FR3112214A1 - Tooth detection sensor on a target for motor vehicle - Google Patents

Abstract

Magnetic field sensor (10) for a motor vehicle heat engine comprising a target (14) comprising an alternating series of teeth (T1, T2, T3) and hollows and being associated with a rotating element (16) of the heat engine, said sensor (10) being in particular capable, on each passage of a tooth (T1, T2, T3), of recording the amplitude of the corresponding extrema of the magnetic signal and of determining and recording the direction of rotation of the rotating element (16), determining that the rotating element (16) has been driven in its forward direction of rotation for a predetermined number of detected teeth (T1, T2, T3), calculating a switching threshold by averaging the values recorded amplitude of the extrema corresponding to the passage of the predetermined number of teeth (T1, T2, T3) detected, and to use the calculated switching threshold in order to detect the teeth (T1, T2, T3) of the target (14) during the operation of the heat engine. Figure for abstract: Fig. 5

Description

Motor vehicle target tooth detection sensor

The invention relates to the field of magnetic field sensors for motor vehicles and more particularly to a sensor for detecting the teeth of a target, associated for example with a crankshaft or a camshaft.

The invention aims in particular to improve the accuracy of existing magnetic field sensors.

The present invention relates to a method for adapting a detection threshold of a crankshaft sensor for a motor vehicle. More particularly, it involves improving the accuracy of the electrical signal delivered by a sensor mounted opposite a toothed wheel located at the end of a crankshaft of an engine of a motor vehicle.

Crankshaft sensors are used in a motor vehicle to determine the crankshaft position, rotational speed and rotational direction of the engine. Used in combination with camshaft sensors, they determine the position of the various cylinders in the engine's combustion cycle (i.e. determine for each cylinder whether it is in the intake phase, in the compression, in the explosion phase or in the exhaust phase) and make it possible to better manage the operation of the engine, by the optimum adjustment of the ignition advance or of the fuel injection instant.

These crankshaft sensors comprise a magnetic field generator (example: a permanent magnet), a means of detecting the magnetic field (Hall effect cell, magneto resistive cell MR, giant magneto resistive cell GMR, etc. for example) and an electronic circuit processing the signal received by the magnetic field detection means. These sensors, called active sensors, deliver a digital signal to a central computer for processing.

The magnetic field generator can also be a target, composed of a magnetic material, having alternating South and North poles. In this case, the sensor may or may not incorporate a permanent magnet depending on the detection means used. Subsequently, we will assimilate the South and North poles to the teeth and hollows of a mechanical target.

In known manner and as illustrated in FIG. 1, a crankshaft sensor 100 is associated with a target 140 secured to a crankshaft 160. This target 140 is in the form of a disc 150 whose periphery is toothed. Between each substantially identical tooth T ₁ , T ₂ , T ₃ there is a (hollow) spacing C ₁ , C ₂ , C ₃ . The target 140 is distinguished by the presence of a hollow Ce of greater length, more commonly called “missing tooth” (or “missing tooth” in English) positioned precisely at a certain angle relative to the angular position of the motor. According to the embodiment described and represented in FIG. 1, a crankshaft sensor 100 comprises, in known manner, a ferromagnetic element 110 and a magnetic field detection means 120 (for example a Hall effect cell). This sensor 100 delivers a digital signal to a processing unit 130.

The operation of such a set of sensor 100 and associated target 140 is described below. When the target 140 is driven in rotation (arrow F in FIG. 1) by the crankshaft 160, the sensor 100 perceives a series of variations in the magnetic field representative of the tooth or teeth T ₁ , T ₂ , T ₃ passing in front of it and of their spacing C ₁ , C ₂ , C _{3 ,} C _e . The signal thus obtained is represented in FIG. 2A.

In FIG. 2A is represented according to the prior art, the signal B of the magnetic field seen by the sensor 100 as a function of the angle of rotation θ of the crankshaft 160, as well as the threshold S ₁ for detecting the rising edge and the rising edge descending from the first tooth T ₁ . FIG. 2B represents the position of the teeth T ₁ , T ₂ , …T _i and of the hollows C ₁ , C ₂ …C _i of the target 140 with respect to the signal B of the magnetic field of FIG. 2A.

