Calendar mechanism for a timepiece movement allowing to display at least the retrograde calendar

Abstract

The present invention relates to a calendar mechanism for a timepiece in which the date is displayed in a retrograde manner and in which the date return rack (7) actuates the month star (13) and moves it forward one step when said date return rack (7) falls from its high position under the action of its return spring (74) when the last day of a month passes to the first day of the following month.

Description

[0001] The present invention relates to a calendar mechanism for a clock movement that allows the date to be displayed retrogradely. Preferably, the calendar mechanism is a perpetual calendar mechanism.

[0002] A retrograde perpetual calendar mechanism is described in François Lecoultre's book "Les Montre compliqués" on pages 231 to 236. In this mechanism, only the date display is retrograde: the date hand moves along an arc of a circle drawn on the dial so that when this hand reaches the end of the month on the 28th, 29th, 30th or 31st, it instantly returns to its starting point on the number 1. The other displays of the day of the week, the month of the year, the phases of the moon and leap years are classic.

[0003] In this mechanism, the date hand is carried by a date wheel with triangular teeth, which is attached to a pinion that meshes with a rack. This rack tends to rotate the date wheel in one direction. The clock's mechanism then advances the date wheel in a second direction, one tooth per day. A pawl prevents the date wheel from rotating in the first direction. The pawl has an arm that bears against a month cam, which is fixed to the twelve-toothed month star. The month cam has increments whose depth determines whether months have 30 or 31 days, as well as a notch in which the leap year cam pivots. This leap year cam has four increments: three equal increments and a fourth, distinct increment, which determines a leap year.Each time the month star completes a full rotation, the leap year cam makes a quarter turn thanks to a suitable mechanism (usually a Maltese cross). The end of the ratchet arm terminates in a four-notched rack. The position of this rack is therefore set by the month cam. A finger attached to the date wheel is used to lift the ratchet by acting against the notches of the rack at the appropriate moment to release the date wheel, which then pivots in the first direction, driven by the rack. This release occurs at the transition from the last day of the month to the first day of the following month; the position of the end of the ratchet arm on the month cam determines the timing of the release and limits the length of the month.

[0004] In this mechanism, only the date is displayed retrogradely. The month display is standard: the month hand is fixed to the month star and must advance one-twelfth of a turn to indicate the next month at the moment the date hand moves retrogradely. To achieve this, the rack has an arm designed to push a tooth of the month star as it moves down.

[0005] EP 3 989 011 A1 and CH 653 841 A3 describe two retrograde calendar mechanisms with a return rake.

[0006] In general, retrograde date mechanisms are bulky, especially in thickness if concentric displays are desired.

[0007] The object of the present invention is to provide a calendar mechanism (simple, annual, or perpetual) for a clock movement that allows at least the retrograde display of the date. One object of the present invention is, in particular, to provide a calendar mechanism that allows, specifically, the retrograde display of the date and the month. Another object of the present invention is to create a calendar mechanism that allows the retrograde display of the date and that is simple and compact, particularly in terms of thickness.

[0008] The present invention relates to a calendar mechanism for a clock movement according to claim 1.

[0009] The accompanying figures schematically illustrate, by way of example, one embodiment of the calendar mechanism according to the invention. In this embodiment, the calendar mechanism allows, in particular, the date and month to be displayed retrogradely. THE figures 1 à 14 illustrate the elements of the calendar mechanism that allow the date to be displayed, while the figures 15 And 16 illustrate the elements of the calendar mechanism that allow the month to be displayed. In particular, the figure 1 is a top view of part of a calendar mechanism according to an embodiment of the invention as of January 31. figure 2 is a top view of the mechanism of the figure 1 illustrating the transition from January 31st to February 1st (before the jump). The figures 3 And 4 These are top and bottom views, respectively, of the mechanism on February 1st (after the jump). figure 5 This is a top view of the mechanism illustrating the transition from February 1st to February 2nd (before the jump). figure 6 This is a top view of the mechanism on February 2nd (after the jump). figure 7 This is a top view of the mechanism as of February 28th. figure 8 This is a top view of the mechanism illustrating the transition from February 28th to March 1st (before the jump). figure 9 This is a top view of the mechanism as of February 29th. figure 10 This is a top view of the mechanism illustrating the transition from February 29th to March 1st (before the jump). figure 11 This is a top view of the mechanism on March 1st (after the jump). figure 12 This is a top view of the mechanism as of April 30th. figure 13 This is a top view of the mechanism illustrating the transition from April 30th to May 1st (before the jump). figure 14 is a view of the mechanism as of May 1st. The figure 15 This illustrates the elements of the calendar mechanism from the previous figures that allow the month to be displayed, with December being the month shown. figure 16 illustrates the elements of the calendar mechanism from the previous figures allowing the month to be displayed, the month displayed being January.

