WO2006129041A2

WO2006129041A2 - Magnetic position sensor with reduced space requirement

Info

Publication number: WO2006129041A2
Application number: PCT/FR2006/050501
Authority: WO
Inventors: Bertrand Legrand; Laurent Dufour; Olivier Andrieu
Original assignee: Electricfil Automotive
Priority date: 2005-06-01
Filing date: 2006-06-01
Publication date: 2006-12-07
Also published as: WO2006129041A3; FR2886726A1; FR2886726B1

Abstract

The invention concerns a rotary position sensor comprising: at least one magnetic encoder (1) rotating about an axis (A), including first (3a) and second (3b) circular magnetic tracks extending adjacent and consisting each of a series of alternating North and South magnetic poles (4a, 5a-4b, 5b); and a detection cell (2) delivering an electric signal corresponding to the evolution of the intensity of the magnetic field of the magnetic poles. The invention is characterized in that the magnetic poles (4a, 5a-4b, 5b) of the two tracks are arranged such that there is provided a succession of magnetic fields (M) alternately in opposite direction, passing from one track to the other; the detection cell (2) is mounted so as to be sensitive to the successive magnetic fields (M) of alternate direction passing from one track to the other.

Description

MAGNETIC POSITION SENSOR WITH REDUCED SIZE

The object of the invention relates to the technical field of magnetic sensors comprising an encoder element moving in the vicinity of a detection cell, and adapted to locate at least one angular position in the general sense.

The object of the invention relates more particularly to the production of a sensor whose encoder is equipped with a series of north poles and south poles mounted alternately.

The object of the invention finds a particularly advantageous application in the automotive field where this sensor can be used for example in the context of ignition functions.

It is known in the preferred field above, to implement a magnetic sensor adapted to measure the change in intensity of a magnetic field when a magnetic encoder passes in front of a sensor cell. Such an encoder is constituted by a multipole magnetic ring provided on its circumference with North poles and South poles alternated and regularly spaced at a given pitch. The regular north and south poles are made in large numbers so that such a speed sensor has a good resolution. The detection cell, such as a Hall effect probe, for example, delivers a periodic sinusoidal signal. The detection cell is associated with a hysteresis level comparator such as a Schmitt trigger making it possible to obtain clear transitions of the output voltage for distinct values of the magnetic induction depending on whether they vary in increasing or decreasing. descending.

To make it possible to determine at least one position corresponding, for example, to the top dead center of ignition of a cylinder, it may be envisaged either to eliminate several magnetic poles while leaving a void space, or to replace one or more poles of a sign given by one or more poles of an opposite sign. It is thus realized a pole said irregular or singular presenting on the one hand a magnetization of a sign opposite to the sign of these two adjacent poles, and secondly a different spacing from the spacing pitch of the other poles.

A position or velocity sensor implements a Hall effect type probe or a magneto-resistive probe. One of the advantages of using a magneto-resistive probe is to be able to detect variations of the magnetic field components located in the plane of the probe. It is thus possible to design a sensor with limited space. In this respect, document DE 102 28 663 describes an angular displacement sensor comprising two circular magnetic tracks extending side by side, one of which is formed by a succession of magnetic poles North separated from each other and the other track is formed by a succession of South magnetic poles separated from each other. The magnetic poles are shifted from one track to another so that the magnetic field lines extend obliquely from one track to the other. A magneto-resistive sensing cell is placed between the two tracks to detect the direction of the field between the two tracks. It should be noted that the spacing of the poles in each of the tracks limits the resolution of such a sensor. In addition, shifting the poles from one track to the other reduces the level of the detected magnetic field. Moreover, such a sensor which implements a magneto-resistive probe has a high cost.

To overcome this cost disadvantage, it is known a sensor with a Hall effect type probe which has a limited cost. However, a Hall effect type sensor detects only the component of the magnetic field perpendicular to the plane of the probe, which leads to a large size of the sensor.

The present invention aims to remedy the drawbacks of the prior art by providing a magnetic position or speed sensor implementing a detection cell having a small footprint. To achieve such an objective, the magnetic position sensor according to the invention comprises: at least one rotary magnetic encoder about an axis, comprising a first and a second circular magnetic track extending side by side and each formed by a succession of alternating north and south magnetic poles, and a detection cell delivering a electrical signal corresponding to the evolution of the magnetic field intensity of the magnetic poles.

