Abstract:
A chronograph clockwork movement for measuring time includes a control lever actuatable by a first control member for alternatively activating or deactivating a time measurement, clutch elements for driving or not a second timer in response to an action produced on the control lever and selective locking members for locking the second timer in response to an action produced on the control lever. A lever and a hammer for resetting the second timer to zero are also provided. The clockwork movement is arranged in such a way that a user does not feel any difference, while measuring a time, whether the second timer is pre-set or not. The clockwork movement has a structure enabling to activate time measuring by delaying the effective departure of the second timer until an external resetting device controlling the lever is released in the rest position thereof.

Description:
TECHNICAL FIELD 
       [0001]    The present invention concerns a chronograph movement for time measuring comprising:
       a going train,   at least one second counter comprising a chronograph second mobile designed to support an analog display organ for measured seconds,   a control lever designed to be actuated by a first control member to alternatively activate or deactivate the time measurement.       
 
         [0005]    In a known manner, this chronograph movement also comprises
       coupling means to connect or not the second wheel to the going train in response to an action on the control lever, and   selective locking means for locking the second counter in response to an action on the control lever.       
 
         [0008]    Moreover, return-to-zero means for the second counter are also provided, these return-to-zero means comprising at least one mobile return-to-zero element designed to be moved by a second control member, at least between a first, locking position and a second, active position, the mobile return-to-zero element being configured to act on the second counter in the second active position. 
         [0009]    More precisely, the mobile return-to-zero element is generally made in the form of a hammer cooperating with a heart-shaped cam integral with the second counter. 
       STATE OF THE ART 
       [0010]    A number of chronograph movements meeting the above definition are known from the prior art. 
         [0011]    Conventionally, the chronograph movement comprises a control lever moved under the impulse of an external control member and acting on a rotating control element to start or stop a time measurement. 
         [0012]    Likewise, the return-to-zero hammer is moved into contact with the corresponding heart under the effect of an action exerted on an external return-to-zero push-piece. The return-to-zero hammer then remains bearing against the heart, in its locking position, while a new unlocking of the chronograph is not ordered, with the goal of maintaining the hand indicating measured time in its initial position. Thus, it is provided that the return of the hammer into its raised or armed position, to release the indicator hand, is caused by an action on the control lever whereof the primary aim is to start a time measurement. In fact, the rotating control element, of the two-level cam or column wheel type, typically has a projecting region brought into contact with a part of the hammer and driving the rotation thereof to bring it back to its armed position. This rotational movement is then done while overcoming the pressure of a spring arranged bearing against a part of the hammer to maintain it firmly against the heart when a time measurement is not in progress. 
         [0013]    However, these conventional chronograph movements have some aspects which are open to improvement. One of these aspects rests on the fact that, in general, when an external return-to-zero member is maintained in its pressed-in position, raising of the return-to-zero lever to its armed position is not possible. As a result, a rotation of the rotating control element is generally not possible while the return-to-zero push-piece is pressed in, due to the mechanical connection between the hammer and the rotating control element mentioned above. Thus, the external control member acting on the control lever is neutralized and cannot be actuated. The result is that the manipulation of the external control members can only be done sequentially, the corresponding pressures of the user being validated by the implementation of conventional notchings. 
         [0014]    Moreover, the first start-up of the time measurement, caused by an action on the control lever, requires an additional effort to overcome the force of the spring serving to keep the hammer lowered, in addition to activating the time measurement mechanisms as such. Thus, when the user stops the time measurement at a given moment, then starts it again without having previously reset the counter(s) to zero, the sensation the user feels upon pressing the control member is different from that felt during the first start-up. In this configuration, in fact, the hammer not having been released to return the counters to zero, the force of its supporting spring does not need to be overcome to restart the time measurement mechanism. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0015]    The present invention aims in particular to offset the abovementioned drawback of the prior art by proposing a chronograph movement having a structure which makes it possible to activate a time measurement while also maintaining the counter for the measured unit of time in its initial position while the external return-to-zero mechanism is not released in its locking position. Thus, the effective start-up of a time measurement takes place at the moment when the user of the watch, in which the chronograph movement according to the present invention is implemented, releases the return-to-zero push-piece. A characteristic of this type results in increased precision of the triggering of the measurement by the user since this user does not have a provide a force of minimal intensity needed to cross a notching, as is the case for the known movements of the prior art. 
