow sensor amplifier 15 (output Q _MON ).
Input to the subtractor 4 and the flow rate command signal input terminal 17
, A flow command (input Q _IN ) is input. Further, a pressure command (input _PIN ) is input from the pressure command signal input terminal 16.

The adder / subtractor 3 for calculating the difference between the pressure command, the detected pressure and the feedback compensation of the pump 13 and outputting a pressure deviation signal is connected to the pressure setting signal input terminal 16.

The output [(pressure deviation = pressure command− (detection pressure + feedback compensation)]] from the adder / subtractor 3 is supplied to the pressure control amplifier 5.
And is input to the minimum value selection circuit 7. The output from the adder / subtractor 4 (flow deviation = flow command−detected flow) is amplified by the flow control amplifier 6 and similarly input to the minimum value selection circuit 7. The minimum value selection circuit 7 outputs a smaller value among a plurality of input signals.

There is a speed-up switching circuit 8 for detecting that the flow command has increased in a step-like manner, and switches to feedback compensation dedicated to speed-up control for a certain time in response to the change. The step-down switching circuit 9 is a circuit that detects that the pressure command has decreased stepwise, and switches to feedback compensation dedicated to the step-down control for a certain time in response to the change.

Further, with respect to the speed-up switching circuit 8 and the step-down switching circuit 9, when the step change is input to both simultaneously, that is, the flow command increases stepwise, and
There is a priority determination circuit 18 that prioritizes feedback compensation during step-down control when the pressure command decreases stepwise.

The output signal of the minimum value selection circuit 7 is a proportional solenoid coil that generates an attractive force by the control current from the power amplifier 11.
In step 12, the variable displacement pump 13 is controlled by swash plate angle control.

It is effective to include a step of performing such pump control by swash plate angle control, but the present invention is not limited to other control means.

Next, the speed-up switching circuit 8 will be described. The output from the pressure sensor amplifier 14 is subjected to feedback compensation according to a transfer function A described later. Its execution depends on SW2. Further, the speed-up switching circuit 8 assigned the same number performs a process according to a transfer function B to be described later on the flow command from the flow command signal input terminal 17. SW2 is controlled from the result.

The switching circuit 9 at the time of step-down will be described. The output from the pressure sensor amplifier 14 is subjected to feedback compensation in accordance with a transfer function C described later. Its execution depends on SW3. The other step-down switching circuit 9 assigned the same number performs a process according to a transfer function D described later on the pressure command from the pressure command signal input terminal 16. SW3 is controlled based on the result.

Further, the adder / subtractor 3 performs feedback compensation on the output from the pressure sensor amplifier 14 in accordance with a transfer function E described later, except at the time of increasing the flow rate and at the time of decreasing the pressure. Its execution is SW
Achieved by one closed circuit.

These transfer functions are as follows for A to E, and are adjusted to obtain optimal control characteristics.

The transfer function _{A T 2 S / (1 +} TS) B T 4 S / (1 + TS) C T 3 S / (1 + TS) D -T 5 S / (1 + TS) E T 1 S / (1 + TS) Here, the speed increase during switching The operation of the circuit 8 is as follows. When the flow rate command increases in a step-like manner, the normally open SW2 is closed for a certain period of time, and at the same time, the normally closed SW1 is opened and the transfer function E is switched to the transfer function A from the transfer function E. Change feedback compensation.

Here, the NOR circuit 19 will be described. When the flow rate command is increased stepwise, the input to the NOR circuit 19 becomes H (high), but otherwise the input becomes L (low).
Similarly, when the step-down switching circuit 9 steps down the pressure command in a stepped manner, the input to the NOR circuit becomes H (high), but otherwise becomes L. Therefore, the NOR circuit closes SW1 when all of the inputs become L inputs. Usually in this state,
Feedback compensation is performed according to the transfer function E.

This means that the transfer function is changed from E to A or C by opening SW1.