As illustrated in FIG. 2A, to determine the position of the crankshaft, the signal B is observed representing the variations of the magnetic field perceived by the sensor 100 of the crankshaft 160 during one revolution of the target 140, that is to say according to a angle of rotation θ of the target 140. This signal presents a series of sinusoids D ₁ , D ₂ ... Di each corresponding to the variation of the magnetic field measured by the sensor 100 when a tooth T ₁ , T ₂ ... T _i (cf 2B) followed by a hollow C ₁ , C ₂ ... C _i passes in front of said sensor 100. By counting the number of sinusoids D ₁ , D ₂ ... D _i, by measuring the duration of each of them, l spacing between each sinusoid D ₁ , D ₂ … D _i , and by detecting the missing tooth (the spacing due to the missing tooth Ce being longer), it is possible to determine the speed of rotation of the motor, the direction of engine rotation and the angular position of the crankshaft.

As illustrated in FIG. 2A, signal B has a minimum B _MIN1 and a maximum B _MAX1 . The detection of the passage of the teeth T ₁ , T ₂ …T _i and of the hollows C ₁ , C ₂ … _Ci of the target 140 is done by the detection of the passage of the signal B above (respectively below) a threshold of detection S ₁ placed between the minimum B _MIN1 and the maximum B _MAX1 , for example equal to , k1 being a constant, for example equal to 0.50.

For explanatory purposes, the signal B illustrated in FIG. 2A comprises a single minimum B _MIN1 and a single maximum B _MAX1 . In reality, the signal B has a plurality of minimums B _MINi and a plurality of maximums B _MAXi and the detection threshold S ₁ continuously adapts according to the minimums and the maximums in order to always be equal to This method of adapting the detection threshold S ₁ is known to those skilled in the art, see patent application FR 2 985 035 A1 filed by the applicant which describes the same method of adapting the detection threshold but applied to a camshaft sensor.

For applications of the 100 crankshaft sensor 160 on vehicles equipped with the "Stop and Restart" function or even "Stop & Go" in English, that is to say vehicles, for which, when they are at the stop (at dipped beam, for example) the engine is stopped temporarily, it is necessary when restarting the vehicle, to know precisely the position of the crankshaft. The purpose of this constraint is to comply with polluting emission standards and to limit fuel consumption.

When the engine stops, because of the inertia of the latter, the crankshaft 160 makes several round trips before coming to a complete stop. The crankshaft 160 sensor 100 is therefore not only capable of incrementing the number of teeth and hollows that it detects but also of decrementing it.

In addition, during the motor stopping phase d (cf. ), which can last a few minutes, the sensor 100 remains energized and the signal B presents a progressive aperiodic drift, that is to say a slope comprising no rising edge, nor falling edge, called thermal drift ΔTAR (cf. figure 3). During the restart R of the engine, the signal B is shifted in value, and presents a new minimum BMIN2 and a new maximum BMAX2. It is then necessary to adapt the detection threshold S1 as a function of these new values BMIN2 and BMAX2 in order to detect, on restarting the engine, the passing of the third and fourth teeth T3, T4 and of the third and fourth hollows C3, C4. If the detection threshold S1 is not adapted to the new minimum BMIN2 and maximum BMAX2 values, and is, for example located below the minimum value BMIN2 (as illustrated in figure 3), then during the restart, no tooth, (neither T3 nor T4) and no hollow, (neither C3 nor C4) can be detected and the position of the crankshaft cannot be determined.

According to the prior art, it is known during the development phase of the sensor 100, to determine an initialization detection threshold S _INIT . The initialization detection threshold S _INIT is applied as soon as the rising edge and the falling edge of the first tooth T ₁ are detected, during the cold start of the engine.

Then, still according to the prior art, once a maximum value B _MAX1 and a minimum value B _MIN1 of the magnetic field have been measured by the sensor 100, among other words, once the first tooth T ₁ has passed in front of the sensor 100, then a use detection threshold S ₁ ′ is applied. Its value is S _1' =k ₂ *(B _MAX1 -B _MIN1 ), k2 being a constant, between 0 and 1 (k2 can be equal to k1). This use detection threshold S _1′ is greater than the initialization detection threshold S _INIT and is applied as soon as the 2 ^nd tooth T ₂ is detected (rising edge or falling edge, depending on which edge occurs first).

