In passenger cars Steer-by-wire (SBW) system is a promising technology in
which a control circuit replaces the mechanical link between the driving
wheel and the vehicle's front wheels. This could improve the design flexibility
and steering capability providing that the steering controller has a good
tracking response to the driver's demand. In this research, a robust sliding
mode control is designed and implemented to an electro-hydraulic SBW
system. Grey-box system identification approach is used to identify the
parameters of the driven mathematical model. The system is given a standard
input signal, Pseudo Random Multi-level Sequence (PRMS), to be stimulated
in the relevant bandwidth. Then, a robust sliding mode controller is designed,
based on a fixed boundary layer, to provide system stability over a wide range
of operating conditions and system disturbances. Finally, the algorithm is
implemented experimentally in a real-time platform in order to evaluate the
tracking performance. The test signals are designed based on the highest rate
of steering provided by a human driver. The results proved the capability of
the steering system to track the driver's demand accurately. At high steering
rate conditions (720 degree/s) the maximum overshoot is found to be 3% with
a setling time of 0.1 s.