Patent Publication Number: US-6712500-B2

Title: Escapement device for timepiece

Description:
BACKGROUND OF THE INVENTION 
     The present invention concerns an escapement device for a timepiece. 
     For a timepiece and particularly a mechanical timepiece, the escapement device constitutes a master part which, on one hand, has to deliver the power required to maintain the oscillatory motion of the mechanical oscillator, balance wheel, and hairspring, and on the other hand, must transmit the oscillation frequency of the oscillator to the gears driving the time display. 
     PRIOR ART 
     Thus, the prior art in devices of this type is considerable. The handbooks published under the titles “Echappements et moteurs pas à pas” (Escapements and step motors) and “Théorie d&#39;horlogerie” (Watch-making theory), ISBN 2-940025-10-X, both by the Swiss Federation of Technical Colleges, describe numerous escapement devices, and in particular those called “anchor”, “detent”, and “Graham” escapements. 
     The major drawbacks of these known devices are: 
     a poor efficiency; the best efficiency that can be obtained with these known devices is of the order of 30 to 40%, which limits the running time of the watch, 
     a limited working frequency; the efficiency of the known escapements drops off considerably when the oscillator frequency is raised to a perceptible degree, and moreover, anchor escapements develop a wear problem of the escapement wheel when the frequency is high, 
     difficulties of manufacture; for efficiencies of the order of 30 to 40%, the anchor escapements require a number of highly precise trimming operations. 
     SUMMARY OF THE INVENTION 
     It is a goal of the present invention, therefore, to propose an escapement device for a timepiece that is improved over known devices, that is, their known drawbacks have been reduced at least in part. 
     It is another goal of the invention to propose an escapement device that is insensitive to external impacts, and will not exhibit galloping effects. 
     It is yet another goal of the invention to propose a timepiece equipped with such an escapement device. 
     These goals are attained by an escapement device for timepieces as described in claim 1, as well as by a timepiece as described in claim 19. Particular embodiments or variants are described in the dependent claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other advantages of the invention will become apparent in the following detailed description, to be read while referring to the attached drawing comprising the figures where: 
     FIG. 1 presents a functional diagram of a mechanical watch, 
     FIG. 2 presents a first embodiment of an escapement device according to the invention, 
     FIG. 3 presents particulars of a blocking device in the escapement device of the preceding figure, 
     FIG. 4 presents a graph of the mechanical torque transmitted, 
     FIG. 5 presents a first embodiment of means to produce a variable torque, 
     FIG. 6 presents a graph of the magnetic torque transmitted, 
     FIG. 7 presents intermediate transmission means, 
     FIG. 8 presents the means of release, 
     FIG. 9 presents the means of power transmission, 
     FIG. 10 presents a graph of the resulting torque, 
     FIG. 11 presents a second embodiment of the means to produce a variable torque, 
     FIG. 12 presents a second embodiment of an escapement device according to the invention, 
     FIG. 13 presents particulars of the blocking device in the escapement device of FIG. 12, 
     FIG. 14 presents the means of release in the escapement device of FIG. 12, 
     FIG. 15 presents the means of power transmission of the escapement device of FIG. 12, 
     FIG. 16 presents another graph of the mechanical torque transmitted, and 
     FIG. 17 presents another graph of the magnetic torque transmitted. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In certain figures among those mentioned above, and described in detail herein-below, certain superimposed parts are represented as if they were transparent, which was done for a better understanding of their interactions. 
     FIG. 1 presents a functional diagram of a mechanical watch in which the mechanical energy that comes from a winding device, which is manual or automatic, is stored in a mainspring  1  so as to be distributed via a set of gears  2  to an escapement device  3  and to a display  4 . 
     The escapement device  3  has the purpose, on one hand to deliver the power required to sustain the oscillations of oscillator  5 , which in a general manner comprises a helical spring and an inertial mass, and on the other hand, to transmit the frequency given off by this oscillator to gears  2  in order to synchronize the time display with this frequency. 
     A good escapement device should not only have a good transmission efficiency between the power source and the oscillator but should also preserve the isochronism of the oscillator. To this end the inertias associated with the escapement device should be minimized and the power transfer between the escapement device and the oscillator should occur within a very short time while the velocity of the oscillator is largest. 
     FIG. 2 shows a first embodiment of an escapement device  3  according to the invention, comprising: a transmission wheel  30  driven by the set of gears  2  seen above, blocking means  31 , means for the generation of a magnetic torque  32 , intermediate means of power transmission  33 , unblocking means  34 , and power transmission means  35 . These different means will be described in greater detail hereinbelow. 
