EQUATION OF TIME MECHANISM CONTROLLED BY A DIFFERENTIAL DEVICE

Description

Technical field of the invention

[0001] The present invention relates to a running equation of time mechanism for a timepiece. More specifically, the invention relates to a running equation of time mechanism driving a true time minute hand concentric with the movement's hand. Technological background of the invention

[0002] As is well known, there is a gap between true solar time, which corresponds to the time elapsed between two consecutive zenith passages of the Sun at the meridian of the same place, and mean solar time or civil time, which is the average, taken over the year, of the duration of all true solar days. This difference between civil time and true time reaches +14 min 22 s on February 11, and -16 min 23 s on November 4. These values ​​vary little from year to year.

[0003] To indicate the time difference between civil time and true time, some timepieces include, in addition to the hand that indicates the civil time minute, a so-called equation of time mechanism which includes a hand that moves opposite a graduated scale to indicate the difference between the civil time minute and the solar time minute for a given day. This true time minute hand is actuated by an equation of time cam whose profile is determined by the difference between mean solar time and true solar time for all days of the year.

[0004] Another mechanism for indicating the time difference between civil time and true time is known as a running equation of time mechanism. The hands of a timepiece equipped with a running equation of time mechanism have two concentric minute hands, one indicating the minute of civil time, and the other indicating the minute of true time. At any instant, the difference between the civil time minute hand and the true time minute hand is determined by the difference between mean solar time and true solar time for the day of the year in question. As with the equation of time mechanism, the true time minute hand of a running equation of time mechanism is actuated by an equation of time cam.

[0005] The equation of time cam is rotated at a rate of one revolution per year from a calendar mechanism that can be simple or perpetual. The simple calendar is a mechanism designed to indicate the day of the week, the date of the month, the month of the year or the phases of the Moon, but which does not take into account the variation in the number of days in the month (months of 28, 29 or 30 days). In other words, the user of a watch with a simple calendar mechanism will have to make a manual correction at the end of every month that has less than 31 days. For example, on February 28 or April 30, manual intervention will be required. As for the perpetual calendar mechanism, it allows, like a simple calendar mechanism, to indicate the day, the date, the month and the phases of the Moon.But unlike a simple calendar mechanism, a perpetual calendar mechanism automatically takes into account the length of the months (28, 29 and 30 days), without manual intervention. A perpetual calendar mechanism therefore automatically takes into account leap years.

[0006] An example of a running equation of time mechanism is disclosed by European patent application EP 1 286 233 A1 in the name of the Applicant. figure 1 attached to this patent application is taken from the European patent application EP 1 286 233 A1 mentioned above and illustrates a running equation of time mechanism driven by a differential device.

[0007] In particular, this figure shows an equation of time cam 1 whose profile is determined by the difference, for each day of the year, between mean solar time or civil time and true solar time. This equation of time cam 1 is rotated at a rate of one revolution per year from a simple or perpetual calendar mechanism included in the timepiece. The equation of time cam 1 carries a month disc 2 which rotates at the same speed as it and which makes it possible to make the position of this equation of time cam 1 coincide with the date indicated by the date mechanism so that the solar time minute hand 4 indicates the exact difference between the minute of civil time and the minute of solar time.

[0008] The date mechanism, simple or perpetual, can be of any known type and will not be described here in its entirety. It is sufficient, in fact, for a good understanding, to know that this date mechanism drives the equation of time cam 1 at the rate of one complete revolution per year. However, for illustration purposes only, a date wheel set 6 driving a hand 8 which indicates the date (from 1 to 31) has been shown. This date wheel set 6 rotates at the rate of one complete revolution per month. It is actuated by the date mechanism and drives the equation of time cam 1 via an intermediate date idler wheel 10 which allows the direction of rotation to be reversed, and a reduction wheel set 12 which allows the rotation speed to be reduced from one complete revolution per month to one complete revolution per year.

