Electro-pneumatic valve actuators are used to eliminate the cam shafts of a traditional internal combustion engine. They are used to control the opening timing, duration, and lift of both intake and exhaust valves. In order to develop model-based control strategies, a control oriented model was developed by piecewisely linearizing the physics-based nonlinear system model. In this paper, an adaptive valve lift control strategy was developed to improve the intake valve lift repeatability. The model reference adaptive system identification technique was employed to estimate system parameters needed for generating feedforward control signals for the closed-loop control scheme. The closed-loop lift control strategies, along with the model reference feedforward control, were developed and implemented in a prototype controller, and validated on a valve test bench with multiple reference valve lifts at both 1200 and 5000 r/min 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 r/min and in two cycles at 5000 r/min. The maximum steady-state lift errors were 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.
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