EP3486735B1 - Second reset clock mechanism with snail cam - Google Patents

Description

Technical area

The invention relates to the field of watchmaking. It relates, more precisely, to a horological mechanism for resetting the seconds to zero as well as a watch equipped with such a mechanism.

Technological background

• dans la plupart des montres à chronographe,
• et dans certaines montres pourvues d'une aiguille trotteuse (également appelée aiguille des secondes, ou plus simplement trotteuse) et dont le réglage de l'heure est accompagné d'une remise à zéro automatique de la trotteuse.

We can find a mechanism for resetting the second:

• in most chronograph watches,
• and in certain watches provided with a second hand (also called a seconds hand, or more simply a second hand) and whose time adjustment is accompanied by an automatic reset of the second hand.

• une came solidaire en rotation de l'arbre des secondes et dont un bord périphérique forme un chemin de came ;
• un marteau portant un suiveur de came, ce marteau étant monté en rotation autour d'un axe de marteau entre une position débrayée dans laquelle le suiveur de came est écarté du chemin de came, et une position embrayée dans laquelle le suiveur de came est en appui sur le chemin de came pour produire un couple moteur sur l'arbre des secondes.

Conventionally, such a mechanism comprises (in addition to the second hand and its seconds shaft):

• a cam integral in rotation with the seconds shaft and of which a peripheral edge forms a cam track;
• a hammer carrying a cam follower, this hammer being mounted in rotation about a hammer axis between a disengaged position in which the cam follower is moved away from the cam track, and an engaged position in which the cam follower is in pressure on the cam track to produce motor torque on the seconds shaft.

The cam usually has a heart shape, which is why it is referred to simply as "heart" as it appears in the reference manual for IT. Reymondin et al, “Theory of watchmaking”, Federation of Technical Schools, 2015 edition, p.238 .

In chronographs, the hammer is a complex part provided with several cam followers which strike several simultaneously. Respective cams, integral with the hour hand, the minute hand, the seconds hand (and, more occasionally, a tenth hand).

In watches with automatic reset of the second hand, such as that described in the European patent EP2224294 (Glasshütte ) the hammer is simpler in shape but the principle is the same.

In all cases, the cam follower is usually formed by one end of the hammer in the shape of a horse shoe, which comes, at the end of its stroke (angular or linear), to rest against a double boss formed on the heart to maintain it in a stable position corresponding to the reset of the second hand.

This type of mechanism, which is very widespread, however suffers from several drawbacks.

First, the position of the second hand when resetting is usually quite random and lacks precision. This is particularly detrimental in the case of a jumping needle, which is supposed to be at every second in a very precise angular position (each angular position being spaced from the next by 6 °).

Second, taking into account the respective geometry of the core and of the hammer, the friction forces at their interface are not constant. This results in non-uniform wear of these parts, which is detrimental in the long term to the reliability of the mechanism.

Third, in certain angular positions of the heart, the hammer rubs against it by a sharp edge, as shown in FIG.11.29 of the aforementioned manual, which increases the stress concentration, wear and mechanical fatigue of these parts.

Fourth, the momentum acquired by the heart during its rotation means that it is not immediately blocked at the end of its stroke by the support of the end of the hammer in the seconds shaft, but remains, before s 'immobilize, animated by damped oscillations which adversely affect the perception of precision expected by an informed user.

Fifth, the complexity of the known mechanisms makes them heavy and tedious to manufacture.

A first objective is to provide a second reset mechanism which provides a precise position of the second hand, exactly opposite a predetermined graduation of the dial (typically a twelve hour index).

A second objective with greater reliability, and therefore greater longevity.

A third objective is to provide a mechanism for resetting the second of simpler architecture (and therefore less bulky, lighter and easier to manufacture) than the known mechanisms.

