CH712154B1 - Watchmaking magnetic escapement. - Google Patents

Abstract

The invention relates to a timepiece escapement mobile (1) comprising a magnetized track (10), with a succession of tracks according to a period of travel according to which its magnetic characteristics are repeated, each comprising a magnetic ramp with increasing field followed of a magnetic field barrier with increasing field of field gradient greater than that of the ramp, this track (10) comprises a magnetic layer (4) continuous and closed over the entire periphery of the exhaust mobile (1), d constant thickness and variable width, the geometry of which defines these magnetic field ramps and barriers. The invention also relates to a magnetic escapement mechanism (100) comprising such an escapement mobile (1) cooperating with a balance-spring by means of a pivoting magnetic retainer (2) comprising a polar mass (20) arranged to cooperate alternately with an internal track (11) and an external track (12) of the magnetic layer (4). The invention also relates to a resonator mechanism, a clockwork movement, as well as a watch comprising such a magnetic escapement mechanism (100).

Description

Description

FIELD OF THE INVENTION The invention relates to an escapement mobile for a magnetic timepiece escapement mechanism, comprising at least one magnetized track, with a succession of tracks according to a running period according to which its magnetic characteristics are repeat, each said range comprising a magnetic field ramp with increasing field followed by a magnetic field barrier with increasing field and whose field gradient is greater than that of said ramp.

The invention also relates to a clockwork magnetic escapement mechanism, comprising, subjected to an engine torque, such an escapement mobile cooperating indirectly with a balance-spring resonator by means of a stopper.

The invention also relates to a resonator mechanism, comprising a power source arranged to drive through a gear train said escape wheel of a said magnetic escape mechanism.

The invention also relates to a movement comprising at least one such resonator mechanism.

The invention also relates to a watch comprising at least one such movement.

The invention relates to the field of clockwork regulating mechanisms, and more particularly field effect escapement mechanisms, contactless or attenuated contact, of magnetic or electrostatic type.

BACKGROUND OF THE INVENTION In a Swiss anchor escapement, the escape wheel interacts with the anchor using a mechanical contact force, which generates significant friction and reduces the efficiency of the exhaust.

Patent application EP 13 199 427, published under the reference EP 2 887 157, in the name of THE SWATCH GROUP RESEARCH & DEVELOPMENT Ltd describes the replacement of this mechanical interaction by contactless forces of magnetic origin, or else electrostatic, which makes it possible, among other things, to minimize friction losses.

The practical realization of a magnetic anchor escapement requires varying the interaction energy according to ramps and barriers as described in the document above.

As regards the magnetic interaction between mobiles, the prior art mentions the use of discrete magnets interacting with other discrete magnets as for example in document US 3,183,426, or else discrete magnets interacting with an iron structure as in documents FR 2 075 383 and GB 671 360. The use of iron is justified by its ease of machining, which makes it possible to produce small structures which are repeated regularly over the circumference of a wheel. However, the magnet-magnet interaction is preferred when it comes to jogging the escapement wheel, since the energy required to stop the wheel is more important than for continuous systems. On the other hand, the use of discrete magnets does not easily make it possible to continuously vary the energy, in a soft and linear manner, to optimally produce ramps as described in the document EP 13 199 427 cited above. .

Claims (22)