According to the invention:

the magnetic poles of the two tracks are arranged in such a way that a succession of alternately opposite magnetic fields is established, going from one track to the other,

the detection cell is mounted to be sensitive to successive magnetic fields of alternating direction passing from one track to the other.

When the encoder comprises at least one irregular pole and in order to obtain good measurement accuracy, it is known for example from the patent

FR 2 753 943 to produce an encoder comprising, for each irregular pole, means for correcting the value of the magnetic field created by the irregular pole so that the signal delivered by the passage of the neighboring poles to said irregular poles is symmetrical with respect to the null value of the magnetic field.

The implementation of such an encoder makes it possible to obtain at the output of the sensor detection cell a magnetic signal whose period is constant with respect to the regular poles. This results in a good measurement accuracy thus achieved especially for the identification of the irregular pole.

If the technical solution described in this patent is satisfactory in practice, such a technique does not allow to implement a detection cell in a small footprint.

Another object of the invention is therefore to provide a sensor with limited space while having a good accuracy for tracking, including the irregular pole. To achieve such an objective, the sensor according to the invention comprises at least one magnetic singularity formed by a singular pole of a track of different polarity to that of a singular pole of the other track placed opposite it, each singular pole comprising, on the one hand, between two adjacent poles, a different spacing with respect to the spacing pitch between the other poles and, on the other hand, correction means so as to stabilize the magnetic signal delivered by the passage of the poles adjacent to said singular poles.

Another object of the invention is to propose an encoder for increasing the level of the magnetic field between the tracks in order to make it possible to detect the passage of the different regular poles.

To achieve such an objective, the sensor according to the invention comprises means for forcing the magnetic field to be established between the magnetic poles of the two tracks of opposite polarities located vis-à-vis. Various other characteristics appear from the description given below with reference to the accompanying drawings which show, by way of non-limiting examples, embodiments of the subject of the invention.

Figure 1 is a schematic perspective view showing an embodiment of a position sensor according to the invention. FIG. 2 is a view taken down in a plane of a first exemplary embodiment of an encoder according to the invention.

FIG. 3 illustrates the evolution of the magnetic induction obtained during the running of an encoder equipped or not with correction means according to the invention. FIG. 3A illustrates the evolution of the magnetic induction obtained during the running of an encoder according to the invention, with air gaps of different values.

Figures 4 to 7 illustrate various alternative embodiments of means for stabilizing the signal in relation to an irregular pole. Figures 8 to 13 illustrate various alternative embodiments of an encoder equipped with means provided to force the magnetic field to pass from one track to another.

Figure 1 shows an embodiment of a position sensor I having a magnetic encoder 1 mounted to scroll in front of a fixed detection cell 2. The encoder 1 is constituted in the form of a multipole magnetic ring rotated about its center along an axis A.

In accordance with the invention and as seen more clearly in Figure 2, the encoder 1 includes a first _3a and a second _3b circular magnetic tracks extending side by side and made contiguously or as shown in Fig . 2, separated by an interval Δ. It must be considered that the two circular magnetic tracks 3 _a , 3 _b each extend on one side of a plane of measurement or symmetry P perpendicular to the axis of the encoder A.

Each magnetic track comprises a succession of alternating north and south magnetic poles respectively 4 _a , 5 _a for the track 3 _a and 4 _b , 5 _b for the track 3 _b . The magnetic poles _4a, _5, _4b, _5b are arranged to present a regular pitch spacing between two adjacent poles. For example, the angular length of each regular pole 4 _a , 4 _b 5 _a , 5 _b is 3 °, taken in a direction parallel to the plane P or the running direction of the encoder.

