Method for determining the angular position of a shaft of a motor vehicle
A method for determining the angular position of a shaft of a motor vehicle. The method includes calculating the mean angular resolution; calculating the time at which the cosine signal passes through zero; using the time at which the sine signal passes through zero and the mean angular resolution; determining the measured angle at the calculated time at which the cosine signal passes through zero; calculating the amplitude of the second harmonic of the measured angle signa;, calculating a second-harmonic error from the calculated amplitude of the second harmonic; and calculating a compensated angle representing the corrected angular position of the shaft from the real-time measured angle and from the calculated second-harmonic error.
1. A method for determining an angular position of a shaft of a motor vehicle by a target fixed to a free end of said shaft and comprising a magnetic element, and of a magnetoresistive position sensor mounted facing said target, said method comprising: at each instant: rotating the shaft, generating a sine signal, storing the values of the sine signal in a first memory zone, generating a cosine signal, storing the values of the cosine signal in a different memory zone, calculating a real-time “measured” angle from the sine and cosine signals representing the angular position of the shaft, storing the calculated measured angle in a memory zone different from the preceding zones, over one period of the sine and cosine signals: determining the measured angle as the sine signal passes through zero, determining the time at which the sine signal passes through zero, calculating the mean angular resolution, said mean angular resolution corresponding to the derivative, with respect to time, of the determined measured angle, calculating the time at which the cosine signal passes through zero, using the time at which the sine signal passes through zero and the mean angular resolution, determining the measured angle at the calculated time at which the cosine signal passes through zero, calculating the amplitude of the second harmonic of the measured angle signal from the measured angle determined at the time at which the sine signal passes through zero, and from the measured angle determined at the calculated time at which the cosine signal passes through zero, calculating a second-harmonic error from the calculated amplitude of the second harmonic, and calculating a compensated angle representing the corrected angular position of the shaft from the real-time measured angle and from the calculated second-harmonic error.
2. The method as claimed in claim 1 , wherein the compensated angle
θ compensated [Math 42]
representing the corrected angular position of the shaft is calculated using the following formula:
θ compensated =θ measured +Err harmonic [Math 43]
where
θ measured [Math 44]
is the measured angle, and
Err harmonic [Math 45]
is the second-harmonic error.
3. The method as claimed in claim 1 , wherein the mean angular resolution is calculated using the following formula:
Res
angular
=
Δ
θ
measured
Δ
t
[
Math
46
]
where
Res angular [Math 47]
is the angular resolution, Δt is the time interval between two measurements and
Δθ measured [Math 48]
is the difference between the angles measured at two successive times.
4. The method as claimed in claim 1 , wherein a time X2 at which the cosine signal passes through zero is calculated using the following formula:
X
2
=
X
1
+
90
Res
angular
[
Math
49
]
where X1 is the time at which the sine signal passes through zero from positive to negative, and
Res angular [Math 50]
is the mean angular resolution.
5. The method as claimed in claim 1 , wherein the amplitude of the second harmonic of the measured angle signal is calculated using the following formula:
Amp
harmonic
=
θ
X
1
+
90
-
θ
X
2
2
[
Math
51
]
where
θ X1 [Math 52]
is the angle determined at the time X1 at which the sine signal passes through zero, and
θ X2 [Math 53]
is the angle determined at the time X2 at which the cosine signal passes through zero.
6. The method as claimed in claim 1 , wherein the second-harmonic error
Err harmonic [Math 54]
is calculated using the following formula:
Err harmonic ( t )=Amp harmonic cos(2ωt) [Math 55]
where
Amp harmonic [Math 56]
is the amplitude of the second harmonic, and ω is the angular velocity of the shaft.
7. A non-transitory computer program product, comprising a set of program code instructions that, when executed by one or more processors, configure the one or more processors to implement a method as claimed in claim 1 .
8. A system for determining an angular position of a shaft of a motor vehicle by a target fixed to a free end of said shaft and comprising a magnetic element, and of a magnetoresistive position sensor mounted facing said target, said system comprising said sensor, said sensor being configured to generate a sine signal and a cosine signal representative of the angular position of the shaft, the system being configured to:
at each instant, generate a sine signal, store the values of the sine signal in a first memory zone, generate a cosine signal, store the values of the cosine signal in a second memory zone, calculate a real-time “measured” angle from the sine and cosine signals representing the angular position of the shaft, and store the calculated measured angle in a third memory zone, over one period of the sine and cosine signals: determine the measured angle as the sine signal passes through zero, determine the time at which the sine signal passes through zero, calculate the mean angular resolution, said mean angular resolution corresponding to the derivative, with respect to time, of the determined measured angle, calculate the time at which the cosine signal passes through zero, using the time at which the sine signal passes through zero and the mean angular resolution, determine the measured angle at the calculated time at which the cosine signal passes through zero, calculate the amplitude of the second harmonic of the measured angle signal from the measured angle determined at the time at which the sine signal passes through zero, and from the measured angle determined at the calculated time at which the cosine signal passes through zero, calculate a second-harmonic error from the calculated amplitude of the second harmonic, and calculate a compensated angle representing the corrected angular position of the shaft from the real-time measured angle and from the calculated second-harmonic error.
9. A motor vehicle comprising a drive shaft and a system as claimed in claim 8 .