Abstract:
The invention concerns a chronograph watch movement, comprising a chronograph mechanism, including: a chronograph gear-train comprising first ( 40 ) and second ( 38 ) wheels completing a revolution in sixty seconds and a revolution in a fraction of an hour respectively and arranged in the center of the movement, a control device ( 48 ) for starting and stopping the rotation of the chronograph gear-train, and a reset device ( 50 ). In said movement, the chronograph mechanism further comprises switching means designed such that, upon activation, they connect the second wheel ( 38 ) of the chronograph gear-train to a finishing mobile, so that the display means borne by the second wheel display the current time unit equivalent to that of the measured time.

Description:
BACKGROUND OF THE INVENTION 
     The present invention concerns movements for chronograph watches. Such movements generally and conventionally comprise a frame, formed of a plate and bridges, and, carried by the frame:
         an energy source,   a time base powered by the energy source,   a first, going train, driven in rotation in synchronism with the time base, and comprising a mobile for units of time selected from among the minutes and hours of the current time, and   a chronograph mechanism, which includes:
           a second, chronograph train, to be driven upon demand, in synchronism with the time base and comprising first and second wheels respectively completing one revolution in sixty seconds and one revolution in a time allowing the units of measured time, selected from among the hours and minutes, to be displayed and arranged coaxially with the first mobile, these wheels being arranged so that they can carry display means for displaying a measured time, for example hands, for indicating respectively the measured time seconds and the selected unit of the measured time,   a control device for starting and stopping the rotation of the second train, and   a device for resetting the display means.   
               

     Chronographs allow time intervals to be measured, by pressure on one or two push-buttons, mounted so as to slide on the watchcase, which control the chronograph mechanism. Successive applications of pressure assure the starting and stopping of the chronograph train, and consequently the start and end of the measurement. 
     The measured time is displayed by a chronograph second hand, carried by the first wheel of the chronograph train. Depending upon the type of chronograph, the first wheel also drives a wheel completing one revolution in thirty or sixty minutes and capable of carrying a measured time minute hand. This wheel is generally off-centre, such that the chronograph minute hand is smaller than the chronograph second hand. 
     Thus, in order to facilitate reading of the measured time minute, it is advantageous to have the chronograph minute hand at the centre of the movement. To prevent it being confused with the chronograph second hand, it has to be wider. As a result it tends to conceal the dial in the midday position when it is not operating. This can be inconvenient for reading the information given by the hands that are situated underneath, namely those for displaying the current time. It is an object of the present invention to overcome this drawback. 
     SUMMARY OF THE INVENTION 
     This object is achieved owing to the fact that the chronograph mechanism further includes switching means arranged so that they can occupy two states and in one of which they connect the second wheel of the chronograph train to the going train mobile, so that the display means carried by the second wheel display the unit of the current time equivalent to that of the measured time. 
     Advantageously the unit of time displayed by the mobile and the second wheel mentioned hereinbefore is the minute. Consequently, while the first member connects the chronograph train wheel for displaying the minutes and the current time minute mobile, the minute hand, carried by the chronograph train wheel, is in a position corresponding to the display of the current time minutes. 
     More specifically, the switching means comprise a hammer pivotably mounted on the current time minute mobile, a cam secured to the second chronograph train wheel and an elastic member holding the hammer abutting against the cam. 
     In order to guarantee that the switching means operate perfectly as defined hereinbefore, the chronograph mechanism further includes an isolation device, which comprises:
         an isolation mobile provided with a first plate, of the same diameter as the first mobile, and a second plate arranged for cooperating with a pawl or click and carrying a pin for activating the hammer,   a retaining member comprising a lever and a retaining wheel, mounted to be mobile in rotation on the lever and comprising first and second plates arranged to be able to mesh respectively with the first plate of the isolation mobile and the going train minute mobile, and connected to each other by a one-directional coupling mechanism, and   isolation control members comprising:
           an isolation lever,   a pawl pivotably mounted on the lever and cooperating with the second plate of the isolation mobile, to move it with reference to the first plate, and with it the pin, which raises the hammer to interrupt the connection between the second wheel of the chronograph train and the going train minute mobile.   
               

