Method for automatic calibration of a camshaft sensor for a motor vehicle engine

1. A method for automatically calibrating a camshaft sensor for a motor vehicle engine, said motor vehicle engine comprising at least one camshaft, a toothed coded target associated with this camshaft and a magnetic field sensor placed in proximity to the target to detect magnetic field variations induced by a passage of teeth (D 1 , D 2 , D 3 ) of the target in proximity to the sensor, said sensor delivering an electrical signal representative of teeth (D 1 , D 2 , D 3 ) and troughs (S 1 , S 2 , S 3 ) of the target as a function of a predetermined switching threshold (S) that is a function of an amplitude of the magnetic field (B), said method continuously measuring a value of the magnetic field, said method comprising:

during a first revolution of the target:

Step E1: measuring a maximum value and a minimum value of the magnetic field (B) for each tooth,

Step E2: calculating an amplitude of the magnetic field for said teeth, and calculating the switching threshold for each tooth rising edge as a function of the duly calculated amplitude,

said method further comprises:

Step E3: measuring an absolute minimum value of the magnetic field over the revolution (N−1) of the target,

Step E4: calculating an average of the maximum values of the magnetic field over the revolution (N−1) of the target,

Step E5: memorizing the maximum values, the absolute minimum value, and the average,

then, on each new revolution (N) of the target:

Step E6: if a minimum value of a tooth (i−1) is greater than the absolute minimum value of the preceding revolution, then:

Step E7: the switching threshold of the rising edge of the next tooth (i) is set equal to

Th ( i,N )=( B max( i− 1, N )− B min( i− 1, N ))× K−B min( i− 1, N )

where Th(i, N) is the switching threshold of the rising edge of the next tooth (i) on each new revolution, B max (i−1,N)) is a maximum value of the magnetic field of the tooth (i−1) on each new revolution (N), and B min (i−1, N) is a minimum value of the magnetic field of the tooth (i−1) for the new revolution (N),

Otherwise: if a minimum value of a tooth (i−1) is equal to the absolute minimum value of the preceding revolution (N−1), and:

Step E8: if, furthermore, the maximum value of said tooth (i−1) is equal to the maximum value of the preceding revolution for the same tooth (i−1), such that B max(i−1, N)=B max(i−1, N−1), then:

Step E9: the maximum value of said (i−1) is removed from the average of the maximum values of the new revolution, such that

Avg( B max, N )=Avg( B max, N− 1)− B max( i− 1, N )

where Avg(B max, N) is an average of the maximum values of the magnetic field over the new revolution (N), and Avg(B max, N−1) is an average of the maximum values of the magnetic field over the revolution (N−1),

otherwise, if the maximum value of the tooth (i−1) is different from the maximum value of the preceding revolution for the same tooth, such that B max(i−1,N)≠B max(i−1, N−1), then:

Step E10: the average of the maximum values for the new revolution (N) is equal to the average of the maximum values of the preceding revolution (N−1), such that: Avg(B max, N)=Avg (B max, N−1)

Step E11: the switching threshold of the rising edge for the next tooth (i) is then calculated as a function of the average of the maximum values of the new revolution (N) and of the minimum value of the preceding tooth; such that:

Th ( i,N )=(Avg( B max, N )− B min( i− 1, N ))× K−B min( i− 1, N )

with k: a factor lying between 0 and 1,

repeating the steps E3 to E11 for each new revolution of the target in order to deliver a signal representative of the teeth (D 1 , D 2 , D 3 ) and of troughs (S 1 , S 2 , S 3 ) of the target.

2. The automatic calibration method as claimed in claim 1 wherein the first revolution of the target is performed each time the camshaft sensor is powered up.

3. A camshaft sensor for a motor vehicle engine, said motor vehicle engine comprising:

at least one camshaft,

a toothed coded target associated with this camshaft and

a magnetic field sensor placed in proximity to the target to detect magnetic field variations induced by a passage of teeth (D 1 , D 2 , D 3 ) of the target in proximity to the sensor, said sensor continuously measuring a value of the magnetic field and delivering an electrical signal representative of the teeth (D 1 , D 2 , D 3 ) and troughs (S 1 , S 2 , S 3 ) of the target as a function of a predetermined switching threshold (S) that is a function of an amplitude of the magnetic field (B),

said camshaft sensor comprising a central processor configured to:

measure a maximum value (Bmax1, Bmax2, Bmax3) and a minimum value (Bmin1, Bmin2, Bmin3) of the magnetic field (B) on the passage of a tooth (D 1 , D 2 , D 3 ),

calculate the amplitude of the magnetic field for each tooth and for calculating the switching threshold,

measure an absolute minimum value (B min(N−1)) over the target revolution (N−1),

calculate an average of the maximum values (Avg(B max, N−1)) over the target revolution (N−1),

store the maximum values (Bmax1, Bmax2, Bmax3), the average of the maximum values (Avg(B max, N−1)) and the absolute minimum value (B min(N−1)) over the target revolution,

compare between each minimum value (B min (i−1, N)) of the new target revolution and the absolute minimum value (B min(N−1)) of the preceding revolution,

compare between each maximum value (B max(i−1,N)) of the new target revolution and the maximum value of the preceding revolution (B max(i−1)) for the same tooth (i−1),

calculate the average of the maximum values Avg(B max, N) over the new target revolution as a function of the result of the comparison between each maximum value (B max(i−1, N)) of the new target revolution and the maximum value of the preceding revolution (B max(i−1)) for the same tooth (i−1), and

calculate a switching threshold (Th(i, N)) as a function of the result of the comparisons.

4. A motor vehicle, comprising a camshaft sensor as claimed in claim 3 .