Abstract:
A minute hand of a timepiece has a central arbor, on which, for driving around the same: a gearwheel is fixed in a first accommodating region, a flyback device is fixed in a second accommodating region, and a snail cam is arranged with an interference fit in a third accommodating region. The snail cam has an opening for accommodating the head of an eccentric and the flyback device has an opening for accommodating the finger of the eccentric, and therefore rotation of the eccentric head, via the flyback device fixed on the central arbor, makes it possible to rotate the snail cam by an angle about the central arbor relative to the gearwheel for setting the triggering point of the advancement operation by the minute control level.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a minute hand of a timepiece, in particular of a chronograph, with a central arbor which bears a seconds hand and which has a plurality of receiving regions, with a gearwheel which is fixedly connected on the central arbor for driving about the latter in a first receiving region, with a heart-shaped reset to zero mechanism which is fixedly fastened on the central arbor for driving about the latter in a second receiving region, with a release snail cam which is arranged on the central arbor for driving about the latter in a third receiving region and which has a radially encircling control cam which rises in a ramp-like manner and along which a trip-dog of a minute control lever, which is pivotable about a pivot axis, slides under resilient prestress during the rotational movement of the release snail cam and, after a sliding distance corresponding to sixty seconds and overcoming the point of the largest radius, drops onto the point of the smallest radius of the release snail cam, with a minute control pawl which is arranged on the minute control lever and by means of which, when the trip-dog of the minute control lever drops onto the point of the smallest radius of the control cam, a minute counter wheel which is mounted rotatably can be advanced by a minute step, wherein the release point of the advancement can be set in an adjustable manner by the minute control lever. 
       PRIOR ART  
       [0002]    A minute hand of a timepiece with the features of the preamble of claim  1  is known from EP 1 953 612. 
         [0003]    In the case of timepieces, at the moment of the zero passage of the seconds hand, both the trip-dog of the minute control lever is intended to drop onto the point of the smallest radius of the release snail cam and the minute counter wheel is intended to advance via the control lever and the control pawl by a step. Due to tolerances during the production and assembly, the simultaneouseous of said two functions cannot easily be achieved. In EP 1 953 612, an adjustment possibility with the aid of an eccentric is provided for this purpose, in which an opening which receives the head of the eccentric is provided in the minute counter wheel. A finger of the eccentric then engages in the release snail cam and, by rotation of the eccentric head, permits a variation in the setting of the angle of the release snail cam with respect to the gearwheel. The angular point at which the trip-dog of the setting lever drops from the point of the largest radius onto that of the smallest radius can thereby be set. 
         [0004]    A disadvantage of the solution according to this prior art document is that, for the use of the eccentric, the gearwheel has to be realized in a corresponding material thickness. A certain moment of inertia is associated therewith because of the radial extension of the gear wheel and the radially remote material provided as a result. 
         [0005]    Another earlier solution to this problem is known from DE 198 52 347, in which the trip-dog of the minute control lever itself can be set in the circumferential direction of the control cam. For this purpose, an eccentric with which the position of the point of the trip-dog can be set is provided on the minute control lever itself. 
       SUMMARY OF THE INVENTION 
       [0006]    Further embodiments are indicated in the dependent claims. Starting from this prior art, the invention is based on the object of indicating a setting possibility for the minute hand of a timepiece, which permits this adjustment possibility in a simple manner. 
         [0007]    According to the invention, this object is achieved with the features of claim  1 . 
         [0008]    Owing to the fact that the minute wheel is designed right at the bottom as a thin gearwheel, it is possible to arrange the release snail cam in an interference fit below the heart-shaped reset to zero mechanism such that the head of the eccentric is inserted in the heart-shaped reset to zero mechanism realized in a greater material thickness, and the finger of the eccentric in the release snail cam likewise realized in a greater material thickness. However, during the construction, these two elements, of course, take up a smaller diameter, and therefore the setting according to the present invention is associated with a lower moment of inertia. 