According to the invention, the magnetic poles 4 _a , 5 _a , 4 _b 5 _b of the two tracks 3 _a , 3 _b are arranged in such a way that a succession of magnetic fields alternately in the opposite direction and from a track is established. to the other. The magnetic poles of the two tracks _3a, _3b are arranged so that are established between the opposite polarity poles vis-à-vis and belonging to two tracks, namely between the poles _4a and 5 _a -5 _b -4 _b , a succession of magnetic fields alternately in the opposite direction and intersecting the measurement plane P. In the example illustrated in FIG. 2, the magnetic fields intersecting the measurement plane P being established between two poles of opposite polarities belonging to two different tracks (4 _a -5b and 5 _a -4b) is represented schematically in a mixed line M.

According to a preferred embodiment characteristic illustrated in FIG. 2, the magnetic poles _4a, _5a, _4b, 5b of the two tracks are arranged so that magnetic fields M established between the two tracks _3, _3b intersect the measurement plane P in a direction perpendicular to measurement plan. In this example, the magnetic fields M are parallel to each other and to the axis of rotation A of the encoder. According to this embodiment, the poles of the tracks are arranged symmetrically on both sides of the plane M being of opposite polarity. In other words, the geometric shape of the pole 4, _{_5a} is symmetrical along the plane P to the geometric shape of the pole 4 _b, 5 _b. Each pole of a track is thus placed vis-à-vis a pole of the other track whose polarity is opposite to his. In addition, since each track has alternating north and south poles, the magnetic field between the two tracks changes direction alternately from a pair of poles 4 _a -5 _b to the neighboring pair of poles 5 _a -4 _b . Of course, it could be envisaged that each magnetic field M established between the two tracks 3 _and _3b cut the measurement plane P not being perpendicular to this plane.

According to another characteristic of the invention, the detection cell 2 is mounted to be sensitive to successive magnetic fields M passing from one track to the other. The detection cell 2 is thus placed above and between the two tracks _3a, 3b. Advantageously, the detection cell 2 is placed in the plane of symmetry P of the encoder, close to the external surface of the encoder. In the example illustrated in the drawings, the detection cell 2 is sensitive to transverse magnetic fields, that is to say parallel to the axis of rotation A of the encoder. For example, the sensitive cell 2 is such as a Hall-effect cell, Hall effect differential, or Hall effect with flux concentrator, or even a magneto-resistive cell or a giant magneto-resistant cell (GMR). The rotary sensor I as described above makes it possible advantageously to implement a Hall effect type cell mounted to extend substantially in the plane of symmetry P of the encoder perpendicular to the axis of rotation A while being able to measuring a transverse magnetic field, that is to say parallel to the axis of rotation A. The Hall effect sensor 2 can thus be mounted with a small footprint in this plane without having to fold the connecting tabs.

It follows from the foregoing description that the sensor I comprises a multipole encoder 1, each regular pole 4 of _which -5 _b or 5 _a -4 _b is formed by a pair of magnetic poles, one of which belongs to the first track and the other at the second track. Of course, the multipolar encoder 1 may be equipped with at least one magnetic singularity to locate a position. In the example illustrated in Fîg. 2, the encoder 1 is provided with a magnetic singularity 6 formed by a singular pole 6 _is formed in the first track _3a and having a polarity different from that of a singular pole _6b arranged vis-à-vis in the second track 3b. In the example shown, the singular pole 6 _has a North pole is surrounded by two adjacent South poles _5A while the singular _6b pole is a south pole flanked by two adjacent poles North 4 _b. Of course, the polarities of the adjacent poles and singular poles can be reversed. Thus, for each magnetic singularity 6, a magnetic field is established between the two tracks _3a, _3b and more precisely between the singular poles _6, _6b. Such a magnetic field is detected by the detection cell 2.

According to an advantageous characteristic of the invention, each single pole _6a, _6b comprises firstly between two adjacent poles, a spacing different from the spacing pitch between the other poles and second correction means 10 the value of its magnetic field so as to stabilize the magnetic signal delivered by the passage of poles adjacent or adjacent said singular pole. In the illustrated example, each single pole _6a, _6b has an angular length of 15 °. For example, the encoder 1 is constituted by a crown forming a support on which is adhered a ring made of elastomer charged with magnetized particles to form the North and South poles of each of the tracks 3 _a , 3 _b .