     At the start of a time measurement, the chronograph second and minute hands must be at zero, to allow the user to know that his counter has been initialised. This could not happen when the measured time minute hand is superposed with the current time minute hand. Thus, in order to prevent any problem of comprehension as to operation, the chronograph mechanism further a locking device arranged for locking the control and reset devices while the switching means are connecting the second wheel of the chronograph train to the going train mobile. 
     In a first variant, the current time minute mobile is arranged to carry a current time minute hand and the second wheel of the chronograph train, a measured time minute hand. In this variant, when the switching means are in the state in which they connect the second wheel of the chronograph train to the going train mobile, the hands carried by the wheel and mobile are superposed. 
     In a second variant, only the second wheel of the chronograph train carries a hand, such that this hand displays the current time minutes while the locking device is locking the control device, and the measured time minutes in the opposite case. The information provided is thus reduced, but the watch is thinner, which improves its aesthetic appearance. It offers the advantage of providing a measured time minute display via a large hand, while only having three hands at the centre of the movement, namely those displaying the current time hour, the current time minute and the measured time minute as well as the measured time second. 
     Other advantages and features of the invention will appear from the following description, made with reference to the annexed drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a watch fitted with a movement according to the invention, in a state in which a measured time measurement is being carried out, 
         FIG. 2  is a logic operating diagram of the movement according to the invention, 
         FIG. 3  is a cross-section of the movement according to the invention, 
         FIGS. 4   a  to  4   d  show the dial side of the movement, in various states corresponding to the steps defined in the diagram of  FIG. 2 , and 
         FIG. 5  illustrates the back cover side of the movement, when the chronograph function is locked. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the following description, the position of certain components is sometimes defined with reference to a time. This position corresponds to the position on the dial occupied by the hour symbol displaying the given time. 
     The watch shown in  FIG. 1  is of the chronograph type. It comprises, in a conventional manner, a case  10  acting as housing for a movement, which carries a dial  12 , a current time hour hand  14 , a current time minute hand  16 , measured time minute hand  18  and a measured time second hand  20 . 
     The current time display is corrected by means of a time setting crown  22 , connected to members of the movement by a time setting stem that is not visible in the drawing. 
     The timing related functions are performed by three push-buttons  24 ,  26  and  28  respectively disposed at two o&#39;clock, four o&#39;clock and eight o&#39;clock. Push-button  24  controls the starting and stopping of a measured time measurement, whereas push-button  26  resets hands  18  and  20  when a measured time measurement has been interrupted. Finally, push-button  28  is for making the chronograph mechanism pass from a first state, in which it is locked, into a second state in which it is unlocked. 
     As will be explained hereinafter, the chronograph mechanism is arranged so that, when it is locked, current time minute hand  16  and measured time minute hand  18  are superposed and rotate together, whereas measured time second hand  20  is at midday. In this state, push-buttons  24  and  26  are inactive. 
       FIG. 2  illustrates the effect of the various push-buttons depending upon the states of the chronograph mechanism, which are identified by a capital letter surrounded by a circle. An application of pressure onto push-buttons  24 ,  26  and  28 , respectively corresponds to the indications P 1 , P 2  and P 3  of the Figure. 
     In the initial state, identified by A and corresponding to the situation illustrated by  FIGS. 4   a  and  4   b , the chronograph mechanism is locked. The chronograph second hand  20  is at midday and measured time minute hand  18  is superposed on current time minute hand  16 , push-buttons  24  and  26  being inactive. 
     An application of pressure P 3  causes the chronograph mechanism to unlock. As a result, measured time minute hand  18  leaves current time minute hand  16  to align at twelve o&#39;clock, thus being superposed on the measured time second hand  20 . This state, shown in  FIG. 4   c , is identified by the letter B. 
     In this state, push-buttons  24  (P 1 ) and  28  (P 3 ) are active. An application of pressure P 1  has the effect of starting the counting of a measured time, the measured time second hand  20  starting to rotate and, more slowly, measured time minute hand  18 . This state, shown in  FIG. 4   d  and identified by the letter C, brings the display to the situation illustrated in  FIG. 1 . 
     In state B, an application of pressure P 3  returns the chronograph mechanism to its initial state A. 
     In state C, only push-button  24  is active. An application of pressure P 1  has the effect of stopping counting of the measured time. Hands  18  and  20  thus stop in the position corresponding to the measured time, which corresponds to state D, which differs from state B only in that the hands are not at zero. 
     Another application of pressure P 1  then has the effect of restarting counting, the mechanism thus returning to state C, whereas an application of pressure P 2  returns hands  18  and  20  to midday, which corresponds to state B. 
     In a variant, achieved by means of a movement like that described with reference to  FIGS. 3 to 5 , current time minute hand  16  is omitted. Consequently, the current time is read by means of current time hour hand  14  and minute hand  18  while the movement is in state A, whereas in the other states, minute hand  18  displays the measured time, the current time minutes having to be evaluated from the position of current time hour hand  14 . 
     In  FIGS. 4 and 5  and in order to avoid overloading the drawings, the springs have only been shown schematically, by means of an arrow showing the force that they generate, associated with a reference Fi, “i” being equal to the reference of the part on which the spring is acting. They are essentially visible in  FIG. 4   b.    
     More precisely,  FIGS. 4   a  and  4   b  show the mechanism in its rest position, corresponding to state A, and  FIGS. 4   c  and  4   d  in positions corresponding respectively to states B and C of  FIG. 2 . In  FIGS. 4   a  to  4   d , which show the dial side of the movement, some parts have been removed or partially torn away from one or other of these Figures, in order for the subjacent parts to be seen more clearly. 
     The terms “wheel” or “mobile” are used to differentiate between the components of the chronograph train and going train respectively. 
     The movement of the invention comprises, in a conventional manner that is not visible in the drawing, an energy source such as a barrel, a time base such as a sprung balance, a going train of which only one mobile  29  is visible in  FIGS. 3 and 4 , and an escapement connecting the going train to the balance in order to maintain the latter, as well as time setting and chronograph mechanisms. These various components of the movement are disposed on a frame  30 , formed of a plate and bridges, which assures the relative positioning of the various mobile parts of the movement. 
       FIG. 3  shows the central part of the movement, seen in cross-section along the line III-III of  FIG. 4   a , with an axis A-A corresponding to the axis about which the hands pivot. Frame  30  carries, rigidly secured to its dial side face, a tube  32  comprising a seat  32   a  secured to frame  30  and two cylindrical portions  32   b  and  32   c , whose axis merges with axis A-A, and arranged one after the other, connected by a shoulder  32   d  and designed to act as a fixed arbour for the pivoting of the mobiles and wheels, as will be explained hereinafter. 
     A current time minute mobile  34  is pivotably mounted so as to pivot on tube  32 . It is provided with a pipe  34   a  engaged on cylindrical portion  32   b  of tube  32  and a plate  34   b  including a toothing  34   c  at its periphery. Pipe  34   a , plate  34   b  and toothing  34   c  are made in a single piece. 
     Mobile  34  meshes permanently, via its toothing  34   c , with mobile  29  of the going train, in a gear ratio selected such that it completes one revolution per hour of current time. 
     Plate  34   b  is provided with:
         a cut out part  34   d  in the form of an annular portion covering an angle of approximately 50°, the function of which will be specified hereinafter,   a stud  34   e , to which a connecting hammer is secured, and   a spring tending to return hammer  36  to the centre and schematically represented by arrow F 36  ( FIG. 4   b ).       

