Model Reference Adaptive Control of a Pneumatic Valve Actuator for Infinitely Variable Valve Timing and Lift

摘要

Electro-pneumatic valve actuators are used to eliminate the cam shaft of a traditional internal combustion engine. They are used to control the opening timing, duration, and lift of both intake and exhaust valves. A physics-based nonlinear mathematical model called the level-one model was built using Newton's law, mass conservation and thermodynamic principles. A control-oriented model, the level-two model, was created by partially linearizing the level-one model for model reference parameter identification. This model reduces computational throughput and enables real-time implementation. A model reference adaptive control system was used to identify the nonlinear parameters that were needed for generating a feedforward control signal. The closed-loop valve lift tracking, valve opening and closing timing control strategies were proposed. The closed-loop lift control algorithm was developed and implemented in a prototype controller, and validated on a valve test bench with multiple reference valve lift set points at both 1200 rpm and 5000 rpm engine speeds. The experiment results showed that the actual valve lift reached the reference lift within 0.5 mm of lift error in one cycle at 1200 rpm and in two cycles at 5000 rpm. The maximum steady state lift errors are less than 0.4 mm at high-valve lift and less than 1.3 mm at low-valve lift. Furthermore, the closed-loop valve lift control improved valve lift repeatability with more than 30% reduction of standard deviation over the open-loop control.