Abstract:
Winding crown for a timepiece, said crown ( 32 ) including an uncoupling mechanism ( 1 ) comprising a rigid drive ring ( 4, 400 ) secured to the crown ( 32 ) and cooperating with at least one elastically deformable element ( 2; 200 ) secured to a pipe ( 12 ) to one end of which a winding stem is secured, the rigid ring ( 4; 400 ) driving the deformable elastic element ( 2; 200 ) in at least one rotational direction until the resistant torque opposed by said elastic element ( 2; 200 ) exceeds a threshold value beyond which said elastic element ( 2; 200 ) is deformed so as to interrupt the drive connection thereof with the rigid ring ( 4; 400 ), the elastically deformable element ( 2; 200 ) therefore having means for temporary coupling said element to said rigid drive ring ( 4; 400 ), the crown ( 32 )) being characterized in that the elastically deformable element ( 2; 200 ) includes means for centring said element relative to the rigid drive ring ( 4; 400 ).

Description:
[0001]    This application claims priority from European Patent Application No. 07120279.0 filed Aug. 11, 2007, the entire disclosure of which is incorporated herein by reference. 
       FIELD OF THE INVENTION  
       [0002]    The present invention concerns a timepiece crown including an uncoupling mechanism. More specifically, the present invention concerns a crown of this type which prevents the user damaging the timepiece movement, in particular when he winds the mainspring. 
       BACKGROUND OF THE INVENTION  
       [0003]    A crown of the aforementioned type is known for example from EP Patent Application No. 1 586 960 in the name of the Applicant. The crown essentially includes a cap delimited at the bottom by a circular skirt, which has a plurality of flutes on the external surface thereof for facilitating handling of the crown by the user. The circular skirt delimits a hollow cylindrical housing inside which the uncoupling mechanism is arranged. The uncoupling mechanism includes, among other things, a rigid ring, which has a plurality of notches on the inner periphery thereof for cooperating with one or more generally circular spring elements in order to achieve the uncoupling function. In fact, the notched ring is secured to the crown whereas the spring elements are secured to a pipe onto which is screwed a winding stem, which acts on the winding mechanism for the mainspring. Provided that the resistant torque opposed by the spring elements is less than a predetermined value, the spring elements are driven in rotation by the rigid ring under the effect of the user activating the crown. In turn, the spring elements drive the pipe on which they are mounted and thus the winding stem. When the resistant torque opposed by the spring elements becomes greater than the predetermined value, because the mainspring is completely wound, said spring elements will deform elastically in response to activation of the rigid ring and will escape therefrom by sliding. The result of this is that the crown activated by the user will rotate without transmission of any torque. The mainspring is therefore protected from any excessive winding which could damage it. 
         [0004]    The top end of the pipe has a projecting portion, for example square-shaped and inscribed in a hole, which is also square, made in the springs via which said springs are secured to said pipe. Thus, when a rotational movement is imparted to the springs, the latter drive the pipe in rotation via its projecting portion. 
         [0005]    With use, the crown described above has a problem. When the pipe is not perfectly aligned axially with the crown and a play thus appears between these two parts, the springs, rigidly coupled to said pipe, are no longer suitably centred relative to the notched rigid crown. When the notched ring is driven in rotation, the springs can then pass from their normal elastic deformation state, to a plastic deformation state in which they undergo irreversible damage. A substantial drop is then observed in the threshold torque value that determines the transition between the state in which the notched ring drives the springs in rotation and the state in which said notched ring slides over said springs without driving them, which consequently means that the user is no longer able to wind the mainspring in an optimum manner. 
       SUMMARY OF THE INVENTION  
       [0006]    It is an object of the present invention to overcome the resistance problems of the aforementioned materials, the tribological and other problems by providing a new type of uncoupling mechanism for a timepiece winding crown whose torque value, which marks the uncoupling between the rigid notched ring and the spring elements, remains stable over time. 
