Abstract:
Crown including a cap formed of a cover integral with a lateral skirt, wherein the crown includes a removable deck ring.

Description:
[0001]    This application claims priority from European Patent Application No. 12197843.1 filed Dec. 12, 2012, the entire disclosure of which is incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention concerns a timepiece crown which can be removed, particularly in order to change a sealing gasket. 
       BACKGROUND OF THE INVENTION 
       [0003]    Crowns are commonly used as adjusting members for mechanical watches. Mounted on a tube which is driven or screwed into the middle part of the watch case, crowns are assembled at the end of a winding or control stem, and can take several distinct axial positions in which they can execute various types of functions, such as for example winding the barrel of the watch, setting the time, adjusting the date etc. 
         [0004]    Screw-in crowns are commonly used for watches in order to improve the sealing of watches on their winding or control stem. This type of crown has the peculiarity of having to be in an unscrewed position to be capable of being actuated, in which the axial position of the crown can be changed to define an adjustment mode. In the screwed-in position, the crown is locked onto a tube, which is fixed inside the middle part and which preferably has a bulged part at the base of the portion thereof projecting outside the middle part of the case, in order to compress a sealing gasket, thereby improving the sealing of the watch. The screwed-in position is therefore the normal position when the watch is being worn and which has the best sealing properties, suitable, in particular, for use during aquatic activities, such as deep sea diving. 
         [0005]    There exist several known manufacturing and assembling methods for assembling these screw-in crowns onto the middle part of a watch. There even exist angular orientation adjustment devices for placing the crown in a determined position relative to the case after the crown has been screwed-in, when there is a marking affixed to the end surface of the crown. This is the case, for example when the crowns are fitted to luxury and high quality goods. 
         [0006]    Most crowns, regardless of whether or not they are screwed-in and orientable, generally include a cap formed by a cover on the top surface of which a trademark or logo can be affixed, and a lateral skirt inside which the securing tube is housed. To guarantee the sealing of this type of crown with respect to the tube, one or more sealing gaskets are provided on the lower end of the skirt, and are radially compressed between the external surface of the tube and the skirt, and covered by means of a crimped or driven-in ring. These covering rings, which are used to hold the sealing gasket axially when the crown is operated, are also commonly called “deck rings”. 
         [0007]    One drawback of these crowns is that sometimes it is impossible to replace a worn sealing gasket where the gasket is not accessible laterally when the crown is dismantled because the deck ring is permanently fixed to the bottom surface of the skirt of the crown. Consequently, during an after-sales service, for example, it may be necessary to replace the entire crown when its sealing properties deteriorate over time, which is very expensive. 
         [0008]    EP Patent No. 0655664 proposes an alternative solution to deck rings for holding the sealing gasket of a crown-push button compressed against a guide tube by using an open, resilient, retaining ring engaged in a groove in the bottom face of the crown. These open resilient rings, also called circlips, are often employed as stop members for assembling and holding components in grooves about an arbour for larger sized parts, where the circlips are easy to handle using pliers which engage in holes at the ends thereof used for the assembly and removal of the circlips. However, the very reduced size of a timepiece crown, which is at most barely a few millimetres, makes the crown very difficult to handle, even simply to assemble, and particularly inconvenient for any subsequent dismantling operation. Moreover, the particular shape of the circlip requires a groove to be arranged in the bottom end of the crown skirt with a beak forming an axial retaining surface, as provided for in the invention disclosed by EP Patent No. 0655664, intended to prevent the circlip from being unintentionally wrenched out. This complicates the machining of the crown and therefore makes it more expensive to manufacture. 
       SUMMARY OF THE INVENTION 
       [0009]    It is an object of the present invention to overcome the drawbacks of the aforementioned prior art by providing a conventional crown of simple, economical construction, which can be assembled without the use of any tedious operation of crimping a ring and/or handling a circlip, and can be more easily dismantled, without, however, impairing its sealing properties. 
         [0010]    The invention therefore concerns a crown including a cap formed of a cover integral with a lateral skirt, characterized in that it includes a removable deck ring. 
         [0011]    The invention also concerns a method of implementing the disassembly of the deck ring of this type of crown, characterized in that it includes a step of deforming the deck ring. 
         [0012]    One advantage of the proposed solution is that it requires almost no structural modification of a conventional crown, or virtually any of the crown&#39;s components, to guarantee equivalent sealing and axial holding properties, yet allows a worn sealing gasket, for example, to be changed when the gasket is not laterally accessible. 
