FR2856144A1 - Position sensor for use in motor vehicle, has encoder with correction unit compensating value of induction field created by irregular pole to stabilize tangential magnetic signal delivered by measuring cell, where signal varies monotonously - Google Patents

Abstract

The sensor has an encoder formed by a magnetic ring (1) with alternate north and south poles. The encoder has a correction unit for compensating the value of a magnetic induction field created by an irregular pole to stabilize tangential magnetic signal delivered by a magnetoresistive measuring cell, by passing the signal from adjacent poles to the irregular pole. The unit is designed such that the signal varies monotonously.

Description

i

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

  The object of the invention relates more particularly, the production of a sensor 5, the encoder of which 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 use a magnetic sensor adapted to measure the change in intensity of a magnetic induction field when a ferromagnetic encoder provided with field disturbing organs, scrolls past a detection cell. The detection cell such as a Hall effect or magnetoresistive probe, for example, delivers a periodic sinusoidal signal. The detection cell is associated with a hysteresis level comparator, such as a Schmitt trigger, in order to obtain frank transitions of the output voltage for values distinct from the magnetic induction as it varies in increasing or decreasing.

  In order to constitute a speed detection sensor, it is known to produce an encoder provided with teeth arranged in a regular manner and in high number to improve the resolution of such a sensor. An improvement to this sensor is known, which consists in producing an encoder constituted by a multipolar magnetic ring provided, on its circumference, with North poles and South poles alternate and regularly spaced at a given pitch.

  To make it possible to determine at least one position, corresponding for example to the top dead center of ignition of a cylinder, it is known to make a mark on the magnetic encoder. It is thus known to remove, for example, two teeth on the toothed wheel. In the solution using an encoder provided with alternating North poles and South poles, it can be envisaged either to delete several magnetic poles while leaving an empty space, or to replace one or more poles of a given sign by a or several poles with a contrary sign. There is thus produced a magnetization pole of a given sign having, between its two adjacent poles of an opposite sign, a different spacing with respect to the spacing pitch of the other poles.

  In order to obtain good measurement accuracy, in particular as regards the detection of the irregular pole, patent FR 2 757 943 teaches to produce an encoder 5 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 pole is symmetrical with respect to the zero value of the magnetic field.

  The use of such an encoder makes it possible to obtain at the output of the detection cell of the sensor, a magnetic signal whose period is constant with regard to the regular poles. This results in good accuracy of the measurements thus carried out, in particular for locating the irregular pole.

  If the technical solution described in this patent is satisfactory in practice, it has been found, under certain operating conditions, on the one hand, a variation in a large range of the width of the air gap defined between the encoder and the measurement cell and, on the other hand, a significant lateral offset between the plane of rotation of the encoder and the axis of the measurement cell, which affects the accuracy of the measurements.

  The present invention therefore aims to remedy the drawbacks of the prior art, by proposing a sensor having good accuracy for locating, in particular the irregular pole, even for significant variations in the measurement gap and the lateral offset between the plane. encoder rotation and the axis of the measuring cell.

  To achieve such objectives, the position sensor according to the invention is of the type comprising an encoder formed by a multipolar magnetic ring, provided, on its circumference, with North poles and alternating South poles and mounted to pass in front of a measurement delivering a periodic signal corresponding to the change in the intensity of the magnetic field delivered by the poles, at least one of said poles of a determined sign is said to be "irregular" and comprises, on the one hand, between 30 its two adjacent poles with opposite signs, a different spacing with respect to the spacing pitch between the other poles and, on the other hand, means for correcting the value of its magnetic field, so that the signal delivered, by the passage from neighboring poles to said irregular pole.

  According to the invention, the position sensor is characterized: * in that the measuring cell is sensitive to the tangential component of the magnetic field delivered by the poles, ò and in that the correction means are produced so that the 5 tangential magnetic signal, generated between the passage of each pole adjacent to said irregular pole, varies monotonously. Various other characteristics will emerge from the description given below with reference to the appended drawings which show, by way of nonlimiting examples, embodiments and implementation of the subject of the invention.

  Fig. 1 is a general view showing an exemplary embodiment of a position sensor according to the invention.

  Fig. 2 is a view, brought back in a plane, of a first embodiment of an encoder according to the invention.

  Fig. 3 is a curve illustrating the evolution of the magnetic induction obtained during the travel of an encoder in accordance with FIG. 2.