Summary of the invention

• un arbre des secondes ;
• une aiguille trotteuse solidaire en rotation de l'arbre des secondes ;
• une came solidaire en rotation de l'arbre des secondes et dont un bord périphérique forme un chemin de came ;
• un marteau pourvu d'un suiveur de came, ce marteau étant monté en rotation autour d'un axe de marteau entre une position débrayée dans laquelle le suiveur de came est écarté du chemin de came, et une position embrayée dans laquelle le suiveur de came est en appui sur le chemin de came pour produire un couple moteur sur l'arbre des secondes ; ce mécanisme étant remarquable :
• en ce que la came se présente sous forme d'un colimaçon, le chemin de came s'étendant en spirale autour de l'arbre des secondes depuis une extrémité interne jusqu'à une extrémité externe reliées entre elles par une surface de butée qui s'étend sensiblement radialement par rapport à l'arbre des secondes et contre laquelle vient buter le suiveur de came dans une position angulaire de fin de course de l'aiguille trotteuse ;
• en ce qu'il comprend un système à cliquet anti-retour comprenant une roue dentée montée sur l'arbre des secondes, et un cliquet porté par la came et qui attaque la roue dentée.

To achieve all or part of the aforementioned objectives, it is proposed, first of all, a horological mechanism for resetting the second to zero, which comprises:

• a seconds tree;
• a second hand rotationally integral with the seconds shaft;
• a cam integral in rotation with the seconds shaft and of which a peripheral edge forms a cam track;
• a hammer provided with a cam follower, this hammer being mounted in rotation about a hammer axis between a disengaged position in which the cam follower is moved away from the cam track, and an engaged position in which the cam follower is resting on the cam track to produce a driving torque on the seconds shaft; this mechanism being remarkable:
• in that the cam is in the form of a spiral staircase, the cam track extending spirally around the seconds shaft from an inner end to an outer end interconnected by a stop surface which s 'extends substantially radially with respect to the seconds shaft and against which the cam follower abuts in an angular end-of-travel position of the second hand;
• in that it comprises a non-return pawl system comprising a toothed wheel mounted on the seconds shaft, and a pawl carried by the cam and which attacks the toothed wheel.

Thanks to this architecture, the mechanism remains efficient while being quite simple, light and compact. When resetting, the seconds hand can find a precise position next to a graduation.

• le mécanisme peut comprendre un ressort de marteau pourvu d'une tête fixe et d'une lame élastique qui sollicite le marteau vers sa position embrayée.
• le marteau peut porter un pion primaire en saillie, contre lequel la lame du ressort est en appui permanent.
• le mécanisme peut comprendre un actionneur monté mobile entre une position de retenue dans laquelle il place le marteau dans sa position débrayée, et une position de libération dans laquelle il permet au marteau d'occuper sa position embrayée.
• le marteau peut porter un pion secondaire en saillie, contre lequel un épaulement formé sur l'actionneur est en appui en position de retenue de celui-ci.
• le mécanisme peut comprendre un système à cliquet anti-retour qui n'autorise la rotation de la came que dans un sens.
• le système à cliquet peut comprendre une roue dentée montée de manière coaxiale à l'arbre des secondes, et un cliquet porté par la came et qui attaque la roue dentée.
• l'axe de marteau peut être pourvu d'un excentrique dont la rotation fait débattre le marteau en ajustant la position angulaire de fin de course de l'aiguille trotteuse.

Various additional features can be provided, alone or in combination. So, for example:

• the mechanism may include a hammer spring provided with a fixed head and an elastic blade which urges the hammer towards its engaged position.
• the hammer can carry a projecting primary pin, against which the leaf of the spring is in permanent support.
• the mechanism may include an actuator mounted to move between a retaining position in which it places the hammer in its disengaged position, and a release position in which it allows the hammer to occupy its engaged position.
• the hammer can carry a projecting secondary pin against which a shoulder formed on the actuator bears in the retaining position thereof.
• the mechanism may include a non-return pawl system which allows rotation of the cam only in one direction.
• the ratchet system may include a toothed wheel mounted coaxially with the seconds shaft, and a pawl carried by the cam and which engages the toothed wheel.
• the hammer axis can be provided with an eccentric whose rotation causes the hammer to debate by adjusting the angular end-of-travel position of the second hand.

Secondly, a watch equipped with such a mechanism is proposed.

According to a preferred embodiment, the watch can be equipped with a dial provided with a graduation including a twelve hour index with which the hand is substantially aligned when it is in the angular end-of-travel position.

