HK1070699B - Winding crown for mechanical timepiece - Google Patents

Description

The present invention relates to a mechanical watch-piece winding crown, in particular a winding crown incorporating a torque limiting device to prevent parts of the watch-piece such as the motor spring, winding rod, gears, etc. from breaking when the user continues to turn the crown after the motor spring has been fully wrapped.

The watch's winding crown is known by document US 352.257 to include a first friction wheel solid in the crown casing and held by an axial spring against a second solid wheel in the winding rod. When the watch is winding, the second wheel is driven by the first wheel to a certain threshold beyond which the first wheel can no longer overcome the resistance of the second wheel and starts to slide on the latter, thus preventing the motor spring and other parts of the watch from being subjected to too much stress.

The document FR 917.982 also refers to a lifting crown comprising an elastic friction disc which leads to a certain lifting threshold of the motor spring to a solid plate of the lifting rod.

CH 274 344 also describes a spring-mounted mechanism for wake-up in which the mounting organ comprises elastic friction means consisting of two opposite cylindrical springs radially extending in relation to the mounting rod.

The present invention aims to remedy the aforementioned disadvantages and proposes, for this purpose, a winding crown according to claim 1 in the annex, with particular embodiments defined in the dependent claims, and a watch part incorporating it.

Further features and advantages of the present invention will be apparent from the following detailed description made by reference to the attached drawings in which: Figure 1 is a view in axial cut of the drawbar crown according to the invention; Figure 2 is a view from above of a drive ring included in the drawbar crown according to the invention; and Figure 3 is a view from below of a drive part included in the drawbar crown according to the invention.

As shown in Figures 1 to 3, a winding crown according to the invention for a mechanical watch part, typically a wristwatch, comprises a helmet 1 and, mounted in the helmet 1 coaxially to it, a drive part 2 and a drive part 3.

The drive part 2 is a ring cast into the casing 1 and thus solidary of the latter. The drive part 3 consists of a transverse plate 30 that is perpendicular to the axis 4 of the crown, and a central fixing element 32 formed of a single holder with the plate 30 and protruding axially from the bottom side 34 of the plate 30 facing the carriage 5 of the watchpiece. The central fixing element 32 has a rough axial groove 36 suitable to receive a corresponding threaded end of the mounting rod (not represented) of the mounting part to make the 30 torque plate solidary of this watchpiece and thus allow it to control the lifting of the engine.

Ring 2 comprises 20 cavities, eight in the example shown, arranged regularly around the crown 4 axis and each housing a 22 boudin compression spring and an associated friction organ 24. Each friction organ 24 is in the form of a nipple or an enclave ball pushed parallel to the 4 axis by its respective spring 22 against the lower face 34 of the 30 plate and cooperates with a corresponding alveoli 38 formed in the said lower face 34.As soon as the threshold is reached, the friction organs 24 fade into the respective cavities 20, the strength of the springs 22 being no longer sufficient to overcome the resistance of the plate 30, and begin to slide onto the lower face 34 of the plate 30, which is then no longer driven. This limitation of the torque applied to the plate 30 prevents parts of the watchmaking part, in particular the engine spring, the mounting rod and the gears, from being subjected to excessive stresses.When sliding on the 30 plate, the friction organs 24 produce a click at each passage through a 38 alveolus, indicating to the user that the motor spring is fully up.

The mounting crown according to the invention is made watertight by first and second O-rings 6, 7 held in respective housing 8, 9 formed in the ring 2. The first O-ring 6 provides the seal between ring 2 and a crown tube 10 cast into the carriage 5 of the watchpiece and surrounding the mounting rod. The second O-ring 7 provides the seal between ring 2 and the cap 1.

The mounting crown of the invention has several advantages over conventional torque limiting crowns. In particular, by using several springs associated with several friction organs respectively, the force and therefore the dimensions of each spring can be relatively small, which reduces the axial and radial encumbrance of the crown.

The present invention, which is defined by the attached claims, has been described above as an example only. It is clear that modifications can be made without going beyond the scope of the claimed invention. In one embodiment, for example, the functions of the ring and the tray could be reversed so that the tray is the solidary drive element of the helmet and the ring is the solidary drive element of the mounting rod.

Claims (10)

1. Winding crown for a mechanical timepiece, comprising a torque-limiting device, said torque-limiting device comprising a first element (2) and a second element (30) which are intended to serve as a drive element and a driven element, the driven element being arranged to control the torsion of the mainspring of the timepiece, the first element (2) comprising several cavities (20) each housing a spring (22) and an associated friction member (24), characterised in that each friction member (24) is arranged to be urged by its respective spring (22) against the second element (30) in parallel with the rotational axis (4) of the crown.
2. Winding crown as claimed in Claim 1, characterised in that the cavities (20) are evenly distributed around the rotational axis (4) of the crown.
3. Winding crown as claimed in Claim 1 or 2, characterised in that the friction members (24) are detent elements co-operating with corresponding pockets (38) formed in the second element (30).
4. Winding crown as claimed in any one of Claims 1 to 3, characterised in that the springs (22) are helical springs.
5. Winding crown as claimed in any one of Claims 1 to 4, characterised in that the first element (2) is a drive ring and the second element (30) is a driven plate (30) coaxial to the ring (2).
6. Winding crown as claimed in Claim 5, characterised in that it further comprises a cover (1) within which are mounted the ring (2) and the plate (30), these latter elements being coaxial to the cover (1), in that the ring (2) is fixedly attached to the cover (1), and in that a fixing element (32) extending axially from the plate (30) allows the plate (30) to be made fixedly attached to a winding rod of the timepiece.
7. Winding crown as claimed in Claim 6, characterised in that it further comprises a seal (7) between the ring (2) and the cover (1).
8. Mechanical timepiece comprising a winding crown as claimed in any one of Claims 1 to 7.
9. Mechanical timepiece as claimed in Claim 8, characterised in that the winding crown is sealed.
10. Mechanical timepiece as claimed in Claim 8, characterised in that a seal (6) is provided between the first element (2) of the winding crown and a crown tube (10) fixed to the case middle (5) of the timepiece.