CH712197B1 - Friction system for watch movement and its assembly process. - Google Patents

Abstract

Friction system (1) for a clockwork movement, comprising: - an axis (3) designed to be mounted in a clockwork movement; - a first toothed member (5) mounted on said axis (3); - a second toothed member (17) mounted on said axis (3), at least one of said toothed members (5, 17) being mounted idle with respect to said axis (3); - a friction spring (13) arranged to form a kinematic link between said first toothed member (5) and said second toothed member (17) up to a predefined limit torque, the friction spring (13) comprising an inner part ( 13a) bearing against a first annular bearing surface (7) integral in rotation with said first toothed member (5) and linked to an outer part (13b) by means of at least one elastic arm (13c). According to the invention: - said at least one elastic arm (13c) at least partially follows the shape of a spiral or an arc of a circle, and - said outer part (13b) is located in abutment against a second surface d 'annular support (15) integral in rotation with said second toothed member (17) such that said at least one resilient arm (13c) undergoes bending so that each of the outer (13b) and inner (13a) parts exerts a force substantially parallel to said axis (3) against its respective annular bearing surface (7, 15).

Description

Technical area

The present invention relates to a friction system for a timepiece, as well as its assembly process.

State of the art

Friction systems are commonly used in timepieces in order to make a first toothed member, such as a pinion, integral in rotation with a second toothed member, such as a wheel, until that a torque limit value is reached. If the value of torque applied between the two toothed members is greater than this value, the latter are no longer integral in rotation with one another and can consequently undergo relative rotation. Typically, this type of system is used in conjunction with the hour and minute display members in order to enable them to be set without having to disengage them completely from the finishing gear. The display members can therefore be driven by the finishing gear train via the friction system, which also allows the relative rotation mentioned above when sufficient torque is applied by the user.

[0003] Numerous systems of this type have been disclosed, which typically comprise at least one elastic element arranged to apply a frictional force making it possible to join directly or indirectly the two toothed members in rotation. In fact, these systems fall broadly into two main categories which are suitable for application in a watch. In the first of these categories, the force is applied substantially radially (or at least with a significant radial component) to an axis or to a cylindrical surface of one of the toothed wheels, as disclosed for example in documents DE8024236U, GB2094518, CN87215550U and CH338146.

In the second category, the force is applied axially relative to the axis of rotation of the toothed members by means of a friction spring which is forced against one or more bearing surfaces, as described in documents FR581847 , GB1538922 and EP0482443. A particularly interesting variant in terms of its compactness and its simplicity is disclosed by the embodiment of FIGS. 3 to 5 of document EP0069814.

[0005] This latter variant consists of an axis formed integrally with a pinion, the pin also comprising an axial extension separated from the pinion by an annular shoulder extending radially beyond the tops of the teeth of the pinion. A friction spring comprising an outer ring and an inner ring linked together by radial elastic arms is introduced with play around the pinion and is secured to a wheel mounted idly on said extension. This joining is carried out by means of spot welding. The spring is thus constrained so that its inner ring applies an axial force on one face of the shoulder towards the wheel, and the wheel also applies an axial friction force in the other direction against the other face of the wheel. shoulder, which is therefore wedged between the wheel and the spring.

However, it should be noted that this construction, admittedly simple and compact, requires the securing of the spring with the wheel, which involves the use of specific tools during assembly of the system and makes it difficult, if not impossible, to dismantle system without damaging it. The welding process also leaves marks on the wheel and on the spring, which is unsuitable for a watch with a high level of finish, or requires expensive post-treatment.

Disclosure of the invention

[0007] A main aim of the present invention is to overcome the drawbacks of the friction systems known from the prior art, by providing a compact, simple friction system which allows assembly and disassembly without special tools.

[0008] To this end, the present invention relates more particularly to a friction system for a clockwork movement, comprising an axis arranged to be mounted in a clockwork movement in known manner, a first toothed member such as a wheel, a pinion or a rake mounted on said axis, and a second toothed member mounted on (that is to say carried by) said axis, at least one of said toothed members being mounted idle with respect to said axis, the other being therefore either mounted loose or mounted integral in rotation with the axis. By the generic term "mounted" is meant not only an additional part mounted loose on, or integral with, the axis, but also that one of the toothed members may have come integrally with the axis.

