Copyright @ IFAC Advances in Automotive Control, Ascona, Switzerland, 1995 A STUDY OF LOW BANDWIDm ACTIVE SUSPENSION SYSTEMS A.C.Webb+, K.J. Burnham+, D.J.G. James+, R.A. Williams· + Control Theory & Applications Centre, Coventry University, U.K. • Chassis Engineering, Jaguar Cars Ltd., Coventry, U.K. Abstract: The paper presents results of investigative studies involving non-linear pitch/bounce and roll half car models in order to assess the performance of flxed gain controllers within a low bandwidth active suspension conflguration. The vehicle is subjected to acceleration, braking and cornering manoeuvres. The results highlight the compromise that exists between the body acceleration and strut deflection loops and it is concluded that an element of adaptivity within the scheme could be used to advantage. Keywords: Active vehicle suspension, Automotive control, Chassis control, Computer simulation, Control systems, Non-linear models, PlO controllers, Vehicle dynamics. 1. INTRODUCTION Vehicle suspensions have until recently consisted of a passive spring and damper. The main ftmction being to support the body mass of the vehicle and to provide both passenger comfort and road holding. Depending upon the application, i.e. sports car or luxmy vehicle, the suspension is tuned to provide a bias towards road holding or passenger comfort. The problem is that of striking a satisfactory compromise between these two conflicting performance criteria. However with the introduction of controlled actuators, microprocessors, variable rate springs and dampers this compromise can be reduced. Developments to date include adaptive damping, semi-active suspensions and low and high bandwidth active suspension systems. A good review of developments in this fleld can be found in (Sharp and Crolla, 1987). The high bandwidth active suspension has an actuator positioned in parallel with the road spring, between the sprung mass (body mass) and the unsprung mass (axle mass). This system is designed such that it controls both the body and axle motions. However, a high bandwidth system requires a sophisticated level of control and yet offers only relatively marginal 55 improvements over a low bandwidth active scheme which requires rather less in terms of controller sophistication (Paterson, 1993; Williams, 1994). The low bandwidth active suspension consists of an actuator in series with the road spring and damper, as shown schematically in Figure 1. In contrast to the high bandwidth system the low bandwidth scheme controls the body motion only, whilst the unsprung mass is controlled by the passive elements. In addition the control system for the low bandwidth scheme consists of well proven and relatively available technology (Williams, et al., 1993). 10 this paper consideration is given to assessing the performance of a low bandwidth active suspension utilising oleo-pneumatic actuators with use being made of half car models. Particular attention is focused on the ability (or otherwise) of fIxed gain manually tuned three term PlO controllers to satisfactorily provide adequate performance over a range of realistic road input conditions. Consideration is initially directed towards describing the physical components required for the design of a low bandwidth active suspension. These include the