Road friction coefficient estimating apparatus and vehicle equipped with road friction coefficient estimating apparatus

• US 6,556,911 B2
• Filed: 06/18/2001
• Issued: 04/29/2003
• Est. Priority Date: 06/29/2000
• Status: Expired due to Fees

• Current Assignee: Fuji Jukogyo KK (Subaru Corp.)
• Original Assignee: Fuji Jukogyo KK (Subaru Corp.)
• Inventors: Matsuno, Koji
• Primary Examiner(s): Nguyen, Tan Q.
• Assistant Examiner(s): Tran, Dalena
• Application Number:
  US09/883,679
• Publication Number:
  US 20020011093A1
• Time in Patent Office: 680 Days
• Field of Search: 701/1, 701/80, 701/41, 701/82, 701/90, 180/422, 180/412, 180/197, 180/415, 303/150, 303/166, 731/46, 731/04, 73/8, 73/9
• US Class Current: 701/80
• 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 30/02 Control of vehicle driving stability
• CPC Class Codes: B60W 30/18172 Preventing, or responsive to skidding of wheels
• CPC Class Codes: B60W 40/064 Degree of grip
• CPC Class Codes: B60W 40/068 Road friction coefficient
• CPC Class Codes: B60W 40/101 Side slip angle of tyre
• 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 slip angle calculating unit calculates a slip angle of a vehicle body corresponding to a steering wheel angle and a vehicle speed, based on a vehicle wheel angle and the vehicle speed, by an observer of a preset vehicle motion model under a motion equation of a vehicle. A front wheel slip angle calculating unit calculates a front wheel slip angle based on the steering wheel angle, a vehicle speed, a yaw rate, and the calculated vehicle body slip angle. A self-aligning torque calculating unit calculates the self-aligning torque based on the hydraulic chamber pressure of the left side and the hydraulic chamber pressure of the right side in a power cylinder. The vehicle speed, an estimated front wheel slip angle, and the self-aligning torque are inputted to a road friction coefficient setting unit, and the road friction coefficient setting unit sets a road friction coefficient by referring to a map based on the input to output the set value. A road friction coefficient is estimated in wide ranges while reducing noises of sensors.

Claims

1. A road friction coefficient estimating apparatus, comprising:

self-aligning torque detecting means for detecting a self-aligning torque of a steered wheel;

steered wheel slip angle detecting means for detecting a slip angle of the steered wheel by inputting a detected value of a vehicle motion parameter to an observer formed by a motion model of a vehicle; and

road friction coefficient setting means for setting a road friction coefficient based on the relationship between the self-aligning torque and the steered wheel slip angle.

2. The road friction coefficient estimating apparatus according to claim 1, wherein the road friction coefficient setting means prohibits the setting of the road friction coefficient based on a preset vehicle speed condition.

3. The road friction coefficient estimating apparatus according to claim 1, wherein the road friction coefficient setting means prohibits the setting of the road friction coefficient based on the preset slip angle of the steered wheel.

4. A vehicle equipped with the road friction coefficient estimating apparatus according to claim 1, wherein the road friction coefficient estimated by the road friction coefficient estimating apparatus is used for one of control parameters of the vehicle.

5. A road friction coefficient estimating apparatus, comprising:

a hydraulic power steering device for assisting a steering force by an oil pressure applied to a pair of hydraulic chambers of a power cylinder;

oil pressure detecting means for detecting each oil pressure of the pair of hydraulic chambers;

self-aligning torque detecting means for calculating a self-aligning torque based on a higher pressure of the pair of hydraulic chambers;

steered wheel slip angle detecting means for detecting a slip angle of the steered wheel by inputting a detected value of a vehicle motion parameter to an observer formed by a motion model of a vehicle; and

road friction coefficient setting means for setting a road friction coefficient based on the relationship between the self-aligning torque and the steered wheel slip angle.

6. The road friction coefficient estimating apparatus according to claim 5, further comprising:

steering speed detecting means for detecting a steering speed, wherein the self-aligning torque detecting means corrects the self-aligning torque according to the steering speed.

7. The road friction coefficient estimating apparatus according to claim 5, wherein the road friction coefficient setting means prohibits the setting of the road friction coefficient based on a preset vehicle speed condition.

8. The road friction coefficient estimating apparatus according to claim 5, wherein the road friction coefficient setting means prohibits the setting of the road friction coefficient based on the preset slip angle of the steered wheel.

9. A vehicle equipped with the road friction coefficient estimating apparatus according to claim 5, wherein the road friction coefficient estimated by the road friction coefficient estimating apparatus is used for one of control parameters of the vehicle.

10. A road friction coefficient estimating apparatus, comprising:

a hydraulic power steering device for assisting a steering force by an oil pressure applied to a pair of hydraulic chambers of a power cylinder;

oil pressure detecting means for detecting each oil pressure of the pair of hydraulic chambers;

self-aligning torque detecting means for calculating a self-aligning torque based on a difference of pressure in the pair of hydraulic chambers;

steered wheel slip angle detecting means for detecting a slip angle of the steered wheel by inputting a detected value of a vehicle motion parameter to an observer formed by a motion model of a vehicle; and

road friction coefficient setting means for setting a road friction coefficient based on the relationship between the self-aligning torque and the steered wheel slip angle.

11. The road friction coefficient estimating apparatus according to claim 10, further comprising:

steering speed detecting means for detecting a steering speed, wherein the self-aligning torque detecting means corrects the self-aligning torque according to the steering speed.

12. The road friction coefficient estimating apparatus according to claim 10, wherein the road friction coefficient setting means prohibits the setting of the road friction coefficient based on a preset vehicle speed condition.

13. The road friction coefficient estimating apparatus according to claim 10, wherein the road friction coefficient setting means prohibits the setting of the road friction coefficient based on the preset slip angle of the steered wheel.

14. A vehicle equipped with the road friction coefficient estimating apparatus according to claim 10, wherein the road friction coefficient estimated by the road friction coefficient estimating apparatus is used for one of control parameters of the vehicle.

15. A road friction coefficient estimating apparatus, comprising:

an electric power steering device for assisting a steering force with an electric motor;

torsion bar torque detecting means for detecting a torsion bar torque;

motor current detecting means for detecting the driving current of the electric motor;

self-aligning torque detecting means for calculating a self-aligning torque based on the torsion bar torque and the motor current;

steered wheel slip angle detecting means for detecting a slip angle of the steered wheel by inputting a detected value of a vehicle motion parameter to an observer formed by a motion model of a vehicle; and

road friction coefficient setting means for setting a road friction coefficient based on the relationship between the self-aligning torque and the steered wheel slip angle.

16. The road friction coefficient estimating apparatus according to claim 15, further comprising:

steering speed detecting means for detecting a steering speed, wherein the self-aligning torque detecting means corrects the self-aligning torque according to the steering speed.

17. The road friction coefficient estimating apparatus according to claim 15, wherein the road friction coefficient setting means prohibits the setting of the road friction coefficient based on a preset vehicle speed condition.

18. The road friction coefficient estimating apparatus according to claim 15, wherein the road friction coefficient setting means prohibits the setting of the road friction coefficient based on the preset slip angle of the steered wheel.

19. A vehicle equipped with the road friction coefficient estimating apparatus according to claim 15, wherein the road friction coefficient estimated by the road friction coefficient estimating apparatus is used for one of control parameters of the vehicle.