         [0016]    An additional aim of the present invention is to improve the sensation felt by the user of a chronograph at the time of activation of a time measurement. In particular, one aim of the present invention is to propose a chronograph movement thanks to which the user does not feel any difference upon activation of the time measurement depending on whether or not the counters of measured units of time have been previously returned to zero. An aim of this type is achieved in particular thanks to the fact that the mobile return-to-zero element has a locking position in which it is not arranged in contact with the chronograph counters and is not coupled to the column wheel. 
         [0017]    To this end, the invention relates to a chronograph movement of the type indicated above, characterized by the fact that it also comprises elastic means exerting a return force on the return-to-zero means, and by the fact that the movements of the mobile return-to-zero elements are controlled exclusively by the second control member, from the locking position toward the active position, and by the elastic means, from the active position toward the locking position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    Other characteristics and advantages of the present invention will appear more clearly upon reading the detailed description of one preferred embodiment which follows, done in reference to the appended drawings provided as non-limiting examples and in which: 
           [0019]      FIG. 1  shows a simplified top view of one part of the chronograph movement according to a first preferred embodiment of the invention; 
           [0020]      FIG. 2  is a view similar to that of  FIG. 1 , in which the additional components of the chronograph movement of  FIG. 1  have been shown, and 
           [0021]      FIG. 3  is a simplified transverse cross-sectional view of the chronograph movement along line III-III of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    The timepiece chronograph clockwork movement according to the present invention is designed to be arranged in a chronograph watch with analog display (not shown) of the conventional type. 
         [0023]    A watch of this type comprises in particular at least one organ for displaying a unit of measured time, generally seconds. In the preferred embodiment as shown and described in the continuation of the text, the clockwork movement comprises a minute counter to drive a display organ for measured minutes, in a manner known in the state of the art, in addition to a second counter to drive the display organ for measured seconds. 
         [0024]      FIGS. 1 and 2  are simplified illustrations of the component elements of the clockwork movement according to the present invention coming into play during the activation or deactivation of the chronograph function or during the return-to-zero of the second and minute counters. Only the elements of the clockwork movement which are essential to a good understanding of the invention have been shown out of a concern for clarity. 
         [0025]    Also, in the following description, the position of certain components is sometimes defined in reference to an hour. This position corresponds to that occupied, on a conventional dial, by the index displaying the given hour. 
         [0026]    In  FIGS. 1 and 2 , a peripheral portion of the plate  1  of the movement has been shown in the region designed to cooperate with the external control members (not shown) in the corresponding timepiece. A return-to-zero lever  2  is arranged to be actuated by an external return-to-zero control member, diagrammed by an axis line bearing the reference R in the figures. More precisely, the lever  2  has a pivot-type connection with the plate  1  and follows a rotational movement relative to the plate in response to a pressure exerted on the external control member. The pivot-type connection is provided by an axis or post  3  which can be press-fitted in a hole (not shown) of the plate having corresponding dimensions. 
         [0027]    The position of a setting organ or stem (not shown) has also been diagrammed by an axis line bearing the reference T. Likewise, the position of an additional control member has been diagrammed by an axis line bearing the reference S, this control member being designed to activate or deactivate the chronograph function. As non-limiting information, one can note that, when the clockwork movement is mounted in a case to assemble a timepiece, the axis R is positioned at four o&#39;clock while the axis T is positioned at three o&#39;clock and the axis S at two o&#39;clock. 
         [0028]    A return-to-zero hammer  4  is mounted integral with the return-to-zero lever  2 , by its base  5 , so as to be moved in response to an action on the external return-to-zero control member. 
         [0029]    The nature of the movement of the hammer  4  is not directly connected to the present invention and can be of any type adapted to the implementation of this invention. Thus, in the present embodiment, the lever  2  is arranged so as to be able to pivot in relation to the plate  1  of the clockwork movement, like the return-to-zero hammer  4 . One sees in particular, in  FIG. 1 , that the base  5  of the hammer  4  comprises a hole  6  inside which is arranged the post  3 , this post thereby also constituting an axis of rotation for the hammer  4 . 
