A wheel slip controller is developed and experimentally tested in a car equipped with electromechanical brake actuators and a brake-by-wire ABS system. A gain scheduling approach is taken, where the vehicle speed is viewed as a slowly time-varying parameter and the model is linearized about the nominal wheel slip. Gain matrices for the different operating conditions are designed using an LQR approach. The stability and robustness of the controller are demonstrated via Lyapunov theory, frequency analysis and experiments using a test vehicle.

Abstract

It is proved that the transient performance of nonlinear adaptive backstepping can be improved by resetting the parameter estimator, without loss of stability. The estimator resetting algorithm is based on multiple model adaptive c o n trol, where a number of models with xed parameter vectors are monitored online in order to detect parameter vectors that gives a negative jump in the control Lyapunov function when replacing the estimate provided by the standard adaptation law. Application to wheel slip control is studied.

The Anti-lock Braking System (ABS) is an important component of a complex steering system for the modern car. In the latest generation of brake-by-wire systems, the performance requirements on the ABS have changed. The controllers have to be able to maintain a specified tire slip for each wheel during braking. This thesis proposes a design model and based on that a hybrid controller that regulates the tire-slip. Simulation and test results are presented.A design method for robust PID controllers is presented. Robustness is ensured with respect to a cone bounded static nonlinearity acting on the plant. Additional constraints on maximum sensitivity are also considered. The design procedure has been successfully applied in the synthesis of the proposed hybrid ABS controller.Trajectory convergence for a class of nonlinear systems is analyzed. The servo problem for piecewise linear systems is treated. Convex optimization is used to describe the behavior of system trajectories of a piecewise linear system with respect to some input signals.

The ABS control problem is described, with a discussion on relevant h ybrid control aspects. Next, we comment o n conventional ABS design methods and present some new ideas and results on model-based ABS control design that relies on elements of hybrid control.

A wheel slip controller for Anti-lock Brake Systems (ABS) is designed using LQ-optimal control. The controller gain matrices are gain scheduled on the vehicle speed. A parameter dependent Lyapunov function for the nominal linear parameter varying (LPV) closed loop system is found by solving a linear matrix inequality (LMI) problem. This Lyapunov function is used to investigate robustness with respect to uncertainty in the road/tyre friction characteristic. Experimental results from a test vehicle with electromechanical brake actuators and brake-by-wire show that high performance and robustness are achieved.

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