Vehicle motion control device and method

• US 6,659,570 B2
• Filed: 11/13/2001
• Issued: 12/09/2003
• Est. Priority Date: 11/20/2000
• Status: Expired due to Term

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Nakamura, Akira
• Primary Examiner(s): Graham, Matthew C.
• Application Number:
  US09/987,180
• Publication Number:
  US 20020109402A1
• Time in Patent Office: 756 Days
• Field of Search: 303/146, 303/147, 303/148, 303/149, 303/150, 303/112, 701/74, 701/71, 701/80, 180/197
• US Class Current: 303/146
• CPC Class Codes: B60T 2201/14 Electronic locking-differential
• CPC Class Codes: B60T 2230/02 Side slip angle, attitude angle, floating angle, drift angle
• CPC Class Codes: B60T 2270/86 Optimizing braking by using ESP vehicle or tire model
• CPC Class Codes: B60T 8/17552 responsive to the tire sideslip angle or the vehicle body slip angle
• CPC Class Codes: B60T 8/1769 specially adapted for vehicles having more than one driven axle, e.g. four-wheel drive vehicles
• CPC Class Codes: B60W 10/184 with wheel brakes
• CPC Class Codes: B60W 2050/0028 Mathematical models, e.g. for simulation
• CPC Class Codes: B60W 40/11 Pitch movement
• CPC Class Codes: B60W 40/112 Roll movement
• CPC Class Codes: B60W 40/114 Yaw movement

Abstract

Vehicle motion control devices and methods systematically treat a conditions of each wheel to acquire and maintain the vehicle behavior stability together with anti wheel lock and wheel spin processing, braking forces distribution. Device for controlling a running behavior of a vehicle estimates a road reaction force on each wheel, calculates a yaw moment around a centroid of the vehicle body generated by the road reaction force on each wheel, and controls driving and braking forces on each wheel based upon the yaw moments so as to stabilize a running of the vehicle. Spin and Drift conditions are detected through presently generated yaw moments and critical yaw moments which can be generated by a road reaction force assumed to be maximized. Physical parameters of each wheels, required for detecting and controlling the behavior of the vehicle are estimated with a theoretical tire model.

Claims

1. A device for controlling a running behavior of a vehicle, the vehicle having a vehicle body and wheels, comprising:

means for estimating a road reaction force generated on each of the wheels;

means for calculating a yaw moment around a centroid of the vehicle body generated by the road reaction force on each of the wheels; and

means for controlling driving and braking forces on each of the wheels based upon said yaw moments so as to stabilize a running of the vehicle,

wherein said driving and braking force controlling means includes calculation means to calculate a yaw moment required to be added to the vehicle body so as to stabilize the vehicle running, and controls the driving and braking forces on each of the wheels so as to add said required yaw moment to the vehicle body, said required yaw moment being calculated based upon a yaw moment presently generated by the road reaction force on each of the wheels and a yaw moment estimated to be realized through the control of the driving and braking forces on each of the wheels.

2. A device according to claim 1, wherein said driving and braking force controlling means calculates target driving and braking forces for each of the wheels based upon said required yaw moment, and controls the driving and braking forces on each of the wheels based upon said target driving and braking forces.

3. A device according to claim 1, wherein said calculation means estimates, based upon a tire model, a road reaction force which can be generated on each of the wheels, and calculates said yaw moment which can be generated on each of the wheel according to the presently generated road reaction force and said road reaction force which can be generated on each of the wheels.

4. A device according to claim 1, wherein said driving and braking force controlling means controls the driving and braking forces on each of the wheels so that a magnitude of a sum of the presently generated yaw moments is reduced by said required yaw moment being added to the vehicle body when the direction of said sum of yaw moments is identical to the turning direction of the vehicle and the magnitude of said sum of yaw moments is too large.

5. A device according to claim 4, wherein said wheels include front left and right wheels and rear left and right wheels;

and said driving and braking force controlling means judges that said magnitude of said yaw moment sum is too large and the vehicle is under a spin condition if M_fl+M_fr+M_rlG+M_rrG is out of a predetermined range, where M_fl and M_fr denote yaw moments around the centroid of the vehicle body generated by the road reaction force on the front left and right wheels, respectively, and M_rlG and M_rrG denote critical yaw moments at the present longitudinal forces on the rear wheels, respectively;

said critical yaw moment being defined as a yaw moment which can be generated around the centroid of the vehicle body assuming that a road reaction force is maximized while maintaining its longitudinal force component.

