FIELD OF THE INVENTION

The invention concerns a timepiece regulating mechanism, comprising, arranged on a main plate, a resonator mechanism with a quality factor Q, and an escapement mechanism which is subjected to the torque of drive means comprised in a movement, said resonator mechanism comprising an inertia element arranged to oscillate with respect to said plate, said inertia element being subjected to the action of elastic return means directly or indirectly fixed to said plate, and said inertia element being arranged to cooperate with an escape wheel set comprised in said escapement mechanism.

The invention also concerns a timepiece movement comprising drive means, and such a regulating mechanism, whose escapement mechanism is subjected to the torque of these drive means.

The invention also concerns a watch, more particularly a mechanical watch, including such a movement, and/or such a regulating mechanism.

The invention concerns the field of timepiece regulating mechanisms, in particular for watches.

BACKGROUND OF THE INVENTION

Most mechanical watches include a balance/balance spring type oscillator, cooperating with a Swiss lever escapement. The balance/balance spring forms the time base of the watch. This is called the resonator here. The escapement performs two main functions, namely maintaining the back and forth motions of the resonator and counting these back and forth motions. The escapement must be robust, not disturb the balance far from its point of equilibrium, resist shocks, avoid jamming the movement (for example, in the event of overbanking), and thus forms a vital component of the timepiece movement.

Typically, a balance/balance spring oscillates with an amplitude of 300°, and the angle of lift is 50°. The angle of lift is the angle through which the balance travels as the lever fork interacts with the impulse pin, also called the roller-pin, of the balance. In most current Swiss lever escapements, the angle of lift is divided either side of the point of equilibrium of the balance (+/−25°), and the lever tilts by +/−7°.

The Swiss lever escapement belongs to the detached escapement category, since, beyond the half-angle of lift, the resonator no longer touches the lever. This characteristic is essential for obtaining good chronometric properties.

A mechanical resonator includes an inertia element, a guide member and an elastic return element. Conventionally, the balance forms the inertia element, and the balance spring forms the elastic return element. The balance is guided in rotation by pivots which rotate in smooth ruby bearings. The associated friction causes energy losses and disruptions of rate. It is sought to remove these disruptions, which, moreover, depend on the orientation of the watch in the field of gravity. Losses are characterized by the quality factor Q of the resonator. It is also generally to sought to maximise this quality factor Q, in order to obtain the best possible power reserve. It is clear that the guide member is an essential factor in losses.

The use of a rotary flexure bearing, instead of the pivots and conventional balance spring, is a solution that maximises the quality factor Q. Flexible strip resonators, provided they are well designed, have promising chronometric properties, independently of orientation in the field of gravity, and have high quality factors, particularly due to the absence of pivot friction. Further, the use of flexure bearings eliminates problems of wear of the pivots.

However, the flexible strips generally used in such rotary flexure bearings are stiffer than balance springs. This results in work at higher frequency, for example on the order of 20 Hz, and with a lower amplitude, for example 10° to 20°. This at first sight seems incompatible with a Swiss lever type escapement.

An operating amplitude compatible with a resonator with rotary flexure bearings, particularly with strips, is typically from 6° to 15°. This results in a certain angle of lift value, which must be twice the minimum operating amplitude.

In the absence of particular precautions, an escapement with a small angle of lift may have mediocre efficiency and cause too great a losing rate. However, the combination of a high frequency and a low amplitude makes possible speeds of motion of the balance which are acceptable, without being too high, and thus the efficiency of the escapement is not automatically mediocre.

The resonator must have acceptable dimensions, compatible with being housed inside a timepiece movement. It is not possible, to date, to make a rotary flexure bearing of very large diameter, or having several pairs of levels of strips, which, theoretically, by placing successive flexure bearings in series, would allow an oscillation amplitude of the inertia element of several tens of degrees: therefore a flexure bearing with one or two levels of strips at most should be used, for example as known from EP Patent No. 3035126 in the name of THE SWATCH GROUP RESEARCH AND DEVELOPMENT Ltd.

In short, the effect of choosing a rotary flexure bearing is that the amplitude of the balance is reduced, and it is no longer possible to use a conventional Swiss lever escapement, which requires a balance amplitude that is considerably higher than half the angle of lift, i.e higher than 25°. A regulator comprising a resonator with flexure bearings thus requires a particular escapement mechanism, of different dimensioning from that of a normal Swiss lever escapement devised to operate with the same inertia element of the resonator.

SUMMARY OF THE INVENTION

It is an overall object of the present invention to increase the power reserve and precision of current mechanical watches. To achieve this object, the invention combines a resonator having rotary flexure bearings with a lever escapement optimised to maintain acceptable dynamic losses and to limit the chronometric effect of the unlocking phase.

In the absence of teaching in the prior art as to the dimensioning of both the resonator and the escapement mechanism, analytical model calculations and a series of simulations have revealed parameters for the resonator and escapement that are compatible with an acceptable loss and acceptable efficiency.

These calculations and simulations demonstrate that the ratio between the inertia of the inertia element, particularly a balance, and the inertia of the pallet lever, is determinant.

To this end, the invention concerns a regulating mechanism according to claim1.

These resonators with rotary flexure bearings have very high quality factors, for example on the order of 3000, compared to a quality factor of 200 for a normal watch. Dynamic losses (kinetic energy from the escape wheel and pallet lever at the end of the impulse) are independent of the quality factor. These losses may thus become too high with a high quality factor, in relative terms, in comparison to the energy transmitted to the balance.

For proper operation of the mechanism, an impulse pin integral with the inertia element must penetrate up to a certain value, referred to as ‘depth’, the opening in the lever fork. Likewise, to ensure safety during the unlocking phase, once the impulse pin is unlocked, it must then be able to be kept at a certain distance, called the safety distance, from the horn of the fork opposite to the horn with which it was in contact immediately prior to being unlocked.

Thus, the invention further endeavours to impose a particular relation between the dimensions of the lever fork, the depth and safety distance values, and the values of the angles of lift of the lever and of the inertia element, to ensure that the impulse pin is properly removed from the fork, once travel through the half-angle of lift is complete.

The invention also concerns a timepiece movement comprising drive means, and such a regulating mechanism, whose escapement mechanism is subjected to the torque of these drive means.

The invention also concerns a watch, more particularly a mechanical watch, including such a movement, and/or such a regulating mechanism.

