  Unexpected yaw disturbances like braking on unilaterally icy road, side wind
forces and tire rupture are very difficult to handle by the driver of a road
vehicle, due to his/her large panic reaction period ranging between 0.5 to 2
seconds. Automatic driver assist systems provide counteracting yaw moments
during this driver panic reaction period to maintain the stability of the yaw
dynamics of the vehicle. An active steering based driver assist system that
uses the model regulator control architecture is introduced and used here for
yaw dynamics stabilization in such situations. The model regulator which is a
special form of a two degree of freedom control architecture is introduced and
explained in detail in a tutorial fashion whereby its integral action
capability, among others, is also shown. An auxiliary steering actuation system
is assumed and a limited integrator version of the model regulator based
steering controller is developed in order not to saturate the auxiliary
steering actuator. This low frequency limited integrator implementation also
allows the driver to take care of low frequency steering and disturbance
rejection tasks. Linear simulation results are used to demonstrate the
effectiveness of the proposed method.
