Coupling system for a chronograph

Abstract

A coupling system for a chronograph mechanism is presented. The system can include an input wheel intended to be driven by a drive member; an output wheel intended to drive at least one display member; an intermediate wheel continuously kinematically connected to the input wheel or the output wheel, where the intermediate wheel changes between a coupled state where the input wheel is kinematically connected to the output wheel and an uncoupled state where the kinematic connection is broken. The system also includes a first friction wheel constrained to rotate with the intermediate wheel and a second friction wheel constrained to rotate with either the input wheel and the output wheel; a first safety wheel constrained to rotate with said intermediate wheel that includes a first set of safety teeth; and a second safety wheel constrained to rotate with the second wheel that includes a second set of safety teeth.

Claims

1. A coupling system for a chronograph mechanism, said system comprising: an input wheel intended to be driven by a drive member; an output wheel intended to drive at least one display member; an intermediate wheel continuously kinematically connected to a first wheel chosen from said input wheel and said output wheel, said intermediate wheel being mounted so that it can change between a coupled state in which said input wheel is kinematically connected to said output wheel and an uncoupled state in which said kinematic connection is broken; wherein said system further includes: a first friction wheel constrained to rotate with said intermediate wheel and a second friction wheel constrained to rotate with a second wheel chosen from said input wheel and said output wheel, said friction wheels being at least partially coplanar and being adapted to transmit rotation between said intermediate wheel and said second wheel, or vice versa, when said system is in the coupled state; a first safety wheel constrained to rotate with said intermediate wheel and comprising a first set of safety teeth and a second safety wheel constrained to rotate with said second wheel and comprising a second set of safety teeth, said sets of safety teeth being conformed in order to interpenetrate mutually when said intermediate wheel is in the coupled state.

2. The system as claimed in claim 1, in which said intermediate wheel is mounted to pivot on a lever controlled by an elastic element.

3. The system as claimed in claim 2, in which said elastic element is carried by a control lever including abutments adapted to prevent said intermediate wheel from changing state in the event of an impact.

4. The system as claimed in claim 3, in which said elastic element comprises a free end that is adapted to interact with said lever, said abutments being situated on respective opposite sides of said free end.

5. The system as claimed in claim 4, in which one of said abutments is adapted to prevent said intermediate wheel and said second wheel being able to interact in the event of an impact when said intermediate wheel is in its coupled state, the other of said abutments being adapted to prevent said sets of safety teeth being able to move out of reach of one another in the event of an impact when said intermediate wheel is in its coupled state.

6. The system as claimed in claim 5, further comprising an intermediate gear wheel meshing on the one hand with said first wheel and on the other hand with said intermediate wheel.

7. The system as claimed in claim 3, in which one of said abutments is adapted to prevent said intermediate wheel and said second wheel being able to interact in the event of an impact when said intermediate wheel is in its coupled state, the other of said abutments being adapted to prevent said sets of safety teeth being able to move out of reach of one another in the event of an impact when said intermediate wheel is in its coupled state.

8. The system as claimed in claim 3, further comprising an intermediate gear wheel meshing on the one hand with said first wheel and on the other hand with said intermediate wheel.

9. The system as claimed in claim 3, in which said sets of safety teeth each comprise teeth having a width of at most one quarter of the pitch of said set of teeth as measured at the maximum depth of interpenetration of said safety teeth.

10. A timepiece movement comprising a chronograph mechanism provided with a coupling system as claimed in claim 3.

11. The system as claimed in claim 2, further comprising an intermediate gear wheel meshing on the one hand with said first wheel and on the other hand with said intermediate wheel.

12. The system as claimed in claim 2, in which said sets of safety teeth each comprise teeth having a width of at most one quarter of the pitch of said set of teeth as measured at the maximum depth of interpenetration of said safety teeth.

13. A timepiece movement comprising a chronograph mechanism provided with a coupling system as claimed in claim 2.

14. The system as claimed in claim 1, further comprising an intermediate gear wheel meshing on the one hand with said first wheel and on the other hand with said intermediate wheel.

15. The system as claimed in claim 14, in which said intermediate gear wheel comprises a set of play compensation teeth.

16. The system as claimed in claim 1, in which said sets of safety teeth each comprise teeth having a width of at most one quarter of the pitch of said set of teeth as measured at the maximum depth of interpenetration of said safety teeth.

17. The system as claimed in claim 1, in which said first wheel is said input wheel and said second wheel is said output wheel.

18. The system as claimed in claim 17, in which upstream flanks of the first safety wheel and downstream flanks of the second safety wheel are curved.

19. A timepiece movement comprising a chronograph mechanism provided with a coupling system as claimed in claim 1.

20. A timepiece comprising a movement as claimed in claim 19.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other details of the invention will become more clearly apparent on reading the following description given with reference to the appended drawings, in which:

(2) FIG. 1 is an isometric view of a coupling system according to the invention in the uncoupled state;

(3) FIG. 2 is an isometric view of the coupling system from FIG. 1 in the coupled state; and

(4) FIG. 3 is a view of the intermediate wheel and the output wheel of the system from FIG. 1, seen from below relative to the FIG. 1 orientation.

