Method for determining a maximum coefficient of friction

• US 20050234628A1
• Filed: 02/26/2003
• Published: 10/20/2005
• Est. Priority Date: 03/01/2002
• Status: Abandoned Application

• Current Assignee: Continental Teves AG & Co. OHG (Continental AG)
• Original Assignee: Continental Teves AG & Co. OHG (Continental AG)
• Inventors: von Frentz, Hubertus Raitz, Raste, Thomas, Oehler, Rainer, Luders, Ulrich
• Application Number:
  US10/506,268
• Publication Number:
  US 20050234628A1
• Time in Patent Office: Days
• US Class Current: 701/80
• CPC Class Codes: B60T 2210/12 Friction
• CPC Class Codes: B60T 2240/03 Tire sensors
• CPC Class Codes: B60T 8/1725 Using tyre sensors, e.g. Sidewall Torsion sensors [SWT] for tyre pressure and temperature detection B60C23/00
• CPC Class Codes: B60W 2510/205 Steering speed
• CPC Class Codes: B60W 2520/10 Longitudinal speed
• CPC Class Codes: B60W 2520/105 Longitudinal acceleration
• CPC Class Codes: B60W 2520/125 Lateral acceleration
• CPC Class Codes: B60W 2520/14 Yaw
• CPC Class Codes: B60W 2520/26 Wheel slip
• CPC Class Codes: B60W 2520/28 Wheel speed
• CPC Class Codes: B60W 2530/20 Tyre data
• CPC Class Codes: B60W 40/068 Road friction coefficient

Abstract

Currently available driving dynamics control systems such as ESP or TCS require in the driving dynamics limit range information about the actual maximum coefficient of friction between tires and roadway to function reliably. A proven approach is to use, once the control is active, the actual utilization of grip as the maximum coefficient of friction. The object of the invention relates to a method for determining the actual maximum coefficient of friction independently of the activation of the control. The method permanently determines values which are representative of the utilization of grip in longitudinal and/or lateral direction, based on measured and/or estimated variables that represent the actual longitudinal forces, lateral forces and vertical forces acting upon the individual wheels and tires, while using measured or calculated actual state variables representative of the tire slip angle and/or the tire slip angle velocity and/or the longitudinal slip and/or the longitudinal slip velocity. The determined values are compared to threshold values and sent to an evaluation unit for defining the maximum coefficient of friction by including further auxiliary variables when the comparison results fall below the threshold values.

Claims

1-12. -12. (canceled)

13. Method for determining a maximum coefficient of friction between tires and roadway of a vehicle from information about force occurring in the contact between tires and roadway,

wherein values are permanently determined which are representative of the utilization of grip in longitudinal and/or lateral direction, based on measured and/or estimated variables that represent the actual longitudinal forces, lateral forces and vertical forces acting upon the individual wheels and tires, while including measured or calculated actual state variables representative of the tire slip angle and/or the tire slip angle velocity and/or the longitudinal slip and/or the longitudinal slip velocity, and the determined values are compared to threshold values and sent to an evaluation unit for defining the maximum coefficient of friction by including further auxiliary variables such as longitudinal force, lateral force, vertical force, longitudinal acceleration, lateral acceleration, vehicle mass, and/or controlled variables when the comparison results fall below the threshold values.

14. Method as claimed in claim 13,

wherein the steps of determining gradients of the utilization of grip between tires and roadway in a longitudinal direction as a function of slip or slip velocity,

determining gradients of the utilization of grip between tires and roadway in a transverse direction as a function of the tire slip angle or the tire slip angle velocity,

comparing the gradients with threshold values and determining the maximum coefficient of friction from the longitudinal, lateral, vertical forces or the longitudinal forces, the vertical forces, the lateral acceleration, the longitudinal acceleration, the vehicle mass and/or controlled variables when the comparison result falls below the threshold values.

15. Method as claimed in claim 13,

wherein an equivalent value is used as the coefficient of friction when a comparison result prevails where the determined value does not fall below the threshold value.

16. Method as claimed in claim 14,

wherein the determination of the gradients from the longitudinal forces and/or lateral forces, standardized with the vertical forces, of at least one wheel or at least one vehicle axle and the tire slip angle or the tire slip angle velocity or the slip or the slip velocity of at least one wheel.

