Clock movement having a balance and a hairspring

Abstract

The invention relates to a clock movement which includes a balance and hairspring oscillator and an escapement engaging with the oscillator. The outer coil of the hairspring includes a stiffened portion (9") arranged such as to at least partially compensate for the variation in the operation of the movement in accordance with the oscillatory amplitude of the balance due to the escapement. The hairspring also includes at least one of the following features: a) a distance (R') between the inner end of the hairspring and the centre of rotation of the hairspring smaller than 400 μm, b) a Grossmann curve (10) defined by the inner coil of the hairspring, and c) a stiffened portion defined by the inner coil of the hairspring.

Description

technical field [0001] The present invention relates to a chronograph movement comprising an oscillator of the balance-and-spring type and an escapement, and more particularly to such a movement whose isochronism is improved. By "isochronism" is meant a change in differential rate depending on the amplitude of the balance wheel and depending on the position of the watch. Background technique [0002] When the balance of a conventional balance-and-hairspring oscillator oscillates, the balance spring unrolls eccentrically due to the fact that the center of gravity of the balance spring is not on the axis of the oscillator and said center of gravity moves. This eccentric spread generates a large restoring force between the pivot center of the shaft of the oscillator and the bearing in which the pivot center of the shaft of the oscillator rotates, which force further varies depending on the amplitude of the vibration. These restoring forces disturb the oscillations of the balan...

AI Technical Summary

Problems solved by technology

[0003] However, it is known that the concentricity of the hairspring expansion is not the only factor having an effect on the isochronism

When mounted inside a movement, especially in the case of a Swiss lever escapement, the oscillator is disturbed by the escapement, which results in a loss of differential

In fact, during the unlocking phase, the oscillator is subjected to a resisting torque ahead of the center line, and this results in a loss of

During the pulse phase, the oscillator is first subjected to a drive torque before the centerline, which results in gain, and then after the centerline, which results in a loss

In general, the escapement thus produces a differential loss and this disturbance caused by the escapement is greater for smaller amplitudes of the balance wheel than for larger amplitudes of the balance wheel

[0004] The two phenomena mentioned above (i.e., the eccentric expansion of the hairspring and the loss of differential rate caused by the escapement) do not depend or hardly depend on the position of the watch

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