Precise lift control in a new variable valve actuation system using discrete-time sliding mode control

• A new engine valve lift control system was designed for the recently proposed valve actuation system.
• The system average dynamic model was developed and used for control design.
• A discrete-time sliding mode controller (DT-SMC) was designed and implemented.
• The engine valve lift control system was tested numerically and experimentally.
• The lift controller's performance was compared with that of an existing system.

Precise engine valve lift control is essential in improving the efficiency of internal combustion engines and avoiding unwanted engine valve closure or mechanical interference between the valve and engine piston at different operating conditions. In this paper, a recently proposed hydraulic variable valve actuation (VVA) system [1] is equipped with a novel lift control architecture. In this technique, the hydraulic supply pressure is controlled using a proportional bleed valve. A discrete sliding mode controller is designed using the average model of the system on the basis of a discrete Lyapunov function. The stability of the designed controller is proven and sufficient conditions of the controller gains to stabilize the system are given. The experimental results show an excellent tracking performance of the proposed lift controller during sudden changes in the reference final valve lift. The results also show that using the proposed valve lift controller, the maximum lift deviation from its reference value does not exceed 0.4 mm during transient operating condition.