FR2688586A1 - Position sensor and application to measuring the angle of the throttle of a carburettor - Google Patents

Abstract

The invention relates to an angular position sensor (400) including a first magnetic armature (410) carrying at least two windings, namely a primary winding (430) and at least one secondary winding (440), and a second magnetic armature (420), placed in front of the first (410) and capable of moving in rotation about a measurement axis (M) with respect thereto, the two armatures (410) and (420) including two pairs of first and second concentric surfaces (414a, 422, 424, 416) arranged opposite to form two air gaps (418, 415), the said surfaces being centred on the measurement axis (M), wherein each of the pairs of opposite concentric surfaces includes a first surface (414a, 424) extending over an angular sector at least equal to the angular extent of the second surface (422, 416) opposite, plus an angle corresponding to the desired measurement range, with a view to having air gaps (418, 415) of constant reluctance for any relative angular displacement of the armatures (410, 420) in the measurement range.

Description

 The present invention relates to the field of position sensors by variation of mutual inductance in a variable magnetic circuit.

 The invention relates more particularly, but not exclusively, to the application of such a sensor to the automotive environment, in particular for measuring the angle of the throttle valve of a carburetor.

 The trend in modern motor vehicles is more and more to electronically control the functioning of mechanical organs. We therefore seek to have reliable electrical sensors to track their movement.

 Resistive track sensors have long been used for this purpose. However, such sensors have contacts which wear out and resist poorly the temperature, humidity and vibration constraints encountered in the automotive environment.

 It is therefore preferred to use sensors without contact between the moving parts.

 Among these, sensors with mutual induction variation, the general principle of which has been known for a long time, offer great reliability of use.

 Thus, document FR-A-1 007 554 describes an angular sensor comprising a first magnetic armature carrying at least two windings, including a primary winding and at least one secondary winding, and a second magnetic armature, placed opposite the first and able to move in rotation around a measurement axis relative to the first frame.

 However, the performance of known sensors is limited as to the linearity, as a function of the angular displacement of the armatures, of the amplitude of the signal produced by the secondary winding when the primary winding is supplied with current; the maximum angular displacement giving good accuracy on a sensor of the prior art as described in document FR-A-1 007 554 is limited to an angle of approximately 15 degrees on each side of a neutral position. Beyond this, the non-linearity of the sensor leads to a significant loss of precision.

 More recently, document EP-A-0 319 826 has proposed an alternative embodiment of a position sensor comprising a first frame having the general shape of a "Y", comprising a primary winding carried by the trunk and a secondary winding carried by one of the branches, as well as a second magnetic armature, placed opposite the first and able to move in rotation about a measurement axis relative to the first armature, the two armatures comprising two pairs of surfaces concentric arranged opposite to form two air gaps, said surfaces being centered on the measurement axis.

 A sensor of this type does not however offer entirely satisfaction, in particular as regards the linearity of the signal delivered by the sensor for angular displacements greater than about twenty degrees on either side of a neutral position.

 For certain applications, such as the measurement of the angle of the throttle valve of a carburetor, it is necessary to have a simple, reliable, economical sensor, allowing precise measurement over a large angular displacement on either side of a reference position. Such a sensor must naturally be insensitive to strong electromagnetic disturbances in the automotive environment.

 The object of the invention is to propose an improved position sensor capable of meeting these requirements and overcoming the drawbacks of the sensors proposed in the prior art.

 The invention achieves this object thanks to an angular position sensor comprising a first and a second magnetic armature, the second armature being placed opposite the first and able to move in rotation around a measurement axis relative to that -this, the two armatures carrying at least two windings, including a primary winding and at least one secondary winding, and comprising two pairs of first and second concentric surfaces arranged opposite to form two air gaps, said concentric surfaces being centered on the axis of measurement. I1 is characterized in that each of the pairs of concentric facing surfaces comprises a first surface extending over an angular sector at least equal to the angular extent of the second facing surface, increased by an angle corresponding to a domain of desired measurement, in order to have air gaps of constant reluctance for any relative angular displacement of the reinforcements in the measurement range.

 According to an advantageous characteristic of the invention, the sensor comprises on the two armatures two elements forming poles, centered on the measurement axis, each placed opposite a concentric surface of the other armature to form a constant reluctance air gap , at least one of said pole-forming elements being traversed, when the primary winding is supplied, by magnetic field lines over an angular sector of its periphery greater than the angular extent of the concentric surface of the facing armature.

 In one embodiment of the invention, the first armature comprises a branch and a trunk connected to each other by an end centered on the measuring axis, arranged radially, the trunk carrying a primary winding and the branch carrying a secondary winding, each extending at its free end by a pole element, centered on the measurement axis.

 Advantageously, at least one of said pole-forming elements is connected to the branch or the trunk which carries it at one end of its periphery.

 Preferably, the sensor comprises two secondary windings, carried by the first frame.

 In a preferred embodiment, the first armature comprises a closed magnetic circuit, passing through each secondary winding along its axis.

 Advantageously, the axes of the two secondary windings are coplanar and contained in a median plane.

 Advantageously, the axes of the two secondary windings are arranged symmetrically with respect to a plane containing the axis of the primary winding.