6. A device according to claim 5, wherein said driving and braking force controlling means judges that M_fl+M_fr+M_rlG+M_rrG is out of a predetermined range if M_fl+M_fr+M_rlG+M_rrG is larger than a negative reference value for judgement when the vehicle is making a left turn or if M_fl+M_fr+M_rlG+M_rrG is smaller than a positive reference value for judgement when the vehicle is making a right turn, where the direction of the left turn of the vehicle is defined as the positive direction of a yaw moment.

7. A device according to claim 6, wherein said driving and braking force controlling means controls the driving and braking forces on each of the wheels such that M_fl+M_fr+M_rlG+M_rrG is not more than a negative control reference value −

Δ

Ms if M_fl+M_fr+M_rlG+M_rrG is larger than said negative reference value for judgement when the vehicle is making a left turn, and M_fl+M_fr+M_rlG+M_rrG is not less than a positive control reference value Δ

Ms if M_fl+M_fr+M_rlG+M_rrG is smaller than said positive reference value for judgement when the vehicle is making a right turn.

8. A device according to claim 7, wherein said driving and braking force controlling means calculates a target yaw moment for an outside one of the front wheels relative to a turning center of the vehicle in order that M_fl+M_fr+M_rlG+M_rrG is not more than said negative control reference value −

Δ

Ms if M_fl+M_fr+M_rlG+M_rrG is larger than said negative reference value for judgement when the vehicle is making a left turn and that M_fl+M_fr+M_rlG+M_rrG is not less than said positive control reference value Δ

Ms if M_fl+M_fr+M_rlG+M_rrG is smaller than a positive reference value for judgement when the vehicle is making a right turn, and said driving and braking force controlling means also calculates a target longitudinal force on said front outside wheel based upon said target yaw moment and controls the driving and braking forces on said front outside wheel based upon said target longitudinal force.

9. A device according to claim 8, wherein said driving and braking force controlling means judges if a spin condition can be suppressed by a control of said front outside wheel;

and calculates a target longitudinal force for said front outside wheel based upon said target yaw moment when the spin condition can be suppressed by a control of said front outside wheel; and

controls the driving and braking forces on the front outside wheel based upon said target longitudinal force.

10. A device according to claim 1, wherein the driving and braking force controlling means controls the driving and braking forces on each of the wheels so as to increase a magnitude of a lateral force on the rear wheels by adding said required yaw moment to the vehicle body when the lateral forces on the front wheels reach to limits of the corresponding wheels while the lateral forces on the rear wheels have not reached to limits of the corresponding tires under a condition where the magnitude of a sum of the yaw moments is not excessive.

11. A device according to claim 10, wherein said wheels include front left and right wheels and rear left and right wheels;

and said driving and braking force controlling means judges that lateral forces on the front wheels reach to the limits of the corresponding tires while lateral forces on the rear wheels have not reached to the limits of the corresponding tires and the vehicle is under a drift condition if a magnitude of a ratio of M_fl+M_fr to M_flG+M_frG is larger than a minimum reference value and M_fl+M_fr+M_rlG+M_rrG is out of a predetermined range, where M_fl and M_fr denote yaw moments around the centroid of the vehicle body generated by the road reaction force on the front left and right wheels, respectively, and M_flG, M_frG, M_rlG and M_rrG denote critical yaw moments at the present longitudinal forces on the front left, front right, rear left and rear right wheels, respectively;

said critical yaw moment being defined as a yaw moment which can be generated around the centroid of the vehicle body assuming that a road reaction force is maximized while maintaining its longitudinal force component.

12. A device according to claim 11, wherein said driving and braking force controlling means judges that the lateral forces on the front wheels reach to the limits of the corresponding tires while the lateral forces on the rear wheels have not reached to the limits of the corresponding tires and the vehicle is under a drift condition if the magnitude of the ratio of M_fl+M_fl to M_flG+M_frG is larger than a minimum reference value and M_fl+M_fr+M_rlG+M_rrG is lower than a negative reference value for judgement when the vehicle is making a left turn or if the magnitude of the ratio of M_rlG+M_rrG to M_flG+M_frG is larger than a minimum reference value and M_fl+M_fr+M_rlG+M_rrG is higher than a positive reference value for judgement when the vehicle is making a right turn, where the direction of the left turn of the vehicle is defined as the positive direction of a yaw moment.

13. A device according to claim 12, wherein said minimum reference value is a positive value smaller than one.

14. A device according to claim 12, wherein said driving and braking forces controlling means controls the driving and braking forces on each of the wheels such that M_fl+M_fr+M_rlG+M_rrG is not less than said negative control reference value −

Δ

Md if M_fl+M_fr+M_rlG+M_rrG is smaller than said negative reference value for judgement when the vehicle is making a left turn, and M_fl+M_fr+M_rlG+M_rrG is not more than a positive control reference value Δ

Md if M_fl+M_fr+M_rlG+M_rrG is larger than said positive reference value for judgement when the vehicle is making a right turn.