17. Method as claimed in claim 16,

wherein the determination of the gradients from the longitudinal force of at least one vehicle axle that is standardized with the vertical forces according to the relation

$\begin{array}{c}{C}_{x,\mathrm{VA}/\mathrm{HA}}=\frac{\Delta }{}\end{array}$

⁢

 

⁢

Fx,n,VA/HATA·

1λ

.VA/HA⁢

 

⁢

withequation⁢

 

⁢

(2.9)Fx,n,VA/HA=Fx,VA/HAFz,VA/HAequation⁢

 

⁢

(2.6)

wherein the longitudinal forces of the front axle of the vehicle are determined according to

$\begin{array}{cc}{F}_{x,\mathrm{VA}}=\frac{1}{r}<br><br>\left(-K_{B,\mathrm{VA}}<br><br>p_{B,\mathrm{VA}}-2<br><br>J_R<br><br>\text{\hspace{1em}<br><br>}<br><br>{\stackrel{.}{\mathrm{\omega <br><br>}}}_{R,\mathrm{VA}}\right)& \mathrm{equation}<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(2.7\right)\end{array}$

and/or the longitudinal forces of the rear axle of the vehicle are determined according to

$\begin{array}{cc}{F}_{x,\mathrm{HA}}=\frac{1}{r}<br><br>\left(M_M<br><br>i_g<br><br>\mathrm{\eta <br><br>}-K_{B,\mathrm{HA}}<br><br>p_{B,\mathrm{HA}}-\left(2<br><br>J_R+J_M<br><br>i_g^2\right)<br><br>\text{\hspace{1em}<br><br>}<br><br>{\stackrel{.}{\mathrm{\omega <br><br>}}}_{R,\mathrm{HA}}\right).& \mathrm{equation}<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(2.8\right)\end{array}$

18. Method as claimed in claim 16,

wherein the determination of the gradients from the lateral force of at least one vehicle axle standardized with the vertical forces according to the relation

$\begin{array}{c}{C}_{y,\mathrm{VA}/\mathrm{HA}}=-\frac{{\stackrel{.}{a}}_{y,\mathrm{VA}/\mathrm{HA}}}{g}·\end{array}$

1α

..equation⁢

 

⁢

(2.11)

19. Method as claimed in claim 14,

wherein the longitudinal-force/circumferential-slip gradients for at least one wheel are determined according to the relation

$\begin{array}{c}{C}_x=\frac{\partial }{}\end{array}$

Fx,n∂

λ

=ⅆ

Fx,nⅆ

t·

ⅆ

tⅆ

λ

≈

Δ

⁢

 

⁢

Fx,nTA·

1λ

..equation⁢

 

⁢

(2.3)

and/or the lateral-force/tire-slip-angle gradients for at least one wheel are determined according to the relation

$\begin{array}{cc}{C}_y=-\frac{\partial <br><br>F_{y,n}}{\partial <br><br>\mathrm{\alpha <br><br>}}=-\frac{d<br><br>F_{y,n}}{d<br><br>t}·<br><br>\frac{d<br><br>t}{d<br><br>\mathrm{\alpha <br><br>}}\approx <br><br>-\frac{\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>F_{y,n}}{T_A}·<br><br>\frac{1}{\stackrel{.}{\mathrm{\alpha <br><br>}}}.& \mathrm{equation}<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(2.5\right)\end{array}$

20. Method as claimed in claim 13,

wherein the vertical forces are determined in a model-based fashion according to the relation

$\begin{array}{c}\begin{array}{c}{F}_{\mathrm{z\_vl}}=\frac{m}{\left(l_v+l_h\right)}\end{array}\end{array}$

(lh⁢

g-h⁢

 

⁢

ax)⁢

(12-h(bvl+bvr)⁢

g⁢

ay)Fz_vr=m(lv+lh)⁢

(lh⁢

g-h⁢

 

⁢

ax)⁢

(12+h(bvl+bvr)⁢

g⁢

ay)Fz_hl=m(lv+lh)⁢

(lv⁢

g+h⁢

 

⁢

ax)⁢

(12-h(bhl+bhr)⁢

g⁢

ay)Fz_hr=m(lv+lh)⁢

(lv⁢

g+h⁢

 

⁢

ax)⁢

(12+h(bhl+bhr)⁢

g⁢

ay)equation⁢

 

⁢

(2.2)

21. Method as claimed in claim 13,

wherein the maximum utilization of grip is determined for each individual wheel according to the relation

$\begin{array}{c}\mu \end{array}$

=Fx2+Fy2Fz.equation⁢

 

