JPH04175480A - Control circuit for hydraulic pump - Google Patents

Abstract

PURPOSE:To allow change-over from speed control to pressure control by providing a drain oil passage which is branched from the discharge circuit o a fixed displacement pump to be connected to an oil tank via an unload change-over valve, and thereby releasing the unload change-over valve when the hydraulic pressure within the discharge circuit of a variable displacement pump is equal to a set value. CONSTITUTION:In a hydraulic pump control circuit for an injection molding machine and the like wherein the machine is furnished with the discharge circuit 3a of a variable displacement pump supplying oil to an injection cylinder 10 out of the variable displacement pump 5, and with the discharge circuit 36 of a fixed displacement pump supplying oil to the injection cylinder 10 out of the fixed displacement pump 6, an unload change-over valve 13 is interposed onto a drain oil passage 3d branched from the discharge circuit 3b of the fixed displacement pump. A pilot pressure change-over valve 12 is switched by means of a control device 11 with the output signal of a pressure sensor 7 detecting the pressure of a main hydraulic circuit compared with a set pressure, pilot pressure is then applied to the unload change-over valve 13 at the II position of the valve while the unload change-over valve 13 is designated to its II position, and hydraulic pressure within the discharge circuit 3b of the fixed displacement pump is constituted to be released into an oil tank.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a hydraulic pump control circuit for operating an actuator using both a variable pump and a fixed pump.

(Prior art) Conventionally, resin that has been heated and fluidized in a heating cylinder is injected into a mold under high pressure, cooled and solidified or hardened therein, and then the mold is opened to take out the molded product. In an injection molding machine, various actuators such as an injection device and a mold clamping device are hydraulically operated.

In this case, a hydraulic control circuit is connected to supply a predetermined flow rate of oil to the cylinder of the actuator, and the oil from the supply source discharged by the hydraulic pump is adjusted to a predetermined pressure and flow rate, and the switching valve is controlled. It is designed to be supplied to the cylinder through the cylinder.

However, in order to drive the above-mentioned cylinder, it is necessary to supply a fairly large amount of oil, so if the capacity is to be controlled with one variable pump, a large capacity variable pump is required. Furthermore, by using a large-capacity variable pump, the structure of the variable-capacity mechanism becomes large, and noise is generated when the variable-capacity mechanism is driven. Additionally, the cost of variable pumps is high.

Therefore, a hydraulic control circuit is provided in which one or more fixed pumps are provided to operate the required number of fixed pumps, and a small-capacity variable pump is used to set the pump discharge flow rate to a predetermined value for the standard oil amount.

(1lff to be solved by the invention) However, in the conventional hydraulic pump control circuit described above, flow rate control is performed by adding up the discharge flow rates of the fixed pump and the variable pump, but when the pump load pressure reaches the set pressure, It becomes difficult to switch the variable pump from flow control to pressure control.

In other words, in the case of setting conditions in which a variable pump and a fixed pump are used together, the control signal is the sum of the discharge flow rates, so the discharge volume of the fixed pump is unloaded in order to perform pressure control. In that case, the circuit pressure will rise to the maximum pressure setting of the fixed pump, and there is a risk of destroying the mold, etc.

The present invention solves the problems of the conventional hydraulic pump control circuit described above, and provides a hydraulic pump control circuit that can switch from speed control to pressure control when operating an actuator using both a variable pump and a fixed pump. The purpose is to provide

(Means for solving the problem) To this end, in the hydraulic pump control circuit of the present invention,
A variable pump whose discharge capacity can be changed; a variable pump discharge circuit which supplies oil from the variable pump to the cylinder; a fixed pump whose discharge capacity is constant; A fixed pump discharge circuit that merges into a variable pump discharge circuit is developed.
A set flow rate can be obtained by controlling a variable pump.

In addition, there is a drain oil line that branches from the fixed pump discharge circuit and connects to the oil tank via an unload switching valve, and detects when the oil pressure in the variable pump discharge circuit reaches the set value. Then, it has means for opening the unload switching valve.

(Function) According to the present invention, a variable pump whose discharge capacity can be changed as described above, a variable pump discharge circuit that supplies oil from the variable pump to a cylinder, and a fixed pump whose discharge capacity is constant. The fixed pump supplies oil to the cylinder and also has a fixed pump discharge circuit that merges with the variable pump discharge circuit, so that a set flow rate can be obtained by controlling the variable pump. .

It also has a drain oil line that branches from the fixed pump discharge circuit and connects to the oil tank via an unload switching valve, and detects when the oil pressure in the variable pump discharge circuit reaches the set value. Then, it has means for opening the unload switching valve.

