ROAD SURFACE FRICTION COEFFICIENT ESTIMATING DEVICE AND ROAD SURFACE FRICTION COEFFICIENT ESTIMATING METHOD

• US 20110118935A1
• Filed: 06/26/2009
• Published: 05/19/2011
• Est. Priority Date: 06/30/2008
• Status: Active Grant

• Current Assignee: Nissan Motor Co., Ltd.
• Original Assignee: Nissan Motor Co., Ltd.
• Inventors: Nawano, Masaaki, Shiozawa, Yuuki, Mouri, Hiroshi
• Granted Patent: US 8,639,412 B2
• Time in Patent Office: Days
• US Class Current: 701/35
• 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: B60W 2520/26 Wheel slip
• CPC Class Codes: B60W 2540/12 Brake pedal position
• CPC Class Codes: B60W 40/06 Road conditions
• CPC Class Codes: B60W 40/068 Road friction coefficient

Abstract

A road surface friction coefficient estimating device includes a braking/driving force detecting section for detecting the braking/driving force of a wheel during traveling, a slip ratio detecting section for detecting the slip ratio of the wheel during traveling, and a road surface μ calculating section for estimating the relationship between the detected braking/driving force and the detected slip ratio on the basis of the ratio between the detected braking/driving force and the detected slip ratio, the correlation between the braking/driving force and the slip ratio in the case of the reference road surface, and at least either the detected braking/driving force or the detected slip ratio.

Claims

1. A road surface friction coefficient estimating device comprising:

a braking/driving force detecting section that detects a braking/driving force of a wheel;

a slip ratio detecting section that detects a slip ratio of the wheel; and

a road surface friction coefficient estimating section that;

stores information about a characteristic curve in a coordinate plane, wherein the coordinate plane has a coordinate axis representing the braking/driving force and a coordinate axis representing the slip ratio, and wherein the characteristic curve represents a relationship between the braking/driving force and the slip ratio under condition of a reference road surface friction coefficient;

finds as a reference point a point in the coordinate plane at which a straight line intersects with the characteristic curve, wherein the straight line passes through an origin point of the coordinate plane and a detected point, and wherein the detected point corresponds to a detected value of the braking/driving force obtained by the braking/driving force detecting section and a detected value of the slip ratio obtained by the slip ratio detecting section; and

calculates an estimated value of road surface friction coefficient, on a basis of a reference value and the detected value of at least one of the braking/driving force and the slip ratio, and the reference road surface friction coefficient, wherein the reference value corresponds to the reference point.

2. The road surface friction coefficient estimating device as claimed in claim 1, wherein the road surface friction coefficient estimating section:

calculates a gradient of the straight line in the coordinate plane by dividing the detected value of the braking/driving force by the detected value of the slip ratio; and

finds the reference point on a basis of the gradient.

3. The road surface friction coefficient estimating device as claimed in claim 1, wherein the coordinate plane has a horizontal axis representing the slip ratio and a vertical axis representing the braking/driving force.

4. The road surface friction coefficient estimating device as claimed in claim 1, wherein the origin point of the coordinate plane is a point at which the braking/driving force is equal to zero.

5. The road surface friction coefficient estimating device as claimed in claim 1, wherein the road surface friction coefficient estimating section:

calculates a ratio to reference on a basis of the reference value and the detected value of at least one of the braking/driving force and the slip ratio; and

calculates the estimated value of road surface friction coefficient on a basis of the ratio to reference and the reference road surface friction coefficient.

6. The road surface friction coefficient estimating device as claimed in claim 5, wherein the road surface friction coefficient estimating section calculates the ratio to reference by dividing the detected value of the at least one of the braking/driving force and the slip ratio by the reference value of the at least one of the braking/driving force and the slip ratio.

7. The road surface friction coefficient estimating device as claimed in claim 5, wherein the road surface friction coefficient estimating section:

calculates as a first distance a distance in the coordinate plane between the detected point and a point at which the braking/driving force is equal to zero;

calculates as a second distance a distance in the coordinate plane between the reference point and a point at which the braking/driving force is equal to zero; and

calculates the ratio to reference on a basis of the first and second distances.

8. The road surface friction coefficient estimating device as claimed in claim 7, wherein the road surface friction coefficient estimating section calculates the ratio to reference by dividing the first distance by the second distance.

9. The road surface friction coefficient estimating device as claimed in claim 1, wherein the road surface friction coefficient estimating section stores information about a second characteristic curve in a second coordinate plane, wherein the second coordinate plane has a horizontal axis representing a ratio of the braking/driving force to the slip ratio and a vertical axis representing the braking/driving force, and wherein the second characteristic curve represents a relationship between the braking/driving force and the slip ratio under condition of the reference road surface friction coefficient.

10. The road surface friction coefficient estimating device as claimed in claim 9, wherein the road surface friction coefficient estimating section:

calculates as a ratio to reference a ratio of the detected value of the braking/driving force to the reference value of the braking/driving force with reference to the information about the second characteristic curve; and

calculates the estimated value of road surface friction coefficient on a basis of the ratio to reference and the reference road surface friction coefficient.

11. The road surface friction coefficient estimating device as claimed in claim 10, wherein the road surface friction coefficient estimating section calculates the ratio to reference by dividing the detected value of the braking/driving force by the reference value of the braking/driving force.

12. The road surface friction coefficient estimating device as claimed in claim 1, wherein the road surface friction coefficient estimating section stores information about a second characteristic curve in a second coordinate plane, wherein the second coordinate plane has a horizontal axis representing a ratio of the braking/driving force to the slip ratio and a vertical axis representing the slip ratio, and wherein the second characteristic curve represents a relationship between the braking/driving force and the slip ratio under condition of the reference road surface friction coefficient.

13. The road surface friction coefficient estimating device as claimed in claim 12, wherein the road surface friction coefficient estimating section:

calculates as a ratio to reference a ratio of the detected value of the slip ratio to the reference value of the slip ratio with reference to the information about the second characteristic curve; and

calculates the estimated value of road surface friction coefficient on a basis of the ratio to reference and the reference road surface friction coefficient.

14. The road surface friction coefficient estimating device as claimed in claim 13, wherein the road surface friction coefficient estimating section calculates the ratio to reference by dividing the detected value of the slip ratio by the reference value of the slip ratio.

15. The road surface friction coefficient estimating device as claimed in claim 13, wherein the road surface friction coefficient estimating section calculates the estimated value of road surface friction coefficient by multiplying the reference road surface friction coefficient by the ratio to reference.

16. A road surface friction coefficient estimating method comprising:

an operation of detecting a braking/driving force of a wheel;

an operation of detecting a slip ratio of the wheel; and

an operation of;

storing information about a characteristic curve in a coordinate plane, wherein the coordinate plane has a coordinate axis representing the braking/driving force and a coordinate axis representing the slip ratio, and wherein the characteristic curve represents a relationship between the braking/driving force and the slip ratio under condition of a reference road surface friction coefficient;

finding as a reference point a point in the coordinate plane at which a straight line intersects with the characteristic curve, wherein the straight line passes through an origin point of the coordinate plane and a detected point, and wherein the detected point corresponds to a detected value of the braking/driving force obtained by the braking/driving force detecting section and a detected value of the slip ratio obtained by the slip ratio detecting section; and

calculating an estimated value of road surface friction coefficient, on a basis of a reference value and the detected value of at least one of the braking/driving force and the slip ratio, and the reference road surface friction coefficient, wherein the reference value corresponds to the reference point.