Apparatus and method for estimating friction coefficient of road surface

A method of estimating a road surface friction coefficient, the method comprising:

• collecting, by a driving state determination module, information for determining a speed of a vehicle from sensors mounted in the vehicle;
• determining, by the driving state determination module, whether to estimate the road surface friction coefficient by determining whether the vehicle is in an inertial driving state, according to the collected information;
• arbitrarily adding, by the driving state determination module, a braking force causing a wheel speed difference to an axle of the vehicle, to which the braking force is applied, and together adding a driving force for canceling the braking force, to an axle of the vehicle to which the driving force is applied, when the driving state determination module determines that the vehicle is the inertial driving state;
• and
• estimating, by the driving state determination module, a state of the road surface friction coefficient by the wheel speed difference caused by the arbitrarily added braking force.

The method of claim 21, wherein the estimating of the road surface friction coefficient further includes:

• determining a value of the wheel speed difference as a corrected wheel speed difference index value by multiplying the wheel speed difference, which is determined in the determining of the magnitude of the difference between the wheel speeds, by a predetermined correction coefficient, depending on a magnitude of a target driving torque acting on the axle, to which the driving force is applied,
• comparing the wheel speed difference index value with a predetermined road surface friction coefficient threshold;
• estimating that the road surface friction coefficient is in a low friction state, when the wheel speed difference index value is greater than the road surface friction coefficient threshold;
• and
• estimating that the road surface friction coefficient is in a high friction state, when the wheel speed difference index value is less than the road surface friction coefficient threshold.