         [0009]    The release snail cam which corresponds to the number  6  in external shape is advantageously provided in the region between the smallest and largest radius with a recess which permits the trip-dog of the minute control lever to spring back. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Preferred embodiments of the invention are described below with reference to the drawings which merely serve for explanation and should not be interpreted as being restricting. In the drawings: 
           [0011]      FIG. 1  shows a perspective exploded view of an exemplary embodiment of a setting device for the minute hand of a timepiece; 
           [0012]      FIG. 2  shows a sectioned side view of the setting device according to  FIG. 1 ; and 
           [0013]      FIG. 3  shows a top view of the setting device according to  FIG. 1  with further components of the minute counter wheel. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0014]      FIG. 1  shows a perspective exploded view of an exemplary embodiment of a setting device for the minute hand of a timepiece according to the invention. The illustrated minute hand of the timepiece, in particular of a chronograph, comprises a central arbor  10  which is drivable rotatably by a movement (not illustrated) and on which a seconds wheel or fourth wheel  20  and a heart-shaped reset to zero mechanism  30  are arranged one above the other for conjoint rotation. Furthermore, a release snail cam  40  is provided in an interference fit on the two elements mentioned. 
         [0015]    Furthermore, the timepiece advantageously has a seconds hand (not illustrated in the drawings), the point of the hand of which follows a seconds dial (likewise not illustrated). The seconds hand here is in a fixed angular position with the fourth wheel  20 . 
         [0016]    The radially encircling lateral surface  41  of the release snail cam  40  has a control cam which rises in a ramp-like manner and merges from the point thereof with the largest radius  42  radially onto a point with the smallest radius  44 . In the process, said control cam overcomes a V-shaped incision  43  which will also be described subsequently. 
         [0017]    The more detailed assembly of the individual elements can be seen better from the sectional view of  FIG. 2  which shows the assembled components from  FIG. 1 . The central arbor  10  which is driven via the gearwheel  20 , which is fixedly connected thereto, is illustrated centrally on the longitudinal axis  100 . The outer edge of the gearwheel  20  has a multiplicity of teeth in which a drive (not illustrated further) engages. The gearwheel  20  rests on a stop flange  11  which protrudes beyond a first receiving region  12  on which the gearwheel  20  is inserted by the fastening hole  22  thereof. The gearwheel  20  is preferably connected to the central arbor  10  by a riveted joint. The diameter of the first receiving region  12  is customarily larger than a spacer step  15  on which the heart-shaped reset to zero mechanism  30  is placed. The heart-shaped reset to zero mechanism  30  is fastened fixedly here and rotates together with the arbor  10 . Said heart-shaped reset to zero mechanism  30  is oriented in such a manner that a reset to zero lever of the seconds hand, said reset to zero mechanism acting on the setting surface  54 , sets the seconds hand to zero on the dial thereof. This fastening of the heart-shaped reset to zero mechanism  30  is realized without tolerances in the second receiving region  13 . 
         [0018]    The third receiving region  14  in turn has a smaller diameter of the arbor  10  than the second receiving region  13 , thus forming a step on which the release snail cam  40  is placed. The release snail cam  40  is in an interference fit here and is mounted rotatably in the event of action of a force in relation to the arbor  10 . The heart-shaped reset to zero mechanism  30  is provided with an eccentric hole  32  which is arranged at a distance from the axis  100  of the central arbor  10 , which axis is denoted in  FIG. 2  by the axis  110 . 
         [0019]    The release snail cam  40  itself has an elongated hole  45  which runs radially with respect to the fastening hole  46  thereof, has a larger diameter than the eccentric hole  32  in the heart-shaped reset to zero mechanism  30  and runs symmetrically with respect to the axis of rotation  110  in the radial direction. 
         [0020]    An eccentric  50 , the cylindrical finger  52  of which is configured substantially matching the hole  32  and engages therein, is inserted into the two holes  45  and  32  mentioned. The cylinder head  51  of the eccentric  50 , which cylinder head is likewise of cylindrical configuration but has a different axis of symmetry, is inserted in the hole  45 . The effect which can therefore be achieved by rotation of the head  51  of the eccentric  50  over the fastening slot  53  is that the position of the eccentric head  51  in the elongated hole  45  changes between the position illustrated in  FIG. 2  (radially outermost position) and the opposite position. During this rotation of the eccentric  50  about the axis  110 , the angular setting of the cam disk  40  in relation to the heart-shaped reset to zero mechanism  30  and therefore in relation to the gearwheel  20  changes. 