  Fig. 4 shows a second embodiment of an encoder according to the invention.

  Fig. 5 is a curve illustrating the evolution of the magnetic induction, obtained during the movement of an encoder in accordance with FIG. 4.

  Fig. 6 is a view of a variant of the second embodiment of the coder according to the invention.

  Figs. 7 and 8 show other examples of mounting an encoder according to the invention.

  Fig. 1 shows an exemplary embodiment of the position sensor I comprising a magnetic encoder 1 mounted to pass in front of a detection cell 2. The encoder 1 is constituted in the form of a multipolar magnetic ring, driven in rotation around its center, along an axis A parallel to the direction OX and provided, on its circumference, with North N poles and alternating South S poles, having a radial magnetization. In the example illustrated, the encoder 1 comprises a series of 30 South S poles and North N poles arranged to have a regular spacing pitch between two neighboring poles. For example, the angular width of each pole is 3.

  According to the invention and as shown more precisely in FIG. 2, the encoder 1 also includes at least one so-called irregular pole Pi, having, between its two adjacent poles Pa, a different spacing relative to the regular spacing pitch between the poles S and N. In the example illustrated, the pole irregular Pi has an angular width of 15 and constitutes a North pole, while the adjacent poles Pa are of opposite signs, namely South. Of course, the polarities of the adjacent poles Pa and of the irregular pole Pi can be reversed. 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 constitute the North and South poles.

  According to a characteristic of the invention, the measurement cell 2 is sensitive to the tangential component of the magnetic field delivered by the poles of the encoder 1.

  Thus, as shown more precisely in FIG. 1, cell 2 is mounted to measure the OY component of the magnetic field, taken along the tangent to the annular encoder 1 and a direction parallel to the plane of rotation B of the encoder perpendicular to the direction OX. The measurement cell 2 thus delivers a magnetic signal, called a tangential signal, corresponding to the measurement of the tangential component of the magnetic field delivered by the poles.

  According to a preferred embodiment characteristic, the measurement cell 2 is a magnetoresistive measurement cell 2 which can thus be placed in the immediate vicinity of the encoder 1.

  Advantageously, the magnetoresistive measuring cell 2 and the encoder 1 are adapted so that said measuring cell is subjected to a magnetic field of less than 30 KA / m.

  According to the invention, for each irregular pole Pi, the encoder 1 comprises means 3 for correcting or compensating for the value of the magnetic induction field created by the irregular pole Pi, relative to the value of the field of magnetic induction created by the neighboring poles, so as to stabilize the magnetic signal delivered by cell 2 by the passage of the neighboring poles to said irregular pole. Thus, the correction means 3 are determined so that the signal, corresponding to the change in the intensity of the magnetic field delivered by the 30 poles adjacent to the irregular pole Pi, is not disturbed by the magnetic induction created by the irregular pole Pi. The means 3 are therefore adapted so as to reduce the magnetic flux created by the irregular pole, while maintaining it at a value sufficient to allow its detection.

  According to a characteristic of the invention, the correction means 3 are produced so that the tangential magnetic signal, delivered by the measurement cell 2 and generated between the passage of each adjacent pole Pa to the irregular pole Pi, varies monotonously. Fig. 3, which shows the evolution of the magnetic induction field 5 I (in Gauss) and, more precisely, its tangential component as a function of the position of the encoder 1 relative to the measurement cell 2, makes it possible to highlight the passage of the irregular pole Pi in front of the measurement cell. The passages of each adjacent pole Pa to the irregular pole Pi correspond to points A and B on the curve of FIG. 3. Between these two points A and B, the magnetic induction field 10 varies monotonously, that is to say varies in a single direction. In the example illustrated, the induction field is always increasing from point A to point B. Insofar as the induction field is continuously increasing (or decreasing) for the irregular pole, there is no risk of detection error of the irregular pole Pi.

  Fig. 2 illustrates a first alternative embodiment of the correction means 3. According to this variant, the correction means 3 are produced by a surface area 4 of the irregular pole Pi, extending to the peripheral or tangential surface of the annular encoder 1. In the example illustrated in fig. 2, the surface area 4 of the irregular pole Pi has a symmetrical shape with respect to a transverse axis t 20 considered parallel to the axis of rotation A of the encoder 1. It should be noted that the thickness of the irregular pole Pi, taken according to the radial direction is constant.