 Preferably, the axis of the primary winding is contained in the median plane containing the axes of the two secondary windings.

 It will be preferred, in all embodiments, that the second armature be movable around the measurement axis to form a rotor and that the first armature is fixed to form a stator.

 In a preferred embodiment, the first frame has the general shape of a "Y", comprising two branches arranged in a "V" shape and a trunk connecting at the junction of the branches, the trunk carrying the primary winding and the at least one of the two branches carrying a secondary winding, the branches being connected together by an element in the form of an arc of a circle, forming a pole, centered on the measurement axis, to form a closed magnetic circuit passing through at least l 'one of the secondary windings along its axis.

 Preferably then, the trunk has at its free end a cylindrical surface centered on the measurement axis.

 Advantageously, the two branches are arranged symmetrically with respect to a plane containing the axis of the trunk.

 Preferably, the second frame comprises a pole-forming element, of essentially annular shape with symmetry of revolution, centered on the measurement axis and placed opposite the cylindrical surface of the free end of the trunk of the first frame to form a first constant reluctance air gap, said element of essentially annular shape comprising on a limited angular sector of its periphery a boss projecting radially towards the measurement axis and disposed opposite the first frame to form a second constant reluctance air gap.

 In another preferred embodiment, the first armature comprises two end branches connected by a base, each carrying a secondary winding, and a pole-forming element, in the form of a semicircle, centered on the measurement axis, connecting the two extreme branches to form a closed magnetic circuit crossing each secondary winding along its axis.

 Preferably, the first frame further comprises a central branch connected to said base and carrying the primary winding.

 Then, preferably, the central branch has at its free end a cylindrical surface centered on the measurement axis.

 Advantageously, the end branches are parallel to each other and arranged symmetrically with respect to a plane containing the axis of the central branch.

 Advantageously, the second frame comprises a first cylindrical surface centered on the measurement axis, placed opposite the cylindrical surface of the central branch, and a second cylindrical surface, centered on the measurement axis, placed opposite the semicircular element of the first armature. Preferably, the second armature comprises a cylinder-shaped element whose surface forms said first cylindrical surface, placed opposite the cylindrical surface of the free end of the central branch to form a first constant reluctance air gap, the cylinder-shaped element being extended radially by a straight branch ending in said second cylindrical surface centered on the measurement axis, placed opposite the semicircular element of the first armature to form a second air gap of constant reluctance.

 In a variant of this embodiment of the invention, the axis of the primary winding is coaxial with the measurement axis. Then, preferably, the primary winding is carried by the first armature, and the base comprises a bore centered on the measurement axis and emerging opposite the primary winding.

 In this alternative embodiment, the second frame comprises a cylindrical shaft passing through the primary winding along its axis and the bore to define a first air gap of constant reluctance, said shaft being extended radially by a cursor disposed opposite the element in the form of semicircle to define a second air gap of constant reluctance.

 Preferably, the primary winding is supplied by a voltage source varying periodically over time.

Advantageously, the sensor further comprises a device for processing the signal delivered by the secondary windings comprising
a selection circuit for selecting as input one or the other of the
secondary windings,
an amplifier, of variable gain, to modify the amplitude of the signal
from the selected winding,
a memory stage to keep the peak voltage in reference
delivered by the variable gain amplifier,
a signal comparator between the voltage kept as reference by the stage
memory and the voltage delivered by the gain amplifier
variable,
a control unit able to switch the selection circuit so
apply the signal from a secondary winding to the amplifier after
storage in reference of the signal from the other secondary winding,
and controlling the gain of the variable gain amplifier accordingly
a signal from the comparator, in order to deliver a representative signal
the relative angular displacement of the two reinforcements.

 Advantageously, the sensor is used to measure the angle of the throttle valve of a carburetor.

Other characteristics and advantages of the invention will appear on reading the following description of embodiments of the invention, given by way of non-limiting examples, and on examining the appended drawing in which - the Figure 1 is a schematic plan view of a sensor according to art
previous, - Figure 2 shows the evolution of the magnetic flux passing through the winding
secondary when the primary is supplied, depending on the displacement
relative angularity of the reinforcements in a sensor according to the prior art,
according to that shown in Figure 1, - Figure 3 is a schematic sectional view taken in a median plane
of a first embodiment of the invention, - Figure 3A is a schematic sectional view taken in a median plane
of a variant of the first embodiment of the invention, - Figure 3B is a schematic sectional view taken in a median plane
of another variant of the first embodiment of the invention, - Figure 4 shows the distribution of the field lines in a sensor
according to the prior art according to Figure 1, - Figure 4A illustrates the electrical equivalence of the magnetic circuit of
sensor according to the prior art according to Figure 4, - Figure 5 shows the distribution of field lines in a sensor
according to the embodiment of Figure 3, - Figure 5A illustrates the electrical equivalence of the magnetic circuit of
sensor according to Figure 5, - Figure 6 is a schematic sectional view taken in a median plane
of a second embodiment of the invention, - Figure 7 shows the evolution of the difference in the voltages collected
by the secondary windings when the primary winding is supplied,
as a function of the angular displacement x of the reinforcements in a sensor
in accordance with the second embodiment of the invention shown in
Figure 6, - Figure 8 is a schematic perspective view of a variant of
realization of a sensor according to the second embodiment of
the invention, - Figure 8A is a side view of the embodiment shown in the
Figure 8, - Figure 9 is a diagram of an electronic circuit adapted to deliver
a signal representative of the angular positioning, - Figure 9A illustrates a detail of an alternative embodiment of the circuit
electronic, - Figure 9B is an exemplary embodiment of a gain amplifier
variable.

