Abstract:
The invention pertains to the field of high frequency watch movements. The invention relates to a timepiece including a movement that has a resonator of the type with a balance and balance spring and an escape system of the type with a wheel and Swiss lever. According to the invention, the balance oscillates at more than 36,000 vibrations per hour and the escape system is at least partially pierced to decrease the inertia thereof.

Description:
This application claims priority from European Patent Application No. 10155490.5 filed Mar. 4, 2010, the entire disclosure of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The invention relates to a timepiece whose chronometric performance is improved and, more specifically, whose mechanical movement is capable of operating at 72,000 vibrations per hour, i.e. at a frequency of 10 Hz. 
     BACKGROUND OF THE INVENTION 
     Fabricating movements that operate at 5 Hz so as to improve the precision of timepieces is known. However, it becomes very difficult to develop a mechanism capable of oscillating beyond this frequency because of the balance speeds generated and the profound alterations to be made. 
     Document EP 2 075 651 proposes making a movement operating at more than 5 Hz while observing a ratio between the number of escape wheel teeth and the frequency equal to 5. This Patent document thus discloses the necessity, for a 10 Hz movement, of using an escape wheel with fifty teeth while still keeping the same diameter. The fabrication of fifty teeth with the same diameter constitutes a significant constraint which makes implementation and development difficult with conventional gear trains. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to overcome all or part of the aforecited drawbacks by proposing a timepiece whose escape system allows an increase in the balance oscillation frequency by altering a limited number of parts of the movement and therefore improves the chronometric performance of the movement. 
     The invention therefore relates to a timepiece that includes a movement having a balance and balance spring type resonator and a wheel—Swiss lever escape system, characterized in that the balance oscillates at more than 36,000 vibrations per hour and in that the escape system is at least partially pierced, so as to decrease its inertia, and includes an escape wheel with less than 25 teeth. 
     Thus, by decreasing the inertia of the escape system, it is possible to conserve a “conventional” movement architecture, i.e., for example, an escape wheel with 20 teeth and/or a usual number of wheel sets even when the balance oscillates at 72,000 vibrations per hour. 
     In accordance with other advantageous features of the invention:
         the balance oscillates at 72,000 vibrations per hour;   the wheel of the escape system includes a main projecting face whose surface density is less than 0.7 mg.mm −2 ;   the wheel is pierced at the toothing and/or felloe thereof;   the pierced wheel forms substantially triangular frames each supporting one tooth, the base being formed by the inner diameter of the felloe and connecting the tooth associated therewith by two sides;   each frame is imbricated with the other two adjacent frames;   the first of the two sides of each frame is secant with the second side of the preceding frame and the second side is secant with the first side of the following frame;   the second side of the preceding frame joins the first side of the following frame substantially in the middle of the base of the frame.   each frame surrounds a substantially quadrilateral shaped recess and two substantially triangular piercings;   the wheel of the escape system includes twenty teeth;   the wheel is formed from monocrystalline silicon coated with silicon dioxide;   the Swiss lever of the escape system includes a main projecting face whose surface density is less than 1 mg.mm −2 ;   the Swiss lever is pierced forming a honeycomb type structure to preserve the mechanical resistance thereof;   the pallet-stones of the Swiss lever are formed of rubies;   the Swiss lever is formed from monocrystalline silicon coated with silicon dioxide;   at least one part of the escape system includes an outer coating to alter the tribology and/or mechanical features thereof;   the balance is of the variable inertia type;   the seconds wheel of the movement is mounted to complete one revolution in 30 seconds to simplify the gear train of said movement.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages will appear clearly from the following description, given by way of non-limiting indication, with reference to the annexed drawings, in which: 
         FIG. 1  is a face view of a timepiece according to the invention; 
         FIG. 2  is a perspective view of a resonator and an escape system according to the invention; 
         FIG. 3  is a top view of  FIG. 2 ; 
         FIG. 4  is a perspective view of an escape system according to the invention; 
         FIG. 5  is a top view of an escape wheel according to the invention; 
         FIG. 6  is a top view of a Swiss lever according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     As illustrated in  FIG. 1 , a timepiece generally referenced  1  can be seen. It includes a case  3  including a middle part  2  closed by a back cover (not shown) and a crystal  4  and which is intended to receive a mechanical movement  5  between said back cover and the dial  6  of timepiece  1 . As visible in  FIG. 1 , timepiece  1  includes several complications. 
