Hydraulic system

Abstract

To provide a hydraulic device that can perform stable pressure control.SOLUTION: A hydraulic device includes: a pressure-reducing valve (20) including a valve element (20a) for decompressing hydraulic fluid to be supplied from a hydraulic source (S) to an actuator (10), a pilot port (20b) to which pilot pressure for controlling operation of the valve element (20a) is input and a spring (20c) for biasing the valve element (20a) in a direction resisting the pilot pressure; a hydraulic pump (P) for supplying the hydraulic fluid from an oil tank (T) to the pilot port (20b) of the pressure-reducing valve (20); a pressure sensor (PS) for detecting pressure of the hydraulic fluid discharged from the hydraulic pump (P); and a control device (30) for controlling revolution speed of the hydraulic pump (P) so as to control the pressure of the hydraulic fluid which is detected by the pressure sensor (PS) to be a predetermined pressure.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to hydraulic systems. [Background technology]

[0002] Conventionally, there is a hydraulic device in which pressure control is performed by a main valve provided in a main line between a hydraulic source and a hydraulic cylinder, and an electromagnetic proportional relief valve connected to a pilot line of the main valve (see, for example, JP 6-94002 A (Patent Document 1)). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-94002 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above hydraulic system, the pilot pressure that controls the main valve is controlled by a small-capacity electromagnetic proportional relief valve, which limits the flow rate that controls the main valve, slowing response and reducing stability, resulting in a problem of poor stability of pressure control by the main valve.

[0005] The present disclosure proposes a hydraulic device capable of stable pressure control. [Means for solving the problem]

[0006] The hydraulic system of the present disclosure comprises: a pressure reducing valve including a valve body for reducing the pressure of hydraulic oil supplied from a hydraulic power source to an actuator, a pilot port to which a pilot pressure for controlling the operation of the valve body is input, and a spring for biasing the valve body in a direction against the pilot pressure; a hydraulic pump for supplying hydraulic oil from an oil tank to the pilot port of the pressure reducing valve; a pressure sensor for detecting a pressure of the hydraulic oil discharged from the hydraulic pump; a control device that controls the rotation speed of the hydraulic pump so that the pressure of the hydraulic oil detected by the pressure sensor becomes a predetermined pressure; Equipped with.

[0007] According to the present disclosure, by controlling the hydraulic pump speed with a control device so that the pressure of the hydraulic oil detected by the pressure sensor becomes a predetermined pressure, the controllability of the pilot pressure of the pressure reducing valve is improved, thereby enabling stable pressure control.

[0008] In addition, in a hydraulic device according to one aspect of the present disclosure, a relief valve for returning hydraulic oil discharged from the actuator to the oil tank; Hydraulic oil from the oil tank is supplied from the hydraulic pump to the pilot port of the relief valve.

[0009] According to the present disclosure, the pilot pressure of the relief valve can be controlled by controlling the rotation speed of the hydraulic pump, and the hydraulic oil discharged from the actuator can be returned to the oil tank. Also, the pilot pressure of both the pressure reducing valve and the relief valve can be controlled by controlling the rotation speed of one hydraulic pump. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic block diagram of a hydraulic device according to a first embodiment of the present disclosure. [Diagram 2] FIG. 4 is a schematic block diagram of a hydraulic device according to a second embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment will be described. In the drawings, the same reference numerals denote the same or corresponding parts.

[0012] [First embodiment] 1 is a schematic block diagram of a hydraulic device according to a first embodiment of the present disclosure, which is used in industrial machinery such as a molding machine.

[0013] 1, the hydraulic device of the first embodiment includes a pressure reducing valve 20 that reduces the pressure of hydraulic oil from a hydraulic source S and supplies the reduced pressure to a hydraulic cylinder 10, a hydraulic pump P that controls the pilot pressure of the pressure reducing valve 20, a motor M that drives the hydraulic pump P, a pressure sensor PS that detects the pressure of the hydraulic oil discharged from the hydraulic pump P, and a control device 30 that controls the pressure of the hydraulic oil discharged from the hydraulic pump P. The hydraulic cylinder 10 is an example of an actuator. The hydraulic pump P is a fixed displacement hydraulic pump.

