EP2362280A1 - Bearing for the balance-shaft of a timepiece and timepiece comprising such a bearing. - Google Patents

Abstract

The bearing has a bush (41) enclosing multiple balls, where axial displacement of the balls is limited by a pivot against element. An element is provided with a hole for permitting insertion of a pivot of a staff balance (50) of a movement of a watch in a space between the balls. The balls and the pivot against element are made of non-metallic and non lubricating material that is chosen from ceramic, zirconium oxide ceramic, silicon and diamond.

Description

Technical area

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

State of the art

Numerous devices are known for maintaining the pivot of the balance shaft of a watch movement, the most common including a pierced stone forming a pad whose hole allows the passage of this pivot, and a counter-pivot stone limiting the movement axial pivot. This arrangement makes it possible to obtain relatively low coefficients of friction, provided that the bearing is lubricated, for example with oil. It is also known to equip these bearings with resilient dampers variously shaped, to allow the stones to move momentarily during a shock, and thus prevent the rupture of the pivots, very fragile. Examples of bearings thus produced 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, forcing periodic revisions of the watch. Moreover, these bearings always have, even new, a certain friction due to the viscosity of the oil.

We know, from the document US2002114225 , a bearing for a balance shaft 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 bearing and corundum balls. In the latter, however, the balls do not roll within a race, but they are held by three apertures in the bottom of the bearing.

Brief summary of the invention

An object of the present invention is to provide a bearing for the balance shaft of a watch without lubrication, impact resistant, with a more favorable coefficient of friction, requiring no periodic maintenance or revisions, and free of lubrication.

According to the invention, these objects are achieved in particular by means of the bearing which has the defined characteristics forming the subject of the main claim.

Brief description of the 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 clockwork movement. The balance wheel (not visible) is integral with an axis 50, of which only one end is shown, which is maintained between the plate and the cock by two bearings. A kitten 41 of cylindrical shape contains within it balls 44 rotatable inside the ring 42, the pierced element 45 and the pivot-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 include recesses.

The balls 44 and the counter-pivoting element 43 are preferably made of a material free from lubrication, for example ceramic, more preferably zirconium oxide ceramics, or a crystalline material with a low coefficient of friction and a low friction coefficient. 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 within a circular path formed by the inner surface of the ring 42, which is preferably made of steel, or stainless steel. Trials with four beads have yielded conclusive results, but the invention also includes variants with a higher or lower number of beads.

The balls 44 and the elements 45 and 43 are preferably assembled inside the kitten 41 permanently and releasably, for example by crimping. Once the bearing is assembled, the four balls 44 necessarily position themselves at 90 °, leaving between them an aperture exactly dimensioned to allow the passage of the pivot 55 with a desired radial contact force, and can in no case out through the hole 46.

The structure of the bearing of the invention does not provide an internal ring for rolling the balls 44, the balls being in direct contact with the lateral surface of the pivot 55. This arrangement makes it possible to limit the diameter outside the bearing, which has 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 comparable or better levels of friction of the 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 beam 51 of the balance shaft 50 without contact or friction. The tip 58 of the pivot 55 is preferably rounded and polished, so as to minimize the friction during pivoting on the counter-pivot 43. Depending on the case, the counter-pivoting element 43 will be made of synthetic corundum or ruby, ceramic zirconium, silicon or diamond oxide or other 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 made of metal.

The level represented at figure 2 comprises a kitten 41 having the features explained above with a conical bearing surface 49. The kitten 41 is housed inside a support member 60 having an internal conical surface 69, whose profile corresponds to that of the bearing surface 49. The kitten 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 resumption of the axial thrust of the balance and alignment of the bearing.

The paired surfaces 49 and 69 define a rest position of the kitten 41 and have a self-centering and self-aligning action. In case of shock the kitten 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 figure 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 has only three radial arms 66 exerting inclined forces on the kitten 41. The centering and the alignment are provided by the symmetry of the elastic forces and by the conical surfaces. 49 and 69, as in the previous example.

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

According to another variant embodiment, visible to the 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 FIG. figure 2 , and "S" centering arms 68 passing through the chamfered hole, and the free end of which bears on one face of the support member 60, while a loop of the "S" arms 68 contacts the surface Lateral kitten 41, with a centering action. A shoulder 47 prevents the kitten from falling when the shaft 50 is disassembled.

In this solution, the automatic centering and alignment of the kitten 41 are provided 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 fastening elements, moreover the machining of the support 60 is limited to a simple chamfered hole. This embodiment thus allows to integrate the bearing of the invention in existing complex parts, for example, a turntable or a watch movement bridge, with a minimum of adaptations.

Reference numbers used in the figures

41

kitten

42

Ring

43

against pivot

44

ball

45

pierced element

46

hole

47

shoulder

49

kitten cone

50

balance shaft

51

shank

55

pivot

58

pivot point

59

connection

60

support

62

shoulder

63

throat

65

spring

66

radial arm

67

centering arm

68

holding arm

69

internal cone

Claims (9)

Bearing for a balance shaft (50) of a watch movement, comprising a kitten (41) enclosing a plurality of balls (44) rotatable within a circular stroke (42), the axial displacement of the balls (41) being limited by a counter-pivot member (43) and a pierced member (45) with a hole (46) for inserting a pivot of the balance shaft into a space between said balls (44) , the bearing being arranged to pivot said pin between said balls (44), the tip of said pivot bearing against said counter-pivot member (43), characterized in that said balls (44) and / or said counter element pivot (43) are made of a non-metallic material and / or free of lubrication. Bearing according to the preceding claim, comprising an elastic holding member (65) of the kitten (41) arranged to allow the momentary movement of the kitten (41) from a rest position during an impact, and to automatically return it to said rest position. Bearing according to one of the preceding claims, wherein said balls (44) are four in number. Bearing according to one of the preceding claims, wherein said balls (44) and / or said counter-pivot (43) are made of a material among: ceramic, ceramic zirconium oxide, silicon, diamond. Bearing according to one of the preceding claims, wherein said kitten (41) has a conical surface (49) and is housed inside a support member (60) with an internal conical surface (69) of the same profile. . Bearing according to one of the preceding claims, wherein said elastic holding member comprises a plurality of radial arms (66) pressing on the kitten (41). Bearing according to one of the preceding claims, further comprising a plurality of centering arms (67, 68) acting on a lateral surface of the kitten (41) Bearing according to one of the preceding claims, in combination with a watch movement with a balance shaft (50), the bearing for pivoting said balance shaft (50). Bearing according to the preceding claim, with an outer diameter less than one millimeter or less than 0.9 millimeters.

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