EP3032349B1 - Drive mechanism of a skipping member - Google Patents

Description

Field of the invention

The invention relates to the field of mechanical watchmaking. It relates, more particularly, to a mechanism for driving a jumping member in a timepiece comprising a drive wheel arranged to rotate at constant speed, an indicator of a unit of time, a jumping member integral with said indicator and coaxial with said drive wheel to which said jumping member is coupled by a spring, a cam arranged to control an anchor, said cam having a profile arranged to tilt the anchor according to an oscillating movement so as to release the member jumping once per unit time. The present invention also relates to a timepiece comprising such a mechanism for driving a jumping member.

Background of the invention

When the driving wheel makes one revolution per minute, the unit of time can be the second. The drive mechanism can then constitute a deadbeat seconds mechanism, arranged to release the jumping member once per second. A deadbeat seconds mechanism includes a deadbeat seconds indicator, usually a large hand in the center of the dial, which makes 1 jump per second. These mechanisms are extremely complicated to produce. However, they sometimes lack precision, the jumps taking place in some cases at 5/6 of a second. They are also very energy consuming.

Some of these mechanisms are powered by a second energy source, specific to the deadbeat seconds mechanism, in addition to the main energy source, necessary for the movement.

Other mechanisms are powered by the energy source of the movement, of the type described in the preamble. Such mechanisms are known to those skilled in the art and described for example in the patent CH 311 865 . In these mechanisms, the dead seconds cam comprises a large number of teeth (30), involving small angular steps, which makes the jumps very sensitive to imperfections in the dead seconds cam. Moreover, the same pallet of the deadbeat seconds anchor is used both to cooperate with the deadbeat seconds cam and the seconds wheel. The deadbeat seconds anchor blocks the jumping member under the effect of the force of the coupling spring and friction. These frictions absorb a relatively large power, so that the energy consumption by the deadbeat seconds mechanism is high.

The constant force device disclosed in the document EP 2 166 419 A1 , which does not include a deadbeat seconds mechanism by means of a jumping member, is on the other hand a timepiece comprising a timepiece movement provided with a going train powered by an energy source and an escapement wheel , comprising a mechanism for driving a jumping member comprising a drive wheel, a jumping member coaxial with said drive wheel to which said jumping member is coupled by a spring, a cam, integral with a drive wheel of cam, arranged to control an anchor, said cam having a profile arranged to tilt the anchor according to an oscillating movement so as to release the jumping member once per unit of time, the cam and the jumping member having axes of separate pivoting mechanisms, said drive mechanism further comprising an intermediate gear train kinematically linking the drive wheel to the cam, and the anchor having four separate arms, two of the four arms constituting feelers rs arranged to cooperate with the cam and the two other arms constituting escapement arms arranged to successively block and release once per unit time the body jumping alternately.

Summary of the invention

The object of the invention is in particular to overcome the various drawbacks of the known mechanisms.

More specifically, an object of the invention is to provide a mechanism for driving a jumping member, and in particular a dead seconds mechanism, reliable, making it possible to have precise jumps at each unit of time, and in particular at each second.

Another object of the invention is to provide a mechanism for driving a jumping member, and in particular a deadbeat seconds mechanism allowing regular jumps throughout its life.

The invention also aims to provide a mechanism for driving a jumping member, and in particular a mechanism for deadbeat seconds, allowing reduced energy consumption, authorizing the use of the same energy source as that of the movement.

To this end, the present invention relates to a timepiece as defined in appended claim 1.

Advantageously, the intermediate gear train may comprise an intermediate wheel set formed of an intermediate pinion arranged to cooperate with the drive wheel and of an intermediate wheel arranged to cooperate with a cam drive wheel integral with the cam.

Preferably, the intermediate gear train can be dimensioned so that the cam comprises less than thirty teeth, each tooth having a forward ramp, and performs more than one revolution per minute.

Advantageously, according to a variant embodiment, the unit of time is the second, the drive wheel being arranged to complete one revolution in 60 seconds, and the indicator being a dead second indicator, the cam can include ten teeth and be arranged to perform three rotations per minute, each tooth having a forward ramp breaking down into six steps.

