HK1174978B - Calendar mechanism - Google Patents

Description

Calendar mechanism

Technical Field

The present invention relates to a multi-stage gear device, and more particularly to a gear device for a perpetual calendar mechanism.

Background

Almanac and perpetual almanac mechanisms have long been known, which enable the display of the dates of the months to be automatically incremented, taking into account the months of less than 31 days, and not requiring any manual intervention to correct these months; the perpetual calendar mechanism additionally takes into account leap years in order to increase the date on the last day of february.

The perpetual calendar mechanism uses a cam of type 12 or 48, the latter performing one revolution per year or every four years, respectively, and having notches for different depths for months of less than 31 days. In the case of a cam of type 12, the february notch additionally comprises a year indexed/transposed (index) by Maltese crosses, which defines a smaller depth for the leap year. The beak of the lever, which is restored by a spring, acts on the cams for these date display mechanisms to determine the advance of the date indicator at the end of the month according to the depth of engagement. This results in a relatively complex structure with a number of important parts, which is not very reliable in operation, for example in the event of shocks. Moreover, such a cam system only allows the date wheel and the basic movement to be synchronized in a given direction, so that the date value can only be increased and not decreased during the hour adjustment operation.

To overcome these drawbacks, the solution disclosed in patent document CH 680630 proposes, for example, a perpetual calendar mechanism comprising a program wheel (program wheel) driven by a projecting tooth of a 24-hour wheel and provided with a gear train so that it always moves along a number of steps corresponding to the difference between the days of the month and 31. This mechanism has no lever, balance or spring at all, except for the jumper spring for the indexed date wheel. However, the transmission system is very complex, with a large number of planets equipped with long teeth for indexing readjustment, which are arranged eccentrically on the program wheel and each of which is dedicated to a specific correction. This results in very high production costs, since the shaft requires a high precision positioning to ensure a reliable engagement with the 24 hour wheel. Furthermore, there is a large space requirement not only in terms of height above the floor due to the different meshing levels, but also in terms of volume due to the relatively large diameter of the 24-hour wheel.

Document EP1351104 proposes an alternative to the above solution, in which the number of components on the program wheel and the overall thickness of the program wheel are reduced. However, the program wheel is still driven by the long teeth provided on the 24 hour wheel. Furthermore, the control device for the indexing readjustment of the calendar still comprises a large number of planet wheels with teeth of unequal length, which act on the cam surface on the sliding element, so that the meshing reliability cannot be guaranteed in use.

There is therefore a need for a gear arrangement for calendar mechanisms, in particular perpetual calendars, which overcomes the above-mentioned limitations of the prior art.

Disclosure of Invention

It is an object of the present invention to provide an alternative to conventional calendar mechanisms which has a simplified structure and in which the adjustment of hours and dates can be synchronized in both directions.

It is a further object of the present invention to provide such a solution that minimizes energy losses during different indexing operations, in particular during indexing readjustments at the end of months of less than 31 days.

These aims are achieved in particular by a gear wheel device 12 for a timepiece mechanism, characterized in that it comprises:

-a gear wheel 12' having a uniform integral peripheral tooth system having at most 16 teeth on a first meshing level a;

a first meshing segment 29, said first meshing segment 29 being rotationally fixed with the gear 12 'and meshing on a second meshing level B, wherein said first meshing segment 29 is superimposed on the first tooth 29 ″ of the gear 12';

a second meshing segment 30, said first meshing segment 30 being rotationally fixed with the gear 12 'and meshing on a third meshing level D, wherein said second meshing segment 30 is superimposed on the second teeth 30 "of the gear 12';

a third meshing segment 31, said third meshing segment 31 being rotationally fixed with the gear wheel 12 'and meshing on a fourth meshing level C, wherein said third meshing segment 31 is superimposed on the third teeth 31 ″ of the gear wheel 12'.

One advantage of the proposed solution is that only a reduced volume is required on the machine plate for engagement with a program wheel, for example for a calendar mechanism.

Another advantage of the proposed solution is that better meshing reliability is ensured since each meshing segment of the gear device according to the invention has an adjustable tooth profile and a better angular travel than a program wheel.

An additional advantage of the proposed solution is that the wheel associated with the base movement, for example the 24-hour wheel, is functionally decoupled from the meshing of the clock module, for example the calendar mechanism, in such a way that it is not necessary to have long teeth on said wheel to perform the respective indexing operation of the calendar mechanism. The fact that one wheel is dedicated to meshing with a timepiece module, for example a calendar mechanism, thus enables the addition and replacement of the module without having to modify or at the same time change any conventional components of the basic movement of the timepiece.

Drawings

Exemplary embodiments of the invention are described below and illustrated in the accompanying drawings, wherein:

fig. 1A is a partial sectional view of a calendar mechanism using a gear device according to a preferred modification of the present invention;

fig. 1B is a partial plan view of a calendar mechanism according to the preferred variant of the invention shown in fig. 1A, in particular with a program wheel and a planet wheel;

fig. 1C is a plan view of a display device of a calendar mechanism using a gear device according to the preferred modification of the present invention shown in fig. 1A and 1B;

fig. 2A is another section of the calendar mechanism using a gear device according to a preferred variant of the invention, which shows in particular the control mechanism of the display of the program wheel and of the months and leap years;

FIG. 2B is a partial plan view of a calendar mechanism using a gear arrangement according to a preferred variation of the present invention shown in FIG. 2A;

FIGS. 3A and 3B show a cross-sectional view and a perspective view, respectively, of a preferred embodiment of a program wheel and gear arrangement according to the invention;

FIG. 4 is a perspective view of a calendar mechanism using a gear arrangement according to a preferred variant of the invention, using the preferred embodiment of the different modules shown in the previous figures;

fig. 5A and 5B show the different indexing sequences of the two first and third planet and indexing tooth systems, respectively, at their respective meshing levels for a perpetual calendar mechanism using gearing according to a preferred embodiment shown in fig. 5, on day 28 of february in non-leap years.

Detailed Description

The gear arrangement according to the invention preferably forms a perpetual calendar mechanism. However, it will be appreciated by those skilled in the art that by adjusting the number of meshing levels, the gear arrangement may equally be adapted to simpler mechanisms, such as a calendar mechanism or a calendar mechanism for the months of 30 days, or may be adapted to other types of clock modules.

Fig. 1A and 1B show a sectional view and a plan view, respectively, of a drive wheel train for displaying the date in the month, forward from the movement, while fig. 1C shows a typical date of the month display device. Fig. 1B particularly shows the position of the wheel train relative to the housing 0 and particularly shows the operation of the adjustment mechanism of the date value effected by the manual date correction actuator 26.

