Abstract:
A timepiece includes a movement and a current-time ringing mechanism that includes: an hour cam ( 40 ) for providing information on the hour of the current time to an hour sampler, quarter cam ( 28 ) for providing information on the quarters of the current time to a quarter sampler, a minute cam ( 22 ) for providing information on the minutes of the current time to a minute sampler, wherein the cams are adapted to be driven by the movement, the quarter cam ( 28 ) and the minute cam ( 22 ) being pivotally mounted and being free relative to each other, and the minute cam ( 22 ) including a snail including a single row of 60/N stages and being adapted to be driven by the movement at N revolutions per hour.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to the field of mechanical horology. It more particularly concerns a timepiece comprising a movement and a current-time ringing mechanism comprising:
       an hour cam for providing information on the hour of the current time to an hour feeler-spindle,   a quarter cam for providing information on the quarters of the current time to a quarter feeler-spindle,   a minute cam for providing information on the minutes of the current time to a minute feeler-spindle,
 
the cams being designed to be driven by the movement.
       
 
       BACKGROUND OF THE INVENTION 
       [0005]    This type of mechanism makes it possible to indicate, upon request, the time to the closest minute, using strokes struck by two hammers on two different gongs. They can thus also make it possible to strike the hours and quarters as they pass. The hammers are actuated by lifts which are raised by a ringing mechanism. This mechanism comprises an hour rack, a quarter rack and a minute rack, provided with twelve, three and fourteen teeth, respectively, to strike the hours, quarters and minutes. 
         [0006]    In the ringing mechanisms of the prior art, in order to adjust the movement of these racks, an hour cam is arranged on a twelve-tooth star, advancing one pitch per hour, while a quarter cam and a minute cam can be adjusted on a pivot shank. Three levers, each provided with a feeler-spindle cooperating with these cams, make it possible to determine the travel of the hour, quarter and minute racks and adjust the number of strokes struck. 
         [0007]    Other details on this type of complication may be found, in particular on the driving force of the repeater or on the unhooking step, i.e. the triggering of the ringing mechanism, in the book “Théorie de l&#39;horlogerie” by Reymondin et al, Fédération des Ecoles Techniques, 1998, ISBN 2-940025-10-X, pages 219 to 224. 
         [0008]    The minute cam is thus driven at a rate of one revolution per hour and comprises four arms, one for each quarter, each arm being provided with fifteen regularly distributed stages. 
         [0009]    It is a very difficult exercise for the watchmaker to adjust the four arms of the minute cam such that, on each of the stages, the minute ringing mechanism works correctly. Indeed, due to the complexity of a striking mechanism, in particular a minute repeater, the minute feeler-spindle has, from one piece to the next, different play or a slightly offset position, which necessarily involves, given the dimensions of the elements, individually adjusting each stage. Furthermore, from one arm to the next, the adjustment must obviously be reproduced faithfully, which is very delicate. 
         [0010]    The aim of the present invention is to propose a ringing mechanism with easier adjustment and implementation by the horologist. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0011]    More precisely, the invention concerns a timepiece in which the quarter cam and the minute cam are pivotally mounted and are free in relation to each other, and in which the minute cam is made up of a snail including a single row of 60/N stages and being designed to be driven by the movement at a rate of N revolutions per hour. Advantageously, the energy transmitted by the movement to the cams is brought to a train coaxial to the minute cam, then transmitted to a train coaxial to the quarter cam and, lastly, transmitted to a train coaxial to the hour cam. 
         [0012]    According to one preferred embodiment, the quarter cam and the minute cam are mounted pivoting on two separate shafts. 
         [0013]    Advantageously, the minute cam is coaxial with a plate designed to transmit the energy received by the movement to the train coaxial to the quarter cam, the gear ratio between said plate and said train being determined such that the quarter cam performs one revolution per hour. 
