Patent Publication Number: US-2021165369-A1

Title: Device for fastening a horological external element or display element

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to European Patent Application No. 19213223.1 filed Dec. 3, 2019, the entire contents of which are incorporated herein by reference. 
     Field of the Invention 
     The invention relates to a device for fastening an external or display element onto a horological structure, comprising at least one retaining key comprising a post arranged so as to be driven or screwed or riveted or brazed or welded into a recess comprised in said structure or comprised in an element fixed to said structure, said at least one retaining key comprising a head with at least one truncated flange that is substantially axisymmetric relative to the axis of said post, the direction of said axis defining the direction in which a said external or display element is inserted relative to said structure, said truncated flange comprising a substantially axisymmetric part which extends about an angular sector of strictly less than 360°, and said truncated flange comprising at least one first lip delimited by a first upper surface and a first lower surface and which is arranged so as to cooperate by bearing, in a blocking manner, with a surface or a face comprised in a fastening element integral with a said external or display element, and which first lip is further delimited at the two ends thereof by edges. 
     The invention relates to the field of fastening external or display elements in a timepiece, in particular a watch. It in particular relates to the fastening of dials. 
     BACKGROUND OF THE INVENTION 
     In order to fasten a horological external or display element such as a dial comprising dial feet, dial keys are used to retain these feet by deformation, such dial keys comprising a vertically truncated and skewed flange, the edge whereof allows for good penetration into the cylindrical part of the dial foot, thus allowing for the immobilisation thereof. However, the rotation of such a dial key generally generates, during the rotation thereof to fasten the dial, a burr originating from the dial foot concerned and which can easily become detached. 
     SUMMARY OF THE INVENTION 
     To prevent such a burr from being generated and potentially falling into and polluting the movement, the invention relates to a fastening device comprising a new retaining key, which is obliquely truncated and angled to the origin of attack of the dial foot, the material of the dial foot whereof can thus be repelled and not cut, with the clot thus created remaining attached to the component. 
     For this purpose, the invention relates to a fastening device according to the claim  1 . 
     The invention further relates to a timepiece, in particular a watch, comprising at least one such fastening device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the invention will be better understood upon reading the following detailed description given with reference to the accompanying drawings, in which: 
         FIG. 1  diagrammatically shows a perspective view of a retaining key comprised in a fastening device according to the invention; this retaining key comprises a truncated flange with a first conical lip, and a second oblique lip; 
         FIG. 2  diagrammatically shows an overhead view of the retaining key in  FIG. 1 ; 
         FIGS. 3 and 4  diagrammatically show a side view, in two perpendicular directions, of the retaining key in  FIG. 1 ; 
         FIG. 5  diagrammatically shows a sectional view along the line AA in  FIG. 2  of a feature of the retaining key in  FIG. 1 ; 
         FIG. 6  diagrammatically shows a perspective view of an alternative embodiment of a retaining key comprising two superimposed flanges; 
         FIG. 7  diagrammatically shows a perspective view of another alternative embodiment of a retaining key comprising two superimposed, angularly offset flanges; 
         FIGS. 8 and 9  diagrammatically show an overhead view of other alternative embodiments of retaining keys according to the invention; 
         FIG. 10  diagrammatically shows a sectional view of the retaining key in  FIG. 1  cooperating with a dial foot by locally repelling the material thereof, in order to fasten a dial onto a structure; 
         FIG. 11  diagrammatically shows a sectional view of the retaining key in  FIG. 1  cooperating with a dial foot by bearing against a groove comprised therein, in order to fasten a dial onto a structure; 
         FIG. 12  diagrammatically shows a front view of a timepiece, in this case a watch, comprising a structure supporting a dial, assembled by a fastening device according to the invention, comprising three retaining keys according to  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention relates to a device  10  for fastening an external or display element  20  onto a horological structure  100 . 
