Rollover Mitigation Controller Development For A Three Wheeled Platform

Abstract

This research work is an investigation of active and passive methods to reduce rollover tendency of a three wheeled platform. This configuration is common in small to medium aircraft landing gears, mobile robots, and fuel efficient futuristic concept vehicles. In developing countries three wheeled vehicles (TWV) have a significant share in point to point public transport. Such vehicles have a higher rollover risk resulting in significant single vehicle fatal crashes, and thus are the main focus of the current research. In Delta configuration the front single wheel offers no roll resistance, hence no lateral load transfer takes place during cornering at the front axle. The effect on directional behaviour is evaluated for this unique lateral load transfer setup. Dynamics of the vehicle are studied in the state space spanned by the yaw rate and side slip angle. These states encompass the directional behaviour of the vehicle fairly well. The effect on roll over and directional behaviour is assessed. For aircraft tricycle landing gears limit handling behaviour in the form of over-steering behaviour appears much before an un-tripped rollover. This is also observed for existing commercial three wheeled vehicles used for public transport when operated on low friction surfaces. This results in immediate loss of control resulting in collision with other vehicles or road sides resulting in tripped rollovers. Factor effecting passive rollover propensity are related to possible changes in directional response of the vehicle. For delta configuration vehicles, braking unloads the rear axle, reducing the lateral load transfer required for rollover. Due relatively low yaw inertia the vehicle response to steering inputs is also better for three wheeled platforms. Based on these observations an iv active front steering based sliding mode controller is presented for rollover prevention. A vehicle model for direct control of roll angle using steering as an input is developed. An adapting reference based on roll angle at steady state conditions corresponding to a threshold lateral load transfer ratio, is used for sliding surface design. The robustness of the controller is demonstrated using a nonlinear model of CarSim software. The yaw rate error introduced by increasing the turn radius by the controller is than compensated using a brake based system. Both differential braking based Dynamic Stability Control (DSC) and proportional braking are evaluated for efficacy. Giving a higher priority to rollover mitigation, the active front steering is always activated after a threshold lateral load transfer value. The brake based systems are also evaluated for directional control of the vehicle on low friction surfaces.