For a crankshaft 160 sensor 100 fitted to a "Stop and Restart" engine, it is known from the prior art, when the engine is hot restarted (detection of passage of a first tooth), to apply the method of prior art described above. That is to say, to use an initialization detection threshold S _INIT , according to the example illustrated in FIG. 3, on passage of the first tooth after the restart, that is to say on passage of the 3 ^rd tooth T ₃ . Then, after the passage of the third tooth T ₃ , to calculate a use detection threshold equal to: S _1' =k ₂ *(B _MAX2 -B _MIN2 ). This new detection threshold S _1′ is then applied (in the example illustrated in FIG. 3) to the passage of the 2 ^nd tooth after the hot restart, this is in the example illustrated in FIG. ascending from the ^4th tooth T ₄ .

However, this method is not reliable when there are vibrations or oscillations of the crankshaft on hot restart. These vibrations and these oscillations create extreme values of the signal B which do not correspond either to the minimums or to the maximums of the passage of the third and fourth teeth T ₃ , T ₄ or of the third and fourth troughs C ₃ , C ₄ in front of the target 140 This falsifies the calculation of the new detection threshold S _1' and impacts the precision on the determination of the position of the crankshaft 160.

However, unlike the cold start of the vehicle, for which it is tolerated several turns of the crankshaft 160 in order to precisely estimate the detection threshold S ₁ , and to precisely detect the passage of each tooth and each hollow in front of the sensor 100, for hot restarting, for reasons of compliance with anti-pollution standards and to reduce consumption (fastest possible restart under optimal consumption and pollutant emission conditions), it is necessary to know precisely the position of the crankshaft 160 and therefore to quickly and precisely estimate the value of the new detection threshold S _{1 '} , and this from the first rising edge of the third tooth T ₃ .

In particular, in hybrid vehicles, it is found that the vehicle driving phases during which the heat engine is interrupted and the electric motor is in operation generate a lot of vibrations and oscillations, in particular due to both the movement of the vehicle and to the electric drive of the clutch. We represented at the an example of speed and direction signals generated by a crankshaft 160 sensor 100 to illustrate these phenomena.

There shows, for the curve in the upper part, a magnetic speed signal obtained by a magnetic sensor 100 of a hybrid vehicle respectively in a thermal propulsion mode MT then in an electric propulsion mode ME causing vibrations, this by measuring amplitudes as a function of time t. The magnetic signal in thermal propulsion mode MT is referenced Sv while the signal in electric propulsion mode ME concerning only random and parasitic vibrations is referenced Svib. During an electric propulsion mode ME, the magnetic sensor 100 dedicated to the heat engine does not fulfill any role of controlling the heat engine then stopped. The two curves in the lower part of the show respectively as a function of time t, for the lowest curve, the magnetic signal seen by the sensor 100 during the passage of the sequences of teeth T1, T2…Ti and of the hollows C1, C2…Ci of the target 140.

In an MT thermal propulsion mode, the detection levels with a switching threshold calculated specifically for this given MT thermal propulsion mode are clearly visible, whereas in an ME electric propulsion mode, the detection levels are random, corresponding to parasitic vibrations.

The problem underlying the present invention is, for a magnetic field sensor associated with a heat engine for the synchronization of this heat engine by an electronic control unit of a motor vehicle, in particular hybrid, not to disturb the precision of the magnetic field sensor after stopping the heat engine or switching to an electric propulsion mode, by guaranteeing that the sensor resumes optimal operation as soon as the heat engine is restarted.

One of the aims of the invention is in particular to relate the stopping phase of the heat engine, which generally ends in wide oscillations with detection of reverse rotations, and the operating phase of the electric motor, extremely rich in oscillations, vibrations and thermal drift.