     This fastening device  10  comprises at least one retaining key  1 , which comprises a post  2 , which is arranged so as to be driven or screwed or riveted or brazed or welded into a recess  8  comprised in the structure  100  or comprised in an element fixed to the structure  100 , or on the structure  100  or such a fixed element. This retaining key  1  comprises a head  9 , with at least one truncated flange  3  which is substantially axisymmetric relative to the axis D of the post  2 . The direction of this axis D defines the direction in which an external or display element  20  is inserted relative to the structure  100 . 
     The truncated flange  3  comprises a substantially axisymmetric part which extends about an angular sector of strictly less than 360°, and this truncated flange  3  comprises at least one first lip  31 , which is delimited by a first upper surface  38  and a first lower surface  39 , and which is arranged so as to cooperate, by bearing thereagainst in a blocking manner, with a surface  42  or a face  41 , which is cylindrical or otherwise, comprised in a fastening element  4  integral with an external or display element  20 . 
     In a first specific alternative embodiment, the first lower surface  39  is planar. 
     In another specific alternative embodiment, the first lower surface  39  is helix-shaped, with a very low pitch, in the order of a few hundredths of a millimetre, or even a tenth of a millimetre. This alternative embodiment ensures good retention on a planar surface  42  of the fastening element  4 , such as a groove face or even a front surface of a dial, or similar. 
     This first lip  31  is delimited at the ends  311 ,  312  thereof by edges  51 ,  52 . 
     According to the invention, and as shown in  FIGS. 1 to 5 , these edges  51  and  52  are not coplanar, and this retaining key  1  comprises, joined to each edge  51 ,  52 , and radially retracted relative to the first periphery  30  of the first lip  31 , a second lip  6 . This second lip  6  comprises a second lower surface  69 , which is shared with the first lower surface  39 , and a second upper surface  68  which is, at each edge  51 ,  52 , tapered relative to the first upper surface  38  of the first lip  31 . 
     More particularly, the edges  51 ,  52  are finely angled edges, and are in particular radius edges with a radius that lies in the range 10 micrometres to 30 micrometres. 
     More particularly, the first lip  31  is more resilient than the fastening element  4  with which it is arranged to cooperate, and this first lip  31  is arranged to repel the material of the fastening element  4  during a relative rotation of the retaining key  1  relative to this fastening element  4 . Preferably, the first lip  31  has a hardness of greater than or equal to 550 HV; more particularly, this retaining key  1  is made of steel. 
     In another specific alternative embodiment, and as shown in  FIG. 6 , the retaining key  1  comprises a plurality of truncated flanges  3 , which are superimposed in the direction of the axis D, and capable of applying different bearing points on the same fastening element  4 . These superimposed lips procure different bearing points, either a plurality of bearing points on a cylindrical face of a dial foot for example, or both a bearing point with a planar surface of one of the lips against an upper surface of a dial for example, combined with another bearing point of another lip on a cylindrical face of a dial foot. It should be noted that, in the preferred application for fastening a dial foot, the dial foot must bear facing the lip, to prevent plastic deformation of the dial foot under bending. 
     In another specific alternative embodiment, and as shown in  FIG. 7 , a plurality of truncated flanges  3  comprise first lips  31 ,  131 , the edges  51 ,  52 , respectively  151 ,  152  whereof are angularly offset relative to one another. Such angularly offset origins of attack thus allow the fastening element  4  to be tightened gradually; this disposition further guarantees good resistance during successive disassembly operations, which clockmakers always carry out by targeting another point of the dial foot. 
     More particularly, the first upper surface  38  is conical with a first half apex angle α, relative to the axis D, which lies in the range 110° to 130°. The more acute the angle of each lip, the easier the penetration into the fastening element, in particular a dial foot or similar, at the expense of the resistance of the lip; conversely, penetration would require too much torque and would tend to bend this fastening element, in particular a dial foot. 
     More particularly, along a cross-section in each radial plane passing through the axis D, the second upper surface  68  forms, with the axis D, a second angle β, which lies in the range 40° to 50°. 
