Abstract:
Wristwatch including a case in or on which there is arranged a first open housing, a wristlet provided with one end arranged in the first open housing, and a fastening means for holding the end of the wristlet in the first housing. The fastening means includes a second housing opening onto the first housing and a fastening element arranged in the second housing and occupying one part of the first housing. The wristwatch further contains a means of retaining the fastening element.

Description:
[0001]    This application claims priority from European patent application No. 13159929.2 filed Mar. 19, 2013, the entire disclosure of which if hereby incorporated by reference. 
         [0002]    The present invention concerns a wristwatch provided with a particular attachment system for a watch wristlet strand. 
       BACKGROUND OF THE INVENTION 
       [0003]    In the field of horology, and more particularly of wristwatches, it is known to secure the ends of a wristlet to the middle part of the watch case using a hinge means. For leather wristlets formed of two distinct strands, this hinge means generally takes the form of a pair of horns or fastenings to which there is fixed a bar, around which there is wound the end of the wristlet strand, which can thus pivot relative to the middle part. For rubber wristlets, variants are often proposed for fastening using central claws which are arranged between the horns and are provided with through holes for the bar to pass through. In this case, the end of the wristlet fastening has a particular cut-out in the form of slots. 
         [0004]    Other fastening methods using screws or rivets are also known. 
         [0005]    The drawback of these fastening methods is that the holes made in the wristlet for the bar, screws or rivets to pass through form stress raisers and thus reduce the mechanical resistance of the wristlet to traction. Further, for wristlets made of synthetic fabric for example, it is impossible to make these holes in the edge. 
         [0006]    Consequently, alternative solutions have been proposed for retaining the end of the wristlet strand, dispensing with the use of holes in the end of the wristlet strand, particularly for wristlets made of synthetic fabric or plastic. EP Patent No 0246449 by the Applicant proposes, for example, to insert the end of the strand into a housing and to hold it therein using a pin whose shape matches that of a channel portion arranged in the wristlet. 
         [0007]    This type of solution has the drawback, however, of not being suitable for cases made of plastic material, whose creep is liable sooner or later to release the end of the strand and the pin from their respective housings because of the constant pressure exerted by the pin on the case. 
         [0008]    Further, no axial retaining means other than friction forces is provided to prevent the pin from moving on its axis. Thus, it is impossible to ensure that the pin is permanently secured to the case, particularly if the strand is pulled off, which presents a risk for products intended for children, such as, for example, Flik Flak™ watches, since children could then swallow the pin. 
         [0009]    There is consequently a need for a wristwatch provided with a device for assembling the strand which is free of these known limitations. 
       SUMMARY OF THE INVENTION 
       [0010]    It is an object of the present invention to provide an alternative device for fastening a wristlet to a watch case which does not require machining through holes in the fastening ends of the wristlet strands. 
         [0011]    In particular, it is an object of the present invention to propose a secure wristlet fastening device. 
         [0012]    These objects are achieved as a result of a wristwatch including a case in or on which there is arranged a first open housing, a wristlet provided with one end arranged in the first open housing, and a fastening means for holding the end of the wristlet in the first housing. The fastening means includes a second housing opening onto the first housing and a fastening element arranged in the second housing and occupying one part of the first housing. The wristwatch is characterized in that it also contains a means of retaining the fastening element. 
         [0013]    These objects are also achieved as a result of a case for a wristwatch of this type, characterized in that it includes a first open housing, a second open housing opening onto the first open housing, and a central radial retaining element. 
         [0014]    These objects are also achieved as a result of a wristlet for a wristwatch of this type, characterized in that it includes a central recess and two mutually extending semi-grooves on either side of the central recess. 
         [0015]    One advantage of the proposed solution is that it enables a fastening element to remain integral with the case even when the end of the wristlet strand is accidentally released and thus, as a result of the permanent securing of the fastening element to the case, removes any danger for children who are not, therefore, at risk of swallowing the fastening element. 