[0010] The calendar mechanism according to the invention is intended to equip a clock movement to allow the display of at least the date of the month. According to the invention, this display is retrograde.

[0011] In the illustrated embodiment, the calendar mechanism is in particular a perpetual calendar mechanism allowing the display of, among other things, the date, month and leap year.

[0012] A 24-hour wheel (not shown) is pivoted at A and arranged to be driven once a day by the clockwork movement, which includes the calendar mechanism. This 24-hour wheel carries a 24-hour finger 1 arranged to drive, once a day, a large rocker 2 pivoted at B on the clockwork movement. Preferably, and as illustrated in the figures, the 24-hour finger 1 cooperates with a correction pawl 21 of the large rocker to allow the clockwork movement's time display to be set counterclockwise without correcting the date and without damaging the mechanism.

[0013] The large rocker arm 2 is subjected to the action of a return spring 22 which tends to maintain it in an initial rest position against a stop (not shown). When the 24-hour finger 1 drives the large rocker arm 2, it pivots it at point B against the action of its return spring 22.

[0014] A drive pawl 23 is pivoted on the large rocker 2 and is subjected to the action of a return spring 230. The drive pawl 23 is intended to cooperate with a date wheel 3 with triangular teeth to advance the latter by one step in a first direction when the large rocker 2 pivots driven by the 24-hour finger 1. The date wheel 3 carries a date indicator (not shown) which can take any suitable shape.

[0015] A jumper 4 positions the date wheel 3 and prevents it from pivoting in a second direction opposite to the first. To achieve this, the jumper 4 includes a first positioning arm 41 arranged to cooperate with the teeth 31 of the date wheel 3 for positioning and locking the latter. A return spring 40 is arranged to constrain the jumper 4 against the teeth 31 of the date wheel 3.

[0016] A locking mechanism 5 is pivoted at C and comprises a first arm 51 arranged to cooperate with a second locking arm 42 of the jumper 4. The locking mechanism 5 is subjected to the action of its return spring 53, which tends to push said locking mechanism 5 into a position in which the first arm 51 abuts against a pin 54 driven into the clockwork mechanism. The locking mechanism 5 also comprises a second arm 52 arranged to cooperate with an arm 24 of the large rocker arm 2. As will be seen later, the locking mechanism 5 holds the jumper 4 away from the teeth 31 of the date wheel at the end of a month to allow the retrograde return of the date wheel 3.

[0017] A date pinion 6 is fixed to the date wheel 3 and meshes with a date rack 7 pivoted at D. The date rack 7 is subjected to the action of its return spring 74, which tends to rotate it towards a stop 75 fixed to the clock movement. In particular, the date rack 7 tends to rotate the pinion 6 and the date wheel 3 in a second direction opposite to the first (the direction of actuation of the large rocker 2 on the date wheel 3). The date rack 7 carries a month pin 71 arranged to cooperate with an intermediate rocker 8 pivoted at E on a month rocker 9, itself pivoted at F on the clock movement.

[0018] The intermediate rocker 8 has a slot 81 through which a pin 43 passes, fixed to the jumper 4 of the date wheel 3. When the date rack 7 reaches its upper position at the transition from the last day of the month to the first day of the following month, the month pin 71 pushes the intermediate rocker 8, which pivots at E and acts on the second pin 43 to rotate the jumper 4, which then releases the date wheel 3 and the locking 5. The latter then falls to lock the jumper 4 out of the teeth 31 of the date wheel 3.

[0019] The month 9 rocker includes a feeler 91 which is arranged to bear against a month 10 cam. The month 10 cam comprises a first portion 101 whose profile is calculated to determine the 30- or 31-day months between March and January, and a second portion 102 for the month of February. This second portion 102 has a notch 1022 in its center to allow passage of a tooth of a leap year cam 11 pivotally mounted on the month 10 cam.