         [0007]    The present invention therefore concerns a winding crown for a timepiece, said crown including an uncoupling mechanism including a rigid driving ring secured to the crown and cooperating with at least one elastically deformable element secured to a pipe to one end of which a winding stem is secured, the rigid ring driving the elastic deformable element in at least one direction of rotation until the resistant torque opposed by said elastic element exceeds a threshold value beyond which said elastic element is deformed so as to interrupt the drive connection thereof to the rigid ring, the crown being characterized in that the elastically deformable element includes means enabling it to be centred relative to the rigid drive ring. 
         [0008]    Owing to these features, the present invention provides a timepiece crown wherein the elastically deformable element of the uncoupling mechanism includes its means of its own for centring said element relative to the rigid drive ring secured to the crown. Axial disalignment between the pipe to which the elastically deformable element is secured and the crown thus has no effect on the centring of said deformable element relative to the drive ring. Consequently, if any such disalignment is observed, the deformable element will remain in a state in which it deforms elastically under the effect of stresses exerted by the rigid ring and will not enter a plastic deformation domain in which it could be irreversibly damaged. Thus, the operating features of the uncoupling mechanism according to the invention will be preserved over time. In particular, no significant drop will be observed in the torque value that marks the passage between the state in which the rigid ring is meshed with the deformable element and the state in which the rigid ring is uncoupled from the deformable element. 
         [0009]    According to a complementary feature of the invention, the elastically deformable element is circular and the centring means are arranged at least in a diametrically opposite manner on the perimeter of said elastically deformable element. 
         [0010]    Owing to this feature, the elastically deformable element is perfectly symmetrically centred relative to the centre of the rigid drive ring. 
         [0011]    According to another embodiment of the invention, the centring means are provided at three places distributed at regular intervals on the perimeter of the elastically deformable element. 
         [0012]    Owing to this variant, the efforts exerted on the elastically deformable element are distributed in an optimum manner if the pipe is not perfectly axially aligned with the crown. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0013]    Other features and advantages of the present invention will appear more clearly from the following detailed description of two embodiments of the crown according to the invention, these examples being given purely by way of non limiting illustration with reference to the annexed drawing, in which: 
           [0014]      FIG. 1  is a plan view of a first embodiment of the elastically deformable element according to the invention; 
           [0015]      FIG. 2  is a plan view of a second embodiment of the elastically deformable element according to the invention, and 
           [0016]      FIG. 3  is a longitudinal cross-section of a crown in which the uncoupling mechanism according to the invention is arranged. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]    The present invention proceeds from the general inventive idea that consists in providing a timepiece crown including an uncoupling mechanism for protecting the timepiece movement against excessive winding of the mainspring, said uncoupling mechanism including an elastically deformable element, which possesses means for centring said element perfectly relative to the rigid drive ring. Thus, if the pipe to which the elastic element is secured is not perfectly axially aligned relative to the crown carrying the rigid drive ring, the elastically deformable element is not off-centre relative to the rigid drive ring and thus is not liable to pass from an elastic deformation state to a plastic deformation state in which it would undergo irreversible plastic deformation. 
         [0018]    A first example of an uncoupling mechanism according to the invention is shown with reference to  FIG. 1 . Designated as a whole by the general reference numeral  1 , this uncoupling mechanism includes an elastically deformable element  2  and a rigid drive ring  4 . 
         [0019]    The elastically deformable element  2  is typically an element of generally circular shape. It includes a base  6  that is also substantially circular, pierced at the centre thereof with a hole  8  of, for example, square shape via which it is secured to a projecting portion  10  of complementary shape to that of hole  8  of a pipe  12  (see  FIG. 3 ) to the end of which a winding stem (not shown) is secured. 
         [0020]    According to the invention, the spring element  2  includes means for centring said element relative to rigid drive ring  4 . In the example shown in  FIG. 1 , these centring means take the form of three Y-shaped arms  14 ,  16  and  18  which extend radially from base  6  and which are spaced at regular angles from each other. 
         [0021]    Spring element  2  also includes means for temporarily coupling it to rigid drive ring  4 . In the example shown in  FIG. 1 , these coupling means are shown as Ω shaped parts  20 . There are three of these parts  20 , each arranged between two successive centring arms. Each coupling part  20  includes a head  22  and two legs  24 , which define an surface open towards the inside of spring element  2 . 