In the following, reference will be made alternately to fig. 1A and 1B, which may be referred to in combination for a better understanding of the drive train of the calendar mechanism according to the preferred embodiment shown. The hour wheel of movement 1 meshes with a 24-hour wheel 2 containing twice the number of teeth. In this case, the 24-hour wheel 2 is provided with a date meshing segment 11, which date meshing segment 11 is composed of 7 teeth spaced apart by 15 degrees, so that the change from one tooth to the other takes place every hour. The date meshing section 11 of the 24-hour wheel meshes on the first level a visible in fig. 3A with the gear wheel 12' of the gear device 12 arranged on several meshing levels. The gear 12' consists of 8 teeth at this meshing level a. Thus, each day, the 24 hour wheel 2 causes the calendar indexing wheel 12 to perform one full revolution when engaging with 7 teeth of the engagement section 11, i.e. within an interval of 8 hours. When the day index wheel 12 is not engaged with the toothed engagement section 11, it still rests on the non-toothed section of the 24-hour wheel (which is indicated by reference numeral 11' in fig. 1A) and is thus held in place. The meshing sector 11 of the 24-hour wheel and the calendar indexing wheel 12 are therefore preferably arranged so that said calendar indexing wheel 12 performs one complete revolution per day between 18.00 hours and 2.00 hours of the morning and the indexing effected by the date program wheel 13 takes place between 20.00 hours and the midnight.

As can be seen from fig. 1A, the gearing 12 has a plurality of toothed segments 28, 29, 30, 31 which are distributed over different meshing levels B, C, D, E. These segments will be more clearly seen in particular in fig. 3B, which fig. 3B shows in perspective view. Moreover, according to the preferred embodiment described, these toothed segments are continuous and therefore can mesh with the date program wheel 13 every hour. Fig. 1B shows the engagement level B of the engagement segment 29 engaging with the program wheel 100, i.e. the second engagement level downwards in fig. 1A. The planet gear 129 rotates about its axis of rotation 129' and additionally meshes with an indexing tooth 451 for the month of february, said indexing tooth 451 being the only tooth of the program wheel 45 for the month of february, said program wheel 45 being integral with the month program wheel 43 visible in fig. 2B. The engagement segment 29 is preferably arranged to engage the planet gears 129 between 21.00 hours and 22.00 hours for readjustment during the month of february from day 29 to day 30, as will be described in detail in fig. 5A and 5B.

The date program wheel 13 comprises a uniform date indexing tooth system 13 'with 31 teeth (i.e. in which the height of each tooth and the spacing between each tooth is the same), and said system 13' is indexed by pitch by one tooth per day by the above-mentioned train starting from the date meshing sector 11 of the hour wheel 1, i.e. the 24 hour wheel 2, the 24 hour wheel, and the gear arrangement 12. In fact, according to the preferred embodiment shown, the meshing segment 31, fixed against relative rotation with the gearing 12, meshes with the corresponding tooth 131 of the day indexing tooth system 13' of the day wheel 13, preferably between 23.00 hours and midnight each day. Unlike the meshing segment 31 of the gearing 12, said teeth 131 are different every day and each time correspond to another tooth of the external day indexing tooth system 13', since they are defined only with respect to the teeth 31 of the gearing 12. The elastic indexing element 14 of the program wheel, which is located between two consecutive teeth after each jump, enables indexing with pitch by a single tooth.

In combination with the corresponding planetary gears 128, 130 provided on the program wheel 100, more precisely on the day program wheel 13, the other meshing sectors 28 and 30 of the gearing 12 (which are visible only in fig. 1A for the sake of clarity) are used to perform an additional readjustment for months of less than 31 days. As is evident in succession, in particular on the basis of fig. 5, 6 and 7, the planet gear 129 meshes on the meshing level B, while the other planet gears 128 and 130 (whose respective axes of rotation 128 'and 130' are integral with the date wheel 13) mesh on levels E and D, respectively, for indexing from 28 to 29 in february months of non-leap years, and for indexing from 30 to 31 in months of less than 31 days. These indexing readjustments preferably take place between 20.00 hours and 21.00 hours and between 22.00 hours and 23.00 hours, respectively.

At the bottom of fig. 1A, a meshing level G can be seen, which corresponds to the meshing of the intermediate month control wheel 42 with the month program gear 43, which month program gear 43 is indexed, i.e. changes the value of the month, by 1/12 revolutions at the end of each month. The intermediate month control wheel 42 is the last link of the control train for such monthly indexing operation of the external date indexing tooth system 13' starting from the date program wheel 13 and will be further described below on the basis of fig. 2A and 2B. A fixed wheel 47 ' is also visible, which allows the maltese cross 46 ' (which can also be seen more clearly in fig. 2A and 2B) to perform 1/4 revolutions per year, during which the month program gear 43, integral with said fixed wheel 47 ', performs one complete revolution. The maltese cross 46' meshes on a meshing level F situated above the meshing level G and is integral with a leap year indexing gear 46, said leap year indexing gear 46 comprising three teeth on the meshing level E (which can be clearly seen in fig. 3B).

In fig. 1A and 1B it can be seen that, at the meshing level C, the day indexing tooth system 13' meshes with the day wheel 16 via an intermediate day wheel 15 arranged coaxially but freely rotatable with respect to the intermediate month control wheel 42, said day wheel 16 also having 31 teeth as the day program wheel 13. Said intermediate day wheel 15 constitutes only one circuit for all indexing movements on the day program wheel 13 to be integrally responsive on the day wheel 16 and, conversely, all rotational movements of the day wheel 16 to be integrally responsive on the day wheel 13 during adjustment using the manual actuator 26, described further below. Thus, there is no need for an elastic indexing element to index the date wheel 16. The unit wheel 17 is divided into 31 equal angular sectors, i.e. a sector with 30 teeth thereon and a sector without teeth. The unit wheel 17 drives a gear for actuating the unit display disc 19 on each day of the month other than No. 1. The ones display disc 20, integral with said gear for actuating the ones display disc 19, is thus indexed by one unit per day, except for the transition from the 31 st day of the month to the 1 st day of the following month, during which only the tens display disc 23 is added. Said gear for actuating the unit display disc 19 comprises 10 teeth and is indexed by pitch by 1/10 revolutions, by means of the elastic indexing element 24 coming to the unit disc between two consecutive teeth.

