Patent Publication Number: US-8985845-B2

Title: Timepiece movement with a tourbillon fitted with a shock protection device

Description:
This application claims priority from European Patent Application No. EP 09155819 filed 23 Mar. 2009, the entire disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention concerns a timepiece movement with a tourbillon, fitted with a shock protection device. The present invention also concerns a watch fitted with this type of timepiece movement. 
     Tourbillon movements are mechanical devices for improving the accuracy of mechanical watches by offsetting interference with the isochronism of the balance due to the Earth&#39;s gravity. In order to do this, the regulating member that includes the balance and the escapement are mounted in a carriage, which is set in rotation, generally at the rate of one complete revolution per minute. 
     The tourbillon carriage is generally held in place between two pivots, respectively provided in the bottom plate of the movement and in a bridge of the movement. Alternatively, the carriage can pivot in a ball bearing, which makes it more visible from the dial side. 
     When it pivots between the bottom plate and a bridge, the carriage is generally formed of a bottom bridge, to which pillars carrying a top bridge are fixed, and these top and bottom bridges carry pivots which respectively rotate in a jewel carried by the bottom plate and a jewel carried by the movement bridge. 
     Depending upon the embodiment, the movement bridge can be formed either by an overhanging beam, or a beam that is embedded at both ends. 
     One drawback of these tourbillon mechanisms is their high sensitivity to shocks. Indeed, it is difficult to make a mechanism this type of resistant to accelerations of more than 3500 G without damage, while NIHS standards require resistance to accelerations of 5000 G. 
     In fact, if significant shocks are applied to the watch, the weight of the tourbillon carriage is such that the movement bridge bends or is deformed so that the carriage moves along its axis of rotation and causes the bottom pivot of the carriage to leave its jewel housing. Depending upon the intensity of the shock and thus the amplitude of movement of the carriage, the pivot may not return to its housing, which abruptly stops the carriage, and therefore the movement, from rotating. After a shock of this type, intervention by a watchmaker is thus necessary in order to get the watch to work again. It should be noted that, in some cases, the movement of the carriage may be such that the escape pinion is released from the toothing of the fixed second wheel, causing the barrel to be let down abruptly, which may lead to the destruction of some parts of the mechanism. This drawback is more significant in the case of a top bridge formed of an overhanging beam which has greater flexibility. 
     Various attempts have been envisaged to overcome this problem, such as making the carriage lighter, making the movement bridge more rigid, particularly by increasing the dimensions thereof, or even lengthening the bottom pivot of the carriage. However, these measures have not been able to provide satisfactory results without making the design more complex, and in doing so, affecting the attractiveness of the watches fitted with these mechanisms. 
     It is an object of the present invention to overcome the aforementioned drawbacks, in addition to others, by providing a timepiece movement with a tourbillon that has improved shock resistance compared to tourbillons of the prior art. 
     It is also an object of the invention to provide a timepiece movement of this type, which is has a simple, economical design and is easy to implement. 
     It is also an object of the invention to provide a timepiece movement of this type without affecting its usual attractive appearance. 
     SUMMARY OF THE INVENTION 
     The invention therefore concerns a timepiece movement that includes a tourbillon with a rotating carriage carrying a sprung balance and an escapement, wherein said carriage includes a top pivot and a bottom pivot respectively carried by a top bridge and a bottom bridge of the carriage, said carriage is pivoted between a bottom plate of said timepiece movement and a bridge of said movement, and the movement is characterized in that it further includes a stop member, arranged for limiting the axial shake or travel of the carriage. 
     Owing to these features, the shock resistance of the timepiece movement can thus be guaranteed insofar as the maximum axial movement of the carriage is predefined, so that it is impossible for the carriage pivots to leave the housing of their respective bearings. 
     According to an advantageous embodiment, the stop member is carried by the bottom plate of the movement and cooperates with the bottom bridge of said carriage. 
     According to one feature of this embodiment of the invention, a socket, carried by the bottom pivot, extends from the central part of the bottom bridge of the carriage, and said socket also carries a shoulder, with the stop member cooperating with the shoulder to limit the axial shake of the carriage. 
