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

A method for estimating a road friction coefficient μ of a vehicle, comprising the steps of:

• detecting a steering angle of the vehicle by a steering angle sensor;
• detecting a lateral acceleration of the vehicle by a lateral acceleration sensor;
• calculating an approximate friction coefficient μ by referring to a road friction coefficient μ determination table comprising a plurality of regions each composed of steering angle and lateral acceleration, wherein each of said regions respectively correspond to one of 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 selecting 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, wherein said corresponding road friction coefficient μi of said selected region is said approximate friction coefficient μ;
• and
• detecting a vehicle speed of the vehicle by a vehicle speed sensor, wherein
• said road friction coefficient μ determination table is either one of a plurality of tables prepared on the basis of a plurality of vehicle speeds and selectively used according to the vehicle speed detected by said vehicle speed sensor or a predetermined table using a corrected steering angle obtained by correcting the steering angle detected by said steering angle sensor with a correction coefficient according to the vehicle speed detected by said vehicle speed sensor, and
• the correction coefficient is substantially linear to the vehicle speed of the vehicle, and
• said step of calculating said approximate friction coefficient μ comprises the steps of detecting a straight running condition and increasing said approximate friction coefficient μ by one step when said straight running condition has been detected for more than a predetermined time and maintaining said approximate friction coefficient μ which is increased by one step until a non-straight running condition is detected.