The ten-position display plate 23 is integrated with an actuating gear, i.e., a gear for actuating the ten-position display plate 22, the ten-position display plate 22 having a cross shape with 4 arms and indexed by 1/4 revolutions during the transition from the 9 th to the 10 th days, from the 19 th to the 20 th days, from the 29 th to the 30 th days, and from the 31 st to the 1 st days. The jump of 1/4 revolutions is ensured by the elastic indexing element 24 coming to the tens display disc between two adjacent arms of the cross; and indexing on these date values is ensured by the long teeth provided on the tens wheel 18, said tens wheel 18 also being divided into 31 sectors, but comprising only 4 long teeth, of which 3 are provided at 9 sector intervals, the 4 th long tooth following the 3 rd long tooth in order to pass from day 31 to day 1 of the next month.

In each of fig. 1A, 1B and 1C, there can be seen, in part, a train for the display of the date in the month, made up of the elements with reference numbers 16 to 24 from the date wheel 16 to the units display 20 and the tens display 23: fig. 1A shows the entire train, but without the elastic indexing elements 21 and 24 of each actuation gear 19 and 22 associated respectively with the units display disc 20 and the tens display disc 23, and fig. 1B shows the meshing levels beneath these units display disc 20 and tens display disc 23, said units display disc 20 and tens display disc 23 thus being visible only in fig. 1C.

The adjustment of the day of the month is carried out by means of a manual actuator 26 provided on the housing 0. According to the preferred embodiment described in fig. 1A and 1B, the manual actuator 26 for date adjustment is a push button which is pressed at most 30 times in succession to reach the desired date. Adjustment mechanism 25 is not shown in fig. 1B for clarity, adjustment mechanism 25 enabling the transmission of the pulse from the push button to date gear 16; however, such mechanisms are known to those skilled in the art. However, according to the preferred embodiment shown, and with the alternative proposed, such a date adjustment cannot be made when one of the meshing sectors 28, 29, 30 or 31 of the gearing 12 is engaged with the date program wheel 13, either directly or via the planetary gears 128, 129, 130, that is to say between 20.00 and 24.00. In fact, the direct engagement of the gear means 12 and of the date meshing sector 11 of the 24 hour wheel tends to transfer these indexing operations to the hour wheel 1, which is unlikely without impairing the normal functioning of the movement.

Fig. 2A and 2B show a section and a plan view, respectively, of a calendar mechanism using a gear device 12 according to a preferred variant of the invention, in which the control train for positioning the month program gear 43 for the proper positioning of the pivoting retractable teeth, and the train for displaying months and leap years are described. Two further manual actuators are shown at the position of the casing 0, the first one, referenced 48 and at 8 o 'clock on the casing, for adjusting the month, the second one at 4 o' clock on the casing 0, in the form of a crown 50, usually provided, for example, on a tie rod, one of the axial positions of which enables the movement to be rewound, the other axial position allowing the hour and minute hands to be adjusted bidirectionally.

In the central part of fig. 2A, a gear wheel can be seen, on which the monthly indexing teeth 32 visible in fig. 2B are provided. Said monthly indexing tooth 32 meshes with a monthly indexing gear 33 having 8 teeth, said monthly indexing gear 33 being fixed together non-rotatably with a month control wheel 41 having 32 teeth, said month control wheel 41 meshing, on a meshing level G, with an intermediate month control wheel 42, said intermediate month control wheel 42 being coaxial with the intermediate date wheel 15 but not fixed non-rotatably with respect to the intermediate date wheel 15, said intermediate month control wheel 42 in turn meshing with a month program gear 43 having 48 teeth. The monthly indexing gear 33 performs exactly 1/8 revolutions per month due to the elastic indexing element 34 coming between two consecutive teeth of the monthly indexing gear 33. The transmission ratio between the monthly indexing gear 33 and the number of month program gears 43 allows the month program gears 43 to be indexed by exactly 1/12 revolutions per month.

The monthly indexing gear 33 additionally meshes with an intermediate monthly indexing wheel having 23 teeth, which in turn meshes with an actuating gear 36 for the month display having 12 teeth. The gear ratio 8/12 between the monthly indexing gear 33 and the actuating gear 36 for the month display ensures that the actuating gear for the month display performs exactly 1/12 revolutions at the end of each month. Said actuating gear 36 for the month display is non-rotatably fixed with respect to a year indexing tooth 37, said year indexing tooth 37 being positioned on a gear that performs one complete revolution per year. The year indexing tooth 37 meshes with a leap year actuating gear 38 having 8 teeth, which leap year actuating gear 38 is shifted by two teeth, i.e. 90 degrees, during each meshing with the year indexing tooth 37. The leap year actuating gear 38 is fixed in a non-rotatable manner relative to an intermediate leap year wheel 39 with 39 teeth, the intermediate leap year wheel 39 meshes with a leap year display wheel 40 which likewise comprises 39 teeth, the leap year display wheel 40 is mounted coaxially with the actuating gear 36 for the month display, so that the indicators of the months and leap years, in particular the hands pointing to concentric rings arranged on the dial, can be set in rotation about the same hand-motion mechanism in order to improve the legibility for the user. It will be understood by those skilled in the art that, for the elements forming the wheel train described in fig. 2A and 2B, i.e. (elements 33-36) for the month display, (elements 37-40) for the leap year display and (elements 33, 41, 42, 43) for the positioning control of the month program gear 43, the number of teeth cited is given as an example, within the framework shown with sufficient meshing efficiency to achieve the preferred variant of the invention, but should not be considered limiting.

Fig. 2B clearly shows the leap year index gear 46 mounted on the month program gear 43. The leap year indexing gear 46 is integral with a maltese cross 46 ', which maltese cross 46 ' meshes at level F with a leap year indexing finger 47 ' provided on a fixed wheel 47. On the 3 arms of the maltese cross are superimposed 3 teeth 461, 462 and 463, which engage on engagement level E to move the date from 28 to 29 days when the year is not a leap year.

The month program gear 43 is synchronized with the displayed and indexed month values so that the planetary gears mesh to perform the readjustment required at the end of the month. This is the reason why the control train, which according to the shown preferred embodiment is formed by the elements 15, 16, 32, 33, 41 and 42, enables a reverse action (retroaction) from the external day indexing tooth system 13' to the month program wheel 43. The day indexing tooth system 13' of the day program wheel 13 performs at least 1/31 revolutions per day (i.e. an additional readjustment of one or more 1/31 revolutions required for months and february of 30 days is performed for a regular day of 1/31 and for the last day of months with less than 31 days) in order to index the month program wheel 43 by 1/12 revolutions after the end of each month. According to the preferred variant shown, the indexing of the month program gear 43 takes place at the same time as the indexing of the gear 36 for actuating the month display, also by 1/12 revolutions, since the indexing of these two gears is effected by meshing with the same elements, namely the monthly indexing teeth 32.