     According to another feature of the invention, the bottom pivot is housed in a bottom bearing carried by the bottom plate, and in the absence of any shock, the distance between the stop member and the shoulder is less than the length of engagement of the bottom pivot in the bearing. 
     According to a preferred feature, the stop member can move between a first position, called the assembly position, in which the stop member is off the axial path of the shoulder to enable the carriage to be mounted on the bottom plate, and a second position, called the operating position, in which the stop member is on the axial path of said shoulder. The stop member advantageously takes the form of an articulated lever that includes a first control part, extended by a second stop part in the arc of a circle, wherein the control part is located in an end portion of the second part, in which the hinged lever pivots. A member that locks the stop member in the operating position may also be provided to hold the stop member in this position, while the watch fitted with the movement is operating. 
     According to another embodiment, the stop member can be carried by the tourbillon carriage and particularly by the bottom pivot of the tourbillon carriage. In this case, the bottom pivot will project outside its bearing on the opposite side to the carriage, and the stop member could be formed, either by a washer driven onto the projecting part of the bottom pivot, or by the head of a screw that is axially screwed into the free end of the projecting part of the bottom pivot. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features and advantages of the present invention will appear more clearly in the following description, which is given with reference to the annexed drawings and gives, by way of explanatory, but non-limiting example, advantageous embodiments of a timepiece movement with a tourbillon according to the invention. In the drawings: 
         FIG. 1  is a partial top view of the timepiece movement according to the invention in the tourbillon area, 
         FIG. 2  is a partial cross-section of the timepiece movement along line II-II of  FIG. 1  in the tourbillon area and in accordance with a first embodiment, 
         FIG. 3  is a plan view of one detail of the tourbillon timepiece movement according to the invention, with the Figure showing the stop member arranged to limit the axial shake of the carriage in the operating position, and with the tourbillon carriage omitted, 
         FIG. 4  is a plan view of one detail of the timepiece movement with a tourbillon according to the invention, with the Figure showing the stop member arranged to limit the axial shake of the carriage in the assembly position, and with the tourbillon carriage omitted, 
         FIG. 5  is a cross-section along line V-V of  FIG. 3 , 
         FIGS. 6 and 7  are respectively similar, perspective views to  FIGS. 3 and 4 , of one detail of the timepiece movement with a tourbillon according to the invention, 
         FIGS. 8 and 9  are partial cross-sections, similar to  FIG. 2 , of two variants of a second embodiment of a timepiece movement with a tourbillon according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF ONE EMBODIMENT 
     The timepiece movement with a tourbillon according to the invention, illustrated partially in  FIGS. 1 and 2  and designated by the general reference  1  is, for example, to be fitted to a wristwatch that typically includes a case closed on top by a crystal and on the bottom by a back cover (not shown). Below the crystal there are hour and minute hands that rotate above a dial that largely covers timepiece movement  1 . Timepiece movement  1  includes a tourbillon  10 , which is visible in a window of the dial or in another opaque element, such as the bottom plate of the movement. In a conventional manner, tourbillon  10  includes a rotating carriage  12 , which rotates about an arbour  14  around which the sprung balance  16 , forming the regulating member, oscillates. The carriage carries, in a conventional manner, an escapement E that cooperates with the regulating member. 
     Tourbillon carriage  12  is held in place between two pivots, bottom pivot  18  and top pivot  20 , respectively provided in bottom plate  22  of the movement and in a bridge  24  of the movement. 
     More specifically, and as is visible in  FIG. 2 , bottom pivot  18  of tourbillon carriage  12  rotates in a jewel  26  carried by bottom plate  22  of the movement via a cup-shaped part  28 . Cup  28  includes a bottom  28   a , which is extended by an annular wall  28   b , which ends in a fixed toothing  28   c  that forms, in a known manner, the fixed toothed wheel  28   c  on which the tourbillon escape pinion P E  rolls. In the example illustrated, toothing  28   c  extends outwards from cup  28 . 