To this end, the invention firstly relates to a magnetic field sensor for a heat engine of a motor vehicle, in particular hybrid, said vehicle comprising a target comprising an alternating sequence of teeth and hollows and being associated with a rotating element of the engine thermal, said rotating element being characterized by a forward direction of rotation defining its rotation during normal operation of the engine and a reverse direction of rotation, opposite to the forward direction of rotation, which can occur in particular during a stop phase of the engine , said sensor being capable of:
- detect magnetic field variations induced by the passage of the teeth of the target close to said sensor by producing a magnetic signal of said variations, the midpoints of the extrema of said magnetic signal characterizing the passage of the teeth and the hollows of the target in front of the sensor ,
- each time a tooth passes, record the amplitude of the corresponding extrema of the magnetic signal and determine and record the direction of rotation of the rotating element,
- determining that the rotating element has been driven in its forward direction of rotation for a predetermined number of detected teeth,
- calculate a switching threshold, for example 50%, by taking the average of the recorded values of amplitude of the extrema corresponding to the passage of the predetermined number of teeth detected,
- use the calculated switching threshold in order to detect the teeth of the target during operation of the heat engine.

Thus, the sensor according to the invention only applies an update of the calculated switching threshold if the rotating element of the motor has been driven in its forward direction of rotation for the predetermined number of teeth detected, which makes it possible to prevent the switching threshold used from taking account of teeth detected during a reverse rotation of the rotating element, which could falsify the value of said threshold and therefore the accuracy of the sensor. The sensor according to the invention therefore proves to be precise and reliable in order to effectively detect the teeth during operation of the heat engine.

The predetermined number of teeth detected may for example be equal to 4, in particular during a restart phase of the heat engine when using the Start & Go type restart function, called “hot start”.

The predetermined number of teeth detected can for example be equal to [1; 2.5 or 58], in particular during a start-up phase of the combustion engine following activation of the ignition key or a start button by the driver, for example during a so-called “cold start ".

According to one aspect of the invention, the sensor being capable of delivering an electrical output signal intended for an electronic control unit of the vehicle with a view to synchronizing the heat engine, the electrical output signal indicating a position of a current value of the magnetic signal with respect to the switching threshold calculated by said sensor.

The invention also relates to a motor vehicle comprising a sensor as presented above.

According to one characteristic of the invention, the rotating element is a crankshaft or a camshaft.

The invention also relates to a method for detecting teeth on a target by a magnetic field sensor for a heat engine of a motor vehicle, in particular hybrid, said vehicle comprising a target comprising an alternating sequence of teeth and hollows and being associated with an element rotating part of the thermal engine, said rotating element being characterized by a forward direction of rotation defining its rotation during normal operation of the engine and a reverse direction of rotation, opposite to the forward direction of rotation, which can occur in particular during a phase of stopping the engine, said method comprising the steps implemented by the sensor of:
- detection of magnetic field variations induced by the passage of the teeth of the target close to said sensor by producing a magnetic signal of said variations, the midpoints of the extrema of said magnetic signal characterizing the passage of the teeth and the hollows of the target in front of the sensor ,
- at each passage of a tooth, recording of the amplitude of the corresponding extrema of the magnetic signal, and determination and recording of the direction of rotation of the rotating element,
- if the rotating element has been driven in its forward direction of rotation for a predetermined number of teeth detected, calculation of a switching threshold by taking the average of the recorded values of amplitude of the extrema corresponding to the passage of the number of teeth detected predetermined,
- use of the calculated switching threshold in order to detect the teeth of the target during operation of the heat engine.

As for the sensor, the predetermined number of detected teeth used in the method can for example be equal to 4, in particular during a restart phase of the heat engine when using the Start & Go type restart function, called "hot start".

Similarly, the predetermined number of detected teeth used in the method can for example be equal to [1; 2.5 or 58], in particular during a start-up phase of the combustion engine following activation of the ignition key or a start button by the driver, for example during a so-called “cold start ".

Advantageously, the method comprises a step of supplying an electrical output signal intended for an electronic control unit of the vehicle with a view to synchronizing the heat engine, the electrical output signal indicating a position of a value in force of the magnetic signal with respect to the switching threshold calculated by said sensor.

