Timepiece movement fitted with an electromagnetic transducer

Abstract

Timepiece movement fitted with an electromagnetic transducer comprising at least one coil and a rotor formed of a central shaft, of two magnetic plates that are mounted on the central shaft and of a plurality of bipolar magnets which are axially polarized and mounted on at least one of the two magnetic plates, said at least one coil penetrating at least partially into a circular space which is defined by the rotor between its two magnetic plates and left free by this rotor. The central shaft comprises a pinion which engages with a wheel of the timepiece movement, this pinion being arranged between the two magnetic plates and said wheel being partially arranged between the two magnetic plates, in an angular sector of the circular space that is left free by the electromagnetic transducer, so as to engage with the pinion. Advantageously, said wheel has a roller that is almost or entirely non-conductive and a non-magnetic staff.

Claims

1. A timepiece movement comprising an electromagnetic transducer formed by a stator and a rotor, the stator comprising at least one coil with a central axis that is parallel to the axis of rotation of the rotor, the rotor comprising a central shaft, two magnetic plates that are mounted on the central shaft and at least one magnet that is mounted on one of the two magnetic plates so as to be located between these two magnetic plates, said at least one coil lying in a general plane, located between the two magnetic plates, axially remote from said at least one magnet, the rotor and said at least one coil being configured so that said at least one coil is located at least partially in a circular space which is defined by the rotor between its two magnetic plates from its central shaft to its periphery and which is left free by this rotor, said central shaft comprising a pinion which engages with a wheel of the timepiece movement; wherein said stator is configured so as to leave an angular sector of said circular space free, the aperture angle of which is selected to allow said wheel to penetrate radially into said circular space up to said central shaft while remaining in this angular sector; wherein said pinion is arranged between the two magnetic plates and has at least one useful portion located between two geometric planes defining said circular space about said axis of rotation; and wherein said wheel is partially arranged between the two magnetic plates, in said angular sector of the circular space, so as to engage with said pinion.

2. The timepiece movement according to claim 1, wherein said at least one coil is a pancake coil.

3. The timepiece movement according to claim 2, wherein the stator comprises two pancake coils.

4. The timepiece movement according to claim 3, wherein said wheel lies in said general plane, said aperture angle is larger than 120 and the staff of the wheel is arranged at the periphery of the rotor.

5. The timepiece movement according to claim 4, wherein the sizes of said wheel and of the two coils are such that the angular areas between them have an angle at the centre that is smaller than 10.

6. The timepiece movement according to claim 3, wherein the rotor comprises a plurality of bipolar magnets which are axially polarized and mounted according to a given angular period on at least one of the two magnetic plates.

7. The timepiece movement according to claim 3, wherein the electromagnetic transducer forms a continuous-rotation motor.

8. The timepiece movement according to claim 3, wherein the electromagnetic transducer forms a generator, said wheel belonging to a wheel train that is interengaged with a barrel of the timepiece movement.

9. The timepiece movement according to claim 1, wherein said wheel has a roller made of an Inconel-type metal alloy or a synthetic material, in particular polyoxymethylene.

10. The timepiece movement according to claim 1, wherein said wheel has a staff made of a non-magnetic material, in particular a copper-beryllium alloy or a plastic material.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The invention will be described below in greater detail with the aid of the appended drawings, which are provided by way of nonlimiting examples, in which:

(2) FIG. 1 is a view of a partial heightwise section, along the line I-I of FIG. 2, of a timepiece movement according to the invention;

(3) FIG. 2 is a partial view of a section of the movement of FIG. 1 along a plane that is perpendicular to the axis of rotation of the rotor of an electromagnetic transducer of the invention, this perpendicular plane being located between the coils and the upper magnetic plate of the rotor;

(4) FIG. 3 is a sectional view of the rotor of FIGS. 1 and 2 along a plane that is perpendicular to its axis of rotation level with its pinion.

DETAILED DESCRIPTION OF THE INVENTION

(5) With reference to FIGS. 1 to 3, one embodiment of a timepiece movement according to the present invention will be described below:

(6) The timepiece movement 2 comprises an electromagnetic transducer 4 formed by a stator 6 and a rotor 8. The stator comprises two coils 10 and 11, each having a central axis 12 which is parallel to the axis of rotation 14 of the rotor. The two coils are advantageously pancake coils, i.e. their thickness along their central axis is substantially less than their maximum dimension in a general plane that is perpendicular to this central axis. The coils shown take the shape of a flat disc. However, outlines other than a circular outline may be envisaged, in particular an ovoid or trapezoidal outline.

