System for controlling the stability of a vehicle using an algorithm comparing average slopes of variation of a parameter

• US 7,197,380 B2
• Filed: 01/18/2005
• Issued: 03/27/2007
• Est. Priority Date: 01/16/2004
• Status: Expired due to Fees

• Current Assignee: Compagnie Generale DES Etablissements Michelin SCA
• Original Assignee: Michelin Recherche et Technique SA (Compagnie Generale DES Etablissements Michelin SCA)
• Inventors: Levy, Georges, Fangeat, Nicolas
• Primary Examiner(s): ARTHUR JEANGLAUDE, GERTRUDE
• Application Number:
  US11/039,108
• Publication Number:
  US 20050187672A1
• Time in Patent Office: 798 Days
• Field of Search: 701/1, 701/71, 701/72, 701/74, 701/80, 701/82, 701/90, 731/46, 303/147, 340/439, 340/442
• US Class Current: 701/1
• CPC Class Codes: B60T 2270/406 Test-mode; Self-diagnosis
• CPC Class Codes: B60T 8/17551 determining control parameters related to vehicle stability used in the regulation, e.g. by calculations involving measured or detected parameters

Abstract

System for controlling the stability of a vehicle, the system comprising means for imparting a longitudinal force on the tire and means for calculating the slip parameter G^Opt at each activation of the means for imparting a longitudinal force on the tire in the following manner: determining coefficients A_[avg/p] by direct calculation or by an appropriate regression, from a sufficient number of pairs (μ_i, G_i), so as to model a first curve of variation μ_i=f(G_i, A_[avg/p]) including the origin, and the pair or pairs (μ_i, G_i), in which μ_i is different from zero, determining an indicator of the average slope α₁ of the first variation curve, determining coefficients B_[avg/p] by direct calculation or by an appropriate regression, from a sufficient number of pairs (μ_i, G_i), so as to model a second variation curve, free not to pass through the origin, μ_i=f(G_i, B_[avg/p]) including the pair or pairs (μ_i, G_i), in which μ_i is different from zero, determining an indicator of the average slope α₂ of the second variation curve, as long as the difference between α₁ and α₂ is below a predetermined slope threshold, repeating the previous operations for each new acquisition of the pair of values (G_i, μ_i), as soon as the difference between α₁ and α₂ exceeds the predetermined slope threshold and determining a target slip G^Cavg using at least the last pair of values (G_i, μ_i).

Claims

1. A vehicle stability control system in which a characteristic parameter Q of a functioning of a tire of the vehicle intended to roll on the ground varies as a function of a parameter P according to a certain law, an optimum value of the parameter P being imposed by a controller directly or indirectly, so as to act on at least one of elements chosen from a group comprising a rotation torque applied to the tire, a steering angle of the tire, a camber angle of the tire, and a vertical force applied to the tire, in which the controller comprises means for:

determining coefficients A_[avg/p], by direct calculation or by a regression, from a sufficient number of pairs (P_i, Q_i), so as to model a first variation curve Q_i=f(P_i, A_[avg/p]) including the origin, and the pair or pairs (Q_i, P_i), in which Q_i is different from zero,

determining an indicator of an average slope α

₁ of the first variation curve,

determining coefficients B_[avg/p], by direct calculation or by a regression, from a sufficient number of pairs (Q_i, P_i), so as to model a second variation curve Q_i=f(P_i, B_[avg/p]) including the pair or pairs (Q_i, P_i), in which Q_i is different from zero,

determining an indicator of an average slope α

₂ of the second variation curve,

as long as the difference between α

₁ and α

₂ is less than a predetermined slope threshold, repeating the previous operations for each new acquisition of a pair of values (P_i, Q_i),

if the difference between α

₁ and α

₂ exceeds the predetermined slope threshold, determining a target slip p^Cavg using at least the last pair of values (P_i, Q_i).