[0009] The solar time minute hand 4 is driven by a differential gear device 14 which has as respective inputs a gear train driving a civil time minute hand 18, and a rack 20 which cooperates with the equation of time cam 1 (on the figure 1 , the rake 20 is represented in its two extreme positions, once in solid line, and the other time in mixed line). More precisely, as can be seen on the figure 1, the differential gear device 14 comprises at least one and, preferably, two satellite pinions 22 driven by the timer of the watch movement. These two satellite pinions 22 are capable of rotating on themselves and rolling on the internal teeth 24 of an equation of time wheel 26. The latter also has on its external periphery a first toothed sector 28 by which it cooperates with a second toothed sector 30 with which the rack 20 is provided at one of its ends. This rack 20 is subjected to the return action of a spring (not shown) fixed to the watch frame and which tends to apply a feeler 32 forming the other end of the rack 20 against the profile of the equation of time cam 1. The solar time display gear train comprises a solar time display pinion 34 placed in the center of the differential gear device 14.This solar time display pinion 34 meshes on the one hand with the satellite pinions 22, and on the other hand carries a solar time display wheel 38 which meshes with a cannon pinion 40 on the barrel of which the solar time minute hand 4 is driven. This gear train 38, 40 makes it possible to bring the solar minute display back to the center 42 of the watch movement, so that the solar time minute hand 4 is concentric with the civil time minute hand 18.

[0010] The running equation of time mechanism just described works as follows.

[0011] In normal operating mode of the watch, the equation of time cam 1, the rack 20 and therefore the equation of time wheel 26 are stationary. On the other hand, the satellite pinions 22 are driven by the watch movement. They therefore rotate on themselves and roll on the internal toothing 24 of the equation of time wheel 26, driving the solar time display pinion 34 in rotation, which allows the solar time minute hand 4 to rotate concomitantly with the civil time minute hand 18. The gap between the solar time minute hand 4 and the civil time minute hand 18 therefore remains constant over a period of 24 hours.

[0012] Once a day, around midnight, the equation of time cam 1 pivots, driven by the date mechanism which moves the calendar from one day to the next. At this precise moment, the feeler 32 which is in contact with the profile of the equation of time cam 1 in turn pivots the rack 20. This rack 20, by pivoting, drives the equation of time wheel 26 in rotation. The satellite pinions 22 being, during this brief interval of time, substantially immobile (they make a complete rotation on themselves in 1 hour), rotate on themselves while being driven in rotation by the equation of time wheel 26, and in turn drive the solar time display pinion 34 so as to adjust the position of the solar time minute hand exactly again.

[0013] The running equation of time mechanism described above therefore makes it possible, by means of a civil time minute hand and a solar time minute hand, to display at any time the time difference between mean solar time and true time. It should be noted, however, that the differential gear device 14 is not located at the center 42 of the watch movement. This therefore results in a construction that is not symmetrical, which is counterintuitive. Furthermore, due to the eccentric positioning of the differential gear device 14, it is necessary to provide an additional gear train (solar time display wheel 38 and cannon pinion 40) to bring the solar time display back to the center 42 of the watch movement and ensure the concentricity of the civil time minute hand 18 and the solar time minute hand 4. This additional gear train takes up space and can be a source of failure.Document CH698613 also discloses a mechanism for riding on a walking time. Summary of the invention

[0014] The present invention aims to overcome the problems described above and others by providing a running equation of time mechanism controlled by a differential gear device which is notably more compact and therefore easier to integrate into a clockwork movement.

[0015] The present invention relates to a mechanism as defined by claim 1 of the patent.

[0016] Thanks to these characteristics, the present invention provides a running equation of time mechanism which is driven by a differential gear device provided with a reduction satellite wheel and pinion via which the civil time minute pipe drives a civil time hour pipe onto which the civil time hour hand is driven, and a multiplier satellite wheel and pinion via which the civil time hour pipe drives a true time minute pipe onto which the true time minute hand is driven. The fact of proposing to integrate into the heart of the differential gear device the functions which make it possible to produce the civil time hour from the civil time minute, and the true time minute from the civil time hour and an equation of time cam, makes it possible to obtain a more compact differential gear device in which the reduction and multiplier satellite wheels are brought back to the center of the clockwork movement.The differential gear device according to the invention is thus easier to house in the watch movement which it equips, which makes it possible to reduce the size of the watch movement and to have more space to house the other components of the movement.