[0020] The leap year cam 11 determines whether the current year is a leap year or not, that is, whether February has 28 or 29 days. In the illustrated embodiment, the leap year cam 11 is a satellite pivoted on the month cam 10 and has 8 teeth, of which six teeth 111 are full for non-leap years and Februarys with 28 days, and two teeth 112 are truncated for leap years and Februarys with 29 days (the reverse is also possible, i.e., six truncated teeth and two full teeth). The leap year cam 11 is driven by a fixed wheel 12 with nine teeth, which is coaxial with the month cam 10.

[0021] Thus, the month 9 switch and by extension the intermediate switch 8 can take four different positions depending on the current month.

[0022] Finally, according to the invention, the date rack 7 also carries a month finger 72 pivotally mounted on said rack 7 and subjected to the action of a return spring 73. The month finger 72 is arranged to drive a month star 13 attached to the month cam 10 when the date rack 7 falls. The month star 13 is subjected to the action of its positioning jumper 14 and in turn drives the display of the months.

[0023] This display of the months can take any suitable form. Preferably, it is also a retrograde display as illustrated in the figures 15 And 16The calendar mechanism in this embodiment further comprises a truncated toothed pinion 15 integral with the month star 13. The truncated toothed pinion 15 comprises a toothed sector 151 and a toothless sector 152 and is arranged to drive a month rack 17 pivoted at G on the clockwork movement. The month rack 17 is subjected to the action of its return spring 171, which tends to rotate it in the opposite direction to the drive direction of the truncated toothed pinion 15. Finally, the month rack 17 meshes with a month display pinion 18, which carries the month indicator (not shown). Preferably, a backlash compensation device is provided between the month 17 rake and the month 18 display pinion. Such a device may take the form of a special toothing for the month 18 display pinion.

[0024] The operation of the calendar mechanism is now described according to the embodiment of the invention illustrated in the figures.

[0025] THE figures 1 , 7 , 9 , 12 illustrate the calendar mechanism as described above at the end of the month, respectively on January 31, February 28 (non-leap year), February 29 (leap year), and April 30. The large rocker 2 is held in its rest position against its stop by its return spring 22. The feeler 91 of the month rocker 9 rests on the area of ​​the profile of the month cam 10 corresponding to the current month.

[0026] In this end-of-month position, the jumper 4 is pushed by its return spring into a position in which its first arm 41 is held in the teeth 31 of the date wheel 3. The date wheel 3, the date pinion 6, and consequently the date rack 7 are thus locked by the jumper 4. The arm 51 of the lock 5 rests against the second arm 42 of the jumper 4, which is pushed by its return spring 53. The date rack 7 is engaged with the date pinion 6, which is locked by the jumper 4, but does not cooperate with either the intermediate rocker 8 or the month star 13.

[0027] In the figure 1 , the probe 91 is in contact with an area of ​​the first portion 101 of the cam of the months 10 corresponding to the least of January to 31 days.

[0028] In the figure 12 , the probe 91 is in contact with an area of ​​the first portion 101 of the cam of months 10 whose depth corresponds to the month of April at 30 days.

[0029] There figure 7 illustrates the case of a non-leap year, with February ending on the 28th. In this case, the feeler 91 is in contact with a whole tooth 111 of the leap year cam 11 which is in the notch 1022 of the second portion 102 of the month cam 10.

[0030] There figure 9 illustrates the case of a leap year, with February ending on the 29th. In this case, the feeler 91 is in contact with a truncated tooth 112 of the leap year cam 11 which is in the notch 1022 of the second portion 102 of the month cam 10.

[0031] THE figures 2 , 8 , 10 And 13 illustrate the transition from the last day of the month to the 1st day of the following month just before the retrograde jump, namely the transition from January 31 to February 1, from February 28 to March 1, from February 29 to March 1 and from April 30 to May 1.

[0032] At the end of a month, the 24-hour finger 1, driven by the 24-hour wheel, contacts the correction pawl 21 and pivots the large rocker 2. The drive pawl 23 contacts the teeth 31 of the date wheel 3 to advance it one step in the first direction. Simultaneously, the arm 24 of the large rocker 2 comes into contact with the second arm 52 of the locking mechanism 5 and pivots it against the action of its return spring 53.

