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

• US 5,216,608 A
• Filed: 01/22/1991
• Issued: 06/01/1993
• Est. Priority Date: 01/25/1990
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Jidosha Kogyo Kabushiki Kaisha
• Original Assignee: Mitsubishi Jidosha Kogyo Kabushiki Kaisha
• Inventors: Yamada, Kiichi, Ito, Masayoshi, Isoda, Keiji, Shigehara, Toshio, Hashiguchi, Masayuki
• Primary Examiner(s): Black, Thomas G.
• Assistant Examiner(s): AUCHTERLONIE, THOMAS
• Application Number:
  US07/644,251
• Time in Patent Office: 861 Days
• Field of Search: 364/426.01, 364/426.02, 364/426.03, 180/197, 180/249, 180/248, 303/15, 303/97, 303/100, 303/103
• US Class Current: 701/90
• CPC Class Codes: B60K 28/16 responsive to, or preventing, skidding of wheels brake control systems for vehicle drive stability B60T8/1755; arrangements responsive to a speed condition for adjusting wheel braking force B60T8/32; control of vehicle driving stability otherwise than by controlling the propulsion unit only B60W30/02; preventing wheel slippage by reducing power in rail vehicles B61C15/00
• CPC Class Codes: B60T 2201/16 Curve braking control, e.g. turn control within ABS control algorithm
• CPC Class Codes: B60T 2210/12 Friction
• CPC Class Codes: B60T 8/172 Determining control parameters used in the regulation, e.g. by calculations involving measured or detected parameters B60T8/17551 takes precedence
• CPC Class Codes: B60T 8/175 Brake regulation specially adapted to prevent excessive wheel spin during vehicle acceleration, e.g. for traction control safety devices for propulsion unit control responsive to, or preventing, skidding of wheels B60K28/16
• CPC Class Codes: B62D 6/006 using a measured or estimated road friction coefficient
• CPC Class Codes: G01N 19/02 Measuring coefficient of friction between materials testing of tyres G01M17/02; determinations of friction coefficient used in vehicle braking or traction control systems B60T8/172

Abstract

An apparatus for effecting a method for estimating the friction coefficient of a road surface according to the present invention comprises front- and rear-wheel rotation sensors for detecting the running speed of a vehicle, a linear G sensor for detecting an actual transverse acceleration of the vehicle, a steering angle sensor for detecting the steering angle of front wheels, and a torque calculating unit supplied with the vehicle speed, actual transverse acceleration, and steering angle detected by means of these sensors. In the torque calculating unit, which takes account of an assumed value of the stability factor of the vehicle in addition to the vehicle speed, actual transverse acceleration, and steering angle, a target transverse acceleration required by a driver is calculated, for example, and whether or not the friction coefficient of the road surface is low is then estimated according to the relationship between the calculated target transverse acceleration and the actual transverse acceleration.

Claims

1. 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;

calculating means for calculating a stability factor of said vehicle on the basis of said running speed, said actual transverse acceleration, and said steering angle detected by said first, second and third detecting means, respectively, 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

first comparing means for comparing said stability factor calculated by said calculating means and a predetermined limit value, and for outputting a first comparison value when said stability factor is greater than said limit value and a second comparison value when said stability factor is smaller than said limit value;

second comparing means for comparing said actual transverse acceleration detected by said second detecting means and a predetermined reference value, and for outputting a third comparison value when said actual transverse acceleration is less than said predetermined reference value and a fourth comparison value when said actual transverse acceleration speed is greater than said predetermined reference value;

estimating means for estimating a friction coefficient of said actual road surface and for determining that when said comparison values output by said first and second comparing means are said first and third comparison values, respectively, said estimated friction coefficient is low as compared said estimated friction coefficient when said comparison values output by said first and second comparing means are not said first and third comparison values, respectively;

said control means controlling said driving condition of said vehicle on the basis of said determination by said estimating means as to whether said estimated friction coefficient of said actual road surface estimated by said estimating means is low.

2. A device according to claim 1, wherein said device further includes means for outputting an alarm signal when said stability factor calculated by said calculating means is greater than said limit value, said alarm signal indicating that said vehicle is in a limit state for steering control.

3. 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.

4. A method according to claim 3, wherein said third step includes outputting an alarm signal when said stability factor calculated at said second step is greater than a predetermined limit value, said alarm signal indicating that said vehicle is in a limit state for steering control.

5. 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.

6. A device according to claim 5, wherein said control means includes:

calculating means for calculating a target driving torque for said vehicle on the basis of said target transverse acceleration set by said setting means and said estimated friction coefficient of said actual road surface estimated by said estimating means; and

control state means for controlling an actual driving torque of said vehicle according to said calculated target driving torque.

7. A device according to claim 6, wherein:

said calculating means of said control means includes;

first calculating means for calculating a first target driving torque for said vehicle suitable for a road surface having a first friction coefficient on the basis of said target transverse acceleration speed set by said setting means; and

second calculating means for calculating a second target driving torque for said vehicle suitable for an actual road surface having a second friction coefficient lower than said first friction coefficient on the basis of said target transverse acceleration speed set by said setting means; and

said control state means of said control means includes;

selecting means for selecting one of said first and second target driving torques in accordance with said estimated friction coefficient of said actual road surface estimated by said estimating means.

8. 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.

9. A method according to claim 8, wherein said fifth step includes:

determining a target driving torque for said vehicle on the basis of said target transverse acceleration set at said second step and on the basis of said estimated friction coefficient of said actual road surface estimated at said fourth step, and

controlling an actual driving torque of said vehicle according to said determined target driving torque.

10. A method according to claim 8, wherein said fifth step includes:

calculating a first target driving torque for said vehicle suitable for a road surface having a first friction coefficient on the basis of said target transverse acceleration set at said second step;

calculating a second target driving torque for said vehicle suitable for a road surface having a second friction coefficient lower than said first friction coefficient on the basis of said target transverse acceleration set at said second step; and

selecting one of said first and second target driving torques in accordance with said estimated friction coefficient of said actual road surface estimated at said fourth step.