Patent Publication Number: US-6340241-B2

Title: Power reserve indicator mechanism and watch fitted with such a mechanism

Description:
FIELD OF THE INVENTION 
     The present invention concerns power reserve indicator mechanisms for movements for timepieces of the type fitted with a power source formed of a motor spring. In a conventional manner, the mechanism according to the invention includes a frame, a power reserve indicator and a differential gear with a first input connected to a wheel driven in rotation when the motor spring is wound, a second input connected to a wheel driven in rotation when the motor spring is let down, and an output connected to the power reserve indicator. In this mechanism, the indicator is capable of covering a given angle comprised between two end positions, the first of which is occupied when the motor spring is wound and the second, defined by a stop, when the motor spring is let down. 
     BACKGROUND OF THE INVENTION 
     A mechanism of this type is described in &lt;&lt;La montre suisse à remontage automatique&gt;&gt; by B. Humbert, Scriptar edition, Lausanne 1955, at page 85. It is provided with an indicator which is friction fitted onto a wheel connected to the output of the differential gear. The indicator moves between two end positions defined by stops. When the indicator reaches one of the stops, of the upper winding or letting down limit of the motor spring, it remains stationary while the motor spring continues to be wound or let down, the friction allowing the gear train to move while the indicator is stationary. 
     Such a solution thus provides an idea as to the real winding of the motor spring, but there may be significant differences from one cycle to another, due to the relative movement of the indicator with respect to the gear train. The object of the present invention is to overcome this drawback. 
     SUMMARY OF THE INVENTION 
     The mechanism according to the invention is thus characterized in that an intermediate wheel is inserted between the output of the differential gear and the indicator and includes a resilient member and two coaxial parts, one formed of a wheel, and the other of an arbor, one connected to the differential gear, the other to the indicator and connected to each other by the resilient member, the wheel being arranged so that the two parts rotate together while the indicator occupies a position comprised between the two end positions and in that, at least when the indicator occupies its second end position, the differential gear continues to rotate freely while the indicator remains in abutment and the resilient member is wound, while the motor spring drives the movement. 
     Advantageously, it is the wheel inserted between the differential gear and the indicator which meshes with the output of the differential gear. 
     In a particularly advantageous embodiment, the first resilient member includes a cam, secured in rotation to the arbor of the intermediate wheel, and a spring which can deform radially and is rigidly secured by one of its ends to the wheel of the intermediate wheel. This cam cooperates with the free end of the spring. The assembly is arranged such that the free end of the spring slides over the cam when the indicator is in abutment and the motor spring continues to be let down and generate an opposite torque to that exerted by the motor spring. 
     Consequently, each position of the indictor corresponds to a winding level of the motor spring. Moreover, the timepiece can continue to operate when the indicator has reached the lower limit. The user is, however, informed that the precision of his watch is liable to have been affected by insufficient driving torque, causing a loss of amplitude of the balance. 
     It is evident that such a mechanism has to include a set of gears to be able to operate normally. This set of gears affects the precision of the displayed information. Also, in order to further improve the agreement between the position of the indicator and the winding of the motor spring, the mechanism according to the invention advantageously includes a second resilient member arranged to exert a permanent torque on the gear train comprised between the two inputs of the differential gear and the intermediate wheel. 
     In a particularly reliable embodiment, the second resilient member includes an arbor rigidly secured to the frame, a drum provided, at its periphery, with a toothing which meshes with the part of the wheel connected to the indicator, and a strip spring arranged in the drum and secured, by one of its ends, to the arbor of the second resilient member and, by the other, to the drum. 
     Depending on the way in which the second resilient member works, fluctuations of more or less significance in the amplitude of the balance may result. Indeed, if the motor spring has to wind the second resilient member progressively as it is itself let down, the useful torque decreases to the same extent. The winding torque increases progressively as the motor spring is let down. This is why, in order to assure optimum amplitude of the balance, the second resilient member is arranged such that it is wound and let down simultaneously with the motor spring. 
     Such a mechanism is particularly well suited to fit a watch including a motor spring assuring a power reserve of 8 days. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     Other features and advantages of the invention will appear from the following description, made with reference to the annexed drawing, in which: 
     FIG. 1 shows a plan of a mechanism according to the invention, and 
     FIGS. 2,  3  and  4  are cross-sections respectively along the lines II—II, III—III and IV—IV of FIG.  1 . 
