Patent ID: 6886332
Filing Date: 2005-05-03
Classification: B63H,F15B

Abstract:
1. In a system for operating a hydraulic actuator, where the actuator has first and second ports, the system including: first and second reversible pumps, each of which has first and second ports which are capable of assuming pressure and suction functions depending on the direction of operation of the respective pump; a prime mover for operating the pumps in one direction or another; a reservoir for supplying fluid to the pumps and for receiving excess fluid; a fluid circuit for directing fluid between the reservoir, the ports of the pumps and the ports of the actuator, the first ports of both pumps fluidly connected via a first circuit portion to the first port of the hydraulic actuator, and the second ports of both pumps being fluidly connected via a second circuit portion to the second port of the hydraulic actuator; a relief valve in the first fluid circuit portion operationally responsive to fluid pressure in the first circuit portion, the relief valve allowing flow from the first circuit portion through a first drain path to the reservoir when the fluid pressure in the first circuit portion increases above a predetermined value; a non-return check valve in the second circuit portion between the second ports of the first and second pumps operationally responsive to fluid pressure in the first and second circuit portions for controlling flow between the second pump and the hydraulic actuator, with the non-return check valve: an unloader valve operationally responsive to fluid pressure in the second circuit portion and fluidly connected to the second pump, the unloader valve allowing flow through a second drain path from the second pump to the reservoir when the fluid pressure in the second circuit portion at the second port of the first pump is above a threshold value; and first and second one-way check valves in the fluid circuit respectively controlling fluid from the reservoir to the first and second circuit portions during operation of the pumps, wherein when the pumps operate in one direction where flow is provided to the first port of the hydraulic actuator, flow is provided i) from the second port of the actuator and through both pumps to the first port of the actuator at low loads when the non-return check valve is open and the unloader valve is in a closed condition; and ii) from the second port of the actuator and through the first pump, and from the reservoir through the second pump, at high loads when the non-return check valve is closed and the unloader valve is in the open position.