         [0021]    It should be emphasized that the radial elongated hole  45  permits this movement to a greater extent since, in the case of a precisely fitting pairing of hole  32  and finger  52  and hole ( 45 ) and head  51 , the setting possibilities would be highly limited since each relatively great rotation of the head  52  of the eccentric  51  is also associated with a radial change in distance of the head  52  in the release snail cam  40  since the finger  52  is not capable of such an adaptation in the precisely fitting hole  32 . 
         [0022]    In an exemplary embodiment which is not illustrated in the drawings, the hole  32  is a radial elongated hole for a radial movement of the finger  52  during a rotational movement of the eccentric with an angular setting between release snail cam  40  and heart-shaped reset to zero mechanism  30 , and the hole  45  is a continuous round hole which precisely receives the head  52 . 
         [0023]    In both cases, the hole  32  in the heart-shaped reset to zero mechanism  30  could also be a blind hole. 
         [0024]      FIG. 3  now shows a top view of the setting device according to  FIG. 1 , in which further components of the minute counter wheel are illustrated. In particular, the pawl lever  60  which rotates about an axis  62 , which is parallel to the axis  100  or  110 , is illustrated. At a free end, the pawl lever  60  has a trip-dog  61  which is pressed against the control cam  41  of the release snail cam by the action of the leaf spring  63 . In the event of rotation of the gearwheel  20  counterclockwise, the trip-dog  61  runs on the control cam  41  at an increasing distance from the axis  100  as far as the point of the maximum radius distance  42  in order then to fall back onto the time (illustrated in  FIG. 3 ) and position of the smallest radius distance  44 . At the time of the largest radial distance, the minute control pawl  71  which is mounted in relation to the pivot axis  62  at another free end of the lever  60  is disengaged from the saw teeth  72  of the minute counter wheel  70 . In this exemplary embodiment, the minute counter wheel  70  has thirty saw teeth  72  with corresponding tooth spaces  73 . In the exemplary embodiment illustrated, the thirty teeth are not all identical; the tooth space  73  in which the pawl  71  engages in the drawing is much deeper than the other tooth spaces. In other exemplary embodiments which are not illustrated in the drawings, the teeth  73  can also all be configured identically. 
         [0025]    It can readily be seen from  FIG. 1  that, with the solution according to the invention, the eccentric wheel  50  is inserted into two components realized in a greater material thickness, namely the heart-shaped reset to zero mechanism  30 , on which a lever (not illustrated in the figures) can act in the region of the setting surface  54  if a zero position is intended to be adopted; and into the release snail cam  40  in which the likewise somewhat thicker trip-dog  61  of the setting lever  60  engages. It is therefore possible for gearwheel  20  to be of thin design and therefore to effectively reduce the mass of the inert system. The terms thin and thick in this respect should be understood as follows. The material thickness of the gearwheel  20  is smaller than the material thickness of the release snail cam  40  in the axial direction of the arbor  20 . The material thickness of the gearwheel  20  is smaller than the material thickness of the heart-shaped reset to zero mechanism  30  in the axial direction of the arbor  10 . Similar or identical material thicknesses of heart-shaped reset to zero mechanism  30  release snail cam  40  are then advantageously produced. The thickness of the setting lever  60  in this axial direction is then comparable, but is not greater than the thickness of the release snail cam  40 . 
         [0026]    It has turned out in tests that the interference fit of the release snail cam  40  is adequate for the two functions associated therewith. Firstly, the release snail cam  40  sits sufficiently securely on the central arbor  10  and, secondly, it is possible with the aid of inserting a tool into the slot  53  and exerting a force for rotating the eccentric head  51 , to change the angular position of the release snail cam  40  with respect to the heart-shaped reset to zero mechanism  30  and gearwheel  20 . Depending on the configuration in terms of the ratio of diameter of the eccentric head  51  to the diameter of the finger  52 , the elongated hole  45  here permits an angular movement by a number of degrees, for example between 1 and 10 degrees or 2 to 5 degrees. 
