CH718048A2 - Chronograph mechanism for a timepiece. - Google Patents

Abstract

The invention relates to a chronograph mechanism (1) for a timepiece movement, comprising: a first counter (5) of a first unit of time arranged to be in disengageable kinematic connection with a basic movement; a second counter (7) of a second unit of time in kinematic connection with said first counter (5) via a reduction gear (9). According to the invention, said reduction gear (9) comprises a cycloidal reduction gear arranged collaterally to each of said first counter (5) and of said second counter (7).

Description

Technical area

The present invention relates to the field of watchmaking. It relates, more particularly, to a mechanical chronograph mechanism for a timepiece.

State of the art

[0002]As a general rule, a chronograph mechanism for a timepiece includes a seconds counter which, on request, can be driven from a base movement via a clutch, this counter in turn driving a minute counter via a gear train. The latter typically comprises a series of mobiles each having a pair of wheels which are coaxial and integral with each other, one being of larger diameter than the other, so as to obtain the desired reduction in angular velocity. As a general rule, each counter is integral in rotation with a respective hand (or similar), the seconds counter being arranged to perform one revolution per minute while the minutes counter is arranged to perform one revolution per hour. The reduction is thus at a ratio of 60:1, but other speeds of rotation for the two counters are also known but certainly less common, the reduction ratio being chosen appropriately.

[0003] The use of such a conventional reduction gear requires the provision of a plurality of axes of rotation, is relatively bulky in the plane of the mechanism, and is relatively energy-intensive because of the friction generated by the multiple teeth which are mesh with each other. The difference in torque requirement that the basic movement must provide can thus vary significantly depending on the state of the chronograph mechanism. Consequently, when the chronograph is disengaged, the drive torque of the regulating system (typically a balance-spring oscillator maintained by an escapement) is significantly higher than when the chronograph is running, which has a detrimental effect on rate of the oscillator tending to delay it during timing.

The object of the invention is therefore to provide a chronograph mechanism in which the aforementioned defects are at least partially overcome.

Disclosure of invention

More specifically, the invention relates to a chronograph mechanism for a watch movement, as defined by claim 1. This mechanism comprises: a first counter of a first unit of time (typically seconds, but which could also be minutes or other) arranged to be in disengageable kinematic connection with a basic movement, for example by means of any clutch; a second counter of a second unit of time (typically minutes, but which could also be hours or other) in kinematic connection with said first counter via a reduction gear, which consequently ensures a ratio of correct gears so that the correct rotational speed is obtained for each of said counters.

According to the invention, said reduction gear comprises a cycloidal reduction gear disposed collaterally to each of said first counter and said second counter.

[0007] This arrangement can be significantly more compact in terms of the mechanism than a chronograph mechanism equipped with a conventional reduction gear, the number of separate pivot axes to be provided for the reduction gear is reduced to a single one, its inertia is low compared to a conventional 60:1 (or similar) gearbox and its energy efficiency is exceptional thanks to the reduction in inertia as well as in friction. With respect to this last point, the influence of the chronograph mechanism on the rate of the basic movement can thus be minimized, and this for reasons which will be explained in the detailed description.

[0008] Advantageously, said cycloidal reducer comprises: an input wheel mounted integral in rotation with an axle; a cycloidal cam mounted free in rotation around an eccentric section of said axis (and therefore eccentrically with respect to the axis of rotation of said axis) and comprising undulations arranged to cooperate with complementary undulations provided on a fixed crown arranged coaxially with said axis ; an output wheel arranged coaxially with said input wheel and mounted free to pivot around said axis. The output wheel further comprises a plurality of studs extending parallel to said axis and each taking place in a respective circular opening with which said cycloidal cam is provided, which serve to drive said output wheel when the cam moves. cycloidal.

[0009] Advantageously, said output wheel is located on the same side of said cycloidal cam as said input wheel, said output wheel being in particular interposed between said input wheel and said cycloidal cam.

[0010] This mechanism can be integrated into a clock movement, the latter being able to be integrated in turn into a timepiece.

Brief description of the drawings

Other details of the invention will appear more clearly on reading the following description, given with reference to the appended drawings in which: Figure 1 is an isometric view of a chronograph mechanism according to the invention; Figure 2 is an isometric view of the reduction gear of the mechanism of Figure 1; and Figure 3 is an isometric view of the reduction gear of Figure 2, cut along a diameter of the latter.

Embodiment of the invention

Figure 1 illustrates a non-limiting embodiment of a chronograph mechanism 1 according to the invention, which is intended to take place in a movement (not shown) of a timepiece.

This mechanism 1 comprises a power take-off wheel 3, arranged to be in disengageable kinematic connection with a basic movement (not shown) by means of a clutch (not shown) of any known form ( horizontal, vertical or other).

[0014] The power take-off wheel 3 is in kinematic connection with a first counter 5 of a first unit of time (in particular the seconds in the illustrated embodiment), which comprises a wheel of the first counted time unit 5a fixed in rotation of an indicator member of the first unit of counted time 5b, these two elements together forming a mobile.

In the illustrated construction, the wheel of the first counted time unit 5a meshes directly with the input wheel 3, but the interposition of one or more references in the kinematic chain is also possible.

[0016] The mechanism 1 also comprises a second counter 7 of a second unit of time (in particular the minutes in the illustrated embodiment), which comprises a wheel of the second unit of time counted 7a fixed in rotation to a member of indication of the second counted unit of time 7b, which is driven from the first counter 5 through a reduction gear 9. The first unit of time is typically seconds and the second is typically minutes, as is the case in the illustrated embodiment, but other units of time (for example fractions of seconds, hours, fractions of hours, days, weeks etc.) can also be used, the reduction ratio being chosen appropriately for the two chosen time units.

