Bearing, particularly a shock absorber, and rotary wheel set of a timepiece movement

Abstract

A bearing for an arbor or staff of a rotary wheel set of a timepiece movement, the bearing including a bearing block provided with a housing and an endstone arranged inside the housing, the endstone having a main body provided with a cavity configured to receive a pivot of the arbor of the rotary wheel set, the pivot having the shape of a first cone having a first solid angle, the apex of the first cone being rounded with a predefined first radius of curvature in a range from 0.2 μm to 50 μm, the cavity having a second cone shape with a second solid angle, greater than the first solid angle, so that the pivot can rotate in the cavity, the apex of the second cone being rounded and having a predefined second radius of curvature. The second radius of curvature is smaller than the first radius of curvature.

Claims

1. A bearing for an arbor or staff (16) of a rotary wheel set of a timepiece movement, the bearing (18, 20) comprising a bearing block (13) provided with a housing (14) and an endstone (22) arranged inside the housing (14), the endstone (22) comprising a main body provided with a cavity configured to receive a pivot (17, 20) of the arbor (16) of the rotary wheel set, the pivot (17, 30) having the shape of a first cone (26) having a first solid angle (31, 36), the apex (29) of the first cone being rounded with a predefined first radius of curvature comprised in a range from 0.2 μm to 50 μm, the cavity having the shape of a second cone (28) having a second solid angle (32) greater than the first solid angle (31, 36), such that the pivot (17, 30) can rotate in the cavity, the apex of the second cone (28) being rounded and having a predefined second radius of curvature, wherein the second radius of curvature is smaller than the first radius of curvature.

2. The bearing according to claim 1, wherein the second radius of curvature is less than 40 μm.

3. The bearing according to claim 1, wherein the second radius of curvature is less than 20 μm.

4. The bearing according to claim 1, wherein the main body of the endstone (22) is formed of a material to be chosen from the following list: an at least partially amorphous metal alloy, an electroformed material, a synthetic material or a composite material.

5. The bearing according to claim 4, wherein the cavity is obtained from a hot deformation process of an at least partially amorphous metal using a tool whose diameter is smaller than the first radius of curvature of the first cone.

6. The bearing according to claim 4, wherein the at least partially amorphous metal alloy is crystallised to create friction-enhancing phases.

7. The bearing according to claim 4, wherein the at least partially amorphous metal alloy is ceramized to harden the surface of the main body, in the second cone (28) of the cavity.

8. The bearing according to claim 4, wherein main body of the electroformed material endstone (22) is obtained from a galvanic growth process, including electroforming in a corresponding mold.

9. The bearing according to claim 4, wherein the main body of the endstone made of synthetic material is obtained by moulding.

10. The bearing according to claim 4, wherein the main body of the endstone (22) made of composite material is obtained by moulding.

11. The bearing according to claim 1, wherein the second solid angle is comprised in a range from 60 to 120°.

12. The bearing according to claim 1, wherein the bearing includes a resilient support (21) for the endstone (22) for dampening shocks.

13. The bearing according to claim 12, wherein the main body of the endstone (22) and the resilient support (21) are formed in one piece.

14. The bearing according to claim 12, wherein the resilient support is formed by a LIGA-type lithography, electroplating and moulding process.

15. The bearing according to claim 12, wherein the main body of the endstone (22) is overmoulded on the resilient support.

16. A rotary wheel set of a timepiece movement, for a bearing (18, 20) according to claim 1, the wheel set being provided with an arbor or staff (16) with at least one pivot (19) having the shape of a first cone (26) having a predefined first solid angle, the apex of the first cone (26) being rounded and having a predefined first radius of curvature, wherein the first radius of curvature is comprised in a range from 0.2 μm to 50.

17. The rotary wheel set according to claim 16, wherein the apex of the first cone (26) of the pivot (19) is cut to form a circular third cone (35), having a third solid angle (42) greater than the first solid angle (32), substantially equal to the second solid angle (31) of the endstone (22).

18. A timepiece movement comprising a plate and at least one bar, said plate and/or the bar comprising an orifice, wherein the movement includes a bearing (22) according to claim 1, the bearing (22) being inserted into the orifice, and a rotary wheel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features and advantages of the present invention will appear upon reading the description of several embodiments given purely by way of non-limiting examples, with reference to the annexed drawings, in which:

(2) FIG. 1 represents a cross-section of a shock absorber support bearing for a rotary wheel set arbor according to a first state of the art embodiment.

(3) FIG. 2 schematically represents an endstone of a bearing and a pivot of a rotary wheel set arbor according to a second state of the art embodiment.

(4) FIG. 3 schematically represents a cross-section of part of a timepiece movement including a balance staff held by two bearings according to the invention.

(5) FIG. 4 represents a schematic view of a resilient support for a shock absorber bearing according to the invention.

(6) FIG. 5 represents an endstone of a support bearing and a pivot of a rotary wheel set arbor according to a first embodiment of the invention.

(7) FIG. 6 schematically represents an endstone of a support bearing and a pivot of a rotary wheel set arbor according to a second embodiment of the invention.

