Abstract:
A timepiece includes a platen ( 10 ) and a barrel mounted on the platen, the barrel including: a drum ( 20 ) with a bottom and side walls; a shaft ( 14 ) extending through the drum at the centre thereof and provided with pivoting elements ( 40, 54 ) on the platen; a leaf spring provided in the drum and co-operating with the shaft at one end and with the drum at the other end; and a lid ( 28 ) through which the shaft extends and closing the drum, a ratchet wheel ( 30 ) being kinematically connected to the shaft for winding the spring. According to the invention, the drum is pivoted via a first ball bearing ( 34 ) having a bushing ( 36 ) connected to the platen and another bushing ( 38 ) connected to the bottom of the drum.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to the field of mechanical horology and more particularly concerns a timepiece whereof the barrel is arranged advantageously. 
         [0002]    The barrel is the motor organ used in mechanical watches. It acts as an energy accumulator by being wound by the user or by an oscillating weight and progressively returning the energy it has stored to the train of the watch. 
       BACKGROUND OF THE INVENTION 
       [0003]    A traditional barrel comprises:
       a barrel drum, which is a sort of cylindrical case comprising a bottom and side walls, the drum being provided with an exterior toothing to drive the train,   a barrel-arbor pivoting between bridge and plate and provided with a hook arranged on its core,   a strip-spring fixed by a first end to a countersink formed on the inner diameter of the side walls of the drum, and by a second end to the hook of the barrel-arbor, and   a lid closing the drum.       
 
         [0008]    The drum and the lid generally serve as a pivot for the barrel-arbor in order to stabilize the latter part. A ratchet is mounted integral with the barrel-arbor, generally square fit. It is driven by a winding device, manual or automatic, to cause the arbor to pivot and wind the barrel spring. 
         [0009]    One skilled in the art knows that one of the main factors to improve the efficiency of a movement is the quality of the pivoting of the different elements and the weakness of the friction involved. This point is particularly essential at the level of the barrel, where the forces exerted are significant and where flaws in guiding of the arbor and drum can have non-negligible consequences for the power reserve. 
         [0010]    Document CH 610178 proposes, with the goal of improving the pivot quality of the barrel, to mount it cantilevered using a ball bearing. The barrel-arbor is driven inside the inner ring of this bearing while the outer ring is fixed in a housing arranged in the plate. Furthermore, the drum is pivoted from the outside using runners with which it cooperates. 
         [0011]    However, the presence of runners is particularly bothersome in terms of the bulk they create. Moreover, experience shows that the precision of the device proposed in the abovementioned document is not very satisfactory. The present invention aims not only to offset this drawback, but also to improve the pivoting of the barrel. 
       BRIEF SUMMARY OF THE INVENTION 
       [0012]    More precisely, according to the invention, the barrel drum is pivoted by a first ball bearing whereof one ring is integral with the plate and another ring is integral with the bottom of the drum. 
         [0013]    Advantageously, the barrel-arbor is pivoted in the plate using a second ball bearing. 
         [0014]    According to one preferred embodiment, the barrel-arbor and the drum are mounted pivoting in relation to the plate using a ball bearing comprising an intermediate ring fixed to the plate, an inner ring integral with the arbor and an outer ring integral with the bottom of the drum. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Other details will appear more clearly upon reading the following description, done in reference to the appended drawing, in which: 
           [0016]      FIG. 1  is a cross-sectional view of a preferred embodiment, 
           [0017]      FIGS. 2   a  and  2   b  are cross-sectional and top views, respectively, of a bearing used in the embodiment of  FIG. 1 , and 
           [0018]      FIGS. 3 to 7  show cross-sectional views of different embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    We have illustrated, in  FIG. 1 , a plate  10  supporting the essential elements of a timepiece movement, only the energy accumulator of which is illustrated. This is formed, traditionally, of a barrel  12  mounted on the plate  10  and comprises an arbor  14  provided with means for pivoting on the plate  10 . The body of the arbor  14  defines a core  16  provided with a hook  18 . 