15. A device according to claim 14, wherein said driving and braking force controlling means calculates a target yaw moment for each of the rear wheels in order that M_fl+M_fr+M_rlG+M_rrG is not less than said negative control reference value −

Δ

Ms if M_fl+M_fr+M_rlG+M_rrG is smaller than said negative reference value for judgement when the vehicle is making a left turn, and M_fl+M_fr+M_rlG+M_rrG is not more than a positive control reference value Δ

Ms if M_fl+M_fr+M_rlG+M_rrG is larger than said positive reference value for judgement when the vehicle is making a right turn, and said driving and braking force controlling means calculates a target longitudinal force on each of the rear wheels based upon said target yaw moment and controls the driving and braking forces on said rear wheels based upon said target longitudinal force.

16. A device according to claim 15, wherein said driving and braking force controlling means calculates a maximum allowable value for a vehicle body turning yaw moment around the centroid of the vehicle body in the same direction of the turning of the vehicle to be generated by the road reaction force on each of the rear wheels, and limits said target yaw moment for each of the rear wheels if said target yaw moment exceeds said maximum allowable value.

17. A device according to claim 8, wherein said driving and braking force controlling means includes means to calculate a slip angle of each of the wheels;

means to calculate a vertical load on each of the wheels;

means to calculate a maximum static frictional coefficient between the wheel and a road surface of each of the wheels;

means for calculating a normal running limit for a target longitudinal force for each of the wheels based upon said vertical load and said maximum static frictional coefficient;

said driving and braking force controlling means preventing the target longitudinal force for each of the wheels other than the front outside wheel from exceeding the corresponding normal running limit.

18. A device according to claim 15, said driving and braking force controlling means includes means to calculate a slip angle of each of the wheels;

means to calculate a vertical load on each of the wheels;

means to calculate a maximum static frictional coefficient between the wheel and a road surface of each of the wheels;

means for defining a normal running limit for a target longitudinal force for each of the wheels based upon said vertical load and said maximum static frictional coefficient;

said driving and braking force controlling means preventing the target longitudinal force for each of the front left and right wheels from exceeding the corresponding normal running limit.

19. A device according to claim 17, wherein said normal running limit defining means defines a first range of longitudinal force in which a composite road reaction force on the wheel is not saturated to its critical value at a slip angle according to a tire model and a second range based upon a vertical load and a maximum static frictional coefficient for each of the wheels, and select, as upper and lower normal running limits for each of the wheels, the larger range from said first and second ranges.

20. A device according to claim 19, wherein said normal running limit defining means defines said second range along a longitudinal direction of the vehicle body.

21. A device according to claim 5, wherein said driving and braking force controlling means estimates a slip angle rate β

dr of the rear wheels and judges that M_fl+M_fr+M_rlG+M_rrG−

KIβ

dr is out of a predetermined range if M_fl+M_fr+M_rlG+M_rrG−

KIβ

dr is larger than a negative reference value for judgement when the vehicle is making a left turn or if M_fl+M_fr+M_rlG+M_rrG−

KIβ

dr is smaller than a positive reference value for judgement when the vehicle is making a right turn, where the direction of the left turn of the vehicle is defined as the positive direction of a yaw moment and KI denotes a positive constant.

22. A device according to claim 21, wherein said driving and braking forces controlling means controls the driving and braking forces on each of the wheels for satisfying that M_fl+M_fr+M_rlG+M_rrG−

KIβ

dr is not more than a negative control reference value −

Δ

Ms if M_fl+M_fr+M_rlG+M_rrG−

KIβ

dr is larger than said negative reference value for judgement when the vehicle is making a left turn, and M_fl+M_fr+M_rlG+M_rrG−

KIβ

dr is not less than a positive control reference value Δ

Ms if M_fl+M_fr+M_rlG+M_rrG−

KIβ

dr is smaller than said positive reference value for judgement when the vehicle is making a right turn.

23. A device according to claim 22, wherein said driving and braking force controlling means calculates a spin avoiding yaw moment Mns which satisfies a condition of M_fl+M_fr+M_rlG+M_rrG+Mns=Δ

Ms−

KIβ

dr, and controls the driving and braking force on each of the wheels so as to generate said spin avoiding yaw moment.

24. A device according to claim 23, wherein said driving and braking force controlling means calculates a target longitudinal forces for each of the wheels for generating said spin avoiding yaw moment, and controls the driving and braking force on each of the wheels based upon said target longitudinal force therefor.

