Timepiece including a power reserve indicator device

The present invention concerns a timepiece including a movement fitted with a power reserve indicator device, said timepiece including a barrel closed by a cover, a mainspring housed in said barrel and respectively connected to a barrel arbour and means for winding said mainspring, said indicator device including a differential gear kinematically connected by a first input to the barrel arbour, by a second input to the barrel and by an output to a power reserve indicator member and wherein the differential gear frame is arranged coaxially to the barrel arbour, characterized in that the second differential gear input is secured to the barrel cover, in that the differential gear output is formed by an inner toothed crown, in that the inner toothed crown is kinematically connected to the first input by at least first and second planetary wheel sets meshed with each other and in that the at least two planetary wheel sets are carried by the cover.

This application claims priority from European Patent Application No. 07104055.4, filed Mar. 13, 2007, the entire disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention concerns a timepiece including a power reserve indicator device, i.e. a device for indicating to the wearer the degree of winding of the barrel spring of a mechanical timepiece.

BACKGROUND OF THE INVENTION

Timepieces including devices for providing this power reserve indication are devised to take account of the rotation of the ratchet wheel during winding of the barrel spring and the rotation of the barrel when the barrel spring is let down. In order to do this, most of these known devices implement a differential gear. A device of this type is disclosed, for example, in EP Patent No. 1 074 897 wherein the two differential inputs are respectively connected to the toothing of the barrel drum and to that of the ratchet wheel, the differential gear output being connected to an indicator member.

In order to display the number of barrel spring winding turns, which is generally of the order of 10 for barrels with a power reserve of the order of 2 days, using an indicator member of the type moving opposite a scale extending at the very most over 360°, reduction wheels have to be associated with the different gear. These reduction gears are typically arranged between the drum barrel and the first differential gear input, between the ratchet wheel and the second differential gear input and between the differential gear output and the indicator member. The presence of these reduction gears is ill suited to an advantageous embodiment is some specific cases, particularly when the movement includes numerous complications multiplying the number of parts and that space available around the barrel is relative limited. Moreover, the inherent construction clearances present in these reduction gears lead to inaccuracies in the power reserve display. These display inaccuracies are greater the greater the arc along which the power reserve indication is displayed.

There is also known from DE Utility Model No. 1638800U a power reserve indicator using a plane differential gear with a double satellite wheel arranged between the barrel bar and the barrel cover for the purpose of omitting the winding and let down reduction trains. However, the reduction ratio offered by this type of differential gear does not allow the power reserve to be displayed over a small arc of a circle, for example of the order of 30° without a display reduction train. Moreover, although this power reserve device is compact horizontally, it has a significant space requirement heightwise, which impedes the use thereof in movements of small thickness.

It is an object of the present invention to overcome the aforementioned problems and drawbacks, in addition to others, by proposing a timepiece including a power reserve indicator that is compact horizontally and heightwise and is of very simple construction, while creating a more judicious arrangement of the power reserve indicator device elements.

It is another object of the invention to provide a timepiece including a power reserve indicator device that limits or omits the winding, let down and power reserve display reduction trains.

It is another object of the invention to provide a timepiece including a power reserve indicator device with improved power reserve display accuracy.

It is yet another object of the invention to provide a timepiece including a power reserve indicator device that can display the power reserve over an arc of a circle of less than 30° without any reduction trains.

SUMMARY OF THE INVENTION

The present invention therefore concerns a timepiece including a movement fitted with a power reserve indicator device, said timepiece including a barrel closed by a cover, a spring housed in the barrel and respectively connected to an arbour of the barrel and to said barrel, a going train driven by said barrel and means for winding said spring, said indicator device including a differential gear kinematically connected by a first input to the barrel arbour, by a second input to the barrel and by one output to a power reserve indicator member, and wherein the differential gear frame is arranged coaxially to the barrel arbour, characterized in that the second input of the differential gear is secured to the barrel cover, in that the output of the differential gear is formed by an inner toothed crown, in that the inner toothed crown is kinematically connected to the first input by at least first and second planetary wheels meshed with each other and in that the at least two planetary wheels are carried by the cover.

