JPS596406B2 - Pressure control method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a pressure control method in a flow path.

Conventionally, it has been impossible to control pressure and flow rate simultaneously in one flow path. That is, when controlling the pressure or flow rate, the possible operating variables can be roughly divided into 1) changing the source pressure of the system; 2) There are two methods: changing the flow path resistance of the system.

However, in these two methods, the controlled quantity pressure,
The flow rates interfere with each other and cannot be controlled independently. This will be explained with reference to FIG. In the figure,
Pin is the source pressure, P is the control point pressure, F is the control flow rate, PC is the pressure regulator, FC is the flow regulator, Zp is the pressure regulating valve, Z
F is a flow control valve. Now, when the flow rate control valve ZF is opened in an attempt to increase the flow rate, the controlled flow rate F increases. However, if the pressure regulating valve Zp is kept at a constant opening degree due to an increase in the control flow rate F, the pressure loss due to the pressure regulating valve Zp becomes large and the control point pressure P decreases. Therefore, if the pressure regulator is in operation, the pressure regulating valve Zp
is opened to bring the control point pressure P to a predetermined value. As the pressure regulating valve Zp is opened, the tipping point pressure P recovers, but the total flow path resistance decreases by the amount that the pressure regulating valve Zp opens, and as a result, the controlled flow rate F increases. Therefore,
Conversely, the flow rate control valve ZF is closed. When this happens, the pressure regulating valve Zp is closed, contrary to the above. In this way, the pressure car flow rate controls interfere with each other and cannot be controlled due to hunting due to the time constants of each system. Therefore, in the past, rather than controlling both control amounts simultaneously, one was prioritized and the other was sacrificed.

This method can be broadly classified into the following two types.

That is, (1) a method of controlling only one control system and not controlling the other; (2) a method of making the degree of interference relatively small by greatly differentiating the time constants of both systems (fastening the response of one control system). However, by slowing down the other control operation, even if the influence of one control operation appears on the other, it is only slowly corrected, improving the controllability of only those with high importance).

However, the methods (1) and (2) above can improve the controllability of only one, but cannot control both.

It is therefore an object of the invention to provide a pressure control method that does not have the above-mentioned drawbacks.

This invention will be explained below.

First, FIG. 2 shows a pressure control system to which the present invention is applied.

In the figure, 1 is a pressure control valve, 2 is a pump, 3 is a pressure tank, 4 is a tank pressure detector for detecting the pressure of the pressure tank 3, 6 is a flow rate detector, 7 is a total flow path resistance control valve,
8 is the flow path resistance from this total flow path resistance control valve 7 to the pressure control point, 9 is the control pressure detector, 10 is the pressure control valve, 11 is the flow path resistance after the pressure control valve 10, and 21 is the flow rate detector 22 is a pressure regulator that operates the pressure regulating valve 1; 23 is a feed forward amount calculator for calculating the feed forward amount from the tank pressure detector 4; 2 is a pressure regulator, and 25 is a total flow path resistance regulator. In addition, the tank pressure is P. , the control point pressure is P,
The control flow rate is F, and the flow path resistance value of the total flow path resistance adjustment valve 7 is R'.
, the resistance value of the flow path resistance 8 is R1, the flow path resistance value of the pressure regulating valve 10 is Rz, and the resistance of the flow path resistance 11 is R2. By the way, the flow path pressure loss formula is as follows. This holds true.

In the above relational expression, the relationship between the controlled variable and the manipulated variable is selected as follows.

Pressure: Rz change {Flow rate: PO change In the above equations (3) and (4), the controlled variables P and F are a mutual interference system of the manipulated variables Rz and PO.

Here, when control is performed such that A=constant, in the above equations (6) and (7), the control point pressure P is the flow path resistance Rz and the tank pressure P. , the control flow rate F is a function of the tank pressure P. As a function of This is shown in FIG.

That is, even if pressure control is performed by changing the flow path resistance Rz, the flow rate will not change as long as the compensation circuit has A=constant. That is, pressure control does not change the total resistance, but only changes the pressure loss before and after the pressure control point. Further, in order to realize A=constant, the following procedure may be performed.