25. A device according to claim 11, wherein said driving and braking force controlling means estimates a slip angle rate β

dr of the rear wheels and judges that the lateral forces on the front wheels reach to the limits of the corresponding tires while the lateral forces on the rear wheels do not reach to the limits of the corresponding tires and the vehicle is under a drift condition if a magnitude of a ratio of M_fl+M_fl to M_flG+M_frG is larger than a minimum reference value and M_fl+M_fr+M_rlG+M_rrG−

KIβ

dr is smaller than a negative reference value for judgement when the vehicle is making a left turn or if the magnitude of the ratio of M_rlG+M_rrG to M_flG+M_frG is larger than a minimum reference value and M_fl+M_fr+M_rlG+M_rrG−

KIβ

dr is larger than a positive reference value for judgement when the vehicle is making a right turn, where the direction of the left turn of the vehicle is defined as the positive direction of a yaw moment.

26. A device according to claim 25, wherein said driving and braking force controlling means controls the driving and braking forces on each of the wheels for satisfying that M_fl+M_fr+M_rlG+M_rrG−

KIβ

dr is not less than said negative control reference value −

Δ

Md if M_fl+M_fr+M_rlG+M_rrG−

KIβ

dr is smaller than said negative reference value for judgement when the vehicle is making a left turn, and that M_fl+M_fr+M_rlG+M_rrG−

KIβ

dr is not more than said positive control reference value Δ

Md if M_fl+M_fr+M_rlG+M_rrG−

KIβ

dr is larger than said positive reference value for judgement when the vehicle is making a right turn.

27. A device according to claim 26, wherein said driving and braking force controlling means calculates a drift avoiding yaw moment Mnd which satisfies a condition of M_fl+M_fr+M_rlG+M_rrG+Mnd=Δ

Md−

KIβ

dr and controls the driving and braking force on each of the wheels so as to generate said drift avoiding yaw moment.

28. A device according to claim 27, wherein said driving and braking force controlling means calculates a target longitudinal force for each of the wheels for generating said drift avoiding yaw moment, and controls the driving and braking force on each of the wheels based upon said target longitudinal force therefor.

29. A device according to claim 24, wherein said driving and braking force controlling means includes means to calculate a slip angle of each of the wheels;

means to calculate a vertical load on each of the wheels;

means to calculate a maximum static frictional coefficient between the wheel and a road surface of each of the wheels;

means for calculating a normal running limit for a target longitudinal force for each of the wheels based upon said vertical load and said maximum static frictional coefficient;

said driving and braking force controlling means preventing the target longitudinal force for each of the wheels other than the wheels required for generation of said spin avoiding yaw moment from exceeding the corresponding normal running limit.

30. A device according to claim 28, wherein said driving and braking force controlling means includes means to calculate a slip angle of each of the wheels;

means to calculate a vertical load on each of the wheels;

means to calculate a maximum static frictional coefficient between the wheel and a road surface of each of the wheels;

means for calculating a normal running limit for a target longitudinal force for each of the wheels based upon said vertical load and said maximum static frictional coefficient;

said driving and braking force controlling means preventing the target longitudinal force for each of the wheels other than the wheels required for generation of said drift avoiding yaw moment from exceeding the corresponding normal running limit.

31. A device according to claim 29, wherein said normal running limit defining means defines a first range of longitudinal force in which a composite road reaction force on the wheel is not saturated to its critical value at a slip angle according to a tire model and a second range of a longitudinal force based upon a vertical load and a maximum static frictional coefficient for each of the wheels, and selects the larger range from said first and second ranges as upper and lower normal running limits for each of the wheels in each of driving and braking terms of the vehicle.

32. A device according to claim 31, wherein said normal running limit defining means defines said second range along the longitudinal direction of the vehicle body.

33. A device according to claim 23, wherein said term of KIβ

dr is omitted.

34. A device according to claim 1, each of the wheels bearing a tire;

wherein said road reaction force estimating means estimates a tire longitudinal force and a tire lateral force on each of the wheels, and further estimates a road reaction force on each of the wheels based upon said tire longitudinal force and said tire lateral force on each of the wheels.

35. A device according to claim 34, wherein said tire longitudinal force on each of the wheels are estimated based upon a vehicle total driving force, a braking force on each of the wheels and a wheel rotational acceleration of each of the wheels.

36. A device according to claim 35, wherein said road reaction force estimating means estimates a vehicle total driving force based upon a steering angle and a tire lateral force on either of the wheels estimated in a previous cycle.

