CH711851A1 - Bidirectional drive spring for timepiece. - Google Patents

Abstract

The invention relates to a bi-directional drive spring (1) for a timepiece, comprising: a hub (3) intended to be integral in rotation with an axis (23) of a driving head (2); an elastic member (7) extending from the hub and around a portion of the hub (3); a finger (5) provided at the free end of the elastic element (7), the finger (5) having an upstream flank (5a) for driving in a first direction of rotation a calendar wheel (9) having a toothing, and a downstream flank (5b) intended to come into contact with an abutment surface (13) that the hub (3) comprises. According to the invention, the finger (5) has a substantially delta-shaped shape, the downstream flank (5b) and the abutment surface (13) being arranged in such a way that they can cooperate so that the finger (5) can cause said calendar wheel (9) in said first direction when the driving spring (1) is driven by the leading hand (2), and so that the finger (5) can retract when the finger (5) penetrates into the toothing of the calendar wheel (9) and when the calendar wheel (9) is driven in a second direction of rotation opposite to said first direction of rotation.

Description

Description TECHNICAL FIELD [0001] The present invention relates to the field of watchmaking. More particularly, it relates to a bidirectional drive spring for a timing mechanism for a timepiece.

STATE OF THE ART [0002] Several kinds of drive system of a date, day or date mobile are known in the prior art. Among the most common are near-instant drive systems, which utilize a drive spring comprising a retractable finger driven by the base motion, typically due to a 24-hour ride. An example of this kind of system is disclosed in the document FR 1 467 726. In this system, the finger is at the end of an elastic element which follows an arc of a circle or a spiral section extending around a part of the hub. The latter is integral in rotation with an axis driven by the movement due to a turn in 24 hours. Around midnight, the finger comes to bear against a tooth of the date mobile, thus bending the spring until a stop forming part of the finger comes into contact with a rigid stop forming part of the hub. The driving wheel continues to rotate, at a certain time the force applied by the finger on the tooth of the date mobile overcomes the retention force generated by a positioning jumper. The date mobile escapes the retention of the jumper, and is propelled by a step in the driving direction by the energy stored in the spring, before being positioned again by the jumper.

During a manual correction of the date, the date mobile is typically driven in the same direction as during a drive by the movement. So that the system does not hang when the correction is made around midnight, the downstream face of the finger is provided with a beveled surface, which acts as a cam to retract the finger during the passage of a date mobile tooth.

However, this kind of trainer spring is poor for an application in which the mobile is driven by the drive spring in the opposite direction, which is often the case in a display mechanism of the day of the week or the month, as shown in fig. 1.

This figure illustrates a drive spring 1 of the modern type, commonly used in timepieces date. This drive spring is arranged to drive a calendar mobile, in this case a star 9 (which may also be any other suitable mobile, for example a date ring, a conventional toothed wheel or the like) to fourteen teeth 11 , the latter being associated with a display of the day of the week (not shown). The driving spring 1 comprises a rigid hub 3, which is integral in rotation with a 24-hour mobile 2, this mobile 2 being driven by the basic movement due to a turn in 24 hours clockwise according to the view of fig. 1, and is therefore a mobile leader. The entire driving spring 1 and the 24-hour mobile 2 form a driving mobile.

The drive spring 1 comprises a finger 5 connected to the hub 3 by means of an elastic element 7 in spiral section or in an arc, the finger extending outside the plane of the element 7. During its journey, the finger enters the toothing of the star 9 so that a rotation of the drive spring 1 of a turn in the clockwise direction causes the star 9 a step in the direction counterclockwise, in the same way as described above. If the force applied by the elastic element 7 is insufficient in itself to drive the star 9, the finger abuts against an abutment surface 13 that the hub 3 has, and the drive spring therefore acts as a rigid element .

For completeness, it is further noted that the end of the elastic element 7 is provided with a first inclined surface 17 which cooperates with a second complementary inclined surface 15 provided on the hub 3. These surfaces ensure that , if the hands of the watch are corrected counterclockwise, which also causes the mobile 24-hour 2 counterclockwise, these inclined surfaces 15, 17 cooperate to retract the finger 7 of the toothing of the star so as not to drag him into this situation.

