Analysis and design of a lateral force estimator for a Formula Student vehicle

Abstract

Vehicle dynamic controls are a very important aspect in the automotive industry, especially in electric or hybrid vehicles, as they allow the car to obtain a better driving performance and power-train management systems. In racing cars, the control systems related to power distribution such as the Torque Vectoring are especially important and they open an amount of possibilities related to the tire forces distribution in order to increase the vehicle dynamics behavior and obtain the maximum efficiency possible. They include the control and use of tire forces, which is a difficult task specially because of their nonlinearities, as they are the only points of interaction with the road and they limit the dynamic behavior of the car. In this work, the lateral vehicle dynamics are analyzed and modeled so a tire cornering force estimator can be designed and integrated to the current Torque Vectoring control system of a Formula Student vehicle to improve its performance. Four different observers (a Luenberger, Extended Kalman Filter, Unscented Kalman Filter and a Moving Horizon Estimator) that will be analyzed and compared are designed with matlab and CasADi and simulated with the IPG CarMaker software in order to validate them. It is a full simulation work and it will require of a future implementation in the actual car. The lateral dynamics of the car are modeled using a seven-variable state-space representation, which is discretized and validated during the project. The different parameters of the observers are tuned so they estimate the tire forces properly and the estimators are finally compared according to some Key Performance Indicators (KPIs) so one of the four estimation options is chosen as the best observer to integrate in the car. The final conclusion of the work is that the Moving Horizon Estimator proposed is the best option to estimate the tire cornering forces properly as it meets all the necessary requirements to be integrated in the car and it can be used to provide the inputs of the Torque Vectoring system.