Method and apparatus for four wheel steering control

• US 5,488,555 A
• Filed: 05/27/1993
• Issued: 01/30/1996
• Est. Priority Date: 05/27/1993
• Status: Expired due to Term

• Current Assignee: Mid-America Commercialization Corporation
• Original Assignee: Ford Motor Company
• Inventors: Asgari, Jahanbakhsh, Tran, Minh N., Hrovat, Davorin D.
• Primary Examiner(s): Teska, Kevin J.
• Assistant Examiner(s): PHAN, THAI Q
• Application Number:
  US08/067,930
• Time in Patent Office: 978 Days
• Field of Search: 364/424.05, 364/426.02, 364/424.1, 180/140, 180/142, 180/79.1, 180/197, 180/233
• US Class Current: 701/41
• CPC Class Codes: B60T 2260/022 Rear-wheel steering; Four-wheel steering
• CPC Class Codes: B60W 2050/0031 Mathematical model of the vehicle
• CPC Class Codes: B60W 2520/14 Yaw
• 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

Method, for use in a vehicle including a four wheel steering system and an electronic control unit having memory, of controlling the four wheel steering system while at least one of the wheels is under a torque load such that the vehicle behaves like a front wheel steering vehicle under no torque load, or a four wheel steering vehicle under no torque load. The method includes determining at least one control gain for the four wheel steering system so that the torque loaded vehicle behaves like a front wheel steering vehicle under no torque load, and controlling the four wheel steering system according to the control gain, thereby improving directional stability of the vehicle travelling on a slippery road surface. Apparatus is provided for carrying out the method.

Claims

1. For use in a vehicle including front wheels, rear wheels, a four wheel steering system and an electronic control unit having memory, a method of controlling the four wheel steering system comprising:

applying a torque load to at least one of the vehicle wheels;

determining at least one control gain for the four wheel steering system so that the torque loaded vehicle behaves like a front wheel steering vehicle under no torque load; and

controlling the four wheel steering system according to the control gain, thereby improving directional stability of the vehicle travelling on a slippery road surface;

the step of determining at least one control gain comprising determining a yaw rate control gain based on vehicle stability requirements,

the step of determining at least one control gain further comprising determining a proportional steer control gain based on the yaw rate control gain;

the proportional steer control gain K_p for a rear wheel drive vehicle being determined according to;

##EQU35##

2. For use in a vehicle including front wheels, rear wheels, a four wheel steering system and an electronic control unit having memory, a method of controlling the four wheel steering system comprising:

applying a torque load to at least one of the vehicle wheels;

determining at least one control gain for the four wheel steering system so that the torque loaded vehicle behaves like a front wheel steering vehicle under no torque load;

controlling the four wheel steering system according to the control gain, thereby improving directional stability of the vehicle travelling on a slippery road surface;

the step of determining at least one control gain comprising determining a yaw rate control gain based on vehicle stability requirements,

the step of determining at least one control gain further comprising determining a proportional steer control gain based on the yaw rate control gain;

determining the front wheel tire steering angle, the step of controlling the four wheel steering system including steering the rear wheels based on the proportional steer control gain, the yaw rate control gain and the front tire steering angle;

storing a plurality of yaw rate control gain and proportional steer control gain pairs in said memory;

determining percent slip of the rear wheels in relation to the road surface; and

retrieving a control gain pair from the memory based on the percent slip of the rear wheels for controlling the four wheel steering system;

the proportional steer control gain K_p for a front wheel drive vehicle having a desired yaw-rate being determined according to;

##EQU36##

3. For use in a vehicle including front wheels, rear wheels, a four wheel steering system and an electronic control unit having memory, a method of controlling the four wheel steering system comprising:

applying a torque load to at least one of the vehicle wheels;

determining at least one control gain for the four wheel steering system so that the torque loaded vehicle behaves like a front wheel steering vehicle under no torque load; and

controlling the four wheel steering system according to the control gain, thereby improving directional stability of the vehicle travelling on a slippery road surface;

the step of determining at least one control gain comprising determining a yaw rate control gain based on vehicle stability requirements,

the step of determining at least one control gain further comprising determining a proportional steer control gain based on the yaw rate control gain;

the proportional steer control gain K_p for a front wheel drive vehicle having a desired lateral velocity being determined according to;

