Patent Publication Number: US-9429913-B2

Title: Coaxial disengageable wheels for a timepiece movement

Description:
This application claims priority from European Patent Application No. 14187570.8 filed Oct. 2, 2014, the entire disclosures of which is hereby incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention concerns a device with coaxial disengageable wheels for a timepiece movement. In particular, the invention concerns coaxial wheels coupled by a jumping elastic member to allow the disengagement of one wheel from the other. One application consists of driving a date disc, in addition to a time indicator hand, and of permitting correction of the position of the date disc, for example when the month has more than 31 days. Another application is for driving a second time zone display hand, for example GMT (Greenwich Mean Time), and permitting modification of the position of the hand for the selected second time zone. 
     BACKGROUND OF THE INVENTION 
     In conventional movements, it is known to use a system of two coaxial wheels with a coupling by means of a spring fixed to the first wheel and pressing radially on a third wheel integral with the second wheel. The known coupling system therefore essentially has three levels and provides a jumper spring that acts radially on a toothing of a third wheel. To overcome this radial elastic force, a disengagement torque must be exerted on one of the two wheels while the other has a sufficiently high reaction torque to permit application of said disengagement torque. The third toothed wheel defines a plurality of discrete relative angular positions for the two wheels. Provided the relative torque between the two wheels is lower than the disengagement torque, the two wheels rotate integrally. Applying a disengagement torque between the two wheels changes the relative angular position by a desired number of steps. This construction takes up a relatively large amount of space as the spring generally has lobes which occupy a large surface area to achieve the required elastic properties. Further, this construction is complex and fragile because the shape of the spring is relatively complex and the spring has a thin section to achieve the aforementioned required elastic properties. Furthermore, the diameter of the third wheel is limited by the space required to mount the radially acting spring, which limits the number of jump steps in one complete revolution. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a device with coaxial disengageable wheels for a timepiece movement which is compact, accurate and reliable over a long period of use. 
     It is another object of the invention to provide a device with coaxial disengageable wheels for a timepiece movement which easily permits fine adjustment of one wheel with respect to the other. 
     It is advantageous to provide a device with coaxial disengageable wheels for a timepiece movement which is easy to produce and therefore economical. Further, the invention is intended to be easily adapted to various variants with steps having different angular distances. 
     The objects of the invention are achieved by a mechanism with coaxial disengageable wheels for a watch movement according to claim  1 . The dependent claims describe advantageous aspects of the invention. 
     The present invention concerns a device with coaxial disengageable wheels for a timepiece movement which includes an input wheel, an output wheel, a hub, and a jumper mechanism including a spring and positioning elements defining a certain number of discrete angular positions of the input wheel with respect to the output wheel around an axis of rotation. The positioning elements include hollow elements and protruding elements. The spring is configured to apply an elastic force pushing the protruding elements against the hollow elements to couple the wheels to each other below a disengagement torque. The protruding elements and the hollow elements extend in the axial direction and the spring is configured to apply an elastic force in the axial direction. 
     In one embodiment, the positioning elements include one or more balls forming the protruding elements, the balls being housed in ball housings in the form of holes disposed either in the input or output wheel, and the hollow elements are formed in a surface of the other wheel. 
     In another embodiment, the spring is entirely formed in either said input or output wheel, and said protruding elements are made in the form of protuberances on the elastic arms of the spring. 
     According to an advantageous embodiment, there is a plurality of protruding elements distributed in a uniform manner around the axis of rotation. 
     According to an advantageous embodiment, the spring is in the form of disc that is essentially flat or of small thickness, including a base portion forming the central hole, configured to be mounted around the hub, and an elastic portion including an elastic arm whose end is configured to press the protruding element into one of said hollow elements. 
     According to an advantageous embodiment, the spring is formed from a stamped metal sheet. 
     According to an advantageous embodiment, the spring includes a securing portion with a central orifice fixed to the hub. 
     According to an advantageous embodiment, the input wheel includes the hollow elements and the output wheel includes or is integral with the spring. 
     In the present invention, there is also described a timepiece movement including a device with disengageable wheels, one of the wheels of the device being engaged with a drive wheel of a drive device of the movement and the other wheel of the device being engaged with a correction wheel of a correction device of the movement. 
     The disengageable wheel device may also engage with a date disc drive wheel. 
     The movement may also include a hand or another display member mounted on the hub of the disengageable wheel device. 