  This surface 4 of the irregular pole Pi is surrounded by a pole 5 connecting with the adjacent poles Pa. The connecting pole 5 is of the same sign or polarity as the adjacent poles Pa, that is to say of sign opposite to the pole irregular Pi. Thus, as shown in FIG. 2, the surface 4 of the irregular pole Pi is surrounded by a magnetic surface of opposite sign. In the illustrated embodiment, the surface area of the irregular pole is a quadrilateral. Thus, the surface 4 of the irregular pole Pi is delimited by each adjacent pole Pa along a straight transition line 41.

  In other words, the surface 4 is contiguous with each adjacent pole Pa along the transition line 41 which is parallel to the other junction lines between the South S and North N poles. As explained above, each transition line 41 extends back from the edges of the encoder 1 along longitudinal lines 42, so that the surface 4 is surrounded by a magnetic surface of opposite sign.

  Fig. 4 illustrates a second alternative embodiment of the correction means 3, produced by a surface area 4 of the irregular pole Pi having a shape 5 asymmetrical with respect to the transverse axis t. According to this alternative embodiment, the surface area 4 of the irregular pole Pi has an asymmetrical shape, so that the magnetic signal, delivered in the middle of the irregular pole is angularly stable. Thus, as is apparent from FIG. 5, the polarity of the magnetic induction, created in the middle of the irregular pole, changes sign at a well determined position. Such a change in sign is obtained whatever the width of the air gap, that is to say the distance between the detection cell 2 and the magnetic ring 1. It turns out that the signal 1 has a definition of the stable singularity, so as to facilitate the work of locating the irregular pole. Thus, the magnetic signal delivered by the passage of neighboring poles Pa to said irregular pole Pi is symmetrical with respect to the zero value of the magnetic field. As shown in fig. 5, the magnetic induction created by the irregular pole Pi between points A and B does not disturb the magnetic induction field of the neighboring regular poles. The signal, giving the change in the intensity of the magnetic field delivered by the regular poles adjacent to the irregular pole Pi, is symmetrical with respect to the zero or zero value of the magnetic field. Such symmetry of the magnetic signal is obtained whatever the width of the air gap, that is to say the distance between the detection cell 2 and the magnetic ring 1. It turns out that the signal I has a constant period T with regard to the regular poles neighboring the irregular pole.

  It follows that good accuracy can be obtained from the measurements made for locating the irregular pole.

  In the example illustrated in fig. 4, the surface area 4 of the irregular pole Pi, of asymmetrical shape, consists of a first area 4a of a given width contiguous to a second area 4b of a width less than that of the first area. The first zone 4a and the second zone 4b each preferably constitute a quadrilateral. As explained for the first alternative embodiment, the surface area 4 of the irregular pole Pi is surrounded by the connecting pole with the adjacent poles Pa, with the same sign as the adjacent poles.

  In a second exemplary embodiment illustrated in FIG. 6, derived directly from the example illustrated in FIG. 4, the first zone 4a has a part of constant width, contiguous to a part whose width decreases, up to a transition line 41, between the irregular pole P1 and the adjacent pole Pa. The part of decreasing width 5 decreases to from the longitudinal edges 42, symmetrically with respect to an axis perpendicular to the transverse axis t.

  The encoder 1 according to the invention, as described above, is intended to be mounted on a generally rotating target, from which at least one position is determined. According to a preferred embodiment characteristic, the encoder 1 according to the invention is intended to be mounted on a drive pulley mounted at the outlet of the engine of a motor vehicle, that is to say on a timing pulley or on one of the auxiliary pulleys. According to an advantageous characteristic, as shown in FIGS. 7 and 8, the encoder 1 is mounted on the drive pulley 6 located in the axis of the crankshaft, in order to allow detection of the top dead center 15 of ignition of a cylinder. In the example illustrated, the encoder 1 is mounted on the internal radial wall or hub 7 (fig. 7) or on the external radial wall 8 (fig. 8) of a drive pulley 6. The elastoferrite ring of the encoder 1 is mounted directly on the pulley 6 which constitutes, by its radial wall, the support ring, or indirectly by its support ring which is fixed by any appropriate means to the pulley. As shown in Figs. 7 and 8, a detection cell 2, preferably magnetoresistive, is mounted in the clearance delimited between the external radial 8 and internal 7 walls of the pulley, so that the encoder 1 can pass in front of it and together form a sensor for position.

