Low power loss electro hydraulic actuator

A system for controlling a structural member of an aircraft, comprising:

• a hydraulic actuator comprising a cylinder having a piston to be coupled to a structural member of an aircraft for moving the structural member and having two fluid actuator ports for receiving and discharging fluid into and from said cylinder for moving said piston to retracted and extended positions,
• a loop gain compensator,
• a summing means having an output coupled to said loop gain compensator,
• means for applying a command signal to said summing means,
• means for sensing the position of said piston and for producing an electrical output representative of said position,
• means for applying said electrical output to said summing means,
• a servo motor coupled to the output of said loop gain compensator,
• a variable displacement fluid pump having two fluid pump ports coupled to said two fluid actuator ports respectively, a rotatable member having bores with pistons, and a swash plate for controlling the flow of fluid through said two fluid pump ports of said variable displacement fluid pump,
• said servo motor having a shaft coupled to said rotatable member for rotating said rotatable member,
• a de-stroking actuator having a de-stroking piston, movable in first and second opposite directions, coupled to said swash plate of said variable displacement fluid pump for controlling the angle of said swash plate,
• means for urging said de-stroking piston in said first direction to increase the swash plate angle,
• a sensor having two conduits coupled to said two fluid actuator ports of said cylinder for directing fluid from the fluid actuator port of said cylinder having the highest pressure, to said de-stroking actuator to move said de-stroking piston in said second direction to decrease the swash plate angle of said variable displacement fluid pump.