         [0013]    Another advantage of the proposed solution is that it allows sealing gaskets to be set in place and replaced more rapidly on a crown. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    Other features and advantages of the present invention will appear more clearly from the following detailed description of preferred embodiments, given by way of non-limiting example, with reference to the annexed drawings, in which: 
           [0015]      FIG. 1  shows a known prior art circlip. 
           [0016]      FIG. 2  is a semi cross-section of a crown provided with a non-removable deck ring of the prior art. 
           [0017]      FIG. 3  is a view of a crown provided with a removable deck ring of the invention without its tube. 
           [0018]      FIG. 4  shows a bottom view of the crown of  FIG. 3 , where the tube for fastening to the middle part is in a disassembled position, more particularly showing a particular gripping area provided for the removable deck ring. 
           [0019]      FIG. 5  is a view of a particular shape of a removable deck ring used according to an alternative embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]      FIG. 1  shows a known prior art circlip C, which consists of an open resilient ring both ends of which adjoin each other in an assembled position to form a circular inner periphery matching the shape of a cylindrical arbour around which the circlip is intended to be fitted. To facilitate the assembly and disassembly of this type of circlip, apertures O are provided in lugs on the ends thereof to allow the circlip to be gripped and handled. 
         [0021]    Within the scope of the invention, open circlips of this type are not used, but a closed ring, referred to below as a “deck ring”, which is therefore more difficult to deform elastically for easy assembly and removal from its housing inside the crown without the risk of damaging the sealing gaskets or scratching the contours and sealing surfaces thereof. 
         [0022]      FIG. 2  shows a sagittal semi cross-section along the axis of rotation A-A of a conventional screw-in crown  1 , on which a logo L can be seen, which is “Omega” here, arranged on the external surface  113  of cover  112  of the cap  11 . There is also shown, on the external periphery of the cap, a toothing D which is intended to make it easier for the user to grip crown  1  during use. Crown  1  is shown in the screwed-in position on a threaded tube  8 , intended in turn to be screwed into the middle part of a watch case (not shown) by means of a first thread  81 , while a tapping  82  cooperates with thread  21  of a central pipe  2  of tubular shape. Cap  11  is formed by a cover  112  and an axial skirt  111 , which together define a central aperture  115  inside crown  1 —referenced only in  FIG. 3  described below for the sake of legibility—and in which there is arranged not only the end of threaded tube  8  integral with the middle part, but also central pipe  2 . According to the illustrated embodiment, the central pipe  2  is integral with cap  11 , but according to a variant it could consist of an intermediate element for controlling the angular orientation of cap  11  relative to the middle part of the watch. 
         [0023]    Piston  7  housed inside central pipe  2  is integral with a stem (not shown but conventionally mounted on the bottom end  72  of piston  7 ? via tapping  71  in a blind hole) interacting with the movement. The piston can slide against a spring  3  stopped on an inner surface  114  of cover  112  of cap  11 , and, in particular, enables cap  11  to emerge from the middle part when crown  1  is unscrewed from tube  2  when the crown is used to adjust a function (for example, to set the time, adjust the date or manually wind the movement). 
         [0024]    A sealing gasket, typically an O ring joint, is inserted between threaded tube  8  and axial skirt  111  of cap  11  so as to guarantee sealing with respect to the crown tube. In the screwed-in position of crown  1 , joint  7  is axially held between a cross-piece  4 , which forms a first ring, and a non-removable deck ring  6 , which forms a second ring covering the joint on the bottom face  116  of crown  1 . Joint  1  is super compressed on a bulged portion  83  of tube  8 , whose thickness matches the axial space e between non-removable deck ring  6  and central pipe  2 , so that the sealing properties are the best possible when the crown is in the screwed-in position. After the crimping operation, non-removable deck ring  6  is housed inside a groove  1160  arranged in the bottom surface  116  of the crown so that it is virtually flush with the surface of bottom face  116  of crown  1 . 
         [0025]      FIG. 3  shows a crown  1  according to the invention whose overall structure is identical to that illustrated in  FIG. 2 , but this time with tube  8  in a disassembled position, in which the deck ring is removable (referenced  60 ), i.e. it can be assembled on cap  11  and then subsequently dismantled. All the references are identical to those of  FIG. 2 , except those relating to tube  8  which is no longer shown, and to groove  1160  which has been replaced by a shoulder  1161 , i.e. which no longer has an axial retaining surface. Sealing gasket  5  is now decompressed; it can be seen that it is doughnut-shaped, has a toroid diameter t, and the central aperture  115  can also be seen inside the crown, in which here is housed, in particular, central pipe  2 . When the ratio between the axial space e available between the inner circumference of removable deck ring  60  and the external circumference of central pipe  2  of the crown is smaller than or equal to around 1.5 times the diameter of toroid section t, it is difficult to grip the sealing gasket through the inside of removable deck ring  60  to replace it without damaging it and thus impairing its sealing performance. Consequently, it may be useful or even necessary, to dismantle removable deck ring  60  beforehand. 
