JPH0148403B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hydraulic system for an injection molding machine, and more particularly to an improvement in a cooling circuit for hydraulic oil when a variable displacement pump is used as a driving source.

Conventional injection molding machines generally use a constant discharge pump as the drive source, and in this case, a large amount of excess oil is discharged from the relief valve, so it is necessary to install a heat exchanger in the discharge circuit. The hydraulic oil was then cooled down.

However, recently, due to energy issues, variable displacement pumps have become widely used. When using this variable displacement pump, the relief valve is used differently from conventional constant displacement pumps, and the amount of oil discharged from the relief valve is very small, and a heat exchanger is inserted here to cool the hydraulic oil. Can not do it. For this reason, a heat exchanger may be installed in either the return oil circuit of the actuator, which discharges a relatively large amount of oil, or the case drain circuit of the variable displacement pump, which discharges a small amount of oil at a relatively high temperature. However, the discharge of hydraulic oil to the return oil circuit of the actuator is intermittent, and the operating time is short compared to the molding cycle, and the amount of oil discharged from the case drain circuit is small. Even if a heat exchanger is provided only on one side, the cooling capacity will be insufficient.

For this reason, as shown in FIG. 1, a heat exchanger is provided in each of the return oil circuit of the actuator and the case drain circuit of the variable displacement pump that constantly discharges a small amount of relatively high temperature oil. To briefly explain the circuit diagram of FIG. 1 showing this conventional example, the hydraulic oil sucked from the oil tank 6 via the suction filter 5 and the pipe line 11 by the variable discharge amount pump 1 is high-pressure oil. Natsute Pipeline 1
2a, and a control valve 7 necessary for controlling the actuator 2 such as pressure, flow rate adjustment, opening/closing control, etc.
is sent to the actuator 2 from the conduit 12b. The return oil from the actuator 2 is sent to one of the heat exchangers 3a through a pipe 13a and cooled, and then passes through a line filter 4 from a pipe 13b to a pipe 13c.
The oil is discharged from the oil tank 6 into the oil tank 6. Further, the case drain of the variable discharge amount pump 1 passes through the pipe line 14a and is cooled by the other heat exchanger 3b.
The oil is discharged from b into the oil tank 6.

Providing a heat exchanger in the return oil circuit of the actuator and the case drain circuit of the variable displacement pump in this way not only makes the injection molding machine more expensive, but also requires a large assembly space. In addition, maintenance is not easy and is troublesome.

However, if the above-mentioned two circuits could be combined and passed through a single heat exchanger, the above problem would be solved, but the allowable pressure of the case drain circuit of a variable displacement pump is several kg/cm ² or less. The pressure in the return oil circuit of the actuator often exceeds this, so if both circuits are combined, the pressure in the case drain circuit will exceed the allowable pressure, which may cause problems such as damage to the variable displacement pump. arise. For this reason, it is not possible to combine both circuits, and conventionally, even with the above-mentioned drawbacks, it was necessary to provide a heat exchanger for each circuit.

The present invention solves the above-mentioned difficulties and enables sufficient heat exchange with a single heat exchanger even when a variable displacement pump is used. A variable discharge amount pump, a heat exchanger connected to the return oil circuit of the actuator that intermittently discharges hydraulic oil and cools the hydraulic oil and releases it to an oil tank, and a case for the variable discharge amount pump that constantly discharges the hydraulic oil. A valve that connects the drain circuit and the return oil circuit and drains hydraulic oil only from the case drain circuit side to the return oil circuit side; and a valve that is connected to the case drain circuit and that the return oil circuit discharges the return oil of the actuator. It consists of a valve that opens to release hydraulic oil into the oil tank when in use.

Hereinafter, preferred embodiments of the present invention will be described in detail based on the accompanying drawings. Components in the drawings that are the same as those in FIG. 1 will be described with the same reference numerals.

The hydraulic oil in the oil tank 6 is sucked into the variable discharge amount pump 1 from the pipe line 11 through the suction filter 5, and is discharged as high-pressure oil into the pipe line 12a.
The pressure and the like are controlled by the control valve 7, and the pipe is arranged so that it is sent to the actuator 2 from the pipe line 12b.

The return oil from the actuator 2 is sent from the pipe line 23a through the line filter 4 and the pipe line 23b to the heat exchanger 3, and the return oil cooled in the heat exchanger 3 returns to the tank 6 through the pipe line 23c. It is piped as follows. Note that a return oil circuit 23 for the actuator 2 is formed by the pipes 23a and 23b.

On the other hand, the case drain line 24a from the variable discharge rate pump 1 is branched into a line 24b and a line 24c from the middle, and the case drain circuit 24 of the variable discharge rate pump 1 is formed by the lines 24a, 24b, and 24c. Ru. The pipe line 24c is connected to the pipe line 2 through the check valve 8.
3d so as to communicate with the pipe line 23b. Note that the backflow prevention valve 8 is connected to the case drain circuit 2.
4 to the return oil circuit 23. Further, the pipe line 24b is connected to the oil tank 6 via the pressure release valve 9 from the pipe line 24d. This pressure release valve 9 is operated at a pressure that is within the allowable pressure range of the case drain of the variable displacement pump 1 and slightly higher than the operating pressure of the check valve 8 when return oil is not discharged from the actuator 2. It is set to be open.