 FIG. 1 shows a position sensor in accordance with document EP-A-0 319 826. This sensor comprises a first frame 10 having the general shape of a Y, comprising a trunk 13 and two branches 17 and 19, the trunk 13 being provided with a primary winding 30 supplied and the branch 19 being provided with a secondary winding 40. A second frame 20, of annular shape, is capable of relative rotation around the first frame 10, so as to cause a variation of reluctance in the magnetic circuit.

 In such a structure according to the prior art, the trunk 13 is widened at its free end to form a bloom 14 facing the frame 20 and define a first air gap 15. The second frame 20 is provided on its internal periphery with a boss 21 projecting radially with respect thereto. The two branches 17 and 19 are respectively provided at their free end with openings 11 and 12, which are disjoint and at least one of which is capable of coming opposite the free edge 22 of the boss 21 to define a second air gap 18. The edge free 22 and flourishing 12 extend over substantially equal angular sectors and have a facing surface which depends on the relative rotation of the armatures, so that the reluctance of the air gap 18 varies according to the angle of relative rotation of the reinforcements.

 When the reluctance of the air gap is minimal, the free edge 22 and the opening 12 are arranged exactly opposite one another. The flux collected by the secondary winding 40 is then maximum.

 When the free edge 22 and the opening 12 are offset as much as possible relative to one another, the reluctance of the air gap 18 is maximum and the flux collected by the secondary winding 40 is minimal.

 This is illustrated in FIG. 2, in which the shape of the magnetic flux collected by the secondary winding 40 is shown on the ordinate as a function of the angular displacement, given on the abscissa, of the second armature relative to the first. , from a reference position for which the magnetic flux generated by the primary winding and passing through the secondary winding is minimal.

 It will be noted on examining this figure, that the flux evolves in a linear fashion up to an angular displacement of approximately 20 relative to the reference position. When the angular displacement exceeds this value, the evolution is no longer linear.

 There is shown in Figure 3, a heart-shaped position sensor to a first embodiment of the invention. This sensor is referenced as a whole 200. The sensor 200 comprises a first magnetic armature 210, carrying a primary winding 230, and two secondary windings 240 and 250. A second magnetic armature 220 is placed opposite the first, and can move in relative rotation about a measurement axis referenced M. In a preferred embodiment, the axes of the coils 230, 240 and 250, respectively referenced 231, 241 and 251, are coplanar in a median plane, perpendicular to the measurement axis M, and corresponding to the section plane of FIG. 3.

 Preferably, these three axes meet on the measurement axis M.

 Preferably, the first frame 210 is mounted fixed around the measurement axis M to form a stator and the second frame 220 is mounted movable around this axis to form a rotor. The opposite situation is of course possible without departing from the scope of the invention.

 The first frame 210 has the general shape of a Y, comprising two branches 211, 213 and a trunk 212 connecting at the junction of the branches, centered on the measurement axis M. Preferably, the branches 211, 213 make an angle between them between 90 "and 1200, and the angle B between a branch 211, 213 and the axis of the trunk 212 is advantageously between 45" and 600. The trunk 212, straight, carries the primary winding 230. The branches 211 and 213, which are also rectilinear respectively carry the coils 250 and 240. According to an advantageous characteristic of the invention, the branches 211 and 213 are connected, as shown, at their free end opposite the measurement axis M by an element in the form of an arc of a circle 214, forming a pole and centered on the measurement axis M. Let R1 be the outside radius of this element 214.

 The element 214 extends beyond the angular sector corresponding to the spacing of the branches 211 and 213, to form openings 219a and 219b. The openings 219a and 219b each extend over approximately 150, symmetrically with respect to the axis 231 of the trunk 212. The branches 211 and 213 joined by the element 214 form a magnetic circuit closed on itself passing through the windings 240 and 250 along their axis.

 The trunk 212 is extended at its free end opposite the measurement axis M by a pole-forming element 217 comprising two openings 217a and 217b projecting transversely relative to the axis 231.

The element 217 has a radially external cylindrical surface 216 centered on the measurement axis M and of radius R2.

 The second frame 220, is composed by an element 224 of essentially annular shape centered on the measurement axis M, provided with an internal surface 223, cylindrical with radius R3, arranged opposite the frame 210. The element 224 is provided on a limited angular sector of its periphery, approximately 20, with a boss 221 projecting radially towards the measurement axis M and disposed opposite the element in the form of an arc of a circle 214 of the first frame.

 The cylindrical surface 216, of radius R2, and the internal surface 223 of the second frame 220 define a first air gap 215, of constant thickness e2 equal to R3 - R2. Likewise, the radially internal free surface 222 of the boss 221, of radius R4, placed opposite the element 214 of the first frame 210, and the radially external surface 214a of the element 214 placed opposite the boss 221, define a second air gap 218 of constant thickness el equal to R4 - R1.