         [0026]    Removable deck ring  60  can be mounted on cap  11  of crown  1  by a conventional driving in operation or by oval deformation. The walls of the crown and the deck ring may be cylindrical or conical. However, according to a preferred embodiment of the invention, the removable deck ring  60  is made in a shape memory material and it is then possible to deform the deck ring beforehand and to allow it to return to its original shape once placed on shoulder  1161  of the bottom face of crown  1 , which both facilitates the deck ring assembling operations, and makes it possible to remove the deck ring without mutilating any elements or parts in proximity. 
         [0027]    When removable deck ring  60  is made of a shape memory alloy, the alloy will preferably be chosen with a transition temperature situated well outside the working temperature range of the watch, comprised between around −20 and +50 degrees Celsius, to prevent any inadvertent dismantling of removable deck ring  60  in extreme use conditions. According to a preferred embodiment of the invention, the material is chosen to be Nitinol (50% nickel and 50% titanium), which has super elastic properties, i.e. of reversible deformation, around −30 degrees. The assembly operation may then consist in cooling the deck ring by applying a freezing spray, for example at −55 degrees, to bring it to a temperature at which it tolerates a deformation rate of more than 8%. By applying stresses to opposite points on a diameter of removable deck ring  60 , for example using pliers, removable deck ring  60  is made slightly oval and it is placed in its housing on the bottom face of cap  11 ; it can therefore return to its original circular shape after around ten seconds at ambient temperature to hold sealing gasket  5  in place. 
         [0028]    To facilitate the assembly and disassembly operations, at least a first gripping area  1162  can be provided on the bottom face  116  of crown  1 , referenced in  FIGS. 2 and 4 . According to the preferred embodiment illustrated for crown  1 , a plurality of first gripping zones  1162  are provided, as seen in  FIG. 4  which shows a bottom view of crown  1  and in which illustrates, in addition to toothing D of the crown, central pipe  2  and the hexagonal shape of the end of piston  7 , four first gripping areas in the form of indentations respectively at midday, 3 o&#39;clock, 6 o&#39;clock and 9 o&#39;clock in the bottom face of crown  116 . Each of these indentations enables a tool for gripping removable deck ring  60  to be engaged and gripped from the exterior. The advantage of the arrangement of a plurality of these gripping areas, particularly in pairs along diameters of removable deck ring  60 , is that removable deck ring  60  can be forced to become slightly oval during disassembly, when this operation requires manual intervention to deform the ring. 
         [0029]    According to a variant, removable deck ring  60  can be made of a shape memory material which has been trained to have a two way memory effect, i.e. to have a first circular shape at ambient temperature in which it holds the sealing gasket in an assembled position on the cap, and a second shape, for example oval, in which it can be disassembled when it is brought to a temperature beyond the critical deformation threshold. In the case of Nitinol for example, the freezing spray would only need to be sprayed onto the crown in order to automatically disassemble the deck ring when its temperature falls below −30 degrees. 
         [0030]    Whichever method is chosen for assembling removable deck ring  60 , when the latter is made of a shape memory material, the disassembly operation involves a plastic deformation which may be either manual or automatic after a preliminary heating or cooling step to take the deck ring beyond a critical temperature threshold above or below which it has super elastic properties. The deck ring is thus made removable without having to interact with other parts of crown  1 , which allows sealing gasket  5  to be replaced more easily. According to an alternative embodiment, removable deck ring  60  is made easier to grip for the assembly or disassembly thereof not via gripping areas arranged on the crown, such as the first gripping areas  1162  illustrated in  FIG. 4 , but via second gripping areas arranged directly on the actual deck ring, such as indentation  61  seen in  FIG. 5 . As for the first gripping areas  1162 , it may be advantageous to arrange these second gripping areas  61  in opposite pairs, along a diameter of removable deck ring  60  to make the latter easier to grip; however the arrangement of these indentations also weakens removable deck ring  60  during deformation. 
         [0031]    Although the invention claimed has been described mainly in relation to the non-limiting example of a screw-in crown  1 , it will be clear that the invention can be applied to any type of crown, and to any shape of deck ring  6 , which may or may not be circular, to be fitted to different shapes of cap  11 .