Stochastic Optimal Control Of Nonlinear Suspension Of Quarter Car Model

The dynamic performance of a vehicle suspension directly influences the ride comfort and handling safety of the driving vehicle. Fixed parameters of a conventional passive suspension always results in a tradeoff between these two factors. Active suspension systems may adjust the control force actively and timely to reduce the vibration according to the working condition of the vehicle. This thesis, hence, presents a study on the stochastic optimal control of vehicle suspensions, mainly on the stochastic response and control of nonlinear suspension of a quarter car model with quadratic damping and hysteretic stiffness under different conditions.Active control of either stationary or non-stationary response of a SDOF vehicle model is considered first. The concept of equivalent linearization and its application to the nonlinear system is introduced. The ground excitation is modeled as a spatial homogeneous random process, being the output of a linear shaping filter to the white noise. The effect of the rolling contact of the tyre is considered by an additional filter in cascade. The influence of nonlinear factors and damping ratio on the stationary response of the suspension at constant speed is analyzed. Then the optimal control law is designed based on the stochastic optimal control theory, and a comparison of dynamic behaviors is made between an active suspension and a passive one. Furthermore, the non-stationary response of the vehicle suspension due to variable velocity or sudden changed excitation is investigated. The effect of the nonlinearities and damping ratio on the passive system performance are also studied. Then, the optimal control law is obtained by using stochastic optimal control theory.Afterwards, a 2-DOF vehicle model with nonlinear suspension elements is studied. The road uneveness is modeled as the stationary response of a linear shaping filter to the whitenoise in spatial domain. The influence of weighting factors on the stationary response of active suspension at constant speed is considered. The non-stationary response with constant deceleration is investigated and the optimal control law is obtained based on full state information.Finally, a Monte Carlo simulation is performed to check the accuracy of the equivalent linearization technique at last...