A Comparison between Passive & Semi Active Suspension Systems

This paper illustrates the mathematical modeling of passive suspension system and the control strategies for semi active suspension system. The Simulink software developed by Matlab is used to evaluate the control characteristics [1], for the same a 2 DOF quarter car model is used. The comparison and evaluation of control result are made using software-in-the-loop simulation (SILS) method. From the result we can see that passive suspension is designed to withstand a particular value of disturbances. Skyhook strategy can provide an improved vehicle ride comfort. Minimax strategy can improve drive safety of vehicle by manipulating wheel load. The skyhook and minimax strategies can be switched to control semi-active suspension system to fulfill different requirement of vehicle in different stages. Keywords—passive suspension, Semi-active Suspension, software in the loop simulation, quarter car model, control strategies. І.INTRODUCTION The duty of a suspension system is to bear the vehicle weight, to cut off the vehicle body from road disturbances, and to preserve the traction force between the tires and the road surface. The function of suspension system is to advance the comfort of riding, road traction handling and steadiness of vehicles. Suspension systems are classified into a passive, semi-active and active suspension system. We can say ac compromise between the passive systems, and the costly higher-performance fully active suspension system is called semi active suspension system. In consideration with an active system, a semi-active system requires much less power, and is less complex and more consistent and can provide great improvement in ride quality. Karnopp [2] introduced the skyhook control strategy, which is unquestionably the most broadly used control policy for semi-active suspension systems. The skyhook control can decrease the resonant peak of the body mass and thus achieves a good quality riding. But, to improve both the ride quality and the safety of vehicle, both resonant peaks of the body and the wheel need to be reduced. For this purpose Minimax control strategy proposed by Prof. Herman Winner and Tobias Niemz is introduced in this thesis. The models of skyhook and minimax are developed using Matlab/Simulink. The passive suspension, minimax and skyhook are compared using SILS. This paper is prepared as follows. In Section II, a two degree-of-freedom quarter car model for the semi-active suspension system is given. In Section III, on/off skyhook algorithm is introduced. Wheel load influence matrix is introduced and minimax controller is designed. In Section IV, the Simulink models are shown. In section V the performances of passive system, skyhook and Minimax strategies are compared and evaluated using SILS and the simulation results are given.