##EQU37##

4. For use with an automotive vehicle including four wheels and a four wheel steering system controlled by an electronic control unit having memory, the four wheel steering system for steering the four wheels while at least one of the wheels is under a torque load, the steering system further comprising:

means for determining at least one control gain for the four wheel steering system so that the torque loaded vehicle behaves like a front wheel steering vehicle under no torque load; and

means for controlling the four wheel steering system according to the control gain, thereby improving directional stability of the vehicle travelling on a slippery road surface;

the means for determining at least one control gain including means for determining a yaw rate control gain based on vehicle stability requirements,

the means for determining at least one control gain further comprising means for determining a proportional steer control gain based on the yaw rate control gain;

the means for determining a proportional steer control gain effecting proportional steer control gain (K_p) for a rear wheel drive vehicle according to;

##EQU38##

5. For use with an automotive vehicle including four wheels and a four wheel steering system controlled by an electronic control unit having memory for steering the four wheels while at least one of the wheels is under a torque load, the steering system comprising:

means for determining at least one control gain for the four wheel steering system so that the torque loaded vehicle behaves like a front wheel steering vehicle under no torque load; and

means for controlling the four wheel steering system according to the control gain, thereby improving directional stability of the vehicle travelling on a slippery road surface;

the means for determining at least one control gain including means for determining a yaw rate control gain based on vehicle stability requirements,

the means for determining at least one control gain further comprising means for determining a proportional steer control gain based on the yaw rate control gain;

the means for determining a proportional steer control gain K_p determining the proportional steer control gain for a front wheel drive vehicle having a desired yaw-rate according to;

##EQU39##

6. For use with an automotive vehicle including four wheels and a four wheel steering system controlled by an electronic control unit having memory for steering the four wheels while at least one of the wheels is under a torque load, the steering system further comprising:

means for determining at least one control gain for the four wheel steering system so that the torque loaded vehicle behaves like a front wheel steering vehicle under no torque load; and

means for controlling the four wheel steering system according to the control gain, thereby improving directional stability of the vehicle travelling on a slippery road surface;

the means for determining at least one control gain including means for determining a yaw rate control gain based on vehicle stability requirements,

the means for determining at least one control gain further comprising means for determining a proportional steer control gain based on the yaw rate control gain;

the means for determining the proportional steer control gain K_p determining the proportional steer control gain for a front wheel drive vehicle having a desired lateral velocity according to;

##EQU40##

7. For use in a vehicle including front wheels, rear wheels, a four wheel steering system and an electronic control unit having memory, a method of controlling the four wheel steering system comprising:

applying a torque load to at least one of the vehicle wheels;

determining at least one control gain for the four wheel steering system so that the torque loaded vehicle behaves like a four wheel steering vehicle under no torque load; and

controlling the four wheel steering system according to the control gain, thereby improving directional stability of the vehicle travelling on a slippery road surface;

the step of determining at least one control gain comprising determining a yaw rate control gain based on vehicle stability requirements,

the step of determining at least one control gain further comprising determining a proportional steer control gain based on the yaw rate control gain;

the proportional steer control gain K_p for a rear wheel drive vehicle being determined according to;

##EQU41##

8. For use in a vehicle including front wheels, rear wheels, a four wheel steering system and an electronic control unit having memory, a method of controlling the four wheel steering system comprising:

applying a torque load to at least one of the vehicle wheels;

determining at least one control gain for the four wheel steering system so that the torque loaded vehicle behaves like a four wheel steering vehicle under no torque load; and

controlling the four wheel steering system according to the control gain, thereby improving directional stability of the vehicle travelling on a slippery road surface;

the step of determining at least one control gain comprising determining a yaw rate control gain based on vehicle stability requirements,

the step of determining at least one control gain further comprising determining a proportional steer control gain based on the yaw rate control gain;

the proportional steer control gain K_p for a front wheel drive vehicle having a desired yaw-rate being determined according to;

##EQU42##

9. For use in a vehicle including front wheels, rear wheels, a four wheel steering system and an electronic control unit having memory, a method of controlling the four wheel steering system comprising:

applying a torque load to at least one of the vehicle wheels;

determining at least one control gain for the four wheel steering system so that the torque loaded vehicle behaves like a four wheel steering vehicle under no torque load; and

controlling the four wheel steering system according to the control gain, thereby improving directional stability of the vehicle travelling on a slippery road surface;

the step of determining at least one control gain comprising determining a yaw rate control gain based on vehicle stability requirements,

the step of determining at least one control gain further comprising determining a proportional steer control gain based on the yaw rate control gain;

the proportional steer control gain K_p for a front wheel drive vehicle having a desired lateral velocity determined according to;

##EQU43##