EMBODIMENT OF THE INVENTION

(5) FIGS. 1 and 2 show a coupling system 1 according to the invention for a chronograph in an uncoupled, respectively coupled state.

(6) As is widely known, the horizontal type system 1 comprises an input wheel 3, adapted to be driven by a base movement (not shown) included in the timepiece in which the system 1 is integrated. The input wheel 3 may, for example, be constrained to rotate with the seconds wheel of said movement, or driven by the latter. Alternatively, another appropriate wheel may be used for the same purpose.

(7) The input wheel 3 is kinematically connected selectively with an output wheel 5, which in this instance is a seconds wheel of the chronograph, and which also carries a reset to zero cam 7.

(8) This selective kinematic coupling is effected by the intervention of a first intermediate wheel 9 mounted to rotate freely on a lever 11 and permanently kinematically connected to the input wheel 3. This lever 11 also carries an intermediate gear wheel 13 that meshes continuously on the one hand with the input wheel 3 and on the other hand with a set of teeth 15 of the intermediate wheel 9. Pivoting of the lever can establish or break a kinematic connection between the first intermediate wheel 9 and the output wheel 5. The coupled, respectively uncoupled state of the intermediate wheel 9 therefore determines the corresponding state of the coupling system 1.

(9) Alternatively, in an opposite construction, the first intermediate wheel 9 may be continuously kinematically connected to the output wheel 5 by means of the intermediate gear wheel 13 in an analogous manner to the first variant, pivoting of the lever thus kinematically connecting the first intermediate wheel 9 and the input wheel. The following description deals with the first of these variants, as shown in the figures; the modifications for implementing the second variant will be evident to the person skilled in the art and do not need to be described in detail.

(10) In the embodiment shown, the intermediate gear wheel 13 comprises a set of play compensation split teeth, but a conventional wheel is equally possible. It may equally be envisaged to provide only one intermediate wheel 9, which therefore meshes directly with the input wheel 3.

(11) The lever 11 is mounted to pivot about the same rotation axis as the input wheel, but a slight offset between the rotation axes of these components is permissible.

(12) In order to drive the output wheel 5 when the system 1 is in the coupled state, the intermediate wheel 9 includes a first friction wheel 17 that is adapted to come into contact with a second friction wheel 19 of the output wheel 5. The materials and the finish (presence of layers, roughness, etc.) of the friction wheels may be chosen according to the requirements of the clockmaker to provide the transmission of torque with an appropriate contact force.

(13) This contact force is produced by an elastic element 21 that also controls the lever 11, as will become more clearly apparent hereinafter.

(14) The elastic element 21 is a leaf spring carried by a control lever 25 mounted to rotate about a rotation axis 29 and subjected to a return force by means of a return elastic element 31 that tends to cause it to pivot in the anticlockwise direction (in the orientation shown in the figures) and thus to maintain its tail 33 in contact with the column wheel 27. The latter controls the control lever 25 in the conventional manner. Alternatively, the control lever 25 may be controlled by a system with a shuttle or a cam or a similar system.

(15) The free end of the elastic element 21 includes a fork 35 that interacts with a tenon 23 situated at an end at a distance from the pivot axis 29 of the control lever 25. When the control lever 25 pivots in the clockwise direction under the control of the column wheel 27, the elastic element applies a force that causes the lever 11 to pivot in the anticlockwise direction. The friction wheels 17, 19 consequently come into contact with one another and the input wheel 3 is therefore kinematically connected to the output wheel 5 (see FIG. 2). The elastic element 21 provides the force necessary for maintaining the friction wheels 17, 19 in contact with one another and to generate the radial force necessary to provide correct transmission of torque with no slippage.

(16) Starting from the orientation of the components shown in FIG. 2, when the column wheel 27 pivots by one step, the return elastic member 31 causes the control lever 25 to pivot in the anticlockwise direction and the elastic element 21 causes the lever 11 to pivot so that the first friction wheel 17 is moved away from the second friction wheel 19. The components therefore revert to their position shown in FIG. 1 and the kinematic connection between the input wheel 3 and the output wheel 5 is broken.

(17) Compared to the force necessary to maintain the meshing between the sets of teeth of the intermediate wheel and of the output wheel in a conventional horizontal coupling, that produced by the elastic element 21 of the present invention is relatively low.

(18) In order to render the system 1 insensitive to impacts despite the relatively low force exerted between the friction wheels 17, 19, a number of arrangements are provided.

(19) Firstly, at the level of the intermediate wheel 9 and the output wheel 5, respective safety wheels 37, 39 are provided. These safety wheels 37, 39 are shown to a larger scale in FIG. 3, in which their orientation is reversed relative to that of FIGS. 1 and 2.

