EP4305385A1

EP4305385A1 - Magnet sensor and ferromagnetic poles

Info

Publication number: EP4305385A1
Application number: EP22712979.8A
Authority: EP
Inventors: Didier Frachon
Original assignee: Moving Magnet Technologie SA
Current assignee: Moving Magnet Technologie SA
Priority date: 2021-03-08
Filing date: 2022-03-08
Publication date: 2024-01-17
Also published as: CN117015689A; JP2024508955A; FR3120434B3; KR20230152706A; WO2022189750A1; FR3120434A3

Abstract

The invention relates to a magnetic position sensor comprising at least one magnetically sensitive element capable of moving relative to a permanent magnet producing a magnetic field, the magnet of which is embedded in a support made of soft ferromagnetic material having two pole shoes located on either side of said magnet.

Description

DESCRIPTION

Title: Magnet sensor and ferromagnetic poles

The present invention relates to the field of magnetic position sensors comprising at least one permanent magnet, to detect the passage in front of a magneto-sensitive probe, for relative movements of the magnet with respect to the probe which are, according to the intended application, linear or angular, even multidirectional.

[0002] These sensors are, for example, suitable for monitoring and detecting the angular position of the output shaft of an actuator such as, for example, an electric gear motor for heat engine control applications of a motor vehicle, truck, transport, agricultural machinery etc.

[0003] The position information returned via the integrated electronics of the electric motor to the centralized control electronics (ECU) of the vehicle is decisive for carrying out the calibration of the actuator (determination of the useful travel between stops), it can also be used to refine control or for diagnostic purposes.

[0004] For these applications, the sensor must be in the form of a digital sensor for a movement of up to 360° with a signal in the "ON" state over a range of 20° to 30° and "OFF" on the complementary angular range, the expected tolerance on switching being ±2°.

[0005] Another possible integration is that of linear position detection sensors of a shaft over strokes of a few tens of millimeters and for which it is important to minimize the volume of magnet necessary for on the one hand to obtain a field sufficient magnetic for it to be measurable by the magneto-sensitive probe and on the other by an accuracy typically less than +/-1%. One can cite for example the case of the detection over 200 mm of the linear displacement of a motor vehicle steering rack or of a clutch. State of the art

[0006] The state of the art offers numerous "cheap" solutions with contact (potentiometer sensitive to wear by friction) or by optical technology (sensitive to fouling and dust).

[0007] For applications having to meet a high level of requirement (very long service life, vibration, high thermal amplitude), these solutions are however not appropriate and magnetic solutions comprising a mobile element exciting a fixed sensitive element are favourites.

[0008] For example, patent application US20190078910 is known describing a vehicle element actuator comprising a housing, an actuator motor in the housing and a rotary output gear shaft assembly in the housing, containing a rotary shaft output and a gear. The output gear contains at least one defined discontinuity therein exhibiting a magnetic flux signature. A position sensor, eg, containing an integrated magnet Hall effect probe, senses the magnetic flux signature of said discontinuity on the output gear to sense and determine the position of the output gear shaft assembly. The discontinuities may be of the same or different sizes/configurations, and equally or unequally spaced from each other. The discontinuities can be slits or protrusions or any other aspect with a unique magnetic flux signature, which the position sensor can detect.

[0009] The use of a discontinuity on the output wheel of the reducer is not completely satisfactory because the limits of the discontinuity can vary with time and temperature, and lead to unexpected switchings. On the other hand, a difficulty inherent in these technologies is to be able to detect small angles, for example 20°, when they are surrounded by very large angles, for example 340°, while guaranteeing good precision of these small angles when the sensor is subjected to air gap tolerances.

[0010] US20190140524 discloses a rotary position sensor comprising a rotary shaped ring magnet, which in one embodiment is mounted on the output shaft of an actuator, and comprises a plurality of pairs of pole sections north and south extending around the circumference of the ring magnet in an alternating relationship and defining a plurality of magnetic field switching points extending circumferential spaced at predetermined distances on the ring magnet corresponding to a plurality of single predetermined positions of the ring magnet adapted for detection by a switch such as a Hall effect switch. In one embodiment, the ring magnet includes a plurality of pairs of north and south pole sections and switch points on the ring magnet of different predetermined lengths and different predetermined locations respectively corresponding to a plurality of switch positions. predetermined ring magnets to be detected.

[0011] The use of a multipolar ring magnet on the output wheel entails relatively high costs.

[0012] In general, these solutions of the prior art strongly constrain the topology of the actuator and the assembly of the reducer to allow the output wheel supporting the magnetic target to be positioned in the immediate vicinity of the printed circuit supporting the magneto-sensitive element. These solutions are also restrictive for the printed circuit which must cover the output wheel carrying the magnet for measuring the axial component: the printed circuit thus greatly restricts the space available for the guide elements to be inserted.

[0013] The implementation of the second solution is complicated. It is indeed necessary to integrate ferromagnetic parts for guiding and concentrating the magnetic flux which are cumbersome. In addition, it requires a large volume of magnet since the latter consists of a complete ring.

