Method for calibrating a radial-acceleration sensor for the wheel of a motor vehicle
A method for calibrating a radial acceleration sensor of a wheel of a vehicle including the following steps: acquisition, by the sensor, of signals S i , each signal S i being acquired during a predetermined time window W i when the vehicle is in motion, the windows W i being different from one another; detection, for each time window W i , of local extrema of the signal S i associated respectively with phase values and detection instants; determination, for each time window W i , of a frequency F i of the rotation of the wheel of the vehicle as a function of the phase values and of the detection instants for the local extrema detected; low-pass filtering of the signals S i , so as to obtain, for each time window W i , a filtered value Z i ; calibration of a constant error E c of the radial acceleration sensor as a function of the filtered values Z i and of the frequencies F i .
1. A method for calibrating a radial acceleration sensor of a wheel of a motor vehicle, said method comprising:
an acquisition step of acquisition, by the radial acceleration sensor, of signals S i , each signal S i being acquired during a predetermined time window W i when the motor vehicle is in motion, the windows W i being different from one another,
a detection step of detecting, for each time window W i , at least three local extrema of the signal S i which are respectively associated with phase values and with detection instants,
a determination step of determining, for each time window W i , a frequency F i of the rotation of the wheel of the motor vehicle as a function of the phase values and of the detection Instants for the local extrema detected in said time window W i ,
a filtering step of low-pass filtering of the signals S i , so as to obtain, for each time window W i , a filtered value Z i associated with the frequency F i , and
a calibration step of calibrating a constant error E c of the radial acceleration sensor as a function of the filtered values Z i and of the frequencies F i .
2. The method as claimed in claim 1 , wherein the step of determining the frequency F i comprises, for each time window W i considered, determining a phase time signal φ i by quadratic interpolation of the respective phase values of three local extrema, the frequency F i being determined by evaluating the derivative of said signal φ i with respect to time at a predetermined instant t p within said time window W i .
3. The method as claimed in claim 2 , wherein the three local extrema considered within each time window W i are consecutive.
4. The method as claimed in claim 1 , wherein the cut-off frequency of the low-pass filter applied to the signals S i is less than or equal to 10 Hz, preferably less than 5 Hz, and more preferably still equal to 1 Hz.
5. The method as claimed in claim 1 , wherein the step of calibrating the constant error E c comprises a linear regression of points P i , each point P i having Z i and F i 2 as its ordinate and abscissa values respectively, the constant error E c being estimated to be equal to the ordinate value at the origin of said linear regression.
6. The method as claimed in claim 1 , said method comprising, after the detection step, a step 600 of estimating, for at least one time window W i , an error R i in the gain of the radial acceleration sensor according to the formula: R i =V i /Q i , where V i represents an amplitude associated with at least one local extremum of the signal S i acquired during said at least one time window W i , and Q i represents an amplitude that is expected on the basis of measurements theoretically supplied by the radial acceleration sensor for said at least one local extremum, the gain error R i being calculated only if a steady-speed phase is detected for the signal S i .
7. The method as claimed in claim 6 , wherein, the step of determining the frequency F i comprises, for each time window W i considered, determining a phase time signal φ i by quadratic interpolation of the respective phase values of three local extrema, the frequency F i being determined by evaluating the derivative of said signal φ i with respect to time at a predetermined instant t p within said time window W i , and the step of estimating a gain error comprises, for each time window W i , making the comparison between the second derivative of the phase time signal φ i and a predetermined value ε, such that if |d 2 φ i /dt 2 |<ε, a steady-speed phase is detected.
8. The method as claimed in claim 7 , wherein the amplitude V i corresponds to the amplitude between two consecutive local extrema of the signal S i in a steady-speed phase, and Q i satisfies:
Q i =2× g×G,
where g is the acceleration due to gravity, and G represents the gain of a filter applied to the signal S i during the detection step so as to reduce measurement noise.
9. The method as claimed in claim 6 , wherein the amplitude V i corresponds to the amplitude between two consecutive local extrema of the signal S i in a steady-speed phase, and Q i satisfies:
Q i =2× g×G,
where g is the acceleration due to gravity, and G represents the gain of a filter applied to the signal S i during the detection step so as to reduce measurement noise.
10. A wheel unit comprising a radial acceleration sensor, said wheel unit comprising means configured for implementing the steps of the calibration method as claimed in claim 1 so as to calibrate said radial acceleration sensor.
11. A motor vehicle comprising a wheel unit as claimed in claim 10 .