37. A device according to claim 34, wherein said tire lateral forces on the front wheels are estimated based upon a yaw rate of the vehicle body, a lateral acceleration of the vehicle body and a longitudinal force on each of wheels.

38. A device according to claim 34, wherein said tire lateral forces on the rear wheels are estimated based upon a lateral acceleration of the vehicle body, said longitudinal forces and said lateral forces on the front wheels.

39. A device according to claim 34, further comprising said vehicle further including a differential gear device;

wherein said road reaction forces are estimated allowing for a torque transmission mechanism in said differential gear device.

40. A device according to claim 34, wherein a sum of the lateral forces on the left and right wheels for each of the pairs of the front and rear wheels is estimated first, and then individual lateral forces on the left and right wheels are calculated from said sum of the lateral forces according to the ratio between the corresponding lateral forces on the left and right wheels obtained from a calculation based upon the tire model.

41. A device according to 29, wherein said normal running limits are defined individually for the pair of the front wheels, rear inside wheel and rear outside wheel.

42. A method for controlling a running behavior of a vehicle, the vehicle having a vehicle body and wheels, comprising steps of:

estimating a road reaction force generated on each of the wheels; and

calculating a yaw moment around a centroid of the vehicle body generated by the road reaction force on each of the wheels; and

controlling driving and braking forces on each of the wheels based upon said yaw moments so as to stabilize a running of the vehicle,

wherein said step of controlling said driving and braking forces includes steps of;

calculating a yaw moment required to be added to the vehicle body so as to stabilize the vehicle running, and;

controlling the driving and braking forces on each of the wheels so as to add said required yaw moment to the vehicle body, said required yaw moment being calculated based upon a yaw moment presently generated by the road reaction force on each of the wheels and a yaw moment estimated to be realized through the control of the driving and braking forces on each of the wheels.

43. A method according to claim 42, each of the wheel bearing a tire wherein said step of estimating the road reaction force includes steps of:

estimating a tire longitudinal force on each of the wheels;

estimating a tire lateral force on each of the wheels; and

estimating a road reaction force on each of the wheels based upon said tire longitudinal force and said tire lateral force on each of the wheels.

44. A method according to claim 43, wherein said tire longitudinal force on each of the wheels are estimated based upon a vehicle total driving force, a braking force on each of the wheels and a wheel rotational acceleration of each of the wheels.

45. A method according to claim 43, wherein said step of estimating the road reaction force further includes a step of:

estimating a vehicle total driving force based upon a steering angle and said tire lateral force on either of the wheels estimated in a previous cycle.

46. A method according to either of claim 43, wherein said tire lateral forces on the front wheels are estimated based upon a yaw rate of the vehicle body, a lateral acceleration of the vehicle body and said longitudinal force on each of wheels.

47. A method according to claim 42, wherein said step of controlling said driving and braking forces further includes a step of:

calculating target driving and braking forces for each of the wheels based upon said required yaw moment, thereby controlling the driving and braking forces on each of the wheels based upon said target driving and braking forces.

48. A method according to claim 42, wherein said step of calculating said required yaw moment includes a step of

estimating a road reaction force which can be generated on each of the wheels based upon a tire model, thereby calculating said yaw moment which can be generated on each of the wheel according to the presently generated road reaction force and said road reaction force which can be generated on each of the wheels.

49. A method according to claim 42, wherein the driving and braking forces on each of the wheels are controlled so that a magnitude of a sum of presently generated yaw moments is reduced by said required yaw moment being added to the vehicle body when the direction of said sum of yaw moments is identical to the turning direction of the vehicle and the magnitude of said sum of yaw moments is too large.

50. A method according to claim 49, wherein said wheels include front left and right wheels and rear left and right wheels;

and said step of controlling said driving and braking forces further includes a step of;

judging that said magnitude of said yaw moment sum is too large and the vehicle is under a spin condition if M_fl+M_fr+M_rlG+M_rrG is out of a predetermined range, where M_fl and M_fr denote yaw moments around the centroid of the vehicle body generated by the road reaction force on the front left and right wheels, respectively, and M_rlG and M_rrG denote critical yaw moments at the present longitudinal forces on the rear wheels, respectively, said critical yaw moment being defined as a yaw moment which can be generated around the centroid of the vehicle body assuming that a road reaction force is maximized while maintaining its longitudinal force component.

51. A method according to claim 50, wherein said M_fl+M_fr+M_rlG+M_rrG is judged out of a predetermined range if M_fl+M_fr+M_rlG+M_rrG is larger than a negative reference value for judgement when the vehicle is making a left turn or if M_fl+M_fr+M_rlG+M_rrG is smaller than a positive reference value for judgement when the vehicle is making a right turn, where the direction of the left turn of the vehicle is defined as the positive direction of a yaw moment.