Brief description of the figures

• la FIG.1 est une vue en plan d'une montre équipée d'un mécanisme de remise à zéro de la seconde ;
• la FIG.2 est une vue de détail en perspective du mécanisme de remise à zéro de la seconde ;
• la FIG.3 est une vue de détail en coupe du mécanisme de remise à zéro, selon le plan de coupe III-III de la FIG.1 ;
• les FIG.4, FIG.5, FIG.6, FIG.7 et FIG.8 sont des vues de détail en plan, à plus grande échelle, du mécanisme de remise à zéro de la seconde et illustrant diverses phases de son fonctionnement.

Other objects and advantages of the invention will emerge in the light of the description of an embodiment, given below with reference to the appended drawings in which:

• the FIG. 1 is a plan view of a watch equipped with a second reset mechanism;
• the FIG. 2 is a detailed perspective view of the second reset mechanism;
• the FIG. 3 is a detailed sectional view of the reset mechanism, according to section III-III of the FIG. 1 ;
• the FIG. 4 , FIG. 5 , FIG. 6 , FIG. 7 and FIG. 8 are detailed plan views, on a larger scale, of the second reset mechanism and showing various phases of its operation.

Detailed description of the invention

On the FIG. 1 is shown a watch 1. This watch 1 comprises a middle part 2, which can be made of metal (eg steel), or a synthetic material (eg a composite material comprising a polymer matrix loaded with fibers, typically of carbon).

Watch 1 may include, for wearing on the wrist, a bracelet 3 (in phantom on the FIG. 1 ) which is fixed on the middle part 2 between horns 4 formed projecting thereon.

In the example illustrated, the caseband 2 has a circular outline, but this shape is not limiting. In particular, this contour could be rectangular (eg square).

The middle part 2 defines an interior space 5. The watch 1 comprises, to close this interior space 5, a crystal and a back (not shown), fixed on either side of the middle part 2.

Watch 1 is equipped with a dial 6 provided with a graduation 7. According to an embodiment illustrated in the drawings, and more particularly in FIG. FIG. 1 , the graduation 7 includes indexes 8 for each hour and intermediate indexes 9 for each minute. The intermediate minute markers 9 are preferably smaller than the hour markers 8.

In the example illustrated, the hour markers 8 are not figurative. However, alternatively, the hour markers 8 could be figurative, and be in the form of numerals (eg Roman, Arabic, Gothic, Greek). Be that as it may, the graduation includes an index 10 of the twelve hours, indicating midnight and noon for the hours, and indicating the zero of the minutes and seconds.

Watch 1 comprises a timepiece movement (hereinafter simply referred to as "movement"), which comprises a plate intended to be housed in the middle part 2 by being fixed to the latter, for example. by means of screws. The mainplate forms a support for various mechanisms such as gear train, escapement, transmission, timer, winder (non-exhaustive list).

The movement comprises a timer mobile 11, which includes an hour wheel and a minute wheel (not shown) as well as a seconds wheel 12. The timer mobile 11 is mounted to rotate about an axis A1.

The timer mobile 11 is driven in rotation by a motor device (not shown). It is preferable that the power source is a barrel spring associated with a spiral balance regulator. However, it would not be outside the scope of the present invention for the energy source to be a battery associated with a quartz regulator.

Watch 1 comprises an hour hand and a minute hand (not shown), respectively for displaying the hours and minutes.

• une position rentrée, illustrée en trait plein sur la FIG.1 et dans laquelle la couronne 14 est désaccouplée des aiguilles des heures et des minutes, qui demeurent entraînées en rotation par le mobile 11 de minuterie, et
• une position sortie, illustrée en pointillés sur la FIG.1 et dans laquelle la couronne 14 est accouplée aux aiguilles pour permettre la remise à l'heure.

The watch is equipped with a reset mechanism 13, which includes a winder coupled to the hour and minute hands. This winder comprises in particular a crown 14 accessible to the wearer on one side of the caseband 2. The crown 14 is movable between:

• a retracted position, shown in solid lines on the FIG. 1 and in which the crown 14 is uncoupled from the hour and minute hands, which remain rotated by the timing wheel set 11, and
• an extended position, shown in dotted lines on the FIG. 1 and in which the crown 14 is coupled to the hands to allow time reset.

As illustrated, watch 1 further comprises a seconds hand 15 (also called a “second hand” or more simply “second hand”), coupled to the seconds wheel 12.

The seconds hand 12 is driven in rotation, by the timing wheel set 11, around an axis A2 around which it makes a complete revolution in one minute. In the example illustrated, the seconds hand 15 is a large central second hand, its axis A2 of rotation coinciding with the central axis of dial 6.