     A minute hand wheel  38  is pivotably mounted on cylindrical portion  32   c  of tube  32 . This wheel  38  is only visible, in plan, in  FIG. 4   c . It comprises a plate  38   a  provided, at its periphery, with a toothing  38   b , and a pipe  38   c  engaged on tube  32  and extending upwards sufficiently for its free end to be released and to allow minute hand  16  to be secured. The latter displays both the current time and the measured time, as will be explained hereinafter. Pipe  38   c  extends underneath plate  38   a . A cam  38   d , generally called a heart-piece, and more particularly visible in plan in  FIGS. 4   a ,  4   b  and  4   d , is secured by being driven in or welded thereto. Its lower face abuts against shoulder  32   d . This cam  38   d  is arranged such that it can cooperate with hammer  36 , as will be explained hereinafter. 
     The movement comprises an isolating device whose components&#39; reference starts with  39  and which includes an isolation mobile  391  mounted on pipe  34   a , a lever  392 , a retaining wheel  393  pivotably mounted on lever  392 , an isolation lever  394  and a pawl or click  395  mounted on lever  394  ( FIG. 4   a ). 
     Mobile  391  comprises two superposed plates  391   a  and  391   b , rigidly connected to each other and provided at their periphery with toothings respectively referenced  391   c  and  391   d , and a pin  391   e  secured in plate  391   a . This lower plate is provided with wolf teeth, clearly visible in  FIG. 4   a , whereas toothing  391   d , of upper plate  391   b  comprises the same number of teeth and has the same profile and same diameter as toothing  34   c . Pin  391   e  is engaged in cut out part  34   d  and extends as far as hammer  36 . 
     Retaining lever  392  is mounted on frame  30 , pivoting in its median part. It carries, at one of its ends, wheel  393  which can rotate on a stud  392   a  driven into lever  392 , whereas the other end forms a nose  393   b  which, as will be explained hereinafter is for controlling the movement of lever  392 . A spring F 392  tends to apply nose  392   b  onto a support surface. 
     As shown schematically in  FIG. 3 , wheel  393  is formed of two plates  393   a  and  393   b , connected to each other by a click  393   c  and respectively capable of being meshed with toothings  34   c  and  391   d . Click  393   c  is arranged such that, when mobile  34  is rotating in the clockwise direction, the click is locked, such that plate  393   b  drives mobile  391  in rotation. If, conversely, it is the latter that is being rotated in the clockwise direction, only plate  393   b  is driven, click  393   c  performing its disconnecting function. 
     Lever  394  comprises ( FIG. 4   a ):
         a body  394   a  pivotably mounted on frame  30 , by the engagement of a hole  394   b  made at one of the ends of body  394   a  of the lever in an unreferenced stud, secured to frame  30 ,   a nose  394   c , located in proximity to hole  394   b  for controlling the movement of lever  394 ,   a stud  394   d  driven into the body at the opposite end to that provided with hole  394   b , on which pawl  395  pivots, and   a pin  394   e , forming a stop member and limiting the movement of pawl  395 .       