     Other advantageous objects and aspects of the invention will appear upon reading the claims, and the detailed description of embodiments below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described below with reference to the annexed drawings, given by way of non-limiting example, and in which: 
         FIG. 1  is a schematic perspective view of one part of a timepiece movement including a disengageable wheel device according to a first embodiment of the invention; 
         FIG. 2 a    is a perspective view of a disengageable wheel device according to the first embodiment of the invention; 
         FIG. 2 b    is a cross-section of the device of  FIG. 2   a;    
         FIG. 2 c    is an exploded perspective view of the device of  FIG. 2 a   ; and 
         FIG. 3  is a perspective view of a disengageable wheel device according to a second embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the Figures, starting with  FIG. 1 , one part of a timepiece movement  2  includes a disengageable wheel device  10  engaged with a drive wheel  4  of a drive device (not illustrated) and with a correction wheel  8  of a correction device (not illustrated). The disengageable wheel device  10  may also engage with a drive wheel  6  of a date disc (not illustrated). 
     The disengageable wheel device  10  includes an input wheel  12 , an output wheel  16 , a hub  14  and a jumper mechanism  18 . A hand  3  or another display member may be mounted on hub  14 . In the illustrated embodiments, hub  14  includes a central hole  40  permitting the passage of one or more coaxial arbors (not illustrated), for example for the device displaying the hours, minutes and/or seconds. 
     Jumper mechanism  18  is configured to allow input wheel  12  to undergo a certain rotation with respect to output wheel  16  over an angular distance defined by one or more notches by applying a relative torque between the two wheels beyond a certain threshold, called the disengagement torque. Input wheel  12  includes teeth  50  engaging with teeth of drive wheel  4 , and input wheel  12  is thus driven by the drive wheel. Output wheel  16  also includes teeth  50  engaging with teeth of correction wheel  8 . According to the variant, the teeth  50  of output wheel  16  engage with the teeth of a drive wheel  6  which is coupled to a date disc or other mechanism for the display of a time related value. 
     Input wheel  12  includes a central orifice  32  configured to house a section  38  of hub  14 . In the illustrated embodiments, the central orifice has a slightly larger diameter than wheel section  38 , so as to allow input wheel  12  to rotate freely with respect to hub  14 . In this embodiment, output wheel  16  has a central orifice  52  configured to be pressed or riveted onto a securing section  36  of hub  14  so that output wheel  16  is integral with hub  14 . It is, however, possible, in a variant, to reverse this configuration, namely so that the input wheel is integral with the hub and the output wheel can rotate with respect to the hub insofar as correction wheel  8  is not required to correct the position of hand  3 . Hub  14  may be a separate part assembled to one of the wheels as in the illustrated embodiments, but it is possible, in a variant, to form the hub as an integral part of either the input or output wheel. 
     In an advantageous variant, hand  3  is used to indicate a second time zone with respect to the main time display of the timepiece movement, however, the time zone indication must be able to be changed without changing the main time indication of the watch. A time zone operating on a 24 hour schedule will require 24 positions or more in a variant indicating the half hours, namely 48 positions, since in some countries time is graduated into smaller units than the hour. It will be noted that, in a variant, the second time zone may have a 12 hour display. 
     When it is desired to correct the time zone or the position of the date disc, a torque is applied to correction wheel  8 , causing output wheel  16  to turn when the torque thereon exceeds the disengagement torque of jumper mechanism  18 , input wheel  12  being locked by drive wheel  4 . In the illustrated variant, by applying a sufficiently high torque to correction wheel  8 , it is thus possible to turn output wheel  16  and hand  3  (made integral with the output wheel by hub  14 ) and the date drive device meshing with the output wheel. 
     Jumper mechanism  18  includes a spring  20  and positioning elements  22  defining a certain number of discrete angular positions of one wheel with respect to the other wheel of disengageable wheel device  10 . In the invention, the spring is configured to apply an elastic force in an axial direction, the axial direction corresponding to a direction parallel to the axis of rotation A of wheels  12 ,  16  of disengageable wheel device  10 . 
     Positioning elements  22  include hollow elements  24  and protruding elements  26 ; protruding elements  26  engage in hollow elements  24  in an axial direction and generate, under the action of spring  20 , a torque making the wheels rotate integrally. While the torque applied between the two wheels remains lower than the disengagement torque defined by the maximum torque required to make the wheels rotate integrally, input wheel  12  and output wheel  16  remain coupled and rotate together. The disengagement torque is defined, on the one hand, by the geometry of the protruding elements and hollow elements engaged therein, and on the other hand, by the axial thrust force applied by spring  20 . 
     One of the important advantages of this configuration is that it is possible to have the positioning elements close to the periphery of wheels  12 ,  16  and thus to enjoy the largest possible diameter for defining the discrete angular positions and therefore the number of jumps or notches per revolution. 