[0014] Also known in the state of the art is European patent EP1989505B1 describing a magnetic rotary, linear or curvilinear displacement sensor using at least one permanent magnet and at least one magneto-sensitive element, movable relative to each other. the other. The magnet has a direction of magnetization which varies linearly according to said direction of displacement of the magnet on a surface defined by the direction of displacement and a normal direction, excluding diametrical magnetization in the case of a rotary sensor. The permanent magnet thus generates a magnetic field whose normal component (Y) on the one hand, and at least one of the tangential (X) and transverse (Z) components on the other hand, measured at the surface of the magnet vary periodically in a sinusoidal way, the normal (Y) and transverse (Z) components varying with the same phase while the tangential component (X) is out of phase by a quarter of a period. [0015] This last solution is very relevant and effective, but it requires a large volume of magnet (therefore expensive) since it has to cover approximately once the race which must be measured and the rotating magnetization is difficult to achieve.

Solution provided by the invention

In order to overcome these drawbacks, the invention relates in its most general sense to a magnetic sensor having the characteristics set out in claim 1.

[0017] Such a magnetic sensor is suitable for applications for which the use of iron poles reduces the volume of magnet required, which brings a significant reduction in costs, and presenting an insensitivity with respect to a modification of the air gap, which can occur in a production line, due to manufacturing dispersions or during the life of the sensor, due to wear.

[0018] Advantageously, the magnetic position sensor comprises: o a magnetized structure provided with a permanent magnet producing a magnetic field and a support made of soft ferromagnetic material in which the magnet is embedded, said support having two pole shoes located on either side of said magnet, o at least one magneto-sensitive element which can be set in relative motion, with respect to said magnet embedded in the support, according to a measurement trajectory, said magnet and said two pole shoes respectively presenting a surface face all being located opposite the at least one magneto-sensitive element during movement along the measurement path, characterized in that during movement along the measurement path, the front surfaces are successively opposite -screw of the sensitive element and in that the ratio between: o the minimum distance between the front surface of the magnet and the center of the magnetic element neto-sensitive and o the minimum distance between one or other of the front surfaces of the pole shoes and the center of the magneto-sensitive element, is between 0.7 and 1.3.

[0019] According to a first variant, during movement along the measurement path, the front surfaces are successively opposite the sensitive element and the minimum distance, between a front surface opposite the magneto-sensitive element and the center of the magneto-sensitive element, presents variations of less than 50% with respect to its mean value.

[0020]According to a variant, the magnetic position sensor is such that the ratios between: o on the one hand, the minimum distance between the front surface of the magnet and the at least one magneto-sensitive element, during movement along the measurement trajectory, and o on the other hand, the minimum distance between one or other of the front surfaces of the pole shoes and the at least one magneto-sensitive element, during movement along the measurement trajectory, are both between 0.7 and 1.3.

[0021] Alternatively, these ratios are both between 0.9 and 1.1.

In another variant, there are recesses between the pole shoes and the magnet such that the front surfaces are not contiguous.

Preferably, the magnetic position sensor according to the invention is characterized in that the measurement trajectory is located in a plane and in that along the direction orthogonal to this plane, the thickness of the pole shoes is less than the thickness of the magnet.

[0024] Still preferably, the sum of the lengths of the front surfaces of the pole shoes, according to the measurement path, is greater than or equal to the length of the front surface of the magnet.

As a possible alternative, the length of the front surfaces of each of the pole shoes along the measurement path is greater than or equal to that of the front surface of the magnet.

According to a variant, the magnetization of said magnet has a unidirectional magnetization direction. As a possible alternative, the magnetization of said magnet is parallel to a plane passing through the magnet and orthogonal to the path of the relative displacement.

[0028] As a second alternative, the magnetization of said magnet is diametrical.

[0029] As a third alternative, the magnetization of said magnet has a direction of magnetization which varies continuously according to the path of movement.

[0030] As a fourth alternative, the magnetization of said magnet has a magnetization whose intensity varies continuously according to the path of movement.

As a fifth alternative, the magnetization of said magnet has a direction of magnetization which varies continuously in 2 directions corresponding to the trajectory of the displacement.

[0032] Advantageously, said magneto-sensitive element is a programmable probe which is temperature compensated according to the characteristics of the magnet.

[0033] According to a particular embodiment, said magneto-sensitive element is a probe for measuring the magnetic angle directly or indirectly via the measurement of the magnetic components constituting a sensor with absolute output as a function of the mechanical position. Alternatively, the relative movement of said permanent magnet with respect to said magneto-sensitive element is linear.

According to another variant, the relative movement of said permanent magnet with respect to said magneto-sensitive element is rotary.

According to another variant, the relative movement of said permanent magnet with respect to said magneto-sensitive element takes place along several dimensions, for example a linear movement along one dimension and a rotary movement along another dimension, without however limiting to the only combinations of these movements or a movement along only two dimensions.

According to one mode of implementation, the magneto-sensitive probe is a magnetic switch, the position sensor having invariant switching positions depending on the air gap.