Preferably, the front ramp of each tooth of the cam has, over the last three pitches of the tooth, a slope greater than the slope of the front ramp over the first three pitches of the tooth.

Advantageously, the four arms of the anchor can be arranged so as to form substantially an X, the feeler arm positioned to cooperate with the cam being arranged opposite with respect to the pivot point of the anchor to the arm escapement positioned to release the jumping organ.

Advantageously, said drive mechanism also comprises a mechanism for securing the relative position of the drive wheel and the jumping member.

Preferably, the mechanism for securing the relative position of the drive wheel and the jumping member may comprise first support means provided on the drive wheel and a first stop provided on the jumping member, said first support means being arranged to press against the first stop and limit the travel of the jumping member, when the drive wheel and the jumping member rotate in opposite directions.

Preferably, the mechanism for securing the relative position of the drive wheel and the jumping member may comprise second support means provided on the drive wheel and a second stop provided on the jumping member, said second support means being arranged to press against the second stop and limit the travel of the drive wheel when the jumping member is stopped.

Advantageously, said first and second bearing means may comprise a pin. In another variant, the first and second bearing means may comprise an eccentric.

Advantageously, the jumping member can be a wheel having at least two recessed zones separated by at least one arm, and the first and second support means are arranged on either side of the arm, said arm constituting at least one of the first and second abutments on which the first and second bearing means are capable of resting respectively.

The drive mechanism of a jumping member according to the invention makes it possible to have precise jumps at each unit of time while allowing reduced energy consumption. In addition, the jumps will be regular, throughout the life of the mechanism.

Advantageously, the drive wheel of the deadbeat seconds mechanism can be powered by the energy source of the movement.

Preferably, the drive wheel can be the second wheel of the going train.

Brief description of the drawings

• les figures 1 à 4 représentent une vue de dessus d'un mécanisme de seconde morte conforme à l'invention, l'ancre de seconde morte occupant différentes positions en fonction des pas d'une dent de la came de seconde morte,
• la figure 5 représente une vue du profil d'une dent de la came de seconde morte,
• la figure 6 est une vue en perspective d'une variante de réalisation du mécanisme de sécurisation de la position relative de la roue d'entrainement et de l'organe sautant, et
• la figure 7 est une vue en perspective de la fixation du ressort-spiral sur l'organe sautant.

Other characteristics and advantages of the invention will appear more clearly on reading the following description of a particular embodiment of the invention, given by way of simple illustrative and non-limiting example, and the appended figures, among which :

• THE figures 1 to 4 show a top view of a dead seconds mechanism in accordance with the invention, the dead seconds anchor occupying different positions depending on the pitches of a tooth of the dead seconds cam,
• there figure 5 represents a view of the profile of a tooth of the deadbeat seconds cam,
• there figure 6 is a perspective view of an alternative embodiment of the mechanism for securing the relative position of the drive wheel and the jumping member, and
• there figure 7 is a perspective view of the attachment of the hairspring to the jumping member.

Detailed description of a preferred embodiment

The following description relates to an embodiment of the invention for which the unit of time is the second. The drive mechanism then constitutes a “dead seconds mechanism”, and will be referred to by this expression below.

With reference to the figure 1 , the deadbeat seconds mechanism according to the invention is integrated into a mechanical timepiece, comprising a timepiece movement provided with a going train powered by an energy source, such as a barrel. The going train traditionally comprises a second wheel 1, comprising 60 teeth and arranged to complete one revolution in 60 seconds. The movement also traditionally comprises an escape pinion 2 and an escape wheel 3 as well as an escape lever and a balance wheel. These elements are known to those skilled in the art and do not require a detailed description. It will however be noted that the frequency of the balance wheel is advantageously chosen at 3 Hz, as will be understood below.

The deadbeat seconds mechanism comprises a drive wheel constituted more specifically here by the seconds wheel 1 of the going train.