[0033] By pivoting, the date wheel 3 drives the date pinion 6, which in turn drives the date rack 7, which pivots against the action of its return spring 74 to reach its upper position. The month pin 71 then comes into contact with the intermediate rocker 8, whose position is determined by the month rocker 9 resting on the month cam 10, and causes it to pivot. The intermediate rocker 8 acts on the pin 43 of the jumper 4 and then raises said jumper 4 into a raised position in which the first arm 41 of said jumper 4 is no longer in the teeth 31 of the date wheel 3 ( figures 2 , 8 , 10 And 13 ).

[0034] The date wheel 3 is released and can then pivot in the second direction under the action of the date rack 7 to return the date indicator to the 1st of the month. This retrograde return is detailed below.

[0035] The 24-hour finger 1 continues its rotation until it releases the correction pawl 21. The large rocker 2 then returns to its rest position pushed by its return spring 22: the drive pawl 23 comes out of the teeth 31 of the date wheel 3 and the arm 24 of the large rocker 2 releases the blocker 5 ( figures 3 And 4 , 11 et 14 In doing so, the locking piece 5 pivots until it rests on its stop 54, pushed by its return spring 53. In this position, it prevents the jumper 4 from falling back into the teeth 31 of the date wheel 3 and holds said jumper 4 in its raised position. Thus, since nothing holds the date wheel 3, the date rack 7 pivots under the action of its return spring 74 and falls until it rests against the stop 75. In doing so, the date rack 7 drives the date pinion 6, which pivots so that the date indicator it carries returns to the rear to show the number 1 again.

[0036] According to the invention, as it falls, the date rake 7 advances the month star 13 by one step thanks to the month finger 72 which, in the rake's upper position, engages with the teeth of the month star 13 as it passes the end of a month. The month star 13 drives the month cam 10, to which it is attached, and the feeler 91 of the month rocker 9 is now aligned with the area of ​​the month cam 10 indicating the following month. It should be noted that in the illustrated embodiment, the month rocker is not spring-loaded. Thus, this month rocker is not always pressed against the month cam 10. At the end of the month, the month pin 71 makes contact with and pushes the intermediate rocker 8 and the month rocker 9 until the feeler 91 of the latter rests against the month cam 10.

[0037] THE figures 3 And 4illustrate the case of the transition to February 1st of a non-leap year, the feeler 91 therefore coming to rest on an entire tooth 111 of the leap year cam 11 which is in the notch 1022 of the second portion 102 of the month cam 10 intended for the month of February.

[0038] THE figures 11 And 14 illustrate the case of the transition to March 1st, respectively to May 1st, the probe 91 therefore coming in relation to an area of ​​the first portion 101 of the cam of the months 10 corresponding to the month of March, respectively May.

[0039] Just after the jump, on the 1st of a month, the blocker 5 is still resting on its pad 54 in a position in which it prevents the jumper 4 from falling back into the teeth 31 of the date wheel 3. Said date wheel 3 is positioned by the rake 7 in rest on its stop 75. This is preferably adjustable to avoid any display discrepancy between the 1st and the other days of the month.

[0040] THE figures 5 And 6 illustrate the transition from the 1st to the 2nd day of the month, more precisely, the transition from February 1st to February 2nd.

[0041] Starting from the situation of the figure 3 Illustrating February 1st of a non-leap year, at the end of the day, the 24-hour finger 1, driven by the 24-hour wheel, contacts the correction pawl 21 and pivots the large rocker 2. The drive pawl 23 contacts the teeth 31 of the date wheel 3 to advance it one step in the first direction. Simultaneously, the arm 24 of the large rocker 2 comes into contact with the second arm 52 of the locking mechanism 5 and pivots it away from the pin 54 against the action of its return spring 53. In doing so, the locking mechanism 5 releases the jumper 4, which falls back into the teeth 31 of the date wheel 3 and resumes its role in positioning and locking this wheel.

[0042] The date pinion 6, which is fixed to the date wheel 3, in turn drives the date rack 7, which pivots against the action of its return spring 74 and moves away from the stop 75. The indicator carried by the date pinion 6 displays the 2. The date wheel 3 pivots until the arm 41 of the jumper 4 falls back into the teeth 31 ( figure 5 ).