Advantageously, the magnetic switch measures a component of the magnetic field and has a switching threshold which can be programmed.

According to a particular mode of implementation, the magneto-sensitive probe reconstructs the analog position information from the components of the magnetic field collinear with the displacement and in a direction orthogonal to said relative displacement. Advantageously, the magneto-sensitive probe reconstructs the analog position information from the component of the magnetic field collinear with the direction of magnetization.

Preferably, said pole shoes have a shape profile sculpted according to an algorithm maximizing the precision of the sensor.

[0042] According to a particular method of manufacture, said ferromagnetic material support consists of a stack of sheets.

[0043] The invention also relates to a mechatronic assembly comprising an actuator formed by a stator constituted by an assembly of ferromagnetic sheets defining teeth of which at least part is surrounded by a coil, and a position sensor according to the preceding claim characterized in that the outer contour of the laminations of said ferromagnetic material support of the sensor is contained in the inner contour of the laminations of said stator of the actuator.

[0044] By measurement trajectory is meant that, in the frame of reference of the magneto-sensitive element, a trajectory representative of the movement described by the center of gravity of the front surface of the magnet over the entire travel useful for the measurement. During the course of the measurement trajectory, the point located on one of the front surfaces having the minimum distance with the center of the magneto-sensitive element varies throughout the course of the measurement trajectory. Thus a sensor of the "end of axis" type known to those skilled in the art, and for which a probe is located on the axis of rotation of the mobile element supporting the magnetized structure, does not present any notion of trajectory in the sense of the invention because this would lead to a point trajectory.

Detailed description of a non-limiting embodiment

The present invention will be better understood on reading the following description, concerning a non-limiting example of embodiment illustrated by the appended drawings where:

[FIGURE 1] Figure 1 shows a perspective view of a rotary sensor according to which the magnet is shown in transparency, [FIGURE 2] FIG. 2 represents the curves of the radial and tangential components of the induction as well as the magnetic angle as a function of the position, of a rotary sensor for a reduced active stroke according to the invention,

[FIGURE 3] FIG. 3 represents for several air gaps the curves of the radial component of the induction as a function of the position of the shaft of a rotary sensor according to the invention as well as the digital signal from the magneto-probe sensitive,

[FIGURE 4] FIG. 4 represents a view of a rotary sensor variant according to the invention based on a multipolar rotor,

[FIGURE 5] FIG. 5 represents a perspective view of a linear sensor according to the invention,

[FIGURE 6] FIG. 6 represents the curves of the components parallel and orthogonal to the direction of magnetization, of the induction as a function of the position, of a linear sensor according to the invention,

[FIGURE 7] figure 7 represents the magnetic angle and linearity curves as a function of the position of the linear sensor of figure 6,

[FIGURE 8] FIG. 8 represents a view of a variant of a linear sensor according to the invention based on a multipolar magnetized structure,

[FIGURE 9] FIG. 9 represents a perspective view of a rotary sensor with axial flux according to the invention,

[FIGURE 10] FIG. 10 represents a view of a variant of an axial flux rotary sensor according to the invention based on a multipolar rotor,

[FIGURE 11] FIG. 11 represents a perspective view of a magnetized structure, optimized for mass production, and for a rotary sensor according to the invention,

[FIGURE 12] figure 12 shows a top view of the cutouts of the ferromagnetic sheets of the sensor and of the motor of the actuator with which the sensor is associated, [FIGURE 13] FIG. 13 represents a view in partial section of an actuator equipped with a sensor according to the invention.

Description of the magnetic structure

For greater clarity, the numberings used in this part are common to the entire document and are to be assessed through the various figures.