[0014] The hydraulic cylinder 10 has a cylinder tube 11, a piston 12 that reciprocates within the cylinder tube 11, and a piston rod 13 one end of which is connected to the piston 12.

[0015] The pressure reducing valve 20 is a three-port normally closed type pressure reducing valve that also performs directional control. A hydraulic source S is connected to a first port 21 of the pressure reducing valve 20, and an oil tank T is connected to a second port 22 of the pressure reducing valve 20. A port 10a of the hydraulic cylinder 10 is connected to a third port 23 of the pressure reducing valve 20.

[0016] The pressure reducing valve 20 has a spool 20a as an example of a valve body, a pilot port 20b to which a pilot pressure for controlling the operation of the spool 20a is input, and a spring 20c for biasing the spool 20a in a direction against the pilot pressure. When the pilot pressure is zero, the pressure reducing valve 20 is switched to the left, the second port 22 and the third port 23 are connected, and the first port 21 is closed. On the other hand, when the pilot pressure is equal to or higher than a preset first pressure, the pressure reducing valve 20 is switched to the right, the first port 21 and the third port 23 are connected, and the second port 22 is closed.

[0017] The discharge pressure (pilot pressure) of the hydraulic pump P is applied to the pilot port 20b of the pressure reducing valve 20, and the hydraulic oil supplied from the hydraulic source S to the first port 21 is reduced in pressure by the pressure reducing valve 20. The hydraulic oil reduced in pressure by the pressure reducing valve 20 is supplied to the hydraulic cylinder 10 from the third port 23 of the pressure reducing valve 20.

[0018] The control device 30 receives a pressure command signal representing a pressure command value and a pressure signal from the pressure sensor PS, and outputs a drive signal for driving the motor M, thereby controlling the rotation speed of the hydraulic pump P.

[0019] The control device 30 controls the rotation speed of the hydraulic pump P to perform pressure control proportional to the pilot pressure while the pilot pressure of the pressure reducing valve 20 changes from a preset first pressure to a second pressure (<first pressure). Next, when the pilot pressure of the pressure reducing valve 20 is reduced from the second pressure, relief control proportional to the pilot pressure is performed to return the hydraulic oil discharged from the hydraulic cylinder 10 to the oil tank T.

[0020] According to the hydraulic device having the above configuration, the pressure of the hydraulic oil from the hydraulic source S is reduced by the pressure reducing valve 20, and pressure control is performed so that the pressure of the hydraulic oil supplied to the port 10a of the hydraulic cylinder 10 (the secondary pressure of the pressure reducing valve 20) becomes a pressure command value (predetermined pressure). Here, since the discharge pressure (pilot pressure) of the hydraulic pump P and the secondary pressure of the pressure reducing valve 20 are proportional to each other, the discharge pressure (pilot pressure) of the hydraulic pump P is controlled by the control device 30 based on a preset equation expressing this proportional relationship. By performing this pressure control by the hydraulic pump P with high accuracy and high speed, the controllability of the pilot pressure of the pressure reducing valve 20 is improved, and therefore the secondary pressure of the pressure reducing valve 20 can be stably controlled.

[0021] In addition, in the above hydraulic device, the spool 20a of the pressure reducing valve 20 is biased by the spring 20c in a direction against the pilot pressure, so that the secondary pressure of the pressure reducing valve 20 can be controlled from a low pressure. If a spring is provided to bias the spool 20a of the pressure reducing valve 20 in the same direction as the pilot pressure, the secondary pressure of the pressure reducing valve 20 can only be reduced to the minimum control pressure even if the pilot pressure is set to zero because of the spring pressure.

[0022] In the conventional hydraulic system of Patent Document 1, the suction force of the solenoid of the electromagnetic proportional relief valve used is about 60 to 80 N (6 to 8 kgf), and the diameter of the needle valve is limited, so the flow rate controlling the main valve is limited, and the inertia of the solenoid movable core also has an effect, resulting in problems such as slow response and low stability. In contrast, the hydraulic system of the above first embodiment makes it possible to obtain a significantly more stable secondary pressure.

