Backstepping-based sliding mode control of an electro-pneumatic clutch actuator

In this paper, a nonlinear control approach is presented for an electro-pneumatic clutch actuator for heavy trucks. A clutch is required at start-up or during gear shifts to disconnect the combustion engine from the gear box. This automated actuator provides the necessary actuation force according to the large torque transmitted through the power train. Based on a control-oriented system representation, a cascaded control structure is designed. The outer loop is related to the mechanical subsystem and guarantees an accurate tracking of desired trajectories for the clutch position using a backstepping-based sliding mode control. Furthermore, hysteresis effects of the nonlinear clutch force are addressed properly by a Bouc-Wen hysteresis model. The inner loop controls the internal pressure of the clutch actuator. A new nonlinear reduced-order observer is designed that estimates both the effective internal pressure and a mass flow offset. The benefits of the proposed control structure are demonstrated by experimental results from a dedicated test rig.