EP2730981B1 - Bearing and balance staff for a timepiece - Google Patents

Description

Technical area

The present invention relates to a bearing for holding and allowing the rotation of a balance shaft of a wristwatch, or of any timepiece.

State of the art

Many devices are known for maintaining the pivot of the balance shaft of a watch movement, the most widespread comprising a pierced stone forming a cushion whose hole allows the passage of this pivot, and a counter-pivot stone limiting the movement axial of the pivot. This arrangement makes it possible to obtain fairly low coefficients of friction, provided that the bearing is lubricated, for example with oil. It is also known to equip these bearings with elastic dampers of various shapes, to allow the stones to move momentarily during an impact, and thus avoid the breakage of the pivots, which are very fragile. Examples of bearings made in this way have been published by FR1393838 , GB1054299 , CH1244360 , and CH192767 .

The oils used for lubrication do not have an indefinite duration; they thicken and degrade after a while, necessitating periodic servicing of the watch. Moreover, these bearings always present, even new, a certain friction due to the viscosity of the oil.

We know, from the document US2002114225 , a balance shaft bearing with a ball bearing. In this document, the axial thrust of the balance is taken up by the balls themselves.

CH191908 describes a miniature ball bearing, while CH299774 describes a corundum bearing and balls. In the latter, however, the balls do not roll within a race, but are held by three circular openings in the bottom of the bearing.

The document FR1129445 describes embodiments of bearings for a balance shaft with ball bearings. In this document, the axial thrust of the balance can be taken up directly by the bearing balls.

Brief summary of the invention

An object of the present invention is to provide a bearing for the balance pin of a watch without lubrication, resistant to shocks, with a more favorable coefficient of friction, not requiring periodic revisions or maintenance, and free of lubrication.

According to the invention, these objects are achieved in particular by means of a bearing and balance shaft assembly, which has the characteristics defined as the subject of the main claim.

Brief description of figures

• La figure 1 est une coupe axiale d'un palier à roulement selon un aspect de l'invention.
• Les figures 2-4 illustrent, en trois dimensions, des variantes d'exécution du palier de l'invention.

Examples of implementation of the invention are indicated in the description illustrated by the appended figures in which:

• The figure 1 is an axial section of a rolling bearing according to one aspect of the invention.
• The figures 2-4 illustrate, in three dimensions, alternative embodiments of the bearing of the invention.

Example(s) of embodiment of the invention

The figure 1 represents a ball bearing for a balance wheel of a clock movement. The balance wheel (not visible) is integral with an axle 50, of which only one end is shown, which is maintained between the plate and the balance cock by two bearings. A kitten 41 of cylindrical shape contains inside it balls 44 which can rotate inside the ring 42, the pierced element 45 and the counter-pivot 43 prevent the axial displacement of the balls 44. The bearing of the invention does not requiring no lubricating oil, the pierced element 45 and the counter-pivot 43 are preferably flat and do not have any recesses.

The balls 44 and the counter-pivot element 43 are preferably made of a material that is free of lubrication, for example of ceramic, more preferably of zirconium oxide ceramics, or of a crystalline material with a low coefficient of friction and a sufficient mechanical strength, for example silicon, corundum or diamond. In particular, satisfactory friction values can be obtained by choosing, for the balls 44 and the counter-pivot 43, a non-metallic material, or a material different from that of the pivot 55, which is usually made of steel.

The balls 44 roll inside a circular race formed by the internal surface of the ring 42, which is preferably made of steel, or stainless steel. Tests with four balls have given conclusive results, but the invention also includes variants comprising a greater or lesser number of balls.

The balls 44 and the elements 45 and 43 are assembled inside the chaton 41 permanently and unremovably, by crimping. Once the bearing is assembled, the four balls 44 are necessarily positioned at 90°, leaving between them an opening exactly sized to allow the passage of the pivot 55 with a desired radial contact force, and can in no case exit through the hole. 46.

The structure of the bearing of the invention does not provide for an internal race for the rolling of the balls 44, the balls being directly in contact with the lateral surface of the pivot 55. This arrangement makes it possible to limit the diameter outside of the bearing, which involves a significant reduction in friction. Tests have shown that bearings according to the invention with an outside diameter of less than one millimeter, more preferably less than 0.9 millimeters, make it possible to achieve friction levels comparable to or better than conventional balance bearings, without the need to be lubricated. with oil.

The hole 46 of the pierced element 45 preferably allows the passage of the rod 51 of the balance shaft 50 without contact or friction. The point 58 of the pivot 55 is preferably rounded and polished, so as to minimize friction during pivoting on the counter-pivot 43. Depending on the case, the counter-pivot element 43 will be made of synthetic corundum or ruby, ceramic of zirconium, silicon or diamond oxide or another material having the required mechanical and tribological properties; the pierced element 45, on the other hand, is not necessarily in direct contact with the axis 50 and, in this case, could be made with the same or with other materials, for example metal.

