Road friction coefficient estimating apparatus for vehicle

• US 6,526,804 B2
• Filed: 05/30/2001
• Issued: 03/04/2003
• Est. Priority Date: 05/30/2000
• Status: Expired due to Fees

• Current Assignee: Fuji Heavy Industries Limited (Subaru Corp.)
• Original Assignee: Fuji Heavy Industries Limited (Subaru Corp.)
• Inventors: Takahashi, Akira
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): Garber, Charles D.
• Application Number:
  US09/866,769
• Publication Number:
  US 20020007661A1
• Time in Patent Office: 643 Days
• Field of Search: 73/9, 73/8, 701/80, 701/82, 303/150
• US Class Current: 73/9
• CPC Class Codes: B60T 2210/12 Friction
• CPC Class Codes: B60T 2210/14 Rough roads, bad roads, gravel roads
• 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: 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

A yaw rate comparison road friction coefficient estimating section estimates a first road friction coefficient based on a high friction road reference yaw rate calculated according to a high friction coefficient road vehicle motion model in a high friction road reference value estimating section, a low friction road reference yaw rate calculated according to a low friction coefficient road vehicle motion model in a low friction road reference value estimating section, and an actual yaw rate calculated in an actual value estimating section. A final road friction coefficient estimating section calculates a present final road friction coefficient by weight-averaging a previous final road friction coefficient and the first road friction coefficient using a weight function established in a weight function establishing section. The weight function is variable according to a road roughness parameter produced in a road roughness detecting apparatus.

Claims

1. A road friction coefficient estimating apparatus for a vehicle, comprising:

estimating means for estimating a road friction coefficient based on motion parameters indicative of a motion of said vehicle, and

road roughness detecting means for detecting roughness of a road surface and for producing a road roughness parameter indicating said roughness of the road surface;

wherein said estimating means is adapted to vary follow-up characteristic for a change of said road friction coefficient by changing responsiveness for estimating said road friction coefficient according to said roughness parameter, wherein

said estimating means is adapted to raise said follow-up characteristic by enhancing responsiveness for estimating said road friction coefficient when the number of concave and convex parts as indicating a state of said roughness is larger than a specified level per a specified distance.

2. A road friction coefficient estimating apparatus for a vehicle, comprising:

estimating means for estimating a road friction coefficient based on motion parameters indicative of a motion of said vehicle, and

road roughness detecting means for detecting roughness of the road surface and for producing a road roughness parameter indicating said roughness of road surface;

wherein said estimating means is adapted to vary follow-up characteristic for a change of said road friction coefficient by changing responsiveness for estimating said road friction coefficient according to said roughness parameter,

said estimating means comprises;

first road friction coefficient estimating means for calculating a first road-friction coefficient based on said motion parameters of said vehicle;

weight function establishing means for setting a weight function according to said road roughness parameter; and

second road friction coefficient estimating means for calculating a weighted average between said first road friction coefficient and said second road friction coefficient previously estimated according to said weight function as a weight multiplier and for outputting said second road friction coefficient.

3. The apparatus according to claim 2, wherein

said weight function varies according to said road roughness parameter to raise said follow-up characteristic by enhancing said responsiveness for estimating said road friction coefficient when the number of concave and convex parts as indicating a state of said roughness of road surface is larger.

4. The apparatus according to claim 2, wherein

said weight function varies according to said road roughness parameter to raise accuracy and stability with respect to the change of said road friction coefficient by reducing said responsiveness for estimating said road friction coefficient when the number of concave and convex parts as indicating the state of said roughness is less than a specified level per a specified distance.

5. A road friction coefficient estimating apparatus for a vehicle, comprising:

estimating means for estimating a road friction coefficient based on motion parameters indicative of a motion of said vehicle, and

road roughness detecting means for detecting a roughness of road surface and for producing a road roughness parameter indicating said roughness of road surface;

wherein said estimating means is adapted to vary follow-up characteristic for a change of said road friction coefficient by changing responsiveness for estimating said road friction coefficient according to said roughness parameter, wherein

said estimating means includes an actual value estimating section in which an actual value of motion parameter is calculated, a high friction coefficient road reference value estimating section in which a high friction coefficient road reference value is calculated based on a high friction coefficient road vehicle motion model, a low friction coefficient road reference value estimating section in which a low friction coefficient road reference value is calculated based on a low friction coefficient road vehicle motion model, and a road friction coefficient estimating section in which said road friction coefficient is calculated based on said high friction coefficient road reference value, said low friction coefficient road reference value and said actual value of said motion parameter, wherein said actual value estimating section includes an observer having a feedback gain matrix to be varied according to said road roughness parameter.

6. The apparatus according to claim 5, wherein:

said motion parameter is adapted to be a yaw rate.

7. The apparatus according to Claim 5, wherein:

said feedback gain matrix is established to be large when said road roughness parameter is large so as to raise follow-up characteristic by enhancing said responsiveness for estimating said road friction coefficient.

8. The apparatus according to claim 5, wherein:

said feedback gain matrix is established to be small when said road roughness parameter is small so as to raise accuracy and stability with respect to the change of said road friction coefficient by reducing said responsiveness to the change of said road friction coefficient.

9. A road friction coefficient estimating apparatus for a vehicle, comprising:

estimating means for estimating a road friction coefficient based on motion parameters indicative of a motion of said vehicle, and

road roughness detecting means for detecting a roughness of road surface and for producing a road roughness parameter indicating said roughness of road surface;

wherein said estimating means is adapted to vary follow-up characteristic for a change of said road friction coefficient by changing responsiveness for estimating said road friction coefficient according to said roughness parameter;

wherein said estimating means is adapted to raise accuracy and stability with respect to the change of said road friction coefficient by reducing said responsiveness for estimating said road friction coefficient when the number of concave and convex parts as indicating the state of said roughness is less than a specified level per a specified distance.