         [0014]    The timepiece according to the invention may also comprise one or the other of the following characteristics:
       N is equal to 4,   the plate drives a setting wheel cooperating with said train coaxial to the quarter cam, a jumper acting on said setting wheel or on said train in order to position the quarter cam,   the plate and the minute cam are mounted with play rotating in relation to each other.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    Other characteristics of the present invention will appear more clearly upon reading the following description, done in reference to the appended drawing, in which  FIGS. 1 and 2  are cross-sectional and top views, respectively, of the cams of a ringing mechanism according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    In the illustrated example, the driving force transmitted by the base movement in order to drive the cams reaches the cam system via a wheel  10  performing four revolutions per hour. This wheel is mounted integral with the first end of an arbor  12  supported by a plate  14  provided with two diametrically opposite fingers  15 . More precisely, the plate  14  is free in rotation on a socket  16  frictionally mounted on the arbor  12 . The socket has a shoulder  17 , into which an index  18  is driven. This cooperates with the rim  19  of an opening provided in the plate  14 . The opening is larger than the index so as to allow relative play between the plate and the arbor. In order to axially maintain the plate  14 , a washer  20  is fitted on the arbor  12  such that the plate is maintained between the shoulder  17  and the washer  20 . 
         [0020]    A minute cam  22  made up of a snail comprising a single row of fifteen stages, resembling a conventional hour cam, is mounted integral on the socket  16 , at its second end. One may refer to the book “Les montres compliquées”, by F. Lecoultre, Editions Horlogères, which explains, on pages 128-131, how to dimension the stages of the cams. It would also be possible to use a cam having a continuous radius variation and which, therefore, would not comprise stages, but would simply be a spiral. In this case, in order to avoid the ringing mechanism being triggered between two minutes, the cam can be driven by pitch, for example by arranging a jumper at the drive system of the cam. 
         [0021]    Thus, according to one important aspect of the invention, the minute cam  22  only comprises a single row of stages forming what one could call a single arm, and does not comprise several arms. The watchmaker adjusting the operation of the timepiece need only perform the adjustment for this one row. The adjustment time is therefore one fourth that of a conventional mechanism. 
         [0022]    A setting wheel  24  is pivotally mounted in the plane of the plate  14 . It is designed to be driven by the fingers  15 . A jumper spring  26  is arranged to cooperate with the teeth of the setting wheel  24  and help the setting wheel complete its jump after having been pushed by one of the fingers  15 . One thus understands the usefulness of the play between the index  18  and the plate  14 . In fact, this play allows the plate  14  to recoil without hindering the action of the jumper  26  at the end of a jump and without modifying the position of the cam  22 . 
         [0023]    More generally, the minute cam is made up of a snail comprising a single row of 60/N stages and designed to be driven by the movement at a rate of N revolutions per hour. 
         [0024]    A pinion  27  meshes with the setting wheel  24 . The gear ratios, on one hand, between the number of fingers comprised by the plate  14  relative to the toothing of the setting wheel  24  and, on the other hand, between the toothings of the setting wheel  24  and of the pinion  27 , are determined such that the latter performs one revolution per hour. According to the example, the setting wheel  24  and the pinion  27  each comprise eight teeth. Given that the plate  14  turns at a rate of four revolutions per hour, the pinion  27  therefore pivots by one revolution in one hour. The pinion  27  is coaxial to and integral with a quarter cam  28  of the conventional type, which therefore also performs one revolution per hour. 
         [0025]    A second plate  30  is mounted coaxial to and integral with the pinion  27  and the quarter cam  28 . The plate  30  has a circular perimeter, interrupted by a finger  32  extending beyond the circle defined by the plate, in an essentially radial direction, the finger being bordered, on both sides, by a recess  33  running on this side of the circle. 
         [0026]    A drive wheel  34  is arranged so as to cooperate with the finger  32 . This wheel  34  has an opening  36  going through it, and which defines a spring organ  38 , formed by the wheel itself. More particularly, the opening  36  is U-shaped and allows a portion of the wheel, dimensioned so as to have elastic properties and forming the spring  38 , to remain between its branches. 
