JP2007-239992A discloses a fluid pressure control device that independently controls operation of a high pressure actuator and a low pressure actuator while preventing pressure of a pressure limit value or higher from acting on the low pressure actuator.
More specifically, the fluid pressure control device includes a supply passage, first and second control valves, a pressure relief passage, and a relief valve. The supply passage guides a working fluid discharged from a pump to the high pressure actuator (lift cylinder) and the low pressure actuator (tilt cylinder). The first control valve is provided in the supply passage to control the operation of the high pressure actuator. The second control valve is provided in the supply passage to respectively control the operation of the low pressure actuator. The pressure relief passage branches from the supply passage on the upstream side of the first and second control valves and passes through the second control valve. The relief valve is provided in the pressure relief passage.
The second control valve allows a flow of the working fluid in the pressure relief passage in a case where a flow of the working fluid to the low pressure actuator is allowed, and blocks the flow of the working fluid in the pressure relief passage in a case where the flow of the working fluid to the low pressure actuator is blocked. The relief valve allows a flow of the working fluid in a case where a flow of the working fluid to the relief valve is allowed and pressure in the pressure relief passage reaches the pressure limit value, thereby prevents pressure exceeding the pressure limit value from acting on the low pressure actuator.
USPTO Backgrounds
USPTO Backgrounds