According to a preferred embodiment of the calendar mechanism described, the control train of the month program wheel, composed of the elements referenced 15, 16, 32, 33, 41, 42, is formed by a first kinematic chain starting from the date indexing tooth system 13' of the date program wheel 13 via the intermediate date wheel 15 to the date wheel 16, the date wheel 16 forming the first element of the date display train (16-24), and by a second kinematic chain starting from the date wheel 16 and the monthly indexing tooth 32, returning to the month program wheel 43 via the monthly indexing gear 33 and the month control wheel 41, which are rotationally fixed to each other, and the intermediate month control wheel 42, the month program wheel being arranged coaxially with the date program wheel 13 but rotationally independent of the date program wheel 13. The intermediate gears 15 and 42, i.e. the intermediate date wheel 15 and the intermediate month control wheel 42, are provided as a single intermediate wheel comprising two gears which are coaxial and rotationally independent, in order to save the maximum amount of space on the board, for example for other clock modules. Said intermediate month control wheel 42 meshes with the month program wheel 43 at level G, while the intermediate date wheel 15 meshes with the date indexing tooth system 13' of the date program wheel 13 at level C. According to the preferred embodiment shown, said intermediate wheels (intermediate date wheel 15 and intermediate month control wheel 42) rotate in opposite directions of rotation to each other, since intermediate date wheel 15 is directly meshed with date wheel 16 and therefore rotates in opposite direction to date wheel 16, whereas intermediate month control wheel 42 is driven by a transmission formed by monthly indexing finger 32 integral with date wheel 16 via gears 33 and 41 and therefore rotates in the same direction as date wheel 16.

The adjustment of the months is carried out by means of a manual actuator 48 provided on the housing 0. According to the preferred embodiment depicted in fig. 2A and 2B, the manual actuator 48 for adjusting the day of the week is a button that is continuously pressed at most 11 times to reach the desired month of the year. According to the described preferred embodiment, the manual actuator 48 is used not only for determining the month, but also for determining the year in a leap year cycle of 4 years, since there is no dedicated actuator for the adjustment of the year. In this case the maximum number of pulses would be 47 instead of 11. To overcome this drawback, in an alternative embodiment another manual actuator can be provided on the central part to act directly on the tooth system of the gear 38 for actuating the leap year display. In this case, however, it will be necessary to ensure that the tooth system of the actuating gear does not engage with the year indexing teeth 37 during the adjustment, i.e. preferably does not engage with the year indexing teeth 37 during the months 12 or 1, which imposes an additional limit on the moment at which the adjustment must be performed.

For the sake of clarity, the adjustment mechanism 49 is not shown in fig. 2B, said adjustment mechanism 49 allowing the pulses of the push-button to be transmitted to the month program gear 43. However, such mechanisms are known to those skilled in the art. However, according to the preferred embodiment shown, and with the proposed alternative, such month adjustments cannot be made while the monthly indexing tooth 32 is in mesh with the monthly indexing gear 33, i.e. during the night from the last day of the current month to the first day of the next month. In fact, the engagement of the indexing tooth 32 will cause the rotation of the date wheel 16, which will cause the same movement of the date program wheel 13, the engagement between the teeth 28, 29, 30, 31 of the date program wheel 13 and the indexing gear 12 at 20.00 and 24.00 will cause the rotation of the date meshing section 11 of the 24-hour wheel. This tends to transmit these indexing operations to hour wheel 1, which, as described previously, is not possible without impairing the normal functioning of the movement if the adjustment of the date takes place between 20.00 hours and 24.00 hours.

Fig. 3A and 3B show a cross-sectional view and a perspective view, respectively, of a preferred embodiment of a program wheel 100 and a gear arrangement 12 according to the invention. The gear arrangement 12 is driven by a movement meshing on level a, while the different meshing stages 28, 29, 30 on meshing level B, D, E allow indexing readjustment to take place while the meshing stage 31 on meshing level C performs a normal daily indexing operation, preferably between 23.00 hours and midnight. The meshing segments 28, 29, 30 and 31 respectively comprise a single tapered tooth according to the variant shown and are superimposed on the teeth 28 ", 29", 30 "and 31" of the gear wheel 12' of the gearing 12, which are arranged consecutively on level a. The meshing levels F and G relate only to the program wheel 100 and enable the indexing of the leap year indexing wheel 46 by means of the maltese cross 46' meshing on the detent of the fixed wheel 47 and the indexing of each month of the program wheel 43 by means of 1/12 revolutions, respectively. According to the described embodiment, the engagement segment 29 is located on level B, the engagement segment 30 is located on level D and the engagement segment 28 is located on level E. This configuration of meshing levels D, E and B on either side of the date meshing level C, respectively, is advantageous in that the planet gears 128, 129, 130 can be positioned set back from the successive teeth of the external date indexing tooth system 13' of the date program wheel 13, as shown in fig. 3B, since the tooth system of the planet gears can pass over the rotational axes of the adjacent planet gears.

It can be seen from fig. 3B that the first, second and fourth meshing stages 28, 29, 30 are identical compared to the teeth 28 ", 29", 30 "of said gears on meshing level a, for each of these stages having a double gear system, said first, second and fourth meshing stages 28, 29, 30 being superposed with said teeth 28", 29 ", 30" on their respective meshing levels E, B and D to ensure better meshing reliability. The meshing segment 31 superimposed on the teeth 31 "of the toothed wheel 12' has the same profile as said teeth 31". The meshing segment 31 is therefore distinct from the meshing segments 28, 29, 30, so that it can be easily indicated which is the meshing level of the date with which the system of date indexing teeth 13' of the date wheel 13 meshes, i.e. meshing level C.

The month program wheel 43 is mounted coaxially and rotationally fixed with the program gear 45 for the months of february on meshing level B and with the program gear 44 for the months of less than 31 days on meshing level D, so that no dedicated wheel train is required for each of these two indexed readjustments. Program gear 45 for the month of february comprises a single tooth 451, and program gear 44 for the months of less than 31 days comprises 5 teeth 441, 442, 443, 444 and 445, each tooth corresponding to february, april, june, september and 11 months, respectively. These teeth are located in the second, fourth, sixth, ninth and eleventh segments of the 12 corner segments corresponding to each month. The program gear 44 for months less than 31 days is therefore set to a gear having 12 teeth over the segment corresponding to the months less than 31 days, 7 of which will be omitted. Moreover, the teeth 441 of the month of february and the teeth 451 of the month of february program gears, corresponding to program gears for months less than 31 days, are superposed and identical, so as to facilitate the assembly of the different program gears by simply checking the required centering, as well as to limit the machining costs due to the similarity of the shapes of the teeth for each indexed readjustment.

