Motor vehicle with supplemental rear steering having open and closed loop modes

• US 6,640,171 B2
• Filed: 08/03/2001
• Issued: 10/28/2003
• Est. Priority Date: 12/15/1999
• Status: Expired due to Fees

• Current Assignee: GM Global Technology Operations Incorporated (Motors Liquidation Co. GUC Trust), Steering Solutions IP Holding Corporation (Nexteer Automotive Group Ltd.)
• Original Assignee: Delphi Technologies, Inc. (BorgWarner Incorporated)
• Inventors: Chen, Hsien Heng, Bedner, Edward John, Boswell, Karen Ann
• Primary Examiner(s): NGUYEN, TAN QUANG
• Application Number:
  US09/921,634
• Publication Number:
  US 20020042671A1
• Time in Patent Office: 816 Days
• Field of Search: 701/41, 701/42, 701/71, 701/69, 701/94, 180/408, 180/411, 180/412, 180/413, 180/422, 180/415
• US Class Current: 701/41
• CPC Class Codes: B60K 28/16 responsive to, or preventing, skidding of wheels brake control systems for vehicle drive stability B60T8/1755; arrangements responsive to a speed condition for adjusting wheel braking force B60T8/32; control of vehicle driving stability otherwise than by controlling the propulsion unit only B60W30/02; preventing wheel slippage by reducing power in rail vehicles B61C15/00
• CPC Class Codes: B60T 2260/022 Rear-wheel steering; Four-wheel steering
• CPC Class Codes: B60T 2260/024 Yawing moment compensation during mu-split braking
• CPC Class Codes: B60T 8/1764 Regulation during travel on surface with different coefficients of friction, e.g. between left and right sides, mu-split or between front and rear
• CPC Class Codes: B60W 2050/0012 Feedforward or open loop systems
• CPC Class Codes: B60W 2520/14 Yaw
• CPC Class Codes: B60W 2520/28 Wheel speed
• CPC Class Codes: B60W 2540/18 Steering angle
• CPC Class Codes: B60W 30/18145 Cornering
• 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 rear steer control for a motor vehicle considers vehicle velocity in three ranges and provides an out of phase rear steer angle in open loop control within a low velocity range for oversteer assistance of parking and similar vehicle maneuvers, an in phase rear steer angle in closed loop control responsive to vehicle yaw rate within a high velocity range for understeer vehicle stability assistance, and a steer angle in closed loop control responsive to vehicle yaw rate within an intermediate velocity range. In a preferred embodiment, the closed loop control in the high velocity range may be combined with an open loop control. The control further provides supplemental throttle adjustments in coordination with the rear steer control for increased traction and stability in a turn.

Claims

1. A method for controlling a steerable rear wheel in a motor vehicle having one or more operator steered front wheels, comprising the steps:

measuring longitudinal vehicle velocity;

measuring a front steer angle;

if the measured longitudinal vehicle velocity is within a predetermined low velocity range, deriving a first rear steer angle command in open loop responsive to the measured longitudinal vehicle speed and front steer angle and applying the first rear steer angle command to the steerable rear wheel out of phase with the front steer angle;

if the measured longitudinal vehicle velocity is within a predetermined high speed range higher than the low velocity range, deriving a second rear steer angle command in closed loop responsive at least to yaw rate error and applying the second rear steer angle command to the steerable rear wheel in phase with the front steer angle; and

if the measured longitudinal vehicle velocity is within an intermediate velocity range between the high velocity range and the low velocity range, deriving a third rear steer angle command in closed loop responsive at least to yaw rate error and applying the third rear steer angle command to the steerable rear wheel.

2. The method of claim 1 wherein the step of deriving a second rear steer angle further includes the steps:

deriving a fourth rear steer angle command in open loop responsive to the measured longitudinal vehicle velocity and front steer angle;

deriving a fifth rear steer angle command in closed loop responsive at least to yaw rate error; and

summing the fourth and fifth steer angle commands to produce the second steer angle command.

3. The method of claim 2 further comprising the step of storing separate first and second sets of data for determining desired yaw rate in closed loop control, wherein the step of determining a second rear steer angle command in closed loop comprises deriving a desired yaw rate from the first set of data and the step of determining a third rear steer angle command in closed loop comprises deriving a desired yaw rate from the second set of data.

4. The method of claim 1 further comprising the step of storing separate first and second sets of data for determining desired yaw rate in closed loop control, wherein the step of determining a second rear steer angle command in closed loop comprises deriving a desired yaw rate from the first set of data and the step of determining a third rear steer angle command in closed loop comprises deriving a desired yaw rate from the second set of data.

5. The method of claim 1 for a vehicle further having a second steerable rear wheel, wherein at least one of the steps of deriving a second rear steer angle command in closed loop responsive at least to yaw rate error and deriving a third rear steer angle command in closed loop responsive at least to yaw rate error further comprises deriving a commanded difference between the right and left wheel velocities for the rear wheels at least from a linear combination of at least two of (a) the yaw rate error, (b) a time derivative of the yaw rate error and (c) a time integral of the yaw rate error.

6. The method of claim 5 wherein the linear combination of at least two of (a) the yaw rate error, (b) a time derivative of the yaw rate error and (c) a time integral of the yaw rate error comprises gain factors stored as a function of estimated surface coefficient of friction.

7. The method of claim 5 wherein the linear combination of at least two of (a) the yaw rate error, (b) a time derivative of the yaw rate error and (c) a time integral of the yaw rate error comprises gain factors stored as a function of a sensed oversteer/understeer condition of the vehicle.

8. The method of claim 1 for a vehicle further having a second steerable rear wheel, wherein at least one of the steps of deriving a second rear steer angle command in closed loop responsive at least to yaw rate error and deriving a third rear steer angle command in closed loop responsive at least to yaw rate error further comprises deriving a commanded difference between the right and left wheel velocities for the rear wheels at least from a time integral of the yaw rate error, and wherein the time integral of the yaw rate error is reset to a predetermined value when the absolute value of the yaw rate error is less than a threshold value.

9. The method of claim 1 for a vehicle further having a second steerable rear wheel, wherein at least one of the steps of deriving a second rear steer angle command in closed loop responsive at least to yaw rate error and deriving a third rear steer angle command in closed loop responsive at least to yaw rate error further comprises deriving a commanded difference between the right and left wheel velocities for the rear wheels at least from a time integral of the yaw rate error, and wherein the time integral of the yaw rate error is reset to a predetermined value when the yaw rate error has a sign different from that of the time integral of the yaw rate error.

10. The method of claim 1 wherein the step of measuring a front steer angle further comprises the steps:

sensing a steering wheel angle δ

_SWA of an operator steering control, and

deriving the front steer angle by multiplying the sensed steering wheel angle by a factor representing a steering gear ratio 1/K_F.