     Thus, watch movement  5  is capable of displaying the current time (hour, minute, small seconds located at 9 o&#39;clock completing one revolution in 30 seconds and an indicator that indicates whether the small seconds is between 0 and 30 seconds or between 30 and 60 seconds, located at 12 o&#39;clock), but also a calendar (located at 6 o&#39;clock), a time zone (time located at 6 o&#39;clock), a 24 hour display of the current time (located at 3 o&#39;clock) and a chronograph (centre seconds completing one revolution of dial  6  in 30 seconds, and centre minutes completing one revolution of dial  6  in 60 minutes). 
     Advantageously, the chronograph and current time seconds are displayed by completing one revolution of the dial in 30 seconds so as to offer chronograph measurement precision of a tenth of a second. This precision is made possible owing to the high frequency of watch movement  5 . 
     Moreover, this type of seconds display, i.e. one complete rotation of the seconds wheel of movement  5  achieved in 30 seconds, also simplifies the gear train. Indeed, the ratio between the seconds wheel and the escape wheel is thus divided by two which avoids the addition of an extra wheel set. 
     Advantageously according to the invention, watch movement  5  is capable of withstanding a frequency of more than 5 Hz, and notably a frequency of 10 Hz. To achieve this result, according to the invention, movement  5  preferably includes an escape system  7  whose inertia is attenuated by decreasing the mass thereof. 
     In the example illustrated in  FIGS. 2 and 3 , it can be seen that movement  5  includes a resonator  9  of the type with a balance  8  and balance spring  10  and an escape system  7  of the type with a wheel  11  and Swiss lever  13 . These same  FIGS. 2 and 3  show that balance  8  is of the variable inertia type, i.e. the four inertia-blocks  40  visible at the periphery of the felloe can be moved individually to adapt the inertia of the balance and, eventually, adjust movement  5 . Balance  8  may, by way of example, be made of copper-beryllium alloy. 
     Balance spring  10  is preferably in a single piece with the collet  41 , which is fitted onto the balance staff  12 . In the example illustrated in  FIGS. 2 and 3 , the outer coil  42  of balance spring  10  is pinned up to the stud on a stationary part of movement  5  such as, for example, a bridge. As seen in  FIG. 3 , the inner coil  43  of balance spring  10  includes a Grossmann curve to compensate for the use of collet  41 . By way of example, balance spring  10  may be formed from monocrystalline silicon and coated with silicon dioxide. 
     In the usual manner, resonator  9  cooperates with escape system  7  via a plate mounted on balance staff  12 . Escape system  7 , seen more clearly in  FIGS. 4 to 6 , includes a Swiss lever  13  formed by a projecting main face (seen in  FIG. 6 ). Swiss lever  13  is mainly formed by a lever  14  connecting the fork  15  and the pallet arms  16 ,  17 . Fork  15  includes two horns  18 ,  19  facing each other underneath which a dart  20  is mounted for cooperating respectively with a pin fixed to said plate of balance staff  12  and the low part of said plate. 
     Lever  14  receives, between the two pallet arms  16 ,  17 , a shaft  21  intended for rotatably mounting Swiss lever  13  between a bridge and the bottom plate of movement  5 . Finally, a pallet stone  22 ,  23 , intended to enter into contact with escape wheel  11 , is mounted on each arm  16 ,  17 . Pallet stones  22 ,  23  may, by way of example, be formed of synthetic ruby. 
     Preferably, according to the invention, lever  14  and arms  16 ,  17  are pierced in order to reduce the inertia of escape system  7 . Preferably, said projecting face (seen in  FIG. 6 ) is pierced to obtain a surface density of less than 1 mg.mm −2  and, depending upon the material used, a surface density reduced to 0.18 mg.mm −2 . To achieve this latter value, Swiss lever  13  may, by way of example, be formed from monocrystalline silicon coated with silicon dioxide. 
     It is clear that, if the thickness of arms  16 ,  17  and/or the lever is 0.1 mm of silicon, the inertia of the unequipped Swiss lever  13  may be as low as 0.75 mg.mm 2  and up to 2.85 mg.mm 2  when Swiss lever  13  is entirely fitted out, i.e. notably with ruby pallet stones  22 ,  23 . 