⁢

(2.13)

22. Method as claimed in claim 13,

wherein the maximum utilization of grip is determined per axle according to the relation

$\begin{array}{c}\begin{array}{c}{\mu }_{}\end{array}\end{array}$

HA=m⁢

ax2+ay2Fz,HA-μ

VA⁢

Fz,VAFz,HA,withμ

VA=Fx,VA2+Fy,VA2Fz,VAequation⁢

 

⁢

(2.15)

for the rear axle of the vehicle, or

$\begin{array}{cc}\begin{array}{c}{\mathrm{\mu <br><br>}}_{\mathrm{VA}}=\frac{m<br><br>\text{\hspace{1em}<br><br>}<br><br>\sqrt{a_x^2+a_y^2}}{F_{z,\mathrm{VA}}}-{\mathrm{\mu <br><br>}}_{\mathrm{HA}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\frac{F_{z,\mathrm{HA}}}{F_{z,\mathrm{VA}}},\mathrm{with}\\ {\mathrm{\mu <br><br>}}_{\mathrm{HA}}=\frac{\sqrt{F_{x,\mathrm{HA}}^2+F_{y,\mathrm{HA}}^2}}{F_{z,\mathrm{HA}}}\end{array}& \mathrm{equation}<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(2.17\right)\end{array}$

for the front axle of the vehicle.

23. Method as claimed in claim 13, wherein the steps of

determining the tire slip angle velocity {dot over (α

)} at the front and rear axle of the vehicle in accordance with the lateral acceleration a_y, the longitudinal speed ν

_x, the yaw acceleration {umlaut over (ψ

)}, the yaw rate {dot over (ψ

)}, the steering angle velocity {dot over (δ

)} and/or the distance between the center of gravity and the front axle l _v or the rear axle l_h,

comparing the tire slip angle velocity {dot over (α

)} with threshold values S_y,a,

determining the lateral-force/tire-slip-angle gradients C_y at each wheel in dependence on the comparison result |{dot over (a)}|≧

S_y,a, |{dot over (a)}|<

S_y,a

determining the maximum coefficient of friction μ

_max according to the relations for the maximum utilization of grip (equations 2.13, 2.15, 2.17), when C_y<

S_y.

24. Microcontroller program product which can be loaded directly into the memory of a driving dynamics control, such as ESP, TCS, ABS control, and like systems and comprises software code sections by means of which the steps according to claim 13 are implemented when the product operates on a microcontroller.

25. Method as claimed in claim 16,

wherein the longitudinal-force/circumferential-slip gradients for at least one wheel are determined according to the relation

$\begin{array}{c}{C}_x=\frac{\partial }{}\end{array}$

Fx,n∂

λ

=ⅆ

Fx,nⅆ

t·

ⅆ

tⅆ

λ

≈

Δ

⁢

 

⁢

Fx,nTA·

1λ

.equation⁢

 

⁢

(2.3)

and/or the lateral-force/tire-slip-angle gradients for at least one wheel are determined according to the relation

$\begin{array}{cc}{C}_y=-\frac{\partial <br><br>F_{y,n}}{\partial <br><br>\mathrm{\alpha <br><br>}}=-\frac{d<br><br>F_{y,n}}{d<br><br>t}·<br><br>\frac{d<br><br>t}{d<br><br>\mathrm{\alpha <br><br>}}\approx <br><br>\frac{\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>F_{y,n}}{T_A}·<br><br>\frac{1}{\mathrm{\alpha <br><br>}}.& \mathrm{equation}<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(2.5\right)\end{array}$

26. Method as claimed in claim 14, wherein the steps of

determining the tire slip angle velocity {dot over (α

)} at the front and rear axle of the vehicle in accordance with the lateral acceleration a_y, the longitudinal speed ν

_x, the yaw acceleration {umlaut over (ψ

)}, the yaw rate {dot over (ψ

)}, the steering angle velocity {dot over (δ

)} and/or the distance between the center of gravity and the front axle l_v or the rear axle l_h,

comparing the tire slip angle velocity &

i with threshold values S_y,a,

determining the lateral-force/tire-slip-angle gradients C_y at each wheel in dependence on the comparison result |{dot over (a)}|≧

S_y,a, |{dot over (a)}|<

S_y,a

determining the maximum coefficient of friction μ

_max according to the relations for the maximum utilization of grip (equations 2.13, 2.15, 2.17), when C_y<

S_y.