Timepiece mobile

Abstract

A clockwork mechanism according to the invention comprises a shaft (1A) and a plate (2), defining a wheel and including a clamp, configured for friction assembly without the need for specific tooling. For this purpose, the shaft includes a cylindrical mounting portion (10) having an oblong cross-section with a major axis and a minor axis perpendicular to each other. During assembly of the mechanism, the cylindrical mounting portion is inserted into a central area located between the arms (6a, 6b) of the clamp without deforming these arms, aligning the minor axis of the cross-section with the opening direction of the clamp. Subsequently, a certain opening of the clamp by elastic deformation is generated by a rotation of approximately ninety degrees (90°) of the shaft (1A) relative to the plate (2), and finally, a terminal axial displacement of the plate is performed to its functional axial position.

Description

Technical field of the invention

[0001] The present invention relates to a friction clockwork mobile, usable in a timepiece. Technological background

[0002] Many watch movements, particularly mechanical ones, include at least one friction wheel, particularly to allow for corrections to the time display or other functions. For example, a mechanical movement equipped with a large-medium wheel generally includes friction at the level of the minute train. Friction allows the cannon pinion to be turned, independently of the finishing train, when setting the time.

[0003] Generally, a friction wheel consists of a shaft, provided with a pivot, and a plate provided with peripheral teeth and defining a wheel. The plate is attached to the shaft in an essentially coaxial manner, by a friction assembly which prevents the relative rotation of the two parts with respect to each other, except when the force torque exceeds a predefined threshold.

[0004] The friction connection is achieved by a plurality of arms of the board, which form a clamp arranged to clamp a lateral surface of the shaft. This lateral surface is located in the vicinity of an axial stop surface of the shaft, which maintains the board in its functional axial position.

[0005] Assembling this type of mobile is a delicate operation that requires the arms of the board to be spread apart to allow one end of the shaft to be inserted. In most mobiles of the type in question, the drive wheel is fitted with two arms arranged on either side of the wheel's rotation axis and having a certain elasticity. For this type of mobile, specific tooling is available to separate the two arms, followed by moving the separated arms along the shaft to their final axial position.

[0006] However, this specific tooling increases the complexity of the assembly method, and for certain geometries, its use can degrade the friction connection between the plate and the shaft. This is the case, for example, when the shaft includes a high end part which is located, relative to the axial stop surface, beyond the final position of the plate. This geometry is encountered on certain calibers, including in particular the caliber A16.593 from the company ETA Manufacture Horlogère Suisse. The movement of the arms apart from the relatively long end part can harm the inner surfaces of the arms which will serve as contact surfaces for the friction connection. The result may be a degradation of the friction assembly as well as additional axial or radial runout of the drive wheel relative to the shaft.Document EP 3 432 081 B1 shows a clockwork mobile comprising a shaft, which extends in an axial direction of this mobile, and a board frictionally mounted on the shaft. Summary of the invention

[0007] The aim of the invention is to provide a clockwork mobile, with a wheel mounted with friction on a shaft provided with a pinion, which does not suffer from the drawbacks described above and which is arranged in such a way that the shaft and the wheel, also called a plate, can be assembled without the aid of specific tools.

[0008] To this end, the invention relates to a clockwork mobile formed from a shaft, which extends in an axial direction of the clockwork mobile, and from a board forming a wheel which is frictionally mounted on the shaft, the shaft comprising an axial stop surface for the board / wheel and being arranged to be able to hold this board / wheel, once mounted, substantially in a functional axial position where it is against the axial stop surface, the board / wheel comprising at least one first arm and at least one second arm together forming a clamp arranged to be able to clamp, by elastic deformation of at least one of these arms in an opening direction of the clamp, a friction revolution surface that said shaft comprises in the vicinity of the axial stop surface.The invention is remarkable in that the shaft comprises a cylindrical mounting part which is located, in said axial direction, beyond the friction surface of revolution relative to the axial stop surface, the cylindrical mounting part having an oblong cross-section having a major axis, in a longitudinal direction of this cross-section, and a minor axis perpendicular to the major axis and of smaller dimension than this major axis and than the minimum diameter of said friction surface of revolution.The shaft is configured to allow the assembly of the watch mobile by inserting the cylindrical mounting part, without significant deformation of the clamp, in a central zone between the arms of the clamp by orienting this cylindrical mounting part so that the minor axis of its cross-section is parallel to the opening direction of the clamp, then by a certain opening of the clamp generated by a rotation of substantially ninety degrees (90°) of the shaft relative to the board / wheel or vice versa, and finally by a terminal axial displacement of this board / wheel towards its functional axial position in which the clamp has an elastic deformation ensuring functional friction for the watch mobile.