The magnetized structure (1) consists of a permanent magnet (10) whose magnetization can be variable in direction and intensity, which is associated with a ferromagnetic support (20) consisting of soft iron sheets, forming a configuration defining two adjacent pole shoes (21, 22). This magnetized structure (1), associated with a first set, aims to generate a magnetic field which is detected by a magneto-sensitive probe (30) associated with a second set, said first and second sets being in relative motion along a trajectory of measure (2). The pole shoes (21, 22) as well as the magnet (10) respectively have a front surface (15, 24, 25), that is to say which can be located directly opposite the magneto probe. -sensitive (30) during the course of the measurement trajectory (2), the air gap formed between these front surfaces (15, 24, 25) and the magneto-sensitive probe (30) having small variations. By front surface is meant a magnetically active surface located in the direct vicinity of the probe, the front surface (15) of the magnet (10) being the emitting surface of the magnetic field measured by the probe and the front surfaces (24, 25) being the surfaces of the pole shoes (21, 22) intended to collect the magnetic flux generated by the magnet. [0048] The small air gap variations make it possible to produce a very compact sensor structure by making it possible to bring the probe as close as possible to the magnetic structure (1). These small air gap variations also make it possible to maximize the induction along the measurement trajectory (2). When the air gap variations are too great, it is necessary to move the magneto-sensitive element (30) away from the magnetized structure to avoid linearity problems. For example, an important criterion is that the magnet must not be further back, vis-à-vis the magneto-sensitive element (30), than the pole shoes (21, 22), in fact this withdrawal leads to a significant drop in the magnetic induction measurable by the probe, and increases the size of the sensor. The reverse, or pole shoes (21, 22) set back relative to the magnet (10), is not desirable for the same reasons. It is defined as a criterion to meet this need that along the trajectory (2) of measurement, the ratio between, on the one hand the minimum distance measured between the frontal surface (15) of the magnet (10) and the magneto-sensitive element (30), and on the other hand the minimum distance measured between one or the other of the front surfaces (24, 25) of the pole shoes (21, 22) and the magneto-sensitive element (30 ), is between 0.7 and 1.3. For more restrictive applications, this ratio can be limited to a variation between 0.9 and 1.1. Another less generic criterion relates to variations in distance within the same frontal surface (15, 24, 25). During the course of the same frontal surface (15, 24, 25) along the measurement trajectory (2), a satisfactory condition is that the ratio between the minimum distance and the maximum distance measured between the frontal surface and the magneto-magnetic probe sensitive remains below 0.5. Another, more restrictive criterion is linked to the variations in air gap between the front surface (15) of the magnet (10) and the front surfaces (24, 25) of one and the other of the pole shoes (21, 22). Indeed in the case where the linearity and the compactness are real concerns, a satisfactory criterion imposes that for any point of the trajectory (2) of measurement for which the probe is vis-à-vis a frontal surface, the The magnetic air gap does not show variations greater than 50% with respect to its average value.

The shape of the permanent magnet (10), its magnetization profile and the profile of the pole shoes (21, 22) may differ depending on the trajectory (2) of the movement to be analyzed, the aim being to obtain the best possible accuracy of the relative position of said first and second sets, while ensuring good resilience to manufacturing dispersions or inherent in aging.

[0050] Various configurations are illustrated through the examples presented, aiming at the detection of linear or rotary movements, without however the latter being limiting of the invention. One could thus also imagine that the trajectory (2) to be analyzed is curvilinear.

The magnetization of the magnet can thus have an intensity and/or a direction (14) which varies continuously or discretely depending on the direction of movement. In the extreme this magnetization can be unidirectional and of maximum intensity to allow the saturation of the magnet. By unidirectional magnetization is meant a magnetization of the material in a single direction of a preferably Cartesian frame of reference. Thus, if we exclude the edge effects at the magnet limit, the magnetization is at all points parallel and in the same direction as a given vector. Of course this type of magnetization is not limiting of the invention and a diametral magnetization, that is to say unidirectional in a cylindrical marker, is also envisaged. Finally, the person skilled in the art could imagine associating a different magnetization with a shaped pole magnet, either by sculpting the magnet or by adding an additional ferromagnetic material, unidirectional magnetization being the simplest to achieve and to be described for the purpose of the invention.

The ferromagnetic support (20) is preferably a stack of sheets of ferromagnetic material in one piece, having between its pole shoes (21, 22) a recess capable of receiving the permanent magnet (10), preferably by driving or by injection or any other type of assembly that a person skilled in the art could envisage. A possible alternative is to produce the pole shoes (21, 22) in two stacks of separate sheets then secured to the magnet by means from among those known to those skilled in the art. This alternative is not preferential in the sense that it requires more precautions for the assembly of the pole shoes (21, 22) to the permanent magnet (10), one possibility would be to secure the pole shoes with an overmolding by a plastic material or directly not the material constituting the magnet. In all cases, the invention involves the mechanical embedding of the magnet (10) in the support part (20) and is not satisfied with the magnetic bonding forces between the pole tips (21, 22) and the magnet. (10) to ensure the integrity of the first set. Indeed, the assembly and maintenance by magnetic forces does not ensure the integrity of the assembly in extreme environments, and is very sensitive to manufacturing dispersions. The pole shoes (21, 22) have for their part a shape profile produced by a cutting tool or any other material removal process known to those skilled in the art. If the support (20) is not the result of a stack of sheets, it can be obtained in a monolithic soft ferromagnetic material, using for example a sintering process. The pole shoes (21, 22) of the ferromagnetic support (20) spread on either side of the permanent magnet (10) leaving a recess (34, 35) with the magnet (10), such so that the front surfaces (15, 24, 25) are not contiguous during the course of the measurement path. This configuration, although not limiting, has the advantage of avoiding a looping back of the flux of the magnet (10) generated at the boundary zone directly into the pole shoes (21, 22) without it being able to cross the probe, this generally leads to a loss of amplitude of the signal, but also to a degradation of the linearity of the sensor. If these two criteria are not essential, as for the realization of a magnetic switch, the realization of these recesses is not necessary this then making it possible to obtain more compact elements and less sensitive to manufacturing tolerances.