(8) FIG. 7 schematically represents an enlarged view of the endstone and of the pivot of the second embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(9) A bearing and an arbor of a rotary wheel set will be described according to two embodiments, with the same numbers used to designate identical objects. In a timepiece movement, the bearing is used to hold an arbor of a rotary wheel set, for example a balance staff, while allowing it to rotate about its axis. The timepiece movement generally includes a plate and at least one bar, not represented in the Figures, said plate and/or the bar comprising an orifice, the movement further including a rotary wheel set and a bearing inserted into the orifice.

(10) FIG. 3 shows a part 15 of a timepiece movement comprising two bearings 18, 20 and a balance staff 16 held at each end by two bearings 18, 20. Staff 16 has a pivot 17 at each end, the pivots being formed of a hard material, preferably ruby. Each bearing 18, 20 includes a cylindrical bearing block 13 provided with a housing 14, an endstone 22 arranged inside housing 14, and an opening 19 made in one face of bearing 18, 20, opening 19 leaving a passage for insertion of pivot 17 into the bearing as far as endstone 22. Endstone 22 has a main body provided with a cavity configured to receive pivot 17 of the staff of the rotary wheel set. Pivots 17 of staff 16 are inserted into housing 14, staff 16 being held but still able to rotate to allow the motion of the rotary wheel set.

(11) The two bearings 18, 20 are shock absorbers and also comprise a resilient support 21 for endstone 22 to dampen shocks and prevent staff 16 from breaking. A resilient support 21, represented in FIG. 4, is, for example, a flat spring with axial and radial deformation on which endstone 22 is assembled. Resilient support 21 is fitted inside housing 14 of bearing block 13 and it holds endstone 22 suspended inside housing 14. Thus, when the timepiece is subject to a violent shock, the spring absorbs the shock and protects staff 16 of the rotary wheel set. Resilient support 21 has a spiral shape with several strands 25 (three here), each strand 25 connecting a rigid central ring 24 to a rigid peripheral ring 23. Peripheral ring 23 is fitted inside housing 14 of bearing block 13 and held by one or more inner faces of the bearing block 13 of FIG. 3. Endstone 22 is fitted inside central ring 24 of resilient support 21. The material and thickness of the resilient support are chosen to allow deformation thereof by a large force, for example following a shock which may produce a force of 100 G or 200 G, one G being the Earth's gravitational pull.

(12) In a first embodiment of FIG. 5, pivot 17 has the shape of a substantially circular first cone 26 with a first solid angle 31. Solid angle 31 is the angle formed inside the cone by its external wall. Apex 29 of first cone 26 is also rounded with a predefined first radius of curvature to allow rotation of pivot 17. The first radius of curvature is comprised in a range, for example, from 0.2 μm to 40 μm, or from 0.2 μm to 25 μm, preferably from 0.2 μm to 15 μm. In FIG. 3, the first radius of curvature is equal to 10 μm.

(13) The cavity of endstone 22 has the shape of a second cone 28 with a second solid angle 32 at the apex. In order for pivot 17 to be able to rotate inside the cavity, second solid angle 32 is greater than first solid angle 31 of first cone 36. Preferably, second cone 28 has a second solid angle 32 comprised in a range from 60 to 120°, or 80 to 100°. Second solid angle 32 is substantially equal to 90° in FIG. 3, since this is the angle that provides substantially equal friction in the different positions of the staff relative to the direction of gravity, as previously explained. Apex 27 of second cone 28 is also rounded and has a predefined second radius of curvature. The curvatures of apexes 27, 29 of the two cones 26, 28 facilitate the rotation of pivot 17 in endstone 22.

(14) According to the invention, the second radius of curvature 27 of second cone 28 of endstone 22 is smaller than first radius of curvature 29 of first cone 26 of pivot 19. This therefore avoids any decentring of pivot 19 in endstone 22 and hence the risk of the staff jamming. The second radius of curvature is, for example, less than 40 μm, or less than 30 μm, or less than 20 μm, or less than 10 μm. The second radius of curvature is preferably at least equal to 0.1 μm, or greater than 1 μm.

(15) In the first embodiment, represented in FIG. 5, the second radius of curvature is equal to 4 μm, while the first radius of curvature is 10 μm. Such radii of curvature improve the centring of pivot 17 in the cavity and further avoid the risk of decentring the staff between bearings 22.

(16) In a variant (not represented in the Figures) the second radius of curvature of the endstone is equal to 10 μm, while the first radius of curvature is 15 μm.

(17) Other examples of values are of course possible, provided that the second radius of curvature is smaller than the first radius of curvature. Preferably, these values lie within one of the aforementioned ranges.

