JP2662256B2 - Control circuit for hydraulic actuator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an improvement in a control circuit of a hydraulic actuator used for an industrial machine or a construction machine.

(Prior art) Hydraulic actuators used for industrial machines such as injection molding machines and press machines and construction machines such as excavators and cranes are:
For example, it is controlled by a control circuit as shown in FIG.

That is, 1 is an oil discharge cylinder as a hydraulic actuator, and oil chambers A and B on both sides of the piston 2 are connected to a hydraulic pump 5 via a switching valve 4 that determines the operation direction of the piston rod 3.

A flow control valve (variable orifice) between the hydraulic cylinder 1 and the switching valve 4 for performing meter-in control (pressure and flow control on the supply side) on each of the inflow side and the outflow side.
6A and 6B and flow control valves (variable orifices) 7A and 7B for performing meter-out control (pressure and flow control on the return side) are interposed, and a flow control valve 6A on the meter-in side is provided.
Check valves 8A and 8B that allow the oil flow on the return side are provided in the bypass passages 6 and 6B, and a flow control valve on the meter-out side.
Check valves 9A and 9B that allow the flow of oil on the supply side are interposed in the bypass passages of 7A and 7B, respectively.

For example, when the switching valve 4 is switched to the contraction side when the hydraulic cylinder 1 is to be contracted, the piston rod 3 is contracted by the pressure oil supplied to the oil chamber A. In this case, meter-in control can be performed by adjusting the flow control valve 6A on the inflow side. Also, meter-out control can be performed by adjusting the flow control valve 7B on the outflow side as necessary.

10A is a relief valve that regulates the maximum pressure on the oil chamber A side, 10B is a relief valve that regulates the maximum pressure on the oil chamber B side, 11 is a pressure reducing valve that reduces the hydraulic pressure from the hydraulic pump 5 to a set value, and 12 is the maximum discharge pressure of the hydraulic pump 5 2 shows a relief valve for regulating the pressure.

(Problems of the Invention) By the way, in this control circuit, the entire amount of hydraulic oil supplied to the hydraulic cylinder 1 passes through the pressure reducing valve 11. Pressure loss is a negative factor. To reduce the pressure loss, the capacity of the pressure reducing valve 11 may be increased, but as a result, there is a problem that the pressure reducing valve 11 becomes large.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and controls a hydraulic actuator capable of performing pressure control using a small valve while minimizing the pressure loss of the valve. It is intended to provide a circuit.

(Means for Achieving the Object) The present invention provides a poppet valve that changes the cross-sectional area of a passage of a working fluid that communicates with a liquid chamber of a hydraulic actuator in response to a pilot pressure, and supplies a pilot pressure to the poppet valve. An electro-oil conversion valve and a bleed-off valve for returning a part of the hydraulic fluid to the reservoir between the poppet valve and the liquid chamber are provided.

(Action) While the bleed-off valve returns a part of the hydraulic fluid to the reservoir between the poppet valve and the fluid chamber of the hydraulic actuator, the poppet valve adjusts the cross-sectional area of the hydraulic fluid passage, thereby allowing the actuator to operate. The liquid chamber pressure is reduced to an arbitrary pressure. Also, since the bleed-off valve allows only a small amount of hydraulic fluid to return to the reservoir, the hydraulic fluid flowing between the poppet valve and the hydraulic chamber of the hydraulic actuator does not exert a pressure loss.

(Embodiment) FIGS. 1 and 2 show an embodiment of the present invention.

In FIG. 1, reference numeral 20 denotes a hydraulic cylinder as a hydraulic actuator, and a piston 21 connected to a piston rod 35.
Are connected to a hydraulic pump 22 and a reservoir 26 via a four-way valve 25.

The four-way valve 25 connects the oil chamber A to the hydraulic pump 22, the contraction position a connecting the oil chamber B to the reservoir 26, and the oil chamber A to the reservoir.
An electromagnetic directional control valve 26 has an extension position b for connecting the oil chamber B to the hydraulic pump 22 and a neutral position c for shutting off both of them, and is switched by a switch (not shown).