Summary of the invention The invention proposes to design an exhaust mobile geometry, in particular an escape wheel, which makes it possible to create a potential for magnetic interaction composed of ramps and barriers. This wheel geometry must be achievable with current technologies for manufacturing micro-magnets. To this end, the invention relates to an escapement mobile for a clockwork magnetic escapement mechanism, according to claim 1. The invention also relates to a magnetic clockwork escapement mechanism, comprising, subjected to an engine torque, such an exhaust mobile cooperating indirectly with a balance-spring resonator by means of a stopper. The invention also relates to a resonator mechanism, comprising an energy source arranged to drive through a gear train said escape wheel of a said magnetic escapement mechanism. The invention also relates to a movement comprising at least one such resonator mechanism. The invention also relates to a watch comprising at least one such movement. Brief description of the drawings [0017] Other characteristics and advantages of the invention will appear on reading the detailed description which follows, with reference to the accompanying drawings, where: fig. 1 shows, schematically, and in plan, a magnetic escapement mechanism described in patent application EP 13 199 427, comprising an escapement wheel with magnetized tracks, internal and external, cooperating with a polar mass of a magnetic anchor; fig. 2 is a graph relating to the mechanism of FIG. 1, which shows the variation in magnetic interaction energy between the escape wheel and the polar mass of the magnetic anchor that this mechanism contains; fig. 3 shows, schematically, and in plan, a magnetic escapement wheel according to the invention, in cooperation with a magnetic anchor cooperating with a pendulum; fig. 4 shows, schematically, and in plan, the arrangement of this escapement wheel with a magnetic layer according to the invention; fig. 5, 7, 9 illustrate the representation in polar coordinates of the magnetic layer with respect to the axis of the escape wheel, with regard respectively to the potential ramp, the potential barrier, and the combination of the two; fig. 6, 8, 10 respectively illustrate the forms of ramps and corresponding associated barriers; fig. 11 shows, schematically, and in section, a wheel made up of two magnetized layers in order to cancel the axial forces by compensation, both in repulsion with the magnet of the anchor; fig. 12 represents, schematically, and in plan, an advantageous variant where the anchor comprises two polar masses arranged angularly to work alternately, in the extreme angular positions of the anchor, one with the inner track, the other with the outdoor track; fig. 13 represents, schematically, and in plan, narrowing of the magnetized track to optimize the linearity of the ramps of the magnetic interaction potential; fig. 14 shows, schematically, and in plan, a mechanical consolidation zone of the wheel, which includes a central ring connected by stiffening spokes to some of the barrier pads of the magnetic layer; fig. 15 represents, similarly to FIG. 11, the use of a ferromagnetic layer, in particular of iron, as a circuit or magnetic shielding of the wheel; fig. 16, 17, 18 show, similarly to FIGS. 5, 7 and 9, the modification of the profile by the integration of nonlinearities, in the form of cusps, so as to compensate for the nonlinearities of the magnetic interaction, and fig. 19 represents, schematically, and in plan, the corresponding wheel; fig. 20 shows, schematically, and in plan, a detail of an anti-shock device produced by mechanical stops on the wheel and on the anchor; fig. 21 shows, schematically, and in perspective, the assembly of a resonator mechanism, comprising, from a barrel, to the balance-spring, a gear train, and such a magnetic escapement mechanism with magnetic anchor; fig. 22 is a block diagram representing a watch comprising a movement equipped with a resonator mechanism with such an escapement mechanism with magnetic anchor; fig. 23 and 24 represent, in plan view and in perspective, a watch comprising such a magnetic escapement. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention relates to an escapement mobile 1 for a magnetic escapement mechanism 100 for watchmaking. This exhaust mobile 1 comprises at least one magnetized track 10, with a succession of tracks according to a scrolling period PD according to which its magnetic characteristics are repeated, each track comprising a magnetic ramp with increasing field followed by a barrier magnetic field with increasing field and whose field gradient is greater than that of the ramp which precedes it. According to the invention the magnetized track 10 comprises a continuous and closed magnetic track. More particularly, this magnetic track is a continuous and closed magnetic layer 4 around the entire periphery of the exhaust mobile 1. More particularly, this magnetic strip is of constant thickness and of variable width. In another particular embodiment, the variations in magnetic potential are generated by a variation in the thickness of the layer. More particularly, this magnetic track extends over a larger surface S of the