Timepiece mechanism with magnetic gears

Abstract

A timepiece mechanism comprising a magnetic gear (3) formed by a first wheel (4) and a second wheel (6), the first wheel being provided with first alternating magnetic poles forming a magnetic toothing (9), and the second wheel being provided with a toothing (7) made of a ferromagnetic material, the toothing (7) having a magnetic coupling with the magnetic toothing, so that when one of the first wheel or the second wheel is driven to rotate, the wheel (4) rolls on a geometric circle centered on the other wheel (6) and linked to the other wheel via the magnetic coupling. The magnetic gear further comprises a ferromagnetic element arranged relative to the first wheel so as to counteract at least a large part of a magnetic interference torque to which the first wheel is subjected, which is generated from the magnetic coupling, the magnetic interference torque having a periodic intensity variation according to the angular position of the first wheel.

Description

Technical Field

[0001] The present invention relates to the field of magnetic gears, which are formed by a first wheel and a second wheel in a magnetic transmission relationship, wherein the first wheel is provided with first magnetic poles arranged in a circular manner and defining a first magnetic tooth portion, and the second wheel is provided with teeth made of ferromagnetic material or provided with second magnetic poles, which are arranged in a circular manner and define a second magnetic tooth portion.

[0002] In particular, the invention relates to a timepiece mechanism incorporating a magnetic gear. Background Art

[0003] Figure 1 A magnetic gear 2 is shown comprising a small wheel 4 provided with six dipole magnets 8 with radial and alternating magnetization, regularly arranged around a central portion of the small wheel so as to define a magnetic toothing 9 with six magnetic teeth, and a large wheel 6 situated in a general plane in which the small wheel also extends and comprising a ferromagnetic rim with a peripheral toothing 7. Wheel 4 has a central axis 32 defining the axis of rotation of the small wheel and wheel 6 has a central axis 34. In the general case where the large wheel also rotates, the central axis 34 defines the axis of rotation of the large wheel. In the specific case, the large wheel is arranged fixedly on a support (a main plate or bridge of a timepiece movement) and the small wheel is arranged to rotate at the periphery of the large wheel when it is driven in rotation by a drive device.

[0004] Figure 2 The curve 10 shows the magnetic interference torque exerted on the small wheel 4 when the small wheel 4 rotates and "rolls" on a geometric circle linked to the large wheel 6 and centered on the central axis 34 of the large wheel 6. This magnetic interference torque has a periodic intensity variation according to the angular position α of the small wheel 4. The angle α is measured from a reference semi-axis 30, which starts from the rotation axis 32 of the small wheel and intersects the central axis / rotation axis of the large wheel 6. By definition, the reference semi-axis 30 is perpendicular to the rotation axis of the small wheel 4. As Figure 2 , the period of the sinusoidal curve 10 corresponds to the central angle between two consecutive dipole magnets and therefore to the angle travelled by the small wheel for one step of the operation of the magnetic gear 2, i.e. the small wheel 4 rotates so as to move from one dipole magnet aligned on the reference semi-axis 30 (which defines a magnetic tooth, or, by analogy with a conventional mechanical gear, corresponds to the space between two magnetic teeth) to the next dipole magnet (which defines the next magnetic tooth or the next space between two magnetic teeth), which next dipole magnet is then aligned on the reference semi-axis, and causes the large wheel 6 to rotate simultaneously (or the axis of rotation of the small wheel rotates about the central axis 34 of the large wheel) so as to move from one tooth aligned on the reference semi-axis to the next tooth, which next tooth is then aligned on the reference semi-axis. Note that the large wheel is also subject to a corresponding magnetic interference torque. For reasons of clarity of the accompanying drawings, Figure 1The rotation angle / angular position indicated by the arrow in is measured from the semi-axis which is complementary to the reference semi-axis 30 (these two semi-axis lines together form the geometrical axis) and therefore corresponds to α‒180°. Figure 2 Point A in corresponds to an angle α equal to 0 or to an integer multiple of 360° / N, wherein N is equal to the number of dipole magnets 8 and thus the number of magnetic teeth of the magnetic toothing 9 . The angle 360° / N thus corresponds to the angular period or angular pitch of the magnetic toothing 9 .