[0009] According to an advantageous variant, said friction revolution surface defines the bottom of a circular housing arranged along the shaft for receiving the board / wheel in said functional axial position and maintaining it in this functional axial position.

[0010] The invention also relates to a method for assembling a timepiece mobile according to the invention, the method comprising the following steps: providing the aforementioned board comprising at least two arms forming a clamp and the aforementioned shaft provided with the cylindrical mounting part; orienting the shaft relative to the board so that said minor axis of the cross-section of said cylindrical mounting part is parallel to the opening direction of the clamp and, substantially maintaining this orientation of the shaft, axially inserting said cylindrical mounting part into the central zone between the arms forming the clamp until the board is located substantially at one end of the cylindrical mounting part located on the side of said friction revolution surface; then rotating the shaft relative to the board so as to cause an elastic separation of the arms forming the clamp and thus open this clamp in its opening direction;and finally moving the board in the axial direction until the board reaches its operative axial position in which the clamp grips the friction revolution surface.; Brief description of the figures

[0011] The invention will be described below in more detail with the aid of the attached drawings, given as non-limiting examples, in which: THE Figures 1a and 1b represent three-dimensional and sectional views of a clockwork mobile according to the state of the art. The Figure 2 represents a sectional view of a mobile shaft as known from the state of the art, provided with a long chimney, beyond the friction surface of revolution between the shaft and the wheel plate, on the side of this surface of revolution opposite the pinion. Figure 3 represents in perspective a shaft of a clockwork mobile according to an embodiment of the invention. Figures 4a to 4crepresent the steps of the method of assembling a timepiece according to the invention. The figure 4d shows an angular position of the wheel board relative to the shaft after the application of a force torque to the wheel or pinion with an intensity greater than a threshold beyond which sliding of the board occurs on the friction revolution surface. Detailed description of the invention

[0012] The technical problem mentioned above will first be established in more detail on the basis of the figures 1 And 2 , followed by a description of one embodiment of the invention.

[0013] THE Figures 1a and 1brepresent an example of a typical clockwork mobile according to the state of the art, which comprises a shaft 1 and a plate 2 defining a wheel (hereinafter a plate), in particular a drive wheel. The shaft 1 comprises a pivot 3, in the form of an elongated tube, and a pinion 4, the upper radial surface 5 of which forms an axial stop surface against which the plate 2 is held. The plate 2 comprises two arms 6a and 6b forming a clamp which clamps a friction revolution surface 7a arranged at the bottom of a lateral housing 7 of the shaft 1. The friction between the inner surfaces of the arms 6a and 6b of the plate 2 and the friction revolution surface 7a of the shaft 1 defines the rotational mobility, and in particular a sliding threshold of the components 1 and 2 of the mobile relative to each other under the influence of an external force torque.

[0014] The shaft 1 comprises an end portion 8, with a diameter slightly greater than the maximum diameter of the bottom of the housing 7, located beyond this housing, observed in the axial direction of the shaft 1 relative to the axial stop surface 5. An assembly tool (not shown) is necessary to spread the arms 6a and 6b in elastic deformation, so that the end portion 8 can be inserted into a central area of the board between the two arms of the clamp. Then the tool is removed and the board 2 is pushed towards its final position shown in section at Figure 1b , the arms 6a and 6b then clamping the friction revolution surface 7a at the bottom of the housing 7. During this last movement, the arms 6a and 6b rub the surface of the terminal part 8 of the shaft, but as this terminal part 8 is low in height ( Figure 1b ), the negative effect of said displacement on the inner surfaces of arms 6a and 6b is negligible.

[0015] On the other hand, when the terminal part 8A is higher, defining a chimney or a barrel, as is the case for the tree 1 represented in the Figure 2 , the axial displacement of the arms 6a and 6b in the separated condition and therefore elastically deformed along the end part 8A towards their final axial position becomes greater and risks damaging the internal surfaces of the arms 6a and 6b or even these arms themselves before reaching this final axial position, i.e. the functional axial position.

