1. Field of the Invention
The present invention relates to a driving member for a timepiece movement.
2. Related Art
In a mechanical timepiece movement, the driving member is the member which provides the energy to the rest of the movement to turn the gear train. The driving member is generally in the form of a barrel having a barrel drum, a spiral driving spring, or “barrel spring”, housed in the barrel drum, a barrel arbor and a barrel cover. The barrel drum pivots around the barrel arbor and has a toothing on its periphery which co-operates with the gear train to drive it. The inner end of the driving spring is fixed to the barrel arbor to which a ratchet-wheel is fixedly attached, which ratchet-wheel is driven by the winding stem of the watch (in the case of a manual winding watch) or by its oscillating weight (in the case of an automatic winding watch). The outer end of the driving spring is fixed to the inner peripheral surface of the barrel drum via a brace which can be fixed or sliding. Rotation of the ratchet-wheel by the winding stem or the oscillating weight rotates the barrel arbor which tightens the driving spring and thus enables the latter to accumulate energy. The driving spring then progressively releases this energy as it relaxes, rotating the barrel drum.
An important feature of a mechanical timepiece movement is its duration of run, i.e., the duration during which it can operate between two windings. In order to increase the duration of run, it is known to arrange several barrels in series in a single movement. Examples of such an arrangement can be seen in the following patents or patent applications: EP 1 115 040, CH 693 516, FR 1 195 976 and CH 599 580. The arrangements described in these documents all have the disadvantage of being bulky and complicated. They indeed require parts such as the centre piece 6′ and barrel covers 9 and 12 in document EP 1 115 040, the hub 35 and the intermediate barrel bridge 14 in document CH 693 516, the disk 9 and the hubs 5 in document FR 1 195 976 and the toothings 1 to 4 in document CH 599 580.