     An additional coating may also be envisaged such as crystallised carbon in diamond-like-carbon (DLC) form at least on fork  15  so as to alter the tribology and/or mechanical features thereof. 
     Finally, in the example illustrated in  FIGS. 4 to 6 , the piercing of lever  14  and arms  16 ,  17  preferably forms a honeycomb type structure so as to preserve the mechanical resistance of Swiss lever  13  while very considerably reducing the mass thereof. 
     Escape system  7  further includes an escape wheel  11 , also formed by a projecting main face (seen in  FIG. 5 ). Wheel  11  is formed in a plate  25  to which a pinion  27  is added via an arbour  24 . Arbour  24  and pinion  27  may be integral with each other. As illustrated in  FIGS. 4 and 5 , pinion  27  includes eight symmetrical leaves  44  which gradually flare out as they get closer to plate  25  to make it easier to drive pinion  27  into wheel  11 . Pinion  27  and arbour  24  may, for example, be formed of a metal or metal alloy like steel. 
     Plate  25  includes a hub  26  connected by five arms  28  to felloe  29 , which includes twenty impulse teeth  30 . Of course, the number of arms  28  and/or teeth  30  may vary. However, advantageously according to the invention, watch movement  5  can operate perfectly at a high frequency, i.e. for example at 10 Hz, with an escape wheel comprising twenty teeth  30 . 
     According to the invention, felloe  29  and/or teeth  30  are pierced to decrease the inertia of escape system  7 . Preferably, the piercing of said projecting main face (seen in  FIG. 5 ) provides a surface density of less than 0.7 mg.mm −2  and, depending upon the material used, a surface density as low as 0.16 mg.mm −2 . To achieve this latter value, board  25  may, by way of example, be formed from monocrystalline silicon and coated with silicon dioxide. 
     It is thus clear that, if the thickness of board  25  is 0.12 mm, the inertia of escape wheel  11  may be as low as 1.59 mg.mm 2 . 
     An additional coating may also be envisaged, such as crystallised carbon in the form of diamond-like-carbon (DLC), at least for teeth  30  so as to alter the tribology and/or mechanical features thereof. 
     Recess  31  of teeth  30  is substantially triangular in the example illustrated in  FIG. 5 , however it is of course possible for the recess to have a different shape. 
     Felloe  29  is pierced with spaces  32  between teeth  30  which are amplified to form an acute angle α. Moreover, from each tooth  30  towards hub  26 , felloe  29  includes quadrilateral shaped recesses  33 , and between each recess  33 , substantially triangular piercings  34 . 
     As illustrated in dotted lines in  FIG. 5 , frame  35  carrying each tooth  30  is thus triangular, base  36  being formed by the inner diameter of felloe  29  and connecting the tooth  30  associated therewith via two substantially rectilinear sides  37 ,  38 . 
     In the example illustrated in  FIG. 5 , each frame  35  thus includes a recess  33  and two piercings  34 . Further, each frame  35  is imbricated with the other two adjacent frames  35 . Thus, each frame  35  includes a side  37  secant with the side  38  of the preceding frame and a side  38  secant with the side  37  of the following frame. Finally, the side  38  of the preceding frame joins the side  37  of the following frame substantially in the middle of base  36  of frame  35 . This architecture of board  25  decreases its mass significantly while maintaining its mechanical properties. 
     Consequently, advantageously according to the invention, because of the aforementioned adaptation of its escape system  7 , watch movement  5  is capable of withstanding a frequency of more than 5 Hz and notably a frequency of 10 Hz. 
     Of course, this invention is not limited to the illustrated example but is capable of various variants and alterations that will appear to those skilled in the art. In particular, each of the piercings  31 ,  32 ,  33 ,  34  made in plate  25  or in Swiss lever  13  can be shaped differently and/or distributed differently and/or not be a through piercing and/or not shaped depending upon the application. 
     Evidently the elementary surface of at least one element, for example  11 ,  13  could be projected in a non-identical thickness, i.e. for example, the thickness of board  25 , each arm  16 ,  17  or lever  14  could be variable or non identical to the others. 
     Further, the materials cited by way of example for each element may also be adapted in accordance with the application and/or if new or other materials are particularly well matched.