CH712197A2 - Friction system for a watch movement and its assembly process. - Google Patents

Abstract

A friction system (1) for a watch movement, comprising: an axle (3) arranged to be mounted in a watch 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 idler 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) to a predefined limit torque, the friction spring (13) having an inner portion (13a ) in abutment against a first annular bearing surface (7) integral in rotation with said first toothed member (5) and connected to an outer portion (13b) via at least one elastic arm (13c). According to the invention: said at least one elastic arm (13c) follows at least partially in the form of a spiral or an arc of a circle, and said outer part (13b) is placed in abutment against a second bearing surface annular member (15) integral in rotation with said second toothed member (17) so that said at least one resilient arm (13c) flexes so that each of the outer (13b) and inner (13a) portions exerts a force against its surface ring support (7, 15) respectively.

Description

TECHNICAL FIELD [0001] The present invention relates to a friction system for a timepiece, as well as to its method of assembly. State of the art [0002] 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 a torque limit value is reached. If the torque value applied between the two toothed members is greater than this value, the latter are no longer integral in rotation with each other and can therefore undergo a relative rotation. Typically, this kind of system is used in connection with the display organs of the hour and minute to allow their setting time without having to disengage them completely from the gear train. The display members can thus 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.

Many systems of this type have been disclosed, which typically include at least one elastic member arranged to apply a frictional force to directly or indirectly secure the two rotating gear members. Indeed, these systems are broadly divided into two main categories that are suitable for an 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 DE 8 024 236 U , GB 2 094 518, CN 87 215 550 U and CH 338 146.

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 the documents FR 581 847, GB 1 538 922 and EP 0 482 443. A particularly interesting variant in terms of its compactness and its simplicity is disclosed by the embodiment of FIGS. 3 to 5 of EP 0 069 814.

This latter variant consists of an axis coming from a piece with a pinion, the axis also having a separate axial extension of 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 interconnected by radial elastic arms is loosely inserted around the pinion and is secured to a wheel mounted idle on said extension. This joining is performed 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 thereby wedged between the wheel and the spring.

However, it should be noted that this construction, certainly simple and compact, requires the solidarity 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, disassembly of the system without damaging it. The welding process also leaves traces on the wheel and the spring, which is not suitable for a watch with a high level of finish, or requires expensive post-processing.

DISCLOSURE OF THE INVENTION [0007] A main object of the present invention is to overcome the disadvantages of friction systems known from the prior art, by proposing a compact, simple friction system which allows assembly and disassembly without special tools.

For this purpose, the present invention relates more particularly to a friction system for a watch movement, comprising a shaft 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 idler with respect to said axis, the other being either mounted crazy, or mounted integral in rotation with the axis. By the generic term "mounted" is meant not only an additional piece mounted idle on, or secured to, the axis, but also that one of the toothed members may have come from a part with the axis.

A friction spring is arranged to form a kinematic link between said first toothed member and said second toothed member to a predefined limit torque. This friction spring comprises an inner portion bearing against a first annular support surface integral in rotation with said first toothed member and connected to an outer portion via at least one elastic arm. The annular surface may form a complete circular or polygonal ring, an interrupted ring (for example, 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 an arc of a circle, and the outer portion of the friction spring is located in abutment against a second bearing surface ring (to which the same considerations as for the first bearing surface also apply) which is rotationally secured to the second toothed member such that said elastic arm undergoes bending so that each of said outer portion and said inner portion 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 requires no fastening of the spring to another component, simplifying its construction and avoiding unwanted traces of manufacture. Furthermore, since the spring is simply supported against the two bearing surfaces and is therefore not rigidly fixed, the system is easily removable for maintenance.

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

Advantageously, said outer portion is in a plane closer to said first toothed member than the plane in which is said inner portion, 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 micromachining techniques.

Advantageously, said outer portion and said inner portion are 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 loosely on a support, for example in a groove or on a shoulder of the latter, which is integral with the axis according to at least the axial direction, typically in all degrees of freedom. This construction makes it possible to simply drive the support on the axis, and avoids the use of other fasteners.

Advantageously, the spring is arranged so that its outer portion and inner portion 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 a conventional use of the system, but that none of them is rigidly attached to another element of the system. .

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

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

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

In the first place, said inner portion 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 portion of the friction spring comes into contact with the second annular bearing surface.