 In accordance with an advantageous characteristic of the invention, the internal surface 223 extends as shown over an angular sector greater than the angular extent of the cylindrical surface 216, increased by the maximum desired measurement angle (approximately 40 of on either side of a reference position in the embodiment described in FIG. 3), and the same is true for the element 214 which extends angularly over an angle (approximately 100 "in FIG. 3 ) corresponding to the angular extent of the radially internal free surface 222 (approximately 20 in FIG. 3) increased by the maximum desired measurement angle (approximately 80 "in FIG. 3).

 FIG. 4 represents the distribution of the magnetic field lines L in a sensor according to the prior art, as previously described with reference to FIG. 1.

 FIG. 5 represents the distribution of the magnetic field lines L in a sensor according to the invention, in accordance with the embodiment of FIG. 3.

 In accordance with a characteristic of the invention, and as can be seen on examining FIG. 5, the element in the shape of an arc of a circle 214 and the element of essentially annular shape 224 are traversed, when the winding primary is supplied by magnetic field lines on an angular sector of their periphery greater than the angular extent of the surfaces 222 and 216, respectively opposite the surfaces 214a and 223 of the elements 214 and 224.

 FIGS. 4A and 5A show electrical equivalents to the magnetic circuits of the sensors respectively represented in FIGS. 4 and 5.

 Indeed, it is customary for those skilled in the art to refer to electrical equivalents in the analysis of a magnetic circuit. According to such an equivalence, the current, the electrical resistance and the electromotive force are respectively analogous to the magnetic flux, to the reluctance and to the magnetomotor force.

In FIG. 4A, reference has been made to R117, Rt19, Ri13, R115,
R118 the electrical equivalents of the respective reluctances of the branches 17 and 19, of the trunk 13 and of the air gaps 15 and 18, visible in FIG. 4.

 The electrical equivalent of the reluctance of the portion 20a of the second frame 20 situated to the left of the air gap 15 and which is not likely to come opposite the opening 14 of the trunk 13 has also been designated by Rl20a. the first frame.

 Likewise, R120b denotes the electrical equivalent of the reluctance of the portion 20b of the second frame 20, located to the right of the air gap 15, and which is not likely to come opposite the opening 14.

 The electrical equivalent of the reluctance of the portion of second armature 20 likely to be located opposite the opening 14 has been referenced by R120.

 The electrical equivalent of the reluctance of the air gap 1 la between the opening 1 1 and the facing surface 20c of the frame 20 has been referenced R11.

 The primary winding 30, when supplied, behaves in electrical equivalents like an electromotive force generator referenced E30 in FIG. 4A.

 Similarly, the currents F17 and F19 correspond to the magnetic fluxes in the branches 17 and 19.

 The electrical resistances R110, R119, Rl13, R120a, R120b, refer to reluctances of magnetic materials of high magnetic permeability and are negligible compared to resistors R1Ila 'R118, RI15, which refer to reluctances of air gap formed in the air with low magnetic permeability.

 Since the air thickness between the opening 11 and the facing surface 20c of the frame 20 is large compared to the air thickness of the air gaps 15 and 18, with equal surfaces, the reluctance of the 'air gap lla is very large vis-à-vis the reluctances of air gaps 15 and 18, and we can therefore consider the resistance Ralla as infinite in the electrical circuit of Figure 4A. I1 follows that the electric current and by equivalence the magnetic flux in the branch 17 is almost zero.

 When the branch 19 is angularly offset with respect to the boss 21, the surface facing the opening 12 and the boss 21 decreases, so that the reluctance of the air gap 18 increases. The flow in the branch 19 decreases from the maximum value reached when the opening 12 and the boss 21 are opposite one another.

 The variation in electric current in resistors R120a and R120b, equivalent to a variation in length of magnetic element on either side of the air gap 15 is negligible compared to the variation in electric current resulting from the. variation of resistance R118. R118.

 The principle implemented by such a sensor of the prior art is therefore essentially a variation in reluctance of an air gap.

 The electrical diagram equivalent to a sensor according to the invention, shown in Figure 5 is drawn in Figure 5A. RI214, RI211, R1213 R1212 'RI215, RI218 are respectively referenced by the electrical equivalents of the reluctances of element 214, branches 211 and 213, the central trunk 212, and air gaps 215 and 218.

 The resistors R1220a and R1220b correspond to the reluctances of the parts 220a and 220b of the armature 220 located respectively to the left and to the right of the air gap 215, and which are not likely to come opposite the cylindrical surface 216. We have referenced R1220 the resistance equivalent to the reluctance of the part of the armature 220 situated between the parts 220a and 220b, and intended to come opposite the surface 216. The primary winding 230 is equivalent to an electromotive force generator referenced E230 on the Figure 5A.

 According to the invention, the air gaps 215 and 218 have a constant air thickness and therefore a constant reluctance. Under these conditions, the distribution of the magnetic flux in each of the branches 211 and 213 takes place in a manner analogous to the distribution of the electric current in the branches 211 and 213 of the electric circuit of FIG. 5A, according to the position that the boss 221 with respect to element 214, similarly to the movement of the cursor of a potentiometer on a resistive track.

