Patent ID: 7260458

Claim:
A steering apparatus provided with a motor generating an assist force for assisting for a steering force on the basis of a steering torque generated in a steering shaft, comprising: a steering force index detecting means for detecting at least one steering force index among steering indexes including a steering torque and a steering force applied to a steering system from a steering wheel of a vehicle to a suspension; a self-aligning torque estimating means for estimating a self-aligning torque generated in a front wheel of said vehicle on the basis of a detected signal of said steering force index detecting means; a vehicle state quantity detecting means for detecting a state quantity of said vehicle; a front wheel index estimating means for estimating at least one front wheel index among front wheel indexes including a side force with respect to the front wheel of said vehicle and a front wheel slip angle on the basis of a detected signal of said vehicle state quantity detecting means; a grip degree estimating means for estimating a grip degree with respect to at least the front wheel of said vehicle on the basis of a change of the self-aligning torque estimated by said self-aligning torque estimating means, with respect to the front wheel index estimated by said front wheel index estimating means; a determining means for determining whether or not the grip degree estimated by said grip degree estimating means is less than a predetermined value; and a notifying means for notifying a driver of a fact that the grip degree of the front wheel of said vehicle is close to a limit, in the case that it is determined by said determining means that said estimated grip degree is less than the predetermined value, wherein the grip degree is indicative of a grip level of tire on a road surface in a vehicle-wheel lateral direction.