When A, R7, and Rz are varied in the above equation (5),
Here, from equation (5) and ΔA=O, that is, as long as the outputs of the total flow path resistance controller 25 and pressure regulator 24 have the relationship of equation (9), A=constant, and the pressure is controlled without changing the flow rate. can be done.

Next, tank pressure P.

To eliminate interference from the control point pressure P to the tank pressure P
. It is sufficient to add in advance to the pressure control system the amount by which the control point pressure P fluctuates due to fluctuations in . In this case, since the interference from the flow path resistance Rz to the control flow rate F has been eliminated by the method described above, advance addition is effective. Further, the amount of advance addition may be performed as follows.

When P, Rz, and PO are varied in the above equation (6),
A+ΔRzΔPOA・・・・・・・・・・・・・・・(
). Here, in order to set ΔP=0, it is sufficient if the following is true.

FIG. 2 shows the above conditions expressed in a control device.

The flow rate controller 21 performs control calculations so that the actual flow rate becomes the set flow rate, and outputs the tank pressure target value at this time. The pressure regulator 22 controls the pump bypass valve to match this target value. Further, the tank pressure fluctuation is sent to the pressure controller 22 as a variable for advance addition to the pressure control system. The pressure regulator 24 performs control calculations so that the actual pressure becomes the set pressure, and opens and closes the pressure regulating valve 10. At the same time, the total flow path resistance controller 25 controls the total flow path resistance to be constant in accordance with the operation of the pressure controller 24, and opens and closes the flow path resistance R'. By the way, the reason why it has not been possible to control pressure and flow rate simultaneously in the past is that the total flow path resistance changes due to force control, which causes disturbance in flow rate control.

Therefore, in FIG. 2, a total flow path resistance control valve 7 and a total flow path resistance controller 25 are added to correct the resistance change caused by the control operation of the pressure regulator 24. That is, the first improvement of the present invention is that even if the pressure regulating valve 10 is operated, the entire flow path resistance regulating valve 7 is operated simultaneously to prevent a change in the total channel resistance and thus not to change the flow rate. The second improvement is that a feed forward amount calculator 23 is added, focusing on the fact that the pressure can be controlled independently of the flow rate using the first method.

In other words, the disturbance from pressure control to flow control has disappeared, but the disturbance from flow control to pressure control remains, so the variable elements of the flow control system are added in advance to the pressure control system (feed forward). By doing so, we were able to suppress fluctuations in the pressure control system. This method can be applied because the first method eliminates interference from the pressure control system to the flow rate control system.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a conventional pressure-flow control system, Fig. 2 is a diagram showing a pressure car flow control system according to the present invention, and Figs. 3 A-C.
is a diagram for explaining the operation. 1...Pressure control valve, 2...Pump, 3
......Pressure tank, 4...Tank pressure detector, 6...Flow rate detector, 7...Full flow path resistance control valve, 8... ...Flow path resistance, 9...
・Control pressure detector, 10...Pressure control valve, 11
DESCRIPTION OF SYMBOLS 1...Flow path resistance, 21...Flow rate controller, 22...Pressure regulator, 23...Feedback amount calculator, 24... ...Pressure regulator, 25...Full flow path resistance control valve.

Claims (1)

[Scope of Claims] 1. A pressure control method for controlling the pressure at a control point of a flow path having a flow rate control system to a constant level, wherein the flow path includes a pressure regulating valve for adjusting the pressure and a correlation with the pressure regulating valve. A flow path resistance control valve that can be operated with A pressure control method comprising: adjusting the flow path resistance adjusting valve to follow the pressure adjusting valve so as to keep the total flow path resistance constant against changes in the flow path resistance value due to adjustment. 2. A pressure control method for controlling the pressure at a control point of a flow path having a flow rate control system to a constant level, in which the flow path includes a pressure regulating valve for adjusting the pressure and a pressure regulating valve that can be operated in correlation with the pressure regulating valve. A flow path resistance control valve is installed, and an amount that compensates for pressure fluctuations at the control point caused by variable force fluctuations in the flow rate control system is added in advance to a controller of the pressure control valve, and the pressure control valve is adjusted. and the flow path resistance adjustment valve is adjusted to follow the pressure adjustment valve so that the total flow path resistance is kept constant against changes in the flow path resistance value due to the adjustment of the pressure adjustment valve. pressure control method.