exhaust mobile 1, and whose geometry in projection on this surface S defines the magnetic ramps and magnetic field barriers. In a particular case, the magnetized track 10 comprises a physical layer composed of discrete elements, not necessarily composed with magnets of simple geometry, but for example with curvilinear pieces, which can also compose a functional mechanism according to the invention. We can, again, obtain a magnetic stripe with a similar effect with a layer whose residual field is not constant. In practice, this can be done either by locally heating the magnetic layer to a controlled temperature, or by superimposing two different magnetic materials, for example SmCo and NdFeB, and by heating to a temperature neutralizing the remanent field of NdFeB without affecting the remanent field. of SmCo. It is understood that the variations in the magnetic field can be angular variations in the field, and that the variation in the gradient of the field between the ramp part and the barriers can also be a variation in the angular component of the field. In a particular embodiment, and as illustrated by the figures, the exhaust mobile 1 is an escape wheel, and comprises at least one ring or a disc or a hollowed out disc, one face of which carries the magnetized track 10, and, in a particular and nonlimiting manner, constitutes the largest surface S of the mobile 1. And the width of the magnetic layer 4 extends in the radial direction relative to the axis A1 of this disc. More particularly, the magnetized track 10 comprises, connected on either side of a border F, an internal track 11 and an external track 12 comprising magnetic field barriers staggered relative to the border F, in half-cycle alternation. In the case of an escape wheel, this border F is a circle G, concentric with the two tracks 11 and 12. More particularly, the magnetic escapement mechanism 100 for timepieces comprises, subjected to an engine torque, such an exhaust mobile 1 cooperating indirectly with a balance-spring balance resonator via a stopper 2, which is a pivoting magnetic retainer comprising at least one pole mass 20 arranged to cooperate alternately with the internal track 11 and the external track 12 of such a magnetic layer 4. [0030] FIG. 1 illustrates the principle of a magnetic escape mechanism 100, comprising an escape wheel 1 with magnetized tracks 10, internal 11 and external 12, separated by a circle G, cooperating with a polar mass 20 of a retainer, in particular a magnetic anchor 2, as described in the document EP 13 199 427 cited above. The magnetic interaction energy between the wheel 1 and the polar mass 20 of the anchor 2, in particular comprising at least one magnet, varies as shown in the graph in fig. 2 showing the PD period on each of the two tracks. The potential barriers 131, 132, indicated ++ in figs. 1 and 2 have the effect of stopping the advance of the wheel 1. The energy ramps which extend, on each of the internal and external tracks 11, from a region - to a region +, and which are seen by the polar mass 20 of the anchor 2 during the rotation of the escapement wheel 1, have the effect of accumulating energy, which is transmitted to a pin 30 of a pendulum 3 during the tilting of the 'anchor 2. The invention is here described in a particular, non-limiting mode, which is that of a magnetic escapement. It can be implemented in an electrostatic mode, with reference to the document EP 13 199 427 cited above. To constitute the ramps and the potential barriers, a first known solution consists in varying the thickness, or the intensity of magnetization, of magnets arranged on each of the tracks 11 and 12, to vary the energy. of interaction with the polar mass 20 of the anchor 2. The variation in thickness of added magnets induces a variation in the air gap between the anchor 2 and the tracks 10, unless these magnets are embedded in the escape wheel 1, so as to have a surface of same level facing the polar mass 20 of the anchor 2. The development therefore requires combining the control of the gradient of the field generated by the magnets of tracks 11 and 12, and control of the interaction between the polar mass 20 and these magnets in the air gap, which is tricky due to the discontinuities. Another alternative is to vary the intensity of magnetization of the magnets, or of the tracks themselves, which proves difficult to control well. In summary, these methods are suitable for laboratory tests, but are difficult to adapt for mass production. Also the invention provides an easier industrial implementation solution than varying the thickness of the magnets or their magnetization intensity, which consists in using a magnetized layer 4 of constant thickness and magnetization, arranged in the plane of the wheel 1 in a particular surface distribution, and whose geometry is designed so as to produce the desired energy variations composed of ramps and barriers. [0038] FIG. 3 presents an example of such a geometry: a magnetic layer 4 is arranged on the escape wheel 1, and constitutes a magnetized track 10, which interacts in a repulsive manner with the polar mass 20 of the anchor 2 which is arranged above the wheel 1. The geometry of the layer 4 is chosen so that the interaction