Study On Modeling About Automotive Semi-active Suspension System

Based on one homemade mini-car, this paper researches the method getting the dynamics parameters of a car, and the way establishing the dynamics model. Moreover, this paper designs the semi-active suspension system based on magnetorheological (MR) fluid damper, and simulates it according to Linear-Quadratic (LQ) optimal control theory. The following four subjects are mainly studied.Adopting three methods to get the dynamics parameters of a car. There are test, 3D modeling and referring to drawings respectively. In the test method, a special double spring inverted-pendulum test rig is designed, which is used to test these parameters of engine, doors and seats; Using the 3D models of car-body, front axle and rear axle to get their parameters; According to the test report, getting the damping and stiffness of suspension and the stiffness of tyres. Then obtaining the whole car dynamics parameters based on mass center coordinates formula of space force system and torque translation theorem. Finally, respectively forming different dynamics parameters tables according to different degree of freedom (DOF) models. Study on the theoretic modeling and experimental modeling about MR fluid damper. In this paper, MR fluid damper work mode is mixed mode. Based on the rheology analysis about parallel-plate model, the damping force theoretic model of MR fluid damper is brought forward. Based on Bingham plasticity model, the damping force experimental model of MR fluid damper is put forward. Taking subsection nonlinear regress to fit test data under low and high speed. The result shows that the simulation model can reflect the force-displacement and force-velocity characteristic well. Furthermore, analyzing the time flag phenomena of MR fluid damper, and getting the conclusion that it results from the transient state response of LR circuit and the response time can be decreased by using the current driver.Using Lagrange method to construct 2, 4, and 7 DOF automobile semi-active suspension system based on MR fluid damper. On the basis of it, writing out the state equation and output equation according to state space method. Moreover, analyzing the inherent characteristics according to different DOF models. At the same time, the road test is carried through for validating the dynamics parameters and model. The natural frequencies of sprung mass heave, pitch and roll acceleration are identified. The result shows that the whole car dynamics model can reflect the real vehicle condition. Discussing the problem how to use LQ optimal control strategy for the automobile semi-active suspension based on MR fluid damper. Based on quarter-car and whole-car models, the stochastic optimal control systems are designed respectively. The simulation result shows that only comprehensively consider each factor and rationally select the weight parameters of the semi-active suspension performance target function, can the riding quality and steering controllability be improved.