Method and system for providing secondary vehicle directional control through braking

• US 20020189889A1
• Filed: 07/25/2002
• Published: 12/19/2002
• Est. Priority Date: 02/11/2000
• Status: Active Grant

• Current Assignee: GM Global Technology Operations Incorporated (General Motors Company), Steering Solutions IP Holding Corporation (Nexteer Automotive Group Ltd.)
• Original Assignee: Delphi Technologies, Inc. (BorgWarner Incorporated)
• Inventors: Demerly, Jon D.
• Granted Patent: US 6,808,041 B2
• Time in Patent Office: Days
• US Class Current: 180/402
• CPC Class Codes: B60T 2260/02 Active Steering, Steer-by-Wire
• CPC Class Codes: B60T 2270/402 Back-up
• CPC Class Codes: B60T 8/1755 Brake regulation specially adapted to control the stability of the vehicle, e.g. taking into account yaw rate or transverse acceleration in a curve road vehicle drive control systems for control of driving stability otherwise than by controlling a particular sub-unit B60W30/02
• CPC Class Codes: B60T 8/885 using electrical circuitry
• CPC Class Codes: B62D 11/08 using brakes or clutches as main steering-effecting means
• CPC Class Codes: B62D 11/183 Control systems therefor
• CPC Class Codes: B62D 17/00 Means on vehicles for adjusting camber, castor, or toe-in
• CPC Class Codes: B62D 5/003 Backup systems, e.g. for manual steering B62D5/30 takes precedence
• CPC Class Codes: B62D 6/002 computing target steering angles for front or rear wheels B62D7/159 takes precedence
• CPC Class Codes: B62D 9/005 Emergency systems using brakes for steering
• CPC Class Codes: B62D 9/007 Emergency systems using the steering system for braking

Abstract

A method for implementing directional control of a motor vehicle is disclosed. In an exemplary embodiment, the method includes determining whether a failure of a primary steering system of the motor vehicle exists. If a failure of the primary steering system exists, then a yaw moment is created on the vehicle by causing a differential longitudinal force to be applied with respect to a first wheel on one side of the vehicle and a second wheel on an opposite side of the vehicle, thereby causing the vehicle to turn in a commanded direction.

Claims

1. A method for implementing directional control of a motor vehicle, the method comprising:

determining whether a failure of a primary steering system of the motor vehicle exists; and

if a failure of the primary steering system exists, then creating a yaw moment on the vehicle by causing a differential longitudinal force to be applied with respect to a first wheel on one side of the vehicle and a second wheel on an opposite side of the vehicle, thereby causing the vehicle to turn in a commanded direction.

2. The method of claim 1, wherein said causing a differential longitudinal force further comprises applying a braking force to at least one of said first and second wheels of the vehicle.

3. The method of claim 2, wherein said creating a yaw moment on the vehicle further comprises:

determining a desired directional response;

determining whether a desired braking operation exists; and

generating a brake torque output signal, based upon said desired directional response and whether said desired braking operation exists, said brake torque output signal being used in said selectively applying a braking force.

4. The method of claim 3, wherein said desired directional response is determined by a closed-loop yaw rate control mechanism, said closed-loop yaw rate control mechanism being implemented by:

generating an error signal, said error signal representing the difference between a desired yaw rate and said vehicle yaw rate; and

said desired yaw rate being determined from a steering wheel angle and a vehicle speed.

5. The method of claim 4, wherein said desired yaw rate is further determined by:

inputting said steering wheel angle and said vehicle speed into a lookup table, said lookup table thereby determining a desired steady state yaw rate; and

filtering said desired steady state yaw rate through a second order filter.

6. The method of claim 4, further comprising:

using a feedforward term to generate an initial brake input component to said braking force, said feedforward term being a function of said vehicle speed.

7. The method of claim 3, further comprising:

configuring a switching mechanism for selectively switching between a first, a second and a third mode of operation;

said first mode of operation corresponding to an operational status of the primary steering system;

said second mode of operation corresponding to a failure of the primary steering system and a commanded directional control operation of the motor vehicle; and

said third mode of operation corresponding to a failure of the primary steering system and a combined directional control operation and a braking operation of the motor vehicle;

wherein said brake torque output signal is dependent upon which of said first, second and third modes of operation is selected by said switching mechanism.

8. The method of claim 7, wherein said switching mechanism is responsive to a braking mode output signal, said braking mode output signal determining which of said first, second and third modes is selected by said switching mechanism.

9. The method of claim 8, wherein:

said braking mode output signal is generated from a steer status signal, said steer status signal indicative of whether a primary steering system failure exists; and

said braking mode output signal is further generated from a brake pedal input signal, said brake pedal input signal indicative of whether a braking operation of the motor vehicle has been commanded.