[0009] A friction spring is arranged to form a kinematic link between said first toothed member and said second toothed member up to a predefined limit torque. This friction spring comprises an inner part bearing against a first annular bearing surface integral in rotation with said first toothed member and linked to an outer part by means of at least one elastic arm. The annular surface may form a complete ring, circular or polygonal, an interrupted ring (e.g., split, formed of a plurality of bumps arranged in a ring), a flat ring, a conical ring, or any combination of these possibilities which makes technical sense. Since the first bearing surface is annular, it extends perpendicularly, or at an angle in the case of a conical ring, to the axis.

According to the invention, at least one elastic arm at least partially follows the curve of a spiral or of a circular arc, and the outer part of the friction spring is located in abutment against a second bearing surface annular (to which the same considerations as for the first bearing surface also apply) which is integral in rotation with the second toothed member such that said elastic arm undergoes bending so that each of said outer part and said inner part exerts a force against said corresponding bearing surface. Thanks to this geometry, said force is therefore exerted substantially parallel to the axis.

This system is compact and does not require any attachment of the spring to another component, simplifying its construction and avoiding unwanted traces of manufacture. Furthermore, since the spring simply rests against the two bearing surfaces and is therefore not rigidly fixed thereto, the system is capable of being easily dismantled for its maintenance.

[0012] Advantageously, said second annular bearing surface is opposite said first toothed member.

[0013] Advantageously, said outer part is located in a plane closer to said first toothed member than the plane in which said inner part is located, which allows the use of a spring which is flat in its rest position before assembly , and is therefore easy to manufacture by stamping, cutting a plate, or by micro-machining techniques.

[0014] Advantageously, said outer part and said inner part are located substantially in the same plane, which makes the system particularly compact.

Advantageously, one of said toothed members, for example said second toothed member, is mounted idle on a support, for example in a groove or on a shoulder of the latter, which is integral with the axis along at least the axial direction, typically according to all the degrees of freedom. This construction makes it possible to easily drive the support on the axis, and avoids the use of other fasteners.

Advantageously, the spring is arranged so that its outer part and its inner part can each slide on its respective bearing surface. This is not to say that the two parts slide at the same time, which is not possible during conventional use of the system, but that neither of them is rigidly fixed to another element of the system. .

Advantageously, the inner part of the friction spring is interposed between said first bearing surface and a mounting surface of said second toothed member on axis 3, which represents a compact construction.

[0018] Advantageously, said inner part and / or said outer part has (have) an annular shape.

[0019] The invention also relates to a method of assembling a friction system as defined above, this method comprising the steps described below.

First, said inner part of the friction spring is introduced around the axis so that it comes into contact with said first annular bearing surface.

Then, said second toothed member is introduced around the axis so that the outer part of the friction spring comes into contact with the second annular bearing surface.

[0022] The second toothed member is positioned along said axis in order to flex said elastic arm to obtain a desired frictional force, which can be predefined during the development of the system and determined by a stop or the like provided on the axis, and said second toothed member is secured at least axially with respect to said axis. This joining can be carried out simultaneously with the positioning step or subsequently.

[0023] Advantageously, said friction spring is flat before assembly and then deformed in the assembled position, which allows simple manufacture of the spring.

[0024] Advantageously, said friction spring is not flat before assembly and is flat in the assembled position, which allows the system to be more compact when it is assembled. As such, the inner part and the outer part of the spring are in two different planes in the rest position of the friction spring, that is to say before assembly and without stress exerted on the spring. Alternatively, its outer part may also be in a plane different from that of its inner part in the assembled position, the relationship between said parts being obviously different before and after assembly.

[0025] Advantageously, said outer part is located in a plane located closer to said first toothed member than that of said inner part in the assembled position of the system.

Brief description of the drawings

Other characteristics and advantages of the present invention will emerge more clearly on reading the detailed description, made with reference to the appended drawings given by way of non-limiting examples and in which: <tb> - <SEP> FIG. 1 represents a simplified cross-sectional view of a friction system according to one embodiment of the invention; <tb> - <SEP> FIG. 2 represents a perspective view of a friction spring in a deformed state according to FIG. 1; and <tb> - <SEP> FIG. 3 represents a simplified cross-sectional view of another variant of a friction system according to an embodiment of the invention.

