The new all-wheel-drive control system has been developed to
improve stability, handling performance and safety under various
road/operating conditions. This system consists of center
differential and hydraulic transfer clutch which is electronically
controlled according to road/operating condition.
The center differential of this control system is in the form of
composite planetary gear system without a starter ring. The output
torque of transmission is distributed by this center differential
35% to front wheels and 65% to the rear wheels. It improves
handling performance on dry road when the transfer clutch is open.
On the other hand, when the slippery road condition is detected or
motion of vehicle is disturbed, the actual torque distribution is
modified by electronically controlled transfer clutch to improve
stability and safety.
In the estimation of the coefficient of road friction (μ),
lateral stiffness of tire is identified with parameter
identification law of adaptive control theory. This logic is based
on the linearized 2-wheels adaptive model of vehicle dynamics. The
estimated lateral stiffness of tire is converted into the value of
μ to control the transfer clutch. Additionally, this μ
estimator is modified by the absolute value of filtered lateral
acceleration of vehicle, and response of estimation is
improved.
The transfer torque is controlled not only according to this
estimated μ, but also according to operating conditions of ABS,
TCS and VDC and disturbance of vehicle motion.
Therefore, stability and handling performance of our production
car equipped with this control system has been improved under
various road/operating conditions.