    
    
     DESCRIPTION OF A PREFERRED EMBODIMENT 
     The mechanism according to the invention is associated with a watch movement such as partially shown in the drawing. This movement includes, in a conventional manner, a frame formed of a bottom-plate  10  and several bars secured to this plate  10 , three of which are visible in the drawing, namely a barrel bar  12  (FIG.  2 ), a differential bar  14  (FIGS. 2 and 3) and a power reserve indicator bar  16  (FIGS.  3  and  4 ). The bottom-plate and the bars are intended to support and position the different moving components of the movement. 
     As can be seen in FIG. 2, this movement includes a power source formed of a barrel  18 , which includes a drum  20 , a cover  22 , an arbor  24  and a motor spring schematically shown at  26 . Motor spring  26  is disposed inside the drum and secured, in a conventional manner, to the wall of the drum by one of its ends and to the arbor by the other. Drum  20  is closed by the cover  22  which is snap fitted into a groove of the drum, which is not referenced to avoid overloading the drawing. 
     Drum  20  and cover  22  together form an assembly mounted so as to move in rotation on arbor  24 . 
     Arbor  24  pivots, on the one hand, in bottom-plate  10 , and on the other hand in barrel bar  12 . It carries, on a square portion  24   a  beyond bar  12 , a ratchet-wheel  28 , provided, at its periphery, with a toothing  28   a.  The driving of arbor  24  in rotation, by means of a winding crown, which has not been shown, assures the winding of motor spring  26 . 
     Drum  20  is provided, at its periphery, with a toothing  20   a  intended to drive the gear train which has also not been shown in the drawing. 
     The mechanism according to the invention includes a setting wheel  29 , a differential gear  30  mounted so as to pivot between bottom-plate  10  and differential bar  14 , an intermediate wheel  32  and an indicator wheel  34  (FIG.  3 ). 
     More precisely, differential gear  30  includes an arbor  36 , a planetary wheel carrier  38  on which are mounted a planetary wheel  40 , a first input wheel  42  and a second input wheel  44 , two assembling rings  46  and  48  and a screw  50 . 
     Arbor  36  is formed of a steel stem one end of which has a toothing forming a pinion  36   a.  It includes two intermediate portions  36   b  and  36   c,  and a pivot  36   d  occupying the other end and engaged so as to move in rotation in a jewel  52  driven into bar  14 . It can rotate about an axis perpendicular to the plane of bottom-plate  10 . 
     Planetary wheel carrier  38  is formed of a metal part provided with a central cylindrical hole  38   a.  It is driven onto arbor  36 , which is engaged via its portion  36   c  in hole  38   a.  It includes, in its median part, a cylindrical protuberance  38   b  extending radially and provided with a threaded hole  38   c  intended to accommodate screw  50 . It further includes two cylindrical portions  38   d  and  38   e  which are coaxial to hole  38   a.    
     Protuberance  38   b  carries planetary wheel  40  which can rotate freely about an axis perpendicular to the rotational axis of arbor  36 . This planetary wheel  40  is provided with a conical toothing  40   a  the function of which will be specified hereinafter. 
     The two cylindrical portions  38   d  and  38   e  carry, respectively, wheels  42  and  44 , adjusted so as to be able to rotate freely therein. These wheels are disposed between protuberance  38   b  and respectively rings  46  and  48 . 
     Wheels  42  and  44  are each formed by a plate, identified by the letter a and the periphery of which carries a toothing b, and a pinion c provided with a conical toothing d. Wheel  42  meshes, via its toothing  42   b,  with the toothing of barrel  20   a.  Wheel  44  meshes, via its toothing  44   b,  with setting wheel  29 , which meshes with toothing  28   a  of ratchet wheel  28  (FIG.  2 ). Finally, toothings  42   d  of pinion  42   c  and  44   d  of pinion  44   c  are meshed with toothing  40   a  of planetary wheel  40  (FIG.  3 ). 
