Abstract:
This clasp comprises at least two branches ( 1, 2 ) articulated on one another via one of their respective ends. One of the free ends of these branches ( 1, 2 ) comprises a lever ( 12, 22, 33 ) articulated about a shaft ( 10, 20, 32 ) parallel to the articulation shaft ( 3 ) of said branches ( 1, 2 ) and fixedly attached to a hook ( 17, 27, 33   c ), the other of the free ends of these branches comprising a coupling element ( 4, 34 ) shaped to allow the hook ( 17, 27, 33   c ) to engage therewith, to keep the branches ( 1, 2 ) in the folded position. The lever ( 12, 22, 33 ) comprises elastic means ( 15, 25, 37 ) to exert a torque thereon and abutment means ( 13, 23 ) to limit its pivoting, under the effect of the torque, about said shaft ( 10, 20, 32 ) in a position corresponding at least to the engagement of said latching hook ( 17, 27, 33   c ) with the coupling element ( 4, 34 ), in which the elastic means ( 15, 25, 37 ) are under tension, such that the lever ( 12, 22, 33 ) must pivot against the elastic means ( 15, 25, 37 ) to engage and to disengage the latching hook ( 17, 27, 33   c ) of the coupling element ( 4, 34 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims priority of European Application No. 04405673.7 filed Nov. 3, 2004, which is included in its entirety by reference made hereto. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to a bracelet clasp comprising at least two branches articulated on one another via one of their respective ends, a latching device for keeping the free ends of these two branches in the folded position and linkage means between their free ends and the respective ends of a bracelet. 
   This type of clasp is well known particularly in the field of clasps for watch bracelets. The folding branches of the clasp are used to very substantially increase the length of the bracelet in the open position of the clasp, which allows the bracelet watch to be passed around the hand without needing to separate the bracelet. 
   DESCRIPTION OF THE PRIOR ART 
   There is a large number of coupling or latching systems for this type of clasp. Most of them use the elasticity of the folding branches of the clasp. The elastic properties of such clasps are therefore a result of the material and the dimensions of the clasp branches. One and the same clasp will therefore not have the same features if it is made of steel or of gold for example, if the branches are machined in a single piece or if they are made of pressed metal sheet. 
   A proposal has already been made in EP 1 279 349 of a clasp with folding branches comprising one or two levers articulated about shafts perpendicular to one of the branches of the bracelet and returned to the latched position by a spring placed transversely to the blades of the clasp, such that these levers can be accessed on the two opposite lateral faces of the clasp on which they protrude. These levers each have an inner rim which extends in a plane perpendicular to the respective pivoting shafts of the levers and that is intended to engage on complementary rims of a latching member fixedly attached to one end of another branch of the clasp. By spreading the rims of the levers by pressures exerted on them against the force exerted by the spring, the latching member may penetrate between the levers and is trapped when the pressure is released from the levers that are returned to their latched position by the pressure of the spring. 
   Although this solution can be used to make the latching independent of the elastic properties of the blades or branches of the clasp, it has a number of defects. One of them concerns safety. The actuation of the levers to control the opening of the clasp is the result of a simple pressure on pushbuttons which protrude laterally from the clasp. Because of this the clasp may be opened accidentally or unintentionally following an unconscious pressure on the pushbuttons. This risk is evidently unacceptable, particularly for a costly watch. 
   A proposal has been made to remedy this disadvantage in EP 1 374 716, in which the device for coupling the two bracelet branches is associated with a latching system which comprises a member for locking the pushbutton preventing it from being actuated unintentionally. 
   Another disadvantage of the two abovementioned devices arises from the fact that the force that the return spring exerts on the levers is not exerted on the branches of the clasp, so that a clearance may subsist between the latter when they are in the closed position, which is seen to be a defect by the wearer of the bracelet watch and is therefore not acceptable for a product of quality. 
   SUMMARY OF THE INVENTION 
   The object of the present invention is to remedy at least in part the abovementioned disadvantages. 
   Consequently, the subject of this invention is a bracelet clasp according to the definition given by claim  1 . 
   Unlike the abovementioned solution in which there are simple pushbuttons on which the force of the return spring acts directly, it will be noticed that the lever of the clasp according to the invention clearly acts on the elastic return means such as a lever, which allows it to obtain a gearing down of the force exerted thereon to cause the elastic return means to flex. Thanks to this gearing down of the manual force exerted on the lever to open the clasp, the force of the elastic return means can be increased and therefore the force that is exerted on the latching hook can be increased. This force continues to be exerted in the closed position, holding the branches tight against one another, thus taking up the clearances between the branches of the clasp. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     There are several other advantages that will be discovered on reading the following description made with the aid of the appended drawings which illustrate, schematically and as an example, three embodiments of the clasp that is the subject of the present invention. 