         [0027]    The eccentric  50  is advantageously arranged remote from the axis  100  by the arrangement of the hole  32  in the heart-shaped mechanism  31  in such a manner that said eccentric is preferably provided in the region of the half of the control cam  41  at the greater radial distance from the center, i.e. on the far side of the imaginary radial line (on the left thereof in the drawing of  FIG. 1 ) between the point of the largest radius  41  and the point of the smallest radius  44  beyond the center of the arbor  10  to the opposite side of the snail cam  41  where said line runs over the point  34  of the heart-shaped reset to zero mechanism  30 . The elongated hole  45  then lies here within an angular segment of 30 degrees to the line of point  34 ⇄arbor  10  in order to profit from the still existing greater portion of material of the heart-shaped reset to zero mechanism  30  close to the point  34 . In general, it is already of advantage if the central axis  110  of the opening  32  in the heart-shaped reset to zero mechanism  30  is provided within an angular range of −30 and +30 degrees about the imaginary connection between the axis of rotation  100  and the point  34  of the heart-shaped reset to zero mechanism  30 . 
         [0028]    Alternatively, the opening  32  can also be an elongated hole and the opening  45  a precisely fitting hole, and therefore the axis of rotation of the eccentric, which then replaces the axis  110 , coincides with the axis of rotation of the head  51 , and the finger  52  moves in an elongated hole. However, the exemplary embodiment described here has the advantage that, as can readily be seen in  FIG. 3 , a part of the eccentric head  51  in the elongated hole  45  is radially outside the control cam  31  of the heart-shaped reset to zero mechanism  30 , and therefore the distance of the two axes of rotation  100  and  110  from each other, which both determine the transmission, is as great as possible. 
         [0029]    In the exemplary embodiment illustrated, the sequence of the elements is release cam—heart-shaped reset to zero mechanism—fourth wheel in the direction of the longitudinal axis of the arbor  10 . In an exemplary embodiment which is not illustrated in the drawings, the sequence is heart-shaped reset to zero mechanism—release cam—fourth wheel where the two upper, thicker elements are therefore provided in a reverse sequence, which is possible because of the functional setting of elongated hole  45  and hole  32 . In a further exemplary embodiment, the fourth wheel  20  is provided with at least one aperture for the eccentric head, and therefore said fourth wheel can also be “at the top” (with respect to the drawing of  FIG. 3 ), i.e. the sequence is fourth wheel—release cam—heart-shaped reset to zero mechanism. The eccentric head  51  is then arranged in such an aperture and acts from there in the release cam  40 , which is illustrated in  FIG. 3 , but is then arranged below the fourth wheel  20 , and in the heart-shaped reset to zero mechanism  30 . 
       LIST OF REFERENCE NUMBERS 
       [0030]      10  Arbor 
         [0031]      11  Stop flange 
         [0032]      12  First receiving region 
         [0033]      13  Second receiving region 
         [0034]      14  Third receiving region 
         [0035]      15  Spacer step 
         [0036]      20  Gearwheel/seconds wheel/fourth wheel 
         [0037]      21  Teeth 
         [0038]      22  Fastening hole 
         [0039]      30  Heart-shaped reset to zero mechanism 
         [0040]      31  Cardiod 
         [0041]      32  Eccentric hole 
         [0042]      33  Fastening hole 
         [0043]      34  Point 
         [0044]      40  Release snail cam 
         [0045]      41  Control cam 
         [0046]      42  Point of largest radius 
         [0047]      43  Recess 
         [0048]      44  Point of smallest radius 
         [0049]      45  Elongated hole 
         [0050]      46  Opening for interference fit 
         [0051]      50  Eccentric 
         [0052]      51  Head 
         [0053]      52  Finger 
         [0054]      53  Slot 
         [0055]      54  Setting surface 
         [0056]      60  Pawl lever 
         [0057]      61  Trip-dog 
         [0058]      62  Pivot axis 
         [0059]      63  Leaf spring 
         [0060]      70  Minute counter wheel 
         [0061]      71  Minute control pawl 
         [0062]      72  Saw teeth (30 in number) 
         [0063]      73  Tooth space 
         [0064]      74  Axis of rotation 
         [0065]      100  Central axis of rotation 
         [0066]      110  Axis of rotation of eccentric finger