Spiral/collet assembly for a horological movement

1. Balance spring-collet assembly for a timepiece movement, comprising a collet and a balance spring having an inner turn and being attached at its inner end to the collet, the attachment defining a point of junction between the balance spring and the collet, the collet being adapted for mounting on a shaft, an external periphery of the collet defining abutments against which the inner turn of the balance spring may come to rest during a shock before the elastic limit of the inner turn is exceeded, wherein said abutments are situated at respective distances from a center of a shaft on which the collet is adapted to be mounted that increase along a direction of the balance spring from its inner end to its outer end starting at said point of junction.

2. Balance spring-collet assembly according to claim 1 , wherein the abutments are spaced from the balance spring so as not to be touched by the balance spring during the normal operation of said spring.

3. Balance spring-collet assembly according to claim 1 , wherein the abutments are defined by discrete segments of an external periphery of the collet.

4. Balance spring-collet assembly according to claim 3 , wherein the number of said abutments is at least three.

5. Balance spring-collet assembly according to claim 3 , wherein the abutments are arranged according to a substantially regular angular distribution.

6. Balance spring-collet assembly according to claim 3 , wherein the abutments comprise substantially circular arcs having as their center a center of a shaft to which the collet is adapted to be mounted.

7. Balance spring-collet assembly according to claim 3 , wherein the collet comprises elastic arms arranged as a polygon between which a shaft is engageable, and at least one of said abutments is situated at a zone of junction between two of said elastic arms.

8. Balance spring-collet assembly according to claim 3 , wherein the collet comprises elastic arms arranged as a polygon between which a shaft is engageable, and at least one of said abutments is defined by an element projecting from an outer side of one of said elastic arms.

9. Balance spring-collet assembly according to claim 1 , wherein each of said distances is selected in such a way that in a configuration where a point of the inner turn of the balance spring is resting against a corresponding abutment under the action of a radial force oriented toward a center of a shaft to which the collet is attachable and exerted at said point, the deformation of the inner turn of the balance spring at said point is a certain percentage of the maximum elastic deformation that the inner turn may undergo at said point, said percentage being substantially the same for all of said distances.

10. Balance spring-collet assembly according to claim 1 , wherein each of said distances is a percentage of the radius of the inner turn of the balance spring at rest at a point of said inner turn facing a corresponding abutment, said percentage being substantially the same for all of said distances.

11. Balance spring-collet assembly according to claim 1 , said assembly being constituted of a single piece.

12. Balance spring-collet assembly according to claim 1 , said assembly being constituted of a material that is not capable of plastic deformation.

13. Balance spring-collet assembly according to claim 12 , wherein said assembly is constituted of a silicon-based material.

14. Timepiece movement comprising a balance spring-collet assembly according to claim 1 .