[0017] According to a preferred embodiment of the invention, the reducing satellite mobile and the multiplying satellite mobile rotate on themselves, describing a circular trajectory, preferably of the same radius, centered on the minute barrel of civil time.

[0018] The differential gear mechanism according to the invention has fewer components and is therefore more reliable. In addition, it has a general radial symmetry centered on the center of the movement, which facilitates its assembly and arrangement. Brief description of the figures

[0019] Other characteristics and advantages of the present invention will emerge more clearly from the following detailed description of an exemplary embodiment of a running equation of time device according to the invention, this example being given purely for illustrative and non-limiting purposes only in connection with the appended drawing in which: there figure 1 , already cited, is a view of a running equation of time mechanism according to the prior art driven by a differential device; the figure 2 is a top view of the walking equation device according to the invention; the figure 3 is a sectional view along line AA of the figure 2 ; there figure 4 is a sectional view along line BB of the figure 2 , and the Figure 5 is a sectional view along line CC of the figure 2 . Detailed description of an embodiment of the invention

[0020] The present invention proceeds from the general inventive idea which consists of equipping a running equation of time mechanism with a differential gear device which is capable of indicating both civil time by means of a civil time hour hand and a civil time minute hand, and the true time minute by means of a second minute hand concentric with the civil time hands. The differential gear device has as respective power take-offs a wheel set of a finishing train of the clockwork movement on the one hand, and an equation of time cam on the other hand.According to the invention, a reduction function which allows to go from the minute of civil time to the hour of civil time, and a multiplication function which allows to go from the hour of civil time to the minute of true time are integrated in the center of the differential gear device, which makes it possible to make the running equation of time mechanism more compact and therefore easier to arrange in the clockwork movement.

[0021] The present invention aims to integrate into a timepiece such as a wristwatch a running equation of time mechanism, that is to say a mechanism whose hands include two concentric minute hands, one indicating the minute of civil time and the other indicating the minute of true time. To this end, and as can be seen in the figure 2, the running equation of time mechanism according to the invention, designated as a whole by the general reference numeral 44, comprises on the one hand a conventional hand whose role is to indicate civil time by means of an hour hand 46 and a minute hand 48, and on the other hand a true time minute hand 50, concentric with the civil time minute hand 48, and which indicates the true time minute. To allow the wearer of the watch to easily differentiate between the civil time minute hand 48 and the true time minute hand 50, the latter may, for example, end with a representation of the astrological symbol of the sun 52.As will be seen in more detail later in this description, the exact position of the true time 50 minute hand for a given day is determined once in 24 hours, around midnight, then the two civil time 48 and true time 50 minute hands move in concert, the gap between these two hands 48 and 50 remaining constant for the given day.

[0022] We can also see on the figure 2 a part of the running equation of time mechanism 44 according to the invention, and in particular an equation of time cam 54 whose profile, let us recall, is determined by the difference between the mean solar time or civil time, and the true time or solar time for each of the days of the year.

[0023] Still in connection with the figure 2, we see that the equation of time cam 54 is fixed on an equation of time wheel 56 which is driven at the rate of one complete revolution per year by a simple or perpetual calendar mechanism (not shown) which the timepiece comprises. This calendar mechanism can be of any known type and will not be described here in detail. It is sufficient, in fact, for a good understanding of the invention, to know that this calendar mechanism drives the equation of time wheel 56 on which the equation of time cam 54 is fixed at the rate of one complete revolution per year. The date mechanism comprises a date wheel 58 which rotates at the rate of one complete revolution per month, driving a date indicator 104.On the other hand, the equation of time wheel 56 is driven by the date wheel 58 via an intermediate date return wheel 60 allowing the direction of rotation to be reversed, and a reduction wheel 62 which allows the rotation speed to be reduced from one complete revolution per month to one complete revolution per year.