Other characteristics and advantages of the invention will become apparent on reading the description which follows. This is purely illustrative and must be read in conjunction with the appended drawings on which:
There , explained previously, is a schematic sectional view, showing a crankshaft sensor and its associated target.
FIG. 2B, explained above, represents according to the prior art, the signal B picked up by the sensor as a function of the angle of rotation of the crankshaft, as well as the detection threshold of the rising and falling edges, without thermal drift. FIG. 2A, explained previously, represents the position of the teeth and the hollows of the target with respect to the signal picked up by the sensor represented in FIG. 2B.
There , explained previously, represents the signal B picked up by the sensor as a function of the angle of rotation of the crankshaft, as well as the detection threshold of the rising and falling edges, in the presence of a thermal drift, according to the prior art.
There , explained previously, illustrates an example of speed and direction signals generated by a crankshaft sensor, between an all-thermal engine mode and an all-electric mode.
There schematically illustrates an embodiment of the sensor according to the invention.
There schematically illustrates an embodiment of the method according to the invention.

The sensor according to the invention is a magnetic field sensor intended to be mounted in a motor vehicle with a combustion engine, that is to say in a vehicle with a pure combustion engine or in a hybrid vehicle. More specifically, the sensor is intended to be mounted opposite a rotating element of the heat engine in order to measure a parameter thereof and to determine, for example, the angular position or the speed of rotation of said rotating element. Such a rotating element can for example be a crankshaft or a camshaft. In the example below, the invention is described in its implementation by a crankshaft sensor, without this limiting the scope of the present invention.

The rotating element is characterized by a forward direction of rotation defining its rotation during normal operation of the engine and a reverse direction of rotation, opposite to the forward direction of rotation, which can occur in particular during a stoppage phase of the engine. In order to allow the sensor to measure the desired parameter, the rotating element comprises a target comprising an alternating series of teeth and hollows, the sensor being placed facing said target.

With reference to the , the sensor 10 according to the invention is electrically connected to an electronic control unit 13 in a motor vehicle with a heat engine (not shown), in particular a hybrid vehicle. The sensor 10 is associated with a target 14 secured to a crankshaft 16. This target 14 is in the form of a disc 15 whose periphery is toothed. In the following, the description of the invention will be made for a target 14 comprising for example 58 teeth.

Between each substantially identical tooth T ₁ , T ₂ , T ₃ there is a (hollow) spacing C ₁ , C ₂ , C ₃ . The target 14 is distinguished by the presence of a hollow Ce of greater length, more commonly called “missing tooth” (or “missing tooth” in English) positioned precisely at a certain angle relative to the angular position of the motor.

Conventionally, the magnetic field sensor 10 is capable of detecting magnetic field variations induced by a passage of the teeth T ₁ , T ₂ , T ₃ of the target 14 close to the sensor 1 by producing a magnetic signal of said variations. To this end, the sensor 10 comprises a ferromagnetic element 11 and a magnetic field detection means 12 (for example a Hall effect cell). This sensor 10 delivers a digital signal to the electronic control unit 13. When the target 14 is rotated (arrow F in FIG. 1) by the crankshaft 16, the sensor 10 perceives a series of variations in the magnetic field representative of the teeth T ₁ , T ₂ , T ₃ passing in front of it and their spacing C ₁ , C ₂ , C _{3 ,} C _e .

The sensor 10 is capable of periodically calculating, in particular each time the thermal engine is started or restarted, a switching threshold as a function of the detected amplitude of the magnetic field. The magnetic field sensor 10, in default operation that the sensor 10 adopts during the operation of the heat engine, is electrically powered by a basic power supply signal delivered by the electronic control unit 13.

The sensor 10 is capable of periodically calculating such a switching threshold as a function of the detected amplitude of the magnetic field, the calculation of said switching threshold being carried out for a predetermined number of detected teeth. For example, when starting the sensor 10, the predetermined number of teeth is advantageously equal to twice the number of teeth of the crankshaft target 14, i.e. here 58 teeth, in order to allow the sensor 10 to detect all the teeth during of a complete rotation of the crankshaft, and thus calculate a reliable switching threshold. For example again, when restarting the engine in the case of a Start & Go function, the predetermined number of teeth can be equal to four, in order to allow the sensor 10 to calculate a switching threshold that can be used quickly.

The sensor 10 is capable of applying a calculated switching threshold only if the crankshaft 16 has been driven in its forward direction of rotation for the predetermined number of teeth T ₁ , T ₂ , T ₃ detected. More specifically, each time a tooth T ₁ , T ₂ , T ₃ passes, the sensor 10 is able to record the amplitude of the corresponding extrema of the magnetic signal and to determine and record the direction of rotation of the crankshaft 16 for the tooth T ₁ , T ₂ , T ₃ detected at the instant of detection.

