Device for autonomous adjustment of the active length of a spiral

A device for autonomous adjustment of the active length of a spiral, for oscillators of the balance-spiral type, comprising a cock mounted on a plate of a horological movement and in which a shaft of a balance pivots, the spiral including an inner end secured to the shaft of a balance and an outer end secured a first balance spring stud fastened to a balance spring stud holder, the balance spring stud holder being pivotably mounted on the cock concentrically to the shaft of the balance, and means for modifying the active length of the spiral;

• wherein the means for modifying the active length of the spiral comprise:
• at least one arm capable of moving between a rest position and a correction position of the device, the at least one arm having a first free end and a second end cooperating with a first pair of pins mounted on the balance spring stud holder, the first pair of pins being angularly offset with respect to the balance spring stud;
• elastic biasing means configured to exert an elastic action on the at least one arm to return the at least one arm in position;
• an inertia block movable in rotation around a shaft on which at least a first cam is mounted, the inertia block being arranged to rotate freely around the shaft according to gravity, the rotation of the inertia block causing a rotation of the at least first cam and a movement of the at least one arm to act on the spiral and simultaneously modify the active length of the spiral;
• damping means comprising a gearwheel coaxial with the inertia block and mounted on the inertia block, and a damping device arranged to cooperate with the inertia block via the gearwheel and limit the modification of the active length of the spiral in the event of a sudden acceleration or deceleration.