Owing to these features, the present invention provides a power reserve indicator device that is compact and simple and able to reduce to a minimum the number of winding and let down reduction trains. This solution also provides a power reserve indicator that is at least partially integrated in the barrel cover or bottom, which substantially reduces the space requirement of said indicator.

According to a preferred feature of the invention, the indicator member is directly carried by said inner toothed crown forming the output of the differential gear. This embodiment allows the display reduction train to be omitted provided that the power reserve indicator member is integrated in the differential gear.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

The views ofFIGS. 1 to 5partially illustrate a timepiece of the wristwatch type, for example, fitted with a power reserve indicator device in accordance with the present invention and designated as a whole by the general reference numeral1. The watch includes a watch movement M including a bottom plate P on which a barrel2is mounted housing a mainspring4. Barrel2includes, in a conventional manner a drum6closed by a cover8and a back cover10. Barrel2is mounted to rotate freely on the barrel arbour12, secured to the core14. Mainspring4is hooked by the inner end thereof to core14and by the outer end thereof to the inner wall of drum6. Barrel2is mounted in a conventional manner between the bottom plate P of the movement and a bridge3including a central portion3afrom which a bridge branch3band a bridge branch3cextend.

In the example illustrated, the power reserve indicator device1is used in connection to a barrel associated with a fusee F also mounted on bottom plate P via bridge branch3c. A chain C, only one link of which is shown in the drawing, is attached by a first end to the barrel drum6. Chain C is gradually wound onto drum6from fusee F to which it is secured by a second end during let down of the barrel. Fusee F is conventionally associated with a ratchet R and includes a toothed portion D meshed, on the one hand, with a going train and on the other hand with a winding train. In this example, the barrel arbour12is fixed relative to the movement plate P. Barrel arbour12is mounted between plate P and bridge branch3b. Bridge branch3balso carries, on the face thereof arranged opposite cover8, a toothed wheel16forming a first differential gear input, which will be described in more detail below. The toothed wheel16is friction mounted on bridge branch3bvia a spring ring17secured to bridge branch3b. The second differential gear input is formed by barrel4and more specifically by the cover8secured to drum6, which can pivot about barrel arbour12with the barrel when the latter is letting down. Cover8, which thus forms the frame of the differential gear is therefore formed coaxially to the barrel arbour. Cover8carries a first planetary wheel set18including a first wheel18aand a second wheel18bcoaxial to wheel18a. Wheel18ais meshed with wheel16, whereas wheel18bis meshed with a second planetary wheel set20, which in turn meshes with a moving inner toothed crown22, which forms the differential gear output. Crown22carries a display member formed of a power reserve hand24which, depending upon the relative position that it occupies opposite a marking26borne by plate P via a leg26a, indicates to the wearer the available power reserve as a function of the number of winding turns of the mainspring.

Referring more particularly toFIGS. 2 and 3, it can also be seen that the power reserve indicator device according to the invention further includes means28,30for limiting the angular travel of the wheel with an inner toothing22such that hand24moves between two fixed and defined winding and let down end positions corresponding respectively to the end degree of winding or let down of marking26. In the example illustrated, limiting means28,30include three studs28secured to bridge3, studs28each moving into an aperture30arranged in the inner toothed wheel22. Preferably, apertures30are hollows open outwards arranged in the periphery of wheel22, these apertures30each defining two radial stop surfaces30aand30bfor the associated stud28.

It will also be noted in the example illustrated, that barrel cover8includes a central recess8aset back relative to the peripheral edge8bthereof and that the inner toothed wheel22extends substantially into the plane of edge8bof cover8. This arrangement advantageously integrates the power reserve display device in the barrel and limits the space requirement thereof heightwise in the movement to a maximum.

