Behnam Riazi

Date of Award


Publication Type


Degree Name



Mechanical, Automotive, and Materials Engineering

First Advisor

A. Ahmadi

Second Advisor

C. Novak

Third Advisor

E. Lang


Semi-active suspension system, Automotive applications, Automotive industry




Modern vehicles are equipped with numerous sensors and systems intended to improve performance and ride quality. Suspension systems in vehicles are essential links between the vehicle body and the pavement, and they play a large role in determining ride comfort and handling stability. this is in fact no easy task since these two goals are in conflict.While active suspension systems could help to solve this trade-off, disadvantages such as high costs and high power consumption prevent their widespread adoption in the automotive industry.On the other hand, a semi-active suspension system can provide desirable performance while providing a more cost-effective solution than a fully active suspension system. Research in this thesis will be conducted on semi-active systems using the MR damper. MR dampers aremodelled in MATLAB/Simulink and then their viscoelasticity characteristics are investigated. A quarter-car model is designed in state-space and modelled in MATLAB/Simulink. Two control systems are proposed for a semi-active suspension system using Linear Quadratic Regulator and Fuzzy Logic Controller. Modelled systems are analyzed for four road profiles, including road type C according to international standards ISO/TC108/SC2N67 and the control system's effectiveness will be evaluated by analyzing the RMS values of vertical body acceleration and tire deflection.Results of simulation show that the designed semi-active suspension system can improve vehicle performance regarding both ride comfort and handling stability.For the following, an additional suspension mechanism has been considered for the seats of vehicles. This suspension system is modelled, which is three degrees of freedom with six state variables in state-space form, and its behaviour is analyzed by using MATLAB/Simulink. It isshown that an additional suspension system can improve the ride quality significantly.