Adaptive Control model of an active automobile suspension system

The suspension system of a passenger car provides isolation between the occupants in the car and the road surface. It also contributes to the handling characteristics of the vehicle. To date, most passenger cars use a passive suspension system that employs springs and damping elements. It seems likely that the use of active elements in the suspension systems can improve suspension performance significantly. Control of these active elements for some optimal cost functional is a problem in itself. The three goals of the suspension system are to provide ride isolation from vibration, limit suspension travel, and maintain road holding characteristics. Each of these three goals conflicts with the others. Thus, the controller must be designed to attain each goal to some extent. This paper proposes the use of a linear quadratic regulator and a fuzzy controller to maintain the ride isolation of a loosely sprung, lightly damped passive suspension while improving the handling characteristics of the vehicle. The suspension performance as pertains to ride isolation can be studied using a simple quarter car model of a suspension system. However, the handling characteristics and the coupling between each quarter of the suspension system must be studied using a full car model. Thus, this paper uses both a quarter car and a full car model to study the performance of suspension systems. The performance of the suspension systems is evaluated by running simulations of the systems subjected to both discrete and random road inputs. This paper shows that an active suspension using a linear full state feedback controller performs better that a passively suspended vehicle. The optimally controlled active suspension system is also compared to a fuzzy controlled active suspension system and the results are discussed.