[0024] According to the invention, the true time minute hand 50 is driven by a differential gear device 64 which has as respective inputs (see figure 3 ) a mobile 66 of a finishing gear train driving the civil time minute hand 48 and an equation of time lever 68 which cooperates with the equation of time cam 54. More precisely, as visible on the figure 3, a civil time minute gun 70 is driven by the wheel 66 of the finishing gear of the timepiece movement via a cannon pinion 72 secured to the civil time minute gun 70. In turn, the civil time minute gun 70 drives a reduction satellite wheel 74 formed of a first satellite wheel 76 and a first satellite pinion 78 secured to the first satellite wheel 76.

[0025] The reduction satellite wheel 74 is pivotally mounted around a first pin 80 driven into an upper differential frame 82, which is secured to a civil time hour pipe 84 onto which the civil time hour hand 46 is driven. Driven by the civil time minute pipe 70 via the first satellite wheel 76, the first satellite pinion 78 rolls on a first internal toothing 86 of a first differential crown 88 which is carried by the clockwork movement and which is fixed. By rolling on the first internal toothing 86 of the fixed differential crown 88, the first satellite pinion 78 thus pivots the upper differential frame 82 and therefore the civil time hour pipe 84 which is secured to the upper differential frame 82.By a judicious choice of the gear ratios between the civil time minute barrel 70, the first satellite wheel 76, the first satellite pinion 78 and the fixed differential crown 88, a reduction of one twelfth is achieved between the civil time minute and the civil time hour and thus the civil time display is obtained. In other words, the reducing satellite wheel 74 allows, by a reduction of one twelfth, to pass from the civil time minute to the civil time hour.

[0026] As visible on the figure 4, a multiplying satellite mobile 90 is formed of a second satellite wheel 92 and a second satellite pinion 94 secured to the second satellite wheel 92. The multiplying satellite mobile 90 is mounted freely around a second pin 96 driven into the upper differential frame 82 with which the civil time hour pipe 84 is secured. When the civil time hour pipe 84 and therefore the upper differential frame 82 rotate, they drive the second pin 96 and, consequently, the multiplying satellite mobile 90 whose second satellite pinion 94 rolls on a second internal toothing 98 of a mobile differential crown 100 which will be seen below to be in mesh with the equation of time cam 54. The second satellite wheel 92 in turn drives a solar time minute pipe 102 onto which the true time minute hand 50 is driven.By a judicious choice of the gear ratios between the civil time hour gun 84, the second satellite wheel 92, the second satellite pinion 94 and the mobile differential crown 100, a multiplication by twelve is achieved between the civil time hour and the true time minute and thus the display of the true time minute is obtained. In other words, the multiplying satellite mobile 90 allows, by a multiplication by twelve, to go from the civil time hour to the true time minute.

[0027] It follows from the above that the reducing satellite mobile 74 and the multiplying satellite mobile 90 rotate on themselves, describing a circular trajectory centered on the civil time minute barrel 70. Preferably, the reducing satellite mobile 74 and the multiplying satellite mobile 90 move on a circle of the same radius, centered on the civil time minute barrel, while being angularly spaced.

[0028] The movable differential crown 100 is controlled in pivoting by the equation of time lever 68 provided with a feeler beak 106 by means of which the equation of time lever 68 is in contact with the profile of the equation of time cam 54. This equation of time lever 68 is held in elastic support against the profile of the equation of time cam 54 by a spring 108. This equation of time lever 68 is also provided with a first tooth 110 in engagement with a corresponding second tooth 112 provided on the movable differential crown 100 to control the movement of the latter. We understand in fact that at a moment close to midnight when the date mechanism changes date, it commands the advancement of the date wheel 58 by one step. During this brief moment when the date change occurs, the upper differential frame 82 and therefore the civil time hour gun 84 can be considered as immobile.By pivoting, the movable differential crown 100 drives the second satellite pinion 94 and thus the second satellite wheel 92 which, in turn, meshes with the solar time minute gun 102 onto which the true time minute hand 50 is driven. The position of the true time minute hand 50 is thus adjusted for the coming day.