In fig. 3B three planet gears 128, 129, 130 can be seen, each planet gear having 8 teeth and having a rotation axis integral with the date program wheel 13. These planet gears 128, 129, 130 are all identical, their axes of rotation 128 ', 129 ', 130 ' being located between successive teeth of the day indexing tooth system 13 ' of the day program wheel 13, so that the tooth system of the meshing segments 28, 29, 30 is able to effectively drive the tooth system of the planet gears 128, 129, 130 in both directions and along an angular distance corresponding to 1/31 revolutions of the day program wheel 13, and said axes of rotation 128 ', 129 ', 130 ' also being located at equal distances from the centre of rotation of the day program wheel 13. The depth of the tips of the teeth relative to the indexing tooth system 13' is determined such that good engagement with the tooth system of each engagement segment 28, 29, 30 is achieved. This configuration of the axes of rotation 128 ', 129 ', 130 ' on the same circular arc is possible because the tooth systems of the program gear 44 for months of less than 31 days, the program gear 45 for the months of february and the leap year program gear 46 are identical and overlap during the months of february of non-leap years. The planet gears 128, 129, 130 mesh with the toothing system of these gears which is rotationally fixed with respect to the month program wheel 43, in order to perform an indexed readjustment at the end of the month. According to the described preferred embodiment, each of the planet gears 128, 129, 130 comprises 8 teeth to improve the meshing efficiency, such arrangement of the wheels between successive teeth of the month program gear being only possible if the wheels 128 and 130 are located on either side of the date meshing level C (on which the third meshing segment 31 of the gearing 12 meshes directly with the external date indexing tooth system 13' each day), so that the tooth system of each planet gear 128, 129 and 130 can span the rotation axis of the adjacent gear. For example, in fig. 3B it can be seen that the tooth system of the planet gears 129 spans the rotational axes 128 'and 130' of the planet gears 128 and 130.

The program wheel 100 shown in fig. 3A and 3B is therefore intended for a perpetual calendar mechanism with a first indexing readjustment on meshing level B for indexing from day 29 to day 30 in february by means of the meshing sector 29, said toothed sector 29 cooperating with the planet gear 129 and the indexing tooth 451 of february to advance the date program wheel 13 by one tooth; the perpetual calendar mechanism also has a second indexing readjustment, by meshing at a second meshing level D, for indexing from day 30 to day 31 in months of less than 31 days by meshing the segments 30, said toothed segments 30 cooperating with the second planetary gears 130. The third indexing readjustment is not a year indexing operation because it only occurs in february, which contains only 28 days. This indexing operation occurs at the third engagement level E by the engagement segment 28, which engagement segment 28 is in engagement with the third planetary gears 128. The date indexing tooth system 13' of the date program wheel 13 itself meshes on the fourth meshing level C.

The leap year program gear 46 of the shown program wheel, which contains three teeth 461, 462, 463, is integrated with a maltese cross 46 ', which maltese cross 46' is mounted to pivot on the month program wheel 43 and meshes with a pawl 47 for leap years on the meshing level F each year. To facilitate the assembly of the program wheel 100 and the machining of the meshing section of the corresponding gear 12, the leap year program gear teeth 461, 462, 463 are identical and overlap on top of the teeth of the february months of non-leap years, i.e. corresponding to the teeth 441 of the february months of the program gear for months less than 31 days and the teeth 451 of the february program gear.

Thus, the illustrated program wheel 100 extends over a total of 6 meshing levels from B to F. However, it will be appreciated by those skilled in the art that the invention is equally applicable to almanac mechanisms by omitting meshing levels E and F for leap years. Similarly, the gearing is provided on 5 meshing levels from a to E, but may also comprise only 4 meshing levels for the annual calendar mechanism.

Figure 4 shows a perspective view of a calendar mechanism according to a preferred embodiment of the invention shown by the different previous views. Proceeding from the hour wheel 1 in the center of the figure, it can be seen that the train of wheels leads to the day program wheel 13 via the 24 hour wheel 2 and the day meshing section 11 with 7 teeth meshing with the gear wheel 12 'of the gear arrangement 12, of which only the upper meshing level B is shown, on which there are a planet gear 129 movable about its axis of rotation 129' and an indexing tooth 451 for the month of february, said axis of rotation 129 'being located slightly below the maltese cross and between the successive teeth 29' and 30 'of the day indexing tooth system 13'.

During each engagement with one of the engagement segments 28, 29, 30 or 31 of the gear means 12 of the calendar mechanism, the date program wheel 13 performs 1/31 revolutions. By means of the intermediate date wheel 15, the date wheel 16 is made to rotate by the same angle. The unit wheel 17 and the tens wheel 18 are visible above the date wheel 16, and it is clearly visible that the 4 long teeth of the tens wheel 18 are arranged at the position of the 9 th, 19 th, 29 th and 31 th teeth of said tens wheel 18, the 31 th tooth of the unit wheel 17 being hollowed out. The date display mechanism is not shown for clarity.

The whole of the train of wheels for the display of the date in the month is also not shown in fig. 4, since the various display disks and indexing elements (the reference numbers 20-24 can be seen in fig. 1C) and the monthly indexing tooth 32, coaxial with the date wheel and rotationally fixed, are hidden under the date wheel 16. However, it is possible to see a monthly indexing gear 33 which enables a month control wheel 41 (said monthly indexing gear 33 being rotationally fixed with said month control wheel 41) to drive in rotation a month program gear 43 through an intermediate month control wheel 42, and also meshing with the wheel train for the month display, the tooth system of said month program gear 43 being hardly visible below the tooth system of the date indexing portion 13' of the date wheel.

At the top of fig. 4, an intermediate monthly indexing wheel 35 can be seen, which meshes with an actuating gear 36 for the month display, hidden under the monthly indexing teeth 37, said actuating gear 36 being coaxial with the monthly indexing teeth 37 and rotationally fixed. The monthly indexing teeth 37 perform one full revolution a year and mesh with an actuation gear 38 for the leap year display, which actuation gear 38 is coaxial and rotationally fixed with an intermediate leap annual ring 39, which intermediate leap annual ring 39 meshes with a leap year display wheel 40 having the same number of teeth. The leap year display wheel 40 is arranged coaxially with the actuation gear for the month display in order to provide better legibility for the user of the watch.

