EP2466393B1 - Spring of a barrel including such a spring - Google Patents

Description

Technical area

The present invention relates to the field of mechanical watchmaking. It relates more particularly to a barrel spring and a barrel having a drum containing the spring and a shaft.

State of the art

• un tambour de barillet, qui est une sorte de boîte cylindrique comprenant un fond et des parois latérales, le tambour étant muni d'une denture extérieure pour entraîner le rouage,
• un arbre de barillet pivotant entre pont et platine et muni d'un crochet disposé sur sa bonde,
• un ressort lame fixé, par une première extrémité à un dégagement opéré sur le diamètre intérieur des parois latérales du tambour et, par une deuxième extrémité au crochet de l'arbre de barillet, et
• généralement, un couvercle fermant le tambour.

A barrel of conventional type comprises:

• a barrel drum, which is a kind of cylindrical box having a bottom and side walls, the drum being provided with an external toothing to drive the gear,
• a cylinder shaft pivoting between bridge and plate and provided with a hook disposed on its bung,
• a leaf spring fixed at a first end to a clearance operated on the inside diameter of the side walls of the drum and, by a second end to the hook of the barrel shaft, and
• generally, a lid closing the drum.

The skilled person knows that one of the main factors to improve the performance of a movement is the quality of the pivoting of the various elements and the weakness of the friction involved. This point is particularly essential at the level of the barrel where the forces which are exerted are important and where the defects in the guidance of the shaft and the drum can have not inconsiderable consequences at the level of the power reserve.

To improve these pivoting conditions, it has been proposed a large number of devices associating ball bearings, arranged at different locations, at the moving parts.

Such barrels are known CH 390 801 , FR 403 943 and JP 11174162 . All these barrels have a drum with a lid rotated on the barrel shaft with two separate ball bearings.

The presence of two ball bearings for pivoting the drum on the barrel axis has several disadvantages such as a loss of efficiency, a delicate alignment of the ball bearings and a poor control of the frills of the cover-spring- drum. In addition, the presence of several ball bearings increases the size of the barrel, makes assembly more delicate and has a significant cost.

The document CH 610178 proposes, with the aim of improving the pivoting quality of the barrel, to mount it cantilevered by means of a ball bearing. The barrel shaft is driven out of the outer ring of this bearing while the inner ring is fixed in a housing in the drum. In addition, the drum is pivoted from the outside by means of rollers with which it cooperates.

However, the presence of the rollers is troublesome in terms of the size that they generate.

The document CH 285199 discloses a spring assembly formed of two blades wound one in the other.

The present invention aims not only to overcome these disadvantages by providing a barrel spring and a barrel optimized at the pivoting and yield provided, while avoiding any difficulty of congestion related to the use of ball bearings.

Disclosure of the invention

More specifically, the invention relates to a mainspring as defined in the claims. The invention also relates to a barrel containing such a spring according to the invention.

Brief description of the drawings

Other details of the invention will appear more clearly on reading the description which follows, made with reference to the Figures 1 to 3 attached and schematically illustrating the invention.

Mode (s) of realization of the invention

In order to illustrate the invention, but in a nonlimiting manner, consider in the present description a uniform and uniform barrel spring, of constant thickness and constant flexural stiffness. Introduce a reference winding, or reference strain, or nominal winding. To fix the ideas, consider a spiral winding of Archimedes with constant pitch. It corresponds to the deformation under the effect of a constant torque only, without radial or axial force. This holding torque is balanced by a variation of curvature throughout the spring, constant in the case of a homogeneous, isotropic and uniform spring. The reference winding corresponds to the unwinding of the barrel about halfway.

The figure 1 represents a first spiral of Archimedes and a second spiral of Archimedes shifted by a half-turn. These two spirals fit perfectly with a constant step. They have a central symmetry of order 2. The figure 2 represents three Archimedes spirals staggered by a third of a turn with a central symmetry of order 3.

For a cylinder of given dimensions, the number of unwinding turns of a barrel with two springs staggered by a half-turn would be reduced by about half. A thickness divided by half allows approximately to keep the number of turns. The gear ratio between the barrel and the center wheel will be adapted according to the torque delivered.

In a particularly interesting way, because of the central symmetry of the springs, the resultant forces exerted on the axis of the barrel would be almost zero if we neglect the reaction of the gear train driven by the barrel.

Thus, in order to implement the advantages resulting from such a spring at a barrel, the barrel spring according to the invention comprises a plurality of coplanar blades 10a, 10b spirally wound into one another.

The blades forming the spring may be independent of one another. Each blade may have its own attachment system and be attached independently on the plug of the barrel shaft, for example by means of a hole provided at the inner end of the blade and acting as eyelet. The barrel plug contains a corresponding number of hooks arranged symmetrically to cooperate with the eyelets of each blade.

Alternatively, the blades forming the spring are connected to each other. In a first variant, a single and common fastening system can be provided for all the blades. For example, the blades meet in a hub, the latter being provided with the fastening system. It can thus have a shape structure, male or female, cooperating with a complementary structure, female or male, located on the shaft. In particular, it is possible to envisage a square assembly or a mounting with a slot, for example arranged at the level of the shaft, into which a lug integral with the hub is inserted.

The outer ends of each blade are arranged substantially symmetrically with respect to the center of the spiral. They are arranged so as to cooperate with the inside of a barrel drum. This cooperation is usually a friction, but can also be a rigid connection.