     FIG. 3 shows the transmission wheel  30  as well as the blocking means  31 . The transmission wheel  30  is set in rotation by the mainspring  1  via the gears  2 , and is driven by a mechanical torque of essentially constant value. The shaft  300  holding the transmission wheel  30  transmits the forward movement to the display device  4 . The blocking means  31  consist here of a shaped part or cam  310  mounted on the same shaft  333  as a pinion  330  that is part of the intermediate means of transmission shown in greater detail in FIG. 7, as well as of bolts  311  fastened to the transmission wheel  30  so as to protrude perpendicularly to the plane of said transmission wheel. The bolts  311  are regularly distributed over a perimeter of said transmission wheel. In the example of an embodiment presented, the transmission wheel  30  has ten bolts  311 , but depending on the requirements it could have a different number of bolts. 
     The shape and dimensions of the cam  310  as well as the diameter of the bolts  311  and of the perimeter along which they are inserted, are determined in such a way that, when the cam  310  which rotates together with the pinion  330  that is driven by the transmission wheel  30 , is turned with one or the other of its long sides  312  to the transmission wheel  30 , the transmission of torque can occur directly from the wheel  30  to the pinion  330 . To the contrary, when one of the short sides  313  arrives in front of a bolt  311 , blocking of this short side  313  of cam  310  on the bolt  311  occurs and the transmitted torque is interrupted. 
     FIG. 4 shows the mechanical torque transmitted to the shaft  333  that holds the pinion  330 , plotted as a function of the angle of rotation of said pinion. At first the curve shows a torque of constant value until the cam  310  arrives in the blocking position marked A l  in the figure, where the transmitted torque becomes zero. Means of unblocking which will be described below then allow the device to become unblocked so that once again the torque of constant value can be transmitted until the next blocking occurs, marked at A 2 , and so forth. 
     The blocking means  31  here described give rise to two blocking positions, A 1  and A 2 , per turn of the pinion  330 , but they could just as well be conceived so as to give rise to a different number of blocking positions. 
     FIG. 5 shows a preferential embodiment of means allowing a torque to be obtained that varies as a function of the angle of rotation of pinion  330 . In this embodiment these means  32  are of a magnetic type, comprising a stator  320  and a rotor  321  that is arranged inside of said stator. The stator  320  consists of a ring of soft ferromagnetic material having along its inner perimeter two cavities  322  that are diametrically opposite to each other. The rotor  321  consists of a permanent magnet of cylindrical shape having a diametrical magnetization represented by the arrow in the drawing. The rotor  321  is mounted on the same shaft  333  as the pinion  330  and the cam  310  that have been described previously. 
     When the rotor  321  is set in rotation, the cavities  322  give rise to a magnetic torque acting on said rotor that is an essentially sinusoidal function, as can be seen in FIG.  6 . When the rotor  321  is oriented so that its axis of magnetization is parallel to the axis C—C in FIG. 5 or perpendicular to the axis B—B containing the two cavities  322 , then the rotor  321  is in a stable equilibrium position, in which a slight angular displacement will tend to return the rotor toward this stable position, but when the same rotor is oriented so that its axis of magnetization is parallel to the axis B—B, it is in an unstable equilibrium position, which means that a slight angular displacement will tend to remove the rotor even further from this unstable position. The stable angular positions are marked S in the curve of FIG. 6, they correspond to a zero crossing of the curve with a negative slope of the torque, while the unstable angular positions are marked  1  in the same curve, and correspond to a zero crossing of the curve with a positive slope of the torque. 
     It should be noted here that the frequency of the curve representing the torque is twice that of rotation of the magnet or of pinion  330 , which is so because of the stator/rotor configuration described. With another configuration one could have a multiple other than two between these two frequencies. 
     The intermediate means of transmission  33  presented in FIG. 7 essentially comprise the pinion  330  already seen above, as well as a second transmission wheel  331  mounted on a shaft  339 . We recall that the shaft  333  holding the pinion  330  also holds the cam  310  as well as the rotor  321 . The intermediate means of transmission  33  allow the different torques coming into play in the device to be combined. 
     The release means  34  of FIG. 8 are of known construction. The release pallet  340  is integral with the oscillator (that is not presented in the figure), and oscillates about the shaft  341 . During its oscillatory motion in the counterclockwise direction, the tooth of pallet  340  encounters a tooth of the escapement wheel  342 , and imparts to it an impulse of torque in the clockwise direction. As the escapement wheel  342  is mounted on the same shaft  339  as the second transmission wheel  331  seen above, this impulse of torque is therefore transmitted from this transmission wheel  331  to the pinion  330 . By appropriate fixation of the escapement wheel  342  on the transmission wheel  331 , viz., in such a way that the impulse of torque be transmitted just after blocking of the pinion  330  by the blocking device described previously, the impulse of torque in a counterclockwise direction that is transmitted to the pinion  330  will release the cam  310  from its blocking position on the bolt  311 , allowing the transmission wheel  30  to perform part of a revolution until the next blocking occurs. The time display  4  has thus advanced by a time segment corresponding to one movement of pallet  340 . 
