Estimation of vehicle side slip angle in nonlinear condition based on the state feedback observer

Estimating the vehicle side slip angle using the signal of the current sensors on-board is very important for the Vehicle Dynamic Control systems and an estimation algorithm is proposed in this paper. This algorithm which can meet the requirement of real-time and nonlinearity is based on a nonlinear observer that contains a modified Dugoff tire model. At first, the longitudinal and lateral forces of the front tires are estimated by a closed loop state feedback observer. Then the value of the parameter f(λ) in Dugoff model is calculated. It is clear that f(λ) is the vital connection between tire longitudinal slip ratio and tire side slip angle. So the tire side slip angle can be calculated by f(λ) and the tire longitudinal slip ratio. At last, the vehicle side slip angle is calculated by the relation between the tire and vehicle side slip angles. The seven degrees of freedom vehicle model is built to test and verify the effect of the algorithm. Simulation result proves that the algorithm can accurately estimate the vehicle side slip angle under linear condition and nonlinear condition to some extent.