JP4858009B2 - Hydraulic system - Google Patents

Description

  The present invention relates to a hydraulic system that is used in, for example, an injection molding machine, a machine tool, and the like and performs pressure holding control.

  Conventionally, in this type of hydraulic system, the pressure of the load line of the switching valve is detected by a pressure sensor when the hydraulic cylinder is in a holding state, and the detected pressure of the pressure sensor is lower than a predetermined set value. In some cases, the controller drives the hydraulic motor through the motor only when the voltage drops, so that the drive of the motor is minimized and the energy loss is reduced (Patent Document 1: Japanese Patent Laid-Open No. 2004-260688). 2005-90705).

However, in the above-described conventional hydraulic system, when the pressure holding operation continues for a long time and the pressure in the load line hardly decreases, the hydraulic pump is hardly driven or is driven for a very short time. The temperature of the oil does not rise, and the viscosity of the hydraulic oil increases during cold weather. Therefore, the conventional hydraulic system has a problem that even when energy can be saved during the pressure holding operation, the response at the time of starting the hydraulic cylinder is deteriorated in cold weather.
JP-A-2005-90705

  SUMMARY OF THE INVENTION An object of the present invention is to provide a hydraulic system that can save energy during a pressure-holding operation and improve the responsiveness of a hydraulic cylinder or the like during cold weather.

In order to solve the above problems, the hydraulic system of the present invention is:
A hydraulic pump;
A motor that drives the hydraulic pump;
A switching valve having a pump port connected to the hydraulic pump via a main line;
A hydraulic actuator connected to the first load port of the switching valve;
A first pressure sensor for detecting the pressure between the first load port and the hydraulic actuator of the switching valve,
A temperature sensor for detecting the temperature of the hydraulic oil discharged from the hydraulic pump;
A relief valve connected to the main line;
During holding pressure operation of the hydraulic actuator, when the detected temperature is above the set temperature a predetermined of the temperature sensor, the pump driving detecting pressure detected is the first pressure sensor is a predetermined lower than the holding pressure between becomes the pressure, the detected pressure of the first pressure sensor until the holding pressure, to drive the hydraulic pump through the motor, and the pump port and the first load port of the switching valve closed so they communicate, while controlling the switching valve, in the case of the below set temperature detected temperature of the temperature sensor is predetermined, between the pump port and the first load port of the switching valve controls the switching valve so that, as the relief valve is opened, and characterized in that the hydraulic pump and a controller for controlling via the motor To have.

  According to the above configuration, the controller detects the pressure detected by the first pressure sensor when the temperature detected by the temperature sensor is equal to or higher than a preset temperature during the pressure holding operation of the hydraulic actuator. When a predetermined pump driving pressure lower than the pressure is reached, the hydraulic pump is driven through the motor until the detected pressure of the first pressure sensor becomes the holding pressure, and the pump port of the switching valve and the first The switching valve is controlled so as to communicate with the load port. In this way, the hydraulic pump is driven by the motor only when the pressure input to the hydraulic actuator becomes equal to or lower than the pump driving pressure, and the hydraulic oil is supplied to the hydraulic actuator, so that the hydraulic pump is always driven. Since there is nothing, energy loss can be reduced.

  On the other hand, the controller is configured to close between the pump port of the switching valve and the first load port when the detected temperature of the temperature sensor is lower than a preset temperature during the pressure holding operation of the hydraulic actuator. In addition to controlling the switching valve, the hydraulic pump is controlled via a motor so that the relief valve is opened.

  As described above, when the pressure is maintained during the pressure holding operation, the high pressure hydraulic oil is discharged from the relief valve to the tank, and the pressure energy of the hydraulic oil is converted into the temperature energy to quickly increase the oil temperature. Even at times, the viscosity of the hydraulic oil can be lowered to obtain sufficient responsiveness.

The hydraulic system of one embodiment
A second pressure sensor for detecting the pressure of the main line;
The controller, at the time of holding pressure operation of the hydraulic actuator, when the detected temperature of the temperature sensor is below a predetermined the set temperature, the detected pressure of the second pressure sensor is preliminarily higher than the holding pressure The hydraulic pump is controlled via the motor so as to obtain a predetermined relief valve opening pressure.

  According to the embodiment, the controller detects the pressure detected by the second pressure sensor when the temperature detected by the temperature sensor is lower than a preset temperature during the pressure holding operation of the hydraulic actuator. The hydraulic pump is controlled via the motor so that a predetermined relief valve opening pressure higher than the pressure and pressure is controlled. Therefore, the pressure on the main line is controlled to the predetermined relief valve opening pressure, and the relief valve is opened. The relief valve can be opened at an optimum pressure without generating excessive pressure and excessive discharged oil.