(18) In a second embodiment of the timepiece movement of FIGS. 6 and 7, endstone 22 is the same as that of the first embodiment, but pivot 30 is different. Indeed, the apex 40 of first cone 33 of pivot 30 is cut again to form a circular third cone 35, having a third solid angle 42 substantially equal to the second solid angle 32 of second cone 28 of endstone 22. In the example, the second solid angle 32 and third solid angle 42 are 90°. The third cone 35 is restricted around apex 40 of pivot 30. In FIGS. 6 and 7, third cone 35 has a mean diameter 37 of 29 μm and a lateral radius 38 of 21 μm, while the height of the first cone is, for example, 500 μm. First cone 33 forms the body of pivot 30, but it is truncated at its apex by third cone 35 whose solid angle 42 is different in order to fit the cavity of endstone 22. Third cone 35 has the same rounded apex with the same radius of curvature as first cone 26 of the first embodiment of FIG. 5, to maintain the same advantages. Thus, additionally, the connection between pivot 30 and endstone 22 is improved by slightly increasing the area of friction, to prevent premature wear of pivot 30 and of endstone 22.

(19) To obtain such a small second radius of curvature in a conical cavity of an endstone, the material used to make the endstone body must be specifically selected. Indeed, materials conventionally used to make endstones are too hard to obtain such a radius of curvature. For example, the machining of a ruby or steel material allows second radii of curvature in the endstone cavity of more than 40 μm to be obtained, since the tool used to make the cavity must be sufficiently thick not to break during the machining of the main endstone body.

(20) Thus, for the two embodiments of the invention, the main body of the endstone is formed of a material to be chosen from the following list: an at least partially amorphous metal alloy, an electroformed material, a synthetic material or a composite material.

(21) In a first preferred embodiment for forming the endstone, the main body is formed of an at least partially amorphous metal containing a metal element. This metal element may be a conventional metal element of the iron, nickel, zirconium, titanium or aluminium type, or a precious metal element such as gold, platinum, palladium, rhenium, ruthenium, rhodium, silver, iridium or osmium. An ‘at least partially amorphous material’ means that the material is capable of at least partially solidifying in amorphous phase, i.e. it is subject to an increase in temperature above its melting temperature causing it to lose any local crystalline structure locally, said increase being followed by cooling to a temperature lower than its glass transition temperature allowing said material to become at least partially amorphous.

(22) The amorphous metal is, for example, chosen from the following compositions: zirconium (Zr)-based Zr58.5Cu15.6Ni12.8Al0.3Nb2.8, palladium (Pd)-based Pd43Cu27Ni10P20, or platinum (Pt)-based Pt57.5Cu14.7Ni5.3P22.5. Other amorphous metal compositions can evidently be used, and the invention is not limited to these examples. The cavity is thus obtained by a hot deformation process. The amorphous metal is heated to a temperature higher than its glass transition temperature which considerably reduces its viscosity and thus makes it possible to faithfully replicate the tool on which it is deformed. The tool will have been pre-machined to have a conical shape whose radius of curvature is substantially equal to the desired second radius of curvature. Thus, the second radius of curvature is smaller than the first radius of curvature. Owing to the use of amorphous metal, the tool is not subject to wear during the forming process and thus maintains its original radius, unlike the case of the machining of very hard materials such as ruby or tempered steel. Consequently, smaller radii of curvature are obtained, like those required for the endstone of the invention. In order to improve tribological properties, the endstone can be crystallised to create friction-enhancing phases.

(23) Advantageously, in this embodiment, the amorphous metal can be ceramized to improve tribological properties and thus harden the surface of the main body, in particular in the second cone of the cavity. Thus, wear due to friction of the e.g. ruby pivot of the arbor is reduced as a result of ceramization. The surface treatment consists in forming a ceramic type layer on this surface. There are several possible means (chemical, thermal, plasma, etc.) of forming this layer. For example, a surface layer of ZrO2 or ZrC or ZrN is obtained for a zirconium (Zr)-based amorphous metal.

(24) In a second embodiment for forming the main body, the main body of the endstone is formed by an electroformed material, for example of the Ni, Ni—P, Ni—Co, Pd, Pd—Co, Pt, Au750, Au9ct type, or otherwise. Galvanic growth is carried out in a corresponding mold. Thus, the mold has the shape of a convex cone whose dimensions correspond to those of the second cone.

(25) A third embodiment for forming the main body consists in making the main body from a synthetic or composite material, such as a polymer material or a reinforced polymer material. The polymer is chosen from the group including polyoxymethylene, polyamide, polyetheretherketone and polyphenylene sulphide. In the case of a composite material, the reinforcement may, for example, be PTFE or graphite particles, to change the tribological properties of the polymer-based material. Other types of reinforcements can be envisaged, such as, for example, nanoparticles of silicon oxides or other ceramics to mechanically strengthen the base polymer. It is evidently also possible to combine several types of reinforcements with a given polymer. For these types of materials, the material is moulded in a mold corresponding to the desired shape. Thus, the mold has the shape of a convex cone whose dimensions correspond to those of the second cone. The body is obtained by moulding this material in the mold.

(26) Advantageously, the main body of the endstone and the resilient support are formed in one piece. In other words, the main body and the resilient support are made of the same material, for example of amorphous metal, to form a one-piece part.

(27) In a variant, the main body of the endstone is overmoulded on the resilient support. The resilient support is pre-formed by a LIGA-type (from the German ‘Röntgenlithographie, Galvanoformung, Abformungtype’) lithography, electroplating and moulding process.

(28) Naturally, the invention is not limited to the embodiments described with reference to the Figures and variants could be envisaged without departing from the scope of the invention.