The deadbeat seconds mechanism also includes a jumping member 6, such as a wheel, integral with a deadbeat seconds indicator, such as a hand (not shown). The jumping member 6 is loosely mounted on the axis of the second wheel 1, so that the jumping member 6 is coaxial with the second wheel 1 and not integral with the latter. The jumping organ 6 is elastically connected to the second wheel 1 by means of a spiral spring 8, which is on the one hand driven onto the second wheel 1 and on the other hand fixed to the jumping member 6. According to a first variant, the spring -hairspring 8 comprises at its end intended to be fixed on the jumping member 6, a fixing notch 9 in which is inserted a holding stud 11 provided on the jumping member. According to a second variant represented on the figure 7 , the spiral spring 8 comprises at its end intended to be fixed on the jumping member 6, a double fixing notch 32 having two housings or notches. The jumping member 6 is provided with two retaining pins 34, each retaining pin 34 being intended to be inserted into one of the housings of the double fixing notch 32. The retaining pins 34 are arranged to limit the axial play . More particularly, each retaining stud 34 has a groove around which each notch is positioned. Thus, the double fixing notch makes it possible to guarantee that the flatness of the hairspring 8 is preserved during operation of the mechanism. The jumping member 6 is a wheel comprising 30 teeth and making one revolution in 60 seconds.

The deadbeat second mechanism also comprises a deadbeat second cam mobile formed by a cam driving wheel 10 and a deadbeat second cam 12, integral with said cam driving wheel 10. The cam driving wheel 10 is arranged to cooperate with the escapement pinion 2. More particularly, the cam driving wheel 10 is in direct engagement with the escapement pinion 2.

According to the invention, the seconds wheel 1 and the cam driving wheel 10 are pivotally mounted on the frame of the movement so as to have separate pivot axes, so that the dead seconds cam 12 and the jumping member 6 (or second wheel 1) are not coaxial.

In addition, the second wheel 1 and the cam driving wheel 10 are kinematically connected by an intermediate gear train, and more particularly an intermediate mobile comprising an intermediate pinion 14 meshing with the second wheel 1 and an intermediate wheel 16, integral with said intermediate pinion 14, and meshing with the cam driving wheel 10. Thus, the main kinematic chain of the movement goes from the wheel 1 to the escape pinion 2 passing successively through the intermediate gear train and the cam drive wheel 10, without direct engagement between the drive pinion and the second wheel. According to a preferred embodiment, the dimensions and the number of teeth of the intermediate wheel set are provided such that the cam drive wheel 10 and the dead seconds cam 12 perform one revolution per 20 seconds, i.e. 3 revolutions per minute, the cam driving wheel 10 comprising 66 teeth and the dead second cam 12 comprising 10 teeth 18. It is obvious that the speed of the cam driving wheel and of the dead seconds cam, as well as the number of teeth can be modified without departing from the scope of the present invention. For example, a period of 16 seconds could be chosen, with a deadbeat seconds cam comprising 8 teeth.

The deadbeat seconds mechanism also comprises a deadbeat seconds anchor 20 pivotally mounted at a pivot point A on the movement frame, and controlled by the deadbeat seconds cam 12 to release and cause the jumping member 6 to jump once per second. . The jumping member 6 thus constitutes a deadbeat seconds escape wheel.

In accordance with the invention, deadbeat seconds anchor 20 comprises four distinct arms 20a, 20b, 20c and 20d. The end of each of the arms acts as a pallet. In the rest of the description, the term “pallet” is used to designate the end of an arm 20a, 20b, 20c and 20d, the pallet therefore forming a single piece with the corresponding arm. Advantageously, deadbeat seconds anchor 20 is made in one piece and made by LIGA. The upper arm 20a and the lower arm 20b constitute upper and lower feelers arranged to cooperate with the cam of deadbeat seconds 12. The upper arm 20c and the lower arm 20d constitute upper and lower escapement arms arranged to successively block and release, once per second, the jumping member 6 alternately. The four arms 20a, 20b, 20c and 20d are positioned with respect to the pivot point A so as to substantially form an X, the end of each arm being curved in order to be able to cooperate either with the dead second cam 12 or with the jumping member 6. The arms 20a, 20b, 20c and 20d work in opposition with respect to the pivot point A. For example, as shown in figure 1 , the upper feeler arm 20a is positioned to be controlled by the profile of the tooth 18 of the deadbeat seconds cam 12 while the opposite escapement arm with respect to the pivot point A, namely the lower escapement arm 20d , is positioned to release the jumping member 6.