However, in case of correction of the star 9 around midnight in the opposite direction to its drive by the drive spring 1, a lock can result. A modeling of this situation is illustrated in fig. 2 in which it clearly appears that the finger 5 abuts against the abutment surface 13 of the hub 3 and thus blocks the rotation of the star 9 since the tooth 11 is blocked by the finger 5. This situation can even damage mechanism if the user tries to force the correction by applying excessive force.

The object of the invention is therefore to provide a drive spring which avoids the aforementioned locking during a correction of the star 9 in the opposite direction around midnight.

DISCLOSURE OF THE INVENTION [0010] More specifically, the invention relates to a bi-directional driving spring for a timepiece, comprising a hub intended to be integral in rotation with an axis of a moving head such as a 24-hour mobile, an elastic element extending from the hub and around a portion of the hub, for example tangentially in an arc or in a spiral section, and a finger provided at the free end of the hub; elastic element. The finger has an upstream flank intended to drive a calendar mobile, which has a toothing, in a first direction of rotation, and a downstream flank intended to come into contact with an abutment surface that includes the hub.

According to the invention, the finger has a shape substantially in a triangle, for example rounded or truncated apex. The downstream flank and the abutment surface are arranged in such a way that they cooperate: on one side to drive the calendar wheel in said first direction via the finger when the driving spring is driven by the mobile leader, and - on the other side to allow the finger to retract when the finger enters the teeth of the calendar mobile and when the calendar mobile is driven in a second direction of rotation opposite to said first direction of rotation, c that is, during a correction in the opposite direction of the calendar mobile some time before it is driven by the drive spring.

The exact geometry of the shape of the tooth as well as that of the abutment surface and the elastic properties of the elastic element can be modeled and calculated to meet the aforementioned conditions depending on the shape of the teeth of the mobile of calendar, and the retention force of this mobile (due for example to a jumper positioning, a friction, a ball trigger or the like which serves to position the mobile).

Therefore, given the fact that the tooth can retract, it does not cause blocking of the system during the correction of the calendar mobile at any time, even just before its usual training by the spring.

Advantageously, in the rest position of the spring, the angle that the upstream side with a radius passing through the top of the finger is different from less than 10%, preferably less than 5%, of the angle that makes the downstream flank with said radius. Said flanks are therefore substantially symmetrical with respect to said radius.

Advantageously, the downstream side is straight, and therefore has no edge, which provides a predictable cooperation with the abutment surface.

Advantageously, the angle between the upstream side and the downstream side, considered in the plane of the drive spring, is between 40 ° and 50 °, preferably between 43 ° and 47 °.

Advantageously, the abutment surface is substantially of circular arc shape.

Advantageously, the diameter of said circle represents between 15% and 30% of the distance between the axis of rotation of the spring and the geometric center of said circle.

The invention also relates to a driving wheel for driving a calendar mobile for a timepiece. This drive wheel comprises a wheel intended to be driven by a watch movement (for example a 24-hour wheel) and a spring as defined above which is integral in rotation with said wheel.

BRIEF DESCRIPTION OF THE DRAWINGS Further details of the invention will appear more clearly on reading the description which follows, made with reference to the appended drawings in which:

Fig. 1 is a view of a portion of a calendar mechanism according to the prior art;

Fig. 2 is a view of a modeling of the interaction between a tooth of a star and the finger of the drive spring when the star is driven in the opposite direction to its usual training direction;

Fig. 3 is a perspective view of a drive spring according to the invention;

Fig. 4 is a partial view of a calendar mechanism comprising a drive spring according to the invention, the spring being in the rest position;

Fig. 5 is a partial view of the mechanism of FIG. 4 when the drive spring drives the calendar mobile;

Fig. 6 is a view of a portion of FIG. 5, in which the distribution of forces acting on the finger has been represented;

Fig. 7 is a partial view of a calendar mechanism comprising a drive spring according to the invention during a correction in the opposite direction of the calendar mobile; and

Fig. 8 is a view of a portion of FIG. 7, on which the distribution of forces acting on the finger has been represented.

