A fault tolerant longitudinal control and tire/road friction estimation system for automated highway systems (AHS)

This dissertation focuses on the study of a "hard" fault management system and a monitoring system for one source of "soft" faults, namely tire/road interactions.; We propose an extended Automated Highway System (AHS) control architecture, including a fault detection and identification (FDI) system and a fault management system. The implementation and testing of these fault management systems is carried out in SmartAHS, a micro-simulator written in SHIFT, a simulation language for hybrid automata. The simulation results show that the proposed fault management system can handle all of failures that can occur in the sensors, actuators and communication devices used in longitudinal vehicle control systems.; Tire/road interactions play an important role in vehicle safety because they are the central factor in determining a vehicle's ability to accelerate and decelerate. The "soft" fault detection and management scheme discussed in this dissertation is based on the estimation of the tire/road friction characteristics under various tire and road conditions. Two estimation approaches are presented.; The first tire/road friction estimation scheme is based on a pseudo-static friction model. In this model, variations in the model parameters are introduced to accommodate for changes in the vehicle and road conditions. A model-based adaptive emergency braking law is developed based on this friction model.; The parameters in the pseudo-static friction model lack a physical interpretation because they were derived from empirical studies and curve-fitting of experimental data. Numerical tests and an approximate linearization analysis reveal that, due to a structural problem in the system, the convergence rates of the estimated vehicle velocity and relative velocity are low, despite the fact that the estimated internal friction state converges to the real value quickly. To overcome this problem, an alternative adaptive observer-based emergency braking controller is designed using both the vehicle longitudinal acceleration and wheel angular velocity information. It is shown that underestimation of maximum friction coefficient and slip can also be achieved in the enhanced design.; In the last part of the dissertation, we extend the LuGre dynamic friction model in two directions. First, an analytical model for calculating the longitudinal and lateral traction/braking forces and the self-alignment moment is derived. Secondly, we explore the effect of wet road conditions on the tire/road friction model. A simplified hydraulic analysis shows that the LuGre dynamic friction model can capture the variations of wet road conditions through changes in structured model parameters. (Abstract shortened by UMI.)...