Dynamic Tire Force Control by Semiactive Suspensions

This paper presents a semiactive suspension control algorithm to reduce dynamic tire forces and it includes the development and application of observers for bilinear systems with unknown disturbances. The peak dynamic tire forces, which are greatly in excess of static tire forces, are highly dependent on the dynamic characteristics of vehicle suspensions. One way to reduce dynamic tire forces is to use advanced suspension systems such as semiactive suspensions. Semiactive control laws to reduce dynamic tire forces are investigated and a bilinear observer structure for bilinear systems with unknown disturbances is formulated such that the estimation error is independent of the unknown external disturbances and the error dynamics are stable for bounded inputs. The motivation for the development of a disturbance decoupled bilinear observer comes from the state estimation problem in semiactive suspensions. An experimental study on the performance of a semiactive suspension to reduce the dynamic tire forces is made via a laboratory vehicle test rig. The semiactive suspension has been implemented by using a modulable damper, accelerometers and a personal computer. Experimental studies show that the performance of the semiactive suspension is close to that of the best passive suspension for all frequency ranges in the sense of minimizing the dynamic tire forces and that the dynamic tire force can be replaced by the estimated one. The dynamic tire forces for both passive and semiactive control test cases are compared to show the potential of a semiactive suspension to reduce the dynamic tire forces.