Running equation of time mechanism controlled by a differential device

Abstract

A running equation of time mechanism includes civil hour and minute hands to indicate civil time and a concentric true minute hand to indicate true time. The running equation of time mechanism includes an equation of time cam and a differential gear device, a first input of which is formed by a civil minute pipe on which a civil minute hand is pressed, and a second input of which is formed by the equation of time cam. The differential gear device includes a planetary reducer wheel set via which the civil minute pipe drives a civil hour pipe on which is pressed the civil hour hand, and a planetary multiplier wheel set via which the civil hour pipe drives a true minute pipe on which is pressed the true minute hand.

Claims

1. A running equation of time mechanism comprising: a hand arrangement whose purpose is to indicate civil time by a concentric civil hour hand and civil minute hand, and a true minute hand concentric with the civil time hands, an equation of time cam having a profile which is determined by a difference, on each day of the year, between civil time and true time, wherein the equation of time cam is driven in rotation at the rate of one revolution per year by a timepiece movement, wherein the position of the true minute hand is determined by the position of the equation of time cam, and a differential gear device, a first input of which is formed by a cannon-pinion integral with a civil minute pipe on which the civil minute hand is pressed, and a second input of which is formed by the equation of time cam, wherein the differential gear device is arranged concentrically with respect to the true minute hand.

2. The running equation of time mechanism of claim 1, wherein an end of the true minute hand includes an astrological symbol.

3. The running equation of time mechanism of claim 1, wherein the second input includes an equation of time lever provided with a feeler beak that directly contacts the equation of time cam.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features and advantages of the present invention will appear more clearly from the following detailed description of an example embodiment of a running equation of time device according to the invention, this example being given solely by way of non-limiting illustration with reference to the annexed drawing, in which:

(2) FIG. 1, cited above, is a view of a running equation of time mechanism according to the prior art driven by a differential device.

(3) FIG. 2 is a top view of the running equation of time device according to the invention.

(4) FIG. 3 is a cross-sectional view along line A-A of FIG. 2.

(5) FIG. 4 is a cross-sectional view along line B-B of FIG. 2.

(6) FIG. 5 is a cross-sectional view along line C-C of FIG. 2.

DETAILED DESCRIPTION OF ONE EMBODIMENT OF THE INVENTION

(7) The present invention proceeds from the general inventive idea consisting in 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 hour hand and a civil minute hand, and the true minute by means of a second minute hand concentric with the civil time hands. The respective power take-offs of the differential gear device are a going train wheel set of the timepiece movement on one hand, and an equation of time cam on the other hand. According to the invention, a gear reduction function that makes it possible to change from the civil minute to the civil hour, and a multiplier function that makes it possible to change from the civil hour to the true minute, are integrated into the differential gear device, which makes the running equation of time mechanism more compact and thus easier to arrange inside the timepiece movement.

(8) It is an object of the present invention to integrate in a timepiece, such as a wristwatch, a running equation of time mechanism, i.e. a mechanism whose hand arrangement includes two concentric minute hands, one indicating the civil minute and the other indicating the true minute. To this end, and as seen in FIG. 2, the running equation of time mechanism according to the invention, designated as a whole by the general reference numeral 44, includes on one hand a conventional hand arrangement whose purpose is to indicate civil time by means of an hour hand 46 and a minute hand 48, and on the other hand, a true minute hand 50, concentric with civil minute hand 48, and which indicates the true solar minute. To enable the wearer of the watch to easily tell the difference between civil minute hand 48 and true minute hand 50, the end of the latter may, for example, include a representation of the astrological symbol of the sun 52. As will be seen in detail in the following description, the exact position of the true minute hand 50 on a given day is determined once in 24 hours, around midnight, and then civil minute hand 48 and true minute hand 50 move in concert, the distance between these two hands 48 and 50 remaining constant for the given day.

(9) FIG. 2 also shows a part of the running equation of time mechanism 44 according to the invention, and particularly an equation of time cam 54 whose profile, it should be recalled, is determined by the difference between mean solar time or civil time, and true time or solar time on every day of the year.

(10) Referring again to FIG. 2, it is seen that equation of time cam 54 is secured to an equation of time wheel 56 which is driven at a rate of one complete revolution per year by a simple or perpetual calendar mechanism (not represented) comprised in the timepiece. The simple or perpetual calendar mechanism may be of any known type and will not be described in detail here. To ensure proper understanding of the invention, it is sufficient to know that this calendar mechanism drives equation of time wheel 56, to which equation of time cam 54 is secured, at the rate of one complete revolution per year. The calendar mechanism comprises a date wheel 58 that rotates at a rate of one complete revolution per month while driving a date indicator 104. Moreover, equation of time wheel 56 is driven by date wheel 58 via an intermediate date wheel 60 making it possible to reverse the direction of rotation, and a reduction wheel set 62 which can reduce the rotational speed from one complete revolution per month to one complete revolution per year.

(11) According to the invention, true minute hand 50 is driven by a differential gear device 64, whose respective inputs (see FIG. 3) are a wheel set 66 of a going train driving the civil minute hand 48 and an equation of time lever 68 which cooperates with equation of time cam 54. More precisely, as seen in FIG. 3, a civil minute pipe 70 is driven by going train wheel set 66 of the timepiece movement of the timepiece via a cannon-pinion 72 integral with civil minute pipe 70. In turn, civil minute pipe 70 drives a planetary reducer wheel set 74 formed by a first planetary wheel 76 and a first planetary pinion 78 integral with first planetary wheel 76.

