Winding crown with torque limitation

Abstract

A winding crown for a mechanical timepiece comprising a torque-limiting device, the torque-limiting device comprising a first element and a second element, one serving as a driving element and the other as a driven element, the driven element being arranged to control the tension of the mainspring of the timepiece, the first element comprising a friction member and a plurality of springs, the friction member being arranged to be pushed by the plurality of springs against a friction surface of the second element parallel to the axis of rotation of the winding crown. A timepiece comprising such a winding crown.

Description

[0001] The present invention relates to a winding crown for a mechanical timepiece, comprising a torque limiting device.

[0002] Winding a mechanical timepiece, particularly a wristwatch, typically involves energizing a mainspring wound inside a barrel within the watch movement, which is itself housed in a watch case. This is usually done using a winding crown, accessible from the outside of the case, which drives a winding stem that transmits the crown's rotation to the movement. As the mainspring is energized by the crown's rotation, the force required to wind it increases. Overwinding beyond a certain point can cause permanent deformation or even breakage of the mainspring.To avoid this, some engine springs include a device for limiting the applied force, for example a sliding flange, to limit the over-tension of the engine spring.

[0003] Another solution for limiting over-tensioning of the mainspring is to use a winding crown incorporating a torque-limiting device. When the torque required to rotate the winding crown exceeds a maximum permissible torque value, the torque-limiting device disengages the winding stem from the crown head, thus limiting the force transmitted to the mainspring by actuating the crown. However, a challenge lies in setting the maximum torque before the torque-limiting device disengages. Excessive maximum torque can damage the mainspring, while insufficient torque prevents the movement from utilizing its maximum power reserve.The maximum torque setting is preferably carried out individually for each winding crown including a torque limiting device in order to compensate for example for variations due to manufacturing tolerances of the components of the torque limiting device.

[0004] Patent CH 711 125 B1, for example, describes a winding crown incorporating a torque-limiting device. The crown comprises a head, an insert rotatably fixed to the head, and a barrel for receiving a winding stem. A friction element rotatably fixed to the insert is pressed against an edge profile of the barrel by a single helical spring. The maximum permissible torque of the winding crown is thus adjustable solely by selecting the strength of the single spring, which does not allow for fine adjustment of the friction element's contact force against the edge profile. Furthermore, the star-shaped configuration of the friction element means that when the maximum permissible torque is exceeded, the edges of the star's points rub against the edge profile, which can cause premature wear.

[0005] Patent EP 1 513 028 B1, filed in the name of the applicant, describes a winding crown comprising a torque-limiting device of a different construction. The torque-limiting device described therein comprises a first element and a second element. The first element includes several friction members, each friction member being pressed against the second element by its respective spring. This torque-limiting device requires individual adjustment of the force of each spring so that they all release at approximately the same torque value applied to the device. Otherwise, there is a significant risk that one of the friction members will remain pressed firmly against the second element beyond the maximum permissible torque, resulting in a malfunction of the torque-limiting device. Adjusting such a torque-limiting device can therefore be a lengthy and difficult process.

[0006] One aim of the invention is to provide a winding crown comprising a torque limiting device whose maximum permissible torque is adjustable in a simple and precise manner.

[0007] This purpose and other advantages are achieved by a winding crown for a mechanical timepiece comprising a torque limiting device, the torque limiting device comprising a first element and a second element intended to serve as a driving element and a driven element, the driven element being arranged to control the tension of the mainspring of the timepiece, the first element comprising a friction member and a plurality of springs, the friction member being arranged to be pushed by the plurality of springs against a friction surface of the second element parallel to the axis of rotation of the winding crown.

[0008] The presence of multiple springs, all acting on the same friction element of the first component to push it against the friction surface of the second component, allows for greater flexibility and finer control of the elastic force with which the friction element presses against the friction surface. This, in turn, allows for greater control of the torque at which the driven component is disengaged from the drive component, as the force of each spring is individually adjustable. The maximum permissible torque can be at least partially adjusted by adding or removing one or more springs and / or by replacing one or more springs with springs of different characteristics during the assembly of the winding crown and / or during maintenance or repair.Since the springs of the plurality of springs all act on the same friction element, the exchange, removal or addition of a single spring allows the characteristics of the torque limiting device to be adjusted globally.