with the polar mass 20 or the magnets of the anchor 2 produces the ramps and barriers necessary for good operation of the magnetic anchor escapement. As visible in Figs. 3 and 4, this magnetized track 10 formed by the magnetized layer 4 extends, partly at the level of the interior track 11, and partly at the level of the exterior track 12, which correspond to the two extreme positions of the polar mass 20 of anchor 2 (support against stars). The internal track 11 has a radial width R1, the external track 12 has a radial width R2. RO is the radius of the circle C which separates the inner track 11 and the outer track 12. To fully understand the method for designing the geometry of the magnetic layer 4, FIGS. 5 to 10 illustrate its representation in polar coordinates relative to the axis of the escape wheel 1 in fig. 5, 7, and 9, with the relative eccentricity of the surfaces as a function of the angle at the center relative to the period PD, and respectively figs. 6, 8 and 10 illustrate the forms of ramps and corresponding associated barriers. [0041] FIG. 5 shows two angular periods of the inner 11 and outer 12 tracks with a magnetic layer 4 which follows a continuous periodic path alternately substantially symmetrical, in particular and not limitingly triangular, in order to produce the potential ramps. The variation in interaction energy with the polar mass 20 of the anchor 2 is shown in fig. 6 in solid lines when the polar mass 20 is on the outer track 12 (position 1) and in broken lines when the polar mass 20 is on the inner track 11 (position 2). The interaction energy increases when the superposition of the magnetic track 4 of the wheel 1 and the polar mass 20 of the anchor 2 increases. The profile of the periodic path can also be substantially sinusoidal, or the like, depending on the desired ramp profiles. The linear profile of this example is advantageous for lowering the minimum maintenance torque CE allowing the operation of the exhaust. In the same way, FIG. 7 represents two angular periods of the inner 11 and outer 12 tracks with a magnetic layer 4 which is composed of discrete barrier pads 41, here made up of rectangular zones, in order to produce the potential barriers. The corresponding interaction energy variation is shown in fig. 8 in solid lines when the polar mass 20 is on the outer track 12 (position 1) and in broken lines when the polar mass 20 is on the inner track 11 (position 2). Finally, FIG. 9 represents two angular periods of the inner 11 and outer 12 tracks with a magnetic layer 4 which is the sum of the ramps in FIG. 5 and the barriers of FIG. 7. The variation of the corresponding interaction energy is shown in fig. 10 in solid lines when the polar mass 20 is on the outer track 12 (position 1) and in broken lines when the polar mass 20 is on the inner track 11 (position 2). It can be seen that what is desired is obtained, that is to say ramps followed by potential barriers, which alternate successively on the two tracks 11 and 12. Naturally, the discrete barrier studs 41 are here rectangular in shape for ease of modeling. They can also adopt other neighboring forms, as long as these forms remain compatible with the desired magnetic potential distribution. When we transform the geometry of FIG. 10 in Cartesian coordinates, the geometry of the magnetic layer shown in FIGS is obtained. 3 and 4, provided of course that the motif is repeated as many times as necessary to fill the entire wheel 1. For the non-limiting example of wheel 1 of FIGS. 3 and 4 we have chosen N = 6 steps per revolution, so that the angular period is PD = 2 Pi / 6. Of course, another value can be chosen for the number N of steps per revolution. In practice it is advantageous to choose N as large as possible, the upper limit being fixed by the technology used as well as by the air gap between the polar mass 20 of the anchor 2 and the wheel 1. It is understood that the geometry of the magnetic layer 4 depends on that of the wheel 1. In particular, if the latter is of small diameter and if N is small, it may be advantageous to have R1 larger than R2 , so as to compensate for the curvature, and to obtain characteristics of identical profiles of ramps and barriers on the two tracks 11 and 12. The example of the figures corresponds to the particular case where R1 and R2 are equal. Different variants, which can generally be combined, make it possible to further improve the proper functioning of the system. Some allow, in particular, to use a plurality of very thin magnetic layers 4, which can then be produced by processes other than mechanical, in particular electrochemical, by plasma deposition, or others. According to a characteristic of the invention, the magnetic layer 4 extends alternately on the internal track 11 and the external track 12. More particularly, the magnetic layer 4 comprises, at each half-period, a barrier pad 41 constituting a magnetic field barrier, extending on one side of the border F, and alternately on the internal track 11 and on the external track 12. More particularly still, these barrier studs 41 are connected, one after the other, by a strip 40 of width less than the smallest width of the barrier studs 41. More particularly still, the