The seconds hand 15 has a distal end 16 which runs, during the rotation of the hand 15, the dial 6 passing successively to the right of each index 8, 9 of the graduation 7.

The seconds hand 15 is mounted (by being driven for example) on a seconds shaft 17 which extends along the axis A2. As seen on the FIG. 3 , the seconds shaft 17 comprises an upper section 18, on which the seconds hand 15 is mounted, and a lower section 19.

On the seconds shaft 17 is mounted a pinion 20 which meshes with the seconds wheel 12. Specifically, as illustrated on FIG. 3 , the pinion 20 is mounted on the lower section 19 of the second shaft 17.

As seen on the FIG. 3 , and more particularly in the detail inset at the bottom left, the lower section 19 of the shaft 17 of the seconds is provided with one or more bead (s) 21 of larger diameter, on which (which) the pinion 20 is fitted. This results in a reduction in the interface between the seconds shaft 17 and the pinion 20.

In this way, the seconds shaft 17 and the pinion 20 are integral in rotation as long as the seconds shaft 17 is not subjected to any driving torque (or resistance) applied independently of the pinion 20.

From then on, on the other hand, that a driving torque (or resistance) exceeding a predetermined threshold is applied to the shaft 17 of the seconds independently of the pinion 20, the shaft 17 of the seconds can rotate freely relative to the pinion 20, which remains fixed because it engages the timer mobile 11. In this case, a slip occurs at the interface between the seconds shaft 17 and the pinion 20.

Watch 1 is equipped with a clock mechanism 22 for resetting the second to zero. By this mechanism 22, the second hand 15 is separated from the timer mobile 11 and reset to the right of the index 10 of the twelve hours (that is to say to zero) when a time reset is initiated by the wearer, in particular by pulling on the crown 14.

In addition to the seconds shaft 17 and the seconds hand 15 already mentioned, the second reset mechanism 22 comprises a cam 23 rotatably secured to the seconds shaft 17 and a peripheral edge of which forms a path 24. cam.

According to a preferred embodiment illustrated in the drawings, and in particular in the FIG. 3 , the cam 23 is an attached part mounted tight (typically by driving) on the shaft 17 of the seconds.

In the example shown on FIG. 3 , the cam 23 is fitted on the upper section 18 of the second shaft 17. Its height position is fixed by a collar 25 formed on the shaft 17 of the seconds at the junction between the upper section 18 and the lower section 19, and against which the cam 23 is wedged.

As we can clearly see on the FIG.4 to FIG.8 , the cam 23 is in the form of a spiral: the cam path 24 extends in a spiral around the axis A2 (that is to say around the shaft 17 of the seconds) from one end 26 internal (close to axis A2), to an external end 27 (remote from axis A2). The cam path 24 is smooth, without roughness.

The inner end 26 and the outer end 27 are interconnected by a stop surface 28 which extends substantially radially with respect to the seconds shaft. When seen from the front (that is to say along the axis A2), the contour of the cam 23 is thus similar to the contour of the shell of a marine cephalopod of the nautilus species.

Cam 23 is advantageously a metal part, e.g. in steel. It is preferably perforated, in order to be light and to have a low moment of inertia.

• une position débrayée (FIG.4, FIG.8) dans laquelle le suiveur 30 de came est écarté du chemin de came, et
• une position embrayée (FIG.5, FIG.6, FIG.7) dans laquelle le suiveur 30 de came est en appui sur le chemin 24 de came pour produire un couple moteur sur l'arbre 17 des secondes.

The second reset mechanism 22 further comprises a hammer 29 provided with a cam follower 30. This hammer 29 is rotatably mounted around a hammer axis A3 between:

• a disengaged position ( FIG. 4 , FIG. 8 ) in which the cam follower 30 is moved away from the cam track, and
• an engaged position ( FIG. 5 , FIG. 6 , FIG. 7 ) in which the cam follower 30 bears on the cam path 24 to produce a driving torque on the second shaft 17.