The magnetized structure (1) preferably has symmetrical adjacent pole shoes (21, 22), particularly well suited for detecting angles or positions along a rectilinear trajectory, but this without being limiting of the invention, the permanent magnet (10) or the pole shoes (21, 22), also called pole shoes, can be asymmetrical to measure a position along a curvilinear trajectory or to obtain better linearity when taking account of integrating the sensor into its environment.

In the example of Figure 1, the height of the ferromagnetic support (20) is less than the height of the permanent magnet (10), typically between 15% and 60% of the height of the permanent magnet (10). This configuration aims at the same time a better fastening of the permanent magnet (10) on the support (20), but also confers a better regularity of the magnetic flux while maintaining a high level of magnetic field which leads to an increased precision of the sensor according to the invention by increasing the signal to noise ratio. These teachings are particularly true when the magnetized structure (1) is of small axial thickness, but is in no way a limiting generality of the invention.

Rotary sensor

Figures 1, 2 and 3 describe a first example of a rotary sensor according to the invention. Figure 1 illustrates in perspective the magnetized structure (1) vis-à-vis the magneto-sensitive probe (30), these being set in relative motion along the trajectory (2) of measurement. The aim here is to provide an angular sensor solution that is robust in terms of endurance and vibration, simple and very economical, guaranteeing a large imbalance between the active angular stroke (typically 30°) and the passive angular stroke (typically 330°), with a dependence to the hysteresis due to the ferromagnetic parts and to the remanent induction of the permanent magnet (11) very reduced and finally a signal stability according to the air gap variations compared to the solutions of the prior art. [0056] By active angular travel is meant the angular travel over which we want to measure an angle, or more simply change the switching state of a magnetic switch, the passive angular travel being the angular range which does not require measurement. or on which the magnetic switch is in the low state.

To this end, the magnetized structure (1) adopts a configuration which concentrates its magnetic variations on a small part of the trajectory (2) of measurement, here a circle of radius R located in the vicinity of the probe. The magnetized structure (1) is composed of a support part (20), consisting of a pack of ferromagnetic sheets having a central zone extended symmetrically on either side by pole shoes (21, 22) called here pole tips , and a permanent magnet (10) injected by overmolding on the support part (20) or having a notch complementary to the central zone of the support part (20) to secure them by radial insertion, the magnet (10) being shown in transparency in Figure 1 allows to appreciate its maintenance on the support piece (20). The magnet (10) is magnetized in a direction (14) of single magnetization and a constant magnetic field amplitude, oriented, for a rotary displacement application, in a direction included in the plane (X, Z) perpendicular to the Y direction (12) of relative displacement of the magnet (10) with respect to the magneto-sensitive probe (30), the mark being fixed with respect to the magnet (10). The magnetization direction (14) being preferentially collinear with the X vector (11), so as to maximize the radial component of the amplitude of the magnetic field, but it can also have a component collinear with the Z vector (13) to adapt to manufacturing constraints or improve the field measured in the case of a particular positioning of the probe. The amplitudes of the radial (50) and tangential (51) magnetic induction measured along this trajectory are typically similar to those represented graphically in figure 2. The measurement of these components, by a magneto-sensitive probe, makes it possible to reconstruct numerically the magnetic angle (52) according to, for example, the formula a _m We ^are then able to measure a variation of 360° magnetic field for a mechanical rotation of approximately 60°, which increases the precision of the sensor when the stroke only needs to be evaluated over a restricted angle.

A second feature of this first embodiment, making it particularly robust to geometric dispersions, is shown in Figure 3. The graph shows the variation of the radial magnetic induction (54, 55, 56) along three circular trajectories, concentric with that represented in figure 1, but of different radius (3), the curve (54) corresponding to the smallest radius and the curve (56) that of greater radius. This amounts, commonly speaking, to increasing the mechanical measuring gap. It can then be noted that, systematically, these measurements have a central lobe of positive induction presenting on either side a point of inflection, the points of inflection (58, 59) varying very little in angle and in amplitude. when the measurement magnetic air gap changes. This embodiment is particularly advantageous for producing a magnetic switch whose transition positions from the low state to the high state are very robust with regard to manufacturing or aging tolerances. Indeed, if the transitions of the magnetic switch are matched with the inflection points (58, 59) of the radial induction, the curve (57) represented in FIG. 3 is obtained, and which is independent of the distance of the magneto-sensitive probe, the switch produced according to the invention then being able to absorb inaccuracies in the positioning of said probe. Another advantage, not shown here, but typically giving the same type of results as those shown in Figure 3, is the insensitivity of these inflection points (58, 59) to the saturation level of the permanent magnet (10 ). Thus the three induction curves (54, 55, 56) presented in FIG. 3 could be obtained for a trajectory of the same radius (3), but corresponding to 3 different magnetization levels. One thus obtains points of inflexions (58, 59) invariant with the level of magnetization and therefore a sensor able both to absorb a dispersion at the level of the magnetizing tool or a partial demagnetization which may occur during the device life.

Finally, the inflection points (58, 59) have a relatively high level of induction, here 60 Gauss, which makes it possible to obtain a magnetic switch insensitive to parasitic transitions which can occur over the entire inactive range. when the transition is close to 0 Gauss and the environment is magnetically disturbed.