[0016] The invention solves the problem described above by a clockwork mobile provided with an arbor 1A which comprises a cylindrical mounting part 10, which takes the place of the terminal part indicated in the preceding figures, in particular of the terminal part 8A. A arbor 1A of a clockwork mobile according to an embodiment of the invention is shown in Figure 3. Like the shaft known from the state of the art, the shaft 1A according to the invention comprises a pivot 3 (cylindrical tube) and a pinion 4, as well as a housing 7 comprising at its bottom the friction revolution surface 7a, which is provided to receive in frictional contact the arms 6a and 6b of the board 2, the latter being able to have the same shape as that shown in Figures 1a and 1b. Beyond this surface of revolution 7a, i.e. beyond the housing 7 observed in the axial direction relative to the axial stop surface 5 defined by the pinion 4, is the cylindrical mounting part 10. This part 10 has the shape of a cylinder with an oblong cross-section. More precisely, the cross-section (perpendicular to the axial direction) has two perpendicular axes of symmetry: a major axis A along the longitudinal direction of this oblong cross-section (also called the major axis for an ellipse in particular) and a minor axis B (also called the minor axis for an ellipse in particular).

[0017] In the advantageous variant shown, the dimension of the major axis A corresponds to the diameter of the upper edge 11 of the housing 7. According to the invention, the minor axis B has a smaller dimension than the major axis and than the minimum diameter of the friction revolution surface 7a (this surface may be slightly frustoconical). In the preferred form shown, the cylindrical mounting part 10 comprises two angular sections 12a and 12b, corresponding to sections of a circular cylinder having the same diameter as the upper edge 11 of the housing 7, and two angular sections 13a and 13b set back from the upper edge 11, that is to say inside said circular cylinder. The angular sections 13a to 13b may have various profiles, in particular a profile defining an arc of a circle at least in the median zone of these angular sections.Other shapes of the cylindrical mounting part 10 are possible, such as for example a shape with a purely elliptical cross-section having the axes A and B as central axes (major axis and minor axis) of this cross-section.

[0018] According to the invention, the shaft 1A is configured to allow the assembly of the timepiece mobile by inserting the cylindrical mounting part 10, without substantial deformation of the clamp formed by the two arms 6a, 6b, in a central zone between these two arms, by orienting this cylindrical mounting part so that the minor axis B of its cross section is parallel to the opening direction of the clamp (direction orthogonal to the general direction of the two arms; in other words: direction orthogonal to the axis of symmetry of these two arms defining a central axis of the clamp). Then the cylindrical part 10 is arranged to allow a certain opening of the clamp, and therefore to obtain an elastic deformation of the two arms forming the clamp, by a rotation of substantially ninety degrees (90°) of the shaft 1A relative to the board 2.Finally, the shaft 1A is arranged to allow, while maintaining the orientation resulting from said 90° rotation, a terminal axial displacement of the board 2 towards its functional axial position in which the clamp has an elastic deformation ensuring functional friction for the watch mobile.

[0019] The method of assembling the clockwork mobile is illustrated in Figures 4a to 4c . It is first intended to orient the shaft 1A relative to the board 2 so that the minor axis B of the cross-section of the cylindrical mounting part 10 is parallel to the opening direction of the clamp and, while substantially maintaining this orientation of the shaft, to axially insert the cylindrical mounting part into the central area between the arms forming the clamp. Then, the shaft 1A is rotated through an angle of approximately 90° relative to the board 2 (see Figure 4b), resulting in an elastic opening of the clamp. Indeed, the cross-section of the cylindrical part 10, in particular the dimension of the major axis A, is configured so that this rotation spreads the arms 6a and 6b elastically. The board 2 can then be pushed axially until the two arms of the clamp enter the housing 7, because the clamp is sufficiently open to allow the clamp to pass the upper edge 11 of the housing 7 since the dimension of the major axis A corresponds substantially to the diameter of this upper edge (see Figure 4c). This latter displacement represents the only axial displacement of the arms 6a and 6b in the separated condition, therefore elastically deformed significantly, relative to the shaft 1A. This terminal displacement can therefore be minimal and thus limits the risk of damaging the friction surfaces of the arms 6a and 6b and the arms themselves. Indeed, in an advantageous variant, it is provided that the cylindrical mounting part is inserted axially in the central zone between the arms forming the clamp until the board is located substantially at one end of the cylindrical mounting part located on the side of the friction revolution surface. In the illustrated variant, the cylindrical mounting part 10 is extended by two ramps 14 (visible at Figure 3) which are located at the foot of each of the retracted sections 13a and 13b and form a short intermediate zone between the cylindrical part 10 and the upper edge 11 of the housing 7, these two ramps being able to serve to stop the insertion of the cylindrical part 10 into the central zone of the clamp before the rotation used to move the clamp apart is carried out.

