Steering Effects Of Active Suspensions

Abstract

Automotive suspension systems have traditionally been a compromise between ride comfort,road handling and load carrying. Due to these conflicting demands, semiactive suspension has been an important feature among premium car manufacturers. The type of active suspension considered in this thesis is an active anti-roll bar system (AARB). The main objective of the AARB system is to provide roll-over protection and better isolation to the passengers from the disturbances induced due to road irregularities. While the active suspension provides better comfort by attenuating the vertical and roll disturbances to a great extent, it has certain adverse effects too. Active control of suspension triggers the lateral vehicle movement due to kinematics and compliance (K&C) of the wheel suspension. The suspension parameters such as bump steer, roll steer and camber steer produces some lateral tyre force which needs to be compensated. To ensure stability of the vehicle, lateral disturbances caused by road bumps, crowned road and road banking needs to be attenuated. The master thesis involves implementation of the AARB controller to improve stability and reduce the steering effort while driving on the road with above mentioned disturbances. The controller can be integrated with active steering system to reduce the overhead on the steering actuator and increase steer-ability in auto-pilot mode. Also, the influence of K&C parameters on steering torque and yaw rate is studied using a linear kinematic model developed in CarMaker. Further, AARB controller is extended to handle cornering scenarios. The control strategy developed includes a state feedback LQR, LQI and robust H1 controller and validated with two different K&C setups and their performance is compared. In conclusion, simulation results show that there is potential in the AARB system to reduce driver steering effort in driver-in-loop and increase steering range in autopilot while using a certain kind of K&C setup.