     It is to be noted that the gearing ratios between toothing  20   a  of the barrel drum and first input wheel  42 , on the one hand, and that of ratchet wheel  28  and second input wheel  44 , on the other hand, must be equal, so that, for a same angle covered by the barrel and the ratchet wheel, wheels  42  and  44  cover equal angles. 
     Ring  46  is formed of a flange  46   a  and a sleeve  46   b.  It is engaged on portion  36   b  of arbor  36  and abuts against pinion  36   a  via the end of sleeve  46   b.  This latter is engaged, via its outer surface, in a jewel  54  driven into bottom-plate  10 . Flange  46   a  forms a stop for planetary wheel carrier  38 . 
     Ring  48 , formed of a round plate pierced at its center, is forcibly driven onto the end of portion  36   c  of arbor  36 . With ring  46 , it assures the assembly of the set of parts forming differential gear  30 . 
     Intermediate wheel  32  is mounted so as to pivot on bottom-plate  10  by means of a pivot-shank  56 . It essentially includes a pinion  58 , a wheel  60 , a cam  62  and a connecting spring  64 . 
     More precisely, pinion  58  includes a sleeve  58   a  mounted so as to pivot on pivot-shank  56 . It is provided, at one of its ends, with a toothing  58   b.  Sleeve  58   a  is formed of two cylindrical portions  58   c  and  58   d,  of different external diameters. 
     As can be seen more particularly in FIG. 1, wheel  60  is formed of a plate the periphery of which is provided with a toothing  60   a  which meshes with toothing  36   a  of pinion  36 . It is mounted so as to rotate freely on portion  58   c.  The plate is provided with an oblong hole of radial orientation  60   c  the function of which will be specified hereinafter. 
     Cam  62  has a shape close to that of a chronograph heart piece, with a concave portion  62   a  and two contiguous raised portions which have not been referenced. It is driven onto cylindrical portion  58   d  and holds wheel  60  axially. 
     Spring  64  is formed of a resilient strip in the shape of an arc of a circle spanning an angle of approximately 270°. It is secured, by one of its ends and in a known manner to the plate of wheel  60 . The other end forms a protuberance  64   a  disposed such that it abuts against cam  62 , in its concave portion  62   a.  A finger  64   b,  disposed in the median portion of protuberance  64   a,  is engaged in hole  60   c.    
     Indicator wheel  34  is mounted so as to pivot on a pin  66  driven into bottom-plate  10 . It includes a plate  34   a  provided, at its periphery, with a toothing  34   b  meshed with toothing  58   b  of pinion  58 , and a pipe  34   c  extending beyond the bottom-plate and intended to carry a power reserve indicator hand, which is not shown in the drawing. 
     Plate  34   a  includes a cut out portion  34   d  in the shape of an annular sector spanning an angle of approximately 150°. A pin  78 , driven into bottom-plate  10 , is engaged in cut out portion  34   d  and acts as a stop for wheel  34 . 
     In a watch movement fitted with a mechanism as described hereinbefore, the motor spring  26 , when being let down, drives in rotation and in a conventional manner barrel drum  20  whose toothing  20   a  meshes with the first wheel of the gear train. This latter is connected to an escapement, which maintains the movement of a sprung balance. 
     If drum  20  rotates during the letting down of motor spring  26 , arbor  24  is, conversely, stationary. Wheel  42  of differential gear  30  is thus driven in rotation, while wheel  44  remains still. Pinion  42   c,  which rotates with wheel  42 , meshes with planetary wheel  40 . 
     Since wheel  44 , and with it pinion  44   c,  is stationary, planetary wheel  40  can only rotate by driving planetary wheel carrier  38 . This latter, which carries pinion  36   a,  causes intermediate wheel  32  to rotate, which in turn drives indicator wheel  34 . 
     Thus, progressively as motor spring  26  is let down, indicator wheel  34  moves facing a scale disposed on the watch dial, until it reaches the lower normal operating limit. Below this limit, the movement can still function for a certain time. However, its precision is liable to decrease, because of the loss of amplitude of the balance. The power reserve indicator thus indicates that it has run down and indicator wheel  34  is immobilized, the end of cut out portion  34   d  abutting against pin  78 . 