[0043] The 24-hour finger 1 continues its rotation until it releases the correction pawl 21. The large rocker 2 returns to its rest position, pushed by its return spring 22: the drive pawl 23 disengages from the teeth 31 of the date wheel 3 and the arm 24 of the large rocker 2 releases the stopper 5. In doing so, the stopper 5 falls back onto the second arm 42 of the jumper 4 ( figure 6 ) which has found its position in the toothing 31 of the date wheel 3. The date indicator now displays the 2.

[0044] During a mid-month date change, the sequence is essentially the same: The 24-hour finger 1, driven by the 24-hour wheel, contacts the correction pawl 21 and rotates the large rocker 2. The drive pawl 23 contacts the teeth 31 of the date wheel 3, advancing it one step in the first direction. Simultaneously, the arm 24 of the large rocker 2 rests against the second arm 52 of the locking mechanism 5 and rotates it. The jumper 4 rises during the rotation of the date wheel 3, driven by the drive pawl 23. As it rises, the pin 43 of the jumper 4 slides in the slot 81 of the intermediate rocker 8 without affecting the position of the latter or the month rocker 9.

[0045] The date pinion 6, attached to the date wheel 3, in turn drives the date rack 7, which pivots a little further against the action of its return spring 74. The date indicator takes a step.

[0046] The 24-hour finger 1 continues its rotation until it releases the correction pawl 21. The large rocker 2 returns to its rest position pushed by its return spring 22: the drive pawl 23 comes out of the teeth 31 of the date wheel 3 and the arm 24 of the large rocker 2 releases the blocker 5. In doing so, the blocker 5 falls back into support on the second arm 42 of the jumper 4.

[0047] Thus, according to the invention, the calendar mechanism as illustrated allows for a simple retrograde display of the date. Furthermore, by rotating the date wheel 7 backward, it also drives the month star 13 for displaying the months. The release of the jumper at the end of the month by the pin carried by the wheel also allows for a calendar mechanism with a reduced thickness at the date wheel. Moreover, by driving the month display with the date wheel, which returns the date indicator to 1 retrogradely, the transition between months is simple and does not increase the power consumption of the movement compared to a known mechanism.

[0048] As previously stated, preferably, the calendar mechanism according to the invention is also arranged to display the month in retrograde order.

[0049] THE figures 15 And 16illustrate the return to the previous display of months when December 31st transitioned to January 1st.

[0050] In the figure 15 The components of the calendar mechanism's month display can be seen in a configuration corresponding to December. This figure shows the month star 13 held by its jumper 14. The month rack 17 engages with the toothed sector 151 of the truncated pinion 15, which is integral with the month star 13, and with the month display pinion 18, which carries the month indicator (not shown). On December 31st, at the end of the day, the 24-hour hand 1, driven by the clockwork mechanism, activates the large rocker 2, which pivots against the action of its spring 230 and advances the date wheel 3 by one step.

[0051] By pivoting, the date wheel 3 drives the date pinion 6, which in turn drives the date rack 7, which pivots again against the action of its return spring 74 to reach its upper position. The month pin 71 then comes into contact with the intermediate rocker 8, whose position is determined by the month rocker 9 resting on the month cam 10, and causes it to pivot. The intermediate rocker 8 acts on the pin 43 of the jumper 4 and then raises said jumper 4 into a raised position in which the first arm 41 of said jumper 4 is no longer in the teeth 31 of the date wheel 3 ( figures 2 , 8 , 10 And 13 ). The date wheel 3 goes back so that the indicator displays the 1st again.

[0052] As it falls, the date rake 7 moves the month 13 star by one step thanks to the month finger 72 which in the high position of the date rake 7 comes into the teeth of the month 13 star. The month 13 star moves the month 10 cam which is attached to it and the feeler 91 of the month 9 rocker is now opposite the area of ​​the first portion 101 of the month 10 cam indicating the month of January.