The cam follower 30 is eg. in the form of a lug which projects at a free end 31 of the hammer, at a distance from the axis A3 of the hammer. The cam follower 30 is advantageously made of a material with a low coefficient of friction, e.g. in a plastic material (in particular polytetrafluoroethylene, also known under the names PTFE and Teflon®), or in a precious stone (in particular in ruby). The cam follower 30 is advantageously rigidly fixed (from non-removable manner) on the hammer 29. Alternatively, the hammer 29 and the cam follower 30 can form a single piece element, formed from a single machined part.

In normal operation of watch 1, hammer 29 is in its disengaged position. In this case, the seconds hand 15 is integral, with the seconds shaft 17, of the pinion 20 which the seconds wheel 12 engages.

When a time reset is initiated by the user, typically by pulling on the crown 14, the hammer 29 is moved to its engaged position to drive in rotation, via the cam follower 30 resting on the path 24 of cam, the seconds shaft 17 (and with it the seconds hand 15) - independently of the pinion 20 - until the seconds hand 15 is brought into an angular end-of-travel position where it is located substantially at the right of index 10 of the twelve hours (reset).

The end-of-travel angular position of the seconds hand 15 (zero position) is determined by the abutment of the cam follower 30 against the abutment surface 28. In this position, shown on FIG. 7 (and more particularly in the detail medallion at the bottom middle), the rotation of the cam 23 (and therefore of the seconds shaft 17 and of the seconds hand 15) is stopped.

The support of the cam follower 30 on the cam path 24 is provided by a lever effect exerted on the hammer 29, which tends to cause it to pivot (here in the clockwise direction) around the axis A3 of the hammer.

For this purpose, the mechanism 22 comprises a hammer spring 32. This hammer spring 32 is provided with a fixed head 33 and an elastic blade 34 which urges the hammer 29 towards its engaged position.

According to one embodiment, the hammer 29 carries a protruding primary pin 35, against which the leaf 34 of the spring bears permanently. The leverage exerted on the hammer 29 by the elastic blade 34 of the hammer spring 32 via the primary pin 35 is illustrated by the black arrow at the top on the FIG. 5 .

The induced rotation of hammer 29 is indicated by the black arrow in the middle of the FIG. 5 . This rotation brings the cam follower 30 into contact with the cam track 24. Since the cam track 24 is smooth, and the cam follower 30 has a low coefficient of friction, the latter can freely slide on the cam track 24.

As the leverage applied by the hammer spring 32 on the hammer 29 continues, the cam follower 30 slides over the cam surface 24, exerting on it (and therefore on the cam 23) a non-concurrent force with the second axis A3, from which results a motor torque induced on the cam 23 (and therefore on the second shaft 17).

The cam 23, the hammer 29 and the hammer spring 32 are configured so that, whatever the angular position of the cam 23, the torque induced thereon by the cam follower 30 is always greater than the threshold beyond of which a slip occurs at the interface between the second shaft 17 and the pinion 20.

As a result, the seconds shaft 17, and with it the seconds hand 15, is driven in rotation around the axis A2, as illustrated by the black arrow at the bottom right of the figure. FIG. 5 , the cam follower 30 sliding on the cam surface 24 until it reaches the stop surface 28, which stops the rotation of the cam 23 (and therefore the seconds hand 15).

• une position de retenue dans laquelle l'actionneur 36 place le marteau 29 dans sa position débrayée (FIG.4, FIG.8), et
• une position de libération dans laquelle l'actionneur 36 permet au marteau 29 d'occuper sa position embrayée (FIG.5, FIG.6, FIG.7).

According to an embodiment illustrated in the drawings, the second reset mechanism 22 comprises an actuator 36 mounted to move between:

• a retaining position in which the actuator 36 places the hammer 29 in its disengaged position ( FIG. 4 , FIG. 8 ), and
• a release position in which the actuator 36 allows the hammer 29 to occupy its engaged position ( FIG. 5 , FIG. 6 , FIG. 7 ).

In the example illustrated, the actuator 36 is in the form of a rod mounted in translation (but it could be mounted in rotation).

The hammer 29 for its part carries a projecting secondary pin 37, against which a shoulder 38 formed on the actuator 36 bears in position. retention of it. This shoulder 38 is eg. defined by a claw 39 protruding from one end of the actuator 36.