     If the user of the watch still does not wind up motor spring  26 , the latter continues to be let down causing the watch movement to operate. Differential gear  30  thus continues to rotate and, with it, wheel  60 . Since pinion  58  meshes with indicator wheel  34 , it is blocked. Wheel  60  thus has a relative movement with respect to pinion  58 . This movement is made possible because wheel  60  is connected to pinion  58  by connecting spring  64 , which is driven by wheel  60 . Protuberance  64   a  slides on cam  62  of concave portion  62   a  towards one of the raised portions. The deformation of spring  64  occurs only radially, because of finger  64   b  engaged in hole  60   c.  The letting down of motor spring  26  can occur until the torque applied to the balance is insufficient to drive its movement, so that the watch stops. 
     When the user of the watch winds motor spring  26  by turning the winding crown, he drives ratchet wheel  28  and, via setting wheel  29 , input wheel  44 . This latter causes planetary wheel carrier  38  to rotate in the opposite direction to that which is generated by the movement of drum  20 . As a result, pinion  36   a  causes wheel  60  to rotate such that protuberance  64   a  slides, in the opposite direction, on cam  62  until it returns to concave portion  62   a.  It is then that pinion  58  is again driven and, with it, indicator wheel  34 , so that the indicator moves facing the scale on the dial. This indicator reaches the upper end of the scale when motor spring  26  is completely wound. 
     In practice, it is difficult to make the maximum winding position of the motor spring coincide exactly with the end position of the indicator corresponding to the largest power reserve. This is why, in this position too, the indicator wheel can be stopped by pin  78 . Here too, spring  64  is involved, protuberance  64   a  sliding on the other flank of cam  62 . 
     The mechanism described relies on a gear train whose wheels must have, between them, sufficient circumferential play to avoid any jamming during operation. Because of this circumferential play, the position of the indicator does not correspond to the same degree of winding of the motor spring, depending on whether the latter is in the process of being wound or let down. As a result, at the beginning of the winding operation by the user, the latter only sees the indicator move after the set of gears has meshed, which gives him the impression that the mechanism is not operating as it should. The device shown in FIG. 4 allows this fault to be removed. 
     More precisely, the mechanism according to the invention includes, advantageously, a complementary resilient member  66  intended to generate a torque on the gear train leading to the power reserve indicator hand, in order to eliminate this gear circumferential play. 
     Member  66  is formed of a barrel including a drum  68 , a cover  70 , an arbor  72  and a spring  74 . It is fixed to a pivot-shank  76  secured to bottom-plate  10 . 
     Drum  68  and cover  70  together form a housing in which spring  74  is located. This latter is connected, in a conventional manner, by one of its ends to arbor  72  and by the other to drum  68 . It is arranged so that is wound and let down at the same time as motor spring  26 . 
     Drum  68  is provided with a toothing  68   a  at its periphery, meshed with toothing  60   a  of wheel  60 . Arbor  72  is rigidly mounted on pivot-shank  76 , so that it cannot rotate. 
     In a variant which has not been shown, it would also be possible for toothing  68   a  to be meshed with indicator wheel  34  rather than with that of wheel  32 . This is not, however, indispensable, since the circumferential play between pinion  58  of intermediate wheel  32  and wheel  34  is extremely small with respect to the circumferential play observed at differential gear  30 . 
     With such a configuration, it should be noted that the torque generated by spring  74  must be less than the torque necessary for protuberance  64   a  to leave concave portion  62   a.  If this were not the case, it would result in a shift of the indicator corresponding to the relative movement of pinion  58  and wheel  60  via the effect of the torque of spring  74 , which would be contrary to the desired objective. 
     Member  66 , as described, exerts permanent torque on the gear train comprised between the two input wheels  42  and  44  of differential gear  30  and intermediate wheel  32 . 
     The mechanism according to the invention is particularly well suited to manually wound watches, in particular to so-called 8 day watches, i.e. those in which the motor spring allows operating autonomy of more than a week. It is also applicable to automatic watches provided with a stopping system which blocks the winding of the motor spring when it is completely wound. 
     This mechanism may be subject to numerous variants without thereby departing from the scope of the invention. Thus, the differential gear could be plane rather than spherical. One could also envisage applying the mechanism to a watch movement including two barrels. In such case, the input wheels of the differential gear can be connected kinematically to the ratchet wheel of one of the barrels and to the drum of the other or of the same barrel.