Vehicular surface traction characteristic estimation techniques

• US 5,563,792 A
• Filed: 12/19/1994
• Issued: 10/08/1996
• Est. Priority Date: 11/12/1992
• Status: Expired due to Term

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Motor Company
• Inventors: Chen, Lee-Fei, Hrovat, Davorin, Simonds, Craig J., Ander, Anthony T.
• Primary Examiner(s): Teska, Kevin J.
• Assistant Examiner(s): Walker, Tyrone V.
• Application Number:
  US08/358,842
• Time in Patent Office: 659 Days
• Field of Search: 364/424.05, 364/426.01, 364/426.02, 364/426.03, 180/197, 180/140, 180/142, 361/238
• US Class Current: 701/82
• CPC Class Codes: B60G 2400/822 Road friction coefficient determination affecting wheel traction
• CPC Class Codes: B60G 2800/70 Estimating or calculating vehicle parameters or state variables
• CPC Class Codes: B60T 2210/12 Friction
• CPC Class Codes: B60T 8/172 Determining control parameters used in the regulation, e.g. by calculations involving measured or detected parameters B60T8/17551 takes precedence
• CPC Class Codes: B60W 2552/40 Coefficient of friction
• CPC Class Codes: F16H 2059/506 Wheel slip
• CPC Class Codes: F16H 59/66 Road conditions, e.g. slope, slippery
• CPC Class Codes: G01N 19/02 Measuring coefficient of friction between materials testing of tyres G01M17/02; determinations of friction coefficient used in vehicle braking or traction control systems B60T8/172
• CPC Class Codes: G01N 2203/0218 Calculations based on experimental data
• CPC Class Codes: G01P 3/56 for comparing two speeds

Abstract

A technique for estimating a traction characteristic of a surface under a moving vehicle, such as the coefficient of friction of the surface. The traction characteristic can be estimated by generating a torque signal representative of at least an estimate of the amount of torque applied to the driven wheels of the vehicle. A load signal representative of at least an estimate of the load or weight applied to the driven wheels also is generated. The value of the torque signal is divided by the value of the load signal in order to generate a characteristic signal. Depending on the amount of slippage between the driven and non-driven wheels of the vehicle, the characteristic signal can be stored in order to provide an estimate of the traction characteristic of the surface in real time.

Claims

1. A method of controlling spin of driven wheels of a moving vehicle with the aid of computer processing means, said moving vehicle traveling over a surface and including a pair of driven wheels and a pair of non-driven wheels, said method comprising the steps of:

generating a plurality of characteristic signals periodically, each of said characteristic signals being representative of at least an estimate of a traction characteristic of a surface under said moving vehicle;

generating a first speed signal representative of the angular speed of said driven wheels;

generating a second speed signal representative of the angular speed of said nondriven wheels;

generating a slip signal responsive at least in part to a difference in value of said first speed signal and said second speed signal;

generating a slip limit signal representative of a predetermined value of slippage between said driven wheels and said non-driven wheels;

generating a first decision signal if the value of said slip signal is greater than the value of said slip limit signal;

generating a second decision signal if the value of a current one of said characteristic signals is greater than a value of a previously stored one of said characteristic signals;

storing a value of a current one of said characteristic signals in place of a previously stored value of one of said characteristic signals in response to said first decision signal or in response to said second decision signal to provide a real-time estimate of a traction characteristic of said surface; and

controlling said driven wheels using said estimate of a traction characteristic of said surface.

2. A method, as claimed in claim 1, wherein said slip signal is proportional to the difference between the angular speed of said driven wheels and the angular speed of said nondriven wheels.

3. A method, as claimed in claim 1, wherein said traction characteristic is coefficient of friction and wherein said characteristic signals are representative of at least an estimate of the coefficient of friction of said surface.

4. A method, as claimed in claim 1 and further comprising the step of displaying the value of said characteristic signal.

