A sliding mode controller for vehicle active suspension systems with non-linearities

Abstract

In this paper, the control of an active suspension system using a quarter car model has been investigated. Due to the presence of non-linearities such as a hardening spring, a quadratic damping force and the ‘tyre lift-off’ phenomenon in a real suspension system, it is very difficult to achieve desired performance using linear control techniques. To ensure robustness for a wide range of operating conditions, a sliding mode controller has been designed and compared with an existing nonlinear adaptive control scheme in the literature. The sliding mode scheme utilizes a variant of a sky-hook damper system as a reference model which does not require real-time measurement of road input. The robustness of the scheme is investigated through computer simulation, and the efficacy of the scheme is shown both in time and frequency domains. In particular, when the vertical load to the sprung mass is changed, the sliding mode control resumes normal operation faster than the nonlinear self-tuning control and the passive system by factors of 3 and 6, respectively, and suspension deflection is kept to a minimum. Other results showed advantages of the sliding mode control scheme in a quarter car system with realistic non-linearities.