Each tooth 18 of the deadbeat second cam 12 has a profile defined by a front ramp 18a, the functional part of the tooth on which the end or the pallet of the feeler arms 20a, 20b rubs, as well as a reverse 18b. Advantageously, the frequency of the balance is chosen at 3 Hz (i.e. 6 vibrations per second) so that each front ramp 18a can be broken down into six steps, each step corresponding to a rotation angle of 3° of the cam dead second. It is quite obvious that another frequency could be chosen. A movement along the front ramp 18a of a tooth 18 therefore corresponding to an angle of rotation of 18° of the deadbeat seconds cam. In order to have a precise jump, the front ramp 18a of each tooth 18 has a slope which is higher over the last three steps corresponding to an angle of rotation of the dead seconds cam of between 9° and 18°, i.e. moment close to the jump, only on the first three steps corresponding to an angle of rotation of the deadbeat seconds cam of between 0° and 9°. As shown more precisely by figure 5 , by determining that at the origin of the tooth, for an angle of 0°, the height is equal to 0, and that the total height of the tooth h corresponds to an angle of rotation of 18° of the dead seconds cam , the height a of the tooth corresponding to the third pitch, i.e. an angle of rotation of 9° of the deadbeat seconds cam, is between 10% and 15% of the height h, and the height b of the tooth corresponding to the fifth pitch, i.e. an angle of rotation of 15° from the deadbeat seconds cam, is between 55% and 60% of the height h.

The profile of the reverse 18b makes it possible to avoid premature jumping of the deadbeat seconds anchor. This profile is the result of the profile of the front ramp 18a, so that, when the pallet of one of the feeler arms is in contact with the front ramp 18a of a tooth 18 of the deadbeat seconds cam 12, a constant clearance is maintained between the deadbeat seconds cam 12 and the passive palette of the other feeler arm (that is to say the palette of the feeler arm which is not in contact with the ramp before a tooth).

In addition, a mechanism is provided for securing the relative position of the seconds wheel 1 and the jumping member 6 in order to ensure permanent indexing of the seconds wheel 1 and the jumping member 6, including when the drive mechanism of the jumping member has stopped following the stopping of the movement. With reference to the figure 4 , said mechanism for securing the relative position of the second wheel 1 and the jumping member 6 comprises a first pin 30 and a second pin 36 driven onto the second wheel 1. Said pins 30 and 36 are represented only on the figure 4 to simplify the drawings. In addition, the jumping member 6 is a toothed wheel having four recessed areas whose edges form four separation arms 6a, 6b, 6c, 6d. The pins 30 and 36 are positioned on the second wheel 1 on either side of one of the separating arms 6a. More particularly, the first pin 30 is positioned so as to be at the front of the separating arm 6a of the jumping member 6 when the second wheel 1 and the jumping member 6 rotate in the same direction, in particular during operation normal of the mechanism. When the seconds wheel 1 rotates in a direction opposite to that of the jumping member 6, in particular when setting the time of the movement, the first pin 30, integral with the seconds wheel 1, comes to bear on the separating arm 6a of the jumping member 6, the separating arm 6a then constituting a stop for the first pin 30. The first pin 30, continuing its movement with the second wheel 1, causes the separation arm 6a and therefore the jumping member 6 in its movement, so that the second wheel 1 and the jumping member 6 move back together and remain indexed, particularly when setting the time.