     It can also be seen that bottom pivot  18  is carried by a bottom bridge  30  of tourbillon  12 . In the example shown, bottom bridge  30  includes a base plate  30   a , which extends upwards in  FIG. 2  via arms  30   b  that have a stepped configuration. Base plate  30   a  also includes a socket-shaped portion  30   c , which extends downwards in  FIG. 2  from its central part. Socket  30   c  carries pivot  18  into which it is driven in this example. The distal end of pivot  18  includes a stud  18   a , which pivots in the housing of jewel  26 . The median part of pivot  18  includes a toothed portion  18   b  which cooperates with a toothed wheel of the movement (not shown) driven by the mainspring thereof to set tourbillon carriage  12  in rotation. Thus, bottom bridge  30 , via pivot portion  18   b , forms the kinematic connection that links tourbillon carriage  12  to the rest of the timepiece movement. The proximal part of pivot  18  has a portion  18   c , whose diameter is larger than the diameter of socket  30   c , to define a shoulder  18   c , carried by said socket. 
     It goes without saying that, according to a variant, bottom bridge  30  could be integral with pivot  18 . 
     Base plate  30   a  also carries, in a conventional manner, escape bridge P and the bearings of the escape wheel set M E  ( FIG. 2 ) and pallets A. 
     Likewise, top pivot  20  of carriage  12  rotates in a jewel  32  carried by tourbillon bridge  24 , which includes an overhanging beam  32  visible in  FIGS. 1 and 2 . This beam is secured to bottom plate  22  of the movement by means of screws. Top pivot  20  is carried by a top bridge  34  of carriage  12 . In the example shown, top bridge  34  includes a base plate  34   a  which carries pivot  20 . Base plate  34   a  extends downwards in  FIG. 2  via arms  34   b  that also have a stepped configuration relative to arms  30   b  of bottom bridge  30  of carriage  12 . Bottom and top bridges  30  and  34  of the carriage are secured to each other via their respective arms. 
     According to the invention, tourbillon timepiece movement  1  further includes a stop member  36  arranged for limiting the axial shake of tourbillon carriage  12 , particularly in the event of any shocks that the watch undergoes, for example during a fall. 
     “Axial shake” means any movement of tourbillon carriage  12  along the axis of rotation  14 , which may result from tourbillon bridge  24  bending in the event of a shock. By way of illustration and given the various manufacturing and assembly tolerances of the various elements in relation to each other, this shake may reach values of around 0.4 mm to 0.50 mm in the event of shocks, in the absence of any limiting means, such as stop member  36  provided by the invention. 
     In the embodiment illustrated in  FIGS. 1 to 5 , stop member  36  is carried by bottom plate  22  of the movement and cooperates with bottom bridge  30  of carriage  12 . 
     More specifically, stop member  36  cooperates with shoulder  18   c  carried by bottom bridge  30 . In the absence of any shock, the distance D ( FIG. 5 ) between stop member  36  and shoulder  18   c  is less than the length of engagement L ( FIG. 5 ) of stud  18   a  of bottom pivot  18  in the housing of bearing  26 , formed in the example by a jewel. Thus, when the watch fitted to the tourbillon timepiece movement according to the invention undergoes a violent shock, the movement of carriage  12  caused by the shock cannot exceed the value D, such that stud  18   a  will not be able to leave its housing under any circumstances. Typically the distance D is around 0.20 mm, while length L is around 0.35 mm. 
     In the embodiment illustrated, stop member  36  is mounted to be mobile between a first position, called the assembly position ( FIGS. 4 ;  7 ) in which stop member  36  is off the axial path of shoulder  18   c  to enable carriage  12  to be mounted on bottom plate  22 ; and a second position, called the operating position ( FIGS. 3 ;  6 ) in which stop member  36  is on the axial path of shoulder  18   c . Stop member  36  is hinged onto the bottom  28   a  of cup  28 , typically by means of a screw V 1  that passes through bottom  28   a  of cup  28  and is screwed onto bottom plate  24 . 
