The present invention is directed to a wheel grip factor estimation apparatus,
which includes a steering factor detection unit for detecting at least one of steering
factors including a steering torque and steering effort applied to a steering system
extending from a steering wheel to a suspension of a vehicle, an aligning torque
estimation unit for estimating an aligning torque produced on at least a wheel
of the vehicle on the basis of the steering factor detected by the steering factor
detection unit, and a vehicle state variable detection unit for detecting a state
variable of the vehicle. The apparatus further includes a wheel factor estimation
unit for estimating at least one of wheel factors including a side force and slip
angle applied to the wheel on the basis of the vehicle state variable, and a grip
factor estimation unit for estimating a grip factor of at least a tire of the wheel,
in accordance with a relationship between the estimated alignment torque and the
estimated wheel factor.