[0023] Furthermore, in the hydraulic system of the first embodiment, the rotation speed of the hydraulic pump P is stably controlled by feedback control of the pressure detected by the pressure sensor PS. Therefore, the above hydraulic system is not affected by the oil temperature characteristics of conventional fixed throttles, flow control valves, electromagnetic proportional relief valves, etc.

[0024] In addition, in the hydraulic device of the first embodiment, by controlling the secondary pressure of the pressure reducing valve 20 using minor feedback control, the pressure command value and the secondary pressure of the pressure reducing valve 20 are in a proportional relationship, and hysteresis and repeatability are significantly improved.

[0025] Second Embodiment 2 is a schematic block diagram of a hydraulic system according to a second embodiment of the present disclosure. The hydraulic system according to the second embodiment has the same configuration as the hydraulic system according to the first embodiment, except for a pressure reducing valve 40 and a relief valve 50.

[0026] 2, the hydraulic device of the second embodiment includes a pressure reducing valve 40 that reduces the pressure of hydraulic oil from a hydraulic source S and supplies it to a hydraulic cylinder 10, a hydraulic pump P that controls the pilot pressure of the pressure reducing valve 20, a motor M that drives the hydraulic pump P, a pressure sensor PS that detects the pressure of the hydraulic oil discharged from the hydraulic pump P, a relief valve 50 that returns the hydraulic oil discharged from the hydraulic cylinder 10 to an oil tank T, and a control device 30 that controls the pressure of the hydraulic oil discharged from the hydraulic pump P. The hydraulic cylinder 10 is an example of an actuator.

[0027] The pressure reducing valve 40 is a two-port normally closed type pressure reducing valve. A hydraulic source S is connected to a first port 41 of the pressure reducing valve 40, and a port 10a of the hydraulic cylinder 10 is connected to a second port 42 of the pressure reducing valve 40.

[0028] This pressure reducing valve 40 has a spool 40a as an example of a valve body, a pilot port 40b to which pilot pressure is input to control the operation of the spool 40a, and a spring 40c that biases the spool 40a in a direction against the pilot pressure.

[0029] The relief valve 50 has an inlet port 51 connected to the port 10a of the hydraulic cylinder 10, an outlet port 52 connected to the oil tank T, and a pilot port 53 connected to the discharge side of the hydraulic pump P. The relief valve 50 is a pilot-operated relief valve. The discharge pressure (pilot pressure) of the hydraulic pump P is supplied to the pilot port 53 of the relief valve 50, and the set pressure of the relief valve 50 is controlled.

[0030] The discharge pressure (pilot pressure) of the hydraulic pump P is applied to the pilot port 40b of the pressure reducing valve 40, and the hydraulic oil supplied from the hydraulic source S to the first port 21 is reduced in pressure by the pressure reducing valve 40. The hydraulic oil reduced in pressure by the pressure reducing valve 40 is supplied to the hydraulic cylinder 10 from the third port 23 of the pressure reducing valve 40.

[0031] The control device 30 receives a pressure command signal representing a pressure command value and a pressure signal from the pressure sensor PS, and outputs a drive signal for driving the motor M, thereby controlling the rotation speed of the hydraulic pump P.

[0032] The control device 30 controls the rotation speed of the hydraulic pump P to perform pressure control proportional to the pilot pressure while the pilot pressure of the pressure reducing valve 40 changes from a predetermined first pressure to a second pressure (<first pressure). Next, when the pilot pressure of the relief valve 50 is reduced from a predetermined third pressure (<second pressure), relief control proportional to the pilot pressure is performed to return the hydraulic oil discharged from the hydraulic cylinder 10 to the oil tank T via the relief valve 50.

[0033] According to the hydraulic device having the above configuration, the pressure of the hydraulic oil from the hydraulic source S is reduced by the pressure reducing valve 40, and pressure control is performed so that the pressure of the hydraulic oil supplied to the port 10a of the hydraulic cylinder 10 becomes a pressure command value (predetermined pressure). This allows stable pressure control, similar to the hydraulic device of the first embodiment.