         [0030]    The lever  2  and the hammer  4  can be made integral using any adapted means making it possible to ensure the transmission of a rotation of the return-to-zero lever  2  to the hammer  4 , without going outside the scope of the present invention. 
         [0031]    According to one preferred embodiment of the present invention, as visible in  FIG. 1 , the return-to-zero lever  2  is provided with a pin  7  press-fitted in a hole (not referenced) arranged in the region of the lever  2  located in superimposition relative to the base  5  of the hammer. The base  5  also comprises a hole adapted to house the pin  7  and thereby make the hammer  4  integral with the return-to-zero lever  2  during rotational movements. 
         [0032]    The return-to-zero lever  2  comprises an additional pin  8 , in its part remote from the post  3 , designed to serve as support for the end of a spring (not shown) exerting a force, diagrammed by an arrow referenced by F 1  in  FIG. 2 , on the lever  2 , this force tending to maintain the lever in its locking position, i.e. in the position shown in thick lines in  FIG. 1 . One preferably provides a notching done conventionally on the spring to allow rapid action of the return-to-zero control. 
         [0033]    The hammer  4  is provided with support surfaces  9  and  10 , two in number in the embodiment shown in the figures non-limitingly, designed to be moved into contact with hearts  11  and  12  when the chronograph counters are returned to zero. 
         [0034]    The hearts  11  and  12  were illustrated diagrammatically insofar as they are conventional and do not present any particular difficulty for one skilled in the art. Each of the hearts is mounted on a counter mobile (not shown in  FIGS. 1 and 2  for more clarity) supporting a hand indicating a timed unit of time. 
         [0035]    Thus, a hand  13  indicating timed seconds and a hand  14  indicating timed minutes have been diagrammed in the figures. The hands  13  and  14  were illustrated in their initial positions in  FIG. 1 , which corresponds to a stopped situation after return-to-zero of the chronograph function. The hammer  4  is shown in solid lines in its raised position to allow any rotation of the hearts  11 ,  12  of the chronograph mobiles relative to their respective axes of rotation  15  and  16 . We have also shown the hammer, in thin lines with the reference  4 A, when it is actuated by the lever  2  to return the chronograph counters to zero, the hearts  11  and  12  then being oriented according to  FIG. 1 . 
         [0036]    One can see that the timed second mobile is, commonly, arranged at the center of the clockwork movement, the indication of the timed second being done by a large second hand centered on the chronograph dial. In this case, which corresponds to the embodiment shown in the figures, the axis of rotation  15  is merged with that of the movement. 
         [0037]    We have also shown a control device in  FIG. 1  designed to initiate or stop time measurements. 
         [0038]    The control device of the clockwork movement according to the present invention in particular comprises a control lever  17  extending substantially between the two o&#39;clock and six o&#39;clock positions, bordering the periphery of the plate  1 . The general production of the control lever  17  is conventional. 
         [0039]    A first end  18  of the control lever, arranged at two o&#39;clock, is located across from the external control member when the movement is housed in a case of the timepiece. 
         [0040]    The second end  19  of the control lever bears an operating-lever hook  20  of the type known in the state of the art. In accordance with the preferred embodiment shown and described, the control device comprises a small plate  21  made integral with the control lever  17  using a plurality of screws  22 . The small plate  21  has a shape such that it superimposes a significant part of the control lever, substantially from the three o&#39;clock position to the second end  19 . One of the screws  22 , arranged at the level of the second end  19  of the control lever, goes through an adapted hole (not visible) arranged in the operating-lever hook  20  to make the latter part integral both with the control lever  17  and the small plate  21 , while also being free to pivot with a small amplitude relative to the axis of the screw  22 . 
         [0041]    Preferably, one or several empty spaces are arranged between the control lever  17  and the small plate  21 . In particular, an empty space is provided in the region of the base  5  of the return-to-zero hammer  4 , said hammer being inserted between the control lever  17  and the small plate  21 . This type of structural characteristic makes it possible to ensure good wedging of the base  5  of the hammer between the two plane portions defined by the control elements. One can provide that the distal part of the hammer, namely that bearing the support surfaces  9  and  10 , rests on adapted support surfaces of the chronograph bar. 