Fig. 5A shows two first indexed sequential operations of the perpetual calendar mechanism according to the preferred embodiment shown in the figures, on day 28 of the month of february in non-leap years. For such dates, the calendar mechanism must be readjusted by 3 date values, which is achieved by the engagement at each level E, B and D; the figure shows a first readjustment at level E at 20.00 and a second readjustment at level B at 21.00.

The upper part of the figure shows the position of the day index segment 11 and the different teeth 28 ", 29", 30 "and 31" on meshing level a that overlap with the meshing segments 28, 29, 30 and 31 on their respective meshing level E, B, D, C at 20.00 on day 28 of the month of february. At this point, the meshing segment 28 of the gearing 12, located below the tooth 28 "of the day indexing wheel on the meshing level a, meshes, on level E, with a planetary gear 128, the planetary gear 128 being mounted so as to pivot about a rotation axis 128' integral with the day program wheel 13. According to the preferred embodiment shown, the axis of rotation 128 'of the pivoting retractable tooth 128 is located slightly below the blank between the successive teeth 28' and 29 'of the day indexing tooth system 13'. The planet gear 128 additionally meshes with the second tooth 462 of the leap year indexing gear 46, which leap year indexing gear 46 is integral with the maltese cross 46 ', which maltese cross 46 ' is indexed once a year by a fixed leap year indexing finger 47, which leap year indexing finger 47 is itself integral with the fixed wheel 47 '. According to the preferred embodiment shown, the fixed wheel 47' is coaxial with the month program wheel 43 and with the date program wheel 13.

As a result of the above arrangement and the cooperation of the tooth system of the planet gear 128 with the tooth 462 of the leap year indexing gear 46 and the tooth system of the meshing section 28, which preferably may comprise one or two teeth, the date program wheel 13 is driven for 1/31 revolutions, for example according to the above-described view of fig. 5A, in the same direction of rotation S1 as the direction of rotation of the 24-hour wheel 2, here clockwise of the hands of the watch. The elastic indexing element 14 of the day program wheel enables the day indexing tooth system 13 'to be indexed by pitch by a precise 1/31 revolutions in the direction S1, said day indexing tooth system 13' then meshing on the day display train (see reference numerals 15-24 shown in the other figures).

A second illustration will be seen from the top of fig. 5A, following downwards arrow S, which indicates the direction in which said indexing sequence operation is carried out at the end of the month of february, and which shows a section of the day program wheel 13 and of the month program wheel 43 in meshing level B, in which the meshing segment 29 of the gearing 12 superimposed on the tooth 29 "of the day index wheel in meshing level a meshes with the pivoting retractable tooth 129 of the day program wheel 13, said pivoting retractable tooth 129 being mounted so as to pivot about a rotation axis 129' integral with the day program wheel 13. According to the preferred embodiment shown, the rotation axis 129 'of the planet gear 129 is located slightly below the blank between the consecutive teeth 29' and 30 'of the day indexing tooth system 13'. This sequential operation occurs at 21.00 when 24 hour wheel 2 has advanced date engaging section 11 of the 24 hour wheel one tooth forward and caused date indexing wheel 12 to rotate 1/8 revolutions to engage tooth 29 "behind tooth 28". Obviously, the indexing tooth 451 for the month of february on level B is identical to and superposed on the leap year indexing tooth 462 on the meshing level E previously shown at the top of fig. 5A, this arrangement enabling the day indexing gear 13' to rotate 1/31 revolutions in the same direction S1, as a result of the cooperation of the tooth system of the planet 129 with the tooth 451 for the indexed month of february and with the tooth system of the meshing segment 29, which preferably may comprise one or two teeth, and preferably has the same number of teeth as the meshing segment 28. The elastic indexing element 14 of the day program wheel enables the day indexing gear 13' to be indexed to rotate once again through exactly 1/31 revolutions in the direction S1. The direction of rotation S2, opposite to the direction of rotation S1 itself, corresponds to the direction of rotation of the month program wheel 43, with respect to which month program wheel 43 the program gear 45 for the months of february is rotationally fixed. However, according to the described preferred embodiment, the indexing of the month program wheel 43 only occurs when going from day 31 of the current month to day 1 of the next month.

The third and final indexing readjustment which takes place on the meshing level D is shown in fig. 5B, which shows a cross-section of the date program wheel 13 and of the month program wheel 43 along the meshing level D, on which meshing level D the meshing segment 30 of the gearing 12 superimposed on the tooth 30 "on the meshing level a meshes with the planetary gear 130 of the date program wheel 13, said planetary gear 130 being mounted so as to pivot about a rotation axis 130' integral with the date program wheel 13. According to the preferred embodiment shown, the rotation axis 130 'is located slightly below the blank between the consecutive teeth 30' and 31 'of the day indexing tooth system 13' and is on the same arc as the rotation axes 128 'and 130' with respect to the rotation centre of the day program wheel 13. This sequential operation occurs at 22.00 when 24-hour wheel 2 has again advanced date engaging section 11 of the 24-hour wheel one tooth forward and caused day indexing wheel 12 to rotate 1/8 revolutions to engage tooth 30 "behind tooth 29" on day indexing wheel 12. Similar to the previous illustration in fig. 5A on the meshing levels B and E, on level D the indexing teeth 441 are identical to and overlap the teeth 462 and 451 respectively on levels E and B, this arrangement on level D enabling the day indexing gear 13' to be driven in the same direction S1 for one 1/31 revolutions, as a result of the meshing of the tooth system of the meshing segment 30, which may preferably comprise one or two teeth, and preferably the same number of teeth as the other meshing segments 28 and 29, with the indexing teeth 441 of the gear 44 for months less than 31 days (here for the month of february), and with the tooth system of the meshing segment 30. The other four teeth 442, 443, 444 and 445, identical to tooth 441, correspond respectively to indexing teeth for readjustments from day 30 to day 31 in april, june, september and undemony, all of which occur similarly from 22.00 to 23.00 of the last date of these months.

The elastic indexing element 14 of the day program wheel enables the rotation of the day indexing gear 13' to be indexed again with pitch for this last indexing readjustment by a precise 1/31 revolutions in the direction of rotation S1. The direction of rotation S2, opposite to the direction of rotation S1 itself, corresponds to the direction of rotation of the month program wheel 43, with which the program gears for the months less than 31 days are also rotationally fixed, as are the gears 45 for the months of february. However, according to the described preferred embodiment, the indexing of the month program wheel 43 only occurs when going from day 31 of the current month to day 1 of the next month.