2. The vehicle stability control system according to claim 1, in which the parameter P is the drift angle δ

of the tire and the characteristic parameter Q is the drift thrust F_y of the tire, the system comprising means for controlling a parameter “

ξ

”

according to instructions entered by a driver of the vehicle on a control means and according to instructions delivered by a path controller, means of modulating the parameter “

ξ

” and

means for calculating the drift angle parameter δ

^Opt at each activation of the means for entering the parameter “

ξ

”

in the following manner;

each time the system for controlling the variation in ξ

is activated, for different levels “

i”

of drift angle, reading a plurality of values of F_Yi, and the associated drift angle δ

_i obtained by estimation or direct measurement,

determining coefficients A_[avg/p] by direct calculation or by a regression, from a sufficient number of pairs (F_i, δ

_i), so as to model a first variation curve F_i=f(δ

_i, A_[avg/p]) including the origin, and the pair or pairs (F_i, δ

_i), in which μ

_i is different from zero,

determining an indicator of an average slope α

₁ of the first variation curve,

determining coefficients B_[avg/p] by direct calculation or by a regression, from a sufficient number of pairs (F_i, δ

_i), so as to model a second variation curve F_i=f(δ

_i, B_[avg/p]) including the pair or pairs (F_i, δ

_i), in which μ

_i is different from zero,

determining an indicator of an average slope α

₂ of the second variation curve,

as long as a difference between α

₁ and α

₂ is less than a predetermined slope threshold, repeating the previous operations for each new acquisition of a pair of values (δ

_i, F_i),

if the difference between α

₁ and α

₂ exceeds the predetermined slope threshold, determining a target slip G^Cavg using at least the last pair of values (δ

_i, F_i).

3. A vehicle stability control system, in which a parameter G is a slip of a tire and a characteristic parameter μ

is a coefficient of friction of the tire, the system comprising means for imparting a longitudinal force to the tire, means of modulating the longitudinal force, and means for calculating an optimal slip parameter G^Opt at each activation of the means for imparting a longitudinal force to the tire in the following manner;

determining coefficients A_[avg/p] by direct calculation or by a regression, from a sufficient number of pairs (μ

_i, G_i), so as to model a first variation curve μ

_i=f(G_i, A_[avg/p]) including the origin, and the pair or pairs (μ

_i, G_i), in which μ

_i is different from zero,

determining an indicator of an average slope α

₁ of the first variation curve,

determining coefficients B_[avg/p] by direct calculation or by a regression, from a sufficient number of pairs (μ

_i, G_i), so as to model a second variation curve μ

_i=f(G_i, B_[avg/p]) including the pair or pairs (μ

_i, G_i), in which μ

_i is different from zero,

determining an indicator of an average slope α

₂ of the second variation curve,

as long as a difference between α

₁ and α

₂ is less than a predetermined slope threshold, repeating the previous operations for each new acquisition of a pair of values (G_i, μ

_i),

if the difference between α

₁ and α

₂ exceeds the predetermined slope threshold, determining a target slip G^Cavg using at least the last pair of values (G_i, μ

_i).

4. The vehicle stability control system according to claim 3, in which, when the slip G_i exceeds a predetermined threshold, the target slip G^Cavg is determined using at least the last pair of values (G_i, μ

_i).

5. The vehicle stability control system according to claim 3, in which:

the first variation curve is a first straight line μ

_i=A_avg·

G_i, including the origin, and the pair or pairs (μ

_i, G_i), obtained by a first linear regression calculating a first coefficient A_avg, and

the second variation curve is a second straight line μ

_i=A_lin·

G_i+B_lin including the pair or pairs (μ

_i, G_i), obtained by a second linear regression calculating coefficients A_lin and B_lin.

6. The vehicle stability control system according to claim 3, in which the target slip G^Cavg is determined as being equal to the last value G_i.

7. The vehicle stability control system according to claim 3, in which the target slip is determined by

$G^{\mathrm{Cavg}}=\beta$

·

μ

MAX A AVG ,

in which β

is a fine-tuning parameter.

8. The vehicle stability control system according to claim 7, in which β

is equal to approximately 1.04.

9. The vehicle stability control system according to claim 7, in which β

is a fine-tuning parameter used in the fine-tuning of the system.

10. The vehicle stability control system according to claim 3, in which the predetermined slope threshold for the difference between α

₁ and α

₂ is around 30%.

11. The vehicle stability control system according to claim 3, in which the means for modulating the longitudinal force acts on a braking control and is initialized (with i=0) at a start of each braking control operation.

12. The vehicle stability control system according to claim 3, in which the means for modulating the longitudinal force acts on the driving torque at the wheels and is initialized (i=0) at each request for a variation in the driving torque above a predetermined torque threshold.

13. The vehicle stability control system according to claim 3, in which, before obtaining the target values for the slip using a curve comprising the determined values of μ

_i as a function of G_i, a correction of a start of the curve is carried out by;

eliminating from the curve at least a first real pair (μ

_i, G_i), as long as the variation in μ

_i as a function of G_i is not substantially constant,

seeking the slip G₀ associated with a zero coefficient of friction, such that the pair (0, G₀) and non-eliminated pairs (μ

_i, G_i) are substantially aligned, and

using a curve starting from (0, G₀) and joining the non-eliminated pairs (μ

_i, G_i), so that, for any value of G_i greater than G₀, G_i is replaced by G_i−

G₀.