The second pin 36 is positioned so as to be at the rear of the separating arm 6a of the jumping member 6 when the seconds wheel 1 and the jumping member 6 rotate in the same direction, in particular during normal operation of the mechanism . A margin of at least one pitch, and preferably equal to one pitch, is provided. When the jumping member 6 is stopped, for example during switching, the second pin 36, integral with the second wheel 1, moving in the normal direction, comes to rest on the separating arm 6a of the jumping member 6, the separation arm 6a then constituting a stop for the second pin 36. The second pin 36 abuts against the jumping member 6 stopped, so that the second wheel 1 stops and consequently the rest of the mechanism. Thus, the second wheel 1 and the jumping member 6 are both stopped and remain indexed, in particular during switching.

Thus, the relative position of the seconds wheel 1 and the jumping member 6 is secured, so that there is no loss of winding on the hairspring 8.

With reference to the figure 6 , another variant of the security mechanism is represented. According to this variant, the first and second bearing means comprise an eccentric 38, 40 instead of the first pin 30 and the second pin 36 respectively, their operation being similar. The advantage of the eccentrics 38 and 40 compared to the pins 30, 36, is that the watchmaker can move them and position to adjust the play between the two eccentrics 38, 40 and the separating arm 6a of the jumping member 6. This makes it possible to depend less on manufacturing tolerances.

According to another variant embodiment, not shown, the first support means are positioned so as to be in front of one of the arms separating the jumping member 6 when the second wheel 1 and the jumping member 6 rotate in the same direction, and the second support means are positioned so as to be at the rear of another arm separating the jumper 6 when the second wheel 1 and the jumper 6 rotate in the same way. Thus, one of the separating arms of the jumping member 6 constitutes the first abutment on which the first bearing means are capable of resting and the other separating arm of the jumping member 6 constitutes the second abutment. on which the second support means are likely to rely.

In another variant embodiment not shown, the first and second abutments are not constituted by the separating arms of the jumping member but are parts driven onto the jumping member 6 and arranged so as to be able to come into contact with their respective bearing means, in particular pins or eccentrics, provided on the drive wheel.

The operation of the deadbeat seconds mechanism is as follows: with reference to the figures 1 to 5 , the second wheel 1 drives the intermediate pinion 14 and therefore the intermediate wheel 16, which in turn drives the cam driving wheel 10 and therefore the dead second cam 12. Said dead second cam 12, by rotating, allows the front ramp 18a of a tooth 18 to act on the pallet of the upper feeler arm 20a of the deadbeat seconds anchor 20, so that said anchor 20 swings around its pivot point A to cause it to come out, at the opposite, the palette of the lower escapement arm 20d of the deadbeat second anchor 20 of the toothing of the jumping member 6.

More precisely, between step 0, represented on the figure 1 , and the fifth step of the front ramp 18a of the tooth concerned (i.e. for an angle of rotation of the dead second cam 12 of 15°, cf. figure 5 ), the pallet of the lower escapement arm 20d does not come out of the toothing of the jumping member 6, regardless of the backlash. The asymmetrical profile of each tooth 18 of the deadbeat seconds cam 12 is such that the lifting of the anchor is done gradually with the pallet of the upper feeler arm 20a while the pallet of the lower feeler arm 20b descends without touching the deadbeat seconds cam 12.