As can be seen in particular from the different illustrations of fig. 5A, all the planet gears 128, 129, 130 preferably have the same geometry, which on the one hand greatly simplifies the manufacture of the date program wheel 13, while also simplifying the manufacture of spare parts, which do not require any machining of special elements for the adjustment of the date in the month. The simple and uniform geometry of each planetary gear 128, 129, 130 together enables the use of indexing gears (gear 45 for the february and gear 44 for months less than 31 days) with the same uniform tooth system on each level (B, D, E) for indexing readjustment as described above. Thus, the complexity of the entire proposed calendar mechanism is greatly reduced compared to conventional mechanisms. The planet gears 128, 129, 130 preferably comprise 8 teeth and mesh with the meshing segments 28, 29, 30 at their respective meshing levels E, B, D, according to the preferred embodiment shown, each of said meshing segments 28, 29, 30 having two teeth.

According to one illustrated preferred embodiment, the meshing segments 28, 29 and 30 each comprise only a single tooth, sufficiently tapered to mesh with the tooth system of each planet gear 128, 129, 130, and also superposed on the teeth 28 ", 29", 30 "of the day indexing wheel 12. This solution enables to simplify the machining of the engagement segments 28, 29, 30. In order to increase the engagement reliability, in an alternative embodiment, a second tooth may be provided in each engagement section. In this case, the two teeth of the meshing segment will be located on either side of, rather than exactly below, the corresponding teeth 28 ", 29", 30 "of the day indexing wheel 12, even if the entirety of said meshing segment is located in a sufficiently superposed position with respect to the teeth 28", 29 "and 30" of the day indexing wheel 12.

In fig. 5A and 5B, of the 31 teeth of the date program wheel 13, only the 1 st and 28 th to 30 th teeth of the date indexing tooth system 13 '(which are respectively given the reference numbers 1, 28', 29 ', 30') and the tooth 131 are marked, said tooth 131 cooperating in the example described with an engagement segment 31 superimposed on the tooth 31 ″ of the gearing 12 for indexing from the 31 st day to the 1 st month of the next month when going from the 28 th day of the february of non-leap years to the 3 rd 1 st day. In the preferred embodiment shown, the meshing segment 31 differs from the other meshing segments dedicated to readjustment (reference numbers 28, 29, 30) in that said meshing segment 31 has exactly the same shape as the teeth 31 "of the gearing 12, said meshing segment 31 overlapping the teeth 31", while the other meshing segments all have tapered teeth in order to mesh with planetary gears having a finer tooth structure.

The diagram at the bottom of fig. 5B shows the last indexed sequential operation of a month, which follows the three previous indexed readjustments for day 28 of february in non-leap years, but which also occurs at 23.00 hours to midnight on all other days in the year. It can be seen that the same arrow S for the last indexing of the month as in the preceding fig. 5A points downwards to indicate the direction in which the indexing sequence operation is performed.

This illustration shows the day program wheel 13 at an engagement level C, which in the preferred embodiment shown, in particular in fig. 1A/B and 2A/B, is located just above level D, at which the engagement segment 31 of the gearing 12 engages with the teeth 131 of the day indexing tooth system 13' of the day program wheel 13. This sequential operation occurs at 23.00 when the 24 hour wheel 2 has caused the date meshing section 11 of the 24 hour wheel to advance one tooth again with respect to the top illustration of fig. 5B and has caused the gear arrangement 12 to rotate 1/8 turns to mesh on the tooth 31 "following the tooth 30" on level a of the gear 12'.

Once the day of the month has been indexed to day 3/1 at midnight, when the gear wheel 12 ' has performed an additional 1/8 revolutions (all meshing sectors 28, 29, 30, 31 rotationally fixed with said gear wheel 12 ' perform the same revolutions), the meshing sector tooth 31 is no longer meshed with the day indexing gear 13 '. The gear means 12, which preferably comprise 8 teeth on level a meshing with the date meshing section 11, of which the teeth 28 ", 29", 30 "and 31" are superposed on the meshing sectors 29, 30 and 31 on the respective level E, B, D, C meshing with the date program gear 13, will continue to mesh with the remaining teeth of the meshing section 11 and this has no effect on the movement of the date program wheel 13. The day indexing tooth system 13' will therefore not be driven in rotation after this moment. However, the control train described above, and in particular based on fig. 2B (reference numerals 15, 16, 32, 33, 41, 42), will still index the month gear 43 by 1/12 revolutions in the direction S2 opposite to the direction S1 each time the 1 st day passes from day 31 to the next month. Furthermore, the gear arrangement 12, which has performed a complete revolution after meshing with the 7 teeth of the toothed meshing section 11, will be held in place by the surface of the section 11' without teeth (which prevents the gear arrangement 12 from rotating) visible in all the illustrations of fig. 5A and 5B until the next time meshing with the same meshing section.

The reliability of the meshing proposed by the calendar mechanism according to the invention is improved compared to mechanisms using complex cam surfaces and/or movements with several translation members for retractable teeth. Moreover, the construction is simplified by using a planetary gear that is identical for each readjustment of the day of the month and by using several coaxial and rotationally fixed program gears having a similar tooth structure at the respective meshing level.

Furthermore, it is clear that neither the gearing 12 nor the date program wheel 13 have long teeth, which simplifies the machining thereof. The preferably identical engagement segments for readjustment can be mounted and positioned modularly on the respective engagement level. Their depth and the number of teeth (doubling the number of teeth on each meshing segment 28, 29, 30 with respect to the corresponding superposed teeth 28 ", 29", 30 "on the meshing level a of the day indexing wheel 12) enable good meshing reliability, while the angular interval between each meshing segment itself ensures a unit increment of the day program wheel 13.

It can be seen from the views of fig. 5A and 5B that readjustment of the missing dates at the end of the months of less than 31 days is carried out by the calendar mechanism according to the invention in turn hourly over a period of at most 4 hours (i.e. from 20.00 hours to 24.00 hours), first at each of the 3 readjustment meshing levels E, B, D and then at the regular day indexing level C, while the gearing 12 is driven by the meshing section 11 of the 24-hour wheel. All the planet gears are driven by the same clockwork train, more precisely by the same component (i.e. the day index wheel 12), so that no dedicated train for each correction is required, which simplifies the construction of the proposed calendar mechanism compared to conventional mechanisms.