     More particularly, in a plane P perpendicular to the axis D, and at an edge  51 ,  52 , the dihedron tangent to the first upper surface  38  and to the second upper surface  68  has a third angle that lies in the range 145° to 165°. 
     In the general case, the retaining key  1  is arranged so as to be used in both directions of rotation. 
     In one specific case, the retaining key  1  is arranged so as to be used in a single direction of rotation, and comprises a first lip  31  in the shape of a helix over less than one revolution, in particular extending about an angle of less than 240° and with a pitch of less than 300 micrometres, however without being limited thereto. In the application for fastening a dial, this alternative embodiment has the advantage of pulling the dial against the bearing point thereof through the dial feet, managing the torque transmitted to the keys to avoid being torn away; it goes without saying that, in order for the dial foot to engage in a contactless manner, a non-threaded area must be provided, which explains the angle of less than one revolution. 
     More particularly, and as shown in the figures, the first lower surface  39  is planar. 
     More particularly, and as shown in the figures, the second upper surface  68  is planar. 
     In an alternative embodiment, and as shown in  FIG. 9 , the second upper surface  68  is concave. More specifically, it is understood that it is important for this truncated surface  6  to escape the cooperation with the foot, and it can take any form, provided that the interface areas at the edges  51  and  52  perform the function of repelling the material at the fastening element  4 . 
     More particularly, when projected on a plane perpendicular to the axis D, the tangents T 1 , T 2 , to the edges  51 ,  52  at the ends of the edges  51 ,  52 , joined with the first periphery  30  of the first lip  31 , form with one another a fourth angle Υ which lies in the range 90° to 130°. 
     More particularly, the first periphery  30  of the first lip  31  is a wire edge, the thickness whereof is less than or equal to 35 micrometres. 
     More particularly, the second lip  6  comprises a second periphery  60 , which is a wire edge, the thickness whereof is less than or equal to 35 micrometres. 
     More particularly, the external or display element  20  is a dial, the retaining key  1  is a dial key, and the fastening element  4  is a dial foot or a part of the dial. 
     The invention further relates to a timepiece  1000 , in particular a watch, comprising a structure  100  comprising at least one recess  8  for receiving a post, at least one external or display element  20  comprising at least one fastening element  4 , and at least one such fastening device  10  for fastening an external or display element  20  onto the structure  100  or onto an element fixed to the structure  100 . 
     More particularly, at least one external or display element  20  comprises a side visible to the user, and each retaining key  1  can be inserted into the structure  100  or into an element fixed to the structure  100  and accessible from the visible side, and comprises a drive surface  91  for inserting a tool capable of causing the retaining key to rotate about the axis D. 
     More particularly, at least one external or display element  20  and a retaining key  1  arranged so as to block this external or display element  20  are fastened on separate elements, each fixed to the structure  100 . 
     More particularly, at least one fastening element  4  for fastening an external or display element  20  comprises a groove  40 , which is arranged so as to cooperate with the first lip  31  of a retaining key  1  arranged so as to block this external or display element  20 . 
     More particularly, at least one retaining key  1  is partially concealed, from the visible side, by the external or display element  20  blocked by the retaining key  1 . 
     Such a retaining key  1  can be used for a plurality of dial or similar assembly and disassembly operations. 
     In the application for fastening a dial using a dial key, the first lip  31  penetrates a cylindrical face of the dial foot, is rigid, and must not be deformed, the base material thereof is in particular a steel, with in particular a hardness of 550 to 670 HV, however without being limited thereto. 
     In an alternative embodiment of the dial foot  4  comprising a groove  40 , the first lip  31  can come to bear against one of the faces of this groove  40 . In other cases, the first lip  31  must deform the dial foot, since without the deformation thereof, resistance is not guaranteed. 
     To summarise, the invention prevents the generation of detachable burrs, and ensures that the horological movement is kept clean when fastening external or display elements.