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The control of automotive braking systems performance and wheel slip is a challenging problem due to the nonlinear of the braking process, vehicle body dynamics during braking and the tire-road interaction. When the wheel slip is not between the optimal limits during braking, the desired tire-friction force cannot be achieved, which influences the braking distance, the loss in steerability and maneuverability of the vehicle. A simple and at the same time realistic vehicle longitudinal braking model is essential for such challenging problem. In this paper, a new longitudinal rolling/braking lumped-vehicle model that takes vehicle aerodynamic forces in consideration is presented. The proposed model takes the rolling resistance force, the braking force and the aerodynamic lift and drag forces in consideration and investigates their impact on the vehicle longitudinal dynamics especially vehicle braking distance and time.

An Undertray is an aerodynamic downforce generator used in racing cars to enhance traction. It has the highest downforce to drag ratio among other aerodynamic devices. The objective of this study is to optimize the performance of a FSAE undertray through full vehicle three-dimensional numerical experiments. Based on Preliminary experiments, the basic undertray features are chosen. A simple sequential analysis approach is taken to study the downforce trends versus the variation of three undertray geometrical parameters. It is found that downforce generated is proportional to the diffuser angle until breakdown caused by separation of flow in the lower diffuser duct. A secondary diffuser guide vane is found to retard said separation, allowing uniform expansion at higher diffuser angles. Lower ground clearances cause boundary layer chocking and advanced separation. Finally the effect of the undertray on the aerodynamic wings is studied, and found to be negligible.

The vehicle dynamics and controls play a significant role in vehicle handling performance characteristics. The control of vehicle braking system and wheel slip is a challenging problem due to the nonlinear dynamics of the braking process and the wheel-road interaction. A simple and at the same time realistic vehicle longitudinal braking model is essential for such a challenging problem. In this paper, a new longitudinal rolling/braking quarter-vehicle model is presented. The proposed model takes both the rolling resistance force and the braking force into consideration and investigates their impact on the vehicle longitudinal dynamics. An anti-lock sliding-mode controller is designed to provide wheel slip control during vehicle motion. This type of controller is chosen due to its expected robustness against varying road friction coefficient.