Timepiece assembly comprising a balance wheel and a balance shaft

Abstract

The invention relates to a watch assembly comprising: - a balance shaft (10) provided with a first annular rim (11) defining a first axial stop, a first bearing surface (13) of diameter D adjoining the first annular rim (11), - a balance (20), comprising a hub (22) provided with a central opening, through which the balance (20) is adjusted on the first bearing surface (13), bearing on the first axial stop, - a locking member (30), rigidly mounted on the balance shaft (10) and arranged so as to lock the balance (20) against the annular rim. According to the invention, the locking member (30) has a concavity in its part situated around the shaft (10), which limits the contact between the locking member (30) and the balance (20) to an area situated around an annular portion, surrounding the shaft (10).

Description

Technical field

[0001] The present invention relates to the field of watchmaking. It relates more particularly to a watch assembly comprising: a balance shaft provided with a first annular rim defining a first axial stop, a first bearing surface of diameter d adjoining the first rim, a balance, comprising a hub provided with a central opening, through which the balance is adjusted on the first bearing surface, bearing on the first axial stop, a locking member, rigidly mounted on the balance shaft and arranged so as to lock the balance against the annular rim. State of the art

[0002] Usually, the balance wheels are driven onto a rim of the balance shaft. This rim forms a stop, on which the balance wheel is positioned.

[0003] The balance wheels are machined from metal bars by turning. The materials used, both for the balance wheel and the balance shaft, allow for dimensional precision and controlled driving forces.

[0004] It is known that parts made of silicon do not withstand driving constraints, due to their fragility caused by the absence of a plastic domain in silicon.

[0005] For wheels or balance springs made of silicon, the issue of fixation has already been addressed. Thus, it has been proposed to use an intermediate sleeve, between the shaft and the silicon part, which absorbs the driving forces. However, controlling the centering during deformation is not easy to guarantee.

[0006] It has been proposed to rivet the silicon part, by deforming a lip formed on the shaft, to fold it down onto the silicon part. While this solution is relatively practical at the end of the shaft, it presents other difficulties, particularly in terms of precision, when components must be mounted on the shaft, on the folded lip.

[0007] There are many solutions that have been described to create elastic structures at the middle of the silicon part, to tighten it on the shaft. However, these solutions are difficult to apply for fixing a balance wheel, due to the mass and the inertial effects that the latter undergoes. Indeed, the friction generated by the elastic pressure remains low and may be insufficient to hold a balance wheel, for example in the event of shocks.

[0008] The present invention therefore aims to propose a solution for assembling a balance wheel, particularly a balance wheel whose hub is made of a fragile material, such as silicon. Disclosure of the invention

[0009] More specifically, the invention relates to a watch assembly as mentioned above and comprising a balance shaft, a balance wheel and a locking member. According to the invention, said locking member has a concavity or a clearance in its part located around the shaft, which limits the contact between the locking member and the balance wheel to an area located around an annular portion, surrounding the shaft.

[0010] In a preferred embodiment, the shaft has a second annular rim, defining a second axial stop, a second bearing surface, for example of diameter d, with D>d, adjoining the second rim, and in that the locking member is driven into abutment on the second rim.

[0011] Advantageously, the locking member is annular in shape, with a central opening sized to allow driving onto the shaft at diameter d.

[0012] Preferably, once assembled, the locking member is elastically deformed.

[0013] In a variant, the balance is made at least partially of a brittle material, i.e. without plastic deformation when rupture occurs, or with an elongation A% before rupture of less than 0.2% or zero when measured during a tensile test, at least at the level of said zone located around an annular portion. Thus, the hub of the balance can be based on silicon.

[0014] In a further preferred variant, the shaft has a proximal sting, on the first edge.