[0020] To the figure 4d we see that, once the board is in place, the shaft 1A can then be rotated, in particular by 90°, relative to the board 2 by applying to this shaft or to the board a torque greater than a threshold from which sliding is obtained on the friction revolution surface.

[0021] As indicated above, the invention applies in the first instance to mobiles whose shaft is provided with an end part with a significant height beyond the friction revolution surface relative to the axial stop surface 5. Nevertheless, the invention is not limited to shafts of this type and it is also applicable when the end part is of reduced height.

[0022] In the illustrated embodiments, the friction surface of revolution is located at the bottom of a housing 7 and is therefore set back from a circle having as its diameter the major axis A of the cross-section of the part 10. This represents a preferred form which allows the assembly to be completed by snap-fastening the board 2 so that it remains in its functional axial position. However, it is also possible to have a friction surface of revolution having a diameter substantially equal to the dimension of the major axis A, preferably with a slightly frustoconical axial profile (diameter decreasing towards the pinion 4), as shown in Figure 2 .

Claims

1. A horology mobile comprising an arbor (1A), which extends in an axial direction of this mobile, and a plate (2) friction-fitted on the arbor and forming a wheel, the arbor comprising an axial stop surface (5) for the plate and being designed to be capable of holding this plate, once fitted, in a substantially functional axial position in which it is against the axial stop surface, the plate (2) comprising at least one first arm (6a) and at least one second arm (6b) together forming a clip designed to be capable of gripping, by resilient distortion of at least one of its arms in a direction of opening of the clip, a friction surface of revolution (7a) comprised by said arbor in the vicinity of the axial stop surface; said horology mobile being such that the arbor (1A) comprises a cylindrical fitting part (10) which is located, in said axial direction, beyond the friction surface of revolution (7a) relative to the axial stop surface (5), the cylindrical fitting part (10) having an oblong-shaped cross-section with a major axis (A), along a longitudinal direction of this cross-section, and a minor axis (B) perpendicular to the major axis and with smaller dimensions than this major axis and than the minimum diameter of said friction surface of revolution, the arbor being configured to enable the mobile to be assembled by inserting the cylindrical fitting part, with no noticeable distortion of the clip, in a central zone between the arms (6a, 6b) of the clip by aligning this cylindrical fitting part so that the minor axis of its cross-section is parallel to the direction of opening of the clip, then by a certain opening of the clip generated by a rotation of substantially ninety degrees (90°) of the arbor (1A) relative to the plate (2), and lastly by a final axial movement of the plate (2) towards its functional axial position in which the clip has a resilient distortion providing functional friction for the horology mobile.

2. The horology mobile according to claim 1, in which said friction surface of revolution (7a) defines the back of a circular bed (7) arranged along the arbor for holding the plate (2) in said functional axial position and keeping it in said functional axial position.

3. The horology mobile according to claim 1 or 2, in which the arbor forms, in the direction of said minor axis of said cross-section, two diametrically opposed ramps (14) between the cylindrical fitting part (10) and the friction surface of revolution (7a).

4. The horology mobile according to any of the preceding claims, in which the arbor (1 A) is provided with a pinion (4) and in which the axial stop surface (5) is one of the radial surfaces of the pinion.

5. A method for assembling a horology mobile according to any of the preceding claims, the method comprising the following steps of: - providing the plate (2) comprising at least two arms (6a, 6b) forming a clip and the arbor (1A) fitted with the cylindrical mounting part (10); - aligning the arbor relative to the plate such that the minor axis of the cross-section of the cylindrical fitting part is parallel to the direction of opening of the clip and, substantially maintaining this alignment of the arbor, axially inserting the cylindrical fitting part (10) into the central zone between the arms forming the clip until the plate is located substantially at an end of the cylindrical fitting part on the side of the friction surface of revolution; - then turning the arbor (1A) relative to the plate (2) so as to generate a resilient separation of the arms (6a, 6b) forming the clip and thereby opening this clip in its opening direction; and - lastly, move the plate in the axial direction until the plate (2) reaches its functional axial position in which the clip grips the friction surface of revolution.

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