The number of teeth of the day indexing wheel 12, which is fixed at 8 according to the preferred embodiment chosen, has been determined to perform a rotation around a sufficient angle to index the day program wheel 13 (on which the planetary gears 128, 129, 130 are mounted) by 1/31 revolutions, with a suitable depth of mesh. To further increase the angular travel during each engagement with the hour wheel, the number of teeth may be further reduced, for example, to 6, or at most to 4 for integration with the perpetual calendar mechanism, or to 3 for the perpetual calendar mechanism, this minimum number corresponding to the number of engagement segments required for the day of the month readjustment. Moreover, the fact that the day indexing wheel 12 performs exactly one complete revolution per day enables a similar movement to be repeated by a day cycle starting from the same position. However, in a variant, it is also conceivable to repeat each meshing segment twice on the gearing 12, so that the gear 12' may for example comprise 16 teeth, i.e. two identical patterns consisting of 8 teeth each, said 8 teeth comprising a set of two teeth on level a not superposed on the meshing level, then 4 teeth superposed on 4 meshing segments, and the last set of two teeth not superposed on the meshing segment. In this case, the gear 12' will perform half a revolution per day instead of one full revolution, which will limit the angular travel during each indexing step of the gear arrangement 12. A drawback of the gear arrangement 12 with a gear wheel 12' comprising a larger number of teeth is that it will take up more space on the machine plate. However, the use of such a gear arrangement 12 can be combined, for example, with a 24-hour wheel having a larger number of teeth in order to perform readjustments of the date with a more limited time span. For example, when using a 24 hour wheel with 48 teeth (the meshing section still has 7 teeth), the first, second, third and fourth meshing segments 29, 30, 31 and 28 will no longer mesh with the date program wheel 13 in turn every hour at their respective meshing level B, D, C, E, but with the date program wheel 13 in turn every half hour, while the date meshing section 11 will mesh with the gear wheel 12' of the gearing 12, so that readjustment at the end of the month will take only 2 hours at most, instead of 4 hours according to the preferred embodiment shown on the basis of the previous figures.

The fact that the meshing level B, D, E is separated from the meshing level C of the day indexing operation for all readjustment operations at the end of the month enables modular substitution, preferably by meshing level, for each component of the program wheel 100 and of the gearing 12. This possibility provided by the calendar mechanism according to the invention is very advantageous because meshing levels C will be used for example daily, while levels B will be used once a year, levels D5 times a year, levels E once a year in three of four years, not leap years.

The calendar mechanism achieves that the date display is always synchronised with respect to the movement, and in both directions, so that the adjustment of the hour (which is normally achieved by rotating the crown provided on the case 0) will be transmitted to the hour wheel 1 and subsequently to the calendar mechanism. This is advantageous during travel to a destination whose time zone lags the original location (e.g., the west coast of the united states lags europe by 9 hours). A user of a watch equipped with a calendar mechanism according to the invention only needs to adjust the hours of his/her watch to less than 9 hours, so that the date will be automatically adjusted backwards, for example from 3 months 1 to 28 or 29 days of february, without any special operation for the adjustment of the date in the month. The use of such a watch is simpler than a watch with a conventional date mechanism, for which no synchronism with the movement is provided during adjustment in the opposite operating direction.

Claims (9)

1. A gear wheel device (12) for a horological mechanism, characterized in that said gear wheel device (12) comprises:

-a gear wheel (12') having a uniform integral peripheral tooth system comprising at most 16 teeth on a first meshing level (a);

-a first meshing segment (29) rotationally fixed with the toothed wheel (12 ') and meshing on a second meshing level (B), wherein the first meshing segment (29) is superimposed on a first tooth (29 ") of the toothed wheel (12');

-a second meshing segment (30) rotationally fixed with the toothed wheel (12 ') and meshing on a third meshing level (D), wherein the second meshing segment (30) is superimposed on a second tooth (30 ") of the toothed wheel (12');

-a third meshing segment (31) rotationally fixed with the gearwheel (12 ') and meshing on a fourth meshing level (C), wherein the third meshing segment (31) is superimposed on a third tooth (31 ') of the gearwheel (12 '),

wherein the first (29 "), second (30") and third (31 ") teeth are each distinct from one another, and wherein the first (A), second (B), third (D) and fourth meshing levels (C) are each distinct from one another.

2. Gear wheel unit (12) for a clockwork according to claim 1, characterized in that said first tooth (29 "), second tooth (30") and third tooth (31 ") are arranged in succession on a tooth system of said gear wheel (12').

3. Gear wheel means (12) for a clockwork according to claim 1, characterized in that said gear wheel means (12) additionally comprise:

-a fourth meshing sector (28) rotationally fixed with the toothed wheel (12 ') and meshing on a fifth meshing level (E), wherein the fourth meshing sector (28) is superimposed on a fourth tooth (28 ") of the toothed wheel (12').

4. Gear wheel unit (12) for a horological mechanism according to claim 3, characterized in that said first (29 "), second (30"), third (31 ") and fourth (28") teeth are arranged in succession on a system of teeth of said gear wheel (12'); a third meshing segment (31) superimposed on a third tooth (31 ") of the toothed wheel (12') has the same profile as the third tooth (31").

5. Gear unit (12) for a clockwork according to claim 3, characterized in that said third and fifth meshing levels (D, E) of said second and fourth meshing segments (28, 30) and said second meshing level (B) of said first meshing segment (29) are located on either side of said fourth meshing level (C) of said third meshing segment (31), respectively.

6. Gear unit (12) for a clockwork according to claim 3, characterized in that the tooth systems of said first, second and fourth meshing segments (29, 30, 28) are identical.

7. Gear unit (12) for a timepiece mechanism according to any one of claims 3 to 6, characterised in that the gear wheel (12 ') comprises at most 8 teeth and meshes with a date meshing sector (11) of a 24 hour wheel (2) of the timepiece movement, so that the gear wheel (12') performs at most one full revolution per day.

8. Gear unit (12) for a clockwork according to claim 7, characterized in that each of said meshing segments (28, 29, 30, 31) is arranged to mesh with a date program wheel (13) and to index said date program wheel (13) with a pitch by 1/31 revolutions.

9. Gear unit (12) for a clockwork according to claim 8, characterized in that said first, second, third and fourth meshing segments (29, 30, 31, 28) of said gear unit (12) are arranged to mesh in sequence with said date program wheel (13) on said first, second, third and fourth meshing levels (B, D, C, E) at least at one hour intervals while the date meshing segment (11) of said 24-hour wheel (2) meshes with said toothed wheel (12') of said gear unit (12).