Abstract:
A timepiece includes:—a barrel bridge ( 33 ), and—a barrel mounted on the barrel bridge, the barrel having:—a drum ( 20 ) which includes an end wall and side walls,—an arbor ( 14 ) which passes through the centre of the drum,—a leaf spring housed in the drum and engaging at a first end with the arbor and at a second end with the drum, and—a cover ( 28 ) through which the arbor passes freely and which closes the drum,—a ratchet wheel ( 30 ) secured to the arbor to tension the leaf spring. The drum is pivoted by a first ball bearing including an intermediate ring ( 36 ), an inner ring ( 42 ) secured to the arbor and an outer ring ( 38 ), one of the intermediate ring and the outer ring being fixed to the barrel bridge and the other being secured to the end wall.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to the field of mechanical horology, and more particularly relates to a timepiece whereof the barrel is arranged in an advantageous manner. 
         [0002]    The barrel is the driving organ used in mechanical watches. It acts as an energy accumulator wound by the user or by an oscillating weight and gradually restoring the energy it has stored to the train of the watch. 
       BACKGROUND OF THE INVENTION 
       [0003]    A conventional barrel comprises:
       a barrel drum, which is a sort of cylindrical box having a bottom and side walls, the drum being provided with an outer toothing to drive the train,   a barrel arbor pivoting between a bridge and a plate and provided with a hook arranged on its core,   a strip-spring fastened 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 cover closing the drum.       
 
         [0008]    The drum and the cover generally serve to pivot the barrel arbor so as to stabilize the latter part. A ratchet is mounted secured to the barrel arbor, generally by a double squared connection. It is driven by a manual or automatic winding device to pivot the arbor and wind the barrel spring. 
         [0009]    One skilled in the art knows that one of the primary factors in improving the efficiency of a movement is the quality of the pivoting of the various elements and the weakness of the friction involved. This point is particularly essential in the barrel, where the forces exerted are significant and defects in the guiding of the arbor and the drum may have non-negligible consequences for the power reserve. 
         [0010]    Document CH 610178 proposes, with the goal of improving the pivot quality of the barrel, winding it cantilevered using a ball bearing. The ball bearing is driven into the inner ring of said bearing, while the outer ring is fastened in a bed formed 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. Furthermore, experience shows that the precision of the device proposed in the aforementioned 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 DESCRIPTION OF THE INVENTION 
       [0012]    More specifically, according to the invention, the drum is pivoted by a first ball bearing having an inner ring secured to the arbor, an intermediate ring, and an outer ring, one of the intermediate and outer rings being fastened to the barrel bridge, the other being secured to said bottom. 
         [0013]    According to another aspect, the invention also relates to a barrel whereof the arbor is mounted flying, i.e. it is only pivoted by one of its ends, using a bearing having three co-planar rings, whereof one ring among the intermediate and outer rings is fastened to an element of the frame (bridge or plate), the other ring among the intermediate and outer rings is fastened to the bottom of the drum, and the inner ring is fastened to the arbor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    Other details will appear more clearly upon reading the following description, done in reference to the appended drawings, in which  FIGS. 1 to 5  show different variants of the invention in cross-section. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]      FIG. 1  shows a plate  10  supporting the essential elements of a clockwork movement, only the energy accumulator of which is shown. The latter is traditionally made up of a barrel  12  comprising an arbor  14  provided with pivot means on the plate  10 . The body of the arbor  14  defines a core  16  provided with a hook (not shown). 
         [0016]    The arbor  14  passes through the center of a drum  20 . The drum is provided with an outer toothing  22  to drive a train of a watch. It comprises a bottom  23  and side walls forming its diameter, which define a bed. A countersink is formed inside the side walls. The drum  20  is flying to pivot in relation to the arbor  14 . 
         [0017]    A strip-spring  24  is arranged in the bed, fastened by a first end to the hook and by a second end to the drum, at the countersink. 
         [0018]    A cover  28  closes the drum  20 . The arbor  14  also passes through the center of said cover, the arbor and the cover being flying in reference to one another. 
         [0019]    A ratchet wheel  30  is mounted secured to the arbor  14 , for example using a screw  32 . This wheel is designed to be driven by winding means known by those skilled in the art in order to wind the strip-spring. 
         [0020]    A barrel bridge  33  is rigidly mounted on the plate, to allow the arbor  14  to pivot. 
         [0021]    The ratchet wheel  30  tops the bridge  33  and is screwed into the arbor  14 . It may also be arranged at the other end of the arbor  14 . 
         [0022]    According to one important aspect of the invention, the bottom of the drum  23  is situated on the side of the barrel bridge  33 . In this way, the drum  20  is pivoted, by means of its bottom  23 , on the barrel bridge  33  using a ball bearing  34 . According to the embodiment illustrated in  FIG. 1 , said ball bearing comprises:
       an intermediate ring  36  fastened to the barrel bridge  33 , for example by screwing as shown in the figure, and   an outer ring  38  made integral with the bottom  23  of the drum by screwing, also shown in the figure, and   an inner ring  42  made integral with the arbor  14 , for example by driving or screwing.       
 
         [0026]    Advantageously, the bottom  23  may have a slight overthickness in order to reinforce it at the screw passage. Furthermore, this overthickness makes it possible to define slight play between the bottom  23  and the other elements of the bearing, preventing any superfluous friction. The heads of the screws fastening the intermediate ring may be placed in a recess  40  formed in the barrel bridge  33 . 
