EP1973013B1 - Balance for a timepiece movement - Google Patents

Description

The subject of the present invention is a pendulum for a clockwork movement that makes it possible to achieve high performances, that is to say to present higher quality factors than current balances both in horizontal position (Qh) and in position. vertical (Qv).

Thus a first object of the present invention is to provide a balance whose quality factors Qh and Qv are the highest possible. A second object of the invention is to provide a balance having good Qh and Qv intrinsic quality factors but which is optimized in the sense that the difference between quality factors Qh and Qv is reduced in order to reduce the differences in amplitudes. in flat-hung and thus ensure that the energy losses for the operation of an exhaust regulator provided with such a pendulum undergo variations as low as possible depending on the position of the balance in space.

A rocker of the prior art is described in the document GB 1,079,370 .

The pendulum for a watch movement according to the present invention is distinguished by the features set forth in claim 1.

• La figure 1 illustre en perspective une première forme d'exécution du balancier selon l'invention.
• La figure 2 illustre en perspective une seconde forme d'exécution du balancier selon l'invention.

The attached drawing illustrates schematically and by way of example two embodiments of the beam according to the invention.

• The figure 1 illustrates in perspective a first embodiment of the pendulum according to the invention.
• The figure 2 illustrates in perspective a second embodiment of the pendulum according to the invention.

The performance of a pendulum for a watch movement is characterized by its ability to oscillate in various positions.

In practice it will be said that a balance spring system oscillates effectively if it loses a minimum of angular amplitude per period or alternation.

Specifically, the oscillation capacity of a balance spring system is measured by quality factors Qv in vertical position and Qh in horizontal position.

où π est la constante pi
freq est la fréquence d'oscillation du balancier
tps est le temps écoulé pour passer de l'amplitude 300 degrés à 200 degrés.The value of Q quality factor between 300 and 200 degrees of amplitude is given by the formula: $$\mathrm{Q}\mathrm{=}\mathrm{\pi }\times \frac{\mathrm{tps}\mathrm{.}\mathrm{freq}}{\ln \left(300\right)-\ln \left(200\right)}$$

where π is the constant pi
freq is the oscillation frequency of the pendulum
tps is the time elapsed to go from 300 degrees to 200 degrees.

• Qh mesuré quand le plan d'oscillation est à l'horizontale
• Qv mesuré quand le plan d'oscillation est en vertical

As the forces acting on the axis of the balance in its pivots depend on the spatial position of the balance, two quality factors are determined in practice:

• Qh measured when the plane of oscillation is horizontal
• Qv measured when the oscillation plane is vertical

Usually the movements of good quality are equipped with a sprung-balance assembly with Qh values of the order of 300 and Qv of the order of 200.

The factor Qv is naturally worse than the factor Qh because the friction in the bearings of the balance shaft are greater in the vertical position thereof than in horizontal position. Sometimes, to obtain a reduced difference in the HorizontalNerticale voluntarily degrades the quality factor Qh of a sprung-balance assembly by modifying the shape of the pivots of the balance shaft.

The objective of the present invention is to provide a better performing balance therefore can lead to quality factors Qv and Qh improved significantly.

To improve the yield, and therefore the quality factors of a balance, it is necessary to reduce the friction of the air on the moving parts of the balance and reduce contact friction in the pivots due to the weight of the balance and the balance spring. In doing so, it is necessary to maintain the weight of the balance at an acceptable value and maintain its inertia or inertial moment to guarantee, for a given diameter compatible with the space available in a movement, an optimal oscillation amplitude avoiding the delay as well as the rebounds.

The balance according to the present invention comprises a hub 1 intended to be fixed on a balance shaft connected to at least two weights 3 by arms 2. The weights 3 are independent, that is to say they are not in contact with each other, but preferably they all have the same size and the same shape and they are evenly distributed around the hub 1. The balance illustrated at Figures 1 and 2 comprises two flyweights 3, but in variants the balance could comprise three, four, or even more flyweights 3. According to the invention, the cumulative angle of the arcs formed by all the flyweights is an angle which is considerably lower than 360 ° so that, compared to conventional balances, the beam of the rod according to the invention is effectively partially reduced or eliminated reducing accordingly the surfaces in contact with the air and thus the friction forces that derive therefrom. Preferably, this cumulative angle is less than or equal to 225 °, but in certain preferred embodiments (such as those of Figures 1 and 2 ), this cumulative angle is equal to or less than 90 °.

In the first embodiment of the pendulum illustrated in FIG. figure 1 the balance is made of a single high density material, such as platinum, gold or their alloys. In this embodiment the two arms 2 are perforated and thin to reduce the weight in order to concentrate the weight of the balance as far as possible from the axis. The arms are profiled so as to oppose less resistance to air during pendulum oscillations. In this case, the frontal slices 2a, 2b of the arms are not perpendicular to the plane of the balance but inclined V-shaped or C to allow better penetration into the air during their oscillations.

Preferably each weight 3 is connected to the hub 1 by a single arm 2, so that each arm 2 carries its own weight 3 at its end. However, in variants, a flyweight can be connected to the hub 1 by several arms, the arms being preferably thinner and / or more perforated in this case. In addition, and as illustrated in the embodiment of the figure 1 , the arms 2 may have a variable geometric section so that they are wider near the hub 1 and thinner near the weights 3.