The second toothed member is positioned along said axis to bend said elastic arm to obtain a desired friction 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 performed simultaneously with the positioning step or later.

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

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 assembled. As such, the inner portion and the outer portion 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 portion may also be in a plane different from that of its inner portion in the assembled position, the relationship between said parts being obviously different before and after assembly.

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

BRIEF DESCRIPTION OF THE DRAWINGS [0026] Other features and advantages of the present invention will appear more clearly on reading the detailed description, made with reference to the appended drawings given by way of non-limiting examples and in which: FIG. 1 shows a simplified cross-sectional view of a friction system according to the invention; fig. 2 shows a perspective view of a friction spring in deformed state according to FIG. 1; and FIG. 3 shows a simplified cross-sectional view of another variant of a friction system according to the invention.

Embodiment (s) of the invention [0027] Lafig. 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 shaft 3 carrying a first toothed element 5, in this case a pinion which comes in one piece with the shaft 3, mounted on this first. Alternatively, this toothed member 5 may be a wheel or even a rake, and the toothed member may alternatively be an additional piece driven, riveted or mounted on a portion of the axis 3 non-circular (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 relative 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 forms according to the needs of the watchmaker, these forms do not need to be explained here.

The axis 3 is also associated with a first annular bearing surface 7, extending perpendicularly to the axis and integral in rotation with the first toothed member 5. As illustrated, this first bearing surface 7 is provided. on a collar 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 portion 13a of a friction spring 13 bears against it. Alternatively, the surface may be interrupted (by means of one or more slots, or formed by bumps, or the like), and / or may be formed as a conical ring. This inner portion 13a is connected to an outer portion 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 with reference to FIG. 2.

The outer portion 13b of the friction spring bears against a second annular support surface 15 provided on a second toothed member 17, illustrated here in the form of a toothed wheel. The second bearing surface 15 also extends perpendicular to the axis and also serves as a second friction surface. The same comments mentioned above with respect to the first support surface 7 also apply here. The second toothed member 17 is mounted loosely on a shoulder of a support 19 in the form of a board, itself integral with the axis 3 by means of driving, gluing, shore, pinning or the like. Alternatively, the support 19 may be integral with the second toothed member 17 and / or idler mounted on the shaft 3 and positioned axially by means of abutments, shoulders or the like. The spring 13, specifically its inner portion 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 portions 13a and 13b outer friction spring are in two different planes in the assembled position of the system to preload the friction spring 13 and thus exert substantially axial forces on each of the bearing surfaces 7 , 15. The second toothed member 17 is thus maintained in axial position on the support 19 by means of the friction spring 13, and therefore no additional holding means is necessary. The prestressing 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 be easily modified.

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

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

In comparison with a spring with radial arms, spirally wound arms allow a reduction of the outer radius of the spring 13 for a given stiffness of the spring 13. Furthermore, for a prestressing force of the spring 13 given and a tolerance on the given preload height, the spiral winding of the elastic arms 13c allows the latter to have a significant length, which allows a reduction of the dispersion around this force and, therefore, a reduction of the dispersion around the torque friction. Indeed, the spring of the 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 prestressing force will be too much strongly influenced by small variations in the axial relationship between the two bearing surfaces 7, 15 to provide good repeatability and easy implementation.

Thanks to the shape of the spring 13 and the fact that the bearing surfaces 7, 15 are annular and therefore extend perpendicular to the geometric axis of the axis 3, the friction forces are exerted substantially axially. and the spring 13

Claims (14)