The differential gear wheels and in particular the gear ratios of wheels16,18a,18b,20and22are devised to provide, between the differential input16and output22, a gear reduction comprised between 60 and 120 and preferably 80. By way of example, with a wheel16with 54 teeth, a wheel18awith 10 teeth, a wheel18bwith 15 teeth, a wheel20with 11 teeth and a wheel22with 80 teeth, a ratio of 1/80eis obtained, namely for 6 revolutions of the barrel there is an angular displacement of 270 of hand22connected to wheel22without any winding, reduction and display trains.

The illustrated embodiment of the power reserve device according to the invention that has just been described operates as follows.

When the timepiece is operating normally, i.e. when the mainspring is letting down, the barrel arbour12and the wheel are stationary. Drum6is being driven in rotation by mainspring4anti-clockwise (arrow FD,FIG. 2). Chain C connected to drum6is then gradually wound onto drum6from fusee F, which is in turn driven in rotation to provide the drive force to the going train. While doing so, wheel18aof planetary wheel set18carried by barrel cover8rolls over the toothing of fixed wheel16, also anti-clockwise. Wheel18bof wheel set18, secured in rotation to wheel18a, then drives wheel20meshed with the inner toothing of crown22in the clockwise direction. Crown22then drives power reserve hand24anticlockwise opposite marking26. Barrel drum6continues to drive power reserve hand24as has just been described until studs28come into contact with the radial stop surfaces30aof apertures30. In this position, power reserve hand24is opposite the zero graduation of marking26, i.e. in the position in which mainspring4is completely let down. During let down, as a function of the power reserve that the winding of mainspring4can still provide, display hand24thus makes a progressive angular movement from the indication representing complete winding of the mainspring, to the indication representing the complete let down of mainspring4. At that moment, chain C which was initially wound onto the fusee has been completely unwound therefrom and has been wound onto barrel drum6.

To wind the timepiece in order to rewind the mainspring, the fusee is acted upon via the toothed portion thereof so as to rewind chain C onto the fusee from barrel6onto which it has been wound. Doing so sets drum6in rotation around barrel arbour12which is stationary relative to the movement plate. Drum6then rotates clockwise (arrow A,FIG. 2). This causes wheel18aof planetary wheel set18carried by barrel cover8to roll over the toothing of fixed wheel16, also clockwise. Wheel18bof wheel set18, secured in rotation to wheel18a, then drives wheel20, meshed with the inner toothing of crown22, anticlockwise. Crown22then drives power reserve hand24clockwise opposite marking26. Barrel drum6continues to drive power reserve hand24as has just been described until studs28come into contact with the radial stop surfaces30bof apertures30. In this position, power reserve hand24is opposite the 100% graduation of marking26, i.e. in the position in which mainspring4is completely wound. Display hand24thus makes a progressive angular movement in the opposite direction to the preceding one, as a function of the power reserve that the number of winding turns of the mainspring can still provide. At this moment, chain C which was initially wound onto the barrel drum6has been completely unwound therefrom and has been wound onto fusee F.

It goes without saying that the invention is not limited to the embodiment that has just been described, and that modifications and variants could be envisaged without departing from the scope of the invention defined by the annexed claims.

It will be noted that the invention can be used with a conventional barrel movement regardless of whether the movement is wound manually or automatically. In the latter case, an uncoupling mechanism would have to be provided to avoid a false power reserve indication being given when the mainspring is fully wound and the bridle slides into the barrel.

In the case of application to a conventional barrel, the barrel arbour is pivotably mounted on the bottom plate and is associated with a ratchet wheel controlled by a winding train. During let down, wheel16, which is secured to the barrel arbour, is stationary, the power reserve indication device thus operates in an identical manner to that previously described. During winding, it is the barrel drum that can be considered to be stationary. Barrel arbour12is thus set in rotation in the clockwise direction by a winding train such that it drives wheel set18anticlockwise. Train18in turn drives wheel20clockwise. Wheel22, carrying the power reserve indicator hand, which is directly meshed with wheel20, is thus driven anticlockwise opposite marking26.