Patent ID: 8639412

Claim:
A road surface friction coefficient estimating device comprising: a braking/driving force detecting section that detects a braking/driving force of a wheel; a slip ratio detecting section that detects a slip ratio of the wheel; and a road surface friction coefficient estimating section that: stores information about a characteristic curve in a coordinate plane, wherein the coordinate plane has a coordinate axis representing the braking/driving force and a coordinate axis representing the slip ratio, and wherein the characteristic curve represents a relationship between the braking/driving force and the slip ratio under a condition of a reference road surface friction coefficient; finds with reference to the stored information a point in the coordinate plane at which a straight line intersects with the characteristic curve, wherein the straight line passes through an origin point of the coordinate plane and a detected point, and wherein the detected point corresponds to a detected value of the braking/driving force obtained by the braking/driving force detection section and a detected value of the slip ratio obtained by the slip ratio detecting section; and calculates an estimated value of a road surface friction coefficient, based on a reference value and the detected value of at least one of the braking/driving force and the slip ratio and the reference road surface friction coefficient, wherein the reference value corresponds to the found point.