strip 40 changes concavity on either side of each barrier pad 41, and remains on the same side of the border F between two successive barrier pads 41. In particular, the strip 40 has a narrowing 42 next to each barrier pad 41. In particular, the strip 40 has a cusp 46 between two successive barrier studs 41. For compensation of axial forces at the escape wheel 1, it is advantageous to use a variant of wheel 1 comprising two magnetic layers 4, upper 4S and lower 4I, between which the polar mass 20 of l anchor 2 is sandwiched, as shown in fig. 11. Recall that the polar mass 20 of the anchor 2 acts in repulsion with the magnetized layers 4S and 4I of the wheel 1. It is naturally possible to design an escape wheel 1 with an even higher number of levels, and an anchor 2 comprising as many polar masses as there are spaces delimited two by two by the different magnetic layers 4 of the different levels to combine the effects, within the limit of the vertical size authorized by the movement in which the exhaust mechanism 100 is integrated. Thus, more particularly, the exhaust mobile 1 comprises a plurality of parallel disks, the faces of which face each other carry a magnetized track 10 in symmetry with respect to each other with respect to a perpendicular median plane to the common axis of the discs, and the width of each magnetic layer 4 extends in the radial direction relative to the axis of the disc. More particularly, the two extreme discs of this plurality of discs each comprise, on the side opposite to the plurality of discs, a ferromagnetic layer constituting a magnetic shielding protecting the mobile from external magnetic fields. More particularly still, the magnetic exhaust mechanism 100 includes such an exhaust mobile 1, and the retainer 2 comprises at least one pole mass 20 in each air gap where the parallel discs whose faces facing each carry each a magnetized track 10. We can thus have a configuration with several stages of anchor magnets, each anchor magnet working between two specific stages of the escapement wheel. [0058] FIG. 12 illustrates an advantageous variant where the anchor 2 comprises two pole masses 201 and 202 arranged angularly to work alternately, in the extreme angular positions of the anchor 2, one with the inner track 11, the other with the outer track 12, so the efforts add up. This configuration has many advantages. First of all, the difference in torque due to the difference in radius between the inner track 11 and the outer track 12 is compensated since there is always one of the polar masses of the anchor 2 which is on the inner track 11 while the other is on the outer track 12. Then, the manufacturing irregularities of the wheel 1, from one angular period to the next, are averaged since the polar masses of the anchor do not see the same defects. Finally, the couples transmitted at each alternation are doubled. To lower the minimum CE operating torque of the exhaust, it is important that the magnetic potential ramp is as linear as possible. To this end, small adjustments can be made to the geometry of the magnetic layer 4. For example, it is advantageous to make a small shrinkage 42 of the magnetic layer 4, when the polar mass of the anchor passes in the vicinity of a barrier which is on the adjacent track as shown in fig. 13. These narrowing 42 of the magnetized track makes it possible to optimize the linearity of the ramps of the magnetic interaction potential. The realization is also important in mass production. An advantageous method of producing the magnetic layer or layers 4 of the escape wheel 1 consists in using a substrate which provides the mechanical strength, and on which the magnetized layer 4 is deposited, which is typically NdFeB or SmCo or platinum (Pt) and cobalt (Co) alloys. Indeed, as the thin layers of rare earth magnets are fragile, it is advantageous to solidify them with a substrate. The layer can be deposited by CVD or PVD type methods or by galvanic growth. The desired geometry can be obtained by placing a removable mask on the substrate before depositing, a mask which can be removed later. It is also possible to deposit the layer uniformly on the substrate (CVD, PVD, or else bonded) and then carry out a chemical attack on the unwanted areas. In all these situations, the geometries presented so far can be used because the mechanical strength is ensured by the substrate. One understands the interest of multi-level escapement wheels in the case of this embodiment. Another variant of production relates to the manufacture of the magnetic layer 4 by machining the desired geometry in a thin magnet plate, either by traditional methods, by laser cutting, by electroerosion or by chemical attack, it is then advantageous to complete the magnetic layer 4 with stiffeners 44 extending in the central zone of the escape wheel 1, outside the surfaces swept by the anchor 2, in order to ensure the mechanical strength of the component made. An example is visible in fig. 14, where the mechanical consolidation zone, which extends towards the axis A1 of the wheel 1, and essentially outside the inner track 11, comprises a central ring 43 connected by stiffening spokes 44 to some of the studs- barriers 41 of the magnetic layer 