Investigation of height control for air suspension system based on sliding mode method

Aiming to improve the precision of vehicle height control in air suspension systems, the nonlinear character existing in the lift and lower process was deeply considered based on the thermodynamics laws for variable mass air system. It includes establishing the equations of air mass flow character through the solenoid valve and gas pipes, and also the equations of pressure gradient in the air spring. Based on these mathematical descriptions, a nonlinear quarter car air suspension model was established to describe the lift and lower process for the research of vehicle height control algorithm. To deal with the nonlinear character in the lift and lower process, the nonlinear model was globally linearized through the state feedback method based on the differential geometry theory. Then a sliding mode controller was able to be designed in the linear domain and then transformed in inverse-linearization ways to obtain the nonlinear control algorithm in the original coordinate system. The simulation tests show that, the proposed sliding mode controller designed based on the state feedback linearization theory, is able to handle the nonlinear character existing in the lift and lower process of air suspension system, can eliminate the over control and improve the vehicle height precision obviously.