The Investigation of Increasing the Degree of Freedom on Improvement of Stability and Reduction of Rollover by using Sliding Mode Control Method

Stability control system is a part of active safety systems in vehicles which is designed to control the vehicles’ dynamic motion in emergency maneuvers. In the present study, design and simulation of sliding mode controller has initially been conducted for a suspension system with 4 degrees of freedom (4 DOFs). In order to improve the efficiency of controlling system, a new suspension system with 6 DOFs and using hybrid semi-active damper is developed. By employing this novel approach, the passive model with 4 degrees of freedom is modified to hybrid semi-active model with 6 DOFs. Thereupon, to examine the effects of enhancing of DOF on the stability, a new hybrid semi-active suspension system with 8 DOFs by combining passive 4 DOFs and hybrid semi-active 6 DOFs suspension system is designed and simulated. Numerical results from a typical vehicle that is simulated in CarSim are the input for MATLAB simulation. Investigations show that increasing DOFs accompany with applying hybrid semi-active damper lead to better stability and good handling characteristics of vehicle.