14. The vehicle stability control system according to claim 3, in which, when the variation in the slip with respect to time becomes greater than a predetermined variation threshold, before obtaining the target values for the slip using a curve comprising the determined values of μ

_i as a function of G_i, a correction to the end of the curve is carried out, by replacing the values of μ

_i corresponding to the values of slip that result in the variation in the slip with respect to time being beyond the predetermined variation threshold, by corrected values as follows;

${\mathrm{\mu <br><br>}}_i^{\mathrm{Corr}}={\mathrm{\mu <br><br>}}_i·<br><br>{\left[\mathrm{Max}<br><br>\left(\frac{d<br><br>G}{d<br><br>t};<br><br>1\right)\right]}^{-A<br><br><br><br>\mathrm{Corr}}$

where “

Acorr”

is a preset parameter.

15. The vehicle stability control system according to claim 14, in which “

Acorr”

is equal to approximately 0.2.

16. The vehicle stability control system according to claim 14, in which “

Acorr”

is used as a fine-tuning parameter.

17. A tire testing system in which a characteristic parameter Q of a functioning of a tire under test varies as a function of a parameter P according to a certain law, an optimum value of the parameter P being imposed by a controller directly or indirectly, so as to act on at least one of elements chosen from a group comprising a rotation torque applied to the tire, a steering angle of the tire, a camber angle of the tire, and a vertical force applied to the tire, in which the controller comprises means for:

determining coefficients A_[avg/p] by direct calculation or by a regression, from a sufficient number of pairs (P_i, Q_i), so as to model a first variation curve Q_i=f(P_i, A_[avg/p]) including the origin, and the pair or pairs (Q_i, P_i), in which μ

_i is different from zero,

determining an indicator of an average slope α

₁ of the first variation curve,

determining coefficients B_[avg/p] by direct calculation or by a regression, from a sufficient number of pairs (Q_i, P_i), so as to model a second variation curve Q_i=f(P_i, B_[avg/p]) including the pair or pairs (Q_i, P_i), in which Q_i is different from zero,

determining an indicator of an average slope α

₂ of the second variation curve,

as long as a difference between α

₁ and α

₂ is less than a predetermined slope threshold, repeating the previous operations for each new acquisition of a pair of values (P_i, Q_i),

if the difference between α

₁ and α

₂ exceeds the predetermined slope threshold, determining a target slip P^Cavg using at least the last pair of values (P_i, Q_i).

18. The tire testing system according to claim 17, using means for imparting a drift angle to a tire under test on the ground, the means being equipped with a system for controlling a parameter “

ξ

”

according to instructions coming from a test control means and according to instructions delivered by a controller aimed at maintaining the functioning of the tire at a predetermined value of the drift thrust F^det, the controller using at least one optimum value δ

^Opt of the drift angle corresponding to the maximum value of the drift thrust F^det, the controller comprising means for performing the following operations;

each time the system for controlling the variation in ξ

is activated, for different levels “

i”

of drift angle, reading a plurality of values of F_Yi, measured or calculated, and an associated drift angle δ

_i, obtained by estimation or direct measurement,

determining coefficients A_[avg/p] by direct calculation or by a regression, from a sufficient number of pairs (F_i, δ

_i), so as to model a first variation curve F_i=f(δ

_i, A_[avg/p]including the origin, and the pair or pairs (F_i, δ

_i), in which μ

_i is different from zero,

determining an indicator of an average slope α

₁ of the first variation curve,

determining coefficients B_[avg/p] by direct calculation or by a regression, from a sufficient number of pairs (F_i, δ

_i), so as to model a second variation curve F_i=f(δ

_i, B_[avg/p]) including the pair or pairs (F_i, δ

_i), in which μ

_i is different from zero,

determining an indicator of an average slope α

₂ of the second variation curve,

as long as a difference between α

₁ and α

₂ is less than a predetermined slope threshold, repeating the previous operations for each new acquisition of a pair of values (δ

_i, F_i),

if the difference between α

₁ and α

₂ exceeds the predetermined slope threshold, determining a target slip G^Cavg using at least the last pair of values (δ

_i, F_i).