     Lever  394  is positioned by nose  394   c  abutting against a support surface, via the action of a spring F 394 . A spring F 395  tends to hold pawl  395  abutting against pin  394   e.    
     Isolation mobile  391  can be moved by an angle of approximately 45° with respect to mobile  34 , by the engagement of pawl  395  in toothing  391   c . During this movement, pin  391   e , moving freely in cut out part  34   d , raises hammer  36  whose free end is brought back towards the exterior. 
     When the chronograph mechanism is locked, by means that will be explained hereinafter, hammer  36 , positioned by spring F 36 , which tends to apply it against cam  38   d , performs the function of connecting member between mobile  34  and wheel  38 , which are thus secured to each other in rotation. This thus means that minute hand  18 , carried by pipe  38   c  of wheel  38 , displays the minutes of the current time. 
     In order to count the measured time, the movement shown in the drawing comprises a chronograph second hand  40 , pivotably mounted in tube  32 , visible in  FIG. 5  and partially in  FIG. 3 , and a sliding gear  42  ( FIGS. 3 and 4   c ). Wheel  40  comprises an arbour  40   a  pivotably mounted in tube  32  and in frame  30 , a plate  40   b  driven onto arbour  40   a  and provided with a toothing, a cam  40   c , also driven onto arbour  40   a , and a drive finger  41 . 
     The chronograph mechanism further includes a coupling mechanism, not visible in the drawing, provided with a wheel which, when the chronograph mechanism is in state C, kinematically connects wheel  40  to the going train, such that it is driven in rotation, at a rate of one revolution per minute. Such a coupling mechanism is well known to those skilled in the art. 
     Slide gear  42  comprises an arbour  42   a  ( FIG. 3 ) rotatably mounted in a jewel  43 , with an olive jewel-hole, driven onto a bridge of frame  30  and onto a lever  44 , itself pivoting on frame  30  and which will be described in more detail hereinafter. It further comprises two wheels  42   b  and  42   c , for cooperating respectively with finger  41  and wheel  38 . Depending upon the position that lever  44  occupies, wheel  42   b  is either in the space swept by finger  41  or not. Moreover, wheel  42   c  is permanently meshed with toothing  38   b . Lever  44  tends to move in the direction of the centre of the movement via the effect of a spring F 44  ( FIG. 5 ). 
     When the chronograph mechanism is in one of states B, C or D, hammer  36  is raised by pin  391   e , such that it is no longer abutting against cam  38   d . Mobile  34  and wheel  38  are thus no longer secured in rotation. Moreover, when the mechanism is in state C, arbour  42   a  is arranged parallel to axis A-A and its wheel  42   b  can be driven in rotation by finger  41 , at a rate of one step for each revolution of wheel  40 . In other words, slide gear  42  performs the function of a connecting member between measured time second wheel  40  and wheel  38 , so that the latter displays the measured time minutes when the mechanism is in state C or D. 
     The connecting members formed by hammer  36 , spring F 36  and cam  38   d  on the one hand, and slide gear  42  on the other hand, perform together the function of switching means. 
     Since current time minute mobile  34  is permanently rotating, driven by the going train, isolation mobile  391  has to rotate with it, otherwise hammer  36  cannot be controlled. Therefore, retaining wheel  393  is made to mesh with toothings  34   c  of mobile  34  and  391   d  of isolation mobile  391 , the two plates  393   a  and  393   b  being secured to each other in rotation by click  393   c.    
     In order to perform the functions as defined with reference to  FIG. 2 , the chronograph mechanism shown in  FIGS. 4 and 5  comprises, in addition to the gear trains and the isolation device described hereinbefore:
         a switch for enabling or disabling the timing function, and whose constituent parts are defined by references starting with  46 ,   a control device, controlling the starting and stopping of a measurement, and whose constituent parts are defined by references starting with  48 , and   a reset device, for reinitialising the measured time counters, and whose constituent parts are defined by references starting with  50 .       