A poppet type cartridge valve 24 that responds to pilot pressure is interposed between one oil chamber B of the hydraulic cylinder 20 and the four-way valve 25, and an electro-hydraulic conversion valve 30 that supplies pilot pressure to the cartridge valve 24 is provided. It is provided between the cartridge valve 24 and the hydraulic pump 22.

The cartridge valve 24 has a poppet valve 29 in a cylinder 28.
The poppet valve 29 increases or decreases the flow area of the hydraulic oil in response to the pilot pressure supplied to the pilot chamber 40 or 41.

The electro-hydraulic converter 30 includes a pilot chamber 40 connected to the hydraulic pump 22, a pilot chamber 41 connected to the reservoir 26, a position a connecting the pilot chamber 40 to the reservoir 26,
A neutral position c is connected to the hydraulic pump 22. The switching position and the opening degree are controlled based on a command signal from the controller 27.

A bleed-off valve 42 is interposed between the cartridge valve 24 and the oil chamber B. Bleet off valve 42 is a controller
A position b in which a part of the hydraulic oil flowing between the cartridge valve 24 and the oil chamber B is returned to the reservoir 26 through an orifice 43 provided therein, A position a for blocking is provided. The cartridge valve 24 and the bleed-off valve
The specific structure of 42 is shown in FIG.

The hydraulic fluid passage of the front and rear of the cartridge valve 24 is a pressure sensor P ₁ and P ₂ for outputting a pressure signal is provided by detecting the hydraulic fluid pressure. The cartridge valve 24 is provided with a position sensor 46 that detects a displacement position of the poppet valve 29 and outputs a position signal. Pressure sensors P ₁ and P ₂ and a position sensor 46
Are connected to the controller 27 by a signal circuit.

The controller 27 is configured using, for example, a CPU and includes an input device for designating control contents. The controller 27 outputs a signal to the electro-hydraulic conversion valve 30 via the amplifier 32, and performs switching and opening control of the electro-hydraulic conversion valve 30, thereby controlling the opening of the cartridge valve 24 according to the specified control content. a feedback control based on the detected pressure detected by the displacement position and pressure sensors P ₁ and P ₂ of the poppet valve 29 of the position sensor 46 Te. The bleed-off valve 42 is switched by the signal output.

 Next, the operation will be described.

To drive the hydraulic cylinder 20 to the extension side, a hydraulic pump
22 is operated, and the four-way valve 25 is switched to the extension position b via the switch. As a result, the oil discharged from the hydraulic pump 22 is supplied to the oil chamber B via the cartridge valve 24, and the hydraulic oil in the oil chamber A returns to the reservoir 26.

At this time, the cartridge valve 24 performs meter-in control. And instructs flow control to the controller 27, the controller 27 calculates the passing guard area of the poppet valve 29 from the position signal inputted from the position sensor 46, which with a pressure sensor P ₁
Based on the pressures p ₁ and p ₂ input from P _2, the flow rate Q of the cartridge valve 24 is calculated as follows.

However, K: flow coefficient A (x): oil passage cross-sectional area of the poppet valve 29 The controller 27 compares this flow rate Q with the commanded flow rate Q _0, and when they do not match, moves Q toward Q ₀ . The poppet valve 29 of the cartridge valve 24 has the oil cross-sectional area A
A signal is output to the electro-hydraulic conversion valve 30 that drives the poppet valve 29 so as to increase or decrease (x). Thus, the pressure sensor P ₁ and P ₂
Of the flow rate Q calculated from the detected pressure p ₁ and p _2, are fed back to the control of the opening degree of the cartridge valves 24, to match the flow rate Q in the command flow rate Q _0. In this flow rate control, since the controller 27 keeps the bleed-off valve 42 at the position a, the entire flow rate of the cartridge valve 24 flows into the oil chamber B of the hydraulic cylinder 20. In addition, there is no risk of pressure loss due to the bleed-off valve 42.

