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

• US 20060041365A1
• Filed: 08/17/2005
• Published: 02/23/2006
• Est. Priority Date: 08/19/2004
• Status: Active Grant

• Current Assignee: Honda Motor Co., Ltd. (Honda Motor Company)
• Original Assignee: Honda Motor Co., Ltd. (Honda Motor Company)
• Inventors: Mori, Atsushi
• Granted Patent: US 7,680,577 B2
• Time in Patent Office: Days
• US Class Current: 701/70
• CPC Class Codes: B60T 2210/12 Friction
• CPC Class Codes: B60T 2220/03 Driver counter-steering; Avoidance of conflicts with ESP control
• CPC Class Codes: B60T 2230/02 Side slip angle, attitude angle, floating angle, drift angle
• 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: B60W 40/068 Road friction coefficient
• CPC Class Codes: B60W 40/103 Side slip angle of vehicle body

Abstract

The estimating method for a road friction coefficient μ includes the steps of detecting a steering angle by a steering angle sensor; detecting a lateral acceleration by a lateral acceleration sensor; and calculating an approximate 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.

Claims

1. An estimating method for a road friction coefficient μ

, comprising the steps of;

detecting a steering angle by a steering angle sensor;

detecting a lateral acceleration by a lateral acceleration sensor; and

calculating an approximate 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 μ

i (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 μ

i as said approximate friction coefficient μ

.

2. The estimating method according to claim 1, further comprising the step of finely adjusting the road friction coefficient μ

on the basis of said approximate friction coefficient μ

so that the difference between an estimated lateral acceleration and the lateral acceleration detected by said lateral acceleration sensor becomes zero.

3. The estimating method according to claim 2, wherein said step of calculating said approximate friction coefficient μ

comprises the step of filtering the steering angle detected by said steering angle sensor and the lateral acceleration detected by said lateral acceleration sensor so that the delay characteristic of the steering angle from the lateral acceleration becomes larger.

4. The estimating method according to claim 3, comprising the step of detecting a vehicle speed by a vehicle speed sensor;

said road friction coefficient μ

determination table being 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.

5. The estimating method according to claim 4, comprising the step of detecting a vehicle speed by a vehicle speed sensor;

said step of calculating said approximate friction coefficient μ

comprising the step of stopping the change of said approximate friction coefficient μ

when the vehicle speed detected by said vehicle speed sensor is not greater than a predetermined value.

6. The estimating method according to claim 5, wherein said step of calculating said approximate friction coefficient μ

comprises the step of decreasing said approximate friction coefficient μ

when said approximate friction coefficient μ

stays for more than a predetermined time in the region where it is smaller than a present estimated value of said approximate friction coefficient μ

.

7. The estimating method according to claim 2, wherein said road friction coefficients μ

i (i=1 to n) are defined with a predetermined step set between any adjacent ones of said road friction coefficients μ

i; and

the absolute value of each of upper and lower limits of a fine adjusting value used in said step of finely adjusting the road friction coefficient μ

is equal to or greater than said predetermined step.

8. The estimating method according to claim 7, wherein said step of finely adjusting the road friction coefficient μ

comprises the step of performing the fine adjustment of the road friction coefficient μ

when the lateral acceleration detected by said lateral acceleration sensor is greater than a present estimated value of said approximate friction coefficient μ

multiplied by a constant value.

9. The estimating method according to claim 8, wherein said step of finely adjusting the road friction coefficient μ

comprises the steps of determining whether or not the present estimated value of said approximate friction coefficient μ

has varied and resetting said fine adjusting value to zero when the present estimated value has varied.

10. The estimating method according to claim 9, wherein said step of finely adjusting the road friction coefficient μ

comprises the step of stopping the fine adjustment of the road friction coefficient μ

when counter steer has been detected.

11. The estimating method according to claim 10, wherein 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

when said straight running condition has been detected for more than a predetermined time.

12. The estimating method according to claim 11, wherein said step of calculating said approximate friction coefficient μ

comprises the step of increasing said approximate friction coefficient μ

when the lateral acceleration detected by said lateral acceleration sensor is greater than a present estimated value of said approximate friction coefficient μ

.

13. 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 μ

i (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 μ

i 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.

14. 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 μ

i (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 μ

i 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.

15. The vehicle slip angle estimating method according to claim 14, wherein said step of estimating said vehicle slip angle derivative comprises the steps of:

estimating a lateral acceleration by using a previous estimated value of said vehicle slip angle derivative;

estimating a coefficient of friction on a road where said vehicle is running so that the difference between an estimated value of said lateral acceleration obtained above and an actual value of said lateral acceleration detected by a lateral acceleration sensor becomes zero;

calculating a lateral force acting on a rear wheel in a lateral direction of said vehicle on the basis of said vehicle dynamic model by using an estimated value of said coefficient of friction obtained above and said previous estimated value of said vehicle slip angle; and

calculating said present estimated value of said vehicle slip angle derivative according to said lateral force, said vehicle speed, and a yaw rate.