19. A tire testing system, in which a parameter G is a slip of the tire and a characteristic parameter μ

is a coefficient of friction of the tire, the system comprising means for imparting a longitudinal force to the tire, means for modulating the longitudinal force and means for calculating a slip parameter G^Opt at each activation of the means for imparting a longitudinal force to the tire in the following manner;

determining coefficients A_[avg/p] by direct calculation or by a regression, from a sufficient number of pairs (μ

_i, G_i), so as to model a first variation curve μ

_i=f(G_i, A_[avg/p]) including the origin, and the pair or pairs (μ

_i, G_i), in which μ

_i is different from zero,

determining an indicator of an average slope α

₁ of the first variation curve,

determining coefficients B_[avg/p] by direct calculation or by a regression, from a sufficient number of pairs (μ

_i, G_i), so as to model a second variation curve μ

_i=f(G_i, B_[avg/p]) including the pair or pairs (μ

_i, G_i), in which μ

_i is different from zero,

determining an indicator of an average slope α

₂ of the second variation curve,

as long as a difference between α

₁ and α

₂ is less than a predetermined slope threshold, repeating the previous operations for each new acquisition of a pair of values (G_i, μ

_i),

if the difference between α

₁ and α

₂ exceeds the predetermined slope threshold, determining a target slip G^Cavg using at least the last pair of values (G_i, μ

_i).

20. The tire testing system according to claim 19, in which, when the slip G_i exceeds a predetermined threshold, the target slip G^Cavg is determined using at least the last pair of values (G_i, μ

_i).

21. The tire testing system according to claim 19, in which:

the first variation curve is a first straight line μ

_i=A_avg·

G_i, including the origin, and the pair or pairs (μ

_i, G_i), obtained by a first linear regression calculating a first coefficient A_avg, and

the second variation curve is a second straight line μ

_i=A_lin·

B_lin including the pair or pairs (μ

_i, G_i), obtained by a second linear regression calculating coefficients A_lin and B_lin.

22. The tire testing system according to claim 19, in which the target slip G^Cavg is determined based on the last value G_i.

23. The tire testing system according to claim 19, in which the target slip is determined by

$G^{\mathrm{Cavg}}=\beta$

·

μ

MAX A AVG ,

in which β

is a fine-tuning parameter.

24. The tire testing system according to claim 23, in which β

is equal to approximately 1.04.

25. The tire testing system according to claim 23, in which β

is a fine-tuning parameter used in the fine tuning of the system.

26. The tire testing system according to claim 19, in which a predetermined slope threshold for the difference between α

₁ and α

₂ is around 30%.

27. The tire testing system according to claim 19, in which the means for modulating the longitudinal force acts on a braking control and is initialized (with i=0) at each start of an operation of the braking control.

28. The tire testing system according to claim 19, in which the means for modulating the longitudinal force acts on a driving torque at the wheels and is initialized (i=0) at each request for a variation in the driving torque above a predetermined torque threshold.

29. The tire testing system according to claim 19, in which, before obtaining the target values for the slip using a curve comprising the determined values of μ

_i as a function of G_i, a correction of a start of the curve is carried out by;

eliminating from the curve at least a first real pair (μ

_i, G_i) as long as the variation in μ

_i as a function of G_i is not substantially constant,

seeking the slip G₀ associated with a zero coefficient of friction, such that the pair (0, G₀) and non-eliminated pairs (μ

_i, G_i) are substantially aligned, and

using a curve starting from (0, G₀) and joining the non-eliminated pairs (μ

_i, G_i), so that, for any value of G_i greater than G₀, G_i is replaced by G_i−

G₀.

30. The tire testing system according to claim 19, in which, when the variation in the slip with respect to time becomes greater than a predetermined variation threshold, before obtaining the target values for the slip using a curve comprising the determined values of μ

_i as a function of G_i, a correction to the end of the curve is carried out, by replacing the values of μ

_i corresponding to the values of slip that result in the variation in the slip with respect to time being beyond the predetermined variation threshold, by corrected values as follows;

${\mathrm{\mu <br><br>}}_i^{\mathrm{Corr}}={\mathrm{\mu <br><br>}}_i·<br><br>{\left[\mathrm{Max}<br><br>\left(\frac{d<br><br>G}{d<br><br>t};<br><br>1\right)\right]}^{-A<br><br><br><br>\mathrm{Corr}}$

where “

Acorr”

is a preset parameter.

31. The tire testing system according to claim 30, in which “

Acorr”

is equal to approximately 0.2.

32. The tire testing system according to claim 30, in which “

Acorr”

is used as a fine-tuning parameter.