[0034] In addition, by controlling the rotation speed of the hydraulic pump P, the pilot pressure of the relief valve 50 can be controlled, and the hydraulic oil discharged from the hydraulic cylinder 10 can be returned to the oil tank T. Therefore, by controlling the rotation speed of one hydraulic pump P, the pilot pressures of both the pressure reducing valve 40 and the relief valve 50 can be controlled.

[0035] In the above first and second embodiments, a hydraulic device that drives the hydraulic cylinder 10 has been described as an actuator, but the actuator is not limited to this and may be a hydraulic motor or the like.

[0036] In the above first and second embodiments, a fixed displacement hydraulic pump P is used, but a variable displacement hydraulic pump may also be used.

[0037] Although specific embodiments of the present disclosure have been described, the present disclosure is not limited to the above first and second embodiments, and can be modified and implemented in various ways within the scope of the present disclosure. [Explanation of symbols]

[0038] 10...Hydraulic cylinder (actuator) 10a…Port 11...Cylinder tube 12…Piston 13...Piston rod 20...Reducing valve 20a…Spool (valve body) 20b…Pilot port 20c…spring 30...Control device 40…Reducing valve 40a…Spool (valve body) 40b…Pilot port 40c...spring 50...Relief valve 51…Inlet port 52…Exit port 53…Pilot port M: Motor P…Hydraulic pump PS…Pressure sensor S…Hydraulic source T…Oil tank

Claims

1. a pressure reducing valve (20) having a valve body (20a) for reducing the pressure of hydraulic oil supplied from a hydraulic source (S) to an actuator (10), a pilot port (20b) to which a pilot pressure for controlling the operation of the valve body (20a) is input, and a spring (20c) for biasing the valve body (20a) in a direction against the pilot pressure; a hydraulic pump (P) for supplying hydraulic oil from an oil tank (T) to the pilot port (20b) of the pressure reducing valve (20); A pressure sensor (PS) for detecting the pressure of the hydraulic oil discharged from the hydraulic pump (P); a control device (30) for controlling the rotation speed of the hydraulic pump (P) so that the pressure of the hydraulic oil detected by the pressure sensor (PS) becomes a predetermined pressure; Equipped with The pressure reducing valve (20) has a first port (21) fluidly connected to the hydraulic power source (S), a second port (22) fluidly connected to the oil tank (T), and a third port (23) fluidly connected to the actuator (10); the valve element (20a) is configured to, when the pilot pressure is less than a preset first pressure, take a first switching position, thereby communicating the second port (22) and the third port (23) with each other and closing the first port (21), and, when the pilot pressure is equal to or greater than the first pressure, take a second switching position different from the first switching position, thereby communicating the first port (21) and the third port (23) with each other and closing the second port (22); The control device (30) controls the rotation speed of the hydraulic pump (P) to perform relief control proportional to the pilot pressure when the pilot pressure is lowered from a second pressure lower than the first pressure, thereby returning the hydraulic oil discharged from the actuator (10) to the oil tank (T).

2. A pressure reducing valve (40) having a valve body (40a) for reducing the pressure of hydraulic oil supplied to an actuator (10) from a hydraulic source (S), a pilot port (40b) to which a pilot pressure for controlling the operation of the valve body (40a) is input, and a spring (40c) for biasing the valve body (40a) in a direction against the pilot pressure; a relief valve (50) that returns the hydraulic oil discharged from the actuator (10) to an oil tank (T) and has a pilot port (53) to which a pilot pressure is input for controlling the operation of returning the hydraulic oil to the tank (T); a hydraulic pump (P) for supplying hydraulic oil from the oil tank (T) to the pilot port (40b) of the pressure reducing valve (40) and the pilot port (53) of the relief valve (50); A pressure sensor (PS) for detecting the pressure of the hydraulic oil discharged from the hydraulic pump (P); a control device (30) for controlling the rotation speed of the hydraulic pump (P) so that the pressure of the hydraulic oil detected by the pressure sensor (PS) becomes a predetermined pressure; A hydraulic device comprising:

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