Adaptive feedforward control of an electro-hydraulic variable valve actuator for internal combustion engines

Electro-hydraulic valve actuators capable of variable valve timing, duration and lift offer potential benefits for significantly improving engine performance. A model-based adaptive feedforward control strategy was developed to improve the accuracy of valve opening timing control with the presence of time-varying valve delay. A discrete-time adaptive estimation algorithm was employed to estimate the system supply pressure, which is the leading factor of the valve opening delay. To make the online estimation feasible, a linear time-invariant model was obtained based on previously developed mathematical model. The valve opening delay determined by the estimated supply pressure was further used for the feedforward control to track the desired valve opening timing. Both the open-loop and closed-loop control schemes with adaptive feedforward were studied in this paper. The discrete-time adaptive parameter estimation algorithm along with the developed control strategies were verified on the test bench under transient operational conditions. The parameter estimation converges in 6 engine cycles with a steady-state mean relative estimation error of 7.1% and the tracking error of valve opening timing is kept within 1 crank angle degree using combined feedforward and feedback control.