Method for automatic calibration of a camshaft sensor in order to correct a reluctor runout

Patent metadata

Field	Value
Publication number	US-11353346-B2
Application number	US-201917043245-A
Country	US
Kind code	B2
Filing date	Mar 28, 2019
Priority date	Apr 5, 2018
Publication date	Jun 7, 2022
Grant date	Jun 7, 2022

Abstract

A method for automatic calibration of a camshaft sensor for a motor vehicle engine. The sensor includes a processing module configured to generate, from a raw signal indicative of the variations in a magnetic field which are caused by a rotation of a target and measured by a primary cell, an output signal indicative of the moments at which teeth of the target pass past the primary cell. The sensor further includes two secondary measurement cells. The calibration method therefore makes it possible to determine two different switching thresholds for each tooth from a differential signal indicative of a difference in magnetic field measurement by the secondary cells. Also disclosed are a camshaft sensor implementing such a method, and a motor vehicle including such a sensor.

First claim

The invention claimed is:

1. A method for automatic calibration of a camshaft sensor for a motor vehicle engine,
said sensor comprising:
a toothed target,
a primary measurement cell configured to supply a first raw signal indicative of variations in a first magnetic field which are induced by a rotation of the target,
two secondary measurement cells configured to supply a respective second raw signal and a third raw signal each indicative of variations in a respective second magnetic field and at third magnetic field which are induced by the rotation of the target, and
a processing module configured to supply, from the first raw signal, the second raw signal, and the third raw signal, an output signal indicative of moments at which teeth of the target pass past the primary cell,

said calibration method comprising:
determining a local minimum of the first raw signal as a space separating two teeth of the target passes past the primary cell,
determining a differential signal as a difference between the second raw signal and the third raw signal,
determining, from said differential signal, a first local maximum of the first raw signal in a vicinity of a falling front of said first raw signal corresponding to an end of the passage of a tooth of the target past the primary cell,
determining a first switching threshold for generation of the output signal as a function of values of the first local maximum and of the local minimum,
determining, from said differential signal, a second local maximum of the first raw signal in a vicinity of a rising front of said first raw signal corresponding to a start of the passage of said tooth of the target past the primary cell,
determining a second switching threshold as a function of the values of the second local maximum and of the local minimum, and
generating said output signal from the first raw signal, from the first switching threshold and from the second switching threshold.

2. The method as claimed in claim 1 , wherein the first local maximum corresponds to a value adopted by the first raw signal when the differential signal adopts a first predetermined value, and the second local maximum corresponds to a value adopted by the first raw signal when the differential signal adopts a second predetermined value, as said tooth of the target passes past the secondary cells.

3. The method as claimed in claim 2 , wherein:
the first local maximum corresponds to a value adopted by the first raw signal in the vicinity of said falling front when the differential signal has a negative gradient and adopts a first predetermined value defined by:
D fe =D m −( D m −D min )× K fe

the second local maximum corresponds to a value adopted by the first raw signal in the vicinity of said rising front when the differential signal has a negative gradient and adopts a second predetermined value defined by:
D re =D m +( D max −D m )× K re

in which:
D max and D min correspond respectively to a maximum value and to a minimum value of the differential signal as the teeth of the target pass past the secondary cells,
D m is a value defined by:

D
m

=

D
max

+

D
min

2

K re and K fe are two factors comprised between 0 and 1.

4. The method as claimed in claim 1 , wherein the local minimum corresponds to a value adopted by the first raw signal when the differential signal adopts a predetermined value as a space separating two teeth of the target passes past the secondary cells.

5. The method as claimed in claim 4 , wherein the local minimum corresponds to the value adopted by the first raw signal when the differential signal adopts a predetermined value defined by:

D
m

=

D
max

+

D
min

2

where D max and D min correspond respectively to a maximum value and to a minimum value of the differential signal as the teeth of the target pass past the secondary cells.

6. The method as claimed in claim 1 , wherein said secondary cells are arranged one on either side of the primary cell, at equal distances from the primary cell and at a distance from the center of the target that is equal to the distance separating the primary cell from the center of the target.

7. A camshaft sensor for a motor vehicle engine, comprising:
a toothed target,
a primary measurement cell configured to supply a first raw signal indicative of variations in a first magnetic field which are induced by rotation of the target,
two secondary measurement cells configured to supply a respective second raw signal and a third raw signal each indicative of variations in a respective second magnetic field and at third magnetic field which are induced by the rotation of the target, and
a processing module configured to supply, from said first raw signal, the second raw signal, and the third raw signal, an output signal indicative of moments at which teeth of the target pass past the primary cell,

wherein:
said sensor further comprises two secondary measurement cells,
the processing module is furthermore configured to:
generate a differential signal indicative of a difference in magnetic field measurement by said two secondary cells,
determine the differential signal as a difference between the second raw signal and the third raw signal,
determine, from said differential signal, a first local maximum of the first raw signal in a vicinity of a falling front of said first raw signal corresponding to an end of the passage of a tooth of the target past the primary cell,
determine, from said differential signal, a second local maximum of the first raw signal in the vicinity of a rising front of said first raw signal corresponding to a start of the passage of said tooth of the target past the primary cell,
determine a local minimum of the first raw signal as a space separating two teeth of the target passes past the primary cell,
determine a first switching threshold as a function of the values of a first local maximum and of a local minimum,
determine a second switching threshold as a function of the values of the first local maximum and of the local minimum, and
generate said output signal from the first raw signal, from the first switching threshold and from the second switching threshold.

8. The sensor as claimed in claim 7 , wherein the first local maximum corresponds to a value adopted by the first raw signal when the differential signal adopts a first predetermined value, and the second local maximum corresponds to a value adopted by the first raw signal when the differential signal adopts a second predetermined value, as said tooth of the target passes past the secondary cells.

9. The sensor as claimed in claim 8 , wherein:
the first local maximum corresponds to a value adopted by the first raw signal in the vicinity of said falling front when the differential signal

Assignees

• Continental Automotive France
• Continental Automotive Gmbh

Inventors

• Bouscaren Denis

Classifications

• G01D18/001 Primary

  Calibrating encoders · CPC title

• G01D18/004 Primary

  Continuous recalibration · CPC title

• G01D5/24476

  Signal processing (G01D5/2448 - G01D5/24495 take precedence) · CPC title