[0060] Of course, the active angular travel is not limited to small angles and its increase is accompanied by an even greater reduction in the volume of the magnet, compared to the sensors conventionally used in the art. prior. However, for the rotary versions of the sensor according to the invention, the permanent magnet (10) preferably has an angular spread close to half the angular travel to ensure good linearity of the sensor. [0061] The rotary variant of such a sensor associated with a digital probe makes it possible, for example, to generate an index at a predetermined angle which will be very precise, making it possible, for example, to search for a start-of-race position with high repeatability.

A variant of an angular sensor, as represented in FIG. 4, consists in multiplying N magnetized structures distributed regularly, or not, over 360°. Associated with a magneto-sensitive probe directly measuring the magnetic angle or the components of the magnetic field, this multipolar ring makes it possible to produce a magnetic encoder to, for example, drive an electric motor in vector mode.

Linear sensor

FIG. 5 represents a view of a linear sensor according to the invention. In this embodiment, the magnetized structure (1) comprises a support (20) notched to accommodate a permanent magnet (10) magnetized in a variable direction (14) and a constant magnetic field amplitude. The magnetized structure (1) is in relative displacement, with respect to a magneto-sensitive probe (30), along a measurement trajectory (2), this trajectory being linear and in the Y direction.

The support (20) is formed by a stack of sheets or a monolithic bar, made of a soft ferromagnetic material, having a notch to receive the magnet (10) by plastic injection or gluing for example. This support has two pole shoes (21, 22) extending laterally, on either side, the magnet (10).

The shape of the pole shoes makes it possible to sculpt the longitudinal and orthogonal components, on the periphery of the magnet, in order to improve the regularity of the variations of the magnetic field and therefore to minimize the non-linearity of the sensor. The calculation of the shape of the horns can be carried out with an optimization algorithm associated with digital magnetic calculation software. This calculation can also involve a shape profile on the magnet or even the variable profile of the magnetization to constitute a second or even a third optimization lever. This type of optimization is particularly interesting in the case where it is sought to measure the displacement along a curvilinear trajectory.

It should be noted that the support (20) can be a part of the mobile whose movement is to be measured, or a part added to the latter. FIG. 6 represents the variations of the magnetic field, generated by the magnetized structure (1), according to two components, when it has in this particular case a direction (14) of single magnetization, or unidirectional magnetization . One orthogonal (60) to the displacement, along the X axis (11), and the other parallel (61) to the displacement, along the Y axis (12). These two components, when associated with a probe with 2 measurement axes or sensitive to the magnetic angle, make it possible to measure the position of the magnet (62) which is presented in figure 7 and which is accompanied by a curve (63) typical linearity defects present in this position measurement. In this example, a measurement over 90 mm of travel is carried out with an error of the order of +/-0.25% with a 50 mm long magnet, ie approximately half of what is traditionally necessary.

[0068] For large strokes, the magnet (10) may have a convex section, to present a greater thickness in the center than at its ends.

The support (20) has, possibly in addition to this feature, an increasing thickness as it moves away from the magnet, as shown in Figure 5.

The linear variant of such a sensor associated with an analog output probe makes it possible, for example, to detect the position of a hydraulic cylinder or else of a mechanical shaft of the rack type in linear displacement in a housing. A possible application would consist in providing a solution for direct measurement of the steering wheel angle in power steering or even a solution for direct measurement of the angle given to the wheels in a steering of the Steer-by-Wire type.

A variant of a linear sensor, as represented in FIG. 8, consists in multiplying N magnetized structures distributed regularly, or not, over the total travel to be measured. Associated with a magneto-sensitive probe measuring the components of the magnetic field, this multipolar structure makes it possible to lengthen the total travel without degrading the precision. Absolute position measurement remains possible via the use of M magneto-sensitive probes or of a magneto-sensitive probe associated with a magnetic tachometer element with, in both cases, signals which will be post-processed to reconstruct an absolute position.

Axial flux rotary sensor FIG. 9 represents a view of the magnetic structure (1) and of the magneto-sensitive probe (30) for a rotary sensor with axial detection according to the invention. It consists of a permanent magnet (10), magnetized in a constant direction and amplitude of the magnetic field, and oriented in a direction included in the XY plane perpendicular to the direction X (11) of relative movement of the permanent magnet (10) compared to a magneto-sensitive probe. In the rotary sensor versions with axial detection, the preferred magnetization direction of the permanent magnet (10) is in the Z direction (13) so as to maximize the magnetic flux collected by the magneto-sensitive probe (30) in this direction.

The support (20) is formed for example of a piece obtained by sintering ring-shaped powder having a notch to receive the permanent magnet (10) by plastic injection or gluing for examples. Said support (20) is extended axially by two pole shoes (21, 22), also called pole shoes, located on either side of the permanent magnet (10). The support (20) has a cylindrical passage (26) so as to be assembled on an axis (70), for example of a rotor, the angular position of which is to be detected, which provides a particularly advantageous solution when the device is intended to be mounted at the end of the axis, the magneto-sensitive probe (30) being able to be directly integrated into a fixed printed circuit.

