Power control units with secondary controlled hydraulic motors - a new concept for application in aircraft high lift systems
Recent Advances in Aerospace Hydraulics, November 24-25, 1998, Toulouse, France
Today’s high lift systems of civil transport aircraft are driven by Power Control Units using valve controlled constant displacement hydraulic motors. This concept leads to complex valve blocks, attended by high power losses to realise discrete speed control, positioning and pressure maintaining functionality. The concept of secondary controlled hydraulic motors with variable displacement offers reduction in flow consumption without pressure losses and decreases the complexity of the valve block design. Instead of controlling flow of the hydraulic motor with valves, torque is adjusted to the load by varying displacement. An electronic control circuit allows flexible digital control concepts e.g. load independent speed control, pressure maintaining functionality, smooth start-up sequences and continuous positioning of the mechanical transmission system. This paper introduces the concept of today’s Power Control Units, the principle and mathematical model of secondary controlled hydraulic motors and the cascade control loop structure. A new hydraulic concept for Power Control Units using secondary controlled hydraulic motors is presented. Theoretical, simulated and experimental results show typical operation sequences under load and a comparison of power requirement to conventional systems.
Secondary controlled hydraulic motor
variable displacement hydraulic motor
aircraft high lift system
secondary flight controls