5. A method of controlling spin of driven wheels of a moving vehicle with the aid of computer processing means, said moving vehicle traveling over a surface and defining a longitudinal axis and including a pair of driven wheels and a pair of non-driven wheels, one of said pairs of said driven wheels and said non-driven wheels being steerable by a steering wheel, said method comprising the steps of:

generating a torque signal representative of at least an estimate of the amount of torque applied to said driven wheels;

generating a load signal representative of at least an estimate of the weight applied to said driven wheels;

dividing the value of said torque signal by the value of said load signal in order to generate a characteristic signal representative of a traction characteristic of said surface under said moving vehicle;

generating a first speed signal representative of the angular speed of said driven wheels;

generating a second speed signal representative of the angular speed of said non-driven wheels;

generating a slip signal responsive at least in part to a difference in value of said first speed signal and said second speed signal;

generating a first decision signal if the value of said slip signal is greater than a predetermined value;

generating a second decision signal if a current value of said characteristic signal is greater than a previously stored value of said characteristic signal;

storing a current value of said characteristic signal in place of a previously stored value of one of said characteristic signals in response to said first decision signal in response to said second decision signal to provide a real-time estimate of a traction characteristic of said surface; and

controlling said driven wheels using said estimate of a traction characteristic of said surface.

6. A method, as claimed in claim 5, wherein said traction characteristic is coefficient of friction.

7. A method, as claimed in claim 5, and further comprising the step of displaying the value of said characteristic signal.

8. A method, as claimed in claim 5, wherein said slip signal is proportional to the difference between the angular speed of said driven wheels and the angular speed of said nondriven wheels.

9. A method, as claimed in claim 8, wherein said predetermined value is obtained by the steps of

generating a wheel angle signal representative of the angle between said steerable pair of wheels and said longitudinal axis;

generating a slip limit signal representative of a predetermined value of slippage between said driven wheels and said nondriven wheels dependent on said wheel angle signal; and

using the value of said slip limit signal as said predetermined value, and wherein said step of generating said wheel angle signal comprises the steps of;

generating a steering angle signal representative of the steering angle of said steering wheel; and

multiplying the value of said steering angle signal by a conversion factor representing different slip requirements while in turns including conversion of said steering angle signal into said wheel angle signal.

10. A method, as claimed in claim 8, wherein said step of generating said slip limit signal comprises the step of adding said scaled wheel angle signal to a constant.

11. A method of controlling spin of driven wheels of a moving vehicle with the aid of computer processing means, said moving vehicle defining a longitudinal axis and including a pair of driven wheels and a pair of non-driven wheels, said method comprising the steps of:

generating a plurality of characteristic signals periodically, each of said characteristic signals being representative of at least an estimate of said traction characteristic, the step of generating a characteristic signal comprising the sub-steps of

generating a torque signal representative of at least an estimate of the amount of torque applied to said driven wheels,

generating a load signal representative of at least an estimate of the normal force applied to said driven wheels, and

dividing the value of said torque signal by the value of said load signal in order to generate one of said plurality of characteristic signals;

generating a first speed signal representative of the angular speed of said driven wheels;

generating a second speed signal representative of the angular speed of said nondriven wheels;

generating a slip signal responsive at least in part to a difference in value of said first speed signal and said second speed signal;

generating a slip limit signal representative of a predetermined value of slippage between said driven wheels and said non-driven wheels;

generating a first decision signal if the value of said slip signal is greater than the value of said slip limit signal;

generating a second decision signal if the value of a current one of said characteristic signals is greater than a value of a previously stored one of said characteristic signals;

storing a value of a current one of said characteristic signals in place of a previously stored value of one of said characteristic signals in response to said first decision signal or in response to said second decision signal to provide a real-time estimate of a traction characteristic of said surface; and

controlling said driven wheels using said estimate of a traction characteristic of said surface.

12. A method, as claimed in claim 11, further comprising the step of generating a wheel angle signal representative of the angle between said steerable pair of wheels and said longitudinal axis, and wherein said step of generating said slip limit signal comprises the step of adding a scaled value of said wheel angle signal to a constant.

13. A method, as claimed in claim 12, wherein said step of generating said wheel angle signal comprises the steps of:

generating a steering angle signal representative of the steering angle of said steering wheel; and

multiplying the value of said steering angle signal by a conversion factor to convert said steering angle signal into said wheel angle signal.