         [0016]    Another advantage of the solution proposed is that it satisfies the legal requirements of certain countries. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    Other features and advantages of the invention will become clear from the following detailed description, and drawings, in which: 
           [0018]      FIG. 1  shows a perspective view of a wristwatch according to a preferred embodiment for implementing the present invention, with a median retaining horn concealed in a slot made in the case and a bar in two parts in an exploded view when the end of the wristlet is mounted in its housing; 
           [0019]      FIG. 2  shows a perspective view of the wristwatch according to the preferred embodiment of  FIG. 1 , with the bar assembled and integrated in the case; 
           [0020]      FIG. 3  shows a top and profile view of the wristwatch according to the preferred embodiment illustrated in  FIG. 1 , showing the shape of the grooves and channel portions for the bar to pass through. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]      FIG. 1  illustrates a wristwatch and a detailed view of the device for fastening wristlet  2  to case  1  according to a preferred embodiment of the invention, preferably made of plastic. On the back cover  10  of the case, there is shown a battery compartment  11  at the end of which there is arranged a peripheral edge  13  projecting slightly from case  1  and in which there is an access recess  131  for the battery cover (not shown, possibly provided with a tongue). The fastening device includes a first open housing formed here by a slot  3  arranged in a lateral wall of case  1 , and a second open housing, formed here by a cylindrical groove  32  arranged in one of the faces of slot  3 . This cylindrical groove  32  is for the insertion and holding of a fastening element, which is formed in this preferred embodiment by a bar  4  whose pin  41  extending along axis A-A is also cylindrical to match the shape of groove  31 . Bar  4  preferably further includes a collar  43  integral with one end of pin  41 , and a cap  42  of identical shape to collar  43 , intended to be assembled to the opposite end of pin  41  via a point of insertion  421  mounted in the hollow part of central pin  41 . An internal bump  411  is arranged at the end of pin  41  to cooperate with a groove arranged behind the point of insertion  421  so as to snap cap  42  into pin  41 . This internal bump  411  is preferably obtained here by deformation of material and consequently causes a groove to form on the external surface of the pin. Although other methods of securing caps  42  may be envisaged, such as for example adhesive bonding, welding or even driving in, this snap fit is very easy to achieve and allows considerable time saving during assembly, in addition to savings in terms of material. According to a variant that is not illustrated, a bar  4  in three parts could also be used, with a second cap  42  in place of the collar  43 . This variant would have the drawback, however, of requiring an additional assembly step. 
         [0022]    Unlike aluminium cases  1 , plastic cases  1  are more susceptible to creep over time and thus more likely to cause the release of bar  4 . In order to overcome plastic creep, a radial retaining element, complementary to groove  32  is provided in slot  3  in the form of a median horn  5  in which there is preferably arranged a channel portion  51  whose shape and depth are complementary here to that of groove  32 , so that pin  41  of bar  4  can never leave slot  3  via a movement of bar  4  in a direction comprised within a plane perpendicular to axis A-A of bar  4 . In  FIG. 1 , it will be noted that channel portion  51  of median horn  5  and groove  32  are arranged on opposite faces of the slot, and that the respective size and depth thereof are configured so that pin  41  of bar  4  no longer has any degree of freedom between channel portion  5  and groove  32  on median retaining horn  5 . This configuration allows the invention to be applied to any type of material for the case, such as for example ceramic, metal, plastic or materials having variable creep over time. However, when creep is relatively low, it will be possible simply to adjust the depth of channel portion  51  of median horn  5 , which could be arranged on the same side of slot  3  as groove  32 . 
         [0023]    According to the preferred embodiment illustrated in  FIG. 1 , slot  3  is delimited laterally by first vertical lateral walls  31 , facing which there are provided lateral recesses  12  in the middle part of case  1  for housing caps  42 . As caps  42  preferably have a cylindrical shape here, lateral recesses  12  have a matching excavated cylindrical shape in case  1 . 
         [0024]    To fix wristlet  2  to case  1 , one of the ends  21  thereof, corresponding for example to the end of a strand, is inserted into slot  3  before bar  4  is also inserted therein to hold said end  21  in the slot. To facilitate the holding of wristlet end  21 , a third housing is provided for cooperating with bar  4 . This third housing takes the form here of two additional semi-grooves  23  arranged on either side of a central recess  22  whose shape matches that of median horn  5 . The size and depth of these semi-grooves  23  are provided for housing one part of pin  41  of bar  4 , and as will be seen below in  FIG. 3 , the size and depth are preferably identical to those of the channel portion of median horn  5  in order to facilitate insertion of pin  41  of bar  4  along axis A-A during the assembly of wristlet  2 . 
