Timepiece transmission mechanism with reduced coupling force

1. A timepiece transmission mechanism, arranged to be integrated in a timepiece movement and comprising at least one differential mechanism including at least one planet wheel set mounted for free rotation and at least three main wheel sets forming the inputs or outputs of said differential mechanism, which three main wheel sets are formed by a frame, a first wheel set arranged to cooperate with a first train, and a second wheel set arranged to cooperate with a second train, only one of said three main wheel sets carrying at least one said planet wheel set permanently meshing with the other two main wheel sets, either directly or through at least one intermediate wheel set which permanently meshes with one of said other two main wheel sets or which is integral in rotation with one of said other two main wheel sets, said differential mechanism being able to kinematically connect said first wheel set and said second wheel set in a coupling position, and to separate them kinematically in an uncoupling position, said transmission mechanism further comprising control means arranged to lock only one of said three main wheel sets in order to couple said differential mechanism, or to completely release said frame and said first wheel set and said second wheel set in order to uncouple said differential mechanism, depending on the position given to said control means by a selector comprised in said transmission mechanism and which is arranged to cooperate with an actuator comprised in said timepiece movement, and/or to be operated by a user, and wherein said control means are returned to a locking wheel set which is whichever of said three main wheel sets on which said differential mechanism is locked in the coupling position, by elastic return means, arranged to exert on said locking wheel set an engaging or friction torque, which is calibrated to allow a safety uncoupling function when the torque transmitted from one to the other of the other main wheel sets distinct from said locking wheel set is higher than said engaging or friction torque, wherein said locking wheel set includes an external toothing with wolf teeth, to allow a safety uncoupling function in one direction of rotation.

2. The transmission mechanism according to claim 1 , wherein said selector comprises at least one column wheel, which is arranged, according to its angular position, to modify the angular position of a lever comprised in said control means, which lever includes a first beak arranged to immobilise or release, depending on its position, a peripheral toothing comprised in said locking wheel set.

3. The transmission mechanism according to claim 1 , wherein said transmission mechanism further comprises mechanical locking means arranged to be operated by an actuator comprised in said timepiece movement and/or by a user, and which are arranged to lock said control means in a coupled or uncoupled position.

4. The transmission mechanism according to claim 1 , wherein said frame, said first wheel set and said second wheel set are arranged to pivot about axes parallel to a same differential direction.

5. The transmission mechanism according to claim 4 , wherein each said planet wheel set is arranged to pivot about an axis parallel to said differential direction.

6. The transmission mechanism according to claim 4 , wherein each said planet wheel set is arranged to pivot about an axis perpendicular to said differential direction.

7. The transmission mechanism according to claim 4 , wherein each planet wheel set is arranged to pivot about an oblique and non-perpendicular axis with respect to said differential direction.

8. The transmission mechanism according to claim 1 , wherein the locking wheel set is whichever of said three main wheel sets on which said differential mechanism is locked in the coupling position, is said frame.

9. The transmission mechanism according to claim 1 , wherein said frame is a crown-wheel.

10. The transmission mechanism according to claim 9 , wherein said at least one planet wheel set is carried by said first wheel set or said second wheel set and permanently meshes with a toothing of an arbor integral at least in rotation with said second wheel set or respectively with said first wheel set, and said at least one planet wheel set permanently meshes with said crown-wheel.

11. The transmission mechanism according to claim 10 , wherein said differential mechanism comprises at least one epicycloidal train wherein said first wheel set forms the planetary carrier, said second wheel set forms the inner planet wheel, and said crown-wheel forms the external planet wheel and is coaxial to said second wheel set and to said first wheel set, and wherein each said planet wheel is confined between said first wheel set and said second wheel set or between said first wheel set and a frame comprised in said transmission mechanism.

12. The transmission mechanism according to claim 11 , wherein said frame is integral with said second wheel set.

13. The transmission mechanism according to claim 11 , wherein said differential mechanism comprises a dual coupling system, with an additional epicycloidal train wherein a third wheel set forms the planetary carrier, said second wheel set forms the inner planet wheel, and wherein a crown-wheel forms the external planet wheel and is coaxial to said first wheel set and to a third wheel set, and wherein each secondary planet wheel is confined between said third wheel set and said frame, and wherein said control means include a lever which includes a first beak arranged to immobilise or release, depending on its position, a peripheral toothing comprised in said locking wheel set, and which includes a second arm including a second beak at its distal end.

14. The transmission mechanism according to claim 11 , wherein each said epicycloidal train includes only gear drive mechanisms.

15. The transmission mechanism according to claim 11 , wherein at least one said epicycloidal train includes at least one friction drive mechanism.

16. The transmission mechanism according to claim 1 , wherein said differential mechanism comprises several levels each having an epicycloidal train.

17. The transmission mechanism according to claim 1 , wherein said transmission mechanism comprises a single coupling system with a spherical differential mechanism, and with frame locking, which includes said frame confined between said first wheel set and said second wheel set, and which carries a hub for guiding the free rotation of each said planet wheel set whose axis is perpendicular to a differential direction to which are parallel the pivot axes of said three main wheel sets, each said planet wheel set permanently meshing with said first wheel set and with said second wheel set.

18. The transmission mechanism according to claim 1 , wherein said transmission mechanism comprises a single coupling system with a differential mechanism having two sun gears, and with frame locking, which includes said frame confined between said first wheel set and said second wheel set, and which carries a hub for guiding the free rotation of each said planet wheel set whose axis is parallel to a differential direction to which are parallel the pivot axes of said three main wheel sets, each said planet wheel set permanently meshing with said intermediate wheel set which permanent meshes with one of said other two main wheel sets, or which is integral in rotation with one of said other two main wheel sets.

19. A timepiece movement comprising at least one transmission mechanism according to claim 1 .

20. The timepiece comprising at least one movement according to claim 19 and/or including at least one transmission mechanism.