[0053] The truncated toothed pinion 15 pivoted at the same time as the month star 13, and it is now the toothless sector 152 that faces the month rake 17. The latter is therefore no longer held in place and pivots, pushed by its return spring 171, until it comes to rest against a stop 172, which is preferably adjustable. As it falls, the month rake 17 drives the month display pinion 18, which carries the month indicator. This then moves backward until it again indicates the month of January ( figure 16). The mechanism is arranged so that at the next step of the month star 13 (that is to say at the next change of month), the toothed sector 151 of the truncated toothed pinion 15 comes into contact again with the month rake 17 to rotate the latter against the action of its return spring 171 and thus rotate the display pinion of the months 18.

[0054] We have therefore also implemented the retrograde display of the months in a simple and secure way, limiting the bulk and energy consumption for the movement.

[0055] In the illustrated embodiment, the calendar mechanism is a perpetual calendar mechanism. Alternatively, it could be a simple or annual calendar mechanism.

[0056] In general, the calendar mechanism according to the invention comprises a date wheel carrying a date indicator arranged to allow the retrograde display of the date; an actuating wheel arranged to be driven by a movement of the timepiece to advance the date wheel one step per day in a first direction at the end of the day; a date return rake subjected to the action of a return spring and engaged with the date wheel so that the date return rake tends to rotate the date wheel in a second direction opposite to the first; a date jumper cooperating with the date wheel to prevent it from rotating in the second direction; a blocking wheel controlled by the actuating wheel; a month star arranged to advance a month wheel one step at each end of the month.

[0057] The mechanism is arranged so that, at the transition from the last day of one month to the first day of the following month, the actuating wheel advances the date wheel one step in the first direction. The date return lever pivots against the action of its return spring to reach its upper position. In this upper position, the date return lever is arranged to move the date jumper to a raised position in which it no longer obstructs the date wheel. Also at the transition from the last day of one month to the first day of the following month, the actuating wheel commands the locking wheel to move it to a position in which it holds the date jumper out of reach of the date wheel, which can thus pivot in the second direction.On the other hand, the date return rake is further arranged to actuate the month star and advance it one step when it pivots from its upper position under the action of its return spring.

[0058] Preferably, the calendar mechanism includes an additional a month cam attached to the month star and whose profile determines the length of the months (28, 29, 30 or 31 days); a month feeler arranged to bear against the month cam; an intermediate mobile pivoted on the month feeler and arranged to cooperate with the date return rake and the date jumper.

[0059] In this variant, when the date return rake pivots to its upper position at the transition from the last day of one month to the first day of the next, it rotates the intermediate wheel, which then moves the date jumper to its raised position. In this position, the jumper no longer obstructs the date wheel, allowing it to pivot in the opposite direction. Preferably, the month cam comprises a first portion for months of 30 and 31 days and a second portion for February, including a slot through which a leap year cam passes.

[0060] Preferably, the month display is also retrograde. To achieve this, the month display mechanism includes a truncated pinion fixed to the month star and comprising a toothed sector and a toothless sector, arranged to drive a return rake. This return rake is subjected to the action of a return spring that tends to rotate it in the opposite direction to the drive direction of the truncated pinion. The return rake meshes with a month wheel that carries the month indicator. At the end of the last day of December, the month star advances one step, driven by the date return rake, and rotates the truncated pinion into a position in which the toothless sector cooperates with the return rake. Since it is no longer held, it pivots under the action of its return spring and causes the month mobile to move backwards in a retrograde manner.

[0061] Preferably, the date and month hands are concentric.

[0062] The calendar mechanism according to the invention, whether simple, annual, or perpetual, allows the date and preferably also the month to be displayed retrogradely. By driving the months via the date return lever, the power consumption of the movement is not increased compared to a conventional solution. The mechanism's compact size, particularly its thickness, offers considerable flexibility in arranging the date and month displays. In particular, they could be concentric and / or positioned at the center of the movement. Furthermore, it is possible to offer large retrograde displays extending over a wide angle or segment.