The sensor 10 is capable of determining that the crankshaft 16 has been driven in its forward direction of rotation for a predetermined number of teeth T ₁ , T ₂ , T ₃ detected.

The sensor 10 is able to calculate the switching threshold by taking the average of the recorded values of amplitude of the extrema corresponding to the passage of the predetermined number of teeth T ₁ , T ₂ , T ₃ detected.

The sensor 10 is capable of delivering, when the teeth T ₁ , T ₂ , T ₃ and the hollows C ₁ , C ₂ , C ₃ of the target 14 pass, an electrical output signal to the electronic control unit 13 for synchronization of the heat engine.

The invention will now be described in its implementation with reference to Figures 5 and 6.

For the first start of the thermal engine during use of the vehicle, that is to say after the manual activation of the start by the driver, the predetermined number of teeth T ₁ , T ₂ , T ₃ is equal to 1 or 2.5 or 58 teeth T ₁ , T ₂ , T ₃ of the crankshaft target 14. For a restart of the engine during use of the vehicle, that is to say an automatic restart of the heat engine (Start & Go function), the predetermined number of teeth T ₁ , T ₂ , T ₃ is set at eight teeth.

When starting or restarting the vehicle, the crankshaft 16 is rotated and the sensor 10 is activated. The sensor 10 detects the magnetic field variations induced by the passage of the teeth T ₁ , T ₂ , T ₃ of the target 14 opposite the sensor 10 by producing a magnetic signal of said variations in a step E1, the extrema of said magnetic signal characterizing the passage of the teeth T ₁ , T ₂ , T ₃ and of the hollows C ₁ , C ₂ , C ₃ of the target 14 in front of the sensor 10.

During this step E1, each time a tooth or recess passes, the sensor 10 records the amplitude of the corresponding extrema of the magnetic signal and verifies that the direction of rotation of the crankshaft 16 is the forward direction of rotation. This information on the direction of rotation of the crankshaft 16 is available at the level of the sensor 10, in a manner known per se. The norm of the direction of rotation is defined by programming internal parameters of sensor 10.

Then, if the crankshaft 16 has been driven in its forward direction of rotation for the predetermined number of teeth T ₁ , T ₂ , T ₃ detected (1 tooth, 2.5 teeth or 58 teeth in the case of a first start and 4 teeth in the case of a restart), the sensor 10 calculates in a step E2 a switching threshold by taking the average of the values recorded on the extrema corresponding to the passage of the number of teeth T ₁ , T ₂ , T ₃ detected predetermined .

Finally, the sensor 10 applies said switching threshold calculated in a step E3 in order to accurately detect the teeth T ₁ , T ₂ , T ₃ of the target 14 during operation of the heat engine.

If, during step E1, the sensor 10 detects, if only for a single tooth T ₁ , T ₂ , T ₃ , that the direction of rotation of the crankshaft 16 is the reverse direction of rotation, the sensor 10 does not calculate a switching threshold and starts the process again at step E1 until the forward direction of rotation of the crankshaft 16 is again detected. Thus, if a reverse direction of rotation is detected during a calculation provided on teeth, the calculation is performed again with eight teeth until the criterion of forward rotation of the crankshaft 16 is satisfied for the eight teeth.

Advantageously, the sensor 10 recalibrates its switching threshold, its offsets and its amplitude calculations, perpetually on 58 teeth, the forward rotation criterion also applying for these calculations here too. In other words, in practice, in addition to the switching threshold, most of the parameters used for the calibration of the sensor 10 are impacted: shift (offset), amplitudes of the crankshaft 16 speed and direction signals, etc. The invention advantageously makes it possible to make the sensor 10 precise and reliable.