     FIG. 9 shows means  35  of power transmission to the oscillator which are of classical design, consisting of a transmission wheel  350  fixed on the same shaft  339  as the wheel  331  and the escapement wheel  342 , and of a shaped part  351  that is mounted on the shaft  341  seen above and attached to the balance wheel of the hairspring (not shown). When the wheel  350  turns clockwise as indicated, and one of its teeth encounters the short side  352  of the shaped part  351  that is moving more slowly counterclockwise, the wheel  350  will furnish kinetic energy to the part  351  or to the hairspring, thus allowing the oscillatory motion of the oscillator to be sustained. 
     As indicated, the release means  34  and the means  35  of power transmission are of known design, and are here described as examples for a realization; other devices performing the same functions may thus be foreseen as a replacement. 
     The resulting torque on pinion  330  which consists of the essentially constant torque transmitted by the wheel  30  and shown in FIG. 4, and of the variable torque transmitted by the magnetic stator/rotor group and shown in FIG. 6, is shown in FIG.  10 . 
     In the example shown for this first embodiment of an escapement device, this torque comprises two stable positions per turn of the pinion  330  which are marked S 1  and S 2  in the figure, and correspond to the two blocking positions in FIG.  4 . These two stable positions S 1  and S 2  are defined as previously by a zero crossing of the curve of torque with negative slope. The torque also comprises two unstable positions per turn of the pinion  330  which are marked I 1  and I 2  and correspond to the two unblocking positions in FIG.  4 . These two unstable positions I 1  and I 2  are defined as previously by a zero crossing of the curve of torque with positive slope. 
     One notices that the resulting torque is always positive, except in the blocking positions where it is negative. 
     In FIG. 11 a second way is shown of how to obtain a variable mechanical torque having two stable points and two unstable points per turn of the wheel. A cam  323  is fixed on the same shaft  333  as the pinion  330  seen above; this cam has two concave portions and two convex portions. A spring lever  324  pivoting around one of its ends rests via a small wheel  325  on the periphery of cam  323 . The resulting torque of this device is a variable function with two stable points while the small wheel  325  is aligned with the axis C—C, and two unstable points while it is aligned with the axis B—B. 
     It can thus be seen that several possibilities exist to obtain a variable mechanical torque having at least one stable point and one unstable point. 
     FIG. 10 shows the mechanical torque acting on the shaft  333  of pinion  330  in the absence of contact with the oscillator, plotted as a function of the angle of rotation of said pinion, now one can describe in parallel the functioning of the device as a function of time. 
     After a first rotation the device arrives in a blocking position as described with reference to FIG. 3, and corresponding to the point S 1  in FIG.  10 . The device remains in this position for a time T 1 . 
     When the pinion  330  receives the unblocking impulse, as described with reference to FIG. 8, it changes from position S 1  to position I 2  in FIG. 10, the transition being accomplished within a very short time called T 2  and being less than one thousandth of a second. This time must be as short as possible in order to cause minimum perturbation of the oscillator. 
     Starting with this position the resulting torque, which becomes positive, furnishes to the oscillator via the power transmission means described the energy that is required by the oscillator during a time T 3  which is of the order of a few thousandths of a second, lasting until the next blocking position S 2  is attained. 
     A mechanical oscillator generally has an oscillation frequency of a few hertz, typically 4 Hz. For this frequency the period T that corresponds to the sum T 1 +T 2 +T 3  is 250 ms. In view of the low values reported above for T 2  and T 3 , the value of T 1  will then be just a few milliseconds smaller than that of T. It follows that the device is in a blocking position during the largest part of time T. 
     While a timepiece equipped with an escapement device such as that described above would satisfy the requirements indicated, such an escapement device when built into a wristwatch could be subject to a galloping effect. 
     In fact, in a wrist watch not subject to perturbations from outside, the amplitude of balance wheel oscillation in the clockwise direction is of the order of +240° relative to the axis that passes through the centers of rotation, and of the order of −240° in the opposite direction. Under these conditions the escapement wheel  30  advances one step in the clockwise direction in each balance wheel oscillation. 