[0015] Advantageously, the central opening of the balance hub and the first rim may have corresponding geometries, defining a non-circular shape and counter-shape pair. Brief description of the drawings

[0016] Other details of the invention will appear more clearly on reading the following description, made with reference to the appended drawing in which: there Figure 1 is an isometric view of a watch assembly according to the invention, the Figure 2 is a sectional view showing the assembly of the components forming the assembly shown in the Figure 1 , and the Figure 3 is a schematic cross-sectional representation of a portion of the locking member. Method of carrying out the invention

[0017] It has been represented on the Figure 1, a watch assembly comprising a balance shaft 10, a balance 20 and a locking member 30 of the balance 20 on the shaft 10. Such a watch assembly is intended to be associated with an elastic return member, typically a spiral spring, to form a resonator of a watch movement.

[0018] More particularly, the balance shaft 10 is provided with a first annular rim 11 defining a first axial stop. This first rim 11 may be relatively wide and take the form of an annular plate. To be sufficiently rigid, without making the balance shaft 10 too heavy, the rim may be extended by a conical portion 12 which makes the connection with the cylindrical part of the shaft 10.

[0019] A first bearing surface 13 of diameter D adjoins the first rim 11. It is intended to receive the balance 20, as described below. Advantageously, a stitch 14 is arranged on the first rim 11, at the junction between the first rim 11 and the first bearing surface 13. In other words, the shaft 10 has a proximal stitch 14, on the first rim 11. This makes it possible to avoid any risk linked to an imprecision of the joint between the first rim 11 and the first bearing surface 13, which could hinder the positioning of the balance 20.

[0020] The balance 20 comprises a hub 22 provided with a central opening, through which the balance 20 is adjusted on the first bearing surface 13, resting on the first rim 11. By adjusted, we mean a positioning without constraint, but with minimal play to allow free positioning on the first rim 11. The central opening and the first bearing surface 13 may be circular in shape.

[0021] The locking member 30 is rigidly mounted on the balance shaft 10 and is arranged so as to lock the balance 20 against the first annular rim 11. The locking member 30 is typically driven onto the shaft 10. To do this, the shaft 10 has a second annular rim 15, defining a second axial stop, a second bearing surface 16 of diameter d, with D>d, adjoining the second rim. The locking member 30 comprises an opening 32, typically circular and central, sized to allow driving onto the shaft 10 at diameter d. The locking member 30 is driven into abutment on the second annular rim 15.

[0022] According to an important aspect of the invention, the locking member 30 has a concavity in its part located around the opening 32 and the shaft 10, which limits the contact between the locking member 30 and the balance 20 to an area located around an annular portion, surrounding the shaft 10. In other words, in this annular portion of the balance 20 and more particularly in an annular portion of the hub 22 surrounding the central opening, there is no contact between the locking member 30 and the balance 20.

[0023] In a preferred embodiment, the locking member 30 is elastically deformable and is of the Belleville washer type. In other words, it is a conical-shaped ring, with a central opening 32 for the passage of the shaft 10. More generally, the locking member 30 may have the shape of an annular part, having a concavity, also circular or having a central symmetry. The concavity is oriented in the direction of the first rim. It may be envisaged, without departing from the invention, that the contact between the locking member 30 and the balance 20 is not continuous, for example with interruptions in the annular wall of the locking member 30, forming arms. These arms may, for example, bear on the arms of the balance 20, connecting the hub 22 and the rim. The arms may optionally cooperate with stop structures formed in the balance in order to make the locking member 30 and the balance 20 rotationally integral.

[0024] Advantageously, when it is driven onto the shaft 10, the locking member 30 is elastically deformed under the effect of the pressure exerted on the balance 20 and the reaction that the locking member 30 undergoes. The balance 20 is thus held against the first rim 11.

[0025] Thus, the locking member 30 has, in its resting state, that is to say without deformation, a gap Δh between the portion 34 intended to be pressed on the second annular rim 15 of the shaft 10 and the portion 36 intended to be pressed on the balance 20 ( Figure 3 ). Δh is greater than the difference between, on the one hand, the height dh between the first rim 11 and the second rim 15 and, on the other hand, the thickness e of the balance 20, at the level of the support of the blocking member 30.