52. A method according to claim 51, wherein the driving and braking forces on each of the wheels are controlled such that M_fl+M_fr+M_rlG+M_rrG is not more than a negative control reference value −

Δ

Ms if M_fl+M_fr+M_rlG+M_rrG is larger than said negative reference value for judgement when the vehicle is making a left turn, and M_fl+M_fr+M_rlG+M_rrG is not less than a positive control reference value Δ

Ms if M_fl+M_fr+M_rlG+M_rrG is smaller than said positive reference value for judgement when the vehicle is making a right turn.

53. A method according to claim 52, wherein said step of controlling said driving and braking forces further includes steps of:

calculating a target yaw moment for the outside one of the front wheels relative to a turning center of the vehicle in order that M_fl+M_fr+M_rlG+M_rrG is not more than said negative control reference value −

Δ

Ms if M_fl+M_fr+M_rlG+M_rrG is larger than said negative reference value for judgement when the vehicle is making a left turn and that M_fl+M_fr+M_rlG+M_rrG is not less than said positive control reference value Δ

Ms if M_fl+M_fr+M_rlG+M_rrG is smaller than a positive reference value for judgement when the vehicle is making a right turn;

calculating a target longitudinal force on said front outside wheel based upon said target yaw moment; and

controlling the driving and braking forces on said front outside wheel based upon said target longitudinal force.

54. A method according to claim 50, wherein said step of controlling said driving and braking forces further includes steps of:

judging if a spin condition can be suppressed by a control of said front outside wheel;

calculating a target longitudinal force for said front outside wheel based upon said target yaw moment when the spin condition can be suppressed by a control of said front outside wheel; and

controlling the driving and braking force on the front outside wheel based upon said target longitudinal force.

55. A method according to claim 42, wherein the driving and braking forces on each of the wheels are controlled so as to increase a magnitude of a lateral force on the rear wheels by adding said required yaw moment to the vehicle body when the lateral forces on the front wheels reach to limits of the corresponding wheels while the lateral forces on the rear wheels have not reached to limits of the corresponding tires under a condition where the magnitude of a sum of the yaw moments is not excessive.

56. A method according to claim 55, wherein said wheels include front left and right wheels and rear left and right wheels;

and said step of controlling said driving and braking forces further includes a step of;

judging that the lateral forces on the front wheels reach to the limits of the corresponding tires while the lateral forces on the rear wheels have not reached to the limits of the corresponding tires and the vehicle is under a drift condition if a magnitude of a ratio of M_fl+M_fr to M_flG+M_frG is larger than a minimum reference value and M_fl+M_fr+M_rlG+M_rrG is out of a predetermined range, where M_fl and M_fr denote yaw moments around the centroid of the vehicle body generated by the road reaction force on the front left and right wheels, respectively, and M_flG, M_frG, M_rlG and M_rrG denote critical yaw moments at the present longitudinal forces on the front left, front right, rear left and rear right wheels, respectively;

said critical yaw moment being defined as a yaw moment which can be generated around the centroid of the vehicle body assuming that a road reaction force is maximized while maintaining its longitudinal force component.

57. A method according to claim 56, wherein it is judged that the lateral forces on the front wheels reach to the limits of the corresponding tires while the lateral forces on the rear wheels have not reached to the limits of the corresponding tires and the vehicle is under a drift condition, if the magnitude of the ratio of M_fl+M_fl to M_flG+M_frG is larger than a minimum reference value and M_fl+M_fr+M_rlG+M_rrG is lower than a negative reference value for judgement when the vehicle is making a left turn or if the magnitude of the ratio of M_rlG+M_rrG to M_flG+M_frG is larger than a minimum reference value and M_fl+M_fr+M_rlG+M_rrG is higher than a positive reference value for judgement when the vehicle is making a right turn, where the direction of the left turn of the vehicle is defined as the positive direction of a yaw moment.

58. A method according to claim 57, wherein said minimum reference value is a positive value smaller than one.

59. A method according to claim 57, wherein the driving and braking forces on each of the wheels are controlled such that M_fl+M_fr+M_rlG+M_rrG is not less than said negative control reference value −

Δ

Md if M_fl+M_fr+M_rlG+M_rrG is smaller than said negative reference value for judgement when the vehicle is making a left turn, and M_fl+M_fr+M_rlG+M_rrG is not more than a positive control reference value Δ

Md if M_fl+M_fr+M_rlG+M_rrG is larger than said positive reference value for judgement when the vehicle is making a right turn.