[0009] According to a preferred embodiment, the friction member is a ring disposed around the axis of rotation of the winding crown comprising a toothed edge intended to cooperate with a toothed edge of the friction surface.

[0010] The edge teeth of the friction element and the edge teeth of the friction surface are, for example, saw-toothed, which allows the torque to be limited only in a first direction of rotation of the winding crown. Since the torque is not limited in a second direction of rotation opposite to the first, the winding crown can be turned in this second direction to wind a second mainspring, preferably equipped with a device to limit the applied force, for example, a sliding flange.

[0011] Preferably, the first element is rotationally fixed to a head of the winding crown and the second element is intended to drive a winding stem.

[0012] Preferably, the springs of the plurality of springs are helical springs compressed between a base of the first element and the friction member.

[0013] Each spring in the plurality of springs is, for example, housed in a blind hole in the base.

[0014] The friction element, for example, is rotationally fixed to the base and movable relative to the base in a direction essentially parallel to the axis of rotation.

[0015] The friction element includes, for example, at least one stud extending parallel to the axis of rotation, each stud being intended to be inserted into a corresponding housing in the base to guide the movements of the friction element relative to the base.

[0016] According to another embodiment, the friction member includes at least one lug extending radially from the axis of rotation, each lug being intended to be inserted into a corresponding slot in the base to guide the movements of the friction member relative to the base.

[0017] The friction element and the friction surface are preferably configured so that the torque limiting device limits the torque transmitted between the driving element and the driven element in a first direction of rotation of the winding crown and does not limit the torque in a second direction of rotation opposite to the first.

[0018] The purpose mentioned above and other advantages are also achieved by a mechanical timepiece including such a winding crown.

[0019] The invention will be better understood upon reading the description below, illustrated by the figures where: there figure 1 is a perspective cross-section of a winding crown according to one embodiment of the invention; the figure 2 is a detail of the crown's torque limiting device figure 1 ; there figure 3 is a front view of the crown of the figure 1 when it is turned in one direction; the figure 4 is a front view of the crown of the figure 1 when it is rotated in a second direction opposite to the first; the figure 5 is a perspective cross-section of a winding crown according to another embodiment of the invention; the figure 6 is a perspective view of the winding crown drive element of the figure 5 .

[0020] With reference to the figure 1 The winding crown 1 of the invention includes a head 2 configured to allow a user to operate the winding crown 1. The head 2 is configured to be grasped by the user, for example between two fingers, in order to rotate the winding crown 1 about its axis of rotation 10. The rotation of the winding crown 1 is transmitted, generally via a winding stem (not shown in the figures), to a watch movement to wind its mainspring. The winding crown 1 includes, for example, a sleeve 40 for receiving and retaining the winding stem, which is, for example, screwed into the sleeve 40. Preferably, the watch movement is housed in a watch case, and the head 2 is accessible from outside the watch case.

[0021] According to the invention, the winding crown 1 includes a torque-limiting device to prevent, for example, damage to the mainspring through overwinding. The torque-limiting device comprises a drive element 3 and a driven element 4. The drive element 3 is rotationally fixed to the head 2 and is intended to rotate the driven element 4, which is arranged to control the winding of the mainspring. In the embodiment illustrated by way of example, the drive element 3 includes a friction member 31 intended to cooperate with a friction surface 41 of the driven element 4 to drive the driven element 4 while limiting the torque between the two elements 3 and 4 in at least one direction of rotation.The drive element 3 comprises, for example, a base 30 fixed in rotation with the head 2, the base 30 preferably being fixed relative to the head 2, and the friction member 31 is configured to be fixed in rotation with the base 30 and movable relative to the latter in a direction parallel to the axis of rotation 10. According to the invention, a plurality of springs 33 disposed between the base 30 and the friction element 31 push the friction element 31 against the friction surface 41 of the driven element 4. It is also conceivable within the scope of the invention to configure the torque limiting device so that the driven element comprises the friction member and the drive element comprises the corresponding friction surface, the plurality of springs then being disposed on the driven element, for example between a base of the driven element and the friction member.