Embodiment of the Invention [0021] FIGS. 3 and 4 illustrate a bidirectional drive spring 1 according to the invention, in a state of rest. This drive spring 1 differs from that of the prior art described with reference to FIG. 1 mainly in the form of the finger 5, as well as that of the abutment surface 13. As is the case for the spring 1 of the prior art, it is integral in rotation with a moving head 2, in the case a mobile 24 hours, and in the example shown this connection is effected by means of lugs 19, which cooperate with complementary notches or grooves 21 provided on the axis 23 of the mobile 24 hours 2 Naturally, other means of coupling between the spring 1 and the 24-hour mobile 2 are known to those skilled in the art, for example riveting, welding, gluing, one or more pin, a polygonal shape or to flutes, or the like.

The drive spring 1 as shown has a constant thickness, but it can not be excluded that the portion that interacts with the toothing of the star 9 may extend perpendicularly to the plane of the rest of the spring 1, as is the case for the spring 1 of FIG. 1.

The finger 5 is of triangular bill shape with rounded apex, its flanks being oriented symmetrically with respect to the radius r intersecting the top of the finger 5. Thereafter, the term "upstream flank" is used to indicate the flank 5a elastic element side 7, which is upstream with respect to the standard drive direction indicated by the arrow, and the term "downstream side" is used to indicate the side 5b abutment surface side 13, which is downstream relative to the direction standard drive.

The flanks are at an angle α between them between 40 ° to 50 °, ideally substantially 45 °, and the downstream side extends sufficiently inwardly of the spring 1 so that it can cooperate with the abutment surface 13, as will flow more clearly thereafter.

The abutment surface 13 is formed by the end of a protuberance 31 substantially rigid, which protrudes from the hub 3 in the direction opposite to the elastic member, towards the finger 5. The surface of stop 13 is, in the illustrated example, rounded in an arc of circle, this circle having a diameter 13d between 15% and 30% of the distance 13r between the axis of rotation A of the spring 1 the geometric center of said circle defining said arc. It goes without saying that the stop can be made by any appropriate means such as a pin or other integral part of the mobile.

Fig. 3 5 illustrates the relationship between the components during the driving of the star 9 by the drive spring I, around midnight. The spring 1 was driven by the mobile 24 hours 2 in the direction of the arrow to the point where the downstream flank 5b abuts against the abutment surface 13, while bending the elastic element 7, and the retention force of a jumper 27, which serves to position the star 9 in a conventional manner, has been partially overcome.

The angle of the upstream flank 5a, the downstream flank 5b, the position and the diameter of the abutment surface, the stiffness of the elastic element 7 and the geometry and the return force of the jumper are chosen so that the downstream flank 5b slides on the abutment surface 13 and the finger 5 does not retract sufficiently to let out a tooth 11 of the star. Indeed, the retention of the jumper 27 is overcome before the finger 5 is sufficiently retracted to let out the tooth II. Therefore, the spring 1 can drive the star 9.

Fig. 6 schematically shows the distribution of forces on the finger 5 in the state illustrated in FIG. 5. In order not to burden this figure, the reference signs have been omitted.

The force F1 is exerted between the top of the finger 5 on the side of the upstream side 5a and the side of the tooth 11 with which it is in contact, in a direction normal to the tangent of the point of contact between these two components . The tangential component (considered with respect to the drive spring 1) of the reaction force to this force F1 generates a torque on the star 9 which is in equilibrium with that generated by the retention force exerted by the jumper 27 (no illustrated in this figure). The radial component of the force F1 tends to retract the finger 5, bringing it closer to the axis of rotation A of the spring 1.