         [0027]    The bearing  34  therefore comprises an inner ring  42  provided with a circular central hole, in which the arbor  14  is designed to be placed. The rings of the bearing are configured so as to have bearing surfaces for the balls, these not needing to be outlined here. Bows may complete the rings so as to define the rolling path of the balls completely. 
         [0028]    Of course, in light of the dimensions of a timepiece barrel  12 , the bearings used are micro-bearings, the precision of which must be maximal so as to guarantee perfect positioning of the pivot axes and optimal guiding of the moving parts. 
         [0029]    It will be noted that, according to the invention, the barrel bridge  33  has an opening for the flying passage of the arbor. In light of the presence of the bearing as described above, there is no need to form a bearing block for the pivoting of the arbor at the barrel bridge  33 . Such a bearing block is also not useful at the bottom  23 . 
         [0030]    There is also no need for other peripheral guide means, which flyings up the entire space around the barrel for other moving parts. Furthermore, the fact that the intermediate ring  36 , which makes up the connecting part to the barrel bridge  33  and therefore the reference element for the pivoting of the arbor  14  and the drum  20 , has a relatively large diameter, in any event larger than if those elements were pivoted directly at their pivot axis, gives the movement of said elements better stability and greater precision. This is beneficial not only for the pivoting of the drum  20 , but also for that of the arbor  14 , which bears stresses much better than the barrel arbors of the state of the art, which are also pivoted by a ball bearing, but that is arranged directly at the center thereof. The efficiency obtained with a barrel as described above is substantially improved in relation to the barrels of the state of the art. 
         [0031]    In the embodiment illustrated in  FIG. 1 , the barrel arbor  14  is not mounted cantilevered. Its end situated on the side of the plate  10  is pivoted by a second ball bearing  49  arranged in the plate. Traditionally, this bearing  49  comprises a first outer ring  52  driven into the plate and a second inner ring  54  secured to the arbor  14 . 
         [0032]    According to a first variant illustrated in  FIG. 2 , the second bearing  49  is directly housed in the cover of the drum  20 , which makes it possible to decrease the thickness of the assembly. The barrel arbor  14  is no longer pivoted in the plate, but pivots in reference to the cover  28 . 
         [0033]    In a second variant proposed in  FIG. 3 , the barrel arbor  14  is mounted completely flying. In other words, the barrel arbor is only pivoted on the barrel bridge  33  and is not pivoted in reference to the plate or the cover  28  of the drum. The barrel arbor may be shortened, and the thickness of the cover of the barrel may be reduced, making the assembly even thinner. It is even possible to completely eliminate the cover of the barrel. This construction is particularly advantageous, as it makes it possible to assemble the barrel on the barrel bridge independently of the assembly of the other parts of the movement. The operations for mounting the movement are thus made easier. Furthermore, it is possible to mount either the arbor or the bottom of the barrel on the bridge and to disassemble them from the bridge, without having to completely disassemble the entire barrel, on the condition that the bottom opening for the passage of the arbor is larger than the outer diameter of the arm. 
         [0034]    Although the proposed embodiments show, for the bearing  34 , that the intermediate ring  36  is fastened to the barrel bridge  33  and the outer ring  38 , at the bottom  23  of the barrel, this construction may be inverted. Thus, it is possible, without going beyond the scope of the invention, to fasten the intermediate ring  36  to the bottom  23  of the barrel and the outer ring  38  to the barrel bridge  33 . 
         [0035]    Furthermore, regarding the variant of  FIG. 3 , it is also advantageously possible to consider mounting the barrel flying on the plate. It has in fact been observed that, owing to the stability imparted by the bearing as proposed by the invention, it is possible to do away with pivoting of the barrel arbor by the two ends thereof. The barrel arbor is then only pivoted on the plate, no pivoting being provided at the cover. 
         [0036]    Thus, as proposed in  FIG. 4 , it is possible to eliminate the barrel bridge and save the corresponding thickness. To mount the ratchet wheel  30  on the arbor, in the absence of a bridge, it is possible to provide a small crosspiece or a slight shoulder  60  on the barrel arbor to position the ratchet wheel heightwise. 
         [0037]    By adapting the construction of the movement, it is also possible to mount the ratchet wheel  30  on the plate side. In  FIG. 5 , the ratchet wheel is mounted on the surface of the plate  10  opposite that which receives the barrel. Also in this variant, it is possible to provide that the intermediate ring  36  is fastened to the bottom of the drum, and the outer ring  38  is fastened to the plate, or that the intermediate ring  36  is fastened to the plate, and the outer ring  38  is fastened to the bottom. 
         [0038]    Thus proposed is a timepiece whereof the various elements of the barrel are pivoted optimally, both in terms of guiding and the level of weakness of the friction. This is obtained without cluttering the plate around the barrel. Furthermore, the versions proposed in  FIGS. 3-5 , with the arbor  14  flying, are particularly advantageous in terms of thickness and friction. 
         [0039]    The power reserve of such a barrel is improved, owing to its efficiency, which is greater than that of the state of the art. It is thus possible to use a weaker, and therefore thinner, spring to give the desired amplitude to the balance. The spring may therefore be wound over a larger number of revolutions in a same volume, and therefore store a greater amount of energy.