         [0022]    More specifically, coupling arms  14 - 18  each include a section  14   a - 18   a , which extends radially from base  6  of spring element  2  and which is separated into two symmetrical branches  14   b - 18   b  which spread apart from each other. The two branches  14   b - 18   b  of each arm  14 - 18  are joined to each other by a centring portion  14   c - 18   c  in the arc of a circle, which is extended at the free ends thereof by connecting portions  26  which connect centring arms  14 - 18  to feet  24  of temporary coupling parts  20 . 
         [0023]    The inner perimeter of rigid drive ring  4  has an uninterrupted series of bumps  28  and hollows  30  which respectively define first and second inner diameters D 1  and D 2 , inner diameter D 1  being smaller than inner diameter D 2 . 
         [0024]    As can be seen upon examining  FIG. 1 , centring portions  14   c - 18   c  in the arc of a circle of arms  14 - 18  define a first external radius R′ 1  of spring element  2 , which corresponds to a diameter equal to first inner diameter D 1  of rigid drive ring  4 . Since, moreover, the length of centring portions  14   c - 18   c  is such that these portions  14   c - 18   c  always rest on two bumps  28  on the inner perimeter of drive ring  4 , it is clear that the position of these centring portions  14   c - 18   c  relative to drive ring  4  will remain unchanged whatever the angular position of said drive ring  4 . Bumps  28  of drive ring  4  thus constitute a rolling path for spring element  2  along which centring portions  14   c - 18   c  move. Spring element  2  is thus perfectly positioned relative to the centre of rigid drive ring  4 , such that any axial alignment of pipe  12 , to which said spring element  2  is secured, relative to crown  32  to which said rigid ring  4  is secured has no effect on the relative positioning of said spring element  2  and said rigid ring  4 . Rigid ring  4  is thus not liable to enter a plastic deformation zone in which it could undergo irreversible damage which could lead to a decrease the threshold torque value that marks the passage between the state in which rigid ring  4  drives spring element  2  and the state in which spring element  2  is elastically deformed to escape from the hold of rigid ring  4  by losing adherence. 
         [0025]    Spring element  2  is driven by rigid ring  4  via the cooperation between the coupling parts  20  and bumps  28 . It should be noted that the tip of heads  22  of coupling parts  20  defines a second external radius R′ 2  of spring element  2 , which corresponds to a greater diameter than the first inner diameter D 1  of rigid ring  4 . Thus, rotating crown  32  drives rigid ring  4  in rotation. In turn, rigid ring  4  will drive in rotation spring element  2 , bumps  28  of said rigid ring  2  abutting against heads  22  of coupling parts  20 . This is true until spring element  2  opposes a resistant torque such that coupling parts  20  are elastically deformed and the heads  22  thereof pass under bumps  28 . At that moment, rigid ring  4  no longer grips spring element  2  and crown  32  rotates without transmitting any torque. It will be noted that coupling parts  20  work partly in compression along a radius in which spring element  2  is inscribed and not only along a tangential direction to the perimeter of said spring element  2 , which limits the fatigue of said coupling parts  20  and also increases their resistance to wear. 
         [0026]    A second embodiment of the uncoupling mechanism according to the invention is illustrated in  FIG. 2 . It includes an elastically deformable element  200  and a rigid drive ring  400 . 
         [0027]    Rigid drive ring  400  has the same shape and structure as rigid ring  4  described with reference to  FIG. 1 . It includes an uninterrupted series of bumps  280  and hollows  300 , which respectively define first and second inner diameters D 1  and D 2 , inner diameter D 1  being smaller than inner diameter D 2 . 
         [0028]    Elastically deformable element  200  is of the spring type and is generally of circular shape. It includes a base  600 , which is also substantially circular, pierced at the centre thereof with a hole  800  of square shape via which said element is secured to the projecting portion  10  of square contour of pipe  32  (see  FIG. 3 ) to the end of which the winding stem (not shown) is secured. 
