Device for autonomously adjusting the active length of a balance spring

A device for autonomously adjusting the active length of a balance spring, for a balance spring oscillator, comprising a cock mounted on a plate of a horological movement and in which cock a staff of the balance pivots, the balance spring including an inner end integral with the staff of the balance and an outer end integral with a first stud fastened to a stud-holder, the stud-holder being pivotally mounted on the cock concentrically with the staff of the balance, and means for modifying the active length of the balance spring;

• wherein the means for modifying the active length of the balance spring comprise:
• a lever capable of pivoting on the stud-holder between a rest position and two correction positions of the device, the lever having a first free end and a second end having two beaks;
• resilient stressing means configured to exert a resilient restoring action on the lever;
• an inertia block rotatable about a shaft on which a cam is mounted, the inertia block being arranged to rotate freely about the shaft as a function of gravity, the rotation of the inertia block rotating the cam and pivoting the lever so that one of the beaks acts on the balance spring and simultaneously modifies the active length of the balance spring;
• and
• damping means comprising a toothed wheel coaxial with the inertia block and mounted on the inertia block, and a damping device arranged to cooperate with the inertia block via the toothed wheel and to limit the change in the active length of the balance spring in the event of sudden acceleration or deceleration.