The movement of the actuator 36 is controlled by the winder, and more precisely by the crown 14. Thus, in the retracted position of the crown 14, the latter places the actuator 36 in the retaining position, which maintains the hammer 29 in the disengaged position and allows rotation of the seconds shaft 17 (and with it of the seconds hand 15) induced by the timer mobile 11.

On the other hand, in the extended position of the crown 14, the latter places the actuator 36 in the release position (horizontal black arrow, top left on the FIG. 5 ), which allows the hammer spring 32 to exert its leverage on the hammer 29 to apply the cam follower 30 to the cam track 24.

According to a preferred embodiment illustrated in particular on the FIG. 4 , and more particularly in the detail inset at the bottom left, the second reset mechanism 22 comprises a non-return pawl system 40 which only allows the rotation of the cam 23 in one direction (the direction time in the example shown).

The ratchet system 40 comprises a toothed wheel 41 mounted coaxially with the seconds shaft 17, and a pawl 42 carried by the cam 23 and which engages the toothed wheel 41.

More precisely, the toothed wheel 41 is integral in rotation with the pinion 20, if necessary (as illustrated in FIG. 2 ) via a doll 43 driven on the pinion 20. According to one embodiment, the doll 43 is integrated into a transmission wheel 44 meshing eg. a ringing mobile (not shown).

According to a preferred embodiment, the toothed wheel 41 has Breguet type teeth, that is to say that the teeth are triangular and asymmetrical. In the example illustrated, the toothed wheel 41 comprises sixty teeth, which each index, via the pawl 42, a determined position of the seconds hand 15 (which is then called "jumping") corresponding to each of the sixty seconds contained in a minute. In other words, the positions of the second hand are separated from each other by an angle of 6 °.

In the example shown on FIG. 4 , the pawl 42 is biased towards the toothed wheel 41 by means of a spring blade 45 also carried by the cam 23.

The operation of the second reset mechanism 22 is as follows.

In the retracted position of the crown 14, the latter maintains the actuator 36 in the retained position, which maintains the hammer 29 (and the cam follower 30) in the disengaged position, away from the cam 23.

The seconds shaft 17 (and with it the seconds hand 15) is integral in rotation with the pinion 20, which, meshed by the timing wheel set 11, drives it in rotation around the axis A2. Under these conditions, the seconds hand 15 plays its role as a second hand and provides the wearer with an indication of the seconds elapsed in the current minute.

In the extended position of the crown 14, the latter places the actuator 36 in the release position, which allows the hammer 29 to move, under the leverage provided by the hammer spring 32, towards its engaged position, wherein the cam follower 30 is slidingly bearing against the cam path 24.

The sliding support of the cam follower 30 against the cam track 24 induces, as explained above, the rotation of the cam 23, and with it of the second shaft 17 (which slides at its interface with the pinion 20 , which remains fixed in rotation around the axis A2 while remaining meshed by the timer mobile 11).

The rotation of the cam 23 (clockwise) and of the seconds hand 15, which is integral with it, continues until the cam follower 30 comes to rest against the stop surface 28, this which stops the rotation of the cam 23 (and therefore of the shaft 17 of the seconds and of the hand 15 of the seconds). The 15 seconds hand is then in its end position. of travel, and is located approximately to the right of the index 10 of the twelve hours on the graduation 7 of the dial 6. The pawl 42 is positioned between two successive teeth of the toothed wheel 41, and thus blocks any rebound of the hand when it reaches the end of its travel, for the benefit of the precision of the reset.

The 15 seconds hand, at the end of its travel, may not be exactly in line with the 10 twelve hour index.

To allow fine adjustment of the end position of the 15 seconds hand, and to ensure that in this position the 15 seconds hand is located exactly to the right of the twelve hour index, axis A3 of hammer is defined by a shaft 46 provided with an eccentric 47.

The rotation of the eccentric 47 causes the hammer 29 to debate by adjusting the angular end position of the second hand 15 (as suggested by the various positions sketched in dotted lines on the FIG. 8 ).

The rotation of the eccentric 47 is e.g. performed by manual action, typically by means of a screwdriver. For this purpose, as illustrated in particular on the FIG. 7 , one end of the eccentric 47 is shaped as a recess 48 (eg, a slot) for a screwdriver. It is illustrated, in the lower left detail medallion on the FIG. 7 , the rotation of the eccentric (double black arrow), and its effect (dotted lines) on the positioning of the hammer 29.