Further, when pressure control is instructed, the controller 27 switches the bleed-off valve 42 to the position b by a signal output. Accordingly, a part of the hydraulic oil that has passed through the cartridge valve 24 flows out of the orifice 43 to the reservoir 26. As a result, although the pressure p ₂ for detecting of the pressure sensor P ₂ decreases, the controller 27 the pressure p commanded the pressure p ₂
Compared to _20, in the case of p _2> p _20, the cartridge valve 2
By outputting a signal to the electro-hydraulic conversion valve 30 to drive the poppet valve 29 of FIG. 4 in the closing direction, and in the case of p ₂ <p _{20 in} the opening direction, the pressure p ₂ of the oil chamber B of the hydraulic cylinder 20 is commanded. to coincide with the pressure p _20. Such pressure reduction control becomes possible only when the bleed-off valve always returns a small amount of hydraulic oil to the reservoir. In addition, the bleed-off valve 42 may be small because only a small amount of hydraulic oil flows.

To stop the extending hydraulic cylinder 20, the four-way valve 25
To the neutral position c. Also the controller
The controller 27 that instructs the stop 27 to output a command signal to close the poppet valve 29 of the cartridge valve 24 to the electro-oil conversion valve 30. At the same time, the controller 27 outputs a command signal to the bleed-off valve 42 to switch the bleed-off valve 42 to the position a. As a result, all the hydraulic oil in and out of the hydraulic cylinder 20 is shut off, and the hydraulic cylinder 20 stops at that position. In a press machine or the like, by switching the bleed-off valve 42 to the position b in this state, the pressing pressure of the piston rod 35 can be reduced slowly.

On the other hand, when the four-way valve 25 is switched to the contraction position a to contract the hydraulic cylinder 20, the hydraulic pump 22
Is supplied, and the hydraulic oil in the oil chamber B returns to the reservoir 26 via the cartridge valve 24. In this case, the meter-out control relating to the flow rate and the pressure is performed in the cartridge valve 24 in the same manner as in the meter-in control. However, in the pressure control, the controller 27 sends a signal to drive the poppet valve 29 in the opening direction when p ₂ > p _{20 and in} the closing direction when p ₂ <p ₂₀ , contrary to the case of the meter-in control. Output to oil conversion valve 30.

(Effect of the Invention) As described above, in the present invention, the bleed-off valve is opened between the liquid chamber of the hydraulic actuator and the poppet valve because the bleed-off valve returns a part of the hydraulic fluid to the reservoir. The liquid chamber pressure of the actuator can be arbitrarily reduced by adjusting the opening degree of the poppet valve in this state. Further, since the bleed-off valve allows only a small amount of hydraulic fluid to flow back to the reservoir, it can be constituted by a small valve and does not exert a pressure loss on the hydraulic fluid flowing through the poppet valve and the hydraulic actuator. . Therefore, according to the present invention, it is possible to easily control the pressure of the pressure reducing actuator without using a large pressure reducing valve.

[Brief description of the drawings]

FIG. 1 is a control circuit diagram of a hydraulic actuator showing an embodiment of the present invention, and FIG. 2 is a sectional view of a cartridge valve and a bleed-off valve. FIG. 3 is a control circuit diagram of a hydraulic actuator showing a conventional example. 20 ... Hydraulic cylinder, 22 ... Hydraulic pump, 24 ... Cartridge valve, 25 ... Four-way valve, 26 ... Reservoir, 27 ...
Controller, 29 ... poppet valve, 30 ... electric oil conversion valve,
40,41 …… Pilot room, 42 …… Bleed-off valve, A, B…
... the oil chamber.

Continuation of the front page (56) References JP-A-62-9805 (JP, A) JP-A-60-201102 (JP, A) JP-A-59-199199 (JP, A) JP-A-57-15102 (JP, A) , A) Japanese Utility Model Showa 63-28976 (JP, U) Japanese Utility Model Showa 63-23014 (JP, U)

Claims (1)

(57) [Claims] 1. A poppet valve for changing a passage cross-sectional area in response to a pilot pressure in a passage of a hydraulic fluid communicating with a liquid chamber of a hydraulic actuator, an electro-hydraulic conversion valve for supplying a pilot pressure to the poppet valve, A control circuit for a hydraulic actuator, comprising: a bleed-off valve that recirculates a part of the hydraulic fluid to a reservoir between a poppet valve and the fluid chamber.