To explain the operation of the present invention configured in this way, the injection molding machine includes an actuator 2 driven by hydraulic pressure such as a mold clamping cylinder, an injection cylinder, and a screw rotation oil motor. The discharged pressure oil passes through various control valves 7 and is sent to these actuators 2 to operate, and normally, the process is performed as follows: mold closing → injection filling →
Repeat the main cycle of screw rotation and mold opening. During this time, each actuator 2 operates only during its role and discharges a relatively large amount of return oil. Note that it is preferable to select a screw rotation oil motor with a large amount of return oil as the actuator 2, and to cool the return oil. On the other hand, the case drain of the variable displacement pump 1 constantly discharges relatively high temperature hydraulic oil, albeit in a small amount.

When the actuator 2 is not operating and therefore the return oil is not being discharged, the pipe 23d
There is no pressure inside, and the oil discharged from the case drain of the variable displacement pump 1 passes through pipes 24a and 24c, opens the check valve 8, passes through pipes 23d and 23b, and is cooled through the heat exchanger 3. , is discharged into the oil tank 6. On the other hand, when the actuator 2 is operated and the return oil is discharged and a pressure higher than that of the pipe line 24c acts on the pipe line 23d, the check valve 8 is thereby closed. For this reason, the case drain circuit 24
The internal pressure rises slightly, and the pressure release valve 9 is opened, and the discharged oil from the case drain of the variable displacement pump 1 is discharged into the oil tank 6.

When the actuator 2 stops again and no longer discharges the return oil, the pressure in the pipe 23d decreases, the check valve 8 opens, and the discharged oil from the case drain of the variable displacement pump flows out into the pipe 23d. The pressure release valve 9 is now closed.

Incidentally, the pressure release valve 9 may be replaced by a pilot check valve 9' as shown in FIG. The pilot check valve 9' is driven by providing a pilot circuit 25 connected to the conduit 12b to the actuator 2. That is, at the same time that the actuator 2 starts operating, the pilot check valve 9' is opened and the discharged oil from the case drain of the variable displacement pump 1 is discharged from the pipe 24d to the oil tank 6, and the pressure in the pipe 12b is reduced. When it runs out, actuator 2 stops operating and conduit 2
As the pressure inside 3b decreases and the pilot check valve 9' is closed, the discharged oil from the case drain of the variable displacement pump 1 flows into the heat exchanger 3 through the non-return valve 8 and is cooled there. and is discharged into the oil tank 6.

By using the pilot check valve 9' linked to the actuator 2 in this way, the case drain of the variable displacement pump 1 can be made to have a lower pressure, and the shock pressure generated when the pressure release valve 9 is activated can be eliminated. Therefore, the reliability of the variable discharge amount pump 1 can be improved. The pilot circuit 25 may be taken from the control valve 7 of the actuator 2, or may be a separate electromagnetic switching valve operated by an electric signal. Further, when the capacity of the variable discharge amount pump 1 is small, a direct electromagnetic switching section may be provided in place of the pilot check valve 9'.

In this way, according to the present invention, the return oil circuit of the actuator and the case drain circuit of the variable displacement pump can be switched alternately without any damage to the variable displacement pump, and can be operated by one heat exchanger. The hydraulic oil can be cooled, and the installation space for the heat exchanger is small, making design easier.
Also, the piping for the cooling water circuit only needs to be one system.
Assembly and maintenance become easy, and the cost of the device can be reduced.

Furthermore, conventionally, the heat exchanger did not work when there was no return oil from the actuator, but the heat exchanger is now effectively used all the time, which has great effects such as helping to save water.

Although the present invention has been variously explained above with reference to preferred embodiments, the present invention is not limited to these embodiments, and it goes without saying that many modifications can be made without departing from the spirit of the invention. It is.

[Brief explanation of drawings]

FIG. 1 is a hydraulic circuit diagram of a conventional example, FIG. 2 is a circuit diagram of a hydraulic system according to the present invention, and FIG. 3 is a circuit diagram showing another embodiment. 1... Variable discharge amount pump, 2... Actuator,
3, 3a, 3b...Heat exchanger, 4...Line filter, 5...Suction filter, 6...Oil tank, 7...Control valve, 8...Return prevention valve, 9...Pressure release valve, 9'...Pilot check valve, 11, 12a,
12b, 13a, 13b, 13c, 14a, 14
b...Pipe line, 23...Return oil circuit, 23a, 23b,
23c, 23d...Pipeline, 24...Case drain circuit, 24a, 24b, 24c, 24d...Pipeline, 2
5...Pilot circuit.

Claims (1)

[Claims] 1. A variable discharge pump as a hydraulic power source for driving an actuator, a heat exchanger connected to the return oil circuit of the actuator that intermittently discharges hydraulic oil and cools the hydraulic oil and releases it into an oil tank, and a heat exchanger that constantly discharges hydraulic oil. A valve that connects the case drain circuit of the variable discharge amount pump and the return oil circuit to drain hydraulic oil only from the case drain circuit side to the return oil circuit side, and a valve that is connected to the case drain circuit and the return oil circuit. A hydraulic system for an injection molding machine consisting of a valve that opens to release hydraulic oil into an oil tank when the circuit is used to drain actuator return oil.