Comparative Study Between Active/Semi-active Suspension With LQR And Fuzzy Logic Control Method

Motive of this thesis is leading to develop complete performance about suspension systems of car in all possible formats. Suspension system is always critical for car design. Suspension performance is directly related to car steering motion load management and ride comfort level of driver and each passengers. All designers are ready to invest time and money to improve its suspension. Suspension system has three types passive, semi active and active suspension system. Passive suspension is basic and purely mechanical structure has fixed dampers and stiffness in it, semi active has variable damper and fixed stiffness,its damping value can be change through some control system to achieve desired suspension performance while most advance system is active suspension in which an additional component is actuator,which can add or dissipate energy in the system.This actuator is controlled by simple to complex control system that interface with electrical circuitry and produce desired actuation.To control suspension system for a car researcher must understand about car body and its all possible models, because they are directly related with each other. So it is important to derive mathematical modeling of car body in the first part. In this thesis a car model is categorized in a quarter car body model, because a quarter car body is most simple and basic model of car which only has one degree of freedom.Optimizing mathematical model is next part of thesis. Mathematical optimization is the selection of a best element with regard to some criteria from some set of available alternatives. Here I use LQR Optimization criteria in which controller optimum parameters are found using mathematical models by minimizing cost function and by setting of appropriate weight function. Through LQR optimization I found optimized stiffness and damping values for passive suspension, optimized damper control law for semi active and optimized actuator control law for active suspension system.Optimization leads us to control system of suspension. As in modern world there are lots of researches are busy developing control laws for active suspension system. The last part of this thesis about compare semi-active and active suspension using LQR and fuzzy logic to control them. Here I use basic classical Fuzzy logic type of control system for active suspension, then compare(LQR, Fuzzy logic) performance analysis for suspension vertical displacement,tire deflection and strength of controller signal with help of Matlab Simulink tool which concludes that modern Fuzzy controller has clear advantage over LQR controller.The thesis provides adequate knowledge about car suspension systems, mathematical modeling of a quarter car body models, suspension system’s mathematical optimizations and car body and tire deflection responses based on different control systems for passive, semi-active and active suspension. Then prove that the active suspension system is better compared with passive and semi-active suspension. Fuzzy controller and LQR controller for both semi-active and active suspension system have obvious advantage.