         [0042]    Moreover, the control lever  17  advantageously has a pivot point located in the alignment of the respective pivot points of the return-to-zero lever  2  and hammer  4 . Thus, it is provided that the post  3  extends to the inside of an adapted hole (not visible) of the control lever  17  and, preferably, to the inside of a hole  23  similar to the small plate  21 . 
         [0043]    One will note that, in this configuration, a space must be provided, between the return-to-zero lever  2  and the hammer  4 , sufficient for the control lever  17  to move freely therein. Moreover, the control lever  17  has a countersink  24 , shown in dotted lines in  FIG. 1 , to allow the movement of the pin  7  connecting the hammer to the return-to-zero lever during actuation thereof. 
         [0044]    Activation of the control lever  17 , through translation of the control member along the axis S, causes a movement of the operating-lever hook  20  acting on a rotating control element, shown here in the form of a column wheel  25 . 
         [0045]    The column wheel  25  comprises a ratchet  26 , whereon the operating-lever hook  20  acts, as well as columns  27  integral with the ratchet  26  and the number of which is, preferably, equal to half the number of teeth of the ratchet. Thus, the column wheel  25  completes a rotation of one half-pitch, in the counterclockwise direction, in response to each pressure exerted on the control lever  17 , one pitch corresponding to the angle separating one column  27  from the following column. A column wheel jumper (not shown) is arranged conventionally to lock the toothing of the ratchet in each of its positions, two adjacent positions being separated by one angular half-pitch. 
         [0046]    The columns  27  cooperate with a plurality of component elements of the movement according to the present invention, which will be described in detail later, depending on the angular state of the column wheel  25  relative to the plate  1 . 
         [0047]    It should, however, be noted here that the hammer  4  does not have any direct mechanical connection with the column wheel  25 . As was mentioned above, such a characteristic results in an elimination of the differences in sensations felt between a first start-up of the chronograph function and a start-up following a first measurement interval without intermediate return-to-zero. 
         [0048]    Of course, the movement of the timepiece according to the present invention is not limited to the implementation of a column wheel as rotating control element, a conventional cam being able to be used in the alternative. 
         [0049]      FIG. 2  shows the principal role of the column wheel  25  in the chronograph movement. 
         [0050]    The movement comprises an axial-type coupling having a structure already known from the state of the art. The axial coupling comprises a pair of coupling clamps  28  and  29  arranged to act simultaneously on the second counter as will appear from the detailed description of  FIG. 3 . 
         [0051]    Each of the clamps  28 ,  29  is rotatably mounted on a post  30 ,  31  integral with the plate  1 , and comprises a first end  32 ,  33 , near the corresponding post, arranged bearing against the first end of the other clamp. Each of the clamps  28 ,  29  comprises a second end bearing an inclined support surface  34 ,  35  designed to drive the coupling or uncoupling of the second counter. 
         [0052]    A clamp spring (not shown) is arranged bearing against the first end  33  of the clamp  29  to exert a force thereon, this force being diagrammed by the arrow referenced F 2  in  FIG. 2 , tending to push said clamp  29  in the direction of the first end  32  of the other clamp  28 . Thus, the force F 2  tends to distance the clamps  28 ,  29  apart from each other from the side of their second respective ends  34  and  35  to release the second counter, the position of which in  FIG. 2  is diagrammed by the illustration of its axis  15 . 
         [0053]    The clamp  28  also comprises a portion  36  extending while forming a lateral protrusion pointed in the direction of the column wheel  25 . The clamps  28 ,  29  are shown in their close position in normal lines in  FIG. 2 , and in their distanced position in thin lines. 
         [0054]    One sees that, in the configuration of the column wheel  25  shown in  FIG. 2 , the lateral protrusion  36  of the clamp  28  is arranged bearing against a column  27  of the column wheel. The column  27  thus plays the role of a banking for the clamp  28 , which results in maintaining the clamps  28 ,  29  in a close relative position. 