 It can be seen, on a comparative examination of FIGS. 4A and 5A, that the operation of a sensor according to the invention is fundamentally different from the operation of a sensor according to the prior art.

 In fact, in a sensor according to the prior art, a variation in air gap reluctance is implemented, while in the invention a variation in the length of magnetic element traversed by the magnetic field lines is implemented.

 In an alternative embodiment, it can be proposed to delete one of the branches 211 or 213 of the sensor according to FIG. 3 without departing from the scope of the invention.

 Indeed, such a variant, shown in FIG. 3A, has two air gaps 215 and 218 of constant reluctance.

 Advantageously, the section of the element in the form of an arc of a circle 214 will be thin, in order to have the greatest possible reluctance variation as a function of the length of the magnetic path of the field lines in this element.

 It is also possible, advantageously, to reduce the section of the essentially annular element 224 of the first frame, so as to have a greater variation in reluctance as a function of the angular displacement of the frames.

As a variant, it is possible to propose having a first and a second armature symmetrical with respect to the measurement axis M, in accordance with what is shown in FIG. 3B. In this case, two bosses 221 are provided which radially project towards the measurement axis.
Mr.

 There is shown in Figure 6 a sensor according to a second preferred embodiment of the invention, referenced as a whole by the index 400. In this second embodiment, the functional elements equivalent to those mentioned in the description of the first embodiment according to FIG. 3 will be referenced by an index simply increased by two hundred. Thus, the sensor 400 includes a first frame referenced 410 of magnetic material, and a second frame referenced 420 of magnetic material placed opposite the first and adapted to move in rotation around a measurement axis referenced M.

 The first frame 410 has the general shape of an E, comprising two extreme branches 411 and 413, connected by a base 410a perpendicular to the direction of the branches, and a straight central branch 412 perpendicular to the base 410a. The straight central branch 412 carries a primary winding 430. At least one of the extreme branches 411 or 413 carries a secondary winding. Preferably, the branch 411 carries a secondary winding 440 and the branch 413 carries a secondary winding 450. Preferably, the axes of the branches 411, 412, 413, correspond respectively to the axis 441 of the winding 440, to the axis 431 of coil 430 and axis 451 of coil 450.

 Preferably, the axes 441 and 451 are coplanar in the same median plane which corresponds to the section plane of FIG. 6. The axes 441 and 451 are advantageously arranged symmetrically with respect to a plane containing the axis 431 and perpendicular to the plane of section of FIG. 6. Preferably the axis 431 is also contained in the median plane of the windings 440 and 450.

 The first frame 410 further comprises a semicircular element 414 centered on the measurement axis M and connecting the two branches 411 and 413 to form an uninterrupted magnetic circuit passing through the windings 440 and 450 along their axis. The element 414 may have come in formation or attached to the branches 411 and 413 at their free end 4110 and 4130. In the embodiment of FIG. 6, the measurement axis M is intersecting the axis 431 and perpendicular in the median plane containing the axis of the windings. The second frame 420, movable relative to the first around the axis M, comprises a cylindrical element 424 of radius R30 centered on the measurement axis M and placed opposite the surface 416 also cylindrical of radius R10 of the branch central 412. The cylindrical element 424 is extended over a limited sector of its periphery, typically 50 by a rectilinear radial branch 421 terminated by a cylindrical surface 422, centered on the measurement axis M of radius R40, and placed opposite the element in the form of a semicircle 414, of radius R20 of the first frame 410.

 The second frame 420 is shown in dotted lines in a position corresponding to an angular displacement of an angle x with respect to a reference position, where the axis of the straight branch 421 is aligned with the axis 431.

 The cylindrical surface 422 and the internal surface 414a of the element in the shape of a semicircle 414 placed opposite it define a first air gap 418 of thickness e10 equal to R20 - R40. Similarly, the cylindrical surface 416 of the free end of the central branch 412 and the surface of the cylindrical element 424 placed opposite the latter define a second air gap 415, of thickness e20 equal to Rlo - R30.

 In an alternative embodiment, not described, it can be proposed to have R30 equal to R40.

 The variation of the difference of the voltages V1 and V2 collected on the secondary windings 440 and 450 when the primary winding 430 is supplied by an alternating current source is represented in FIG. 7. On examination of this figure, one notes a very good linearity of the difference V1-V2 (represented on the ordinate) as a function of the relative angular displacement x of the reinforcements (given on the abscissa), up to values close to 50 ". This remarkable linearity obtained thanks to a device according to the invention allows an easier exploitation of the signal delivered by the secondary windings as well as an improved precision compared to a sensor according to the prior art, as the person skilled in the art can easily be convinced from the comparative examination of the figures 2 and 7.

 In an alternative embodiment of the invention, the measurement axis M can no longer be perpendicular to the median plane containing the axes 441, 451 and 431 of the windings, but coaxial with the axis 431. We have shown in Figures 8 and 8A, schematically, a sensor 600 according to this variant embodiment. The sensor 600 comprises functional elements equivalent to the constituent elements of the embodiment previously described with reference to FIG. 6, which will be referenced by an index simply increased by two hundred and will not be described in more detail. In this figure, there is in particular a first armature made of magnetic material 610 and a second armature 620, adapted to move in rotation relative to the first around a measurement axis M.

