JPS59199199A - Liquid pressure maintaining device - Google Patents

Abstract

PURPOSE:To reduce the time when a prescribed pressing pressure is attained and to maintain the stable pressure with inexpensive parts by interposing a flow control valve to a bypass circuit provided between a pump and a selector valve and providing a stop valve which operates the bypass line at the lower limit of a control pressure. CONSTITUTION:When a change-over valve 19 is opened toward a pressing side by a command for pressing, the entire oil quantity Q1 discharged from a hydraulic pump 16 is supplied through a check valve 18 and the valve 19 to an operating cylinder 15, by which the pressure in the cylinder 15 is sharply increased. When the pressure in the cylinder 15 attains the lower limit of a control pressure, a stop valve 22 is opened by the signal from a controller 26 to operate a bypass circuit 20 and therefore the flow Q3 set by a flow rate control valve 21 is returned through the circuit 20 to a tank. The remaining flow Q2 is therefore supplied to the cylinder 15 and the pressure in the cylinder 15 rises gently from the lower limit of the control pressure until the pressure attains the upper limit of the control pressure, when the valve 19 returns to neutral and the galve 22 is shut off so that the entire oil quantity Q1 from the pump 16 returns through the valve 19 into the tank.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hydraulic pressurization holding circuit used for static pressurization such as dome tightening of a tire press and pressurization of a powder molding press.

Conventionally, the pressure control circuit used when pressurizing the pressurized member (2) by the actuating cylinder (1) includes a pressure control circuit using a servo valve (3) shown in Fig. 1, and a pressure control circuit using a relief valve (Fig. 2). 4
), pressure control using a pressure compensated variable discharge pump (5) shown in FIG. 3, and pressure control using an air-operated pump (6) shown in FIG. 4.

However, in Fig. 1, the pressure detector (7) detects the internal pressure of the operating cylinder (1), and compares it with the pressure set by the pressure setting device (8).
and controls the pressure oil from pump αO,
Although the control accuracy was good, the servo valve (3) was expensive and difficult to maintain. In addition, in Fig. 2, the electromagnetic switching valve 0D is used and the relief valve (4) is used for control.
Although this is the simplest circuit, it requires manual pressure adjustment and has the disadvantage that when pressure is maintained for a long time, the pressure decreases due to wear of the valve seat of the relief valve (4). In Fig. 8, the electromagnetic switching valve αB is used, but since it uses a variable discharge pump (5) equipped with a pressure compensation valve, it is not suitable for high pressure applications. However, there was a problem with pressure reduction when the pressure was maintained for a long time, and the pressure had to be adjusted manually. Furthermore, in Fig. 4, the electric switching valve (9) (2) is combined with an air-operated pump (6), and in addition to the problem of manual pressure adjustment, the air-operated pump (6) As shown in Figure 5, the discharge rate decreases as the pressure approaches the set pressure, so it is suitable for ultra-high pressure applications, but it has the disadvantage that it takes a long time to reach the predetermined pressure. there were.

In view of these conventional problems, the present invention uses inexpensive parts to shorten the time it takes to reach a predetermined pressure, and at the same time prevents overshoot when the pressure rises and maintains stable pressure. This device provides a hydraulic pressurization holding device that can hold the pressure, and its features are that it is equipped with a switching valve between the pump and the operating cylinder, and that the pressure is controlled within the upper and lower limits of the control pressure. In this pressure control circuit, a bypass circuit is provided between the pump and the switching valve to vary the amount of fluid flowing into the working cylinder, and this bypass circuit is designed to prevent the internal pressure of the working cylinder from overshooting the upper limit of the control pressure. A flow rate control valve is interposed to adjust the flow rate, and an on-off valve is provided to operate the bypass circuit at the lower limit of the control pressure.

Hereinafter, the present invention will be described in detail with reference to the illustrated embodiment.
The figure shows a first embodiment of the present invention, 04) is a pressurized member,
α9 is an operating cylinder, and αQ is a hydraulic pump, which is driven by motor α force. Hydraulic pump αG and operating cylinder u9
A check shaft and an electromagnetic switching valve surface are connected in series between. C30) is a relief valve,! 211 is hydraulic pump α
A bypass circuit is connected between G and the switching valve σ mark, and this bypass circuit (201) is connected in series with a flow rate adjustment valve (21) for setting a controlled flow rate and an electromagnetic on-off valve.

1 is a pressure detector that detects the internal pressure of the operating cylinder (151), 1 is a pressure setting device, - is an amplifier, and group 1 is 011・O
The FF controller is driven by the comparison value between the detected pressure and the set pressure, and switches the switching valve i19 according to the pressurization command and release command, and also switches the switching valve [i19] at the control pressure upper limit Pl.
191 from pressurized to neutral, and lower limit pressure P2
Therefore, the bypass circuit ω operates at the control pressure lower limit P2, and part of the discharge tQlO from the hydraulic pump α0 is transferred from the bypass circuit (5)) to the on-off valve (22+). The flow is diverted to the tank, and the flow tQ2 to the operating cylinder α9 is limited to a range that does not cause overshoot.

