Recently, significant research has been reported on the
integration of two or more control systems [7-10] . These control
systems calculate tire longitudinal force directly from direct
yaw moment and then calculate tire lateral forces based on
simple force sharing tire load. Higuchi and Saito [11] used
the optimal control theory to derive a four steering control
system. The target of the control was to minimize vehicle
side-slip angle. The control signals were consisting of yaw
velocity and sideslip angle feedback control and steering
wheel angle feed-forward control. More recently, Komatsu
et al. [12] applied linear control theory to the four-wheel steer
vehicle using a simple linear reference model. The main aim
of the chosen cost function was to obtain a vehicle with good
controllability for the driver. Peng and Hu [13] concentrated
on the optimum longitudinal tire force distribution to achieve maximum longitudinal acceleration or deceleration
of a vehicle. The traction or braking forces of the tires
were assumed to be regulated by a control system that was
constrained not to generate any yawing moment. Hattori et
al. [14-15] proposed a vehicle dynamics integrated management
(VDIM) to control the force of each wheel. They used a feed-
forward control to calculate the desired longitudinal and
lateral forces and yaw moment of the vehicle. A nonlinear
optimum distribution method was used to distribute the target
force and the moment of the vehicle to longitudinal and lateral
forces of each wheel.