Method and System for Determining an Optimal Steering Angle in Understeer Situations in a Vehicle

• US 20090319128A1
• Filed: 04/26/2007
• Published: 12/24/2009
• Est. Priority Date: 04/27/2006
• Status: Active Grant

• Current Assignee: Continental Teves AG & Co. OHG (Continental AG)
• Original Assignee: Continental Teves AG & Co. OHG (Continental AG)
• Inventors: Raste, Thomas, Lauer, Peter
• Granted Patent: US 8,244,435 B2
• Time in Patent Office: Days
• US Class Current: 701/42
• CPC Class Codes: B60W 30/045 Improving turning performance
• CPC Class Codes: B60W 50/16 Tactile feedback to the driver, e.g. vibration or force feedback to the driver on the steering wheel or the accelerator pedal
• CPC Class Codes: B62D 6/003 in order to control vehicle yaw movement, i.e. around a vertical axis B62D6/007 takes precedence
• CPC Class Codes: B62D 6/006 using a measured or estimated road friction coefficient
• CPC Class Codes: B62D 6/008 Control of feed-back to the steering input member, e.g. simulating road feel in steer-by-wire applications
• CPC Class Codes: B62D 7/159 characterised by computing methods or stabilisation processes or systems, e.g. responding to yaw rate, lateral wind, load, road condition

Abstract

A method for determining an optimal steering angle in understeer situations of a vehicle is described. To assist a driver in reliably stabilizing the vehicle during an understeer situation while driving, a model-based driving traction coefficient factor, a model-based kinematic factor, and a float angle are taken into account in the determination of a steering angle. A limited steering angle δ_v,lim at which a maximum lateral force is set, is determined by addition of the driving traction coefficient factor, the kinematic factor, and the float angle. A system suitable for implementation of the method is also described.

Claims

1-8. -8. (canceled)

9. A method for determining an optimum steering angle (δ

_v,lim) in understeering situations of a vehicle comprising the steps of;

(a) accounting for a first portion which represents an adhesion coefficient in a lateral direction;

(b) accounting for a second portion which represents a kinematic portion,

(c) accounting for a third portion which represents an attitude angle, and

(d) adding the portion of the adhesion coefficient, the kinematic portion and the attitude angle to calculate the steering angle (δ

_v,lim).

10. The method as claimed in claim 9, wherein step (c) comprises the sub-step of estimating the attitude angle during the understeering according to a relationship β

≈

0, wherein β

is defined as the attitude angle.

11. The method as claimed in claim 9, wherein step (a) comprises the sub-step of accounting for a coefficient of friction of an underlying surface (μ

̂

₀) that is defined by the equation μ

̂

₀=max(μ

_va, μ

_CoG, μ

_HA), wherein μ

_va represents the adhesion for a front axle of the vehicle and is defined by the equation

${\mathrm{\mu <br><br>}}_{V<br><br><br><br>A}=\frac{\sqrt{{\left(a_x-l_V<br><br>{\stackrel{.}{\mathrm{\psi <br><br>}}}^2\right)}^2+{\left(a_y+l_V<br><br>\stackrel{\mathrm{¨<br><br>}}{\mathrm{\psi <br><br>}}\right)}^2}}{g},$

μ

_CoG represents the adhesion at a center of gravity of the vehicle and is defined by the equation

${\mathrm{\mu <br><br>}}_{\mathrm{CoG}}=\frac{\sqrt{a_x^2+a_y^2}}{g},$

and μ

_HA represents the adhesion at a rear axle of the vehicle and is defined by the equation

${\mathrm{\mu <br><br>}}_{H<br><br><br><br>A}=\frac{\sqrt{{\left(a_x+l_H<br><br>{\stackrel{.}{\mathrm{\psi <br><br>}}}^2\right)}^2+{\left(a_y-l_H<br><br>\stackrel{\mathrm{¨<br><br>}}{\mathrm{\psi <br><br>}}\right)}^2}}{g},$

wherein a_x is defined as a longitudinal acceleration of the vehicle, a_y is defined as a lateral acceleration of the vehicle, I_v is defined as a distance between a center of gravity and the front axle of the vehicle, I_H is defined as a distance between a center of gravity and the rear axle of the vehicle, ψ

is defined as Yaw of the vehicle, and g is a gravity constant.

12. The method as claimed in claim 11, wherein the steering angle is determined by the equation:

${\mathrm{\delta <br><br>}}_{V,\lim }=\frac{l_V}{v_x}<br><br><br><br>\stackrel{.}{\mathrm{\psi <br><br>}}<br><br>+\frac{2}{C_{\mathrm{\alpha <br><br>}<br><br><br><br>0}}<br><br>{\widehat{\mathrm{\mu <br><br>}}}_0,$

wherein v_x is defined as the velocity of vehicle and C<sub>α

0</sub> is defined as an initial rise in the adhesion coefficient.

13. The method as claimed in claim 9 further comprising the step of using the steering angle δ

_v,lim or a steering angle δ

_v,lim which is multiplied by a factor k as a setpoint value for a steering angle control means or a steering torque control means.

14. The method as claimed in claim 13, wherein a steering torque control means is activated according to a relationship that is defined by the equation δ

_v,lim<

|δ

_v|, wherein δ

_v is defined as a wheel steering angle of a front axle of the vehicle.

15. The method as claimed in claim 13, wherein a steering torque control means is deactivated according to a relationship that is defined by the equation δ

_v,lim<

|δ

_v|, wherein δ

_v is defined as a wheel steering angle of a front axle of the vehicle.

16. A device for determining an optimum steering angle in understeer situations of a vehicle, comprising:

a determining unit configured to determine a stabilizing steering angle by accounting for a model-based portion of an adhesion coefficient, a model-based kinematic portion and an attitude angle.