[0005] exist Figure 2 The angular positions of the magnetic gear 2 at points A and E on the graph correspond to the stable equilibrium position of the magnetic gear, while the angular position of the magnetic gear at point C corresponds to the unstable equilibrium position. Figure 2 Points B and D on the graph of correspond to the two maximum intensities (positive and negative respectively) and therefore to the amplitude of the magnetic interference torque. It is noted that the magnetic interference torque occurs in the absence of torque transmission between the two wheels, which tends to move the dipole magnet 8 in front of the ferromagnetic teeth of the wheel 6 and thus align the poles of the wheel 4 and the ferromagnetic teeth of the wheel 6 on the reference semi-axis 30 (the case at points A and E of the curve 10), the angular position of the two wheels then corresponding to the minimum potential energy of the magnetic gear.

[0006] The magnetic interference torque can be significant, possibly as large as (or even larger than) the magnetic torque that can be transmitted between the two wheels of the magnetic gear. In order to overcome this interference torque, the drive device driving one of the two wheels must be able to provide a torque much higher than the magnetic torque transmitted in the magnetic gear, in order to prevent it from blocking, which unnecessarily increases its energy consumption. Moreover, due to its sinusoidal variation, the interference torque introduces relatively large variations in the magnetic torque transmitted in the magnetic gear. In fact, when the pinion 4 is driven in the positive direction of rotation, from each position in which the bipolar magnet 8 is aligned on the reference semi-axis 30, the interference torque brakes the pinion during a first angular half-period of the magnetic toothing 9 and drives it during a second angular half-period following this first angular half-period (see Figure 2 ). This also applies to the large wheel 6 per magnetic period of its magnetic toothing 7, but with the opposite mathematical sign. Summary of the invention

[0007] The object of the present invention is to overcome the problem of magnetic interference torque in magnetic gears by eliminating at least a large part of this interference torque.

[0008] To this end, the invention relates to a mechanism comprising a magnetic gear formed by a first wheel and a second wheel, the first wheel being provided with N first alternating magnetic poles arranged circularly and defining a first magnetic toothing, the second wheel being provided with teeth made of ferromagnetic material or with second alternating and circularly arranged magnetic poles defining a second magnetic toothing having a magnetic coupling with the first magnetic toothing so that when one of the first or second wheels is driven in rotation, the wheel rolls via the magnetic coupling on a geometric circle centered on and linked to the other wheel. According to the invention, the mechanism also comprises a ferromagnetic element or a group of ferromagnetic elements arranged relative to the first wheel so as to counteract at least a large part of a magnetic disturbance torque to which the first wheel is subjected, arising from said magnetic coupling, the magnetic disturbance torque having a periodic intensity variation according to the angular position of the first wheel relative to a reference semi-axis starting from the central axis of the first wheel and intersecting the central axis of the second wheel.

[0009] Note that the rolling of one of the two wheels on a geometric circle centered on and linked to the other wheel occurs without mechanical contact, said geometric circle having a radius according to the angular pitch of each of the two wheels and according to the distance between the central axes of each of the two wheels. "Magnetic torque" means the torque of a magnetic force.

[0010] According to the main embodiment, the ferromagnetic element or group of ferromagnetic elements is arranged to generate a magnetic compensation torque which also has a periodic intensity variation according to the angular position of the first wheel relative to the reference semi-axis, the magnetic compensation torque and the magnetic interference torque having a phase shift of substantially 180°.

[0011] According to an advantageous variant, the ferromagnetic element or the group of ferromagnetic elements has a plane of symmetry comprising the reference semi-axis and the central axis of the first wheel.

[0012] According to an advantageous variant, the ferromagnetic element or group of ferromagnetic elements is arranged to generate on the first wheel a total compensating magnetic attraction aligned on the reference semi-axis with a direction opposite to that of the total magnetic attraction exerted by the second wheel on the first wheel. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The invention will now be described in detail with reference to the accompanying drawings, given by way of non-limiting examples, in which:

[0014] - Already described Figure 1 A magnetic gear according to the prior art is shown.

[0015] - Already described Figure 2 Graphically represent what happens in Figure 1 Magnetic interference torque in magnetic gears.

[0016] - Figure 3 A first embodiment of a mechanism comprising a magnetic gear according to the invention is shown (only the magnetic gear is shown).

[0017] - Figure 4 Graphically represent the Figure 3 The additional ferromagnetic elements involved in the magnetic gearing generate a magnetic compensation torque.

[0018] - Figure 5 Graphically represented in Figure 3 The residual magnetic interference torque in the magnetic gear.

[0019] - Figure 6 A first modification of the first embodiment of the present invention is shown.

[0020] - Figure 7 A second variation of the first embodiment of the present invention is shown.

