Estimating method for road friction coefficient and vehicle slip angle estimating method

A vehicle slip angle estimating method for estimating a vehicle slip angle defined as an angle formed between a running direction of a vehicle and a longitudinal axis of said vehicle by regressively using a previous estimated value of said vehicle slip angle in calculating a present estimated value of said vehicle slip angle on the basis of a vehicle dynamic model calculated by using a road friction coefficient μ, said vehicle slip angle estimating method comprising the steps of:

• detecting a steering angle by a steering angle sensor;
• detecting a lateral acceleration by a lateral acceleration sensor;
• calculating an approximate friction coefficient μ of said road friction coefficient μ by referring to a road friction coefficient μ determination table where a plurality of regions each composed of steering angle and lateral acceleration are defined so as to respectively correspond to a plurality of road friction coefficients μi (i=1 to n, n is an integer not less than 2) on the basis of a boundary line derived from lower limits of the lateral acceleration over various values of the steering angle, and by specifying one of said regions according to the steering angle detected by said steering angle sensor and the lateral acceleration detected by said lateral acceleration sensor to thereby specify one of said road friction coefficients μi as said approximate friction coefficient μ;
• detecting a vehicle speed of said vehicle;
• determining whether or not said vehicle speed is less than or equal to a predetermined speed;
• and
• forcibly resetting said present estimated value of said vehicle slip angle to zero when said vehicle speed is less than or equal to said predetermined speed, thereby preventing the divergence of said present estimated value of said vehicle slip angle.

A vehicle slip angle estimating method for estimating a vehicle slip angle defined as an angle formed between a running direction of a vehicle and a longitudinal axis of said vehicle by regressively using a previous estimated value of said vehicle slip angle in calculating a present estimated value of said vehicle slip angle on the basis of a vehicle dynamic model calculated by using a road friction coefficient μ, said vehicle slip angle estimating method comprising the steps of:

• detecting a steering angle by a steering angle sensor;
• detecting a lateral acceleration by a lateral acceleration sensor;
• calculating an approximate friction coefficient μ of said road friction coefficient μ by referring to a road friction coefficient μ determination table where a plurality of regions each composed of steering angle and lateral acceleration are defined so as to respectively correspond to a plurality of road friction coefficients μi (i=1 to n, n is an integer not less than 2) on the basis of a boundary line derived from lower limits of the lateral acceleration over various values of the steering angle, and by specifying one of said regions according to the steering angle detected by said steering angle sensor and the lateral acceleration detected by said lateral acceleration sensor to thereby specify one of said road friction coefficients μi as said approximate friction coefficient μ;
• estimating a vehicle slip angle derivative on the basis of said vehicle dynamic model;
• detecting a vehicle speed of said vehicle;
• determining whether or not said vehicle speed is less than or equal to a predetermined speed;
• forcibly resetting the present estimated value of said vehicle slip angle derivative to zero when said vehicle speed is less than or equal to said predetermined speed, thereby preventing the divergence of said present estimated value of said vehicle slip angle derivative;
• and
• integrating said present estimated value of said vehicle slip angle derivative with respect to time, thereby obtaining said present estimated value of said vehicle slip angle so that when said vehicle speed is less than or equal to said predetermined speed, said present estimated value of said vehicle slip angle becomes zero, whereas when said vehicle speed is greater than said predetermined speed, said present estimated value of said vehicle slip angle becomes an integral of said present estimated value of said vehicle slip angle derivative.