As soon as the crown 14 is returned to its retracted position, the actuator 37 is returned to its retaining position ( FIG. 8 ). The movement of the actuator 37 exerts a traction on the secondary pin 37 and drives the hammer 29 in rotation against the return force of the spring 32. The rotation of the hammer causes the cam follower 30 to slide along. the abutment surface 28, then release the cam follower 30 from the cam 23. Consequently, no motor or resistive torque is applied on the second shaft 17, including the frictional forces at the interface between the (S) bead (s) 21 and the pinion 20 re-couples it in rotation to the latter.

It follows that the rotation of the pinion 20, meshed by the timer mobile 11 (and more precisely by the seconds wheel 12) rotates the seconds shaft 17, and with it the seconds hand 15 in the movement. ordinary cyclic.

The seconds reset mechanism 22 which has just been described has the following advantages.

First, compared to known core mechanisms, the present mechanism 22 is of simpler architecture. Hammer 29, in particular, is less complex in shape. The absence of a heel, and the presence of the cam follower 30 which, at the end of the stroke, simply abuts against the abutment surface 28, prevents rebounds of the seconds hand 15, to the benefit of the reliability of the mechanism 22 .

As already mentioned, rebounds are also prevented by the ratchet system 40, which ensures the unidirectional nature of the rotation of the second hand 15 when it is reset to zero.

Being simpler, this mechanism 22 is light, compact, and easy to manufacture.

This results in particular in greater reliability, and consequently in greater longevity of the mechanism 22 (and therefore of the watch 1).

Claims (10)

1. Timepiece mechanism (22) for returning the seconds hand to zero, which includes:

   - a seconds arbor (17);

   - a seconds hand (15) integral in rotation with the seconds arbor

   - a cam (23) integral in rotation with the seconds arbor (17) and a peripheral edge of which forms a cam path (24);

   - a hammer (29) provided with a cam follower (30), said hammer (29) being rotatably mounted about a hammer axis (A3) between a disengaged position in which the cam follower (30) is removed from the cam path (24), and an engaged position in which the cam follower (30) presses on the cam path (24) to produce a drive torque on the seconds arbor (17);

   said mechanism (22) being characterized:

   - in that the cam (23) takes the form of a snail, the cam path (24) extending in a spiral around the seconds arbor (17) from an inner end (26) to an outer end (27) which are connected to each other by a stop surface (28) which extends substantially radially relative to the seconds arbor (17) and against which the cam follower (30) comes into abutment in an angular end-of-travel position of the seconds hand (15);

   - in that it includes a retaining ratchet system comprising a toothed wheel (41) mounted on the seconds arbor (17), and a click (42) carried by the cam and which engages with the toothed wheel (41).
2. Mechanism (22) according to claim 1, characterized in that the mechanism includes a hammer spring (32) provided with a fixed head (33) and an elastic strip (34) which draws the hammer (32) towards its engaged position.
3. Mechanism (22) according to claim 2, characterized in that the hammer (29) carries a primary protruding post (35) against which the strip (34) of the spring permanently presses.
4. Mechanism (22) according to claim 2 or claim 3, characterized in that the mechanism includes an actuator (36) movably mounted between a retaining position in which it places the hammer (29) in its disengaged position, and a release position in which it allows the hammer (29) to occupy its engaged position.
5. Mechanism (22) according to claim 4, characterized in that the hammer (29) carries a secondary projecting post (37), against which a shoulder (38) formed on the actuator (36) presses in the retaining position of said actuator.
6. Mechanism (22) according to any of the preceding claims, characterized in that the toothed wheel (41) has a Breguet type toothing.
7. Mechanism (22) according to claim 6, characterized in that the toothed wheel (41) has sixty teeth.
8. Mechanism (22) according to any of the preceding claims, characterized in that the hammer axis (A3) is formed by an arbor (46) provided with an eccentric (47) whose rotation causes the hammer (29) to move by adjusting the angular end of travel position of the seconds hand (15).
9. Watch (1) provided with a timepiece mechanism (22) for returning the seconds hand to zero according to any of the preceding claims.
10. Watch (1) according to claim 9, provided with a dial (6) having a graduation (7) that includes a twelve o'clock symbol (10) with which the hand (15) is substantially aligned when it is in the angular end of travel position.

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