         [0025]    Median horn  5 , arranged here at the centre of slot  3  for reasons of symmetry and therefore even distribution of stresses on the wristlet end, is thus totally concealed once wristlet  2  is assembled to case  1 . In order to compensate at best the machining tolerances of wristlet  2 , particularly in terms of width, median horn  5  is provided with second lateral walls  52 , which are preferably also vertical, and whose shape and inclination preferably match that of central recess  22  of wristlet  2 , to form stop surfaces preventing any lateral movement of end  21  along axis A-A of bar  4 , independently of caps  42  arranged on either side of axis A-A and which are also capable of performing this stop function relative to the lateral ends of wristlet  2 . According to an alternative embodiment (not shown), these two lateral walls  52  of median horn  5  could, for example, be inclined in a V or inverted V-shape to minimise the volume of material required to form median horn  5 , so as to provide economies of scale for mass production. 
         [0026]      FIG. 2  illustrates the same elements as those illustrated in  FIG. 1 , i.e. case  1 , wristlet  2  and bar  4 , but however with a bar  4  integrally mounted with cap  42  assembled to the right end of central pin  41 , and a wristlet  2  whose end  21  is no longer housed inside slot  3 . All the references are thus identical to those of  FIG. 1 , except for the fact that groove  32  and channel portion  5  are no longer visible, since they are occupied by pin  41  of bar  2  on axis A-A.  FIG. 2  therefore shows a case in which end  21  of wristlet  2  was able to be released from slot  3  in which it was housed, without however taking bar  4  with it. The radial retaining element formed by median horn  5  made it possible to prevent pin  41  from being pulled out of slot  3 ; however, when friction forces are insufficient to prevent any lateral movement of pin  41  along axis A-A of the bar, it is also necessary to provide axial retaining elements to prevent the pin from sliding out. To achieve this, first lateral walls  31  delimiting slot  3  act as axial stop members for caps  42 , so that once wristlet  2  is assembled using the bar, any movement of bar  4  along axis A-A is impossible, apart from machining tolerances for the length of pin  41  relative to the width of slot  3  and tolerances for the case to allow cap  42  to be assembled without crushing first lateral wall  31 . 
         [0027]      FIG. 3  shows various views of the wristwatch according to the preferred embodiment of the preceding Figures. In the centre, there is a top view showing the other side of case  1  covered in a conventional manner by a crystal  14 , and to the left and right there are lateral views of each side of the middle part, in the plane of axes A-A of insertion for the pins  41  of the bar (not shown). On the left, there is shown a set-hands stem  6  located in a conventional manner at 9 o&#39;clock on case  1  which is closed by crystal  14  and on the back cover of which the peripheral edge  13  of the battery compartment on the opposite side can be seen. The Figure on the right shows the opposite side of the wristwatch, at three o&#39;clock. It can be seen in these two Figures, as already suggested in  FIG. 1 , that two slots  3  are preferably located on either side of case  1 , at six o&#39;clock and midday here, arranged symmetrically and parallel to the axis of the stem preferably for receiving the ends of two strands. It will be noted that groove  32  is extended by channel portion  51  of median horn  5  to form a complete virtual cylinder, whose diameter will preferably be slightly greater than that of pin  41  of bar  4  to facilitate the insertion thereof along axis A-A, illustrated in the preceding  FIGS. 1 and 2 , and into which the virtual cylinder extends. These Figures also show first and second lateral walls, respectively referenced  31  and  52  for slot  3  and median horn  5 , which form the axial stop surfaces for end  21  of wristlet  2  and caps  42  of bar  4 . 
         [0028]    In the embodiment described above, the wristlet is preferably formed of synthetic fabric, but could also be made of plastic, leather, metal, ceramic or composite. Likewise, bar  4  is preferably made of metal but could also be made of plastic, ceramic or composite. This bar  4 , formed here in three parts, could however have only two parts, with one of caps  42  pre-moulded at one of the ends of pin  41 , or even a single for example moulded part, in which case the pin housing could consist of walls added outside the middle part of the watch case, and secured to the case by screws or welding. Further, the sections both of pin  41  and of caps  42  of bar  4  were preferably chosen to be cylindrical to facilitate a degree of freedom in rotation about axis A-A, but could take another shape, for example, oval, square or triangular according to production constraints, and in order to reduce manufacturing costs.