[0021] - Figure 8 A second embodiment of a mechanism comprising a magnetic gear according to the invention is shown (only the magnetic gear is shown). DETAILED DESCRIPTION

[0022] refer to Figures 3 to 7 , a first embodiment of a magnetic gear according to the present invention will be described below.

[0023] exist Figures 3 to 5 In the first variant shown in FIG. 1 , the magnetic gear 3 is formed by a first wheel 4 and a second wheel 6, which are described above with reference to Figure 1 is described. Typically, the first wheel is provided with N first alternating magnetic poles arranged in a circle and defining a first magnetic tooth portion. In the variant considered, the first wheel 4 comprises six bipolar magnets with radial magnetization, the six outer magnetic poles forming the first magnetic tooth portion 9. Since the magnetic poles are arranged in a circular manner with alternating polarization, there are an even number of said poles. Typically, the second wheel is provided with teeth made of ferromagnetic material or second alternating magnetic poles arranged in a circle, the teeth or second magnetic poles defining a second magnetic tooth portion, the second magnetic tooth portion having a magnetic coupling with the first magnetic tooth portion, so that when one of the first wheel or the second wheel is driven to rotate, the wheel rolls on a geometric circle centered on the other wheel and linked to the other wheel via magnetic coupling. In the variant considered, the second wheel 6 comprises a rim of ferromagnetic material defining teeth at its outer periphery forming a second magnetic tooth portion 7. The two wheels 4, 6 extend in the same general plane and are arranged so that their magnetic tooth portions do not touch. Reference is made above to Figure 2 The magnetic interference torque occurring between the two wheels 4 and 6 is presented.

[0024] In order to compensate for the aforementioned magnetic interference torque, the magnetic gear 3 also includes a ferromagnetic element 12, which is arranged relative to the first wheel 4 to compensate for and thus offset the magnetic interference torque ( Figure 2 At least a large part of the curve 10).

[0025] The ferromagnetic element 12 is preferably arranged in the general plane of the two wheels of the magnetic gear 3. The ferromagnetic element comprises two end portions 13 and 14 extending in the direction of the first toothing 9 of the wheel 4, the first end portion 14 being located at an angular position equal to 90° and the second end portion being located at an angular position equal to 270°. In general, each of the end portions is positioned at an angle relative to the reference semi-axis 30, the value of which is equal to , where M is an integer greater than '1' and less than N. It is noted that, in a more complex variant, in addition to the two end portions, other protrusions may be provided, each positioned at a different angle among the angles defined by the value M between '1' and N in the above mathematical formula. An intermediate portion 12A connects the two end portions. This intermediate portion has a semicircular shape, which extends in the general plane of the wheel 4, on the opposite side of the wheel 6. It is noted that this intermediate portion generates a low magnetic torque on the wheel 4, much lower than the magnetic interference torque generated by the wheel 6, and much lower than the magnetic compensation torque generated in general by the ferromagnetic element 12 and mainly by the two end portions 13 and 14, which are arranged to turn inwards towards the toothing 9 of the wheel 4 relative to the circle defined by the intermediate portion, and therefore have a radial orientation.

[0026] The ferromagnetic element 12 is arranged to generate a magnetic compensation torque 18 with periodic intensity variation (given by Figure 4 ), which has the same period as the periodic intensity variation of the magnetic interference torque as a function of the angular position α of the wheel 4 relative to the reference semi-axis 30. Advantageously, the magnetic compensation torque and the magnetic interference torque have a phase shift of substantially 180°. Preferably, the ferromagnetic element 12 is configured so that the maximum intensity (amplitude) of the magnetic compensation torque is substantially equal to the maximum intensity (amplitude) of the magnetic interference torque. Figure 5 represents the residual magnetic torque that can be exerted on the wheel 4. In addition, the ferromagnetic element 12, in particular its two end portions, has a symmetry plane 36 including the reference semi-axis 30 and the central axis 32 (rotation axis) of the first wheel 4. This feature is advantageous in preventing the ferromagnetic element from generating a magnetic attraction force on the wheel 4 in an orientation perpendicular to the reference semi-axis 30. Such a magnetic attraction force would be perpendicular to the total radial magnetic attraction force exerted by the wheel 6 on the wheel 4, so that such a perpendicular magnetic attraction force would generate a friction force of the pivot of the wheel 4 in the associated bearing (not represented) defining the rotation axis 32.