In addition, the geometry of the arms is optimized to tend to a beam of equal strength which reduces the thickness or width of the arms towards their ends. The arms are therefore thinner from the center to the outside which allows to obtain a minimum weight and stresses tending to be substantially constant along the arms. These arms are therefore more variable section to the center than to the end thus allowing to lighten the arms.

Most of the weight of the balance is concentrated in the weights 3 fixed on or come from a workpiece with the ends of the arms, These weights 3 comprise front portions 3a, 3b contoured to optimize their penetration into the air.

Each weight 3 comprises peripheral housing 4 in which are arranged the heads of the adjusting screws 5 screwed into the counterweight and allowing balancing and perfect adjustment of the balance.

Compared to a traditional balance wheel balance according to the invention allows to reduce the weight for a given size by the removal of the continuous serge which is replaced by individual weights and the openwork of the arms.

Compared to a traditional balance wheel the rocker according to the invention can significantly reduce the friction with air moving parts, the surfaces in contact being reduced and the arms and the weights being aerodynamically profiled.

The second embodiment of the pendulum according to the invention illustrated in FIG. figure 2 is a bi-material balance. The arms 2 are made of a light material such as titanium, aluminum, magnesium or their alloys or even a lightweight composite material and are also openwork. The weights 3 are similar to those described with reference to the first embodiment and are fixed by screws, rivets or overmoulding, gluing or any other way on the end of the arms 2. As in the first form of The execution of the arms 2 and the weights 3 are aerodynamically profiled to reduce friction in the air.

With such balances, it is possible to obtain for a total idientic clutter quality factors for a balance-hairspring assembly, the hairspring being identical. Qh of the order of 400 to 600 and Qv of the order of 300 to 400 which represents a very substantial increase, almost of the simple doubling.

This improvement in efficiency (loss of energy dissipated) of the balance according to the invention makes it possible to substantially increase the choice or combination of either the power reserve or the operating amplitude.

Which in both cases makes it possible to achieve a greater accuracy of adjustment because the energy consumed by the pendulum is less than the impulse phase during which the energy necessary for the maintenance of the oscillation is transmitted to the pendulum is less disruptive of the regularity of pendulum oscillations.

That the balance is made of one or more materials it always comprises several, at least two, arms distributed uniformly around a hub 1, each of these arms 2 carrying a weight 3 independent. Preferably all the weights have the same size and the same shape,

Although a flyweight 3 can be connected to the hub 1 by several arms, each weight 3 is preferably connected by a single arm to said hub.

Claims (12)

1. Balance for clockwork-movement comprising a hub (1) intended to be fastened to a balance staff and at least two independent inertia blocks (3), each being linked by at least one arm (2) to the hub (1), the inertia blocks (3) being uniformly distributed around the hub (1) and having all the same size and the same shape, characterised in that each inertia block (3) has the general shape of a circular arc centred on the hub (1); in that the cumulated angle of the circular arcs formed by all the inertia blocks (3) is less than 225°; and in that most of the weight of the balance is concentrated in the inertia blocks (3).
2. Balance according to claim 1, characterised in that the cumulated angle of the circular arcs formed by all the inertia blocks (3) is less than or equal to 90°.
3. Balance according to one of the preceding claims, characterised in that each inertia block (3) is linked to the hub (1) by a single arm (2), so that each arm (2) holds at its end its own inertia block (3).
4. Balance according to one of the preceding claims, characterised in that the arms (2) are perforated to reduce their weight.
5. Balance according to one of the preceding claims, characterised in that the front edges (2a, 2b) of the arms have a C or V profile so as to facilitate their air penetration during the oscillations of the balance.
6. Balance according to one of the preceding claims, characterised in that the front edges (3a, 3b) of the inertia blocks (3) have a profile such as to facilitate their air penetration during the oscillations of the balance.
7. Balance according to one of the claims 1 to 6, characterised in that the arms (2) are made of a light material selected from magnesium, aluminium, titanium and their alloys or of a light composite material, while the inertia blocks (3) are made of a dense material selected from platinum, gold, molybdenum or their alloys.
8. Balance according to one of the preceding claims, characterised in that the quality factors of a sprung-balance assembly measured when the plane of oscillation is horizontal respectively vertical are 400 to 600 for Qh and 300 to 400 for Qv, these factors being defined as follows: $$\mathit{Qh}/v=\pi \frac{\mathit{tps}\mathit{\cdot }\mathit{freq}}{\ln \left(300\right)\cdot \ln \left(200\right)}$$

   

   
   where freq is the oscillation frequency of the balance and tps is the elapsed time to pass from a 200° amplitude to a 300° amplitude.
9. Balance according to one of the preceding claims, characterised in that the arms (2) have a variable geometric cross section, such that their cross section is larger close to the hub (1) and smaller close to the inertia blocks (3).
10. Balance according to one of the preceding claims, characterised in that each inertia block (3) comprises at least one adjustment screw (5).
11. Balance according to claim 10, characterised in that each inertia block (3) comprises two adjustment screws (5) whose heads are arranged in peripheral housing (4) of the inertia blocks (3).
12. Manufacturing method of a balance according to one of the preceding claims, characterised in that the independent inertia blocks (3) are made as a one piece construction together with the arms (2), the balance thus being made of a single material.

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