Nonlinear modelling and sliding mode control of a piezo-hydraulic valve system

Camless internal combustion engines offer significant improvements over classical ones with cam-driven valves: a better torque performance, an increased fuel economy as well as reduced emissions and pumping losses. The paper presents a nonlinear model for a hydraulic engine valve, which is regulated by an innovative piezo-hydraulic valve spool described by a linear model. Based on these models, a nonlinear control design is proposed using a combination of feedforward and feedback control. For the positioning of the valve spool, a decoupling feedforward control is employed, whereas a sliding mode control guarantees an accurate tracking of desired trajectories for the engine valve position. Simulation results are provided to point out the performance and the effectiveness of the proposed control strategy.