The downstream side 5b of the finger 5 being in contact with the abutment surface 13, a force F2 perpendicular to the downstream side 5b, at the point of contact with the abutment surface 13, is generated, this force having a tangential component s opposed to that of the force F1, and a slight radial component towards the axis of rotation of the spring 1. Finally, the elastic element 7 exerts a restoring force F3 which applies mainly in the radial direction towards the outside , but also slightly in the tangential direction in the clockwise direction, and opposes the other forces F1, F2.

FIG. 7 illustrates the relationship between the components of the mechanism during a correction in the backward direction of the star 9 by means of a correction wheel 29, which is of conventional shape, around midnight. The correction device 29 comprises rigid fingers which drive the star 9 against the holding force provided by the jumper 27. At the same time, if the finger 5 of the drive spring 1 is penetrating the tooth of the star 9, as is the case in FIG 7, the side of a tooth 11 of the star 9 bears against the upstream side 5a of the finger 5 until the downstream side 5b of the finger 5 comes into contact with the abutment surface 15, on which the downstream side 5b slides against the restoring force provided by the elastic element 7, which flexes accordingly and allows the finger 5 of retract sufficiently that it escapes the tooth 11, and the mobile 9 is not blocked.

FIG. 8 illustrates the distribution of the forces exerted on the finger 5 when the components of the mechanism are in the configuration illustrated in FIG. 7.

Again, a flank of a tooth 11 of the star 9 bears in a force F1 against the top of the finger 5, towards the side of the upstream side 5a, this force F1 being normal to the tangent of the contact point between these two components. The F1 force

Claims (7)

has a radial component relative to the drive spring towards its axis of rotation, and a tangential component in the counterclockwise direction relative to the view of FIG. 8. Furthermore, the contact surface 13 exerts a force F2 perpendicular to the downstream side 5b of the drive spring 1, and the elastic element exerts a force F3 in flexing, these three forces F1, F2 and F3 being in balance. The drive spring 1 described above is also capable of driving a mobile or a conventional date ring in a direction of rotation identical to the direction of rotation, because the elastic element 7 has sufficient stiffness to perform the training of such a crown even if the finger 5 moves during the drive away from the abutment surface 13. Claims 1. driving spring (1) for a timepiece, comprising: - a hub (3) intended to be integral in rotation with an axis (23) of a leading wheel (2); - an elastic member (7) extending from the hub and around a portion of the hub (3); - a finger (5) provided at the free end of the elastic element (7), the finger (5) having an upstream flank (5a) for driving in a first direction of rotation a calendar mobile (9) comprising a toothing, and a downstream flank (5b) intended to come into contact with an abutment surface (13) that the hub (3) comprises; characterized in that the finger (5) has a substantially triangular shape, the downstream flank (5b) and the abutment surface (13) being arranged such that they can cooperate so that the finger (5) can cause said movable calendar (9) in said first direction when the drive spring (1) is driven by the leading mobile (2), and so that the finger (5) can retract when the finger (5) enters in the toothing of the calendar wheel (9) and when the calendar wheel (9) is driven in a second direction of rotation opposite to said first direction of rotation. 2. Drive spring (1) according to the preceding claim, wherein, in the rest position of the drive spring (1), the angle made by the upstream side (5a) with a radius (r) passing through the the top of said finger (5) differs by less than 10%, preferably less than 5%, from the angle made by the downstream flank (5b) with said radius (r). 3. Drive spring (1) according to the preceding claim, wherein the downstream side (5b) is straight. 4. Drive spring (1) according to one of the preceding claims, wherein the angle between the upstream side (5a) and the downstream side (5b) is between 40 ° and 50 °, preferably between 43 ° and 47 °. 5. Drive spring (1) according to one of the preceding claims, wherein the abutment surface (13) is substantially arcuate shape. 6. Drive spring (1) according to the preceding claim, wherein the diameter of said circle is between 15% and 30% of the distance between the axis of rotation of the drive spring (1) and the geometric center of said circle . 7. Mobile driving a calendar mobile for a timepiece comprising a wheel (2) intended to be driven by a watch movement and a drive spring (1) according to one of the preceding claims secured in rotation with said wheel (2).