[0022] According to the illustrated embodiment, the friction element 31 is a ring disposed on the base 30 around the axis of rotation 10 and comprising, on its surface oriented towards the base 30, at least one stud 32, preferably at least two studs 32, for example three studs 32, extending essentially parallel to the axis of rotation 10. The studs 32 are intended to be inserted each into a corresponding recess (not shown) in the base 30 to prevent the friction element 31 from rotating relative to the base 30 while allowing its movement relative to the latter in a direction essentially parallel to the axis of rotation 10. The friction element 31 is pushed against the friction surface 41 of the driven element 4 by the plurality of springs 33 disposed between the friction element 31 and the base 30.The springs 33 are for example helical springs partially housed each in a blind hole 34 of the base 30 opposite the friction member 31 and are compressed between the bottom of the blind hole 34 and the friction member 31 when the winding crown 1 is assembled.

[0023] With reference to the figure 2 The friction element 31, according to the illustrated embodiment, comprises saw-toothed edge teeth for meshing with complementary edge teeth on the friction surface 41. According to this embodiment, the torque-limiting device is unidirectional in that the torque transmitted from the drive element 3 to the driven element 4 is limited only in a first direction of rotation of the winding crown. Preferably, the torque is not limited in a second direction of rotation opposite to the first.

[0024] As illustrated in the figure 3 As indicated by the arc-shaped arrow, when the head 2 of the winding crown 1 is turned counterclockwise, the driving element 3 drives the driven element 4 in the same direction as long as the torque required to rotate the driven element 4 is less than or equal to the friction torque between the friction member 31 and the friction surface 41. When the torque required to rotate the driven element 4 is greater than the friction torque, for example due to the increased resistance of the mainspring to its winding, the inclined planes of the respective edge teeth slide against each other and the friction member 31 is pushed towards the base 30 as illustrated by the downward arrow in the figure, against the force of the plurality of springs 33.The edge teeth of the friction member 31 and the friction surface 41 disengage and the driven element 4 is no longer driven by the drive element 3.

[0025] The friction torque between the friction member 31 and the friction surface 41 in the first direction of rotation depends on the angle, material, condition, and surface area of ​​the inclined planes of the teeth in contact with each other, as well as the pressure force of the friction member 31 against the friction surface 41. According to the invention, this last parameter is adjustable by selecting springs 33 with appropriate characteristics and / or by determining the number of springs 33. Preferably, the friction torque between the friction member 31 and the friction surface 41 is adjusted during the assembly of the winding crown 1 so that the torque-limiting device disengages when the torque in the first direction of rotation exceeds the maximum permissible torque.This adjustment of the friction torque is preferably at least partially achieved by removing or adding one or more springs 33 between the base 30 and the friction element 31, depending on whether the friction torque needs to be decreased or increased. The base 30, for example, includes a number of blind holes 34 greater than the number of springs 33 generally required to achieve the target friction torque. Thus, if variations in the friction torque due to manufacturing tolerances of the parts, including the springs 33, necessitate an increase in the contact force of the friction element 31 against the friction surface 41, one or more springs 33 can be added to reach the target value. It is also possible to adjust the friction torque by exchanging one or more springs 33 from the plurality of springs 33 with one or more springs 33 having slightly different technical characteristics.The adjustment method according to the invention offers great flexibility and allows fine adjustment of the friction torque of the torque limiting device.