[0027] In an improvement of the first variant, the ferromagnetic element is arranged to be configured to generate a total compensating magnetic attraction force on the first wheel 4, which is aligned on the reference semi-axis 30 and has a direction opposite to the direction of the total radial magnetic attraction force exerted by the second wheel 6 on the first wheel 4. It is noted that the first variant already has a small compensating magnetic attraction force generated from the middle part of the semicircle, but the middle part is mainly used to form a magnetic circuit with low magnetic resistance between the two end parts 13 and 14, and its magnetic attraction force on the first wheel is much lower than the radial magnetic attraction force exerted by the second wheel on the first wheel, because the two attractions are not on the same order of magnitude. The specific embodiment corresponding to the provided improvement is formed respectively in Figure 6 and Figure 7 The subject of the second and third variations shown in .

[0028] exist Figure 6 In a second variant, the magnetic gear 3A comprises a ferromagnetic element 16 which, in addition to the two aforementioned end portions 13 and 14, is provided with a compensating portion 15 which projects from the middle portion 16A in the direction of the first toothing 9, which is positioned at an angle of 180° relative to the reference semi-axis 30 and serves to form the majority of the compensating magnetic attraction force. It is noted that the compensating portion 15 has the disadvantage of increasing the total magnetic interference torque exerted on the wheel 4. However, the ferromagnetic element 16 can be configured so that the two end portions 13 and 14 counteract the majority or preferably substantially all of the two magnetic torques generated on the wheel 4 by the wheel 6 and the compensating portion 15, respectively. In an advantageous variant, the additional magnetic torque generated by the compensating portion can be reduced by enlarging the compensating portion (if necessary and increasing the distance to the first magnetic toothing) so that its free end has a semicircular profile centered on the axis of rotation 32 of the first wheel, at the minimum distance from the first magnetic toothing 9 and extending substantially over the angular period of this first magnetic toothing, which can be slightly smaller. A person skilled in the art knows how to optimize the profile and the angular extent of the free end of the compensating portion in order to reduce the additional magnetic torque as much as possible.

[0029] exist Figure 7 In a third variant of , the magnetic gear 3B comprises a ferromagnetic element 22, the intermediate portion 22A of which is configured so that it is closer to the first magnetic tooth portion 9 of the first wheel 4 in the direction of the angular position equal to 180° measured from the reference semi-axis 30, and therefore has a minimum distance from the first magnetic tooth portion at the angular position of 180°. This third variant has the advantage of allowing to obtain a relatively large compensating magnetic attraction force, in particular substantially equal to the total radial magnetic attraction force exerted by the second wheel 6 on the first wheel 4, without generating a high magnetic torque on the first wheel 4. In fact, the magnetic torque generated by the intermediate portion 22A is significantly lower than that generated by the intermediate portion 22A as in Figure 6The magnetic torque generated by the middle part 16A of the second variant shown in FIG. In order to further reduce the additional magnetic torque applied to the first wheel, a person skilled in the art knows how to optimize the shape of the middle part 22A, in particular its middle part.

[0030] refer to Figure 8 , describes a preferred variant of the second embodiment of the magnetic gear 3C according to the invention, characterized by the arrangement of a group of separate ferromagnetic elements, which serves to counteract the magnetic interference torque to which the first wheel 4 is subjected (curve 10, Figure 2 ), the magnetic interference torque resulting from the magnetic coupling with the second wheel 6, in particular with the second magnetic toothing 7. The set of ferromagnetic elements comprises at least two elements 24 and 26, each positioned at a different angle relative to the reference semi-axis 30, the value of which is equal to , where M is an integer greater than '1' and less than N.

[0031] As in the first embodiment, in a general variant, the group of ferromagnetic elements is arranged to generate a magnetic compensation torque 18 (see Figure 4 ), the magnetic compensation torque also has a periodic intensity variation according to the angular position of the first wheel relative to the reference semi-axis 30, the magnetic compensation torque has the same angular period as the magnetic interference torque and has a phase shift of substantially 180° relative to the latter.

[0032] In a first advantageous variant, the group of ferromagnetic elements is mainly arranged on the side opposite to the second wheel 6 relative to a geometrical plane 38 including the central axis 32 of the first wheel and perpendicular to the reference semi-axis 30. The group of ferromagnetic elements is thus arranged to generate on the first wheel 4 a total compensating magnetic attraction force aligned on the reference semi-axis 30 and having a direction opposite to that of the total radial magnetic attraction force exerted by the second wheel on the first wheel. Figure 8 In the preferred variant represented in , the group of ferromagnetic elements formed by the two elements 24 and 26 is arranged completely on the side of the geometrical plane 38 opposite the second wheel 6 .