The correction means 10 make it possible to correct the value of the magnetic induction created by the singular poles so that it does not disturb the inductions of the neighboring poles. Thus, the correction means 10 are determined so that the signal corresponding to the evolution of the magnetic field delivered by the neighboring poles to the magnetic singularity 6 is not disturbed by the magnetic induction created by each singular pole 6 _a , 6 _b -

As illustrated in FIG. 3, in the absence of the correction means 10 according to the invention, it thus appears, on the curve A, a drift amplitude and phase of the induction, which is all the more accentuated that the regular pole is close to the singular pole 6 _a , 6 _b - There follows a phase shift in the induction signal. Examination of the curve B makes it possible to observe that the magnetic induction created by the singularity 6 does not disturb the magnetic induction field of the adjacent regular poles. The signal giving the change in the intensity of the magnetic field delivered by the adjacent regular poles to the singular pole 6 has a constant period on all the regular poles, even those adjacent to the singularity 6. Thus, the regular poles adjacent to the singularity , have, seen by the measuring cell, an angular pitch identical to the other regular poles. As is more particularly apparent from FIG. 3A, the signal obtained B, Bi retains a constant period regardless of the width of the gap, that is to say the distance between the detection cell 2 and the magnetic encoder 1.

In the exemplary embodiment illustrated in FIG. 2, each single pole _6a, _6b comprises as correcting means 10, a gradual magnetization between the two adjacent poles. Advantageously, the level of magnetization of each singular pole 6 _a , 6 _b evolves between the two adjacent poles so that the level of magnetization in the part The center of the singular pole is greater than the magnetization level of its lateral portions contiguous to the adjacent poles.

According to another embodiment of a gradual magnetization of each singular pole, it may be provided to intercalate in each singular pole, a saturated magnetic pole having a polarity opposite to the singular pole.

In the example shown in Figure 4, each single pole _6a, _6b comprises as correcting means 10, a corrector lt _division, ll _b contiguous with each adjacent pole singular pole. In other words, a correction pole is interposed between each singular pole and each of the poles adjacent to said singular pole. Each checker ll _division, ll _b is a non-magnetic pole or the same polarity as the poles adjacent to the singular pole _6, _6b. In the exemplary embodiment illustrated in FIG. 4, each checker ll _division, ll _b has a shape such that each singular pole _6a, _6b has an isosceles trapezoid whose largest base is located on the side of the measuring plane P. The singular poles _6a, _6b have a symmetrical shape with respect to the plane P.

In the example illustrated in Fîg. 4, each singular pole _6a, _6b is contiguous at its largest base with two adjacent poles. In other words, the larger base of each singular pole coincides with the edge of the adjacent track plan to die P. Each checker ll _division, ll _b thus has a triangular shape.

Figure 5 illustrates another embodiment wherein each singular pole 6 _a, 6 _b is not contiguous with its adjacent poles. According to this embodiment, each single pole _6a, _6b has an isosceles trapezoidal shape whose larger base has a length less than the distance separating two adjacent poles. Each single pole _6a, _6b is thus completely separated from its adjacent poles.

Figure 6 illustrates another alternative embodiment of the correction _lt poles, llb- According to this exemplary embodiment, the corrector lt _division, ll _b contiguous to an adjacent pole is connected to the corrector pole contiguous to the other pole adjacent by a connecting zone 12 _a, 12 _b extending along the edge of the track located on the side opposite the edge adjacent the measurement plane P. In this embodiment, each single pole _6a, 6b _b is surrounded on its sides with the exception of the one placed opposite the other singular pole. Of course, the implementation of a connection area _12, _12b for correcting poles can be realized in the variant illustrated in Fig. 4 in which the large base of each singular pole 6 _a , 6b is equal to the distance separating the two adjacent poles.

Figure 7 illustrates another alternative embodiment wherein each singular pole 6 _a, 6 _b extends to the adjacent poles with a limited part of continuity of the width of each adjacent pole. Each checker ll _pole, _11b is limited on the surface to obtain continuity between the singular pole and its adjacent pole at the edge of the neighboring track of the measuring plane P. Of course, it may be provided that corrective poles _ll, _11b are provided with a connecting area _12, _12b as described in Fig. 6.