         [0029]    Base  600  of spring element  200  is extended by two diametrically opposite bent portions  210  and  220  which are followed by arms  230  and  240  of similar shape to that of the arc of a circle. As can be seen upon examining  FIG. 2 , arms  230  and  240  both extend anticlockwise. Of course, it would be entirely possible for arms  230 ,  240  to extend in the same clockwise direction. 
         [0030]    More specifically, each of the two arms  230  and  240  includes a centring portion  230   a ,  240   a  and a coupling portion  230   b ,  240   b . Centring portions  230   a ,  240   a  have the shape of an arc of a circle and define a first external diameter D′ 1  of spring element  200  which is equal to the first inner diameter D 1  of rigid drive ring  400 . The length of centring portions  230   a ,  240   a  is such that these centring portions  230   a ,  240   a  always rest on two successive bumps  280  of the inner perimeter of rigid drive ring  400  whatever the relative position of said ring  400  with respect to spring element  200 . These centring portions  230   a ,  240   a  thus guarantee that whatever the circumstances, spring element  200  will always be centred relative to rigid drive ring  400 . 
         [0031]    Beyond centring portions  230   a ,  240   a , coupling portions  230   b ,  240   b  of arms  230 ,  240  become progressively closer to the centre of spring element  200  and the free end of said coupling portions has a protruding portion  230   c ,  240   c  whose highest point defines a second external diameter D′ 2  of spring element  200 , which is larger than the first inner diameter D 1  of rigid ring  400 . Thus, when rigid ring  400  is driven in rotation, it drives in turn spring element  200  by abutting, via bumps  280 , against protruding portions  230   c ,  240   c  of coupling portions  230   b ,  240   b  of arms  230 ,  240  of spring element  200 . This is true until spring element  200  opposes a resistant torque such that arms  230 ,  240  are elastically deformed and the protruding portions  230   c ,  240   c  thereof pass under bumps  280  of rigid ring  400 . At that moment, rigid ring  400  no longer grips spring element  200  and crown  32  rotates without transmitting any torque. 
         [0032]    An example of the uncoupling mechanism according to the invention integrated in a winding crown  32  is illustrated in  FIG. 3 . In its hollow inner housing, crown  32  has a circular shoulder  34 , which delimits, on the one hand, an abutment surface  36  for a cover  38  mounted with the insertion of a sealing gasket  40  in an aperture  42  made in said crown  42 , and, on the other hand, a stop surface  44  for rigid drive ring  4 ,  400  and for one, and preferably two, spring elements  2 ,  200  mounted one above the other. 
         [0033]    Pipe  12  has a main part  46  of cylindrical shape in which a threaded hole  48  is made for mounting a winding stem (not shown). A disc shaped head  50 , whose diameter is larger than the diameter of main part  46 , is mounted on said main part  46  of pipe  12 . The projecting portion  10 , on which the two spring elements  2 ,  200  are positioned is mounted on head. 
         [0034]    The two spring elements  2 ,  200  are supported partly on head  50  of pipe  12  and partly on a bush  52 , which is mounted in the inner volume of crown  32  via any appropriate means such as driving in, welding, bonding or other means. 
         [0035]    Crown  32  is mounted with its uncoupling mechanism in the middle part of a timepiece via a tube  54  fixed to said middle part for example by being driven therein. 
         [0036]    The bush has two circular grooves  56  and  58  which house two sealing gaskets  60  and  62  providing a seal between crown  32  and bush  52  on the one hand, and between bush  52  and tube  54  on the other hand. 
         [0037]    Finally, a screw  64  is screwed into projecting portion  10  such that springs  2 ,  200  are held between head  66  of the screw and head  50  of pipe  12 . 
         [0038]    Rigid drive ring  4 ,  400  is secured to crown  32 , whereas spring elements  2 ,  200  are secured to pipe  12 . 
         [0039]    It goes without saying that the present invention is not limited to the embodiments that have just been described and that various simple alterations and variants could be envisaged by those skilled in the art without departing from the scope of the invention as defined by the annexed claims. In particular, it is entirely possible to envisage the spring elements comprising coupling springs that deform along a parallel direction to the tangent to the circle in which said spring elements are inscribed.