         [0020]    The center of a drum  20  is passed through by the arbor  14  and, according to one important aspect of the present invention which will be explained in detail below, is pivoted on the plate  10 . The drum is provided with an exterior toothing  22  to drive a train of a watch. It comprises a bottom located on the side of the plate and side walls forming its diameter which define a housing  24 . A countersink  26  is formed inside the side walls. The drum  20  is free to pivot in relation to the arbor  14  and it can constitute a bearing for the latter part. 
         [0021]    A strip spring, not visible in the drawing, is arranged in the housing  24 , fixed by a first end to the hook  18  and by a second end to the drum, at the level of the recess  26 . 
         [0022]    A lid  28  closes the drum  20 . The arbor  14  also passes through its center, and said lid  28  can constitute a bearing for the arbor  14 . 
         [0023]    A ratchet wheel  30  is mounted integral with the arbor  14 , for example using a screw  32 . This wheel is intended to be driven by winding means known by one skilled in the art in order to wind the strip spring. 
         [0024]    Particularly to the invention, the drum  20  is pivoted on the plate  10  using a ball bearing  34 . According to the preferred embodiment illustrated in  FIG. 1 , this bearing comprises:
       an intermediate ring  36  fixed to the plate, for example by screwing, and   an outer ring  38  made integral with the bottom of the drum, for example by screwing also.       
 
         [0027]    In this preferred embodiment, the means for pivoting the arbor  14  on the plate  10  are also formed by a ball bearing  40 , comprising a first interior ring  42  made integral with the arbor, for example by driving in, and a second ring  44  (visible in  FIGS. 5 and 6 ) integral with the plate  10 . Advantageously, the second ring of the bearing through which the arbor pivots is formed by the intermediate ring  36 . 
         [0028]    In this way, the barrel-arbor  14  and the drum  20  are mounted pivoting in relation to the plate via a ball bearing comprising an intermediate ring  36  fixed to the plate, an inner ring  42  integral with the arbor and an outer ring  38  integral with the bottom of the drum. Advantageously, the bottom of the drum  20  can have a slight extra thickness in order to strengthen it where the screws pass. Moreover, this extra thickness makes it possible to define a slight clearance between the bottom of the barrel  12  and the other elements of the bearing, avoiding any superfluous friction. 
         [0029]    An example of bearing used is particularly visible in  FIG. 2 . It defines a general plane. In the following passage, the lower side of the bearing is arranged on the plate  10  side in  FIG. 1  and its upper side is oriented from the side of the ratchet wheel  30 . 
         [0030]    The bearing therefore comprises an inner ring  42  provided with a circular central hole, in which the arbor  14  is intended to be placed. The inner ring  42  has a foot  42   a  extending at the lower level of its outer wall, in the general plane of the bearing. The end of this foot  42   a  is formed so as to have a bearing surface for the balls. 
         [0031]    The intermediate ring  36  comprises a first groove  36   a  parallel to the general plane of the bearing, arranged on the inner wall, substantially in the middle of its thickness. It also has a foot  36   b  extending from the upper side of its outer wall, in the general plane of the bearing. The groove  36   a  is modeled so as to form a track, while the foot  36   b  has a bearing surface for the balls. The grooves are typically V-shaped. The ring  36  is passed through by holes  46  allowing it to be fixed to the plate  10 . 
         [0032]    The outer ring  38  comprises a second groove  38   a  parallel to the general plane of the bearing, arranged on the inner wall, substantially in the middle of its thickness. The groove  38   a  is modeled so as to form a track path for the balls, it is typically V-shaped. The outer wall is cylindrical and fits a recess with an adapted shape, arranged in the plate  10 . Holes  46  extend through the ring  38 , allowing the latter part to be fixed to the drum  20 . 
         [0033]    Bows  48  are arranged, respectively, on the inner ring  42  and on the intermediate ring  36 , across from their foot, so as to form a track with them for the balls. The bows  48  are driven in and welded to the rings after placement of the balls, also ensuring maintenance of the assembly. 
