Sliding-mode observers for systems with unknown inputs: application to estimating the road profile

In this paper, a sliding-mode observer for systems with unknown inputs is presented. The system considered is a vehicle model with unknown inputs that represent the road profile variations. Coefficients of road adhesion are considered as unknown parameters. The tyre-road friction depends essentially on these parameters. The developed observer permits these longitudinal forces acting on the wheels to be estimated. Then another observer is developed to estimate the unknown inputs. In the first part of this work, some results are presented which are related to the validation of a full-car modelization, by means of comparisons between simulation results and experimental measurements (from a Peugeot 406 as a test car).