When the pallet of the upper feeler arm 20a arrives at the fifth step of the front ramp 18a, as shown in the figure 2 , the jumping member 6 has not yet jumped, and is still blocked by the pallet of the lower escapement arm 20d. Once the pallet of the upper feeler arm 20a has reached the fifth pitch of the front ramp 18a, if the deadbeat seconds anchor 20 undergoes play compensation following a shock for example, the pallet of the lower feeler arm 20b is positioned in contact of the back 18b of the relevant tooth 18 of the deadbeat seconds cam 12, as shown in the picture 3 . Even in this configuration, the jumping member 6 has not jumped, but remains at the limit of jumping. The jumping member 6 jumps when the pallet of the upper feeler arm 20a moves between the fifth and the sixth pitch. When the pallet of the upper feeler arm 20a arrives at the sixth step of the front ramp 18a, as shown in the figure 4 , the jumping member 6 has jumped. The deadbeat seconds anchor having swung, the pallet of the lower escapement arm 20d emerged from the jumping member 6 and released it. The jumping member 6, returned by the spiral spring 8 fixed to the seconds wheel 1, rotates by 6°, ie an advancement or a jump of one second of the deadbeat seconds indicator. The jumping organ is then again blocked by this time the pallet of the upper escapement arm 20c, on which it is held in contact by means of the spiral spring 8, as shown in the figure 4 . It is the pallet of the lower sensor arm 20b, opposite with respect to the pivot point A, which will come into contact with the ramp before 18a of a tooth of the deadbeat seconds cam 12, to tilt the deadbeat seconds anchor 20 in the other direction and again release the jumping member. Thus, the movement of the deadbeat seconds anchor is an alternating movement which makes it possible to release, tooth after tooth, the jumping member 6, once with the pallet of the upper escapement arm 20c, then with the pallet of the upper escapement arm 20c. lower exhaust 20d, successively and alternately. Accordingly, the dead second indicator advances in increments of 1 second.

The deadbeat seconds mechanism of the invention makes it possible to have precise jumps every second with less energy consumption. Indeed, the mechanism of the invention is powered by the same energy source as the going train. A second power source is not required. Furthermore, the arrangement on separate axes of the jumping organ and the deadbeat seconds cam makes it possible to provide optimized shapes for the pallets of the escapement arms on the one hand and for the pallets of the feeler arms on the other hand. , in connection with optimized forms of the teeth of the deadbeat seconds cam. Energy consumption due to the spiral spring between the seconds wheel and the jumping organ is almost nil. In particular, the steeper the slope of the ramp before the teeth of the deadbeat seconds cam over the last three steps of the tooth, the more the jump will be marked and therefore precise. A lower slope on the first three pitches of the tooth means that the angular pitch of the deadbeat seconds anchor is relatively low over this period. Torque consumption is therefore low. The slope over the last three steps is, on the contrary, greater but must nevertheless remain measured in order to avoid overconsumption of torque on the deadbeat second cam mobile. As a result, the angular pitch of the deadbeat seconds anchor is higher over the last three pitches, which allows execution of the jump over a greater measurement range, and consequently increases the precision of the jump. Moreover, the use of a dead second cam having only 10 teeth makes it possible to obtain larger angular steps, and therefore jumps less sensitive to imperfections in the dead second cam.

All the parts of the deadbeat seconds mechanism directly linked to the deadbeat seconds indicator are hollowed out, in order to lighten them as much as possible and reduce inertia as well as torque consumption. In addition, these recesses make it possible to balance the parts, in order to obtain an unbalance close to zero.

Furthermore, the radius forming the flank of the toothing of the jumping member is chosen to be concentric and equal to that of the deadbeat seconds anchor with which it is in contact. As a result, when the deadbeat seconds anchor tilts, the jumping member does not move, which ensures the stability of the deadbeat seconds indicator.

Finally, the arrangement on separate axes of the jumping organ and the deadbeat seconds cam means that a large number of parts are not added on the same axis and therefore limits the accumulation of tolerances and the misalignment of the mobiles, unlike to the coaxial mechanisms of the prior art. The precision on the axis of the jumping member is therefore greater while simplifying the assembly of the parts.

It is quite obvious that the dead second mechanism described above can be adapted to a unit of time other than the second. Thus, the mechanism for driving a jumping member according to the invention can be adapted to the display of any unit of time: second, minute, ten seconds, ten minutes, etc. To do this, a person skilled in the art knows how to adapt the number of teeth on the cam as well as on the jumping member accordingly, as well as the gear ratios in the going train.