     Another advantage of this configuration is that the spring for applying an axial force is relatively simple to construct and assemble to the device. This also makes it possible to obtain a robust, reliable mechanism that can be easily calibrated to define with high precision the desired disengagement torque. 
     In a first embodiment illustrated in  FIGS. 2 a  to 2 c   , spring  20  of jumper mechanism  18  is a separate part assembled to output wheel  16  and made integral therewith. In the illustrated variant, spring  20  includes a securing portion  44  having a central orifice  54  and riveted to hub  14 , for example on the wheel securing portion  36  of hub  14 . However, other means of securing spring  20  to make it integral with output wheel  16  may be envisaged, for example soldering, adhesive bonding, crimping or riveting. However, driving output wheel  16  and spring  20  onto hub  14  is advantageous due to the simplicity and low cost of this manufacturing step. 
     In the variant illustrated in  FIGS. 2 a  to 2 c   , positioning elements  22  include one or more balls  28  housed in ball housings  30  in the form of holes arranged in output wheel  16  and hollows  24  formed in a surface of input wheel  12 . Balls  28  thus define protruding elements  26  configured to engage in hollow elements  24  formed in the surface of input wheel  12 . The number of hollows  24  formed in the surface of the input wheel and arranged circularly in a regular manner around the axis of rotation defines the number of notches or relative angular positions between the output wheel and the input wheel. 
     It is possible to have only one protruding element, for example in this embodiment a single ball  28 , however it is preferable to have at least two balls in diametrically opposite positions in order to balance the axial thrust force on wheels  12 ,  16 . Preferably, there are at least four protruding elements distributed in a uniform manner, i.e. every 90°, to obtain a stable and balanced axial thrust force on input wheel  12 , and the number of protruding elements may be greater than four. By having at least four protruding elements  26  engaging in hollow elements  24 , the force applied to each protruding element can be reduced compared to a configuration having one, two or three protruding elements, which overall provides improved control of the disengagement torque. Indeed, by increasing the number of protruding elements, the pressing force in the hollow of each element is reduced and consequently shocks are reduced when the protruding element jumps from one hollow and then engages in the next. 
     In the embodiment of  FIG. 2 a   , spring  20  may take the form of a flat disc, for example a disc formed from a stamped metal sheet including a base portion  42  forming central hole  54  configured to be riveted to hub  14 , and an elastic portion  46  including elastic arms  48 , the end of which is configured to bear against a ball  28 . The base portion of the spring may be pressed against wheel  16 , however, it is also possible to have a space between the spring and the wheel. In a simplified variant, the spring is formed by a simple, flat, relatively thin disc which presses on the balls. In another variant, this disc has openings which increase its capacity for axial elastic deformation. 
     The diameter of balls  28  is greater than the thickness of output wheel  16  so that each ball projects beyond the two main faces of the wheel in order to be pressed on one side by the elastic arm of the spring and on the other side to be housed inside one of hollows  24 . It is however possible to envisage, in a variant, having a ball whose diameter is essentially identical or smaller than the thickness of the output wheel, and in that case the end of the spring may include an extension configured to be inserted into the hole and to press on the ball under the surface of the wheel. 
     In an alternative variant, it is also possible to have a protruding shape at the end of the spring arm which extends across housings  30  configured to engage with hollows  24 , i.e. without having balls or other intermediate parts. 
     In a variant, it is also possible to form the ball housings in the input wheel and to make the spring integral with the input wheel, mounted on the underside of wheel  12  illustrated in  FIG. 2 c   , and to form the hollows in output wheel  16 . More generally, the protruding elements may be mounted in input wheel  12  and the hollows in output wheel  16  without departing from the scope of the invention. 
     Referring to  FIG. 3 , another embodiment is illustrated, in which jumper mechanism  18  is integrated directly in the output and input wheels  16 ,  12 . Input wheel  12  may be identical or similar to the input wheel of the first embodiment described above. Output wheel  16  includes a spring  20  and protruding elements  26 , forming an integral part of the output wheel. In an advantageous variant, wheel  16  may take the form of a disc that is essentially flat or of small thickness, for example a disc formed from a stamped metal sheet, spring  20  then including elastic arms  48  stamped in the disc. The protruding elements may be made by stamping a protuberance in each arm  48  close to the end thereof, the protuberances being configured to engage in hollows  24  of input wheel  12 . In this embodiment, output wheel  16  may also be driven onto hub  14  or made integral therewith by other means such as soldering, adhesive bonding or crimping. Again in this embodiment, the spring arms and the protruding elements may be integrated in input wheel  12  and the hollows integrated in output wheel  16  without departing from the scope of the invention.