 The first magnetic frame 610 carries two branches 611 and 613 connected at one end to a base 610a and at the other end to a semicircular element 614, centered on the measurement axis M. The branches 611 and 613 each carry a secondary winding 640 and 650.

The axes 641 and 651 of the windings 640 and 650 extend parallel to the measurement axis M.

A primary winding 630, with an axis parallel to the measurement axis
M, is fixed to the base 610a by means of a support 6301. The base 610a is provided with a circular bore 6305, centered on the measurement axis M, opening facing the interior space at the primary winding 630.

 The second frame 620 comprises a cylindrical shaft 624, passing through the primary winding 630 along its axis 631. The shaft 624 is immobilized axially at one end 6303 by a radial flange 6306. The shaft 624 exits at the opposite end 6302 by the bore 6305. A ring 6300, preferably bearing on one face of the base 610a, is provided for axially retaining the shaft 624 engaged in the winding 630 and the bore 6305. Preferably, the ring 6300 is detachably connected to tree 624.

 The shaft 624 and the bore 6305 have opposite concentric cylindrical surfaces which define a first air gap 615 of constant reluctance.

 The shaft 624 is extended radially at the end 6303 by a slider 621, which preferably comprises two blades made of magnetic material 621a and 621b.

 The blades 621a and 621b are connected at one end to the shaft 624 and are connected to each other at the opposite end 6310 so as to surround the element in the shape of a semicircle 614. A second reluctance gap 618 is thus defined constant.

 This alternative embodiment advantageously makes it possible to have a small footprint sensor.

 The armatures of a sensor according to the invention are advantageously covered with a non-magnetic material, capable of mechanically stiffening the armatures, not shown in the figures.

 This material is advantageously a plastic material. This improves the rigidity of the sensor, its mechanical resistance to vibrations, and air gaps are obtained with a constant thickness.

The primary winding P of the sensor C is connected to a generator
O delivering a current varying periodically over time. It is advantageously an alternating current of constant frequency and amplitude.

 As a function of the relative positioning of the armatures, and therefore of the flux passing through a secondary winding referenced S in FIG. 9, the latter has an induced voltage at its terminals.

 In the case of variant embodiments of FIGS. 3A and 3B, which have only one secondary winding, the flux collected on the secondary winding is directly representative of the angle of rotation of the sensor.

 In the case of other embodiments comprising two secondary windings, it is easy to propose electronic circuits known per se for processing the signal supplied by the sensor by difference of the voltages V1 and V2, induced on each secondary winding, which will not be described.

 One can also propose to calculate the angle of rotation of the sensor by measuring the ratio V1 / V2 or V2 / V1.

 Such a device for calculating the angle of rotation from the measurement of the ratio of the voltages V1 and V2 will now be described, with reference to FIGS. 9, 9A and 9B.

 A selection circuit 808 selects one of the voltages V1 or V2, according to a first signal 851 delivered to this circuit by a control unit 850.

 The selected voltage drives a unit gain differential amplifier 810. The output signal 811 from the differential amplifier 810 is sent to an amplifier 820 with variable gain G controlled by a second signal 852 from the control unit 850. The maximum gain G can be less than or equal to unity.

 In accordance with FIG. 9A, the amplifier 820 can be constituted by a network of resistors 821 arranged in series between the input voltage 822 and a reference voltage 823, a network of programmable switches 824 being disposed between each resistor 821 and an output signal connection 825. The network of switches 824 is controlled by a signal 852 coming from the control unit 850.

 In an alternative embodiment, in accordance with FIG. 9B, it could be proposed to connect each of the two secondary windings by an output terminal to form a common grounded point, and to connect the two other output terminals to a selector 8080 controlled by signal 851 from the control unit 850.

 The output signal of the amplifier 820 is applied to a rectifier stage 830. The rectifier stage 830 notably comprises a diode 831 in series to rectify the signal from the amplifier 820, applied to the anode of the diode 831 and a filtering capacitor 832, placed between the cathode of the diode 831 and the ground.

 At the output of the rectifier stage 830, the rectified and filtered signal 834 is applied to the input of a storage circuit which includes an electronic switch 844 and a capacitor 842. More specifically, the cathode of the diode 831 is connected by via switch 844 to a frame 8420 of capacitor 842 while the other frame is grounded.

 The armature 8420 of the capacitor 842 is connected to the inverting input of a comparator 840.

 An electronic switch 833, placed in bypass on the capacitor 832 and controlled by the control unit 850 makes it possible to discharge the capacitor 832 by closing.

 The cathode of diode 831 is also connected to the non-inverting input of comparator 840.

 To store the signal, the switch 844 is commanded to close by the control unit 850 and the signal 834 charges the capacitor 842 under a reference voltage V '. In the signal storage phase 834, the switch 844 is closed and the inverting and non-inverting inputs are at the same potential.

