Low power loss electro hydraulic actuator

DETAILED DESCRIPTION It is an object of the invention is to reduce the peak electrical input power requirements of the EHV actuator.
It is a further object of the invention to reduce the EHA system weight by the reduction in the required size of the servo-motor and thus reducing the size of the associated driver electronics, wire size and the size of the power generating and cooling equipment needed to meet aircraft and control system requirements.
It is a further object of this invention to reduce electrically induced heat losses in the EHA under high sustain actuator loadings.
The present invention uses a variable displacement pump in lieu of the constant displacement unit and a hinge moment sensor is added to de-stroke the pump.
A de-stroking Actuator is employed which is powered by absolute differential cylinder port pressure.
When the absolute value of the differential port pressure is less than a given percentage of maximum, the swash plate angle in the pump is at maximum and the pump piston stoke is at a maximum.
As port differential pressure is increased above this percentage the swash plate angle is reduced linearly which shortens the piston stroke thus increasing the mechanical advantage of the motor over the pump and reducing the motor torque needed to produce that differential pressure.
At maximum actuator load, the pump piston stroke is reduced to 10% or less thus reducing the electrical input power to 1% or less of that power required to maintain the same load using a constant displacement pump.
As the swash plate angle is decreased; the mechanical advantage to the motor is increased, the maximum actuator rate is reduced and if loop compensation is not supplied, the actuator bandpass is lowered.
In the embodiment disclosed, the hinge moment sensor comprises a Free Floating Piston and the appropriate porting needed to maintain a volume balance between the surface actuator cylinder ports and to detect which port has the greater pressure.
The port having the highest pressure shuttles the free floating piston to that position required to retract the de-stroking actuator piston when the load on the surface actuator exceeds the given percentage of maximum