A Robust Lift Control Technique in Electro-Hydraulic Camless Valves Using System Average Model

Abstract

In electro-hydraulic camless valvetrains, both valve timing and lift are simultaneously controlled through precise control of solenoid actuated servo-valves at each cycle. In fact, the desired maximum lift is obtained by accurate controlling of the servo-valve opening interval. However, at high engine speeds, due to the slow servo-valve response time, concurrent control of both timing and peak lift becomes more difficult and sometimes impossible. In this paper a new valve lift control technique is proposed based on the average model of the mechanism introduced in [1]. Using this method, it is possible to control the valve lift without precise control of the high pressure servo-valve opening interval and the servo-valves are only responsible for controlling the valve timings and duration. This eliminates the need for high precision servo-valves and measuring devices and consequently cut the system cost. In contrast to the existing lift control methods in which the maximum lift should be repeatedly controlled within each cycle, employing this technique, it is possible to adjust the maximum valve lift after few engine cycles. To this end, an average model of the system is developed based on system energy balance and a non-linear sliding mode controller is designed and implemented on the proposed mechanism. To compensate for the model uncertainties, the designed sliding mode controller is equipped with adaptive law. A conventional boundary layer method is used to solve the controller chattering problem. Finally, the performance of the proposed lift control technique is evaluated through simulation.