  In the embodiment illustrated above, the position sensor 25 includes, as a drive pulley, a crankshaft pulley provided with a magnetic ring adapted to locate a single position. It should be noted that the object of the invention can also be applied to the production of a sensor comprising a magnetic ring 1 provided with several irregular poles Pi making it possible to identify several positions. Advantageously, the magnetic ring 1 comprises, for example, four irregular poles Pi making it possible to identify 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 by having a single irregular pole.

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

  According to another preferred implementation characteristic, the encoder 1 according to the invention is set in rotation on a shaft of an engine of a motor vehicle or 10 is rotated by the crankshaft or the camshaft of an engine of a motor vehicle, being mounted inside the engine block of such a vehicle, in proximity relation to a detection cell 2 so as to constitute a position sensor.

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

Claims (13)

  1 - Position sensor, of the type comprising an encoder formed by a multipolar magnetic ring (1) provided, on its circumference, with alternating North poles (N) and South poles (S) and mounted to pass in front of a measuring cell ( 2) 5 delivering a periodic signal corresponding to the change in the intensity of the magnetic field delivered by the poles, at least one of said poles of a determined sign is said to be "irregular" (Pi) and comprises, on the one hand, between its two adjacent poles (Pa) of opposite signs, a different spacing with respect to the spacing pitch between the other poles and, on the other hand, means (3) for correcting the value of its magnetic field , so as to stabilize the magnetic signal delivered, by the passage of neighboring poles to said irregular pole, characterized: a in that the measuring cell (2) is sensitive to the tangential component of the magnetic field delivered by the poles, a and in what means to correct tion (3) are made so that the tangential magnetic signal, generated between the passage of each pole adjacent to said irregular pole, varies monotonously.   2 - sensor according to claim 1, characterized in that the correction means are produced by a surface area (4) of the irregular pole (Pi) having a symmetrical shape with respect to a transverse axis (t) and surrounded by a pole of connection (5) with the adjacent poles, of the same sign as the adjacent poles.   3 - Sensor according to claim 2, characterized in that the surface area (4) of the irregular pole (Pi) having a symmetrical shape, is a quadrilateral.   4 - Sensor according to claim 1, characterized in that the correction means (3) are made by a surface area (4) of the irregular pole (Pi) having an asymmetrical shape relative to a transverse axis (t) and surrounded by a connecting pole (5) with the adjacent poles, with the same sign as the adjacent poles.   - Sensor according to claim 4, characterized in that the surface area (4) of the irregular pole (Pi) has an asymmetrical shape so that the magnetic signal delivered by the middle of the irregular pole, has a stable angularly changed polarity.   6 - Sensor according to claim 4 or 5, characterized in that the surface area (4) of the irregular pole of asymmetrical shape consists of a first area (4a) of a given width contiguous to a second area (4b) d 'a width less than that of the first zone.   7 - A sensor according to claim 6, characterized in that the first (4a) and the second (4b) areas of the surface area each constitute a quadrilateral.   8 - Sensor according to claim 6, characterized in that the first zone (4a) has a portion of constant width contiguous to a portion of decreasing width to a transition line between the irregular pole and the adjacent pole.   9 - Sensor according to claim 1, characterized in that the measurement cell (2) is a magneto-resistive measurement cell.   - Position sensor according to claim 9, characterized in that the magnetoresistive measuring cell (2) and the encoder (1) are adapted so that said cell is subjected to a magnetic field of less than 30 KA / m.   11 - Position sensor according to one of claims 1 to 10, characterized in that the encoder (1) is locked in rotation on a shaft of an engine of a motor vehicle.   12 - Position sensor according to claim 11, characterized in that the encoder (1) is attached or is an integral part of a drive pulley.   13 - Position sensor according to claim 12, characterized in that the drive pulley is a crankshaft pulley.   14 - Position sensor according to claim 12, characterized in that the drive pulley is a cam pulley.   - Position sensor according to claim 11, characterized in that the encoder 25 (1) is mounted inside a support plate for a dynamic seal, mounted between the crankshaft and the gearbox d 'an engine of a motor vehicle.   16 - position sensor according to claim 11, characterized in that the encoder (1) is rotated by the crankshaft or the camshaft, being mounted inside the engine block of a motor vehicle .