     It should be noted that these devices interact and that some parts are arbitrarily defined as forming part of one device rather than another. 
     Switch  46  is controlled by push-button  28 . It allows minute hand  16  to be returned to zero, and push-button  24  to be made active. It comprises, for this purpose ( FIG. 4   a ):
         a switching member  461 , comprising:
           a bird-shaped body  461   a , with a head  461   b  provided with a hole  461   c  in which there is engaged a stem passing right through frame  30  and carrying a finger  461   d  visible in  FIG. 5 , a beak  461   e , two wings  461   f  and  461   g , wing  461   g  being provided with a pin  461   h , and a tail  461   j , the head being disposed on the centre side of the movement and tail  461   j  at the periphery, in proximity to 7 o&#39;clock,   a lever  461   k  pivotably mounted on tail  461   j  and extending over the periphery of the movement from 7 to 9 o&#39;clock, provided with a pin  461   m  disposed so that it is or is not located on the path travelled by push-button  28 , when it is activated depending upon the position occupied by lever  461   k , and a stop member  461   n  arranged at its free end,   a pawl  461   p  pivotably mounted on lever  461   k  and limited in its movement by stop member  461   n,      
           a switching cam, for example a column wheel  462 , shown schematically, controlled in rotation by pawl  461   p , rotating on frame  30  at  462   a , and cooperating with noses  392   b  of lever  392  and  394   c  of lever  394 ,   an interlocking lever  464 , comprising a body of elongated shape  464   a , pivotably mounted on frame  30  in its median part, and one of whose ends is provided with a nose  464   b  arranged for cooperating with the columns of wheel  462 , whereas the other end comprises a first oblong hole  464   c  in which a stud  465  is mounted to slide, for cooperating with control device  48 , and a second oblong hole  464   d , in which a pin  466  with a head is housed, itself secured to frame  30 , for positioning the lever in the plane of the movement.       

     The constituent parts of switch  46  are positioned by springs shown schematically in  FIG. 4   b  and more particularly:
         body  461   a  by spring F 461   a,      lever  461   k  by spring F 461   k  which tends to return it when pressure has been applied to push-button  28 ,   pawl  461   p  by spring F 461   p  which holds it pressed against pin  461   n,      body  464   a  by spring F 464   a , which tends to apply nose  464   b  against wheel  462 , and   stud  465  by spring F 465 , which tends to press it on the external side of oblong hole  464   c.          