60. A method according to claim 59, wherein said step of controlling said driving and braking forces further includes steps of:

calculating a target yaw moment for each of the rear wheels in order that M_fl+M_fr+M_rlG+M_rrG is not less than said negative control reference value −

Δ

Ms if M_fl+M_fr+M_rlG+M_rrG is larger than said negative reference value for judgement when the vehicle is making a left turn, and M_fl+M_fr+M_rlG+M_rrG is not more than a positive control reference value Δ

Ms if M_fl+M_fr+M_rlG+M_rrG is larger than said positive reference value for judgement when the vehicle is making a right turn,

calculating a target longitudinal force on each of the rear wheels based upon said target yaw moment; and

controlling the driving and braking forces on said front outside wheel based upon said target longitudinal force.

61. A method according to claim 60, wherein the step of controlling said driving and braking forces further includes:

calculating a maximum allowable value for a vehicle body turning yaw moment around the centroid of the vehicle body in the same direction of the turning of the vehicle to be generated by the road reaction force on each of the rear wheels, and

limiting said target yaw moment for each of the rear wheels if said target yaw moment exceeds said maximum allowable value.

62. A method according to claim 53, further comprising steps of:

calculating a slip angle of each of the wheels;

calculating a vertical load on each of the wheels; and

calculating a maximum static frictional coefficient between the wheel and a road surface of each of the wheels; and

wherein said step of controlling said driving and braking forces further includes steps of;

calculating a normal running limit for a target longitudinal force for each of the wheels based upon said vertical load and said maximum static frictional coefficient; and

preventing the target longitudinal force for each of the wheels other than the front outside wheel from exceeding the corresponding normal running limit.

63. A method according to claim 60, further comprising steps of:

calculating a slip angle of each of the wheels;

calculating a vertical load on each of the wheels; and

calculating a maximum static frictional coefficient between the wheel and a road surface of each of the wheels; and

wherein said step of controlling said driving and braking forces further includes steps of;

defining a normal running limit for a target longitudinal force for each of the wheels based upon said vertical load and said maximum static frictional coefficient; and

preventing the target longitudinal force for each of the wheels other than the front outside wheel from exceeding the corresponding normal running limit.

64. A method according to claim 62, wherein said step of defining said normal running limit includes steps of

defining a first range of a longitudinal force in which a composite road reaction force on the wheel is not saturated to its critical value at a slip angle according to a tire model and a second range based upon a vertical load and a maximum static frictional coefficient for each of the wheels;

and

selecting the larger range from said first and second ranges as upper and lower normal running limits for each of the wheels.

65. A method according to claim 64, wherein said second range is defined along the longitudinal direction of the vehicle body.

66. A method according to claim 50, wherein said step of controlling said driving and braking forces includes steps of

estimating a slip angle rate β

dr of the rear wheels; and

judging that M_fl+M_fr+M_rlG+M_rrG−

KIβ

dr is out of a predetermined range if M_fl+M_fr+M_rlG+M_rrG−

KIβ

dr is larger than a negative reference value for judgement when the vehicle is making a left turn or if M_fl+M_fr+M_rlG+M_rrG−

KIβ

dr is smaller than a positive reference value for judgement when the vehicle is making a right turn, where the direction of the left turn of the vehicle is defined as the positive direction of a yaw moment and KI denotes a positive constant.

67. A method according to claim 66, wherein the driving and braking forces on each of the wheels are controlled such that M_fl+M_fr+M_rlG+M_rrG−

KIβ

dr is not more than a negative control reference value −

Δ

Ms if M_fl+M_fr+M_rlG+M_rrG−

KIβ

dr is larger than said negative reference value for judgement when the vehicle is making a left turn, and M_fl+M_fr+M_rlG+M_rrG−

KIβ

dr is not less than a positive control reference value Δ

Ms if M_fl+M_fr+M_rlG+M_rrG−

KIβ

dr is smaller than said positive reference value for judgement when the vehicle is making a right turn.

68. A method according to claim 67, wherein said step of controlling said driving and braking forces includes steps of:

calculating a spin avoiding yaw moment Mns which satisfies a condition of M_fl+M_fr+M_rlG+M_rrG+Mns=Δ

Ms−

KIβ

dr; and

controlling the driving and braking force on each of the wheels so as to generate said spin avoiding yaw moment.

69. A method according to claim 68, wherein said step of controlling said driving and braking forces includes steps of:

calculating a target longitudinal forces for each of the wheels for generating said spin avoiding yaw moment;

controlling the driving and braking force on each of the wheels based upon said target longitudinal force therefor.