[0033] In a second advantageous variant, the set of ferromagnetic elements has a symmetry plane 36 comprising the reference semi-axis 30 and the central axis 32 of the first wheel. Figure 8 The preferred variant represented in also belongs to this second advantageous variant. The advantages resulting from such an arrangement are described above.

Claims

1. A timepiece mechanism comprising a magnetic gear (3) formed by a first wheel (4) and a second wheel (6), the first wheel being provided with N first alternating magnetic poles arranged circularly and defining a first magnetic toothing (9), the second wheel being provided with teeth made of ferromagnetic material or provided with second alternating and circularly arranged magnetic poles, the teeth or the second alternating and circularly arranged magnetic poles defining a second magnetic toothing (7), the second magnetic toothing having a magnetic coupling with the first magnetic toothing, so that when one of the first wheel or the second wheel is driven to rotate, the wheel (4) rolls on a geometric circle centered on the other wheel (6) and linked to the other wheel via the magnetic coupling; characterized in that The mechanism further comprises a ferromagnetic element (12, 12A, 16) or a group of ferromagnetic elements (24, 26) arranged relative to the first wheel so as to counteract at least a large part of a magnetic interference torque (10) to which the first wheel is subjected, generated by the magnetic coupling, the magnetic interference torque having a periodic intensity variation according to the angular position (α) of the first wheel relative to a reference semi-axis (30) starting from the central axis (32) of the first wheel and intersecting the central axis (34) of the second wheel.

2. The timepiece mechanism according to claim 1, characterized in that: The ferromagnetic element or the group of ferromagnetic elements is arranged to generate a magnetic compensation torque (18), which also has a periodic intensity variation according to the angular position of the first wheel relative to the reference semi-axis (30), and the magnetic compensation torque and the magnetic interference torque have a phase shift of substantially 180°.

3. The timepiece mechanism according to claim 1 or 2, characterized in that: The ferromagnetic element or the group of ferromagnetic elements has a symmetry plane (36) comprising the reference semi-axis (30) and the central axis (32) of the first wheel.

4. The timepiece mechanism according to claim 1 or 2, characterized in that: The ferromagnetic element or the group of ferromagnetic elements is arranged to generate on the first wheel a total compensating magnetic attraction aligned on the reference semi-axis (30) and having a direction opposite to that of the total magnetic attraction exerted by the second wheel on the first wheel.

5. The timepiece mechanism according to claim 4, characterized in that: The ferromagnetic element (12, 16, 22) comprises two end portions (13, 14) extending in the direction of the first magnetic tooth portion (9) and a middle portion (12A, 16A, 22A) connecting the two end portions, each of the two end portions being positioned at an angle relative to the reference semi-axis (30), the value of the angle being equal to (M-1 / 2)·360° / N, wherein M is an integer greater than '1' and less than N.

6. A timepiece mechanism according to claim 5, characterized in that The ferromagnetic element (16) further comprises a compensating portion (15) protruding from the intermediate portion (16A) in the direction of the first magnetic tooth portion (9), the compensating portion being positioned at an angle relative to the reference semi-axis (30), the value of the angle being equal to 180° and being used to form a large part of the compensating magnetic attraction force.

7. A timepiece mechanism according to claim 5, characterized in that The middle portion (22A) of the ferromagnetic element (22) is configured so that it is closer to the first magnetic tooth portion (9) in the direction of an angular position equal to 180° measured from the reference semi-axis (30), thereby presenting a minimum distance from the first magnetic tooth portion at the angular position of 180°.

8. The timepiece mechanism according to claim 4, characterized in that: The set of ferromagnetic elements comprises two elements (24, 26) each positioned at an angle relative to the reference semi-axis (30) equal to (M-1 / 2)·360° / N, where M is an integer greater than '1' and less than N.

9. A timepiece mechanism according to claim 8, characterised in that The group of ferromagnetic elements (24, 26) is arranged mostly on the side opposite to the second wheel (6) relative to a geometrical plane (38) including the central axis (32) of the first wheel and perpendicular to the reference semi-axis (30).

10. A timepiece mechanism according to claim 8, characterized in that The group of ferromagnetic elements (24, 26) is all arranged on the side opposite to the second wheel (6) relative to a geometrical plane (38) including the central axis (32) of the first wheel and perpendicular to the reference semi-axis (30).

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