Surface friction testing

• US 3,893,330 A
• Filed: 01/07/1974
• Issued: 07/08/1975
• Est. Priority Date: 12/18/1972
• Status: Expired due to Term

• Current Assignee: George A. Shute, Richard A. Zimmer
• Original Assignee: George A. Shute, Richard A. Zimmer
• Inventors: Shute, George A., Zimmer, Richard A.
• Primary Examiner(s): Woodiel, Donald O.
• Application Number:
  US05/431,358
• Time in Patent Office: 547 Days
• Field of Search: 73/9,146,126,128 324/174,173
• US Class Current: 73/9
• CPC Class Codes: G01L 5/28 for testing brakes
• 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: G01P 3/489 Digital circuits therefor

Abstract

An apparatus for measuring speeds and distances to determine the coefficients of friction between a tire of a braked vehicle wheel and a road surface. A speed unit and distance units are provided to measure the speed and distances for alternately determining the coefficient of friction as a function of percent slip, the stopping coefficient of friction, and the skidding coefficient of friction.

Claims

1. An apparatus for measuring speed and distance in testing to determine the skidding coefficient of friction between a road surface and a tire of a vehicle wheel to which a braking force is applied causing the wheel to lock, comprising:

speed measuring means for measuring the speed of said vehicle at the time a braking force is applied to the vehicle wheel; and

distance measuring means operably connected to said speed measuring means for measuring the distance travelled by said vehicle after said wheel has locked, whereby the vehicle speed at the time of braking and the distance travelled by said vehicle from the time said vehicle wheel locks until the vehicle comes to rest are determined.

2. The apparatus set forth in claim 1, wherein said speed measuring means includes:

vehicle distance signal generating means for generating a vehicle distance signal having pulses proportional in number to the distance travelled by said vehicle;

time signal generating means for generating a time signal having periodic pulses of a constant time duration;

brake engagement signal generating means for generating a brake engagement signal of a substantially constant magnitude initiated at the time the braking force is applied to said vehicle wheel; and

speed counting means for counting the number of pulses of said vehicle distance signal occuring during the duration of a pulse of said time signal and upon initiation of said brake engagement signal, whereby said speed counting means counts pulses proportional to the distance travelled by said vehicle within a known time period upon application of said braking force.

3. The apparatus set forth in claim 2, wherein said vehicle distance signal generating means includes:

a rotating member of a known diameter mounted with said vehicle and operatively engaging said raod; and

signal producing means for producing a signal having pulses proportional to the rotation of said rotating member, whereby said signal producing means produces a signal having pulses proportional to the distance travelled by said vehicle.

4. The apparatus set forth in claim 3 wherein said signal producing means includes:

a magnet mounted with said rotating member and spaced from the center thereof;

magnetically actuated switching means operatively connected to a voltage source and to said speed counting means for temporarily closing and allowing a pulse to pass to said speed counting means, and said switching means being mounted in a fixed position relative to said rotating member and spaced from the center thereof a distance substantially equal to that of said magnet, whereby rotation of said magnet with said rotating member causes said magnet to come into close proximity with and actuate said switching means to allow a pulse to pass to said speed counting means.

5. The apparatus set forth in claim 1, wherein said speed measuring means includes:

display means for displaying the speed of said vehicle at the time said braking force is applied.

6. The apparatus set forth in claim 1, wherein said distance measuring means includes:

vehicle distance signal generating means for generating a vehicle distance signal having pulses proportional in number to the distance travelled by said vehicle;

braked wheel signal generating means for generating a braked wheel signal having pulses proportional in number to the rotational movement of said vehicle wheel to which said braking force is applied;

distance counter means for counting the pulses of said vehicle distance signal; and

distance counter reset means operatively connecting said distance counter means and said braked wheel signal generating means for resetTing the count of said distance counter means to zero when a pulse is received from said braked wheel signal generating means, whereby said distance counter means counts the pulses of said vehicle distance signal after said braked wheel stops rotating.

7. The apparatus set forth in claim 6, wherein said braked wheel signal generating means includes:

a magnet mounted with said braked wheel and spaced from the center thereof;

magnetically actuated switching means operatively connected to a voltage source and to said distance counter means for temporarily closing and allowing a pulse to pass to said distance counter means; and

said switching means being mounted in a fixed position relative to said braked wheel and spaced from the center thereof a distance substantially equal to that of said magnet whereby rotation of said magnet with said braked wheel causes said magnet to come into close proximity with and actuate said switching means to allow a pulse to pass to said distance counting means.

