Combining Slip and Deceleration Control for Brake-by-wire Control Systems: A Sliding-mode Approach

In road vehicles, wheel locking can be prevented by means of closed-loop Anti-lock Braking Systems (ABSs). Two output measured variables are usually considered for regulation: wheel deceleration and wheel longitudinal slip. The traditional controlled variable used in ABS is the wheel deceleration, since it can be easily measured with a simple wheel encoder; however, it can be dynamically critical if the road-surface rapidly changes. On the other hand, the regulation of the longitudinal slip is more robust from the dynamical point of view, but the slip measurement is critical, since it requires the estimation of the longitudinal vehicle speed. In this work we propose a control strategy whose regulated variable is a combination of wheel deceleration and longitudinal slip. In particular, this work proposes a Sliding Mode approach to the design of an active braking controller whose controlled variable is a convex combination of wheel deceleration and wheel slip.