Method for determining the coefficient of friction between a vehicle tire and a roadway

Claim 1

A mehod for determining the coefficient of friction between a vehicle tire and a roadway comprising: (a) pressurizing during normal brake operation one of the vehicle wheels at a higher brake pressure than another wheel, (b) comparing the rotational speed of said one wheel with the rotational speed of the other wheel for determining the wheel slip of said one wheel from the difference in the rotational speeds of the other wheel and said one wheel when the pressure on said one wheel reaches a value indicative of a predetermined braking torque on said one wheel; (c) measuring the axle load on said one wheel; and (d) determining the coefficient of friction between the tire of said one wheel and said roadway from said measured axle load, said predetermined braking torque, and the inverse proportion of said determined wheel slip.

Claim 6

A method for determining the coefficient of friction between a vehicle tire and a roadway comprising: (a) pressurizing during normal brake operation one of the vehicle wheels at a higher brake pressure than another; (b) comparing the rotational speed of said one wheel with the rotational speed of the other wheel for determining the wheel slip of said one wheel from the difference in the rotational speeds of the other wheel and said one wheel; (c) terminating the pressurizing of said one wheel when said determined wheel slip of said one wheel reaches a predetermined value; (d) measuring the brake pressure indicative of a braking torque at the time when said predetermined wheel slip is reached; (e) measuring the axle load of said one wheel; (f) determining the coefficient of friction between the tire of said one wheel and said roadway from said measured axle load, said measured brake pressure and said predetermined wheel slip.

Claim 7

A method for determining the coefficient of friction between a vehicle tire and a roadway comprising: (a) pressurizing during normal brake operation one of the vehicle wheels at a higher brake pressure than another; (b) comparing the rotational speed of said one wheel with the rotational speed of the other wheel for determining the wheel slip of said one wheel from the difference in the rotational speeds of the other wheel and said one wheel; (c) terminating the pressurizing of said one wheel when said determined wheel slip of said one wheel reaches a predetermined value; (d) measuring the brake pressure indicative of a braking torque at the time when said predetermined wheel slip is reached; (e) measuring the axle load of said one wheel; (f) determining the coefficient of friction between the tire of said one wheel and said roadway from said measured axle load, said measured brake pressure and said predetermined wheel slip.

Claim 8

A method according to one of the claims 1 or 5, characterized in that said another vehicle wheel is free rolling.

Claim 14

The method as claimed in claims 1 or 5, including determining a stopping distance to be expected from the coefficient of friction between the tire of said one wheel and the roadway and the speed of the vehicle and indicating said stopping distance.

Claim 15

The method as claimed in claims 1 or 5, including preventing operation of a determination of the coefficient of friction when the pressure in a master cylinder of the vehicle's brake system exceeds a predetermined value for a predetermined period of time.

Claim 16

The method as claimed in claims 1 or 5, including preventing the determination of the coefficient of friction whenever a steering wheel is turned by a certain angle.

Claim 17

The method as claimed in claims 1 or 5, wherein said one and said another wheel are non-driven wheels of the vehicle.

Claim 18

A method as claimed in claims 1 or 5, wherein the axle load of said one wheel is reduced by lifting said one wheel during pressurizing it at a higher brake pressure than another wheel.

Claim 19

The method as claimed in claims 1 or 5, including determining a distance of said vehicle to another vehicle from a radar distance measuring system, measuring the speed of said vehicle, calculating a stopping distance on the basis of the determined coefficient of friction and said vehicle speed, comparing said stopping distance with said determined distance to said other vehicle and sounding an alarm if the stopping distance is fallen below said distance to said other vehicle.

Claim 20

A method of determining the coefficient of friction between a tire on one wheel of a vehicle and a roadway, the wheels of said vehicle being braked by pressurized fluid, comprising: (a) pressurizing the brake of said one wheel to a greater extent than another brake of another wheel; (b) at a predetermined pressure measuring the speed of said one wheel relative to said other; (c) determining the slip of said one wheel from the difference in the rotational speeds of said one and said other wheels; (d) measuring the axle load on said one wheel; and (e) calculating the actual coefficient of friction between a tire of said one wheel and the roadway from the measured axle load and the inverse proportion of the determined slip of said one wheel.

Claim 21

A method of determining the coefficient of friction between a tire on one wheel of a vehicle and a roadway, the wheels of said vehicle being braked by pressurized fluid, comprising: (a) pressurizing the brake of said one wheel to a greater extent than another brake of another wheel; (b) at a predetermined pressure measuring the speed of said one wheel relative to said other; (c) determining the slip of said one wheel from the difference in the rotational speeds of said one and said other wheels; (d) measuring the axle load on said one wheel; and (e) calculating the actual coefficient of friction between a tire of said one wheel and the roadway from the measured axle load and the inverse proportion of the determined slip of said one wheel.