10. The method of claim 9, wherein in said third mode of operation, said brake torque output signal causes the braking force one of said first and second wheels to be increased by a given magnitude and the braking force on the other of said first and second wheels to be decreased by said given magnitude.

11. The method of claim 7, wherein said brake torque output signal is set to zero in said first mode of operation.

12. The method of claim 7, wherein said brake torque output signal is further multiplied by a filtered signal, said filtered signal being derived from said braking mode output signal, and said filtered signal providing a first order lag for transitioning between said first, second and third modes of operation.

14. The steer-by-brake system of claim 13, wherein said failed steering brake controller further comprises:

a switching mechanism for selectively switching between first, second and third modes of operation of the steer-by-brake system;

said first mode of operation corresponding to an operational status of said primary steering system;

said second mode of operation corresponding to a failure of said primary steering system and a commanded directional control operation of the motor vehicle; and

said third mode of operation corresponding to a failure of said primary steering system and a combined directional control operation and a braking operation of the motor vehicle;

wherein said brake torque output signal is dependent upon which of said first, second and third modes of operation is selected by said switching mechanism.

15. The steer-by-brake system of claim 14, further comprising:

a steer-by-brake transition block, coupled to said switching mechanism, said steer-by-brake transition block having a steer status signal and a brake pedal input signal as inputs thereto;

said steer status signal indicative of whether a primary steering system failure exists, and said brake pedal input signal indicative of whether a braking operation of the motor vehicle has been commanded;

wherein, based upon said steer status signal and said brake pedal input signal, said steer-by-brake transition block generates a braking mode output signal, said braking mode output signal determining which of said first, second and third modes is selected by said switching mechanism.

16. The steer-by-brake system of claim 13, wherein said failed steering brake controller further comprises a closed-loop yaw rate control mechanism for providing a desired directional response to a driver command.

17. The steer-by-brake system of claim 16, wherein said closed-loop yaw rate control mechanism further comprises:

an error signal, said error signal generated by the difference between a desired yaw rate and said vehicle yaw rate;

wherein said desired yaw rate is determined from said steering wheel angle and said vehicle speed.

18. The steer-by-brake system of claim 17, wherein said closed-loop yaw rate control mechanism further comprises:

a lookup table, said lookup table determining a desired steady state yaw rate based upon said steering wheel angle and said vehicle speed; and

a second order filter, said second order filter having said desired steady state yaw rate as an input thereto and said desired yaw rate as an output therefrom.

19. The steer-by-brake system of claim 16, wherein said brake torque output signal includes a feedforward term for providing an initial brake input component thereto, said feedforward term being a function of said desired steady state yaw rate and said vehicle speed.

20. The steer-by-brake system of claim 14, wherein in said third mode of operation, said brake torque output signal causes the braking force on a first of said pair of wheels to be increased by a given magnitude and the braking force on a second of said pair of wheels to be decreased by said given magnitude.

21. The steer-by-brake system of claim 14, wherein said brake torque output signal is set to zero in said first mode of operation.

22. The steer-by-brake system of claim 14, wherein said brake torque output signal is further multiplied by a filtered signal, said filtered signal being derived from said braking mode output signal, and said filtered signal providing a first order lag for transitioning between said first, second and third modes of operation.

13. A steer-by-brake system for a motor vehicle, comprising:

a failed steering brake controller in communication with a braking system of the motor vehicle;

said failed steering brake controller having a steering wheel angle as a first input thereto, a vehicle speed as a second input thereto, a vehicle yaw rate as a third input thereto, and a brake torque output signal as an output therefrom;

wherein said brake torque output signal is used to selectively apply a braking force to at least one of a pair of wheels of the motor vehicle when a failure of a primary steering system of the motor vehicle is detected, thereby creating a yaw moment on the motor vehicle so as to cause a turn in a commanded direction.

23. A storage medium, comprising:

a machine readable computer program code for synchronizing data utilized in a redundant, closed-loop feedback control system; and

instructions for causing a computer to implement a method for implementing directional control of a motor vehicle, the method further comprising;

determining whether a failure of a primary steering system of the motor vehicle exists; and

if a failure of the primary steering system exists, then creating a yaw moment on the vehicle by selectively applying a braking force to one or more wheels of the vehicle, thereby causing the vehicle to turn in a commanded direction.

24. A computer data signal, comprising:

code configured to cause a processor to implement a method for implementing directional control of a motor vehicle, the method further comprising;

determining whether a failure of a primary steering system of the motor vehicle exists; and

if a failure of the primary steering system exists, then creating a yaw moment on the vehicle by selectively applying a braking force to one or more wheels of the vehicle, thereby causing the vehicle to turn in a commanded direction.