         [0027]    The wheel  34  is mounted coaxial to an hour cam  40  of the traditional type. The cam  40  is free in rotation on the arbor of the wheel  34 . A pin  42  is fixed to the cam  40  and assumes a position in the opening  36 . It is capable of cooperating with the rim of the opening  36  or with the spring  38 , thereby forming an elastic connection between the cam  40  and the wheel  34 , making it possible to secure the jump of the hour cam, as will be better understood below upon reading about the operation of the mechanism. 
         [0028]    The hour cam  40  is driven by a drive and blocking organ arranged so as to ensure driving of the hour cam by pitch and blocking thereof between two successive pitches. 
         [0029]    In the illustrated embodiment, the drive and blocking organ comprises the plate  30  and the wheel  34 . More precisely, the wheel  34  is provided with twelve notches  34   a  regularly distributed at its periphery and oriented along a radial direction and defining twelve pads  34   b . The notches  34   a  are dimensioned such that the finger  32  can be housed there with very little play. The end of the pads  34   b  has a curvature  34   c  which fits the circular perimeter of the plate  30 . On each side of this curve  34   c , i.e. between the curve  34   c  and each of the notches  34   a , each pad  34   b  has a bevel  34   d , oriented such that two bevels  34   d  arranged opposite each other, on either side of a notch  34   a , form a guide organ, in the shape of a funnel, narrowing toward the notch  34   a . The centers of the plate  30  and of the wheel  34  are arranged such that the pads  34   b  are flush with the perimeter of the plate  30 . 
         [0030]    Thanks to the particular shape of the wheel  34  and the plate  30 , when the pinion  27  is driven in rotation and the finger  32  is at the entry of a notch  34   a , the finger can be inserted therein, without being blocked by the walls of the notch  34   a , the upstream bevel  34   d  cooperating with the upstream recess  33 . The finger can then push the wheel  34  and thereby cause the snail  36  to advance. When the finger comes out of the notch  34   a , the downstream bevel  34   d  cooperates with the downstream recess, without blocking. The length of the finger  32  and the depth of the notch  34   a  are determined such that the advance made by pushing the finger allows the latter part, on the following revolution, to cooperate with the following notch  34   a . When the finger  32  is not in the notch  34   a , the wheel  34  is blocked in rotation, as the pad  34   b  is parallel to the perimeter of the plate  30  and cannot assume another position. Thus, when the finger  32  advances, its pitches are defined precisely by the jumper  26 . Upon each revolution of the plate  30 , the wheel  34  and the cam  40  move forward by jumping and their position is perfectly defined, which guarantees the accuracy of the ringing. 
         [0031]    Advantageously, the quarter cam  28  and the hour cam  40  both advance by jumping, but using only one jumper, which is favorable to the level of energy consumed by the mechanism. 
         [0032]    Furthermore, thanks to the elastic connection between the cam  40  and the wheel  34 , if a jump occurs when the hour feeler-spindle is engaged on the lowest stage of the cam  40 , the wheel  34  can advance and the cam  40  remain immobile abutting against the feeler-spindle, which results in winding the spring  38 . Then, under the effect of the spring, the cam  40  will be able to return to its normal position relative to the wheel  34 , after the feeler-spindle has returned to its locking position. 
         [0033]    The description above was provided as a non-limiting illustration of the invention. Thus, in particular, the connections, with or without play, between the different elements, such as between the arbor  12  and the plates it supports, can be realized by means other than those described, within the grasp of one skilled in the art. By modifying its rotational speed, the drive wheel  34  could be provided with a different number of notches, but multiples of twelve. Moreover, although, in the embodiment described above, the quarter cam and the minute cam are mounted pivoting on two separate shafts, these could also be coaxial without being rigidly connected to each other. They could be connected by a setting wheel system ensuring the appropriate gear ratio between the two cams. 
         [0034]    It is of course possible, without any particular effort for one skilled in the art, to mount a surprise-piece of the conventional type on the minute cam. The aim of the surprise-piece is to extend the highest stage at the time of the jump of the plate  14 , so that the feeler-spindle does not fall on the lowest stage when the time to be rung is at the beginning of a quarter.