         [0055]    Likewise, one understands that, when the control lever  17  is actuated, the column wheel  25  is driven in rotation by one half-pitch in the direction indicated in  FIG. 2 . This rotation drives a movement of the column  27  which is then no longer across from the lateral protrusion  36 . Once the banking of the lateral protrusion  36  is removed, the clamp  28  can distance itself from the clamp  29  under the effect of the pressure F 2  exerted by the coupling spring on the first end  33  of the clamp  29 . This distanced position of the clamps  28 ,  29  is that shown in thin lines in  FIG. 2 . 
         [0056]    One skilled in the art will be able to implement any adapted known means to limit the amplitude of the rotation of the clamps  28  and  29  when these clamps are remote from each other, without going outside the scope of the present invention. 
         [0057]    Preferably, one provides an additional yoke  37  rotatably mounted on a post  38  integral with the plate  1 . A first end  39  of the yoke  37  is arranged bearing against the clamp  28  while the second end  40  of the yoke is located near the free end of the return-to-zero lever  2 . 
         [0058]    Depending on whether the clamp  28  is remote from or close to the clamp  29 , the yoke  37  also has two extreme positions, one of which, corresponding to the close position of the clamp  28 , is shown in normal lines, while the other, corresponding to the remote position of the clamp  28 , is shown in thin lines in  FIG. 2 . 
         [0059]    One will note that a spring not shown is arranged in the movement according to the present invention to exert a pressure force F 3  on the yoke  37  tending to maintain contact between its first end  39  and the clamp  28 . 
         [0060]    One sees that the second end  40  of the yoke  37  is only arranged across from the free end of the return-to-zero lever  2  when the clamp  28  is in its remote position. In this position of the yoke  37 , it is visible in  FIG. 2  that the return-to-zero lever  2  cannot be actuated and, as a result, the activation of the return-to-zero mechanism of the movement is not possible in this position. 
         [0061]    Conversely, we see that if the return-to-zero lever  2  is pressed in, the rotation of the column wheel  25  remains possible by actuating the control lever  17 , such a rotation not, however, immediately causing the distancing of the clamps  28  and  29  in this example. In fact, in this case, the clamps  28  and  29  are kept close, despite the pressure F 2  of the clamp spring, under the action of the first end  39  of the yoke  37  on the clamp  28 , the yoke itself being retained by locking of its second end  40  by the free end of the return-to-zero lever  2 . The distancing of the clamps  28 ,  29  can then only be done by releasing the return-to-zero lever  2  causing the rotation of the yoke  37 , due to the pressure F 2  of the clamp spring on the first end  33  of the clamp  29 . 
         [0062]    The relationship between the clamps  28 ,  29  and the second counter as well as the start and stop of time measurements using a timepiece movement will now be explained based on  FIG. 3 . 
         [0063]      FIG. 3  shows a partial transverse cross-sectional view, along line III-III of  FIG. 2 , of the center of the chronograph movement according to the present invention. 
         [0064]    The second counter is arranged in the chronograph movement between the plate  1  and a chronograph bar  50 . For this purpose, the chronograph second mobile is positioned in the movement via its arbor  51 , maintained coaxial to the axis of rotation  15  defined above by two jewels  52  and  53 , one of which is press-fitted in the plate and the other in the chronograph bar. 
         [0065]    While traveling along the arbor  51 , from the chronograph bar  50 ,  FIG. 3  shows a first end  54 , housed in the jewel  53 , followed by a first cylindrical portion  55  of the arbor  51 , the latter ending with a first shoulder  56 . This is followed by a second cylindrical portion  57  having a diameter larger than that of the first cylindrical portion  55 , and ending with a second shoulder  58 . A third cylindrical portion  59  follows the shoulder  58 , this having a diameter and a length smaller than those of the first two cylindrical portions  55  and  57 . The third cylindrical portion  59  ends with a generally disc-shaped step  60  integral with the arbor  51 . Continuing after the step  60 , the diameter of the arbor  51  narrows, before forming a pivot engaged in the jewel  52 , to extend to its second free end (not shown) designed to bear a hand indicating timed seconds, above a dial. 
         [0066]    Conventionally, a plurality of elements are arranged on the arbor  51  before its placement between the plate  1  and the chronograph bar  50 . 
