Apparatus and a method for estimating the friction coefficient of a road surface and controlling a driving condition of a vehicle in accordance with the estimated friction coefficient

A method for estimating a friction coefficient of an actual road surface on which a vehicle is running and for regulating a driving condition of said vehicle in accordance with said estimated friction coefficient, said method comprising:

• a first step of detecting a running speed of vehicle, a steering angle of said vehicle, and an actual transverse acceleration acting on said vehicle at substantially a right angle to the running direction of said vehicle;
• a second step of calculating a stability factor of said vehicle on the basis of said running speed, said steering angle, and said actual transverse acceleration detected at said first step, said stability factor being an index indicating a relationship between an increase of said actual transverse acceleration acting on said vehicle and an increase of said steering angle;
• a third step of outputting a first comparison value when said stability factor calculated at said second step is greater than a predetermined limit value, outputting a second comparison value when said stability factor calculated at said second step is less than said limit value, outputting a third comparison value when said actual transverse acceleration of said vehicle detected at said first step is less than a predetermined reference value, and outputting a fourth comparison value when said actual transverse acceleration of said vehicle detected at said first step is greater than said reference value;
• a fourth step of estimating a friction coefficient of said actual road surface and determining that when said first and third comparison values are output at said third step, said estimated friction coefficient is low, as compared with said estimated friction coefficient of said actual road surface when said comparison values output at said third step are not said first and third comparison values;
• and
• a fifth step of controlling a driving condition of said vehicle on the basis of said determination at said fourth step as to whether said estimated friction coefficient of said actual road surface is low.

A device for estimating a friction coefficient of an actual road surface on which a vehicle is running and for regulating a driving condition of said vehicle in accordance with said estimated friction coefficient, said device comprising:

• control means for controlling a driving condition of said vehicle;
• first detecting means for detecting a running speed of said vehicle;
• second detecting means for detecting an actual transverse acceleration acting on said vehicle at substantially a right angle to a running direction of said vehicle;
• third detecting means for detecting a steering angle of said vehicle;
• setting means for setting a target transverse acceleration for said vehicle on the basis of said running speed and said steering angle detected by said first and third detecting means, respectively, and on the basis of an assumption that said vehicle is running on a reference road surface having a predetermined friction coefficient;
• comparing means for comparing said target transverse acceleration set by said setting means and said actual transverse acceleration detected by said second detecting means to obtain a comparison value;
• estimating means for estimating a friction coefficient of said actual road surface on the basis of the comparison value obtained by said comparing means;
• and
• said control means controlling said driving condition of said vehicle on the basis of said estimated friction coefficient of said actual road surface estimated by said estimating means;
• said setting means including:
• determining means for determining a predetermined stability factor of said vehicle based on the assumption that said vehicle is running on a road surface which has said predetermined friction coefficient, said stability factor being an index indicating a relationship between an increase of said actual transverse acceleration acting on said vehicle and an increase of said steering angle;
• and
• means for setting a target transverse acceleration speed of said vehicle on the basis of said stability factor determined by said determining means and on the basis of said running speed and said steering angle detected by said first and third detection means, respectively;
• said comparing means including:
• means for outputting a first comparison value when said actual transverse acceleration of said vehicle detected by said second detecting means is smaller than said target transverse acceleration set by said setting means;
• and
• means for outputting a second comparison value when said actual transverse acceleration of said vehicle detected by said second detecting means is greater than said target transverse acceleration set by said setting means;
• and
• said estimating means including means for determining that when said first comparison value is obtained, said estimated friction coefficient of said actual road surface is low as compared with said estimated friction coefficient of said actual road surface when said second comparison value is obtained.

A method for estimating a friction coefficient of an actual road surface on which a vehicle is running and for regulating a driving condition of said vehicle in accordance with said estimated friction coefficient, said method comprising:

• a first step of detecting a running speed of said vehicle, a steering angle of said vehicle, and an actual transverse acceleration acting on said vehicle at substantially a right angle to a running direction of said vehicle;
• a second step of setting a target transverse acceleration for said vehicle on the basis of said running speed and said steering angle detected at said first step, and on the basis of an assumption that said vehicle is running on a reference road surface having a predetermined friction coefficient;
• a third step of comparing said actual transverse acceleration detected at said first step and said target transverse acceleration set at said second step to obtain a comparison value;
• a fourth step of estimating a friction coefficient of said actual road surface on the basis of the comparison value obtained at said third step;
• and
• a fifth step of controlling a driving condition of said vehicle in accordance with said estimated friction coefficient estimated at said fourth step;
• said second step including:
• determining a predetermined stability factor of said vehicle based on the assumption that said vehicle is running on a road surface which has said predetermined friction coefficient, said stability factor being an index indicating a relationship between an increase of said actual transverse acceleration acting on said vehicle and an increase of steering angle;
• and
• setting a target transverse acceleration for said vehicle on the basis of said determined stability factor and on the basis of said running speed and said steering angle detected at said first step;
• said third step including:
• outputing a first comparison value when said actual transverse acceleration of said vehicle detected at said first step is smaller than said target transverse acceleration set by said second step;
• and
• outputting a second comparison value when said actual transverse acceleration of said vehicle detected at said first step is greater than said target transverse acceleration set at said second step;
• and
• said fourth step including:
• determining that when said first comparison value is obtained, said estimated friction coefficient of said actual road surface is low, as compared with said estimated friction coefficient of said actual road surface when said second comparison value is obtained.