Therefore, for example, when the load pressure of the injection cylinder increases during the injection process and this value reaches an arbitrary set pressure, the process is switched to the pressure holding process.

Then, when switching to the pressure holding process, the discharge amount by the fixed pump is released to the oil tank at low pressure, and the variable pump supplies only the minimum necessary amount of oil, allowing accurate pressure control.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram of a hydraulic pump control circuit of the present invention.

In the figure, 1 is a hydraulic control circuit, 2 is a check valve, and 3a
is a variable pump discharge circuit, 3b is a fixed pump discharge circuit, 3
c and 3d are drain oil passages branched from the fixed pump discharge circuit 3b. Since there is a check valve 2 between the variable pump discharge circuit 3a & fixed pump discharge circuit 3b,
Oil does not flow from the variable pump discharge circuit 3a to the fixed pump discharge circuit 3b.

4 is a safety valve disposed in the drain oil passage 3c and opened when the pressure in the fixed pump discharge circuit 3b reaches a set value;
5 is a variable pump, 6 is a fixed pump, 7 is a pressure sensor for detecting the pressure of the main hydraulic circuit consisting of the variable pump discharge circuit 3a, and 8 is a pressure sensor for comparing the output signal from the pressure sensor 7 with an arbitrary set pressure. It is a comparator. The output of the comparator 8 is sent to a control device 11 in the hydraulic control circuit 1, and the pilot pressure switching valve 12 is switched by the control device 11. The pilot pressure switching valve 12 takes the ■ position and the ■ position, and sends pilot pressure to the unload switching valve 13 in the ■ position. The unload switching valve 13 is disposed in the drain oil passage 3d, and has two positions: (1) and (2), and releases the hydraulic pressure in the fixed pump discharge circuit 3b to the oil tank at (2).

Further, 9 is a cylinder direction switching valve. The cylinder direction switching valve 9 takes the summer position, the ■ position, and the N position, and in the summer position supplies oil to the oil chamber 10a of the injection cylinder 1G;
Oil is supplied to the oil chamber 10b at the position.

In the hydraulic pump control circuit configured as described above, when oil is supplied to the oil chamber 10b of the injection cylinder IO, a screw (not shown) moves to the left to perform injection.

At this time, the load pressure P of the injection cylinder 1G increases at the final stage of the injection stroke, but when P matches the arbitrarily set set pressure P1, it is determined that the injection stroke has ended, and the pressure holding stroke is started. to move to.

At this time, a switching signal is output from the comparator 8 to the control device 11, the fixed pump 6 is unloaded by the hydraulic control circuit 1, and the subsequent pressure holding control is performed only by the variable pump 5.

Note that the present invention is not limited to the above embodiments,
Various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

(Effects of the Invention) As described in detail above, according to the present invention, there is provided a variable pump capable of changing the discharge capacity, a variable pump discharge circuit that supplies oil from the variable pump to a cylinder, and a variable pump whose discharge capacity is variable. It has a fixed pump and a fixed pump discharge circuit that supplies oil to the cylinder from the fixed pump and joins the variable pump discharge circuit, and it is possible to obtain a set flow rate by controlling the variable pump. It is now possible to do so.

It has a drain oil path branched from the fixed pump discharge circuit and connected to the oil tank via an unload switching valve, and detects when the oil pressure in the variable pump discharge circuit reaches the set value. Then, a means is developed to open the unload switching valve.

Therefore, even when switching from the injection process to the pressure holding process, pressure control can be performed by the variable pump, and power consumption can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a hydraulic pump control circuit of the present invention. 1... Hydraulic control circuit, 2... Check valve, 3a...
・Variable pump discharge circuit, 3b... Fixed pump discharge circuit, 3c, 3d... Drain oil path, 4... Safety valve, 5
... Variable pump, 6... Fixed pump, 7... Pressure sensor, 8... Comparator, 9... Cylinder direction switching valve, 10... Injection cylinder, 10a. 10b...Oil chamber, 11...Control device, 12...Pilot pressure switching valve, 13...Unload switching valve.

Claims (1)

[Claims] (a) A variable pump whose discharge capacity can be varied; (b) A variable pump discharge circuit that supplies oil from the variable pump to a cylinder; (c) A fixed pump whose discharge capacity is constant. (d) A fixed pump discharge circuit that supplies oil from the fixed pump to the cylinder and merges with the variable pump discharge circuit; (e) A fixed pump discharge circuit that branches from the fixed pump discharge circuit and supplies oil to the cylinder through an unload switching valve. A drain oil passage connected to an oil tank; and (f) means for detecting that the oil pressure in the variable pump discharge circuit reaches a set value and opening the unload switching valve. Hydraulic pump control circuit.