In one embodiment,
Connect the check valve between the first load port and the hydraulic actuator of the switching valve,
The first pressure sensor detects the pressure between the check valve and the hydraulic actuator.

  According to the above-described embodiment, since the check valve is connected between the first load port of the switching valve and the hydraulic actuator, it is possible to reduce the leakage of hydraulic oil during pressure holding. In general, the check valve has less leakage than the switching valve, and the hydraulic oil is blocked by both the check valve and the switching valve, so that leakage of the hydraulic oil during holding can be reduced.

  Moreover, since the first pressure sensor detects the pressure between the check valve and the hydraulic actuator, the input pressure of the hydraulic actuator can be directly detected, and the pressure control during holding is accurately performed. Can do.

  According to the present invention, in the hydraulic system, energy can be saved during the pressure holding operation, and the responsiveness of the hydraulic actuator such as the hydraulic cylinder can be improved during cold weather.

  Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

  As shown in FIG. 1, a pump port P of a three-position electromagnetic switching valve 2 as an example of a switching valve is connected to a hydraulic pump 1 via a main line 3. A hydraulic cylinder 5 as an example of a hydraulic actuator is connected to a first load port A of the electromagnetic switching valve 2 via a check valve 6. The check valve 6 is configured such that the flow from the first load port A toward the hydraulic cylinder 5 is in the forward direction. A first pressure sensor 7 is connected between the check valve 6 and the hydraulic cylinder 5.

  On the other hand, a second pressure sensor 8 is connected to the main line 3. A relief valve 11 is connected to the main line 3. The hydraulic oil discharged from the relief valve 11 is returned to the tank 12. Further, the hydraulic oil discharged from the tank port T of the electromagnetic switching valve 2 is also returned to the tank 12.

  Further, a temperature sensor 13 for detecting the temperature of the hydraulic oil discharged from the hydraulic pump 1 is provided in the main line 3.

  The hydraulic pump 1 is driven by a motor 15. The operation of the motor 15 is controlled by the controller 20. The controller 20 receives the outputs of the first pressure sensor 7, the second pressure sensor 8 and the temperature sensor 13 and controls the hydraulic pump 1 and the electromagnetic switching valve 2.

  The controller 20 includes an inverter unit 21, a control unit 22, a temperature determination unit 23, a pressure holding control unit 24, and a temperature increase control unit 25. The control unit 22 also serves as a control unit for the inverter unit 21 and controls pressure and flow rate. Specifically, the control unit 22 controls the rotation speed of the motor 15 via the inverter unit 21 so that the output of the second pressure sensor 8 becomes a value according to the pressure command, and also according to the flow rate command. The rotational speed of the motor 15 is controlled via the inverter unit 21 so as to be the rotational speed of the hydraulic pump 1. Further, the control unit 22 outputs a signal for controlling the switching position of the electromagnetic switching valve 2 to the electromagnetic switching valve 2.

  The temperature determination unit 23 receives a signal indicating the detected temperature from the temperature sensor 13 and determines whether or not the detected temperature is equal to or higher than a preset temperature.

  The pressure holding control unit 24 performs pressure holding control when receiving a pressure holding command. That is, when the holding pressure command is received, the holding pressure control unit 24 drives the motor 15 via the inverter unit 21 until the first pressure sensor 7 detects the holding pressure, as shown in FIG. When the first pressure sensor 7 detects the holding pressure, the electromagnetic switching valve 2 is positioned at the neutral position S0 that blocks all the ports, and the driving of the motor 15 is stopped to make the discharge flow rate zero. Then, while the holding pressure command is valid, the detected pressure output from the first pressure sensor 7 is monitored, and when the detected pressure becomes a predetermined pump driving pressure lower than the holding pressure, the first pressure sensor The hydraulic pump 1 is driven through the inverter unit 21 and the motor 15 until the detected pressure 7 becomes the holding pressure, and the electromagnetic switching valve 2 is positioned at the switching position S1, and the pump port P and the first load Communication with port A is established.

  As described above, during the pressure holding operation, the hydraulic pump 1 is activated only when the first pressure sensor 7 detects that the pressure input to the hydraulic cylinder 5 is equal to or lower than the predetermined pump driving pressure. Although it is driven by the motor 15, in other cases, the hydraulic pump 1 is not driven, so that energy loss can be reduced.

  On the other hand, the temperature increase control unit 25 determines whether the pressure holding command is valid, that is, during the pressure holding operation, a signal indicating that the temperature detected by the temperature sensor 13 is lower than a preset temperature. When received from the section 23, the electromagnetic switching valve 2 is controlled to be positioned at the neutral position S0, the space between the pump port P and the first load port A is closed, and the pressure of the main line 3 is set to the relief valve opening pressure. The hydraulic pump 1 is driven via the inverter unit 21 and the motor 15 so that the relief valve 11 is opened. This relief valve opening pressure opens the relief valve 11, but is not excessively high, and the amount of oil discharged from the relief valve 11 does not become excessive. Optimal pressure.