(20) A first safety wheel 37 comprising a first set of safety teeth is constrained to rotate with the intermediate wheel 9 and a second safety wheel 39 comprising a second set of safety teeth is constrained to rotate with the output wheel 5. These sets of teeth are conformed so that, in normal operation of the coupling, they do not come into contact with one another. There is therefore no meshing between these wheels 37, 39 and they do not contribute to the transmission of torque between the intermediate wheel 9 and the output wheel 5 during normal operation of the coupling system 1.

(21) In this regard, when the coupling is in the uncoupled state (see FIG. 1), these sets of teeth are out of reach of one another. When the coupling is in the coupled state (see FIGS. 2 and 3), the teeth of the sets of teeth interpenetrate and are within reach of one another.

(22) In the event of an impact that displaces the output wheel 5 angularly relative to the intermediate wheel 9, the sets of safety teeth interact in order to limit that angular displacement. This displacement is therefore limited to the angle travelled until a tooth of the first set of safety teeth comes into contact with a tooth of the second set of safety teeth. The pitch of these teeth being small, the user will not notice this slight displacement of the seconds hand of the chronograph.

(23) The shape of the teeth of the sets of safety teeth is also particular because the teeth do not participate in the transmission of torque and serve only as abutments in the event of an impact. In fact, during normal operation of the system 1, they do not mesh in the usual meaning of that term, because they interpenetrate freely and without contact or transmission of torque. The teeth are consequently relatively thin compared to their length. In the variant shown in the figures the width of the teeth is substantially one quarter of the pitch of said set of teeth, as measured at the maximum depth of interpenetration.

(24) The summits of the teeth are pointed and asymmetrical; considering the first safety wheel 37, the downstream faces of its teeth are substantially radially oriented, whereas the upstream faces of said teeth feature a curvature. The teeth of the second safety wheel 39 have the opposite shape so that if the sets of teeth come into abutment in the operating rotation direction the respective flanks with the greatest curvature interact, the respective flanks with the least curvature interacting in the event of an impact driving rotation of the output wheel in the contrary direction.

(25) The small width of the teeth minimizes the probability of the sets of teeth interacting during coupling of the system 1 and minimizes the jump if it occurs. Moreover, the asymmetrical shape chosen for the safety teeth favors a forward “jump”. In the event of this kind of interaction the curved upstream face of one tooth slides on the curved face of the other tooth until the friction wheels 17, 19 act again to drive the output wheel 5. At the moment of starting the chronograph, this interaction of the sets of safety teeth generates a small momentary and interceptible acceleration of the second hands of the chronograph and not a visible jump. A perceptible unwanted jump is therefore eliminated. It should be noted here that the “inactive” flanks of the teeth in the sense of the patent EP1437633, i.e. the downstream flanks of the teeth of the first safety wheel 37 and the upstream flanks of the teeth of the second safety wheel, are steeply sloped and extend in an essentially radial direction. However, other shapes of the sets of teeth are equally possible.

(26) The elastic element 21 is relatively weak so as to be able to absorb any manufacturing imperfections such as out-of-rounds, inaccurate positions of the pivots, etc. and to minimize the stresses exerted on the latter. The first friction wheel 17 is therefore pressed less strongly against the second friction wheel 19 than with conventional sets of teeth and consequently there also exists a risk that an impact can displace the lever 11 angularly from its normal position. Without the provision of the safety means described hereinabove, this displacement could for example momentarily interrupt the kinematic connection in the coupled state or could create a transitory kinematic connection between the intermediate wheel 9 and the output wheel 5 in the uncoupled state of the coupling.

(27) In order to prevent this risk, the control lever 25 also includes a first safety arm 41 and a second safety arm 43 situated on respective opposite sides of the fork 35 at the end of the elastic element. These safety arms 41, 43 are constrained to rotate with the control lever 25 and each serves as an abutment for the fork 35 in the event of an impact.

(28) The first safety arm 41 is positioned and shaped so that, in the uncoupled state (FIG. 1), it is impossible for the teeth of the first safety wheel 37 to be within reach of those of the second safety wheel 39. In other words, the fork 3 abuts against the first safety arm before these teeth can interact.

(29) In the same way, the second safety arm 43 is positioned and shaped so that, in the coupled state (FIG. 2), it is impossible for the teeth of the two safety wheels 37, 39 to move out of reach of one another. In this case, the delay of the seconds hand generated by an impact breaking the kinematic connection is limited to the arc travelled until a tooth of the first safety wheel abuts against a tooth of the second safety wheel. Then, a fraction of a second later, the friction wheels 17, 19 will re-establish their kinematic connection because of the effect of the elastic element 21 and the driving of the output wheel 5 by continuous friction as described hereinabove.

(30) In this kind of situation, although the seconds indicator of the chronograph has been shifted by a fraction of a second one way or the other, it is unlikely that the user will notice it following the impact.

(31) Although the invention has been described in connection with one particular embodiment, variations are possible without departing from the scope of the invention as defined by the appended claims.