In the examples described above, it should be considered that the regular and singular poles of the two tracks have a geometric shape symmetrical with respect to the measurement plane P, while each pole of a track has a polarity opposite to that of the pole. of the other track placed in vis-à-vis. Moreover, the implementation of the correction means 10, as described above, makes it possible to obtain a good accuracy of the measurements taken for the identification of the singularity 6.

Another aspect of the invention aims to promote the establishment of magnetic fields from one track to another, that is to say to reduce the establishment of magnetic fields between the poles of the same track.

According to another characteristic according to the invention which more particularly emerges from FIGS. 8 to 13, the sensor 1 comprises means 15 for forcing the magnetic field to be established between the regular magnetic poles 4 _a -5 _b and 5 _a -4 _b of the two tracks, of opposite polarities located opposite each other. . Such means 15 make it possible to increase the level of the field magnetic between the tracks and consequently, to increase the signal accuracy and the detection capability with a wide gap.

According to an embodiment illustrated in FIG. 8, the means 15 for forcing the magnetic field to be established between the two magnetic tracks 3 _a , 3 _b are formed by the geometrical shape of the poles of the two tracks. Thus, the geometric shape of the poles of the same polarity belonging to the two tracks is different from the geometrical shape of the poles having the other polarity. As can be seen from FIG. 8, each such pole regular 5 _a, 5 _b has a bottom surface at regular pole of opposite polarity, namely 4 _a, 4 _b. Each regular pole _5, _5b extends along a limited width of the track from the adjacent edge of the measuring plane P. On this track width, each regular pole _5, _5b has a length of constant while each regular pole _4a, _4b has a length of constant value over the entire width of the corresponding track. Each regular pole 5 _a, 5 _b and defines a non-magnetic region 15 with the edge of the track opposite to that adjacent to the measurement plane P. The tracks _3a, _3b are not symmetrical with respect to the measurement plane P. The tracks are symmetrical with respect to the plane P with an offset pitch equal to one pole. According to another variant embodiment illustrated in FIG. 9, the means 15 for forcing the magnetic field are formed by non-magnetic zones extending between each pole of the two tracks. In the example illustrated, each regular pole _4a, _5a, 4b, 5b has an identical width taken between the two opposite edges of a track while each non-magnetic region 15 has a constant length over the entire width of the track and separates two consecutive poles of the same track. In the example illustrated, each regular pole _5a, 5b has a reduced length with respect to that of a regular pole 4 _a, 4 _b as each regular pole _5a, _5b is flanked by two non-magnetic regions 15. note that in this embodiment, the poles of the track 3 _was not built symmetrically to the poles of the track 3 _b in relation to measuring plane P. The tracks are symmetrical with respect to the plane P with an offset pitch equal to one pole.

In another exemplary embodiment illustrated in FIG. 10, each nonmagnetic zone 15 has a length that increases from the edge of the adjacent track of the measurement plane P towards the opposite edge of the track. As can be seen from FIG. 10, each nonmagnetic zone 15 has a right triangle shape. Thus, each regular pole _5, _5b is separated from its adjacent poles by a non-magnetic region 15 has a shape of isosceles trapezoid while regular poles 4 ₄ _b have a constant length of a non-magnetic area to the other.

According to another variant embodiment illustrated in FIG. 11, the two non-magnetic zones 15 located on either side of a regular pole are connected by a connecting part 16 which extends on the edge of the track located opposite the adjacent edge to the measurement plane . In the example illustrated in FIG. 11 which derives directly from the example illustrated in FIG. 10, each pole _5, _5b surrounded by the non-magnetic region 15 has a shape of an isosceles trapezium whose major base corresponds to the distance separating the two adjacent poles, is coincident with the edge of the neighboring track measurement plan P. regular poles _4, _4b have a constant length from one side to the other of the track.

Of course, it can be provided, as illustrated in FIG. 12 that the larger base of each regular pole _5a, _5b is less than the distance between adjacent poles so that said regular pole is surrounded by a nonmagnetic zone 15 except for the side located vis opposite the pole of the other track.