  In this way, in the pressure holding state during cold weather, as shown in FIG. 3, the hydraulic pump 1 is controlled so that the detected pressure of the second pressure sensor 8 becomes the relief valve opening pressure, and the relief valve 11. The high-pressure hydraulic oil is discharged from the tank 12 to the tank 12, and the pressure energy of the hydraulic oil is converted into temperature energy to quickly increase the oil temperature. Therefore, the viscosity of the hydraulic oil can be lowered and sufficient responsiveness can be obtained in the subsequent operation even in cold weather or in the pressure holding operation.

  In the above embodiment, since the check valve 6 is connected between the first load port A of the electromagnetic switching valve 2 and the hydraulic cylinder 5, leakage of hydraulic oil can be reduced during pressure holding. In particular, since the hydraulic oil is blocked by both the check valve 6 and the electromagnetic switching valve 2, leakage of the hydraulic oil at the time of holding pressure can be reduced.

  In the above embodiment, the controller 20 determines that the detected pressure of the second pressure sensor 8 is higher than the holding pressure when the detected temperature of the temperature sensor 13 is lower than a preset temperature during the holding operation of the hydraulic pump 1. Although the rotational speed of the hydraulic pump 1 is controlled via the inverter unit 21 and the motor 15 so as to obtain a higher predetermined relief valve opening pressure, the rotational speed of the motor should not be controlled during the temperature raising operation. Alternatively, the motor may be simply turned on and the hydraulic oil may be discharged from the relief valve to raise the temperature of the hydraulic oil.

  In the above embodiment, the check valve 6 is connected between the first load port A of the electromagnetic switching valve 2 and the hydraulic cylinder 5, but the check valve is not provided, and the hydraulic oil is blocked by the switching valve. You may make it do.

1 is a circuit diagram of a hydraulic system according to an embodiment of the present invention. It is a graph which shows the normal pressure-holding driving | operation of the said embodiment. It is a graph which shows the temperature rising operation of the said embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hydraulic pump 2 Electromagnetic switching valve 3 Main line 5 Hydraulic cylinder 6 Check valve 7 1st pressure sensor 8 2nd pressure sensor 11 Relief valve 13 Temperature sensor 15 Motor 20 Controller 21 Inverter part 22 Control part 23 Temperature discrimination part 24 Holding pressure control Part 25 Temperature rise control part

Claims (3)

A hydraulic pump (1);
A motor (15) for driving the hydraulic pump (1);
A switching valve (2) having a pump port (P) connected to the hydraulic pump (1) via a main line (3);
A hydraulic actuator (5) connected to the first load port (A) of the switching valve (2);
The first load port of the switching valve (2) (A) and the first pressure sensor (7) for detecting the pressure between the hydraulic actuator (5),
A temperature sensor (13) for detecting the temperature of the hydraulic oil discharged from the hydraulic pump (1);
A relief valve (11) connected to the main line (3);
During the pressure holding operation of the hydraulic actuator (5), when the temperature detected by the temperature sensor (13) is equal to or higher than a preset temperature, the detected pressure detected by the first pressure sensor (7) is the pressure holding pressure. becomes a predetermined pump drive pressure less than the above to the detection pressure of the first pressure sensor (7) is the holding pressure, through the motor (15) to drive the hydraulic pump (1) while between said pump port (P) and the first load port of the switching valve (2) (a) is to communicate, to control the switching valve (2), said temperature sensor (13) in the case of the below set temperature detected temperature is predetermined, the switching valve (2) of the switching valve so as to close between the pump port (P) and the first load port (a) (2) And the relief valve ( As 1) is opened, the hydraulic system, characterized in that the hydraulic pump (1) and a controller (20) controlled via the motor (15). The hydraulic system according to claim 1,
A second pressure sensor (8) for detecting the pressure of the main line (3);
The controller (20), at the time of holding pressure operation of the hydraulic actuator (5), in the case of the less than the set temperature the detected temperature is determined in advance of the temperature sensor (13), said second pressure sensor (8) hydraulic system detected pressure, so that the higher predetermined relief valve opening pressure than the dwell pressure, characterized in that for controlling the hydraulic pump (1) through the motor (15). The hydraulic system according to claim 1 or 2,
The connecting check valve (6) between the switching valve (2) of the first load port (A) and said hydraulic actuator (5),
It said first pressure sensor (7), hydraulic system and detects the pressure between the check valve (6) and the hydraulic actuator (5).

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