Design and implementation of clutch control for automotive transmissions using terminal-sliding-mode control and uncertainty observer

This paper investigates the clutch control problem for automotive transmission systems. This paper focuses on the pressure tracking control for a wet clutch, which has a much shorter stroke and asks for a more precise position and pressure regulation. The system dynamics are highly nonlinear, and the developed model includes unmodeled dynamics and parameter uncertainties. All these factors will influence the closed-loop system performance if not considered carefully during the control design, which makes the control synthesis for clutch systems challenging. Compared with the existing sliding-mode control (SMC) method, an improved method based on nonlinear sliding mode is presented in this paper to further improve the convergence rate and tracking precision of the closed-loop clutch system. This controller ensures that the pressure tracking error not only reaches the sliding manifold in finite time but converges to the equilibrium point in finite time as well. Moreover, considering the chattering phenomenon caused by high switching gains, a composite terminal SMC (TSMC) method based on uncertainty observer is proposed to reduce chattering. Using an extended state observer (ESO) technique, an uncertainty observer is designed for estimating the model uncertainties of pressure dynamics, pressure-reducing-valve flow dynamics, and estimation error of piston displacement. Then, a feedforward compensation term is combined with the terminal-sliding-mode feedback control. Thus, the composite terminal-sliding-mode controller may take smaller control gains for the whole pressure tracking procedure without sacrificing uncertainty compensation performance. Experimental results based on an xPC Target platform of the clutch system are provided to show the superiority of the proposed methods.