         [0067]    From the plate side of the arbor  51 , one finds a second mobile wheel  61  arranged around the third cylindrical portion  59  of the arbor  51 , bearing against an annular clot  63  of the step  60 . The wheel  61  is thus mounted freely in rotation relative to the arbor  51 . The wheel  61  is also arranged permanently engaged with an element  62  of the going train of the movement, the latter only being partially diagrammed in  FIG. 3 . The going train element  62  can, depending on different known variations, correspond to different parts of the movement without going outside the scope of the present invention such as, for example, a wheel driving the chronograph, integral with a second mobile of the going train, or an escape-pinion directly. Thus, one should provide adapted means to drive the wheel  61 , corresponding to the desired rhythm for the rotation of the second wheel. 
         [0068]    A bush  64  is press-fitted on the arbor  51 , arranged abutting against the second shoulder  58 , in particular to allow wedging of the wheel  61  in the longitudinal direction of the arbor  51 , with a small play. 
         [0069]    The bush  64  also bears a spring  65  having a circular central opening, via which it is press-fitted in an adapted recess  66  of the end of the bush opposite the location of the wheel  61 . The bush  64  and the spring  65  are integral with each other. 
         [0070]    Preferably and in a known manner, the spring  65  has a plurality of radial arms  67  curved in the direction of the plate  1 , under the effect of a prestressing. 
         [0071]    A ring  68  is also engaged freely around the bush  64 . The ring  68  comprises a first tube-shaped portion  69 , whereof one end is extended by a second portion, made in the form of an annular surface  70  extending in a plane substantially parallel to the plane of the wheel  61 . The diameter of the annular surface  70  is substantially equal to the length of the arms  67  of the spring  65 . The annular surface  70  has an annular boss  71 , in the region of its periphery, bearing against which the arms  67  are pre-stressed. 
         [0072]    The second end of the tube  69 , located on the side of the wheel  61 , has an annular support surface  72  arranged substantially across from the annular clot  63  of the step  60 . 
         [0073]    Thus, one understands that, under the effect of the pressure exerted by the spring  65  on the annular surface  70 , the ring  68  is pushed back in the direction of the wheel  61 , which then finds itself compressed between the annular clot  63  of the step  60 , on one hand, and the support surface  72  of the ring  68 , on the other. 
         [0074]    The mechanical properties of the spring  65 , the ring  68 , the wheel  61  and the annular clot  63  are adjusted without particular difficulty for one skilled in the art, during production of the movement, such that the pressure of the spring  65  on the ring  68  is sufficient, when locked, for the wheel  61  to be made integral in rotation with the arbor  51 . In  FIG. 3 , we have shown such a locked situation of the ring  68  in broken lines. This situation corresponds to a period measuring a time interval during which a hand indicating the second, supported by the arbor  51 , is driven in rotation when the movement according to the present invention is implemented in a timepiece. 
         [0075]    The respective ends of the clamps  28  and  29  have been illustrated in  FIG. 3  and, in particular, the inclined support surfaces  34  and  35  are visible on both sides of the ring  68 . The clamps  28 ,  29  have been shown in their close position, in solid lines, and in their remote position, in broken lines, the latter position corresponding to the locked position of the ring  68 , as explained above. 
         [0076]    An illustration of this type makes it possible to see that, when the clamps  28 ,  29  are distanced, they are not in contact with the ring  68 , this ring then exerting pressure on the wheel  61 . Conversely, the periphery of the annular surface  70  has a chamfer  73  designed to cooperate with the inclined support surfaces  34 ,  35  of the clamps when these are brought from their remote position toward their close position. During a movement of this type, the support surfaces  34  and  35  slide under the annular surface  70  while distancing the ring  68  from the step  60 , by exerting a force opposing the pressure of the spring  65  on the ring  68 . The ring, while distancing itself from the step  60 , releases the wheel  61 , which can once again slide in rotation relative to the arbor  51 . Thus, driving of the wheel  61  from the going train element  62  is no longer transmitted to the arbor  51 . 
         [0077]    It is important to note that at the same time, the friction taking place, on one hand, between the clamps  28 ,  29  and the annular surface  70  and, on the other hand, between the annular boss  71  and the arms  67  of the spring  65 , are sufficient to ensure rapid and precise rotational immobilization of the arbor  51  when the clamps  28  and  29  are close together. Of course, the form and control of the clamps are also determining in achieving this result. 