makes the kinematic connection between the two toothed members when the limit torque is not exceeded. Indeed, 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 to the axis or the second toothed member 17. In practice, only one of the parts 13a, 13b will slide when the limit torque is exceeded, especially that 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 one or the other, no specific tool is necessary for the assembly of the system 1, and the The system can be easily disassembled for maintenance. The spring of this embodiment can be constructed of metallic material, plastic, or optionally of silicon-based material (that is to say monocrystalline silicon, polycrystalline or amorphous, or its carbide, nitride or oxide ), diamond, alumina or the like. FIG. 3 represents a variant of a system 1 according to the invention. This variant differs from that of FIG. 1 regarding the shape of the friction spring 13, which is in a single plane in the assembled position. Its shape in the rest position is illustrated in broken lines, its outer part in the rest position 13bi being in a plane different from that of its inner part 13a. Indeed, 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 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 so that it resumes the form illustrated in FIG. 1. In doing so, for a spring having given dimensions, a greater friction force than that possible with a spring 13 which is flat in the rest position can be applied to the bearing surfaces 7, 15. [0038] Moreover, in the case where the spring 13 is flat in assembled position, the height of the board 19 can be minimized, because it has no need to be hollow to be able to surround the first bearing surface 7. [0039] In order to manufacture the spring 13 of this embodiment, the spring may be cut, stamped or etched from a metal plate and then plastically deformed by axially separating the inner portion 13a and the outer portion 13b, for example in a matrix or via a template. Depending on the chosen material, the spring may subsequently be quenched to harden it. Alternatively, it is also conceivable to build the spring directly into its final form by means of an additive manufacturing process (3D printing) of plastic or metal material. 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 portion 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 portion 13b is further away axially of the first bearing surface as the inner portion 13a, i.e., the outer portion is downwardly oriented and the inner portion is upwardly oriented in the orientation of the figures, as illustrated in FIG. lined in fig. 3. [0042] Then, the second toothed member 17 and its support 19 are introduced around the axis 3 so that the outer portion 13b of the spring 13 bears against the second bearing surface 15. The force of friction is set by positioning the support 19 along the axis 3. This adjustment can be performed beforehand in the design of the system 1 and thus 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 the 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 a hunting of the support 19 on the axis 3, or by providing other positioning means axial (shore, crimping, welding, pin, driving an additional stop, or the like). Although the invention has been described above in connection with specific embodiments, additional variants are also conceivable without departing from the scope of the invention as defined by the claims. claims A friction system (1) for a watch movement, comprising: - an axle (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 idler with respect to said axis (3); a friction spring (13) arranged to form a kinematic link between said first toothed element (5) and said second toothed element (17) to a predefined limit torque, the friction spring (13) having an inner portion ( 13a) in abutment against a first annular bearing surface (7) integral in rotation with said first toothed member (5) and connected to an outer portion (13b) via at least one elastic arm (13c); characterized in that: - said at least one elastic arm (13c) follows at least partially in the form of a spiral or an arc of a circle, and - said outer portion (13b) is located in abutment against a second surface of annular support (15) integral in rotation with said second toothed member (17) so that said at least one elastic arm (13c) flexes so that each of the outer (13b) and inner (13a) portions exerts a force against its respective 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 portion (13b) is in a plane closer to said first toothed member (5) than the plane in which said inner portion (13a). 4. System (1) according to one of claims 1-2, wherein said outer portion (13b) and said inner portion (13a) are 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 loosely on a support (19), the latter being secured to 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 portion (13b) and inner portion (13a) can each slide on its bearing surface ( 7, 15) respectively. 7. System (1) according to one of the preceding claims, wherein said inner portion (13a) of said friction spring (13) is interposed between said first surface (7) and the 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 portion (13a) and / or said outer portion (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 steps of: - introducing said inner portion (13a) of the friction spring (13) about the axis (3) such that it comes into contact with said first annular bearing surface (7); - introducing said second toothed member (17) about the axis (3) so that the outer portion (13b) of the friction spring (13) comes into contact with the second annular support surface (15); positioning said second toothed member (17) along said axis (3) in order to bend said at least one resilient arm (13c) to obtain a desired frictional force; axially securing said second toothed element (17) with respect 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 portion (13b) is in a plane different from that of its inner portion (13a). assembled position of said system (1). 11. The method of claim 9, wherein before assembly of said system (1), the outer portion (13b) of said friction spring (13) is in a plane different from that of the inner portion (13a), and the friction spring (13) is flat, or its outer portion (13b) is in a plane different from that of its inner portion (13a), in the assembled position of said system (1). 12. Method according to one of claims 9 or 11, wherein said inner portion (13a) and said outer portion (13b) are in two different planes before assembly of said system (1). 13. Method according to one of claims 9, 10 or 12, wherein said outer portion (13b) is in a plane located closer to said first toothed member (5) than that of said inner portion (13a) in assembled position of the 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 axial securing step of said second toothed member (17) relative to said axis. (3) at the same time, for example by means of a chase.