8. The apparatus set forth in claim 1, wherein said distance measuring means includes:

display means for displaying the distance travelled by said vehicle after said braked wheel has locked.

9. An apparatus for measuring speed and distance in testing to determine the coefficient of friction as a function of the amount of slip between a road surface and a tire of a vehicle wheel to which a braking force is applied, comprising:

speed measuring means for measuring the speed of said vehicle at the time the braking force is applied to the vehicle wheel;

first distance measuring means operably connected to said speed measuring means for measuring the distance travelled by said vehicle after said braking force is applied to said wheel; and

second distance measuring means operably connected to said speed measuring means for measuring the horizontal distance of rotation of the braked wheel for all amounts of slip of said tire on said road surface, whereby the speed of said vehicle at the time of braking and the distance travelled by said vehicle after braking are obtained and the horizontal distance of rotation of said braked wheel are determined for calculating the percent slip of said braked wheel on the road surface.

10. The apparatus set forth in claim 9, wherein said first distance measuring means includes:

vehicle distance signal generating means for generating a vehicle distance signal having pulses proportional in number to the distance travelled by said vehicle;

brake engagement signal generating means for generating a brake engagement signal of a substantially constant magnitude initiated at the time said braking force is applied to said vehicle wheel; and

vehicle distance counting means for counting the number of pulses of said vehicle distance signal after initiation of said brake engagement signal, whereby said vehicle distance counting means counts pulses proportional to the distance travelled by said vehicle after application of said braking force.

11. The apparatus set forth in claim 9, wherein said second distance measuring means includes:

braked wheel distance signal generating means for generating a braked wheel signal having pulses proportional in number to the horizontal distance of rotation of said braked wheel;

brake engagement signal generating means for generating a brake engagement signal of a substantially constant magnitude initiated at the time said braking force applied to said vehicle wheel; and

braked wheel distance counting distance means for counting the number of pulses of said braked wheel distance signal after initiation of said brake engagement signal, whereby said braked wheel distance counting means counts pulses proportional to the horizontal distance of rotation of said braked wheel after application of said braking force.

12. An apparatus for measuring speed and distance in testing to determine the stopping distance coefficient of friction and the skidding distance coefficieNt of friction between a road surface and a tire of a vehicle wheel to which a braking force is applied, comprising:

speed measuring means for measuring the speed of said vehicle at the time the braking force is applied to the vehicle wheel; and

distance measuring means operably connected to said speed measuring means for alternatively measuring the distance travelled by said vehicle after said braking force is applied and the distance travelled by said vehicle after said vehicle wheel locks, whereby when said distance measuring means measures the distance travelled by said vehicle after application of said braking force the values of speed and distance for calculating the stopping distance coefficient of friction are determined and when said distance measuring means measures the distance travelled by said vehicle after said wheel locks the speed and distance for calculating the skidding distance coefficient of friction are determined.

13. A method of measuring speed and distance in testing to determine the skidding distance coefficient of friction between a road surface and a tire of a wheeled vehicle comprising:

applying a braking force to a wheel of a vehicle while said vehicle is moving to cause said wheel to lock at a time subsequent to said application of the braking force;

measuring the speed of said vehicle at the time said braking force is applied; and

measuring the distance travelled by said vehicle after said wheel locks, whereby the vehicle speed at the time of braking and the distance travelled by said vehicle from the time said vehicle wheel locks until said vehicle comes to rest are determined.

14. A method of measuring speed and distance in testing to determine the coefficient of friction between a road surface and a tire of a vehicle wheel as a function of the slippage of the wheel on the road surface, comprising:

applying a braking force to a wheel of a vehicle while said vehicle is in motion;

measuring the speed of said vehicle at the time said braking force is applied;

measuring the distance travelled by said vehicle after said braking force is applied; and

measuring the horizontal distance of rotation of the braked wheel, whereby the speed of said vehicle at the time of braking and the distance travelled by said vehicle after braking are obtained and the distances for calculating the percent slip of said vehicle wheel on the road surface are determined.