Study, Modeling, Optimization And Comparison Of Car Suspension System Based On Different Car Body

Motive of this thesis is leading to develop complete knowledge about suspension systemsof car in all possible formats. Suspension system is always critical part of car design and alldesigners are ready to invest time and money to improve its suspension. Suspension isdirectly related to car steering motion load management and ride comfort level of driver andeach passengers. Suspension system has three types passive, semi active and activesuspension system. Passive suspension is basic and purely mechanical structure has fixeddampers and stiffness in it, semi active has variable damper and fixed stiffness,its dampingvalue can be change through some control system to achieve desired suspension performancewhile most advance system is active suspension in which an additional component isactuator,which can add or dissipate energy in the system.This actuator is controlled bysimple to complex control system that interface with electrical circuitry and produce desiredactuation.To design suspension system for a car researcher must understand about car body and it’sall possible models because they are directly related with each other so it is important toderive mathematical modeling of car body in this thesis with respect to each type suspensionsystem. Car models are categorized in quarter, half and full car body models. Quarter carbody is most simple and basic model of car which only has one degree of freedom while halfcar has four and full car has seven degrees of freedom. The most complex car model is fullcar model but it gives good information about behavior of car body models on road and loaddisturbances.Optimizing mathematical model is next part of thesis. Mathematical optimization is theselection of a best element with regard to some criteria from some set of availablealternatives. Here I use LQR Optimization criteria in which controller optimum parametersare found using mathematical models by minimizing cost function and by setting ofappropriate weight function. Through LQR optimization I found optimized stiffness anddamping values for passive suspension, optimized damper control law for semi active andoptimized actuator control law for active suspension system.Optimization leads us to control system of suspension. As in modern world there are lots ofresearches are busy developing control laws for active suspension system. Here I use basic,classical PID and modern Fuzzy type of control systems for active suspension thencompare their performance analysis for suspension vertical displacement,tire deflection andstrength of controller signal with help of Matlab Simulink tool which concludes that modernFuzzy controller has clear advantage over PID controller.During every era there are lots of new concepts and research had achieved in field ofsuspension system as such here I like to introduce a new road disturbance input simulationmethod with help of two parallel Stewart platforms. Stewart platform has ability to give sixdegree motion to any body placed on top of its base so through this new concept by placingcar’s front and rear axles on two parallel Stewart platform in laboratory it can experience anykind similar real time road inputs from tiny holes to big bumps in its suspension system andcan help to observe behavior of our suspension design thus avoid to take vehicles on timeconsuming and harsh environment real road test. Most control system for active suspensionsystems designed has problem of slow response or response delay with compare to roadinputs which directly affects ride comfort performance by considering this issue thesis alsogives an idea about fast responsive control system based on measuring vehicle attitudethrough inertial control. Vehicle attitude determine through acceleration sensors around carbody then through differential and integral control then resultant reactive force generated foreach valve. For feedback a stroke sensor also used to detect the displacement of spring whichthrough differential process gives track of vertical relative displacement. To support the ideasimulation has performed on Matlab via bump input and observed fast steady state time forvehicle vertical acceleration, pitch and roll behaviors has achieved. Finally thesis concludeswith developing energy efficient hydraulic control system uses hydraulic base actuatingsystem provided with an accumulator to maintain the pressure of system which saves thepower of hydraulic motor.A Simulink model is developed and response plot obtained.In nutshell thesis provides adequate knowledge about car suspension systems,mathematical modeling of car body models, suspension system’s mathematical optimizationsand car body and tire deflection responses based on different control systems for activesuspension then suggest new concepts and develop efficient control system for activesuspension system.