Mode (s) for carrying out the invention

[0027] Figure 1 illustrates a first embodiment of a friction system 1 according to the invention, seen in cross section. This system comprises, in a known manner, an axis 3 arranged to be mounted in a clockwork movement, this axis 3 carrying a first toothed member 5, in this case a pinion coming in one piece with the axis 3, mounted on this first. Alternatively, this toothed member 5 can be a wheel or even a rake, and the toothed member can alternatively be an additional part driven out, riveted or mounted on a part of the non-circular axis 3 (typically polygonal) so that it is integral with the axis 3 at least in rotation. Furthermore, it is conceivable that the first toothed member 5 is free to rotate with respect to the axis 3, the latter being fixed. The axis can also carry several pinions and / or toothed members, and can take a large number of known shapes according to the needs of the watchmaker, these shapes not needing to be explained here.

The axis 3 is also associated with a first annular bearing surface 7, extending perpendicular to the axis and integral in rotation with the first toothed member 5. As illustrated, this first bearing surface 7 is provided on a flange 9 driven, glued, riveted or welded around the axis 3 and positioned longitudinally by a shoulder 11. The first bearing surface 7 extends perpendicular to the axis 3 and serves as a first friction surface, and for this purpose, the inner part 13a of a friction spring 13 bears against it. Alternatively, the surface can be interrupted (by means of one or more slits, or formed by bumps, or the like), and / or can be formed as a conical ring. This inner part 13a is connected to an outer part 13b by means of at least one elastic arm 13c which at least partially follows the curve of a spiral turn. The shape of the friction spring 13 will be described in more detail below in connection with FIG. 2.

The outer part 13b of the friction spring bears against a second annular bearing surface 15 provided on a second toothed member 17, shown here in the form of a toothed wheel. The second bearing surface 15 also extends perpendicular to the axis and also acts as a second friction surface. The same comments mentioned above with respect to the first bearing surface 7 also apply here. The second toothed member 17 is mounted idle on a shoulder of a support 19 in the form of a board, itself secured to the axis 3 by means of driving, gluing, shoring, pinning or the like. Alternatively, the support 19 can come integrally with the second toothed member 17 and / or mounted idle on the axis 3 and positioned axially by means of stops, shoulders or the like. The spring 13, specifically its inner part 13a, is thus interposed between the first bearing surface and the support 19, particularly the surface 18 which forms the interface between the support 19 and the axis 3.

The inner 13a and outer 13b of the friction spring are located in two different planes in the assembled position of the system in order to pre-stress the friction spring 13 and thus to exert substantially axial forces on each of the bearing surfaces 7 15. The second toothed member 17 is thus held in an axial position on the support 19 by means of the friction spring 13, and therefore no additional holding means is necessary. The preload of the friction spring 13 can be modified by acting on the distance between the planes of the bearing surfaces 7, 15, for example by moving the support 19 along the axis 3, and consequently the maximum torque that can undergo the system before the toothed members 5, 17 pivot relative to each other can thus be easily modified.

The friction spring 13 is illustrated in more detail in Figure 2, in the form of a modeling of the spring 13 in the working position as illustrated in Figure 1. In the rest position, the spring 13 is flat and is therefore in a single plane. In the working position when assembled in the system shown in figure 1, the inner part 13a and the outer part 13b lie in two different planes, which flexes the elastic arms 13c in order to pre-stress them as described above. and thus to apply forces F in the directions indicated by arrows F on the bearing surfaces 7, 15 respectively.

In the illustrated embodiment, the inner part 13a as well as the outer part 13b of the friction spring 13 are formed of generally annular-shaped frames, which are linked by three elastic arms 13c which at least partially follow the curves of turns of a spiral, and which each join the inner part 13a and the outer part 13b in substantially radial directions. Two, four or even more resilient arms 13c are also possible. In another variant, not illustrated, the elastic arms 13c can at least partially follow arcs of a circle. Other shapes are also conceivable for the inner part 13a and / or for the outer part 13b, for example shapes of polygonal rings, split rings or the like.