     During an impact having a component in the plane of rotation of the escapement device, additional energy is transmitted to the oscillator via the inertia of the balance wheel, the result being that the amplitude of oscillation of the balance wheel may increase to a value higher than 360°. Under these conditions the unblocking means  34  in an escapement device such as that presented in FIG. 2 provide more than one impulse per oscillation period, which provokes a fast advance of the watch here called galloping. 
     FIG. 12 presents another embodiment of an escapement device  3  according to the invention with which the drawback mentioned above can be avoided. This embodiment of the escapement device comprises as previously a transmission wheel  30  driven by the set of gears  2  (cf. FIG.  1 ), blocking means  31 , means for the generation of a magnetic torque  32 , intermediate transmission means  33 , unblocking means  34 , and power transmission means  35 , the description of these different means being given hereafter. 
     The blocking means  31  of the escapement device of FIG. 12 can be seen in FIG. 13, they consist of a toothed wheel  354  that cooperates with the pinion  330 . Here the teethed wheel  354  has eight teeth of asymmetric shape, is mounted on the same axle  300 , and pivots together with the transmission wheel  30  seen above. 
     In the position called rest position shown in FIG. 13, the end of tooth  332  of the pinion  330  rests against the straight flank of an asymmetric tooth of the wheel  354 . 
     When a torque is applied to the axis  300  of wheel  354  in the direction of the arrow, it exerts a force going through the center of rotation of shaft  333  of the pinion  330 . For this reason no torque is transmitted to the pinion, and this set of wheel and pinion remains blocked, a situation which persists until unblocking occurs by the unblocking means described below. 
     The unblocking means  34  of this embodiment can be seen in FIG.  14 . The release pallet  344  is integrated into the oscillator (not shown in the figure) and oscillates about the shaft  341 . During its oscillatory motion, the tooth  3441  of pallet  344  encounters either the tooth  3451  or the tooth  3452  of an intermediate part  345 , depending on whether the pallet  344  turns counterclockwise or clockwise. The oscillatory motion of the intermediate part  345  about the axis  3450  is limited by bolts  347  and  348 . The unblocking impulse coming from the balance wheel is transmitted to the pallet  346  that is mounted on the same axle  333  and pivots together with the pinion  330  seen above, which currently is blocked. This transmission of impulse actually occurs via the teeth  3454  and  3455  of the intermediate part  345  to one of the teeth,  3461  or  3462 , of the pallet  346 , and acts so as to unlock the set of wheel  300  and pinion  330  of FIG. 13, so that pinion  330  now can freely rotate. 
     FIG. 15 shows another embodiment of the power transmission means  35 ; these means function in a manner similar to those described with reference to FIG.  9 . 
     The means for generation of a magnetic torque  32  that varies in time are similar to those described with reference to FIG.  5 . 
     This embodiment of the escapement device according to FIG. 12 has the advantage over the embodiment of FIG. 2 that in the case of an impact, the amplitude of oscillation of the balance wheel can be limited by bolts  347  and  348 , which thus prevent a loss of synchronization between the movement of the balance wheel and the movement of the wheel  30 , and the gallop mentioned above. 
     FIG. 16 shows another graph of the torque transmitted by an escapement device. As before, this torque is superimposed on that produced by the magnet in order to obtain the one shown in FIG.  17 . 
     An escapement device intended to function according to these graphs comprises blocking means having two stable positions in each direction of the oscillatory motion, in other words, four stable positions per period, which is another way of avoiding the galloping mentioned above. 
     Other embodiments and variants than those described above can yet be envisaged, and more particularly, pinion  330  could be replaced by an anchor performing an oscillatory motion, the arms of the anchor fork bearing two opposing magnets. 
     Relative to the escapement devices of the prior art, an escapement device according to the invention and according to one or other of the embodiments described in addition offers several marked advantages: 
     since the diameters of the rotating parts of the device according to the invention are smaller than those of corresponding parts in known devices, the inertia of said rotating parts is distinctly lower; 
     the power required for unblocking is lower; moreover, this unblocking is generally not attended by a recoil motion as in known anchor escapements; 
     thanks to the torque varying according to a curve, which is sinusoidal in the embodiments described, a maximum of torque is available just behind the unblocking position, which implies that the maximum power is transmitted immediately after unblocking, that is, over a limited angle of oscillation of the oscillator, at the moment when this oscillator has its highest velocity; in this way the isochronism of the oscillator is maximally preserved; 
     the transmission wheels have classical profiles with transmission efficiencies of the order of 90%; 
     Since certain transmissions of motion occur via gear wheels, greasing is not required as often as with traditional transmissions. 
     An escapement device as described according to one or the other of its embodiments is readily built into a timepiece, and particularly into a wristwatch, when considering the small diameter of the components of said device.