Claims

1. Calendar mechanism for a timepiece, comprising • a date mobile (3, 6) bearing an indicator of the date arranged to allow the retrograde displaying of the date; • an actuation mobile (2) arranged to be driven by a movement of the timepiece to cause the date mobile (3, 6) to advance by one step per day in a first direction at the end of the day; • a date return rack (7) subject to the action of a return spring (74) and engaged with the date mobile (3, 6) such that the date return rack (7) tends to cause the date mobile (3, 6) to pivot in a second direction, opposite to the first direction, the date return rack (7) being arranged to pivot against the action of its return spring (74) to reach a top position when the actuation mobile (2) causes the date mobile (3, 6) to advance by one step in the first direction in passing from the last day of a month to the first day of the following month; • a date jumper (4) cooperating with the date mobile (3, 6) to prevent same from pivoting in the second direction; • a blocking mobile (5) controlled by the actuation mobile (2); • a month starwheel (13) arranged to drive a month mobile (18) by one step at the end of each month, the month mobile (18) bearing a month indicator; characterised in that the calendar mechanism is arranged such that, when the date return rack (7) pivots into its top position, it cooperates with the date jumper (4) to move said jumper (4) into a position in which it no longer prevents the date mobile (3, 6) from pivoting in the second direction and such that, in passing from the last day of a month to the first day of the following month, the actuation mobile (2) controls the blocking mobile (5) to move it into a position in which it keeps the date jumper (4) in its position in which it no longer prevents the date mobile (3, 6) from pivoting in the second direction, said date mobile (3, 6) thus being able to pivot freely in the second direction to return to its position at the start of a month; and in that the calendar mechanism is arranged such that the date return rack (7) actuates the month starwheel (13) and causes it to advance by one step when said date return rack (7) drops from its top position under the action of its return spring (74) in passing from the last day of a month to the first day of the following month.

2. Calendar mechanism as claimed in claim 1, characterised in that it further comprises: • a month cam (10) fixedly attached to the month starwheel (13) and the profile (101, 102) of which determines the length of the months (28, 29, 30 or 31 days); • a month feeler spindle (9) which can move in rotation and is arranged to cooperate with the month cam (10); • an intermediate mobile (8) pivoted on the month feeler spindle (9) and arranged to cooperate with the date return rack (7) and the date jumper (4); the mechanism being arranged such that, when the date return rack (7) pivots against the action of its return spring (74) to return to its top position in passing from the last day of a month to the first day of the following month, it cooperates with the intermediate mobile (8) which thus moves the date jumper (4) into its position in which the latter no longer prevents the date mobile (3, 6) from pivoting in the second direction.

3. Calendar mechanism as claimed in the preceding claim, characterised in that the intermediate mobile (8) is a lever arm (8) pivoted on the month feeler spindle (9) and comprising a slot (81) through which a pin (43) of the date jumper (4) passes such that, apart from at the end of a month, the date jumper (4) can pivot when it is raised by the date mobile (3, 6) which pivots in the first direction driven by the actuation mobile (2).

4. Calendar mechanism as claimed in claim 2 or 3, characterised in that the profile of the month cam (10) comprises a first portion (101) characterising the months with 30 and 31 days from March to January and a second portion (102) for the month of February, said second portion comprising a slot (1022) through which a leap-year cam (11) passes, said leap-year cam being arranged to determine the length of the month of February.

5. Calendar mechanism as claimed in any one of the preceding claims, characterised in that it is arranged to allow the retrograde displaying of the months and comprises a truncated tooth pinion (15) fixedly attached to the month starwheel (13) and comprising a toothed sector (151) and a toothless sector (152) and arranged to drive a month return rack (17) in a first direction, said month return rack (17) being subject to the action of a return spring (171) which tends to cause it to pivot in a second direction opposite to the first direction, the month return rack (17) engaging with the month mobile (18) such that, in passing from the last day of the month of December to the first day of the month of January, the month starwheel (13) advances by one step driven by the date return rack (7) and causes the truncated tooth pinion (15) to pivot into a position in which the toothless sector (152) cooperates with the month return rack (17) such that, with the latter no longer being held, it pivots in the second direction under the action of its return spring (171) and drives the month mobile (18) which moves backwards.

6. Calendar mechanism as claimed in any one of the preceding claims, characterised in that the date return rack (7) bears a month finger (72) mounted so as to be pivotable on said rack (7) and subjected to the action of a return spring (73), said month finger (72) being arranged to drive the month starwheel (13) when the date return rack (7) drops from its top position under the action of its return spring (74).

7. Calendar mechanism as claimed in any one of the preceding claims, characterised in that the date (3, 6) and month (18) mobiles are concentric.

8. Timepiece movement comprises a calendar mechanism as claimed in any one of the preceding claims.

9. Timepiece comprises a movement as claimed in the preceding claim.

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