4. More specifically, the stiffening spokes 44 are connected to the barrier pads 41 of the inner track 11 because these are the parts which are the least sensitive to a disturbing field. The mechanical consolidation zone thus produced makes it possible to ensure mechanical solidity, without significantly changing the potential for magnetic interaction between the anchor 2 and the wheel 1. Another variant relates to the use of a ferromagnetic layer 5, in particular of iron, as a circuit or magnetic shielding of the wheel 1. This layer can also be used as a substrate for the magnetized layer 4 and therefore ensure the resistance mechanical. Fig. 15 shows an arrangement similar to that of FIG. 11, where the wheel 1 comprises an upper ferromagnetic layer 5S external, and a lower ferromagnetic layer 5I external, each of them carrying respectively the upper magnetized layer 4S and lower 4I. This arrangement makes it possible to best separate the magnetic fields external to the wheel 1 and whose effects on the exhaust are to be stopped, from the internal fields of the magnetic exhaust mechanism 100, which are necessary for the operation of the exhaust. It may be necessary to adapt the shape of the ramps of the magnetic layer 4 according to the constitution of the wheel 1, with or without ferromagnetic material, iron in particular. Indeed, the presence of such a shielding of ferromagnetic material introduces non-linearities in the magnetic anchor-wheel interaction. These non-linearities must be compensated to obtain potential ramps as linear as possible. It is possible, as above, to introduce variations in the width of the magnetic layer 4 by narrowing 42. Another method consists in slightly modifying the shape of the triangular profile visible in FIG. 5 which is used to produce the ramps. For example in fig. 16, this profile is modified by the integration of non-linearities 45, in particular in the form of cusps 46, so as to compensate for the non-linearities of the magnetic interaction. This profile is then combined with the barrier studs 41 of FIG. 17 to obtain the geometry of FIG. 18 in polar coordinates. Finally the geometry is transformed into Cartesian coordinates and we get fig. 19 which is an alternative to the geometry of FIG. 13. [0065] FIG. 20 shows a variant with mechanical stops 19 on the wheel 1 and complementary mechanical stops 29 on the anchor 2, in order to ensure that the system does not stall in the event of an impact. These stops must be arranged to block the advance of the wheel 1 when the polar mass of the anchor crosses a magnetic barrier following an impact. In a variant, the anti-detachment stops are of the magnetic type. An advantageous variant thus comprises a small magnet on each point of the anti-drop star, and a ferromagnetic part on the stop of the anchor: in this case, during the first rebound, the magnetic attraction makes it possible to dissipate almost all of it. impact energy by stopping rebounds at once. The correct pulling position is then taken up thanks to the main magnetic potential (paddle-magnet wheel). In a second variant, the magnets located on each point of the star work in repulsion with magnets located on the anti-detachment stops of the anchor: in this case, any risk of collision (destroying the stops) is excluded, all leaving more freedom in the design of the magnetic wheel and in the indexing of the star. Lafig. 21 shows the assembly of a resonator mechanism 200, comprising, from an energy source comprising here a barrel 7, up to the balance-spring resonator, with the balance 3 and the balance spring 6, a gear train 8, and such magnetic escape mechanism 100 with magnetic anchor 2. Naturally, if the examples described relate to an escapement mobile constituted by a wheel, the teachings of the invention are applicable to a mobile of any shape, for example the variants of document EP 13 199 427 where the mobile exhaust is a cylinder, or a continuous strip, in which case the profile of magnetic layer 4 can be directly that of FIGS. 9 or 18, or even a left exhaust mobile, for example and without limitation with fins at the level of the ramps and / or potential barriers. The invention also relates to a movement 300 comprising at least one such resonator mechanism 200. The invention also relates to a watch 400 comprising at least one such movement 300. claims 1. Mobile escapement (1) for a clockwork magnetic escapement mechanism (100), comprising at least one magnetized track (10), with a succession of tracks according to a scrolling period (PD) according to which its magnetic characteristics are repeated, each said range comprising a magnetic field ramp with increasing field followed by a magnetic field barrier with increasing field and whose field gradient is greater than that of said ramp, characterized in that said magnetized track (10) is a continuous and closed magnetic track, extending over a larger surface (S) of said exhaust mobile (1), and whose geometry in projection on said surface (S) defines said magnetic ramps and magnetic field barriers. 2. exhaust mobile (1) according to claim 1, characterized in that said magnetized track (10) comprises a magnetic layer (4) continuous and closed over the entire periphery of said exhaust mobile (1). 