Patent ID: 6457487
Filing Date: 2002-10-01
Classification: F15B,Y10T

Abstract:
A valve assembly for controlling a hydraulic motor, that valve assembly comprising:a fluid supply line for receiving pressurized hydraulic fluid; a return line for connection to a tank; a first intermediate conduit and a second intermediate conduit; a first work port and a second work port for connection to the hydraulic motor; a direction control valve coupled to the fluid supply line and the return line, and having a first position and a second position which provide different fluid paths between the fluid supply line and the return line and the first and second intermediate conduits a bidirectional first proportional control valve connected between the first intermediate conduit and the first work port to control a flow of hydraulic fluid there between, the first proportional control valve comprises a pilot operated valve having a pilot valve element and a main valve element with a control chamber formed on one side of the main valve element; a bidirectional second proportional control valve connected between the second intermediate conduit and the second work port to control a flow of hydraulic fluid there between, the second proportional control valve comprises a pilot operated valve having a pilot valve element and a main valve element with a control chamber formed on one side of the main valve element; a first pressure relief valve which connects the control chamber of the first proportional control valve to the return line in response to pressure at the first work port exceeding pressure in the return line by a first predefined amount; and a second pressure relief valve which connects the control chamber of the second proportional control valve to the return line in response to pressure at the second work port exceeding pressure in the return line by a second predefined amount.