(7) The rotor 8 comprises a central shaft 16, two magnetic plates 18 and 20 that are mounted on the central shaft and a plurality of bipolar magnets 22, 23 which are axially polarized and mounted on at least one of the two magnetic plates so as to be located between these two magnetic plates. In the variant shown, the plurality of magnets is arranged only on the lower magnetic plate 18 to which they are attached in particular by bonding. In this case, the upper magnetic plate 20 serves only as a plate for closing the field lines of the magnetic flux generated by the magnets. The two magnetic plates together form a shielding structure for the purpose of substantially confining the magnetic flux of the magnets within the volume defined by the rotor and a relatively small lateral volume at its periphery. In another variant, the bipolar magnets are shared equally between two magnetic plates. In this case, the magnets are aligned axially in pairs of magnets both having a polarity in the same direction so as to generate a substantially axial magnetic flux between them. The magnets are arranged with a given angular period on only one of the two magnetic plates or on both magnetic plates. In the variant shown, the polarities of the magnets alternate, which differentiates the magnets 22 from the magnets 23. It should be noted that although the bipolar magnets may be formed by distinct and initially mutually separate elements before their attachment to one of the two magnetic plates, these bipolar magnets may also be formed by an annular multipolar magnet having 2N magnetic poles forming axially magnetized pairs of poles, N being greater than 1. It should be noted that these variants are nonlimiting.

(8) The two coils lie in a general plane 25, located between the two magnetic plates 18 and 20, axially remote from the plurality of magnets. The rotor and the two coils are configured so that these two coils are located partially in a circular space 26 which is defined by the rotor between its two magnetic plates from its central shaft 16 up to its periphery 28 and which is left free by this rotor. The central shaft comprises a pinion 30 which engages with a wheel 32 of a mechanism of the timepiece movement. According to the invention, the stator is configured so as to leave an angular sector 34 of the circular space 26 free, the aperture angle of which is selected to allow the wheel 32 to penetrate radially into the circular space up to the central shaft 16 while remaining in this angular sector. It is noteworthy that the pinion 30 is arranged between the two magnetic plates 18 and 20 and has least one useful portion located between two geometric planes 38 and 39 defining the circular space about the axis of rotation 14. Thus, according to the invention, the wheel 32 is partially arranged between the two magnetic plates, in said angular sector of the circular space, so as to engage with the pinion 30. Preferably, the wheel 32 is configured and/or made of a specific material so as to decrease, or even eliminate, energy losses by Foucault current. Specifically, if the roller of the wheel is formed by a substantially flat disc made of a highly conductive metal material, the passage of the magnets of the rotor past this roller results in relatively substantial losses by Foucault current. If the roller has a plurality of apertures, in particularly substantially radial apertures or apertures defining empty angular sectors, such losses are decreased. By way of example, the roller of the wheel 32 has a hub and a rim linked by several substantially thin spokes. In one advantageous variant, the material forming the roller is an Inconel-type metal alloy, the resistivity of which is much higher than that of brass. By using such a metal alloy, it is possible to envisage a substantially solid roller, i.e. a non-apertured disc. To completely eliminate the losses in question, the roller may be made of a synthetic material, for example polyoxymethylene (POM). In general, using a magnetic material for the roller of the wheel is to be avoided. The same applies for the staff of the wheel 32, so as to avoid the rotor exerting an attractive force on this axis. Specifically, in the opposite case, losses by friction will be generated at the bearings within which the wheel 32 pivots. The staff will for example be made using a copper-beryllium alloy or of a plastic material.

(9) According to one advantageous variant, the wheel 32 lies in the general plane 25 of the two coils 10 and 11 with its axis 42 arranged at the periphery of the rotor. In particular, the aperture angle of the angular sector 34 provided for this wheel is larger than 120.

(10) According to one advantageous variant, the sizes of the wheel 32 and of the two coils 10 and 11 are such that the angular areas between them have an angle at the centre that is smaller than 10.

(11) In a first embodiment of the invention, the electromagnetic transducer forms a continuous-rotation motor. In a second embodiment of the invention, the electromagnetic transducer forms a generator and the wheel 32 belongs to a wheel train that is interengaged with a barrel of the timepiece movement.