       FIG. 1  is an exploded view of a first embodiment; 
       FIG. 2  is a first view in longitudinal section on a first sectional plane, in the closed position of a first embodiment; 
       FIG. 3  is a second view in longitudinal section on a second sectional plane, in the closed position of this same embodiment; 
       FIG. 4  is a view in longitudinal section of the clasp according to this embodiment, in the open position; 
       FIG. 5  is a view in section of a second embodiment, in the open position of the clasp; 
       FIG. 6  is a view in longitudinal section of a third embodiment. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The clasp illustrated in  FIGS. 1 to 4  comprises two branches  1 ,  2  articulated by one of their ends about a shaft  3  ( FIG. 4 ). The free end of the branch  1  has a coupling element  4  which, in this embodiment, has the shape of a transverse element, parallel to the articulation shaft  3 . This coupling element  4  is situated in a portion  1   a  of the free end of the branch  1 , curved outward. A space is made between this coupling element  4  and the bottom of this curved portion  1   a  to make it possible to insert a coupling member between the coupling element  4  and the bottom of the curved portion  1   a  as will be explained hereinafter. This same free end is again fixedly attached to the two articulation shafts  5 ,  6 , parallel to the articulation shaft  3  of the branches  1 ,  2 . One  5  of these shafts is used for the articulation of a latching cover  7 , while the other is used for the articulation of an end of one of the lengths of the bracelet (not shown). 
   The free end of the branch  2  is thicker than the rest of this branch, in order to receive an articulation shaft  8 . This extra thickness is obtained by curving the face of this branch  2  turned toward the branch  1 , such that, in the closed portion, this curved face of the branch  2  substantially matches the shape of the beginning of the curved position  1   a  due to the fact that it is shorter than the branch  1 , as can be seen in  FIG. 3 . 
   A linkage member  9  is articulated at the free end of the branch  2  about the articulation shaft  8  so that it can articulate freely through at least 180° in order to facilitate the deployment of this branch  2  for the hand to pass freely through it in the open position. This linkage member  9  comprises two other shafts  10  and  11 . The shaft  10  is used for the articulation of a latching lever  12  and the shaft  11  is used to connect a cover  13 . The latter has two parallel lateral walls in which is made a plurality of pairs of positioning elements formed by circular recesses  14  on their opposite internal faces, for the attachment of a bar (not shown) in one or other pair of recesses, depending on the length desired for the bracelet. 
   The linkage member  9  has a surface  9   a  adjacent to the internal face of the top wall of the cover  13 . This surface  9   a  serves to prevent the cover  13  from pivoting about the shaft  11 . The end of this cover  13 , situated on the side of the free end of the branch  2 , covers the rear end of the latching lever  12 . 
   As can be seen in particular in  FIG. 3 , one end of a spring  15  presses on a rod  16  fixedly attached to the linkage member  9 , passes around the articulation shaft  10  between this linkage member  9  and the latching lever  12  and the other end of this spring  15  presses against the internal face of the top wall of the latching lever  12 . Consequently, this spring creates a torque on the latching lever  12  which tends to make it rotate anticlockwise in  FIGS. 1–4 . In reality, preferably, two springs  15  are placed along the pivot shaft  10 , either side of the linkage member  9  which, for its part, is in the center of the pivot shaft  10 . 
   The latching lever  12  supports a latching hook  17  shaped to be able to engage between the latching element  4  fixedly attached to the free end of the branch  1  and the bottom of the curved portion  1   a  of this branch  1 , a position in which it is held by the torque applied thereto by the springs  15 . In this latched position, the rear end of the latching lever  12 , situated beneath the front end of the cover  13 , transmits a torque to the latter via the linkage member  9 . This torque is used to hold the cover  13  very close, or even to press it against the length of bracelet whose end is attached in one of the pairs of positioning elements formed of recesses  14  and prevents it from moving away therefrom. This means that the cover  13  does not risk getting caught during the movements made by the person wearing a bracelet furnished with the clasp according to the invention. In addition, a clasp whose cover may move freely away from the bracelet because of its clearance, spoils the look of this clasp and constitutes a depreciation factor thereof. 
   Dot and dash lines on  FIG. 4  have been used to show the respective trajectories of the branch  2  about its articulation shaft  3  and of the latching hook  17  about its pivot shaft  10 . It can be seen that the two trajectories intersect at an angle greater than 60°. Thanks to this disposition, in the latched position, any force exerted on the branches  1 ,  2  in a bid to separate them generates a force tangential to the circle of the trajectory of these branches passing through the point of contact between the latching hook  17  and the latching element  4 , while the reaction of the hook  17  will be a perpendicular to the tangent at its trajectory about the pivot shaft  10  passing through this same point of contact. This perpendicular passes through the pivot shaft  10  and therefore creates no torque that would be likely to favor the opening of the clasp and does so, irrespective of the magnitude of the force applied to separate the branches  1  and  2 . It is therefore a true latching device. 
