Aeronautics and astronautics – Aircraft control – Pilot operated
Reexamination Certificate
1998-02-27
2001-04-03
Poon, Peter M. (Department: 3644)
Aeronautics and astronautics
Aircraft control
Pilot operated
C244S215000, C244S078200
Reexamination Certificate
active
06209825
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
A system for reducing the electrical losses of an electro-hydraulic actuator used for aircraft control purposes.
2. Description of the Prior Art
The present Electro Hydraulic Actuator (EHA) for controlling aircraft components such as control surfaces comprises a Hydraulic Surface Actuator, powered by a DC Servo-motor driving a multi-piston constant displacement Bi-directional Hydraulic Pump and contains an electrical Actuator Feedback Sensor installed on the Actuator Piston Rod. The actuator servo input is an Electrical Command Signal coming from a computer that processes signals from cockpit controllers and control switches, from internal sensors in the airframe, from aerodynamic sensors and, in some cases, from external signals. This command signal is summed in a Summing Amplifier with the Actuator Output Position Voltage as detected by an Actuator Feedback Sensor. The difference between the input and the output voltage, the Error Signal is applied to the DC Servo-motor to drive the pump in a direction to hydraulically force the Actuator Piston Rod to reduce that error. Under no-load conditions, the actuator is driven to that position where the voltage from the Actuator Feedback Sensor equals the input voltage. When an airload is applied to the actuator, the actuator displaces the small amount needed to create an Error Signal voltage on the output of the Summing Amplifier equal to that voltage required to produce the motor winding current and the associated motor torque necessary to balance the applied load. When maximum actuator load is applied, this Error Signal voltage, as measured at the motor, equals the line voltage, and the motor current required to balance that load is line voltage divided by the DC resistance of the motor windings (stalled rotor current). The input power required to produce and maintain stall hinge-moment equals stall hinge-moment times maximum no-load surface rate (ft-lbs./sec.). This EHA design results in extremely high current draw and power losses at high hinge moments, particularly stall, resulting in high heat losses.
SUMMARY OF THE INVENTION
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. As the load is increased above the given percentage, the de-stroking actuator piston is retracted and the swash plate angle reduced accordingly.
In a further aspect, a pump gain sensor is provided to measure the reduction in pump gain (increase in mechanical advantage) by producing a measurement representative of the angular position of the swash plate. The output voltage from the pump gain sensor is used by the loop gain compensator in the forward path of the servo-loop to increase the forward path electrical gain and compensate for the corresponding reduction in pump gain, thus maintaining the EHA bandpass.
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Dinh Tien
Lockheed Martin Corporation
Poon Peter M.
Zobal Arthur F
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