[0029] We now refer to the Figure 5 in which it can be seen that at least one and preferably two screws 114 make it possible to close the upper differential frame 82 onto a lower differential frame 116. The upper 82 and lower 116 differential frames therefore rotate together when the differential gear device 64 according to the invention operates.

[0030] It goes without saying that the present invention is not limited to the embodiment which has just been described and that various simple modifications and variants can be envisaged by those skilled in the art without departing from the scope of the invention as defined by the appended claims. Nomenclature

[0031] 1. Equation of time cam 2. Month disc 4. Solar time minute hand 6. Date wheel 8. Hand 10. Date intermediate idler wheel 12. Reduction wheel 14. Differential gear device 18. Civil time minute hand 20. Rack 22. Satellite pinions 24. Internal teeth 26. Equation of time wheel 28. First toothed sector 30. Second toothed sector 32. Feeler 34. Solar time display pinion 38. Solar time display wheel 40. Cannon pinion 42. Center 44. Running equation of time mechanism 46. Civil time hour hand 48. Civil time minute hand 50. True time minute hand 52. Astrological symbol of the sun 54. Cam of equation of time 56. Equation of time wheel 58. Date wheel 60. Intermediate date wheel 62. Reduction wheel 64. Differential gear device 66. Wheel 68. Equation of time lever 70. Minute gun of civil time 72.Roadway 74. Reduction satellite wheel 76. First satellite wheel 78. First satellite pinion 80. First pin 82. Differential upper frame 84. Civil time hour barrel 86. First internal toothing 88. Fixed differential crown 90. Multiplier satellite wheel 92. Second satellite wheel 94. Second satellite pinion 96. Second pin 98. Second internal toothing 100. Mobile differential crown 102. True time minute barrel 104. Date indicator 106. Feeler beak 108. Spring 110. First tooth 112. Second tooth 114. Screw.

Claims

1. An equation of time mechanism comprising a set of hands whose purpose is to indicate civil time by means of a concentric civil hour hand (46) and of a concentric civil minute hand (48), and a true minute hand (50), concentric to the civil minute hand (48), which is driven in on a pipe on the true minute hand (102), the equation of time mechanism (44) also comprising an equation of time cam (54) with a profile that is determined by the difference, on every day of the year, between civil time and true time, said equation of time cam (54) being rotated at the rate of one revolution per year by a horology movement, the position of the true minute hand (50) being determined by the position of the equation of time cam (54), the equation of time mechanism (44) also comprising a differential gear device (64) whose first entry is formed by a cannon pinion (72) integral with a civil minute pipe (70) on which is driven said civil minute hand (48), and whose second entry is formed by the equation of time cam (54), the differential gear device (64) comprising a planetary gear (100) engaging with the equation of time cam (54) on one hand, and which, via a satellite mobile, meshes with the pipe on the true minute hand (102) on the other hand, this planetary gear (100) being concentrically arranged relative to the true minute hand (50), the equation of time mechanism being characterised in that it also comprises an equation of time lever (68) resiliently pressed against the profile of the equation of time cam (54) and which has a first tooth (110) engaging with a corresponding second tooth (112) provided on the planetary gear (100) to control the pivotal displacement of this planetary gear (100).

2. The equation of time mechanism according to claim 1, characterised in that the equation of time lever (68) has a feeler beak (116) via which the equation of time lever contacts the profile of the equation of time cam (54).

3. The equation of time mechanism according to any of claims 1 and 2, characterised in that the equation of time lever (68) is kept resiliently pressed against the profile of the equation of time cam (68) by a spring (108).