70. A method according to claim 56, wherein said step of controlling said driving and braking forces includes steps of

estimating a slip angle rate β

dr of the rear wheels; and

judging that the lateral forces on the front wheels reach to the limits of the corresponding tires while the lateral forces on the rear wheels have not reached to the limits of the corresponding tires and the vehicle is under a drift condition if a magnitude of a ratio of M_fl+M_fl to M_flG+M_frG is larger than a minimum reference value and M_fl+M_fr+M_rlG+M_rrG−

KIβ

dr is smaller than a negative reference value for judgement when the vehicle is making a left turn or if the magnitude of the ratio of M_rlG+M_rrG to M_flG+M_frG is larger than a minimum reference value and M_fl+M_fr+M_rlG+M_rrG−

KIβ

dr is larger than a positive reference value for judgement when the vehicle is making a right turn, where the direction of the left turn of the vehicle is defined as the positive direction of a yaw moment.

71. A method according to claim 70, wherein the driving and braking forces on each of the wheels are controlled such that M_fl+M_fr+M_rlG+M_rrG−

KIβ

dr is not less than said negative control reference value −

Δ

Md if M_fl+M_fr+M_rlG+M_rrG−

KIβ

dr is smaller than said negative reference value for judgement when the vehicle is making a left turn, and that M_fl+M_fr+M_rlG+M_rrG−

KIβ

dr is not more than said positive control reference value Δ

Md if M_fl+M_fr+M_rlG+M_rrG−

KIβ

dr is larger than said positive reference value for judgement when the vehicle is making a right turn.

72. A method according to claim 71, wherein said step of controlling said driving and braking forces includes steps of:

calculating a drift avoiding yaw moment Mnd which satisfy a condition of M_fl+M_fr+M_rlG+M_rrG+Mnd=Δ

Md−

KIβ

dr; and

controlling the driving and braking force on each of the wheels so as to generate said drift avoiding yaw moment.

73. A method according to claim 72, wherein said step of controlling said driving and braking forces includes steps of:

calculating a target longitudinal forces for each of the wheels for generating said drift avoiding yaw moment; and

controlling the driving and braking force on each of the wheels based upon said target longitudinal force therefor.

74. A method according to claim 69, further comprising steps of:

calculating a slip angle of each of the wheels;

calculating a vertical load on each of the wheels; and

calculating a maximum static frictional coefficient between the wheel and a road surface of each of the wheels; and

wherein said step of controlling said driving and braking forces further includes steps of;

calculating a normal running limit for a target longitudinal force for each of the wheels based upon said vertical load and said maximum static frictional coefficient; and

preventing the target longitudinal force for each of the wheels other than the wheels required for generation of said spin avoiding yaw moment from exceeding the corresponding normal running limit.

75. A method according to claim 73, further comprising steps of:

calculating a slip angle of each of the wheels;

calculating a vertical load on each of the wheels; and

calculating a maximum static frictional coefficient between the wheel and a road surface of each of the wheels; and

wherein said step of controlling said driving and braking forces further includes steps of;

defining a normal running limit for a target longitudinal force for each of the wheels based upon said vertical load and said maximum static frictional coefficient; and

preventing the target longitudinal force for each of the wheels other than the wheels required for generation of said drift avoiding yaw moment from exceeding the corresponding normal running limit. braking terms of the vehicle.

76. A method according to claim 74, wherein said step of defining said normal running limit includes steps of

defining a first range of a longitudinal force in which a composite road reaction force on the wheel is not saturated to its critical value at a slip angle according to a tire model and a second range based upon a vertical load and a maximum static frictional coefficient for each of the wheels;

and

selecting the larger range from said first and second ranges as upper and lower normal running limits for each of the wheels in each of driving and braking terms of the vehicle.

77. A method according to claim 76, wherein said second range is defined along the longitudinal direction of the vehicle body.

78. A method according to claim 68, wherein said term of KIβ

dr is omitted.

79. A method according to either of claim 43, wherein said tire lateral forces on the rear wheels are estimated based upon a lateral acceleration of the vehicle body, said longitudinal forces and said lateral forces on the front wheels.

80. A method according to claim 43, said vehicle further including a differential gear device;

wherein said road reaction forces are estimated allowing for a torque transmission mechanism in said differential gear device.

81. A method according to claim 43, wherein a sum of the lateral forces on the left and right wheels for each of the pairs of the front and rear wheels is estimated first, and then individual lateral forces on the left and right wheels are calculated from said sum of the lateral forces according to the ratio between the corresponding lateral forces on the left and right wheels obtained from a calculation based upon the tire model.

82. A method according to claim 74, wherein said normal running limits are defined individually for the pair of the front wheels, rear inside wheel and rear outside wheel.