An Investigation of the Use of a New Non-linear Control Strategy for Integration of Active Suspension and Anti-Lock Braking Systems

Various systems have been introduced recently in the automotive industry to improve the safety, ride and handling qualities of passenger vehicles, such as anti-lock braking system (ABS), active suspension system, four wheel steering system, traction control system, etc. Although each system has been shown to impose positive effects on the performance of a vehicle, the benefits of integrating various systems is yet to be determined.

A feasibility study was conducted of a new non-linear control law for integration of anti-lock braking system and active suspension system. The control law is based on the use of a candidate Lyapunov function. Lyapunov stability theorem is applied to synthesize the control law and the adaptation law necessary to estimate the unknown parameters of the vehicle/road system. The proposed MIMO non-linear control strategy can maintain desired values of various variables while estimating the unknown parameters of the system. The desired values for various states are obtained by solving an optimal control problem for a simple vehicle model. Simulations of braking maneuvers were conducted using a non-linear vehicle model together with a non-linear tire model. The preliminary study indicates that the controller designed is capable of maintaining desired front and rear wheel longitudinal slip values as well as generating sufficient suspension forces to minimize sprung mass vibrations.