[0017] Even if the two indicator members 5b, 7b are illustrated in the form of hands integral in rotation with the wheel 5b, 7b of the respective counter 5, 7, other forms of indicator members are possible. (discs, rings, drums etc.), and it is not mandatory that they are integral in rotation with the respective wheel 5a, 7a. Alternatively, the indication members 5b, 7b can be pivoted around axes which are not coaxial with those of the wheels 5b, 7b, and simply be driven by the respective wheel 5a, 7a. Furthermore, a complete revolution of an indicator member 5b, 7b may or may not correspond to a typical cycle of the counted time unit, and the indicator members may also be of the retrograde type, where appropriate.

The reduction gear 9 is arranged collaterally to the first counter 5 and to the second counter 7, and comprises a cycloidal reduction gear, of which an input wheel 9a meshes with a transmission 11 which in turn meshes with the wheel of the first unit of time counted 5a. However, the presence of this reference 11 is not compulsory, and it is also possible to provide several references according to the manufacturer's choice.

The reduction gear 9 also includes an output wheel 9b, which meshes directly with the wheel of the second counted time unit 7a, but the interposition of one or more references is also possible. It is also possible to provide a third counter of a third time unit, driven by the second counter 7 via a reduction gear of any type (conventional, cycloidal, epicyclic or similar)

Although the operation of the type of cycloid reducer illustrated in Figures 1 to 3 is known to those skilled in the art, its particular construction will now be described.

The input wheel 9a is integral in rotation with an axis 9c mounted between conventional bearings. This axis 9c comprises an eccentric section 9d on which is mounted, by means of a first ball bearing 9h, a cycloidal cam 9f which cooperates with a fixed crown 9g arranged to be fixed to a frame element (not shown). Each of these elements 9f, 9g comprises regular undulations which resemble teeth in the shape of an arc of a circle, and which will be called “teeth” and “toothing” subsequently in order to simplify reading, even if their interaction is rather cam-to-cam instead of a gear between conventional teeth. Indeed, there is a "rolling" of one surface on the other and very little slipping, which contributes to reducing friction and thus the energy losses associated with it in comparison with a conventional gear between two teeth. . Of course, other forms of cycloidal cam 9f and fixed wheel 9g are also known to those skilled in the art (one or the other of these elements comprising for example a plurality of pins) and can be used in a mechanism 1 according to the invention, but the illustrated construction is particularly compact in thickness and comprises relatively few individual components which must be assembled to form the reduction gear 9.

[0022] The number of teeth of the cycloidal cam 9f is lower than that of the ring gear 9g with internal teeth (typically at the rate of one tooth), and a rotation of the axis 9c generates a translation of the geometric center of the cam 9f cycloidal so that the teeth of the 9f cycloidal cam roll on the teeth of the fixed crown 9g, and the geometric center of said cam 9f thus follows a cycloidal trajectory.

The output wheel 9b is driven by means of a plurality of studs 9j fixed to said wheel 9b and which take place in corresponding circular openings 9k provided in the cycloidal cam 9f. The displacements, composed in translation and in rotation, of the cycloidal cam 9f consequently cause the studs 9j, and therefore a continuous rotation of the output wheel 9b around the axis 9c, on which it is pivoted by means of 'a second ball bearing 9m, is spawned.

[0024] In order to minimize the overall height of the chronograph mechanism 1, the output wheel 9b is adjacent to the input wheel 9a, each of these two wheels being on the same side of the cycloidal cam 9f.

[0025] The advantages of using such a gear are multiple. Its compactness in the plane of movement is exceptional, the number of separate pivot axes required is reduced to just one, its inertia is low compared to a conventional 60:1 (or similar) gearbox and its energy efficiency is exceptional thanks to reduction in inertia as well as in friction. Regarding this last point, and as explained in the preamble, a chronograph mechanism is typically very energy-intensive and can influence the rate of the regulating organ (typically a balance-spring oscillator associated with an escapement mechanism) of the base movement (not illustrated) since the driving torque to which the escape wheel is subjected can vary significantly depending on whether the chronograph mechanism is running or stopped.

[0026] Although the invention has been previously described in connection with specific embodiments, other additional variants are also possible without departing from the scope of the invention, as defined by the claims.

Claims (6)

1. Chronograph mechanism (1) for a watch movement, comprising: – a first counter (5) of a first unit of time arranged to be in disengageable kinematic connection with a basic movement; – a second counter (7) of a second unit of time in kinematic connection with said first counter (5) via a reduction gear (9); characterized in that said reduction gear (9) comprises a cycloidal reduction gear disposed collaterally to each of said first counter (5) and said second counter (7). 2. Chronograph mechanism (1) according to the preceding claim, wherein said cycloidal reducer (9) comprises: – an input wheel (9a) mounted integral in rotation with an axis (9c); - a cycloidal cam (9f) mounted freely in rotation around an eccentric section (9d) of said axis and comprising undulations arranged to cooperate with complementary undulations provided on a fixed crown (9g) arranged coaxially with said axis (9c); – an output wheel (9b) arranged coaxially with said input wheel (9a) and mounted free to pivot around said axis (9c), said output wheel (9b) comprising a plurality of studs (9j) extending parallel to said axis (9c) and each taking place in a respective circular opening (9k) with which said cycloidal cam (9f) is provided. 3. Chronograph mechanism (1) according to the preceding claim, wherein said output wheel (9b) is on the same side of said cycloidal cam (9f) as said input wheel (9a). 4. Chronograph mechanism (1) according to the preceding claim, wherein said output wheel (9b) is interposed between said input wheel (9a) and said cycloidal cam (9f). 5. Clock movement comprising a chronograph mechanism (1) according to one of the preceding claims. 6. Timepiece comprising a clockwork according to the preceding claim.