In the case of frictional engagement, the outer ends of each blade may each be extended by a torque limiting system for cooperating with the interior of the side wall of the barrel drum. This torque limiting system may consist of a flange associated with each of the blades, forming a sliding flange. The sliding flanges being known to those skilled in the art, this element will not be described in more detail. The flanges are preferably arranged symmetrically. One can also provide a tooth disposed on the outer end of the blades and intended to cooperate with notches or a crenellated structure, formed inside the side wall of the barrel drum. A torque limitation is thus achieved by elastic deformation of the blades in a radial direction.

In a further variant, the inner ends of each blade are independent and each comprise a fastening device, similar to what has been described above for independent blades. In contrast, the blades can be joined by an outer frame 14. A connecting zone 16 may be provided between the end of the blades and the frame 14.

The outer ends of each blade are arranged symmetrically with respect to the center of the spiral and join the frame 14. The latter is arranged so as to cooperate with the inner wall of a barrel drum. This cooperation is usually a friction, but can also be a rigid connection.

Like what has been proposed above, the cooperation can also be of the sliding type, in order to limit the winding torque of the barrel. With a frame 14 connecting the outer ends of the blades and rubbing against the inner wall of the barrel drum, the torque limiting system can be obtained by making one or more slots in the frame 14 to allow it to deform when the maximum torque is reached, allowing the spring to move relative to the drum to reduce the torque.

Even with a hub uniting the blades at their inner end, the outer ends can also be joined by a frame 14, which can optionally be slotted to provide the torque limiting system.

Preferably, the torque limiting system and the blades 10a, 10b are made in a monolithic piece. The fastening device 12 can also be integrally assembled with the blades and, where appropriate, with the torque limiting system.

Although the above examples relate to a barrel spring provided with two blades, it is conceivable that the spring has n blades shifted by 360 ° / n. Preferably, n is between 2 and 4 (inclusive).

As regards the materials, one will choose a material with adequate elasticity characteristics and allowing the shaping of the spring, in particular, by deep etching or growth techniques. Indeed, given the dimensions, traditional formatting techniques (cutting, machining, rolling ...) are not suitable. The spring may, for example, be made of silicon, in particular monocrystalline silicon, optionally covered with a layer of silicon or a diamond layer. It will also be possible to make the polycrystalline diamond spring, shaped by deep etching.

The invention also relates to a barrel comprising a barrel drum, a barrel spring as proposed above and contained in the drum, and a shaft on which is mounted freely the barrel drum. Naturally, the shaft is arranged to cooperate with the fastening devices of each of the blades. Alternatively, the shaft is arranged to cooperate with the single fastening device located on the hub joining the inner ends of the blades.

Depending on the possible presence of a torque limiting system and the solution chosen to achieve it, the drum is arranged to cooperate with this torque limiting device. In particular, in the case of a torque limiting system by a tooth disposed on the outer end of the blades, the drum has notches or a crenellated structure formed inside its side wall.

The examples above have been proposed by way of non-limiting example. It can be provided that the pitch of the turns is variable or that the thicknesses of the blades also vary, regularly or not, in order to act on the regularity of the transmitted torque, on the stored energy density (distribution of the stresses along the blades) or on the concentric development of the blades so as to have a radial force resulting almost zero exerted on the shaft.

Claims (13)

1. Barrel spring for a watch movement comprising a plurality of coplanar blades (10a, 10b) wound in a spiral in one another, the inner ends of each blade each being secured to a fastening device (12), to be fastened on a barrel arbor, characterized in that the outer ends of each blade are positioned substantially symmetrically relative to the center of the spiral and are arranged so as to be able to cooperate with a barrel drum.
2. Barrel spring according to claim 1, characterized in that the fastening system is unique and shared for all of the blades.
3. Barrel spring according to one of claims 1 and 2, characterized in that the blades (10a, 10b) and the fastening system (12) are made in a monolithic piece.
4. Barrel spring according to one of the preceding claims, characterized in that the outer ends of each blade are each extended by a torque limiting system intended to cooperate with the inside of the wall of a barrel drum.
5. Barrel spring according to claim 4, characterized in that said torque limiting system and the blades (10a, 10b) are made in a monolithic piece.
6. Barrel spring according to claim 5, characterized in that said torque limiting system, the blades (10a, 10b) and the fastening device (12) are made in a monolithic piece.
7. Barrel spring according to one of claims 4 to 6, characterized in that the torque limiting system is a clamp associated with each of the blades, said clamps being positioned substantially symmetrically.
8. Barrel spring according to one of claims 4 to 6, characterized in that the torque limiting system is a slotted frame, to which each of the blades are connected.
9. Barrel spring according to one of the preceding claims, characterized in that it includes n blades offset by 360°/n.
10. Barrel spring according to claim 9, characterized in that n is comprised between 2 and 4, inclusive.
11. Barrel spring according to claim 1, characterized in that the blades are connected by a frame joining the outer end of said blades.
12. Barrel comprising:

    - a barrel drum,

    - a barrel spring according to one of the preceding claims, and contained in the drum,

    - an arbor on which the barrel drum is freely mounted,

    characterized in that the arbor is arranged to cooperate with said fastening devices or said single fastening device.
13. Barrel according to claim 12, containing a spring according to one of claims 4 to 10, characterized in that the drum is arranged to cooperate with the torque limiting device.

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