[0026] We therefore have Δh>dh-e.

[0027] Thus, when the locking member 30 is driven onto the shaft 10, it is elastically deformed. By controlling and mastering the dimensions of the first rim 11 and the second rim, on the one hand, and the thickness of the balance 20 on the other hand, as well as by controlling the geometry of the locking member 30, it is advantageous to guarantee the clamping force exerted on the balance 20 by the locking member 30. As soon as the locking member 30 comes into abutment on the second rim, the clamping force is independent of the driving force of the locking member 30.

[0028] Preferably, the balance 20 is made of a material without plastic deformation, at least at the hub 22 and the arms. Thus, more particularly, the balance 20 is made of a material without plastic deformation, at least at the said contact zone between the blocking member 30 and the balance 20, as defined above. This material without plastic deformation is advantageously silicon or silicon-based, which makes it possible, by producing this component from a wafer, or a platelet, to perfectly control the thickness e.

[0029] The embodiment described above mentions a hub 22 with a circular opening, as well as a first rim 11 of corresponding shape. It is also possible to provide a non-circular shape and counter-shape pair on the balance 20, and on the shaft 30, to eliminate the degree of freedom of relative rotation between these two parts when the balance 20 is supported on the first rim 11. This can be obtained by a flat, a finger or a lug, or a polygonal-shaped structure, such as a triangle, a square, or another polygon with n sides, the polygon being able to be regular, with n being able to typically go up to 10. It is then possible to limit the clamping force of the locking member 30, to an axial hold.

[0030] In a variant, it is possible to envisage carrying out structuring or micro-structuring at the interface between the locking member 30 and the balance 20. Advantageously, the structuring or micro-structuring is carried out on the balance, preferably made of silicon, the silicon being able to be structured chemically or by plasma, or even by applying a mask in order to choose the areas to be structured. Alternatively, structuring can also be carried out, for example by a mechanical treatment of the sanding type, on the interface of the locking member 20. This increases the coefficient of friction between the balance and the clamping member and improves the holding of the balance, particularly in rotation, relative to the locking member.

Claims

1. Watch assembly comprising: - a balance shaft (10) provided with a first annular rim (11) defining a first axial stop, a first bearing surface (13) of diameter D adjoining the first annular rim (11), - a balance (20), comprising a hub (22) provided with a central opening, through which the balance (20) is adjusted on the first bearing surface (13), bearing on the first axial stop, - a locking member (30), rigidly mounted on the balance shaft (10) and arranged so as to lock the balance (20) against the annular rim, characterized in that the locking member (30) has a concavity in its part located around the shaft (10), which limits the contact between the locking member (30) and the balance (20) to an area located around an annular portion, surrounding the shaft (10).

2. Watch assembly according to claim 1, characterized in thatthe shaft (10) has a second annular rim (15), defining a second axial stop, a second bearing surface (16) of diameter d, with D>d, adjoining the second rim, and in that the locking member (30) is driven into abutment on the second edge.

3. Watch assembly according to one of the preceding claims, characterized in that the locking member (30) is annular in shape, with a central opening sized to allow driving onto the shaft (10).

4. Watch assembly according to one of the preceding claims, characterized in that the locking member (30) is elastically deformed.

5. Watch assembly according to one of the preceding claims, characterized in that the balance (20) is made at least partially of a fragile material, without plastic deformation at break, at least at the level of said zone located around an annular portion.

6. Watch assembly according to claim 5, characterized in thatsaid hub (22) of the balance wheel (20) is made of silicon.

7. Watch assembly according to one of the preceding claims, characterized in that the shaft (10) has a proximal sting (14), on said first annular rim (11).

8. Watch assembly according to one of the preceding claims, characterized in that the central opening of the hub (22) of the balance wheel (20) and the first annular rim (11) have corresponding geometries, defining a non-circular form and counter-form pair.

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