     Control device  48  is more particularly visible in  FIG. 5 . It comprises:
         a control lever  481  comprising:
           a body  481   a  disposed at the periphery of the movement from 2 to 7 o&#39;clock, which pivots at  481   b  on frame  30  slightly below 4 o&#39;clock, and which is provided, at one of its ends, with a bent portion  481   c  extending into the thickness of stud  465 , and   a pawl  481   d , pivotably mounted on the other end of body  481   a , whose function will be specified hereinafter,   
           a cam  482 , for example of the column wheel type, driven by pawl  481   d , which controls the coupling mechanism of the chronograph, not shown in the drawing, and positions switching member  461  via its finger  461   d.          

     The constituent parts of control device  48  are positioned by springs and more particularly:
         body  481   a , by spring F 481   a  which tends to return it when pressure has been applied to push-button  24 , and   pawl  481   d , by spring F 481   d , which applies it against cam  482 .       

     Reset device  50  comprises:
         a reset lever  501  ( FIG. 4   a ) arranged and pivotably mounted at the periphery of frame  30  and extending from 4 o&#39;clock to 6 o&#39;clock, provided at its end in proximity to 4 o&#39;clock with a pin  501   a  for cooperating with push-button  26 , and at its other end with a groove  501   b  for cooperating with pin  461   h,      a hammer  502  for resetting the minutes arranged in proximity to column wheel  462  and extending as far as the central part of the movement to cooperate with cam  38   d  via a support surface  502   a  provided with:
           a nose  502   b  which cooperates with column wheel  462 , and   a pin  502   c  for cooperating with wing  461   f , and   
           a hammer  503  for resetting the seconds ( FIG. 5 ) pivotably mounted on the opposite face of frame  30  in proximity to cam  482 , provided with:
           a nose  503   a  cooperating with cam  482 ,   a retaining finger  503   b  cooperating with lever  44  via a pin  44   a  comprised in the latter, and   a support surface  503   c  for returning the second hand to zero by abutting against cam  40   c.      
               

     The constituent parts of reset device  50  are positioned by springs and more particularly:
         lever  501  by spring F 501 , which tends to return it after pressure has been applied on push-button  26 ,   hammer  502  by spring F 502 , which tends to apply support surface  502   a  against cam  38   d , and   hammer  503  by spring F 503 , which tends to apply it against cam  40   c.          

     The movement further comprises a current time hour mobile  52 , pivotably mounted on pipe  38   c  of minute hand wheel  38 . Mobile  52  carries current time hour hand  14 . It is kinematically connected to mobile  34  by a motion work, which divides the movement by a factor of  12 . This motion work has not been shown to avoid overloading the drawing. 
     When the chronograph mechanism is at rest, namely in state A defined with reference to  FIG. 2 , its constituent parts are in the position shown in  FIGS. 4   a ,  4   b  and  5 . More particularly, nose  392   b  of retaining lever  392  is between two columns of column wheel  462  via the effect of spring F 392 , such that retaining wheel  393  is not meshed with toothings  34   c  and  391   d . Nose  394   c  of lever  394  is also between two columns via the effect of spring F 394 , so that pawl  395  is withdrawn from toothing  391   c . Thus, via the action of spring F 36 , hammer  36  is abutting against cam  38   d . Wheel  38  of the minute hand is rotating, consequently, in synchronism with current time minute mobile  34 . 
     The interlocking lever  464  is abutting, via its nose  464   b  and via the effect of spring F 464   a , against a column of wheel  462 , such that stud  465  is not inserted between push-button  24  and bent portion  481   c , which disables push-button  24 . Moreover, an action on push-button  26  causes lever  501  to pivot, but without it acting on any of the other parts. 
     An application of pressure on push-button  28  activates pin  461   m , which drives with it lever  461   k , which causes the chronograph mechanism to switch. More precisely, the tipping of lever  461   k  drives pawl  461   p , which rotates column wheel  462  and generates the following movements, which occur practically simultaneously or in the following order:
         nose  392   b  of retaining lever  392  is raised by a column, which causes wheel  393  to mesh with toothings  34   c  and  391   d;      nose  394   c  of lever  394  is raised, such that pawl  395  meshes with toothing  391   c , driving in rotation, clockwise, mobile  391  and the single plate  393   b , plate  393   a , meshed with mobile  34 , being disconnected, because of click  393   c;      during the relative movement of mobile  391  with reference to mobile  34 , pin  391   e  raises hammer  36 , such that cam  38   d  of wheel  38  is no longer maintained in phase with mobile  34 ;   nose  502   b  of hammer  502  falls, via the effect of spring F 502 , between two columns of wheel  462 , support surface  502   a  cooperating with cam  38   d  such that wheel  38 , which carries hand  18 , brings the latter to midday, and   nose  464   b  of interlocking lever  464  falls between two columns of wheel  462  via the effect of spring F 464   a , bringing stud  465  between push-button  24  and bent portion  481   c.          