In comparison with a spring with radial arms, arms wound in a spiral allow a reduction in the outer radius of the spring 13 for a given stiffness of the spring 13. Furthermore, for a given spring 13 pre-stressing force and a tolerance on the given prestress height, the spiral winding of the elastic arms 13c allows the latter to have a significant length, which allows a reduction in the dispersion around this force and, therefore, a reduction in the dispersion around the torque friction. Indeed, the spring of document EP0069814, although it has dimensions similar to the spring 13 of the invention, will be significantly too stiff for use in the friction system 1 according to the invention, and the pre-stress force will be too much. strongly influenced by small variations in the axial relationship between the two bearing surfaces 7, 15 to give good repeatability and easy handling.

Thanks to the shape of the spring 13 and the fact that the bearing surfaces 7, 15 are annular and therefore extend perpendicularly to the geometric axis of the axis 3, the frictional forces are exerted substantially axially and the spring 13 forms the kinematic connection between the two toothed members when the limit torque is not exceeded. In fact, each of the inner 13a and outer 13b parts can slide on its respective bearing surface 7, 15, because the spring 13 is not secured either to the axis or to the second toothed member 17. In practice, only one of the parts 13a, 13b will slide when the limit torque is exceeded, in particular the part which has the least friction with its bearing surface 7, 15. Because the spring simply rests on the two bearing surfaces 7, 15 without being rigidly attached to either one, no specific tools are required for the assembly of the system 1, and the system can easily be disassembled for maintenance.

The spring of this embodiment can be constructed from metallic material, plastic, or optionally from silicon-based material (that is to say monocrystalline, polycrystalline or amorphous silicon, or its carbide, nitride or oxide. ), diamond, alumina or the like.

[0036] FIG. 3 represents a variant of a system 1 according to the invention. This variant differs from that of Figure 1 as regards the shape of the friction spring 13, which lies in a single plane in the assembled position. Its shape in the rest position is illustrated in dashed lines, its outer part in the rest position 13b1 being in a plane different from that of its inner part 13a. In fact, in this embodiment, the shape of the spring 1 in its rest position resumes that of the first embodiment in the assembled position.

During assembly of the mobile, the spring 13 is thus compressed between the first bearing surface 7 and the second bearing surface 15 so that the spring 13 is brought flat. Alternatively, the spring 13 of this embodiment can be compressed less strongly. Still alternatively, the spring 13 of this embodiment can be compressed more strongly and in such a way that it resumes the form illustrated in FIG. 1. In doing so, for a spring having given dimensions, a friction force greater than that possible with a spring 13 which is flat in the rest position can be applied to the bearing surfaces 7, 15.

Furthermore, in the case where the spring 13 is flat in the assembled position, the height of the board 19 can be minimized, because it does not need to be hollow in order to be able to surround the first bearing surface 7.

In order to manufacture the spring 13 of this embodiment, the spring can be cut, stamped or engraved from a metal plate, then plastically deformed by axially separating the inner part 13a and the outer part 13b, by example in a matrix or through a template. Depending on the material chosen, the spring can subsequently be tempered in order to harden it. Alternatively, it is also conceivable to construct the spring directly in its final form by means of an additive manufacturing process (3D printing) in plastic or metal.

For all the embodiments described above, the assembly is carried out as follows.

After having provided all the elements of the system 1, the collar 9 (if present) being assembled to the axis 3, the friction spring 13 is assembled to the axis 3 by introducing its central part 13a around the axis 3 until it comes into contact with the first bearing surface 7. If the spring 13 is not flat in the rest position, it is oriented so that the outer part 13b is further away axially of the first bearing surface than the inner part 13a, that is to say that the outer part is oriented downwards and the inner part is oriented upwards according to the orientation of the figures, as illustrated in dotted in figure 3.

Then, the second toothed member 17 and its support 19 are introduced around the axis 3 so that the outer part 13b of the spring 13 bears against the second bearing surface 15. The friction force is adjusted by positioning the support 19 along the axis 3. This adjustment can be carried out beforehand in the design of the system 1 and therefore predetermined by means of a stop or the like provided on the axis 3 and against which the support 19 is positioned. Alternatively, the watchmaker can adjust this force at the time of assembly by driving the support to a desired position along axis 3 according to his needs.