Special realization of the rotary sensor

Figures 11 to 13 show an embodiment particularly well suited to industrial production and its integration into a mechatronic system.

FIG. 11 represents a particular configuration of a support (20) extended behind the pole shoes (21, 22), also called pole shoes, by an annular yoke in a stack of annular ferromagnetic sheets defining a cylindrical passage (26 ) facilitating the mounting of the support (20) on a rotary axis causing the angular displacement of the permanent magnet (10) relative to a fixed magneto-sensitive probe. The two pole shoes (21, 22) delimit a housing (23) for the overmoulding injection of the permanent magnet (10).

Said permanent magnet (10) is an injected isotropic magnet, the injection point (16) of which is located axially to avoid having an injection residue in radial excess on the outer diameter (and thus limit the risk of contact with the nearby printed circuit). The magnet has tapers of 0.5° to 1° max to facilitate demoulding, except in the thickness zone of the sheet pack (2.5mm) where the edges of the magnet are straight / cylindrical, the joint plane of the mold is coplanar with one of the 2 faces of the stack of sheets. The injection of the magnet is however not limiting of the invention and any other type of magnet and its means of connection to the iron poles are envisaged, such as for example the overmoulding of a compressed magnet.

More particularly, the unipolar magnet is made by overmolding the support (20). A PPS-NdFeB material having good mechanical temperature resistance with high magnetic performance (Br, Hcb) is used: a high switching threshold (>70G) and a steep slope are thus obtained for clean and well-controlled switching. The metal support also has a specific shape to radially lock the overmolded magnet. The choice of the stack of laminations as a support makes it possible to magnetize the magnet after overmolding without significant effect of the residual magnetization in the laminations (very low coercive field) on the switchings and therefore the precision of the targeted stroke.

To limit sensitivity to external disturbances and to assembly tolerances, the magnet has a thickness in the axial direction greater than the thickness of the stack of sheets, typically 7mm for 2.5mm of iron, i.e. a ratio greater than 2:1, this not being limiting of the invention. Nominally, the axial median plane of the magnet and of the stack of laminations is coplanar with the sensitive element of the probe.

A variant of a rotary sensor with axial flux, as represented in FIG. 10, consists in multiplying N magnetized structures distributed regularly, or not, over 360°. Associated with a magneto-sensitive probe directly measuring the magnetic angle or the components of the magnetic field, this multipolar ring makes it possible to produce a magnetic encoder to, for example, drive an electric motor in vector mode.

As shown in FIG. 12, the ferromagnetic support (20) of the sensor can be produced by using the scrap material at the center of the stack of stator laminations (40) of the electric motor integrated in the actuator. This solution is very economical (recovery of offcuts, no surface treatment to be applied...) and it also and above all makes it possible to have very precise manufacturing tolerances without re-machining for the press fit of the support (20) on the axis and for the shape of the two pole shoes (21, 22).

Mechatronic assembly according to the invention

[0081] Figure 13 shows a partial sectional view of an actuator equipped with a sensor according to the invention. The support (20) is embedded on the axis (70) output of a rotary actuator. It drives the permanent magnet (10) which rotates to temporarily position itself opposite the magneto-sensitive probe (30) mounted on a fixed printed circuit (31). The realization presents a great simplicity of manufacture and assembly, a very low cost, and a great robustness in endurance-vibration-temperature and also a "precision" below the specified ±2° (of the order of ±0.50 °)

[0082] The sheet metal package is tightly fitted on the output shaft of the actuator, it is stopped axially on a shoulder (27) and does not need to be angularly indexed (360° actuator). The shoulder (27) also makes it possible to limit the swiveling of the support (20) (short adjustment: 2.5mm thick for 09.8) on the axis by guaranteeing orthogonality between the median plane of the magnet and the axis rotation. The low mass of the sensor assembly (5g) makes it possible to estimate that under 28.9Grms of vibrational disturbances (i.e. 28.9 x 3 x V2 = 122G), the assembly will only undergo 6N of acceleration. Relative to the driving forces which can vary from 250N to 1250N, the safety margin of the maintenance is very good.

The cutout (26) is engaged on the axis of a member whose angular position is to be measured, for example the axis (70) of an actuator, for a mechatronic assembly.

The axis on which the support (20) is mounted is carried by 2 ball bearings, the upper bearing being guided in the cover, the lower bearing close to the sensor assembly being guided by the housing, the PCB bearing the hall probe being fixed on the housing. Thus, the reading radius is precise thanks to a chain of dimensions with few links and thanks to easily controllable nominal dimensions (aluminum machining, bearing seat, axle seat, stamped sheet metal package, overmoulding of the magnet).

Such a structure makes it possible to reduce the magnet volume to 171 mm3, ie a reduction of more than 25% compared to a structure consisting solely of magnets.