     The mechanism is then in state B defined in  FIG. 2  and shown in  FIG. 4   c . The connecting member formed by hammer  36  and cam  38   d  then no longer provides a connection between wheel  38  and mobile  34 . Switch  46  thus plays the part of control member, and deactivates the connecting member. 
     In this state, push-buttons  24  and  28  are operational. If push-button  28  is pressed again, lever  461   k , tips and drives pawl  461   p . This causes column wheel  462  to rotate, which generates the following movements, which occur practically simultaneously or in the following order:
         nose  392   b  of retaining lever  392  falls between two columns of wheel  462  via the effect of spring F 392 , wheel  393  thus being released from toothings  34   c  and  391   d;      nose  502   b  is raised by a column, such that hammer  502  releases cam  38   d;      nose  394   c  falls back between two columns and lever  394  returns to the position shown in  FIG. 4   a  via the effect of spring F 394 ;   via the effect of spring F 36 , hammer  36  tips and abuts against pin  391   e , which causes isolation mobile  391  to rotate, then against cam  38   d  which drives wheel  38  until hand  18  again displays the minutes of the current time; and   nose  464   b  of interlocking lever  464  is raised by a column of wheel  462  such that stud  465  leaves the space comprised between bent portion  481   c  and push-button  24 .       

     The mechanism has thus returned to state A shown in  FIG. 4   a.    
     From state B, shown in  FIG. 4   c , it is also possible to actuate push-button  24 , which has the effect of starting a measured time measurement. More specifically, push-button  24  abuts against stud  465 , which slides into oblong hole  464   c  and, applied against bent portion  481   c , causes body  481   a  of lever  481  to pivot. Its pawl  481   d , more particularly visible in  FIG. 5 , causes cam  482  to rotate through one step. This movement of cam  482  generates the movements described hereinafter, which occur practically simultaneously or in the following order:
         hammer  503 , visible in  FIG. 5 , is raised via its nose  503   a , such that support surface  503   c  is released from cam  40   c;      the chronograph coupling mechanism causes the coupling wheel to mesh both with the going train and the chronograph second wheel  40 , so that the latter is driven in rotation and, with it, chronograph second hand  20 ;   retaining finger  503   b  releases pin  44   a  from lever  44 , such that spring F 44  causes lever  44  to pivot, wheel  42   b  being then positioned such that it is in the space swept by finger  41 , which can then rotate slide gear  42  and, via the latter, minute hand wheel  38 , at a rate of one step per minute, and   finger  461   d  is raised by a column of cam  482 , which causes body  461   a  ( FIG. 4   b ) and lever  461   k  of switching member  461  to tip. Consequently, pin  461   m  is shifted with respect to push-button  28 , thus disabling the latter. Moreover, wing  461   f  raises hammer  502  via its pin  502   c , thus allowing minute hand wheel  38  to rotate.       