3. Mobile exhaust (1) according to claim 1 or 2, characterized in that said magnetized track (10) comprises a magnetic layer (4) of constant thickness and variable width. 4. exhaust mobile (1) according to one of claims 1 to 3, characterized in that said exhaust mobile (1) comprises at least one disc, one face of which constitutes said surface (S) and carries said magnetized track. (10), and in that said width of said magnetic layer (4) extends in the radial direction relative to the axis of said disc. 5. Mobile exhaust (1) according to one of claims 1 to 4, characterized in that said magnetized track (10) comprises, connected on either side of a border (F), an internal track ( 11) and an external track (12) comprising said magnetic field barriers staggered with respect to said border (F), alternating by a half period. 6. mobile exhaust (1) according to claim 5, characterized in that said magnetic layer (4) extends alternately on said internal track (11) and said external track (12). 7. exhaust mobile (1) according to claim 6, characterized in that said magnetic layer (4) comprises, at each half-period, a barrier pad (41) constituting a said magnetic field barrier, extending on one side of said border (F), and alternately on said internal track (11) and on said external track (12). 8. exhaust mobile (1) according to claim 7, characterized in that said barrier pads (41) are connected, one after the other, by a strip (40) of width less than the narrower width of said barrier studs (41). 9. Exhaust mobile (1) according to claim 8, characterized in that said strip (40) changes concavity on either side of each said barrier pad (41) and remains on the same side of said border ( F) between two said successive barrier studs (41). 10. Mobile exhaust (1) according to claim 9, characterized in that said strip (40) has a narrowing (42) next to each said barrier pad (41). 11. mobile exhaust (1) according to claim 10, characterized in that said strip (40) has a cusp (46) between two said successive barrier pads (41). 12. exhaust mobile (1) according to claim 4 and one of claims 7 to 11, characterized in that said magnetic layer (4) comprises a central ring (43) connected by stiffening spokes (44) to certain said barrier studs (41) of said inner track (11), the central ring (43) and the stiffening spokes (44) thus forming a zone of mechanical consolidation. 13. exhaust mobile (1) according to one of claims 1 to 12, characterized in that said exhaust mobile (1) comprises at least one substrate providing mechanical strength which is covered with a magnetized layer of NdFeB or SmCo or alloys of Pt and Co constituting a said magnetic layer (4). 14. exhaust mobile (1) according to one of claims 4 to 13, characterized in that said exhaust mobile (1) comprises a plurality of parallel discs whose faces facing each carry a said magnetized track ( 10) in symmetry with respect to each other with respect to a median plane perpendicular to the common axis of said discs, and in that said width of each said magnetic layer (4) extends in the radial direction by relative to the axis of said disc. 15. exhaust mobile (1) according to claim 14, characterized in that the two end discs of said plurality of discs each comprise, on the side opposite to said plurality of discs, a ferromagnetic layer constituting a magnetic shielding protecting said mobile from external magnetic fields. 16. Magnetic escapement mechanism (100) for timepieces, comprising, subjected to an engine torque, an exhaust mobile (1) according to one of claims 5 to 15, cooperating indirectly with a spiral balance resonator by the intermediate of a stopper (2), characterized in that said stopper (2) is a pivoting magnetic stopper comprising at least one polar mass (20) arranged to cooperate alternately with said internal track (11) and said external track (12) a so-called magnetic layer (4). 17. Magnetic escape mechanism (100) according to claim 16, characterized in that said magnetic escape mechanism (100) comprises an exhaust mobile (1) according to claim 14 or 15, and in that said retainer (2) comprises at least one polar mass (20) in each air gap where said parallel discs, the faces of which face each other carry a said magnetized track (10). 18. Magnetic escape mechanism (100) according to claim 16, characterized in that said retainer (2) comprises two polar masses (201; 202) arranged angularly to work alternately, in the extreme angular positions of said retainer (2), one with said inner track (11), the other with said outer track (12). 19. Magnetic escape mechanism (100) according to one of claims 16 to 18, characterized in that said escape wheel (1) comprises mechanical stops (19) and in that said retainer (2) comprises additional mechanical stops (29) to prevent detachment in the event of an impact. 20. Resonator mechanism (200), comprising an energy source (7) arranged to drive through a gear train (8) said escape wheel (1) of a magnetic escape mechanism (100) according to l 'one of claims 16 to 19. 21. Clock movement (300) comprising at least one resonator mechanism (200) according to claim 20. 22. Watch (400) comprising at least one movement (300) according to claim 21. 4S 4I ~~ T ~ A1 1 1 19