         [0078]    Moreover, the return-to-zero heart  11  of the second counter, described in relation to  FIG. 1 , is press-fitted on the first cylindrical portion  55  so as to abut against the first shoulder  56  of the arbor  51 . A counterpoise  74 , of the conventional type and making it possible to balance the contribution of the return-to-zero heart  11  at the time of inertia of the mobile relative to the arbor  51 , is press-fitted on the first cylindrical portion  55  until it abuts against the heart. 
         [0079]    One also sees in  FIG. 3  that the return-to-zero heart  11  bears a finger or index  75  designed to drive an inter-counter wheel  76  in a known manner, said wheel being only partially illustrated diagrammatically and being designed, itself, to drive the minute counter mobile whereof the heart  12  is visible in  FIG. 1 . 
         [0080]    We have also shown, in  FIG. 3 , the support surface  9  of the return-to-zero hammer  4 , when said hammer is in its raised or locking position. 
         [0081]    We will now describe the operation of the movement which has just been described, based on  FIGS. 1 to 3 . 
         [0082]    Initially, we consider that the configuration of the chronograph movement according to the present invention, locked, corresponds to the illustration of  FIGS. 1 to 3 , in thick lines in  FIGS. 1 and 2  and in solid lines in  FIG. 3 . 
         [0083]    Thus, the return-to-zero lever  2  and hammer  4  are in their locked, i.e. raised, position, while the lateral protrusion  36  of the clamp  28  is arranged bearing against a column  27  of the column wheel  25 . As a result, the clamps  28 ,  29  are in their close position, the ring  68  being remote from the wheel  61 . As previously mentioned, the arbor  51  of the second counter is not driven by the going train element  62 , in this situation, due to insufficient frictional forces between the wheel  61  and the step  60  under the action of the clamps  28 ,  29  on the spring  65 , via the ring  68 . Initially, the hands indicating the second  13  and minute  14  are therefore located, immobile, across from the positions corresponding to a null time measurement. 
         [0084]    From this configuration, the time measurement can be triggered conventionally, i.e. by an action on the external control member (in S) acting on the control lever  17 . Such an action causes the column wheel  25  to turn by one half-pitch and distance the clamps  28  and  29  from each other. The distancing of the clamps causes the release of the ring  68  which, under the pressure of the spring  65 , is pressed against the wheel  61 . The latter, permanently driven by the going train element  62 , then transmits its movement, through significant friction on the step  60 , to the arbor  51  which begins to move. The finger  75  acts on the inter-counter wheel  76  to retransmit the rotational movement of the second counter to the minute counter. 
         [0085]    Alternatively and preferably, the time measurement can be initiated by an action on the return-to-zero lever  2 , prior to an action on the external control member (in S) acting on the control lever  17 . In this case, the return-to-zero hammer  4  is arranged abutting against the return-to-zero hearts  11  and  12 , preventing any rotation of the second and minute counters. However, unlike the conventional method for throwing into gear described above, the prior action on the return-to-zero lever  2  results in locking the yoke  37  in its position shown in solid lines in  FIG. 2 . Thus, when the column wheel  25  is driven in rotation following an action on the control lever  17 , the lateral protrusion  36  of the clamp  28  is no longer held by a column  27 , but the clamp  28  is, in spite of everything, immobilized by the first end  39  of the yoke  37 . At the same time, the clamp  28  acts on the clamp  29  by its end  32 , such that the two clamps remain in their close position, in which the driving of the second and minute counters is neutralized by sliding of the wheel  61  relative to the arbor  51 . When the return-to-zero lever  2  is released, the yoke  37  is again free to turn around its post  38  to place itself in the configuration shown in thin lines in  FIG. 2 . At the same time, the clamps  28  and  29  distance themselves from each other, under the effect of the pressure F 2  of the coupling spring on the clamp  29  itself acting on the end  32  of the clamp  28  so as to distance the latter part. Thus, the release of the return-to-zero lever  2  causes the coupling of the arbor  51  with the wheel  61  driven by the going train via the ring  68 , as explained above. 
         [0086]    When a time measurement is in progress, the yoke  37  is in its position shown in thin lines in  FIG. 2 , and provides a locking function of the return-to-zero lever via its second end  40 . 