Claims

1 - Magnetic position sensor comprising:

• a magnetized structure (1), provided with a permanent magnet (10) producing a magnetic field and with a support (20) of soft ferromagnetic material in which the magnet (10) is embedded, said support (20) having two pole shoes (21, 22) located on either side of said magnet (10),

• at least one magneto-sensitive element (30) which can be moved relative to said magnet (10) along a measurement trajectory (2), characterized in that said magnet (10) and said two pole shoes (21 , 22) respectively have a front surface (15, 24, 25) all of which are located opposite the at least one magneto-sensitive element (30) during movement along the measurement path (2), and in this that, during movement along the measurement trajectory (2), the front surfaces (15, 24, 25) are successively opposite the sensitive element (30) and in that the ratio between: the minimum distance between the front surface (15) of the magnet (10) and the center of the magneto-sensitive element (30) and the minimum distance between one or other of the front surfaces (24, 25) of the pole shoes (21, 22) and the center of the magneto-sensitive element (30) is between 0.7 and 1.3.

2 - magnetic position sensor according to claim 1 characterized in that during movement along the trajectory (2) measurement, the end surfaces (15, 24, 25) are successively vis-à-vis the sensitive element (30) and in that the minimum distance between a front surface (15, 24, 25) facing the magneto-sensitive element (30) and the center of the magneto-sensitive element (30 ), presents variations lower than 50% compared to its average value. 3 - magnetic position sensor according to claim 1 characterized in that the ratios between: on the one hand, the minimum distance between the front surface (15) of the magnet and the at least one magneto-sensitive element (30) , when moving along the measurement trajectory (2), and on the other hand, the minimum distance between one or the other of the end surfaces (24, 25) of the pole shoes (21, 22) and the other at least one magneto-sensitive element (30), during movement along the measurement trajectory (2), are both between 0.7 and 1.3.

4 - magnetic position sensor according to claim 2 characterized in that the ratios are both between 0.9 and 1.1.

5 - magnetic position sensor according to claim 1 characterized in that recesses (34, 35) are formed between the pole shoes (21, 22) and the magnet (10) such that the end surfaces (15, 24, 25 ) are not contiguous.

6 - magnetic position sensor according to claim 1 characterized in that the measurement path (2) is located in a plane and in that along the direction orthogonal to this plane, the thickness of the pole shoes (21, 22) is less than the thickness of the magnet (10).

7 - magnetic position sensor according to claim 1 characterized in that the sum of the lengths of the front surfaces (24, 25) of the pole shoes (21, 22) along the measurement path is greater than or equal to the length of the front surface (15) of the magnet (10).

8 - magnetic position sensor according to claim 1 characterized in that the length of the front surfaces (24, 25) of each of the pole shoes (21, 22) along the measurement path is greater than or equal to that of the front surface ( 15) of the magnet (10). 9 - magnetic position sensor according to claim 1 characterized in that the magnetization of said magnet (10) has a direction (14) of single magnetization, or unidirectional magnetization.

10 - magnetic position sensor according to claim 2 characterized in that the magnetization of said magnet (10) is diametrical.

11 - Magnetic position sensor according to one of the preceding claims, characterized in that the magnetization of said magnet (10) has a magnetization whose intensity varies continuously according to the path of movement.

12 - magnetic position sensor according to claim 1 characterized in that the magnetization of said magnet (10) has a direction (14) of magnetization which varies continuously according to the path of movement.

13 - Magnetic position sensor according to claim 1 characterized in that said magneto-sensitive element is a probe for direct measurement of the magnetic angle or indirect via the measurement of the magnetic components constituting a sensor with absolute output as a function of the mechanical position .

14 - magnetic position sensor according to at least one of claims 1 to 8 characterized in that the relative movement of said permanent magnet (10) relative to said magneto-sensitive element (30) is linear.

15 - Magnetic position sensor according to at least one of claims 1 to 8 characterized in that the relative movement of said permanent magnet (10) relative to said magneto-sensitive element (30) is rotary. 16 - magnetic position sensor according to claim 1 characterized in that the magneto-sensitive probe is a magnetic switch, the position sensor having invariant switching positions depending on the air gap.

17 - magnetic position sensor according to the preceding claim characterized in that the magnetic switch measures a component of the magnetic field and in that the switching threshold is programmed.

18 - Magnetic position sensor according to one of claims 1 to 10 characterized in that the magneto-sensitive probe reconstructs the analog position information from the components of the magnetic field collinear with the displacement and in a direction orthogonal to said relative displacement.

19 - Magnetic position sensor according to one of claims 1 to 10 characterized in that the magneto-sensitive probe reconstructs the analog position information from the component of the magnetic field collinear with the direction of magnetization.

20 - Mechatronic assembly comprising an actuator formed by a stator consisting of an assembly of ferromagnetic sheets defining teeth of which at least part is surrounded by a coil, and a position sensor according to the preceding claim characterized in that the outer contour of the sheets of said support (20) made of ferromagnetic material of the sensor is contained in the inner contour of the sheets of said stator of the actuator.