         [0034]    Of course, the feet and the grooves can be reversed, which is to say that the inner ring can have a groove on its outer wall, the inner wall of the intermediate ring then having a foot cooperating with a bow, etc. . . . 
         [0035]    It is clear that, in light of the dimensions of a timepiece barrel  12 , the bearings used are micro-bearings which must have maximal precision so as to guarantee perfect positioning of the pivot axes and optimal guiding of the elements in movement. These micro-bearings are, for example, produced by the company Micro Precision System AG. 
         [0036]    Pivoting the barrel drum  20  in this way makes it possible to position it excellently and to obtain pivot conditions creating very little friction. Moreover, there is no need for peripheral guide means, which frees up all of the space around the barrel for other elements of the movement. Moreover, the fact that the intermediate ring  36 , which constitutes the connecting element to the plate  10  and therefore the reference element for pivoting of the arbor  14  and the drum  20 , has a relatively significant diameter, in any case more significant than if these elements were pivoted directly at the level of their pivot axis, grants the elements a better stability and greater precision in their movement. This is beneficial not only for the pivoting of the drum  20 , but also for that of the arbor  14 , which undergoes stresses much better than the barrel-arbors of the prior art also pivoted by a ball bearing, but arranged directly at their center. The efficiency obtained with a barrel as described above is substantially improved in relation to the barrels of the prior art. 
         [0037]    In the illustrated embodiment, the barrel arbor  14  is not mounted cantilevered in order to improve the precision of its positioning. Its end located at the side opposite the plate is pivoted by a third ball bearing  49  arranged using an arbor bridge  50 , screwed on the plate. Traditionally, this bearing  49  comprises a first outer ring  52  driven into the bridge  50  and a second inner ring  54  integral with the arbor  14 . The ratchet wheel  30  tops the bearing  49  and the bridge  50  and is screwed into the arbor  14 . It may also be arranged at the other end of the arbor  14 . 
         [0038]    According to a first variation illustrated in  FIG. 3 , the third bearing  49  is directly housed in the lid of the barrel, which makes it possible to do away with the bridge  50 , thereby decreasing the thickness of the assembly. 
         [0039]    According to three other variations illustrated in  FIGS. 4 ,  5  and  6 , the means for pivoting the arbor on the plate and those for the drum on the plate are independent. The arbor is pivoted by a ball bearing  40  ( FIGS. 4 and 5 ) or by a traditional pivot ( FIG. 6 ), through a jewel  54 . The bearing  34  through which the drum  20  is pivoted on the plate  10  can then be fixed to this by its inner ring  36  ( FIG. 4 ) or by its outer ring  38  ( FIG. 5 ). The bottom of the drum is fixed to the outer ring  38  ( FIG. 4 ) or the inner ring  36  ( FIG. 5 ) of the bearing, respectively. 
         [0040]    In an additional variation, illustrated in  FIG. 7 , the drum  20  and the arbor  14  are pivoted by a single bearing comprising three rings  36 ,  42  and  38 , as in the preferred embodiment, but the bottom of the drum is integral with the intermediate ring  36 , while the outer ring  38  is fixed to the plate  10 . Advantageously, this outer ring  38  is driven into a hollow of the plate provided for this purpose. 
         [0041]    Thus is proposed a timepiece whereof the different elements of the barrel are pivoted optimally, both in terms of guiding and in terms of the weakness of the friction. This is obtained without cluttering up the plate around the barrel and even, according to the chosen embodiment, makes it possible to avoid using a bridge for the barrel or the ratchet wheel. 
         [0042]    The power reserve for such a barrel is improved, thanks to its efficiency, greater than that of the prior art. It is thus possible to use a less strong spring, therefore with a smaller thickness, to give the desired amplitude to the balance. The spring can therefore be wound on a larger number of turns in a same volume and therefore store more energy.