Claims (10)

Magnetic field sensor (10) for a heat engine of a motor vehicle, in particular hybrid, said vehicle comprising a target (14) comprising an alternating series of teeth (T ₁ , T ₂ , T ₃ ) and hollows and being associated with an element rotating element (16) of the heat engine, said rotating element (16) being characterized by a forward direction of rotation defining its rotation during normal operation of the engine and a reverse direction of rotation, opposite to the forward direction of rotation, which may in particular occur during of an engine stopping phase, said sensor (10) being capable of:
- detecting magnetic field variations induced by the passage of the teeth (T ₁ , T ₂ , T ₃ ) of the target (14) near said sensor (10) by producing a magnetic signal of said variations, the midpoints of the extrema of said magnetic signal characterizing the passage of the teeth (T ₁ , T ₂ , T ₃ ) and of the hollows of the target (14) in front of the sensor (10),
- at each passage of a tooth (T ₁ , T ₂ , T ₃ ), record the amplitude of the corresponding extrema of the magnetic signal and determine and record the direction of rotation of the rotating element (16),
- determining that the rotating element (16) has been driven in its forward direction of rotation for a predetermined number of teeth (T ₁ , T ₂ , T ₃ ) detected,
- calculating a switching threshold by taking the average of the recorded values of amplitude of the extrema corresponding to the passage of the number of teeth (T ₁ , T ₂ , T ₃ ) detected predetermined,
- using the calculated switching threshold in order to detect the teeth (T ₁ , T ₂ , T ₃ ) of the target (14) during operation of the heat engine. Sensor (10) according to claim 1, in which the predetermined number of teeth (T ₁ , T ₂ , T ₃ ) detected is equal to 4. Sensor (10) according to claim 1, in which the predetermined number of teeth (T ₁ , T ₂ , T ₃ ) detected is equal to 58. Sensor (10) according to one of the preceding claims, said sensor (10) being capable of delivering an electrical output signal intended for an electronic control unit (13) of the vehicle with a view to synchronization of the combustion engine, the electrical output signal indicating a position of a current value of the magnetic signal with respect to the switching threshold calculated by said sensor (10). Motor vehicle comprising a sensor (10) according to one of the preceding claims. Vehicle according to the preceding claim, in which the rotating element is a crankshaft (16) or a camshaft. Method for detecting teeth (T ₁ , T ₂ , T ₃ ) on a target (14) by a magnetic field sensor (10) for a heat engine of a motor vehicle, in particular hybrid, said vehicle comprising a target (14) comprising a alternating series of teeth (T ₁ , T ₂ , T ₃ ) and recesses and being associated with a rotating element (16) of the thermal engine, said rotating element (16) being characterized by a forward direction of rotation defining its rotation during normal operation of the engine and a reverse direction of rotation, opposite to the forward direction of rotation, which can occur in particular during an engine stopping phase, said method comprising the steps implemented by the sensor (10) of:
- detection (E1) of the magnetic field variations induced by the passage of the teeth (T ₁ , T ₂ , T ₃ ) of the target (14) close to the said sensor (10) by producing a magnetic signal (Smag) of the said variations, the midpoints of the extrema of said magnetic signal characterizing the passage of the teeth (T ₁ , T ₂ , T ₃ ) and of the hollows of the target (14) in front of the sensor (10),
- at each passage of a tooth, recording of the amplitude of the corresponding extrema of the magnetic signal, and determination and recording of the direction of rotation of the rotating element (16),
- if the rotating element (16) has been driven in its forward direction of rotation for a predetermined number of teeth (T ₁ , T ₂ , T ₃ ) detected, calculation (E2) of a switching threshold (SC) in realizing the average of the recorded values of amplitude of the extrema corresponding to the passage of the number of teeth (T ₁ , T ₂ , T ₃ ) detected predetermined,
- Use (E3) of the calculated switching threshold in order to detect the teeth (T ₁ , T ₂ , T ₃ ) of the target (14) during operation of the heat engine. Method according to claim 7, in which the predetermined number of teeth (T ₁ , T ₂ , T ₃ ) detected is equal to 4. Method according to claim 7, in which the predetermined number of teeth (T ₁ , T ₂ , T ₃ ) detected is equal to 58. Method according to any one of Claims 7 to 9, comprising a step of supplying an electrical output signal intended for an electronic control unit (13) of the vehicle with a view to synchronizing the heat engine, the signal electric output indicating a position of a current value of the magnetic signal with respect to the switching threshold calculated by said sensor (10).