Patent Publication Number: US-9411311-B2

Title: Device for driving an analogue indicator, particularly a date ring

Description:
This application claims priority from European Patent application 14158625.5 of Mar. 10, 2014, the entire disclosure of which is hereby incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention concerns the field of timepiece movements having an analogue display. In particular, the invention concerns a device for driving an analogue indicator, particularly a date ring. 
     BACKGROUND OF THE INVENTION 
     Various analogue indicator drive devices are known to those skilled in the art. A known problem of analogue indicators arises from the fact that they are driven by a drive device that generally includes intermediate elements between a motor and the analogue indicator. In the case where there are provided distinct stationary display positions for a certain duration, given manufacturing tolerances and the play required between the various elements of the drive device, precise positioning of the indicator is not guaranteed without position maintaining means. 
     In the case of date display devices, the positioning of the indicator in the distinct display positions is generally ensured by a jumper spring associated with the date ring toothing. Conventional drive systems do not ensure sufficient locking of the date ring in the event of a shock. It is therefore the jumper spring which has to ensure this locking function, which is why it has a high elastic constant. Thus, to overcome the elastic force of the jumper spring, it is necessary to provide high torque at the date ring, which is a problem given the generally large reduction ratio? between the motor and the date ring. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a device for driving an analogue indicator, particularly a date ring, which can ensure precise positioning of the indicator without requiring a positioning jumper spring. It is another object of the invention to provide a drive device of this type which is resistant to shocks. 
     To this end, the present invention concerns a timepiece movement provided with an analogue indicator of a plurality of distinct data which is arranged for this purpose to be held stationary at least temporarily in any one position of a plurality of distinct display positions, this analogue indicator having a toothing mechanically coupled to a drive device. The drive device includes a motor, a drive wheel and pinion provided with means for meshing with the toothing and a support on which the drive wheel and pinion is mounted. The drive wheel and pinion support is mounted on a base in order to pivot about a first axis and the drive wheel and pinion is rotatably mounted on the support about a second axis distinct from the first axis. The drive device further includes an elastic means exerting a lateral force on the support so that the meshing means of the drive wheel and pinion press against the toothing of the analogue indicator, the meshing means and the toothing having respective profiles selected such that, at least in said plurality of distinct display positions of the analogue indicator, the drive wheel and pinion and the analogue indicator mesh with each other with substantially no tangential play under the action of the elastic means. 
     In a variant, the elastic means is formed by a strip spring which presses laterally against the drive wheel and pinion support. 
     Other particular features of the invention will be set out below in the detailed description of the invention. 
    
    
     