     It will be noted in this regard that it is particularly advantageous to mount this stop member in the cup of the second steady pin of the tourbillon mechanism since it then occupies an existing volume in the mechanism that has been unused until now. 
     Stop member  36  takes the form of a hinged lever including a first control part  36   a , in the form of a rectilinear arm extended by a second stop part  36   b , which takes the form of a solid block shaped in the arc of a circle. Control arm  36   a  extends from an end part of block  36   b , in which the hinged lever pivots at  36   c . The thickness of solid block  36   b  is substantially greater than that of arm  36   a . It can also be seen that the top, inner, peripheral edge of solid block  36   b  has a projecting portion  36   d , defining a stop surface that is perpendicular to shoulder  18  when the stop member is in the operating position The bottom, inner, peripheral edge of solid block  36   b  also has a groove  36   e , whose profile has a complementary shape to that of a screw V 2 , used both as a guide during pivoting and for axially blocking stop member  36  in the event of shocks. 
     In order to keep stop member  36  in the operating position, movement  1  further includes a locking member  38 , which is formed of a pin driven into the bottom plate of the movement. This pin  38  will be housed in an oblong aperture  40  provided in control arm  36   a  of stop member  36  in the operating position. It will be noted in this regard that the annular wall  28   b  of cup  28  includes an oblong aperture  42  through which control arm  36   a  of stop member  36  extends. It will be noted in this regard that the cup also includes an aperture O for the passage of a drive wheel (not shown) of carriage  12  towards pinion  18   b.    
     Making a stop member mobile between the aforementioned two positions facilitates assembly of the tourbillon. Indeed, once cup  28 , fitted with bearing  26 , has been assembled on bottom plate  22 , stop member  36  is mounted in the bottom of the cup then pivoted into its assembly position, in which carriage  12  can easily be mounted in its pivots. Once the tourbillon carriage has been set in place, stop member  36  need only be pivoted and locked in its operating position, in which edge  36   c  of the block of member  36  is placed perpendicular to shoulder  18   c  of the bottom bridge of carriage  30 . The axial shake of carriage  12  is thus limited, in all circumstances, to the distance D that separates shoulder  18   c  from edge  36   c.    
       FIG. 8  shows partially a tourbillon timepiece movement according to a second embodiment of the invention in which those elements that are identical to those described with reference to  FIGS. 1 to 7  are designated by the same reference numerals. 
     This second embodiment differs from that described with reference to  FIGS. 1 to 7  in that stop member  36  is no longer carried by bottom plate  22 , but by tourbillon carriage  12 . In particular, stop member  36  is carried by stud  18   a  of bottom pivot  18  of the tourbillon carriage. In order to do this, the length of stud  18   a  of the bottom pivot is adapted so that it projects from bearing  26  on the opposite side to carriage  12  and the stop member is formed by a washer driven onto the projecting part of the bottom pivot stud. In a variant, the projecting part of stud  18   a  may include an annular groove and the washer may take the form of an elastic ring  36 . 
       FIG. 9  shows another embodiment of the second embodiment of  FIG. 9  in which the stop member is formed by the head of a screw that is axially screwed into the free end of the projecting part of the bottom pivot. 
     It goes without saying that the present invention is not limited to the embodiments that have just been described and that those skilled in the art can envisage various simple variants and alterations without departing from the scope of the invention defined by the annexed claims. 
     In particular, one could envisage mounting the stop member of the first embodiment so that it slides rather than pivots on the bottom plate of the movement or in the cup. In the first embodiment described above, two stop members could be provided, preferably arranged facing each other. In another variant of the first embodiment the stop member could be immobile. In this case, for example, it would be screwed into the bottom of the cup in the operating position from underneath the cup once the carriage had been mounted. Finally, according to yet another variant, the stop member could be mounted outside the cup at a distance from the bottom pivot, although it is advantageous to limit the shake to a place that is as close as possible to said pivot. 
     The tourbillion timepiece movement that has just been described concerned an application to a wristwatch, but it is clear that this application is in no way limiting and that the timepiece movement according to the invention can be used to equip other types of timepieces, such as, in particular, pocket watches.