Robust Motion Control for Tracking Time-Varying Reference Signals and Its Application to a Camless Engine Valve Actuator

Robust motion control for tracking time-varying reference signals and its application to an electrohydraulic camless engine valve actuator is presented. Two challenging issues encountered in many engineering applications, especially reciprocating machines, are addressed: 1) nonlinear system dynamics and 2) time-varying reference signals. Motion control of the electrohydraulic camless engine valve actuator is a typical example. The electrohydraulic actuator has the critical nonlinear dynamic features such as oil flow through the spool valve orifice and friction force exerting on the piston. The reference valve motion is time-varying since its frequency contents change with the engine speed. Prior to studying the time-varying motion control of a nonlinear system, the time-invariant case is investigated by means of internal model principle. Based on the frequency-domain analysis of a nonlinear feedback system, the high-order time-invariant internal model is designed for tracking performance. Motivated by the time-invariant case, the high-order time-varying internal model is designed for robust tracking of time-varying reference signals. The effectiveness of the proposed time-varying internal model is demonstrated by application to the electrohydraulic camless engine valve actuator.