In the example illustrated in FIG. 12, each regular pole _5a, _5b is set back from the edge of the adjacent one of the opposite track the measurement plane P, since each non-magnetic area 15 is provided with a connecting portion 16 as illustrated in Fig. 11. Of course, it can be envisaged that the regular pole 5 _a , 5 _b extends over the entire width of the track so that the connecting portion 16 is removed. Conversely, it should be noted that in the example illustrated in FIG. 9, there can be provided a connecting portion 16 between the two adjacent non-magnetic zones 15 at two adjacent poles. According to this variant, each regular pole 5 _a, 5 _b is surrounded by a non-magnetic region 15, with the exception of its portion located vis-à-vis a pole of the other track.

In the example illustrated in FIG. 13, each non-magnetic region 15 has a triangular shape whose apex is turned towards the edge of the adjacent track to the plane P so that each magnetic pole 4, _{_5a,} _4b, _5b has a shape of an isosceles trapezium whose the large base is coincident with the edge of the adjacent track of the measurement plane P and the small base coincides with the edge of the track opposite to the adjacent edge of the measurement plane P. According to this variant, the poles of the tracks are symmetrical by report to measurement plan P.

The encoder 1 according to the invention, as described above, is intended to be mounted on a rotating target in the general sense, from which at least one position is determined. According to a preferred embodiment, the encoder 1 according to the invention is intended to be mounted on a rotating shaft of a motor vehicle and for example on a transmission shaft of a motor vehicle. For example, the encoder 1 is adapted to be mounted on the drive pulley mounted at the output of the engine of a motor vehicle, that is to say on a distribution pulley or on one of the auxiliary pulleys. According to an advantageous characteristic, the encoder 1 is mounted on the drive pulley located in the axis of the crankshaft, in order to allow detection of the top dead center of ignition of a cylinder. It should be noted that the subject of the invention can also be applied to the production of a sensor comprising a magnetic ring 1 provided with a plurality of irregular poles Pi making it possible to locate several positions. Advantageously, the magnetic ring 1 comprises, for example, four irregular poles Pi for locating the position of the cylinders of an engine. In this case, the encoder 1 is mounted integral with the camshaft of a motor vehicle engine. Of course, the encoder 1 can be mounted on the camshaft with only one irregular pole.

According to another preferred embodiment, the encoder 1 according to the invention is intended to be mounted inside a support plate of a dynamic seal for a transmission shaft, mounted between the crankshaft and the gearbox of an engine of a motor vehicle. The encoder 1 is rotated by the transmission shaft and is mounted in close relation with at least one detection cell 2 mounted on the support plate of the seal, to form a position sensor.

According to another preferred embodiment, the encoder 1 according to the invention is rotated on a motor shaft of a motor vehicle or is rotated by the crankshaft or the camshaft of a motor vehicle. engine of a motor vehicle, being mounted inside the engine block of such a vehicle, in proximity relation of a sensor cell 2 to form a position sensor.

The invention is not limited to the examples described and shown, since various modifications can be made without departing from its scope.

Claims

1 - Rotary position sensor comprising:

at least one magnetic encoder (1) rotatable around an axis (A), comprising a first (3a) and a second (3b) circular magnetic strip extending side by side and each formed by a succession of alternating magnetic poles North and South (4 _a , 5 _a -4b, 5b),

- and a detection cell (2) delivering an electrical signal corresponding to the evolution of the magnetic field intensity of the magnetic poles, characterized in that:

- the magnetic poles (4 _a, 5 _a -4 _b, 5b) of the two tracks are arranged so as to establish a succession of magnetic fields (H) alternately in opposite directions, going from one track to another,

- The detection cell (2) is mounted to be sensitive to successive magnetic fields (M) of alternating direction passing from one track to another.

2 - rotary position sensor according to claim 1, characterized in that the two circular magnetic tracks (3 _a , 3 _b ) each extend on one side of a measuring plane (P) perpendicular to the axis ( A) of the encoder and in which is placed the detection cell (2).

3 - Rotary position sensor according to claim 2, characterized in that the magnetic poles (4 _a, 5 _a -4 _b, 5b) of the two tracks are arranged that are established between the opposite polarity poles vis with respect to two tracks (4 _a -5b; 5 _a -4b), a succession of magnetic fields (M) intersecting the measurement plane in a direction preferably substantially perpendicular to the measurement plane (P).

