Application US20190143767

METHOD FOR DETERMINING A WHEEL TIRE GROUND PRINT
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US20190143767

1. A method for determining a footprint (ΔL) of a tire (3), corresponding to a length of contact of said tire (3) with the ground, of a vehicle equipped with a monitoring system that includes one wheel unit (4) for each tire (3), each wheel unit (4) comprising a microcontroller (14), a speed sensor (12′), a transmitter (10), a reference clock (16) of the transmitter (10) configured to operate at a given frequency (F₀) , and at least one time control device for the system, where an actual frequency (F) output by said reference clock (16) is subject to variations (ΔF) with respect to the given frequency (F₀) when the wheel unit is within the footprint of the tire, the method comprising: (2) (3)

continuously measuring, by way of said time control device, for the variations (ΔF) of the output frequency (F) of the reference clock (16) with respect to the given frequency (F₀), as a function of time;

determining a time interval (T_ΔL) during which said variations (ΔF) of the frequency of the reference clock (16) occur; and

on the basis of the rotation speed of the tire (3), deducing therefrom an angular contact range (Θ) corresponding to the footprint (ΔL) of the tire (3).

2. The footprint determination method as claimed in claim 1, wherein the time control device is a clock (13) of the microcontroller (14), which generates a signal representative of the variations (ΔF) of the output frequency (F) of the reference clock (16) as a relative variation (ΔF/F₀) of the frequency (F) timed by the frequency of the clock (13) of the microcontroller (14). (0)

3. The footprint determination method as claimed in claim 1, wherein the time control device is a phase lock detector (32) of a phase lock loop (20) with which the transmitter (10) is equipped, which generates a signal representative of the variations (ΔF) of the frequency (F) of the reference clock (16) as a phase locking state information signal (S, S′) supplied by the phase lock detector (32) to the microcontroller (14). (2) (0)

6. A method for determining a footprint (ΔL) of a tire (3) of a wheel (1), corresponding to a length of contact of said tire (3) with the ground, of a vehicle equipped with a monitoring system that includes one wheel unit (4) for each tire (3), each wheel unit (4) comprising a microcontroller (14), a speed sensor (12′), a transmitter (10), a reference clock (16) of the transmitter (10) configured to operate at a given frequency (F₀), and at least one time control device for the system, where an actual frequency (F) output by said reference clock (16) is subject to variations (ΔF) with respect to the given frequency (F₀) when the wheel unit is within the footprint of the tire, the method comprising the following successive steps: (2) (9)

measuring continuously, and recording (30, 60, 60′), as a function of time, the frequency (F) at the output of the reference clock (16) and the variations (ΔF) of the output frequency (F) with respect to the given frequency (F₀);

determining and recording the time interval (T_ΔL) during which said variations (ΔF) of the frequency of the reference clock (16) occur;

recording a rotation speed of the wheel (1) as a function of time based on an output of the speed sensor;

using the recorded time interval (T_ΔL) of the variations of frequency (ΔF) of the reference clock (16) and the recorded rotation speed of the wheel (1) to calculate and record an angular contact range (θ) of the tire (3);

defining a detection threshold (F_Min) below which said frequency variations (ΔF) are disregarded;

if the frequency variations (ΔF) are above the frequency threshold (F_Min), calculating the footprint (ΔL) on the basis of the contact angle (Θ), the time interval (T_ΔL) and the speed of the wheel (1);

defining boundaries (ΔL_min, ΔL_max) of the value of the footprint (ΔL) beyond which the calculated value of the footprint (ΔL) is not accepted;

defining a frequency of calculation for determining the value of the footprint (ΔL) of the tire (3); and

restarting the calculation at the frequency thus defined.

7. The footprint determination method as claimed in claim 6, wherein the time control device is a clock (13) of the microcontroller (14), which generates a signal representative of the variations (ΔF) of the output frequency (F) of the reference clock (16) as a relative variation (ΔF/F₀) of the frequency (F) timed by the frequency of the clock (13) of the microcontroller (14). (0)

8. The footprint determination method as claimed in claim 6, wherein the time control device is a phase lock detector (32) of a phase lock loop (20) with which the transmitter (10) is equipped, which generates a signal representative of the variations (ΔF) of the frequency (F) of the reference clock (16) as a phase locking state information signal (S, S′) supplied by the phase lock detector (32) to the microcontroller (14). (2) (0)

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Application US20190143767

METHOD FOR DETERMINING A WHEEL TIRE GROUND PRINT

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