JPS6179002A - Pressure control circuit for relief valve - Google Patents

Abstract

PURPOSE:To suppress pressure overshoot by inputting control signals, which correspond to the value of comparison between the fluid pressure in a spring chamber and the target pilot pressure, into a pilot relief valve connected to the spring chamber of a main relief valve. CONSTITUTION:A pilot relief valve 26 and pressure source 31 are connected to the spring chamber 16 of a main relief valve 13, while signals, which correspond to the value of comparison between the fluid pressure in the spring chamber 16 and the target pilot pressure, are input into the pilot relief valve 26. A feed-back system 27 is prepared that regulates the fluid pressure in the spring chamber 16 to the target pilot pressure. With this contrivance, in a transitional period in which a pressure control state is started, the pressure can be restrained to the overshoot equivalent to the conventional open control, maintaining the pressure control accuracy equivalent to that of the conventional pressure feed back control.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a relief pressure control circuit which is particularly effective for pressure control of injection molding, for example.

2. Prior Art Conventionally, there is a pressure control circuit for relief as shown in FIG. (Refer to Hydraulic and Pneumatic Design, Vol. 17, No. 10, Page 71, Figure 4.) This relief pressure control circuit is connected to the main line (3) connecting the pressure source (1) and the injection sill (2). An electromagnetic relief valve (5) is connected to the operational amplifier (6), and a detected pressure signal (rcl) from a pressure detector (7) that detects the pressure of the main line (3) is connected to the operational amplifier (6).
and the target pressure signal (Io), and control the electromagnetic relief valve (5) based on the comparison value between the detected pressure signal (Id) and the target pressure signal (Io), that is, the main line (3 ) is used to control the pressure in the main line (3) using pressure feedback control. Furthermore, this relief pressure control circuit is equipped with a safety valve (
7) is connected to the main line (2).

<Problems to be Solved by the Invention> By the way, in the conventional pressure control circuit for relief, the curve (A) in FIG. The problem is that large and long-lasting pressure overshoots occur as shown. .

The reason why such pressure overshoot occurs is as follows. In Figure 3, (PO) is electric.

Target pressure to be controlled by magnetic relief valve (5), (Pm) is set pressure of safety valve (7), (E) is injection cylinder (2)
This is the time when the flow rate reaches the stroke end and transitions from the flow rate control state to the pressure control state. In the flow rate control state before the above time <E), the pressure detector (7
) is detecting an extremely low pressure in the main line (3), the operational amplifier (6) is outputting its maximum output and the electromagnetic relief valve (5) is completely closed. In this state, the control elements of the feedback system, such as the operational amplifier (6) and the electromagnetic relief valve (5), are in a saturated state with respect to the signal magnitude. When the fluid pressure in the main line (3) exceeds the target pressure (Po) after time (E), the operational amplifier (6) is reversed from the saturation state with a certain time constant unique to this feedback system. do. Due to the delay in the output of the electromagnetic relief valve (5) by this time constant, the third
As shown by curve (A) in the figure, a large pressure overshoot exceeding the target pressure (Po) will continue for a long time. This pressure overshoot is caused by the electromagnetic IJ leaf valve (5
) The pressure overshoot determined by the inherent characteristics of the device itself (1) is also large and lasts for a long time.

In order to solve this problem, it is conceivable to shorten the time constant of the feedback system including the operational amplifier (6) to make the overshading smaller and for a shorter time, but this may cause the problem of oscillation.

In addition, in order to eliminate the drawback of pressure overshoot caused by pressure feedback control, it is conceivable to control the electromagnetic relief valve (5) with an oven loop. Drift F occurs due to the temperature change (5), and the accuracy of pressure control deteriorates.

Therefore, the purpose of the present invention is to maintain static pressure control accuracy equivalent to pressure feedback control, and to avoid small and short-term pressure overshoots in the transition period when the pressure control state is entered, as with conventional open loop control. The key is to hold it down.

Means for Solving the Problems In order to achieve the above object, the relief pressure control circuit of the present invention has a main line (11) as shown in FIG.
A pilot relief valve (26) is connected to the spring chamber (16) that is not connected to the main line (11) of the main relief valve (13) that controls the pressure of the pilot relief valve (26). A feedback system that controls the fluid pressure in the spring chamber (16) to the target pilot pressure by inputting a control signal corresponding to a comparison value between the fluid pressure in the spring chamber (16) and the target pilot pressure. (
27), while a pressure of 1 (3 G) is provided in the spring chamber (1G).
1) is connected.

<Operation> Through the above (1' and 4), fluid flows from the pressure source (31) capable of generating the target pilot pressure to the pilot relief valve (
26). The pilot relief valve (26) operates constantly to discharge the fluid, and feeds back the fluid pressure in the spring chamber (16) that is not connected to the main line (11) of the main relief valve (13). The control signal from the system (27) accurately controls the target pilot pressure.

In this way, the main relief valve (13) is a pilot relief valve that is operating regardless of whether the main line (11) is under flow control, pressure control, or in a transient state from flow control to pressure control. (26) by spring chamber (16)
The pressure in this spring chamber (16) is always controlled to a constant pressure.
The pressure of the main line (11) is controlled corresponding to the fluid pressure of the main line (11).

<Example> Hereinafter, the present invention will be explained in detail with reference to illustrated embodiments.

