Method of determining the state of a road

1. A method of determining a level of quality of a road from a vibration sensor mounted in a wheel of a motor vehicle traveling on said road, said vibration sensor able to measure vibrations perceived by the tread of the tire of said wheel, said method comprising:

selecting a predetermined vibrational frequency within a frequency range, the predetermined vibrational frequency referred to as the distinguishing frequency, measuring, by the vibration sensor at the distinguishing frequency, the vibrations perceived by the tread of the tire of the wheel as the motor vehicle is traveling on said road,

calculating, by a processor of the motor vehicle, a strength of the vibrations measured at the distinguishing frequency, the distinguishing frequency is maintained constant as the speed of the motor vehicle and wear of the tire vary as the motor vehicle is traveling on said road, comparing, by the processor, the calculated strength with predetermined strength values which are characteristic of various road quality levels, and determining, by the processor, the level of quality of the road from the comparison.

2. The method as claimed in claim 1 , wherein the distinguishing frequency is chosen in the frequency range comprised between 300 Hz and 500 Hz.

3. The method as claimed in claim 2 , wherein the distinguishing frequency is chosen in the frequency range comprised between 400 Hz and 460 Hz.

4. The method as claimed in claim 3 , wherein the distinguishing frequency is of the order of 450 Hz.

5. The method as claimed in claim 1 , in which the road is qualified as rough or wet when the strength of the vibrations is above a first predetermined strength threshold, referred to as the roughness threshold or the wetness threshold, respectively.

6. The method as claimed in claim 5 , in which the road is qualified as smooth or dry when the strength of the vibrations is below a second predetermined strength threshold lower than the first strength threshold and referred to as the flatness threshold or the dryness threshold, respectively.

7. The method as claimed in claim 6 , in which the quality of the road is said to be intermediate when the strength of the vibrations is comprised between the roughness threshold and the flatness threshold.

8. The method as claimed in claim 1 , wherein the motor vehicle has four wheels.

9. A vehicle system able to be mounted in a motor vehicle so as to determine a level of quality of a road, said vehicle system comprising:

a vibration sensor mounted in a wheel of the vehicle to measure vibrations perceived by the tread of the tire of said wheel; and

a processor for:

selecting a predetermined vibrational frequency within a frequency range, the predetermined vibrational frequency referred to as the distinguishing frequency, calculating a strength of the vibrations measured by the sensor at the distinguishing frequency, the distinguishing frequency is maintained constant as the speed of the motor vehicle and wear of the tire vary as the motor vehicle is traveling on said road, comparing the calculated strength against predetermined strength values which are characteristic of various levels of quality of a road, and determining the level of quality of the road from the comparison made.

10. A motor vehicle comprising a vehicle system as claimed in claim 9 .

11. The vehicle system as claimed in claim 9 , wherein the motor vehicle has four wheels.