The step-down switching circuit 9 performs feedback compensation according to the transfer function C. Its execution depends on SW3 which is always open.
Therefore, when the condition that SW3 is closed, that is, when the pressure command is stepped down, the SW3 is closed by the output of the step-down switching circuit 9. As a result, feedback compensation according to the transfer function C is performed. The other transfer functions A and E are cut off.

Further, the transfer function of the step-down switching circuit 9 will be described. The transfer function C is changed to the transfer function C by stepwise step-down of the pressure from the control by the transfer function E. In this case, the value of the transfer function E is the pressure during the step-up. The detected waveform rises as close to a rectangular waveform as possible without overshooting.
This is because it is effective in boosting response. However, the falling response at the time of step-down becomes very slow. In the present invention, so-called waveform shaping can be achieved by switching to the transfer function C of the step-down switching circuit 9. This is the selection of the transfer function C that reduces the feedback compensation amount.

C. Advantageous Effects of the Invention Since the present invention is configured as described above, the following effects can be obtained.

The feedback compensation in the simultaneous control of the pressure and the flow rate of the variable displacement pump is automatically switched between three cases, that is, normal time, step-down control and speed-up control, and each can be adjusted independently. As a result, optimal adjustment of dynamic control of pressure and flow rate can be performed regardless of the pressure command, the flow rate command, and the load state of the variable displacement pump.

[Brief description of the drawings]

FIG. 1 is a control circuit diagram of a closed-loop control device of a variable displacement pump showing an example of the present invention, FIG. 2 is a pressure / flow control circuit diagram of a conventional variable displacement pump, and FIG. It is a figure showing the state of simultaneous step increase. In step # 1, the detected flow rate decreases when the feedback control is activated for the flow rate command and the pressure control state is established. 1: pressure sensor, 2: flow rate sensor, 3: adder / subtractor 4: adder / subtractor, 5: pressure control amplifier 6: flow control amplifier, 7: minimum value selection circuit 8: speed-up switching circuit, 9: step-down Switching circuit 10: Feedback compensation circuit 11: Power amplifier, 12: Proportional solenoid 13: Variable displacement pump 14: Pressure sensor amplifier 15: Flow sensor amplifier 16: Pressure command signal input terminal 17: Flow command signal input terminal 18: Priority determination circuit

Claims (2)

(57) [Claims] 1. A pressure deviation between a pressure detection output of a pump and a pressure command is calculated, a flow deviation between a flow detection output and a flow command is calculated, and the pressure deviation and the flow deviation are calculated. In comparing the amounts and selecting the smaller one to perform the simultaneous control of the pressure and the flow rate of the variable displacement pump, a plurality of feedback compensations for selectively compensating the pressure deviation amount are selectively provided. When a step-like increase in the flow command is detected by the circuit, the change is switched to feedback compensation at the time of increasing the flow for a certain period of time in response to the change. For a certain time in response to the change, switch to feedback compensation at the time of step-down control. A step-wise decrease of the pressure command at the same time, the priority order determining circuit switches to the feedback compensation at the time of the flow rate increase or the feedback compensation at the time of the step-down control. . 2. A means for calculating a pressure deviation between a pressure detection output of a pump and a pressure command; a means for calculating a flow deviation between a flow detection output and a flow command; Means for comparing the flow rate deviation amount and selecting a smaller one thereof; a plurality of feedback compensations; a means for selecting the plurality of feedback compensations to compensate for the pressure deviation amount; Means for detecting an increase in a step-like manner, switching to feedback compensation at the time of a flow rate increase for a fixed time with respect to a flow rate change, and detecting that the pressure command decreases in a step-like manner with respect to a pressure change; Means for switching to feedback compensation at the time of step-down control for a certain period of time, stepwise change of the flow rate command by the switching circuit at the time of speed increase, and step of the pressure command by the circuit at the time of step-down. And feedback compensation means dependent on the change, addition, when the decrease stepwise the pressure command by the acceleration time switching circuit by step increase and step-down at the switching circuit of the flow rate command occurs at the same time,
Means for switching to the feedback compensation at the time of flow rate increase or the feedback compensation at the time of step-down control by a priority order determination circuit.