Claims (14)

1. Timepiece comprising a horological movement provided with a going train powered by an energy source, an escapement pinion (2) and an escapement wheel (3), said timepiece including a drive mechanism for driving a jumping element comprising a drive wheel (1), an indicator of a unit of time, a jumping element (6) integral with said indicator and coaxial to said drive wheel (1) to which said jumping element (6) is coupled by a spring (8), a cam (12), integral with a cam drive wheel (10), arranged to control a pallet-lever (20), said cam (12) having a profile arranged to cause the pallet-lever (20) to rock in an oscillating motion so as to release the jumping element (6) once per unit of time, the cam (12) and the jumping element (6) having distinct pivot arbours, said drive mechanism, further comprising an intermediate train kinematically connecting the drive wheel (1) to the cam (12), and the pallet-lever (20) having four distinct arms (20a, 20b, 20c, 20d), two (20a, 20b) of the four arms forming feelers arranged to cooperate with the cam (12) and the other two arms (20c, 20d) forming escapement arms arranged to successively block and release the jumping element (6) once per unit of time, alternately, and said cam drive wheel (10) being directly engaged with the escapement pinion.
2. Timepiece according to claim 1, characterised in that the intermediate train comprises an intermediate wheel set formed of an intermediate pinion (14) arranged to cooperate with the drive wheel (1) and an intermediate wheel (16) arranged to cooperate with the cam drive wheel (10) integral with the cam (12).
3. Timepiece according to any of the preceding claims, characterised in that the intermediate train is dimensioned such that the cam (12) comprises less than thirty teeth (18), with each tooth (18) having a front ramp (18a), and makes more than one revolution per minute.
4. Timepiece according to any of the preceding claims, characterised in that, the unit of time being the second, the drive wheel (1) being arranged to make one revolution in 60 seconds, and the indicator being a deadbeat seconds indicator, the cam (12) comprises ten teeth (18) and is arranged to make three revolutions per minute, each tooth (18) having a front ramp (18a) divided into six steps.
5. Timepiece according to claim 3 or 4, characterised in that the front ramp (18a) of each tooth (18) of the cam (12) has, on the last three steps of the tooth (18), a greater slope than the slope of the front ramp (18a) on the first three steps of the tooth (18).
6. Timepiece according to any of the preceding claims, characterised in that the four arms (20a, 20b, 20c, 20d) of the pallet-lever (20) are arranged substantially to form an X-shape, the feeler arm (20a, 20b) positioned to cooperate with the cam (12) being arranged oppositely, relative to the pivot point of the pallet-lever (20), to the escape arm (20c, 20d) positioned to release the jumping element (6).
7. Timepiece according to any of the preceding claims, characterised in that the timepiece comprises a mechanism for securing the relative position of the drive wheel (1) and the jumping element (6).
8. Timepiece according to claim 7, characterised in that the mechanism for securing the relative position of the drive wheel (1) and the jumping element (6) comprises first means of abutment provided on the drive wheel (1) and a first stop member provided on the jumping element (6), said first means of abutment being arranged to abut on the first stop member when the drive wheel (1) and the jumping element (6) rotate in opposite directions.
9. Timepiece according to any of claims 7 and 8, characterised in that the mechanism for securing the relative position of the drive wheel (1) and the jumping element (6) comprises second means of abutment provided on the drive wheel (1) and a second stop member provided on the jumping element (6), said second means of abutment being arranged to abut on the second stop member when the jumping element (6) is stopped.
10. Timepiece according to claims 8 and 9, characterised in that the first and second means of abutment comprise a pin (30, 36).
11. Timepiece according to claims 8 and 9, or claim 10, characterised in that the first and second means of abutment comprise an eccentric (38, 40).
12. Timepiece according to claims 8 and 9, or claims 10 or 11, characterised in that the jumping element (6) is a wheel having at least two recessed areas separated by at least one separating arm (6a), and in that the first and second means of abutment are disposed on either side of said at least one separating arm (6a), said separating arm (6a) forming at least one of the first and second stop members on which the first and second means of abutment are respectively capable of abutting.
13. Timepiece according to any of claims 1 to 12, characterised in that the drive wheel (1) is powered by the energy source of the movement.
14. Timepiece according to any of claims 1 to 13, characterised in that the drive wheel (1) is the fourth wheel of the going train.

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