(12) Planetary reducer wheel set 74 is mounted to pivot about a first pin 80 driven into an upper differential frame 82 with which a civil hour pipe 84 onto which is pressed civil hour hand 46 is integral. Driven by civil minute pipe 70 via first planetary wheel 76, first planetary pinion 78 rolls over a first inner toothing 86 of a first differential crown wheel 88 which is carried by the timepiece movement and which is immobile. By rolling over first inner toothing 86 of immobile differential crown wheel 88, first planetary pinion 78 thereby pivots upper differential frame 82 and thus civil hour pipe 84 which is integral with upper differential frame 82. The right choice of gear ratios between civil minute pipe 70, first planetary wheel 76, first planetary pinion 78 and immobile differential crown wheel 88 produces a reduction of one twelfth between the minutes and hours of civil time and the civil time display is thus obtained. In other words, by a reduction of one twelfth, planetary reducer wheel set 74 makes it possible to change from the civil minute to the civil hour.

(13) As seen in FIG. 4, a planetary multiplier wheel set 90 is formed of a second planetary wheel 92 and a second planetary pinion 94 integral with second planetary wheel 92. Planetary multiplier wheel set 90 is freely mounted about a second pin 96 driven into upper differential frame 82 which is integral with civil hour pipe 84. When civil hour pipe 84 and therefore upper differential frame 82 rotate, they drive second pin 96 and consequently planetary multiplier wheel set 90, whose second planetary pinion 94 rolls over a second inner toothing 98 of a mobile differential crown wheel 100, which, as will be seen below, is in mesh with equation of time cam 54. Second planetary wheel 92 in turn drives a solar time minute pipe 102, on which is pressed true minute hand 50. The right choice of gear ratios between civil hour pipe 84, second planetary wheel 92, second planetary pinion 94 and mobile differential crown wheel 100 produces a multiplication-by-twelve between the hours of civil time and the minutes of true time and the true time display is thus obtained. In other words, by a multiplication-by-twelve, planetary multiplier wheel set 90 makes it possible to change from the civil hour to the true solar minute.

(14) It follows from the above that planetary reducer wheel set 74 and planetary multiplier wheel set 90 rotate on themselves describing a circular trajectory centred on civil minute pipe 70. Preferably, planetary reducer wheel set 74 and planetary multiplier wheel set 90 move on a circle of the same radius, centred on the civil minute pipe, angularly spaced apart from each other.

(15) The pivoting of mobile differential crown wheel 100 is controlled by equation of time lever 68, provided with a feeler beak 106 via which equation of time lever 68 is in contact with the profile of equation of time cam 54. This equation of time lever 68 is held elastically bearing on the profile of equation of time cam 54 by a spring 108. This equation of time lever 68 is also provided with a first tooth 110 in mesh with a second corresponding tooth 112 provided on mobile differential crown wheel 100 to control the movement of the latter. It is understood that, at a moment close to midnight, when the calendar mechanism changes the date, it causes date wheel 58 to advance one step. During this brief moment when the date change occurs, upper differential frame 82 and therefore civil hour pipe 84 may be considered to be immobile. By pivoting, mobile differential crown wheel 100 drives second planetary pinion 94 and thus second planetary wheel 92, which, in turn, meshes with solar minute pipe 102 onto which is pressed true minute hand 50. The position of true minute hand 50 is thus set for the next day.

(16) Referring now to FIG. 5, it can be seen that at least one and preferably two screws 114 allow upper differential frame 82 to be closed onto a lower differential frame 116. The upper and lower differential frames 82 and 116 therefore rotate together when differential gear device 64 according to the invention is operating.

(17) It goes without saying that this invention is not limited to the embodiment that 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 annexed claims.

NOMENCLATURE

(18) 1. Equation of time cam 2. Month disc 4. Solar minute hand 6. Date wheel set 8. Hand 10. Intermediate date wheel 12. Reducer wheel set 14. Differential gear device 18. Civil minute hand 20. Rack 22. Planetary pinions 24. Inner toothing 26. Equation of time wheel 28. First toothed sector 30. Second toothed sector 32. Feeler spindle 34. Solar time display pinion 38. Solar time display wheel 40. Cannon-pinion 42. Centre 44. Running equation of time mechanism 46. Civil hour hand 48. Civil minute hand 50. True minute hand 52. Astrological symbol of the sun 54. Equation of time cam 56. Equation of time wheel 58. Date wheel 60. Intermediate date wheel 62. Reducer wheel set 64. Differential gear device 66. Wheel set 68. Equation of time lever 70. Civil minute pipe 72. Cannon-pinion 74. Planetary reducer wheel set 76. First planetary wheel 78. First planetary pinion 80. First pin 82. Upper differential frame 84. Civil hour pipe 86. First inner toothing 88. Immobile differential crown wheel 90. Planetary multiplier wheel set 92. Second planetary wheel 94. Second planetary pinion 96. Second pin 98. Second inner toothing 100. Mobile differential crown wheel 102. True minute pipe 104. Date indicator 106. Feeler beak 108. Spring 110. First tooth 112. Second tooth 114. Screw