   Only the lifting of the front portion of the lever  2  to make it pivot in the clockwise direction, against the torque of the springs  15 , may cause the clasp to open. Theoretically, it would also be possible to exert a pressure on the portion of the lever  12  situated to the right of its articulation shaft  10  when looking at  FIGS. 1–4 . However, because the rear end of this portion of the lever  12  is situated beneath the cover  13 , there is insufficient space available to exert this pressure manually. In addition, it would be necessary to act directly against the force of the springs  15 , whereas by lifting the lever  12  by its front end, the user benefits from the lever arm that reduces the effort necessary to overcome the force of the springs. 
   It is therefore practically impossible to open the clasp unintentionally by exerting a pressure only on the right portion (with reference to  FIGS. 1–4 ) of the lever  12 , because the user has only difficult access to the portion closest to the shaft and the closer the user is to the shaft the greater is the force necessary to pivot it, all the more so because the user is then acting directly on the place where the force of the springs  15  is exerted on the lever  12 . Conversely, the lifting of the lever  12  makes it possible to benefit from the lever arm, so that the pressure of the springs  15  may be chosen to be relatively high since the effort necessary to tilt the lever  12  for opening is reduced thanks to the lever arm. The accidental or inadvertent opening of this clasp is therefore practically out of the question. 
   The latching cover  7  is provided for additional security. It is intended to cover the latching lever  12  by flipping down, once the latching hook  17  has been coupled to the latching element  4 . This latching cover  7  may be held in the pressed down position thanks to two recesses  7   a  made on the internal faces of its lateral walls which may come and snap onto the opposite ends of the pivot shaft  10  of the lever  12  which then protrude from the lateral faces of this lever  12  and can retract against the pressure of a helical spring placed in the pivot shaft  10 , after the fashion of a piston bar well known for attaching a bracelet to the horns of a bracelet watch case. 
   The second embodiment ( FIG. 5 ) differs essentially from the first embodiment by the absence of the second latching cover  7 . Another difference lies in the fact that a shaft  20  serves as the articulation of the lever  22  on the linkage member  19 , and serves to connect the cover  23  to this linkage member  19 . The lever  22  is covered with a cap  28  which increases the length of the lever arm. This lever  22  supports a hook  27  intended to couple to the latching element  4  of the branch  1  exactly as in the first embodiment. 
   In this case, the return spring or springs  25  press on a pin  26  fixedly attached to the lever  22  at one of their ends and against the internal face of the upper wall of the linkage member  19  at their other ends, thus applying to the lever  22  a torque about the articulation shaft  20  directed in the anticlockwise direction. 
   The third embodiment illustrated by  FIG. 5  is intended to incorporate the clasp into an articulation chain link bracelet formed of at least three longitudinal rows of chain links, in which the links of one row are offset longitudinally by a half pitch from those of the adjacent row, the pitch corresponding to the longitudinal distance between two adjacent links of the same row. 
   The free end of the branch  1  is fixedly attached to at least one link  29 , several similar links being able to be aligned transversely with the link  29  according to the number of rows of links that the bracelet to be connected to the clasp comprises. This or these links  29  comprise a transverse latching rod  34  and a screw shaft  35  to make the connection with the bracelet (not shown). 
   Similarly, the linkage member  30  that is articulated about an articulation shaft  31 , at the free end of the branch  2 , comprises a second articulation shaft  32  on which is articulated the latching lever  33  which has the external shape of a link  33   a  to which a grasping element  33   b  is attached. The lower face front portion of the latching lever  33  is recessed to form a hook  33   c . A housing  33   d  is made in the rear portion of the lower face of the link-shaped lever  33   a  to house a cylinder  36  which encloses a helical spring and a piston  37  pressed outward by the helical spring. The stroke of this piston  37  is limited at its rear, larger diameter portion, so that the latter, at the end of the stroke, butts against the front face of the cylinder  36  through an opening in which the external visible portion, of smaller diameter, of the piston  37  passes. The outer end of this piston  37  presses against the upper face of the branch  2  of the clasp and applies to the lever  33  a torque about the articulation shaft  32  in the anticlockwise direction. 
   The articulation shaft  32  of the linkage member again serves for the articulation of two linkage links  38 , situated transversely either side of the latching lever  33  in the shape of a link  33   a . These linkage links  38  comprise a screw articulation shaft  39  for the attachment of one end of a length of the bracelet (not shown). The latching hook  33   c  is coupled to the latching rod  34  by lifting the lever  33  or causing it to pivot in the clockwise direction about the articulation shaft  32  against the force of the return spring exerted by means of the piston  37 .