     Moreover, the pivoting of body  461   a  brings its pin  461   h  into groove  501   b  of reset lever  501 . During this operation, the connecting member formed by slide gear  42 , controlled by control device  48  via hammer  503 , passes from the deactivated state to the activated state. 
     The mechanism is then in the position shown in  FIG. 4   d , which corresponds to state C of  FIG. 2 . In this state, only push-button  24  is active. In fact, pin  461   m  is shifted with respect to push-button  28 , which disables the latter. Moreover, body  461   a , whose position is defined by finger  461   d  abutting against a column of cam  482 , remains in this position, even if groove  501   b  releases pin  461   h . In other words, an application of pressure on push-button  26  has no effect. 
     An application of pressure on push-button  24  causes it to abut against stud  465  which slides into oblong hole  464   c  and, applied against bent portion  481   c , causes lever  481  to pivot. Its pawl  481   d  ( FIG. 5 ) causes cam  482  to rotate through another step. This movement of cam  482  generates the movements described hereinafter, which occur practically simultaneously, or in the following order:
         the chronograph coupling mechanism is moved, such that chronograph second wheel  40  is no longer connected to the going train, which means that it stops;   finger  461   d  passes from abutting against a column of cam  482  to a position in which it is between two columns, without, however, body  461   a  and finger  461   d  pivoting, since body  461   a  is retained by pin  461   h  engaged in groove  501   b  of lever  501 ; and   nose  502   a  of hammer  502  is between two columns of wheel  462 , but it does not change position, because of pin  502   c  which is abutting against wing  461   f  of body  461   a.          

     Hammer  503  is retained by similar means to those retaining hammer  502 , but they have not been shown in order to avoid overloading the drawing. The chronograph mechanism is then in state D of the logic diagram of  FIG. 2 . This state, which is not shown in the drawing, allows action on push-buttons  24  and  26 . An application of pressure on push-button  24  starts the time count, the mechanism returning to state C via another rotation of cam  482 . Thus, the chronograph coupling mechanism is coupled again, whereas nose  503   a  of the hammer and finger  461   d  are abutting against a column of cam  482 . 
     When the mechanism is in state D, an application of pressure on push-button  26  drives lever  501  which, by pivoting, releases pin  461   h . Since finger  461   d  is between two columns of cam  482 , nothing is holding it any longer, such that spring F 461   a  returns switching member  461  to the position shown in  FIG. 4   b . Moreover, hammer  502  is no longer held by wing  461   f , such that its spring F 502  causes it to tip and abut against cam  38   d , which has the effect of resetting minute hand  18  to zero. 
     A similar process is applied to hammer  503 , such that cam  40   c  is also subjected to a force that returns measured time second hand  20  to midday. The chronograph mechanism is then again in state B defined hereinbefore, such that it is possible to press on push-button  28 , to return the mechanism to state A, where push-buttons  24  and  26  are disabled and where minute hand  18  displays the minutes of the current time. It is also possible to press on push-button  24  in order to start a new measurement, the mechanism then being in state C. 
     The mechanism described with reference to  FIGS. 3 to 5  comprises only one minute hand, which either displays the current time, or the measured time. It would also be possible, with a minor alteration, to have a hand  16  permanently displaying the current time minutes, whereas hand  18  displays the measured time minutes, as shown in  FIG. 1 . In order to do this, one need only provide mobile  34  with a pipe extending in the direction of the dial and which would insert the end thereof carrying hand  16  between pipe  38   c  of wheel  38  and tube  32 . 
     Many other variants can also be envisaged, wherein the constituent parts of the members of the chronograph mechanism could take other forms and cooperate very differently, without thereby departing from the scope of the invention. Thus, column wheels  462  and  482  could advantageously be replaced by pivoting cams. It would also be possible to use an axial and/or friction coupling device, instead of mobile  42 . 
     It is also entirely possible to envisage placing the current time hour hand off-centre and keeping only the measured time minute and second hands and the current time minute hand at the centre of the movement. 
     It is evident that the principle described is also applicable to the current time and measured time hour display, the hour hands either being central or off-centre. 
     In a variant that has not been described, it is also possible to omit switch  46 , and consequently push-button  28 , such that, when push-button  26  is activated, second hand  20  starts to rotate whereas minute hand  18  passes from the position where it is superposed on hand  16  to alignment at midday. 
     Thus, owing to the features described in the chronograph mechanism forming the subject of the present invention, it is possible to make a watch wherein the measured time minute and/or hour hand does not overload the display during the time when the mechanism is not in operation. Moreover, the mechanism enables the start, stop and reset functions to be locked, when there is no measurement being carried out.