4 - rotary position sensor according to one of claims 1 to 3, characterized in that the two magnetic tracks (3 _a , 3b) are joined or separated by a gap (Δ). 5 - rotational position sensor according to claim 1 or 2, characterized in that the sensor cell (2) is a Hall effect cell, Hall effect or Hall effect with flux concentrator.

6 - Rotary position sensor according to one of claims 1 to 5, characterized in that it comprises at least one magnetic singularity (6) formed by a singular pole (6 _a ) of a different polarity track to that of a singular pole (6 _b) of the other track placed vis-à-vis, each single pole (6 _a, 6 _b) having a part between two adjacent poles, a spacing different from the no spacing between the other poles and secondly, correction means (10) so as to stabilize the magnetic signal delivered by the passage of the poles adjacent to said singular poles.

7 - Rotary position sensor according to claim 6, characterized in that each single pole _(6a, 6b) is provided as correction means (10), a gradual magnetization between the two adjacent poles.

8 - rotary position sensor according to claim 7, characterized in that the magnetization level of each singular pole (6 _a , 6 _b ) evolves between the two adjacent poles so that the magnetization level in the central part of the singular pole is greater than the magnetization level of its lateral portions contiguous to the adjacent poles.

9 - Rotary position sensor according to claim 6, characterized in that each single pole _(6a, 6b) is provided as correction means (10), a corrector pole _(lt, lt _b) adjacent each adjacent pole . 10 - rotary position sensor according to claim 9, characterized in that each correction pole (ll _a , llb) is a non-magnetized pole or the same polarity as the adjacent poles.

11 - The rotary position sensor of claim 9 or 10, characterized in that each loop pole (II _a, IIb) has a shape such that each single pole _(6a, 6b) has a shape of an isosceles trapezium whose larger base is located on the side of the measurement plane (P). 12 - rotary position sensor according to claim 9, 10 or 11, characterized in that the corrector pole (ll _a , ll _b ) contiguous to an adjacent pole is connected to the adjoining corrective pole of the other adjacent pole by a zone of connection (12 _a, 12 _b) located along the track of the opposite side to the measuring plane (P).

13 - Rotary position sensor according to one of claims 6 to 12, characterized in that the magnetic poles (4 _a, 5 _a, 4 _b, 5 _b) of the two tracks have a geometric shape symmetrical with respect to the measurement plane (P), each pole (4, _{_5a} -4 _b, 5b) of a track having an opposite polarity to the pole of the other track placed vis-à-vis.

14 - rotary position sensor according to one of claims 1 to 5, characterized in that it comprises means (15) for forcing the magnetic field to be established between the magnetic poles of the two opposite polarity tracks located screwed -a-vis. 15 - rotational position sensor according to claim 14, characterized in that the means (15) for forcing the magnetic field, are formed by the geometric shape of the poles of the two tracks of the same polarity which is different from the geometric shape of the poles of the two tracks with the other polarity. 16 - rotational position sensor according to claim 15, characterized in that the means (15) for forcing the magnetic field are formed for each track, by non-magnetic areas extending between each pole of the same polarity and the adjacent poles.

17 - rotary position sensor according to claim 16, characterized in that each non-magnetic zone (15) has a constant length from one edge to the other of the track.

The rotary position sensor according to claim 16, characterized in that each non-magnetic zone (15) has a length which increases from the edge of the track located on the measurement plane side towards the opposite edge of the track. 19 - rotary position sensor according to claim 17 or 18, characterized in that each non-magnetic zone (15) has a connecting portion (16) between two adjacent poles, extending on the side of the track located on the opposite side the measurement plan. 20 - The rotary position sensor of claim 18, characterized in that each non-magnetic region (15) has a triangular shape so that each magnetic pole (4 _a, 4 _b, 5 _a, 5 _b) has a trapezium-shaped isosceles.

21 - Rotary position sensor according to one of claims 1 to 20, characterized in that the encoder (1) is set in rotation on a rotating shaft of a motor vehicle.

22 - Rotary position sensor according to claim 21, characterized in that the encoder (1) is mounted on the shaft of an engine of a motor vehicle. 23 - Rotary position sensor according to claim 21, characterized in that the encoder (1) is mounted on a transmission shaft of a motor vehicle.