In FIG. 1, (11) is a main line connected to a pressure source (12), and (13) is a relief main valve connected to the main line (12).

The relief main valve (13) has a piston (15) slidably fitted into the valve chamber (14). One spring (17) is compressed in the spring chamber (16) at one end of the piston (15), and the second spring (17) causes the piston (15) to
is biased toward the valve seat (131) to open and close between the valve seat (n1) and the outlet (22).

A pylon relief valve (26) is connected to the spring chamber (16) of the main relief valve (13) through a throttle (25)!
Furthermore, this pilot relief valve (26) and the spring chamber (16) are connected by a feedback system (27) to perform feedbank control of the pressure inside the spring chamber (16). The feedback system (27) includes a pressure detector (28) and an operational amplifier (29). The pressure detector (28) is connected to the spring chamber (1) of the relief main valve (13).
6) and inputs a signal representing this fluid pressure to an operational amplifier (29). The above operational amplifier (2
9) further inputs a target Byrond pressure signal (Ip) corresponding to the specified fluid pressure of the main line (11) to be controlled. The operational amplifier (29) is a pressure detector (
The signal representing the fluid pressure in the spring chamber (16) detected by the spring chamber (16) is compared with the target pilot pressure signal (Ip), and a control signal obtained by amplifying this comparison value is sent to the pilot relief valve (
26). Therefore, the pilot relief valve (26) is connected to the spring chamber (16) of the main relief valve (13).
) is feedback-controlled to the target pilot pressure corresponding to the target pilot pressure signal (Ip).

On the other hand, between the spring chamber (16) of the relief main valve (13) and the throttle (25), there is a pressure source that is not directly related to the pressure source (12) having a pressure higher than the target Byront pressure. (31) is connected via a pressure compensated flow rate regulating valve (32). For this reason, the spring chamber (16) and the aperture (
A constant flow of fluid always flows between the pilot relief valve (25) and the pilot relief valve (26), and as a result, the pilot relief valve (26) is always in operation at a certain opening degree.

With the above configuration, the pilot relief valve (26) is always in operation at a certain opening degree as described above, and the fluid pressure in the spring chamber (16) of the main valve (13) for 26), the main valve for the leaf (
13), ie, the flow control state, pressure control state, and transient state from flow control to pressure control of the main line (11), the target pilot pressure is accurately controlled.

Now, assume that the main line (11) shifts from the flow rate control state to the pressure control state, and the pressure of the main line (11) suddenly increases.

Then, the piston (15) of the relief main valve (13)
) is the target pilot pressure (as soon as the fluid pressure in the main line (11) becomes higher than the sum of the precisely controlled fluid pressure in the spring chamber (16) and the spring force of the spring (17): It retreats to the spring chamber (16) side and the main line (11
) to control the pressure. When this piston (15) retreats -
Although the fluid pressure in the two spring chambers (16) is about to rise,
A pilot relief valve that is operating at a certain opening (
Since the fluid in the spring chamber (16) is quickly discharged from the spring chamber (16), the fluid pressure in the spring chamber (16) does not increase excessively.
The piston (15) quickly retreats and the main line (1
The pressure overshoot of 1) is small and lasts only for a short period of time, as shown by curve (B) in FIG. From a different perspective, the pressure source (31) with a pressure higher than the target pilot pressure is connected to the pressure compensated flow regulating valve (32).
Since fluid is flowing into the pilot relief valve (26) through the operational amplifier (29) and the pilot relief valve (26), the operational amplifier (29) and the pilot relief valve (26) are not in a saturated state but in an equilibrium state, so that they operate with good responsiveness. As a result, the pressure overshoot of the main line (11) is reduced. In other words, the pressure overshoot inherent in pressure feed control due to the saturation of the operational amplifier, etc. in conventional pressure feedback control does not occur, and the pressure overshoot caused by the relief main valve (13) itself, that is, the open control, eliminates the pressure overshoot. Only an equivalent pressure overshoot will occur.

In addition, statically, the spring chamber (1
6) is precisely controlled to the target pilot pressure by the pilot relief valve (26), so the fluid pressure in the main line (11) has static characteristics of highly accurate pressure control equivalent to conventional pressure filled pack control. can get.

In the above practical example, a pressure-compensated flow rate regulating valve is used as the flow rate regulating valve, or a throttle may be used instead.

<Effects of the Invention> As is clear from the above explanation, the relief j
According to the pressure control circuit, it maintains the same static characteristics (pressure control accuracy) as conventional pressure feedback control, but suppresses the pressure overshoot equivalent to conventional open control in the transient state when it enters the detected pressure control state. be able to.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, FIG. 2 is a circuit diagram of a conventional example, and FIG. 3 is a graph illustrating pressure overshoot in the above embodiment and the conventional example. 11... Main line, 12.31... Pressure source, 1
3...Main valve for relief, 26...Pilot relief valve, 27...Feedback system, 32...Pressure compensation 1 inch flow rate adjustment valve.

Claims (1)

[Claims] (1) A pilot relief valve ( 26
) and connect the pilot relief valve (26
) a feedback system that controls the fluid pressure in the spring chamber (16) to the target pilot pressure by inputting a control signal corresponding to a comparison value between the fluid pressure in the spring chamber (16) and the target pilot pressure; (27), and a pressure source (31) connected to the spring chamber (16).