In the above configuration, when the switching valve am opens to the pressurizing side in response to a pressurization command, the total amount of oil Q] discharged from the hydraulic pump αQ is all transferred to the operating cylinder 09 via the check valve (18) and the switching valve (1gl). The internal pressure of the working cylinder rises rapidly as shown in Fig. 7.At this time, the rise characteristic becomes smaller as the pump capacity becomes smaller, but becomes more gradual as the cylinder capacity becomes larger. (When the internal pressure of 151 reaches the control pressure lower limit P2, the on-off valve (2) is opened by the signal from the controller, and the bypass circuit group is activated, so that the flow EE Q3 set by the flow rate adjustment valve is transferred to the bypass circuit (branch). ) and then returned to the tank.
The remaining flow rate Q2 is supplied to the operating cylinder mark, and the internal pressure of the operating cylinder α9 gradually increases from the control pressure lower limit P2 in accordance with Q2, as shown in FIG. When the control pressure reaches the upper limit P1, the switching valve (I9) returns to neutral and the on-off valve shuts off the bypass circuit t2o+, and the discharge amounts Q and l from the hydraulic pump αQ are all transferred to the switching valve 1.
91 and return to the tank. After reaching the control pressure lower limit P2, the flow rate Q2 to the working cylinder section is determined by the flow rate control valve t21.
This is done by adjusting the flow rate Q3 according to 1, but the 8th
As shown in the figure, it is necessary to set the pressure so that it does not rise steeply and exceed the control pressure upper limit P1 and overshoot (A). Note that this gradient becomes gentler if the bypass flow rate Q3 is increased. However, the cylinder capacity is assumed to be constant. After reaching the control pressure upper limit P1 and returning the switching valve 119) to neutral, the internal pressure gradually decreases due to leakage from the operating cylinder a9, but when it drops to the control pressure lower limit P2,
The switching valve (1!I) opens again to the pressurizing side and the opening/closing valve opens, so that the internal pressure of the operating cylinder α9 begins to rise in accordance with the flow rate Q2. By repeating the same operation,
The internal pressure of the actuating cylinder 09, that is, the pressurizing force F is maintained between the control pressure upper limit P1 and the control pressure lower limit P2. In this case, since the control pressure can be monitored electrically, there is no pressure drop (rise) phenomenon even when the Ω pressure is maintained for a long time, and the set pressure can be changed as shown in Figure 7 using the pressure setting device
It can be easily operated using only the □□ operation switches, can be operated from a central control room, and can also be connected to a computer. Further, the time required to reach a predetermined pressure can be shortened, and there is no overshoot, and the accuracy of pressure control for maintaining pressure can be significantly improved.

This effect is particularly noticeable when an air-operated pump is used as an energy-saving measure. In addition, in Figure 7,
In the case of the pump ◇o (5) in Figure 2 and Figure 8, the vessel shows the pressure characteristics of the air-operated pump (6) in Figure 4, respectively.

FIG. 9 shows a second embodiment. The present invention is not limited to the embodiment shown in FIG. 6, but as shown in FIG. 9, an on-off valve is connected in series between the hydraulic pump αQ and the check valve device, and the flow rate is Bypass circuit f2 with regulating valve I211
0+ may be connected in parallel to the on-off valve ■, so that a portion Q3 of the discharge amount Ql from the hydraulic pump OQ is returned to the tank via the relief valve m+.

As detailed in the above embodiments, the present invention has a configuration that combines a switching valve, a bypass circuit, a flow rate adjustment valve, and an on-off valve, so there is no need to use a servo valve, etc., and it is inexpensive and easy to maintain. . Furthermore, when the control pressure reaches the lower limit, the on-off valve operates the bypass circuit and limits the flow to the operating cylinder, reducing the time it takes to reach the predetermined pressure. By adjusting the pressure, it is possible to prevent the phenomenon of exceeding the control pressure upper limit and causing an overshoot. Therefore, the necessary pressure can be obtained in a short time, and the control accuracy for maintaining the applied pressure can be significantly improved compared to the conventional method.

[Brief explanation of drawings]

1 to 4 are hydraulic circuit diagrams showing a conventional example, FIG. 5 is a diagram showing a performance curve of an air-operated pump, FIG. 6 is a hydraulic circuit diagram showing a first embodiment of the present invention, and FIG. 7 is a hydraulic circuit diagram showing a conventional example. 8 is a pressure characteristic diagram at an appropriate controlled flow rate, FIG. 8 is a pressure characteristic diagram at an excessively controlled flow rate, and FIG. 9 is a hydraulic circuit diagram showing the second embodiment. α9... Working cylinder, αQ... Hydraulic pump, [1
gl... Solenoid switching valve, 2 (l... Bypass circuit, Z
ll...Flow rate adjustment valve,...Solenoid on/off valve.

Claims (1)

[Claims] 1. In a pressure control circuit that is equipped with a switching valve between the pump and the operating cylinder and is configured to control the pressure within the upper and lower limits of the control pressure, there is a connection between the pump and the switching valve that allows fluid to flow into the operating cylinder. A bypass circuit is provided to vary the amount, and this bypass circuit is equipped with a flow control valve that adjusts the flow rate so that the internal pressure of the operating cylinder does not overshoot the upper limit of the control pressure, and the bypass circuit is activated at the lower limit of the control pressure. A hydraulic pressurization holding device characterized by being provided with an on-off valve for controlling the pressure.