The landing shown in figure 2 comprises a kitten 41 having the characteristics explained above with a conical bearing surface 49. The kitten 41 is housed inside a support element 60 having an internal conical surface 69, the profile of which corresponds to that of the bearing surface 49. The bezel 41 is held elastically by the elastic flexible element 65, retained by the shoulder 62. In this embodiment the elastic element 65 comprises radial arms 62, imparting an axial force (relatively in the direction of the balance shaft 50) on the base of the kitten 41, as well as centering arms 27 pressing radially on the side face of the kitten 41. In this way the elastic element 65 has both a function of recovery of the axial thrust of the pendulum and alignment of the bearing.

The paired surfaces 49 and 69 define a resting position of the kitten 41 and have a self-centering and self-aligning action. In the event of an impact, the bezel 41 can move momentarily thanks to the elasticity of element 65; the geometry of the surfaces 49 and 69 is such that the kitten is automatically brought back by the elastic element 65 to a position aligned and centered with respect to the axis 50 in an exact and reproducible manner.

The picture 3 illustrates a different arrangement of the bearing of the invention. In this case, the elastic element 65 is held in a groove 63 and comprises only three radial arms 66 exerting inclined forces on the kitten 41. Centering and alignment are ensured by the symmetry of the elastic forces and by the conical surfaces 49 and 69, as in the previous example.

The support element 60 could, depending on the case, be a removable element or else a part machined directly in a more complex element of a watch movement, such as the plate for example. According to a preferred variant, the support 60 is a removable element with standardized dimensions, which can take the place, with a minimum of modifications, of the pendulum bearing supports in stone-built movements of the conventional type.

According to another variant embodiment, visible in figure 4 , the kitten 41 is housed in a chamfered hole passing through the support 60 and held by an elastic element 65 comprising radial arms 66, as in the figure 2 , and "S"-shaped centering arms 68 passing through the chamfered hole, and the free end of which rests on a face of the support element 60, while a handle of the "S"-shaped arms 68 contacts the surface lateral kitten 41, with a centering action. A shoulder 47 prevents the bezel from falling when the pin 50 is removed.

In this solution, the automatic centering and alignment of the kitten 41 is ensured by the "S" arms 68 exerting symmetrical radial forces, and the radial arms 66 exerting axial forces. Advantageously, this variant makes it possible to fix the bearing on the support 60 by the single elastic element 65 without other fixing elements, moreover the machining of the support 60 is limited to a simple chamfered hole. This embodiment therefore makes it possible to integrate the bearing of the invention into existing complex parts, for example, a plate or a watch movement bridge, with a minimum of adaptations.

Reference numbers used in the figures

41

kitten

42

Ring

43

counter-pivot

44

ball

45

pierced element

46

hole

47

shoulder

49

kitten cone

50

balance shaft

51

tigron

55

pivot

58

pin point

59

connection

60

support

62

shoulder

63

throat

65

competence

66

radial arm

67

centering arm

68

retaining arm

69

internal cone

Claims (9)

1. A bearing and balance shaft (50) for a watch movement, the bearing comprising a settingl (41) enclosing a plurality of balls (44) rotatable within a circular race (42), the axial movement of the balls (41) being limited by a counter-pivot element (43) and a drilled element (45) with a hole (46) allowing insertion of a pivot of the balance shaft into a space between said balls (44), the bearing being arranged to pivot said shaft between said balls (44), wherein said balls (44) and/or said counter-pivot element (43) are made of a non-metallic material,

   the balls (44), the drilled element (45) and the counter-pivot (43) being assembled inside the setting (41) by crimping, the balls (44) leaving between them an opening allowing the passage of the pivot of the balance wheel (50) and not being able to come out through the hole (46) of the drilled element (45) in any case,

   characterised in that

   when said pivot is inserted into said space, the tip of said pivot is in abutment with said counter-pivot element (43).
2. Bearing and shaft according to the preceding claim, the bearing comprising a elastric holding element (65) for the setting (41) arranged to allow momentary displacement of the bezel (41) from a rest position when there is an impact, and to return it automatically to said rest position.
3. Bearing and shaft according to any of the preceding claims, wherein said balls (44) are four in number.
4. Bearing and shaft according to any of the preceding claims, wherein said balls (44) are more than four in number.
5. Bearing and shaft according to any of the preceding claims, wherein said balls (44) and/or said counter-pivot (43) are made of a material among: ceramic, Zirconium oxide ceramic, silicon, diamond.
6. Bearing and shaft according to any of the preceding claims, wherein said setting (41) comprises a conical surface (49) and is housed inside a support element (60) with an internal conical surface (69) of the same profile.
7. Bearing and shaft according to any of claims 2 to 6, wherein said elastic holding element comprises a plurality of radial arms (66) pressing on the setting (41).
8. Bearing and shaft according to any of the preceding claims, the bearing further comprising a plurality of centering arms (67, 68) acting on a lateral surface of the setting (41).
9. Bearing and shaft according to any of the preceding claims, the bearing having an outer diameter of less than one millimetre or less than 0.9 millimetres.

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