         [0087]    Thus, the chronograph movement according to the present invention offers its user the possibility of starting a time measurement using two different sequences of manipulation of the external control members according to the user&#39;s preferences, either by simple pressure on the control member in S, or sustained pressure on the return-to-zero organ in R, followed by pressure on the control member in S then a release of the return-to-zero organ. 
         [0088]    A new action on the control lever  17 , from the measurement situation above, causes the column wheel  25  to rotate by one half-pitch, one column  27  of said column wheel exerting pressure on the lateral protrusion  36  of the clamp  28  tending to push said clamp back toward its close position. At the same time, the clamp  29  is also pushed toward its close position under the effect of the pressure applied to the lateral protrusion  36 , opposed to the pressure F 2  of the coupling spring, transmitted by the clamp  28  via its end  32 . 
         [0089]    Bringing the clamps  28 ,  29  close together causes the uncoupling of the arbor  51  relative to the wheel  61  and ensures the immobilization of the hands  13  and  14  indicating time measurements. 
         [0090]    By moving toward its close position, the clamp  28  releases the yoke  37  which resumes its locked position, under the effect of the pressure force F 3 , as shown in solid lines in  FIG. 2 . 
         [0091]    At this stage, the result of the time measurement can be read on the display means of the timepiece integrating the movement according to the present invention. 
         [0092]    The following step may either be to continue the time measurement or to return the second and minute counters to zero. 
         [0093]    Continuing the time measurement is done by actuating the control lever  17 , which causes the column wheel  25  to rotate and brings about all of the consequences described above in relation with the first start, with the exception that the initial position of the second  13  and minute  14  hands is not at zero, but corresponds to the value of the first measured time interval. 
         [0094]    It should be noted that starting the time measurements, on one hand, from the null position of the counters and, on the other hand, from an intermediate position corresponding to a pause between two measurements without return to zero, only differ by the positions of the chronograph mobiles. 
         [0095]    Indeed, when the chronograph counters are stopped, the configurations of the movement according to the present invention are the same, whether the counters are in their null position or in an intermediate position following a first measurement. 
         [0096]    Thus, an action on the control lever  17  under these conditions acts on the same component elements of the movement and in the same way, in either case. As a result, the user actuating the control member of a timepiece integrating the movement according to the present invention, to activate the time measurement, does not feel a difference depending on whether or not the chronograph counters are at zero. 
         [0097]    A characteristic of this type is advantageous from a perspective of comfort provided for the user, insofar as the difference in the force to be exerted on a control member of a movement of the prior art is noticeable, depending on whether a time measurement is activated from the null state of the chronograph counters or from a non-null state. The additional force to be provided corresponds to the raising of the return-to-zero hammer(s), the locking position of which is generally the lowered position in the movements of the prior art. 
         [0098]    From the stopped position, a return-to-zero of the second and minute counters can be done by an action on the return-to-zero lever  2 . Such an action causes the movement of the return-to-zero hammer  4 , which strikes the hearts  11  and  12  of the chronograph counters to replace the hands in their locked position, conventionally. 
         [0099]    One may note that at the time of activation of the return-to-zero, the clamps  28  and  29  are in their close position and ensure the immobilization of the chronograph mobiles. When the return-to-zero hammer  4  strikes the hearts  11  and  12 , the arbor  51  is driven in rotation due to the rotation of the heart  11 , this being done via a sliding of the arms  67  of the spring  65  on the annular boss  71  of the ring  68 , under the effect of the couple transmitted by the hammer  4  to the arbor  51 . 
         [0100]    Furthermore, one skilled in the art can implement a jumper to ensure the immobilization of the minute counter, conventionally, when a time measurement is not activated. The jumper can thus be raised by known means to release the minute counter during return-to-zero operations. 
         [0101]    The preceding description corresponds to one preferred embodiment of the invention described as a non-limiting example. In particular, the forms shown and described for the various component elements of the chronograph movement are non-limiting. 
         [0102]    Of course, the implementation of the characteristics described here is also possible in a cam-type chronograph movement without going outside the scope of the invention. Likewise, one skilled in the art will not encounter any particular difficulties in adapting this teaching to the production of a chronograph movement also comprising an hour counter, for example.