The effect of active suspension control on vehicle ride behaviour

This work is concerned with a theoretical investigation into the ride behaviour of actively suspended vehicles. It is based on the concept of developing control laws for active suspension systems fitted to full vehicle models and then comparing the performances of competing systems using a fair basis for comparison. A review of published work was revealed the need for further work on active control laws for full vehicle models. Theoretical techniques necessary to generate random road profiles and various methods for evaluating vehicle ride response are explained. This is followed by an evaluation of the performance of the passive suspension systems. Techniques for obtaining control laws for an active suspension implemented at all four wheel stations of a vehicle are outlined. It is shown that the classical control law based on ignoring the correlation between the road inputs can be replaced by one which involves limited state feedback and includes the effect of the wheelbase time delay. Performance of this system is better than the system which ignores the time delay and almost as good as that of the full state feedback active system with time delay. In addition, it is much more attractive in terms of its practical implementation. The general strategy of keeping seat accelerations, dynamic tyre load under control and the fore/aft and lateral dynamic tyre load transfers is used, within the realistic design constraint of a specified amount of available working space. The effect of road surface representation, including the cross correlation and the measurement errors in deriving the control laws is examined. Finally the performances of all the active suspensions considered are compared with those obtained from passive systems and conclusions and recommendations for future work are made.