Finally, the support is secured axially along the axis 3, either simultaneously with the previous step in the case of driving the support 19 on the axis 3, or by providing other positioning means axial (a shore, crimp, weld, pin, drive out an additional stop, or the like).

[0044] Although the invention has been described above in connection with specific embodiments, additional variants are also possible without departing from the scope of the invention as defined by the claims.

Claims (14)

1. Friction system (1) for a watch movement, comprising: - an axis (3) arranged to be mounted in a clockwork movement; - a first toothed member (5) mounted on said axis (3); - a second toothed member (17) mounted on said axis (3), at least one of said toothed members (5, 17) being mounted idle with respect to said axis (3); - a friction spring (13) arranged to form a kinematic link between said first toothed member (5) and said second toothed member (17) up to a predefined limit torque, the friction spring (13) comprising an inner part ( 13a) bearing against a first annular bearing surface (7) integral in rotation with said first toothed member (5) and linked to an outer part (13b) by means of at least one elastic arm (13c); characterized in that: - said at least one elastic arm (13c) at least partially follows the shape of a spiral or an arc of a circle, and - Said outer part (13b) is located in abutment against a second annular bearing surface (15) integral in rotation with said second toothed member (17) so that said at least one elastic arm (13c) undergoes bending so that each of the outer (13b) and inner (13a) parts exerts a force substantially parallel to said axis (3) against its respective annular bearing surface (7, 15). 2. System (1) according to claim 1, wherein said second annular bearing surface (15) is opposite said first toothed member (5). 3. System (1) according to one of the preceding claims, wherein said outer part (13b) is in a plane closer to said first toothed member (5) than the plane in which is said inner part (13a). 4. System (1) according to one of claims 1 to 2, wherein said outer part (13b) and said inner part (13a) are located substantially in the same plane. 5. System (1) according to one of the preceding claims, wherein one of said two toothed members (5, 17) is mounted idle on a support (19), the latter being integral with the axis at least in the axial direction. . 6. System (1) according to one of the preceding claims, wherein said friction spring (13) is arranged so that its outer part (13b) and its inner part (13a) can each slide on its bearing surface ( 7, 15) respectively. 7. System (1) according to one of the preceding claims, wherein said inner part (13a) of said friction spring (13) is interposed between said first bearing surface (7) and a mounting surface (18) of said. second member (17) toothed on the axis (3). 8. System (1) according to one of the preceding claims, wherein said inner part (13a) and / or said outer part (13b) has (s) an annular shape. 9. A method of assembling a friction system (1) according to one of claims 1 to 8, comprising the following steps: - Introducing said inner part (13a) of the friction spring (13) around the axis (3) so that it comes into contact with said first annular bearing surface (7); - Introducing said second toothed member (17) around the axis (3) so that the outer part (13b) of the friction spring (13) comes into contact with the second annular bearing surface (15); - positioning said second toothed member (17) along said axis (3) in order to flex said at least one elastic arm (13c) to obtain a desired frictional force; - axially securing said second toothed member (17) relative to said axis (3). 10. The method of claim 9, wherein said friction spring (13) is flat before assembly of said system (1) and its outer part (13b) is in a plane different from that of its inner part (13a) in assembled position of said system (1). 11. The method of claim 9, wherein, before assembly of said system (1), the outer part (13b) of said friction spring (13) is in a plane different from that of the inner part (13a), and, in the assembled position of said system (1), the friction spring (13) is flat, or its outer part (13b) is in a plane different from that of its inner part (13a). 12. The method of claim 9, wherein said inner part (13a) and said outer part (13b) are in two different planes before assembly of said system (1). 13. Method according to one of claims 9, 10 and 12, wherein said outer part (13b) lies in a plane located closer to said first toothed member (5) than that of said inner part (13a) in the assembled position. system (1). 14. Method according to one of claims 9 to 13, wherein said step of positioning said second toothed member (17) along said axis (3) and said step of axially securing said second toothed member (17) relative to said axis (3) are done at the same time, for example by means of driving.