       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  shows an embodiment of a timepiece movement according to the invention and more specifically the device for driving a date ring. 
         FIG. 2  shows certain elements of the drive device of  FIG. 1 . 
         FIG. 3  is a top view of a variant of the date ring drive wheel and pinion of the first embodiment. 
         FIG. 4  shows a first advantageous embodiment of the meshing between the date disc toothing and the drive wheel and pinion in a date display position. 
         FIG. 5  shows a second advantageous variant of the meshing between the date disc toothing and the drive wheel and pinion in a date display position. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIGS. 1 to 3 , there will be described hereafter an embodiment of a timepiece movement  2  provided with a drive device  4  for a date ring  6  according to the invention. The drive device includes a motor, of which only the pinion of the rotor  9  is shown in the Figures, an intermediate wheel  10  and a wheel  8  or  8 A driving the date ring. It will be noted that, in a first variant, the motor is a mechanical motor of the barrel type, whereas in another variant there is provided an electromechanical timepiece motor. Intermediate wheel  10  is arranged between rotor  9  of the motor and the drive wheel, with its pinion meshing with the drive wheel. 
     Drive wheel  8  or  8 A is provided with only two pins, which rise from the central portion of the wheel and which are aligned with the axis of rotation of the drive wheel and diametrically opposite. These two pins form means for meshing the drive wheel with the inner toothing  18  of the date ring. In the variant of  FIG. 1 , the two pins  12  and  13  are respectively provided with two roller bearings  14  and  15 . In the variant of  FIG. 3 , the two pins  12 A and  13 A do not have roller bearings. The term “meshing means” is understood to signify means of mechanical coupling between the date ring and the drive wheel. Thus, the meshing means are formed here on the one hand of the two pins, in this case provided with their respective roller bearings, and on the other hand of inner date ring toothing  18 . 
     Drive wheel  8  or  8 A is mounted on a support  22  which has a fixed pivot  34  arranged on a base  32  of larger diameter, this base defining a stop member on which the drive wheel rests. The fixed pivot defines the axis of rotation  36  of the drive wheel which has a central hole  38  into which the fixed pivot is inserted. According to the invention, the support is mounted on a main plate  24  and pivots about a pivot axis  26  which is defined by an arbor  28  traversing the support. Axis of rotation  36  is remote from pivot axis  26  so that the axis of the drive wheel follows an arc of a circle when the support pivots. Intermediate wheel  10  is also mounted on pivoting support  22  and its axis of rotation is merged with pivot axis  26  of the support. Thus, the axis of rotation of the intermediate wheel remains fixed relative to main plate  24  when support  22  pivots, which ensures the coupling to rotor  9  of the motor regardless of the angular position of the support. 
     Given that the date ring passes partially above the drive wheel and the intermediate wheel, the drive wheel is maintained in position axially by the date ring and the intermediate wheel is maintained in position axially by a button  30  forming a stop member. For the button to be able to be underneath the date ring, the central portion of the drive wheel has a truncated cone shape. This makes it possible to obtain a difference in level between the drive wheel toothing and the two drive wheel pins and therefore to provide a space for the button above the intermediate wheel pinion. 
     The drive device further includes a strip spring  40  which exerts a lateral force on support  22  so that the two pins press laterally on the date ring toothing  18  towards the bottom of the toothing. The strip spring is in tension and is pressed against a lateral surface of support  22  so as to exert a torque force thereon. Other types of spring or other alternative elastic means providing the torque force necessary for the given function may be provided by those skilled in the art. The date ring toothing has a profile with teeth  19  having hollows  20  between them, this profile being arranged to cooperate with the two pins, or, where appropriate, the two roller bearings so that, when the two pins (with or without roller bearings) are in a tangential orientation relative to the date ring, the drive wheel and the date ring mesh with each other with substantially no tangential play under the action of strip spring  40 . In  FIG. 1 , hollows  20  are provided in order to house pins  12  and  13  provided with their roller bearings with very little tangential play when the two roller bearings press against the bottom of the toothing, that is to say against the bottom of hollows  20  here. 
     It is provided that the distinct display positions of the analogue indicator, here the date ring positions corresponding to the display of different dates in an aperture in a dial intended for the timepiece movement according to the invention, correspond to a tangential orientation of the two date wheel pins. Thus, the drive device according to the invention ensures both the driving of the date ring and the precise positioning thereof in the different date display positions. Moreover, especially in the preferred embodiment with a drive wheel provided with two pins which are aligned with the axis of rotation of the drive wheel, the drive device also forms a very effective shock resistant system. Indeed, when a shock produces a torque force on the date ring, the drive wheel exerts a reaction force which maintains the date ring in position. 
     It will be noted that, in another less effective embodiment as regards the shock resistant function, the drive wheel has more than two pins, particularly three or four, arranged in an equidistant manner on a circle whose centre is the axis of rotation of the drive wheel. These pins may also be provided, in a variant, with roller bearings. Apart from this difference, and thus the fact that moving the date ring forward through an angular distance corresponding to one tooth is obtained with a smaller rotation of the drive wheel than in the case described above with two pins, the drive device is similar to the embodiment described with reference to  FIGS. 1 to 3 . 
       FIGS. 4 and 5  show two variants of the association between a profile of date ring toothing  18 A and two adjacent pins meshing with toothing  18 A. Teeth  19 A of the toothing have non parallel flanks each defining a monotonically increasing curve relative to central axis  44  of the corresponding tooth towards the bottom of the toothing. The distance L 1  between the two pins  12 A and  13 A or, where appropriate, the distance L 2  between the two respective roller bearings  14  and  15 , is arranged, in the date ring display positions, to have two points of contact between the two pins or, where appropriate, between the two respective roller bearings, and respectively two flanks of one tooth ( FIG. 4 ) or of two teeth having an intermediate tooth between them ( FIG. 5 ), without touching the bottom of the toothing. These variants are particularly advantageous since, in cooperation with strip spring  40 , the arrangement of the toothing and the space between the pins are such that there is no longer any tangential play when the two pins have a tangential orientation, as shown in  FIGS. 4 and 5 . It will be noted that this characteristic is obtained despite the usual manufacturing tolerances. Indeed, the only effect of these tolerances will be a greater or lesser penetration of the pins in the date ring toothing. The mean angular opening defined by the teeth flanks and the depth of the toothing are selected such that, throughout the range of tolerance (i.e. the various cumulative tolerances), the pins or, where appropriate, the roller bearings, do not abut the bottom of the toothing hollows  20 A. 
     Finally, in an embodiment in which the motor is an electromagnetic motor, the timepiece movement includes a control unit arranged to drive the electromagnetic motor, preferably in an accelerated mode, during the change from one display position to the next display position of the date ring. Thus, the transitional periods are of short duration, which limits the risk of a shock during rotation of the drive wheel. Indeed, when the two pins are in a substantially radial position relative to the date ring, a moment of force exerted on the ring generates a moment of force on the drive wheel which has only one pin in the toothing.