Method and apparatus for determining an individual wheel surface coefficient of adhesion

A method of determining a coefficient of adhesion between a road surface and a plurality of tires disposed on a vehicle, comprising:

• providing an estimated coefficient of adhesion for each of the plurality of tires, the plurality of tires including at least two front tires and at least two rear tires;
• determining a tire longitudinal slip value and a tire slip angle for each of the plurality of tires;
• determining a tire normal force value for each of the plurality of tires;
• determining a first tire longitudinal force value and a tire lateral force value for each of the plurality of tires, the first tire longitudinal force value and the tire lateral force value being based on the tire longitudinal slip value, the tire slip angle, the tire normal force value and the coefficient of adhesion;
• determining an axle lateral force value;
• determining a second tire longitudinal force value for each of the plurality of tires;
• determining a vehicle handling state;
• determining a longitudinal adaptation speed;
• determining a lateral adaptation speed;
• estimating a coefficient of adhesion adjustment for each of the plurality of tires based on the longitudinal adaptation speed and the lateral adaptation speed;
• and
• updating the estimated coefficients of adhesion for each of the plurality of tires with the estimated coefficient of adhesion adjustment.

A computer usable media for storing a program for determining a coefficient of adhesion between a road surface and a plurality of tires disposed on a vehicle, comprising:

• computer readable program code that determines a longitudinal adaptation speed as a function of a tire longitudinal force value for each of the plurality of tires;
• computer readable program code that determines a lateral adaptation speed as a function of a tire lateral force value for each of the plurality of tires;
• computer readable program code that estimates for each of the plurality of tires a coefficient of adhesion adjustment, each being based on the longitudinal adaptation speed, the lateral adaptation speed and a provided coefficient of adhesion;
• and
• computer readable program code that updates for each of the plurality of tires the estimated coefficient of adhesion with the estimated coefficient of adhesion adjustments.

An apparatus for determining a coefficient of adhesion between a road surface and a plurality of tires disposed on a vehicle, comprising:

• means for determining a longitudinal adaptation speed as a function of a tire longitudinal force value for each of the plurality of tires;
• means for determining a lateral adaptation speed as a function of a tire lateral force value for each of the plurality of tires;
• means for estimating for each of the plurality of tires a coefficient of adhesion adjustment, each being based on the longitudinal adaptation speed and the lateral adaptation speed and a provided coefficient of adhesion;
• and
• means for updating for each of the plurality of tires the estimated coefficient of adhesion with the estimated coefficient of adhesion adjustments.

A braking system disposed within an automobile, comprising:

• means for providing an estimated coefficient of adhesion for each of a plurality of tires;
• means for determining a longitudinal adaptation speed as a function of a tire longitudinal force value;
• means for determining a lateral adaptation speed as a function of a tire lateral force value;
• and
• means for estimating for each of the plurality of tires a coefficient of adhesion adjustment, each being based on the longitudinal adaptation speed and the lateral adaptation speed.

A method of determining a coefficient of adhesion between a road surface and a tire disposed on a vehicle, comprising:

• providing an estimated value of the coefficient of adhesion;
• determining a first value of a force on the tire from a first set of vehicle dynamic parameters requiring no explicit knowledge of the coefficient of adhesion;
• determining a second value of the force on the tire from a second set of vehicle parameters in an analytic tire model including the estimated value of the coefficient of adhesion;
• determining a difference between the first and the second values of the force on the tire;
• updating the estimated value of the coefficient of adhesion in direction to reduce the difference;
• and
• repeating the previous steps using the updated value of the coefficient of adhesion as the provided value thereof.

A method of determining coefficients of adhesion between a road surface and a set of a front tire and a rear tire disposed on a vehicle, comprising:

• providing an estimated value of the coefficient of adhesion for the front tire;
• determining a first value of a force on the front tire from a first set of vehicle dynamic parameters requiring no explicit knowledge of the coefficient of adhesion;
• determining a second value of the force on the front tire from a second set of vehicle parameters in an analytic tire model including the estimated value of the coefficient of adhesion;
• determining a difference between the first and the second values of the force on the front tire;
• updating the estimated value of the coefficient of adhesion of the front tire in direction to reduce the difference and storing the resulting updated estimated value;
• repeating the previous steps using the updated value of the coefficient of adhesion of the front tire as the provided value thereof;
• and
• repeatedly deriving the coefficient of friction of the rear tire from one of the stored updated estimated values of the coefficient of friction for the front tire determined at an earlier time determined responsive to vehicle speed.