 When the switch 844 is controlled to open, the comparator 840 can compare the signal 834 and the reference voltage V ', to deliver a result signal 841 to the control unit 850.

 The operation of the device is as follows.

 The control unit 850 generates a first signal 851 which commands the selection circuit 808 to apply the voltage V1 to the input of the differential amplifier 810.

 The unit 850 also positions, by the second signal 852, the amplifier 820 on the maximum gain, the switch 833 in the open position and the switch 844 in the closed position.

 The amplified signal then rectified and filtered by the circuit 830 provides a reference voltage V'1 which is memorized by the capacitor 842.

Then the unit 850 controls the opening of the switch 844, closes for a few moments the switch 833 to discharge the capacitor 832, then switches the selection circuit 808 to the voltage
V2 from the second secondary winding, and decreases the gain G of the amplifier 820 until the comparator 840 switches, possibly resulting in a change of sign of the result signal 841 used by the control unit 850. If the comparator 840 toggles, the change of sign of the result signal takes place for a value of the gain G corresponding to the ratio of the voltages V1 / V2 = G.

 If the comparator does not switch when the gain is reduced to a minimum, it is that V2 is greater than V1 and then it suffices to repeat the previous operations by first selecting V2, then V1. In this case we obtain G = V2 / V1.

 To reset the circuit 800 between each series of measurement of the ratio V2 / V1 or V1 / V2, the control unit 850 closes for a few moments the electronic switch 833 and the switch 844 to discharge the capacitors 832 and 842.

 Those skilled in the art then easily deduce by calculation the angular displacement of the sensor C as a function of the ratio of the voltages V1 / V2 and one can provide an electronic circuit capable of performing this calculation automatically.

 The control unit 850 delivers to the user a signal 853 representative of the angular displacement of the sensor C.

 A sensor according to the invention is advantageously incorporated in a metal case serving as shielding against external electromagnetic disturbances.

 A sensor according to the invention has many advantages, in particular robustness, reliability and absence of wear, because the measurement is carried out without contact between the facing plates, and because of the simplicity of the devices for processing the signal delivered by this sensor that can be proposed.

 Such a sensor offers great precision for angular displacements which can reach more than 50 on either side of a neutral position.

 This sensor is therefore particularly well suited to measuring the angle of the throttle valve of a carburetor, rotated with large angular deviations or a level gauge.

 A sensor according to the invention is particularly resistant to external electromagnetic disturbances.

 By virtue of its qualities, the application of a sensor according to the invention is not limited to the automotive sector, but also covers all the sectors where it is advantageous to have robust and precise rotation sensors.

Claims (27)

 1 / Angular position sensor (200; 400; 600) comprising a first and a second magnetic armature, the second armature being placed opposite the first and able to move in rotation around a measurement axis (M) by relative to the latter, the two reinforcements carrying at least two windings, including a primary winding and at least one secondary winding, and comprising two pairs of first and second concentric surfaces arranged opposite to form two air gaps, said concentric surfaces being centered on the measurement axis (M), characterized in that each of the pairs of concentric facing surfaces comprises a first surface extending over an angular sector at least equal to the angular extent of the second facing surface, increased by an angle corresponding to a desired measurement range, in order to have air gaps of constant reluctance for any relative angular displacement of the reinforcements in the range of measured.  2 / sensor according to claim I, characterized in that it comprises on the two armatures two elements forming poles, centered on the measurement axis (M), each placed opposite a concentric surface of the other armature for forming an air gap of constant reluctance, at least one of said pole-forming elements being traversed, when the primary winding is supplied, by magnetic field lines over an angular sector of its periphery greater than the angular extent of the concentric surface of the armature opposite.  3 / sensor according to claim 1 or 2, characterized in that the first frame (210) comprises a branch (213) and a trunk (212) connected together by an end centered on the measurement axis (M), arranged radially, the trunk (212) carrying a primary winding (230) and the branch (213) carrying a secondary winding (240), the trunk (212) and the branch (213) each extending at its free end by an element ( 217, 214) forming a pole, centered on the measurement axis (M).  4 / A sensor according to claim 3, characterized in that at least one (214) of said pole-forming elements is connected to the branch (213) or the trunk (212) which carries it at one end of its periphery.  5 / A sensor according to claim 1 or 2, characterized in that it comprises two secondary windings (240, 250; 440, 450; 640, 650), carried by the first frame.  6 / sensor according to claim 5, characterized in that the first armature comprises a closed magnetic circuit (211, 213, 214; 410a, 411, 413, 414; 610a, 611, 613, 614), passing through each secondary winding (240 ; 440; 640) along its axis (241; 441; 641).  7 / A sensor according to claim 5 or 6, characterized in that the axes (241, 251; 441, 451; 641, 651) of the two secondary windings are coplanar and contained in a median plane.  8 / sensor according to one of claims 5 to 7, characterized in that the axes of the two secondary windings are arranged symmetrically with respect to a plane containing the axis of the primary winding (231 431; 631).  9 / A sensor according to claim 7 or 8, characterized in that the axis of the primary winding (231; 431; 631) is contained in the median plane containing the axes of the two secondary windings.  10 / sensor according to one of claims 1 to 9, characterized in that the second frame (220; 420; 620) is movable around the measurement axis to form a rotor and the first frame (210; 410; 610 ) is fixed to form a stator.  11 / Sensor according to one of claims 5 to 10, characterized in that the first frame (210) has the general shape of a "Y", comprising two branches (211, 213) arranged in "V" and a trunk (212) connecting at the junction of the branches, the trunk (212) carrying the primary winding (230) and at least one of the two branches (211, 213) carrying a secondary winding (240), the branches being interconnected by an element (214) - in the form of an arc of a circle, forming a pole, centered on the measurement axis (M), to form a closed magnetic circuit (211, 213, 214) crossing at least the one of the secondary windings (240) along its axis (241).  12 / A sensor according to claim 11, characterized in that the trunk (212) has at its free end a cylindrical surface centered on the measurement axis (M).  13 / A sensor according to claim 11 or 12, characterized in that the two branches (211, 213) are arranged symmetrically with respect to a plane containing the axis of the trunk.  14 / Sensor according to one of claims 11 to 13, characterized in that the second frame (220) comprises an element (224), forming a pole, of essentially annular shape with symmetry of revolution, centered on the measurement axis ( M) and placed opposite the cylindrical surface (216) of the free end of the trunk (212) of the first frame (210) to define a first air gap (215) of constant reluctance, said element (224) of essentially annular comprising on a limited angular sector of its periphery a boss (221) projecting radially towards the measurement axis (M) and disposed opposite the first frame (210) to form a second air gap (218) of constant reluctance.  15 / sensor according to one of claims 5 to 10, characterized in that the first armature (410; 610) comprises two extreme branches (411, 413; 611, 613) connected by a base (410a; 610a), each carrying a secondary winding (440, 450; 640, 650), and a pole-forming element, in the shape of a semicircle (414; 614) centered on the measurement axis (M), connecting the two branches (411, 413; 611, 613) extremes to form a closed magnetic circuit crossing the secondary windings (440, 450; 640, 650) along their axis (441, 451; 641, 651).  16 / sensor according to claim 15, characterized in that the first frame (410) comprises a central branch (412) connected to said base (410a) and carrying the primary winding (430).  17 / A sensor according to claim 16, characterized in that the central branch (412) has at its free end a cylindrical surface (416) centered on the measurement axis (M).  18 / A sensor according to claim 16 or 17, characterized in that the end branches (411, 413) are mutually parallel and arranged symmetrically with respect to a plane containing the axis (431) of the central branch (412).  19 / sensor according to claim 18, characterized in that the second frame (420) comprises a first cylindrical surface (424) centered on the measurement axis, placed opposite the cylindrical surface (416) of the central branch (412 ) and a second cylindrical surface (422), centered on the measurement axis (M) placed opposite the semicircular element (414) of the first frame (410).  20 / sensor according to claim 19, characterized in that the second frame (420) comprises a cylinder-shaped element (421), the surface of which forms said first cylindrical surface (424), placed opposite the cylindrical surface (416 ) from the free end of the central section (412) to form a first air gap (415) of constant reluctance, the cylinder-shaped element being extended radially by a straight branch (421) terminated by said second cylindrical surface (422 ), placed opposite the semicircular element (414) of the first frame (410) to form a second air gap (418) of constant reluctance.  21 / A sensor according to claim 15, characterized in that the axis of the primary winding (631) is coaxial with the measurement axis (M).  22 / sensor according to claim 21, characterized in that the primary winding (630) is carried by the first frame (610).  23 / A sensor according to claim 22, characterized in that the base (610a) comprises a bore (6305) centered on the measurement axis and emerging opposite the primary winding (630).  24 / A sensor according to claim 23, characterized in that the second frame comprises a cylindrical shaft (624) passing through the primary winding (630) along its axis (631) and the bore (6305) to define a first air gap (615) of constant reluctance, said shaft being extended radially by a cursor arranged opposite the element in the shape of a semicircle (614) to define a second gap of constant reluctance (618).  25 / sensor according to one of claims 1 to 24, characterized in that the primary winding (230; 430; 630) is supplied by a voltage source varying periodically over time.  26 / Sensor according to one of claims 5 to 25, characterized in that the sensor further comprises a device for processing the signal delivered by one of the two secondary windings (240, 250; 440, 450; 640, 650) comprising a selection circuit (808) for selecting one or the other as input  secondary windings (240, 250; 440, 450; 640, 650), an amplifier (820), of variable gain, to modify the amplitude of the  signal from the selected winding, a storage stage (830) to keep the voltage of reference  peak delivered by the variable gain amplifier (820), a signal comparator (840) between the voltage kept in reference by  the memory stage and the voltage delivered by the amplifier (820)  variable gain, a control unit (850) capable of switching the selection circuit  (808) in order to apply to the amplifier (820) the signal from a winding  secondary after storage in reference of the signal from the other  secondary winding and controlling the gain of the gain amplifier  variable (820) as a function of a signal from the comparator, in order to  deliver a signal representative of the relative angular displacement of the two  frames.  27 / A sensor according to one of claims 1 to 26, characterized in that it is used to measure the angle of the throttle valve of a carburetor.