[0026] As illustrated in the figure 4 According to the illustrated embodiment, the torque transmitted by the drive element 3 to the driven element 4 is not limited in a second direction of rotation opposite to the first. When the head 2 is rotated clockwise, as illustrated by the arc-shaped arrow, the saw-toothed teeth of the friction member 31 bear against the saw-toothed teeth of the friction surface 41 by the vertical parts of the teeth, so that the force transmitted between the drive element 3 and the driven element 4 is oriented perpendicular to the direction in which the friction member 31 is movable relative to the friction surface 41.In this second direction of rotation, there is therefore no component of the force transmitted between the two elements 3, 4 that is directed against the force of the springs 33, so there is no component of the force transmitted between the two elements 3, 4 that is likely to cause movement of the friction element 31 parallel to the axis of rotation 10. Since the increase in torque between the two elements 3, 4 does not cause any displacement of the friction element 31 along the axis of rotation 10, no disengagement of the edge teeth can occur. In the second direction of rotation, the driven element 4 is rotationally fixed to the driving element regardless of the applied torque.

[0027] According to the illustrated embodiment, the friction surface 41 and the corresponding surface of the friction element 31 comprise saw-toothed edge teeth. However, other configurations of the friction element and the friction surface are possible within the scope of the invention to allow unidirectional or bidirectional limitation of the torque transmitted between the driving element and the driven element of the torque-limiting device. For example, it is possible within the scope of the invention to give the edge teeth an asymmetrical profile allowing torque limitation in both directions of rotation, but with the maximum permissible torque in one direction of rotation being different from the maximum permissible torque in the second direction of rotation.

[0028] According to the embodiment illustrated by the figures 1 à 4 The movements of the friction member 31 relative to the base 30 are guided by the stud(s) 32 of the friction member 31, each inserted in a corresponding housing of the base 30. Other guiding means are however conceivable within the framework of the invention to lock the friction member in rotation with a base of the drive element or of the driven element, while allowing a displacement of this friction member relative to the base in a direction parallel to the axis of rotation of the winding crown.

[0029] THE figures 5 et 6 The figures illustrate, for example, an embodiment in which the guiding means for the friction element 31 comprise at least one lug 32', for example two lugs 32', extending radially around the periphery of the friction element 31 and each inserted into a slot 35 in the base 30. Each slot 35 is dimensioned and configured to allow movement of the corresponding lug 32' within the slot 35 only in a direction parallel to the axis of rotation 10 of the drive element 3. This configuration has the advantage that the surface of the friction element 31 facing the base 30 is preferably free of any stud or other guiding element. The entire surface of the friction element 31 facing the base 30 can thus serve as a bearing surface for the springs 33 of the plurality of springs.This allows, for example, the springs 33 to be distributed more regularly and / or more densely between the base 30 and the friction element 31, thus offering greater flexibility in adjusting the support force of the friction element 31 against the corresponding friction surface and thus a finer adjustment of the maximum permissible torque.

[0030] The other elements illustrated in the figures 5 et 6 and designated by the same reference numbers as in the figures 1 à 4 are identical to those described in relation to these figures and fulfill the same functions.

Claims

1. Winding crown (1) for a mechanical timepiece comprising a torque limiting device, the torque limiting device comprising a first element and a second element intended to serve as a driving element (3) and a driven element (4), the driven element (4) being arranged to control the tension of the mainspring of the timepiece, the first element comprising a friction member (31) and a plurality of springs (33), the friction member (31) being arranged to be pushed by the plurality of springs (33) against a friction surface (41) of the second element parallel to the axis of rotation (10) of the winding crown (1).

2. Winding crown (1) according to the preceding claim, the friction member (31) being a ring disposed around the axis of rotation (10) of the winding crown (1) and comprising a toothed edge intended to cooperate with a toothed edge of the friction surface (41).

3. Winding crown (1) according to the preceding claim, the edge teeth of the friction member (31) and the edge teeth of the friction surface (41) being saw-tooth teeth.

4. Winding crown (1) according to any one of the preceding claims, the first element being rotationally fixed to a head (2) of the winding crown (1) and the second element being intended to drive a winding stem.

5. Winding crown (1) according to any one of the preceding claims, the springs (33) of the plurality of springs being helical springs compressed between a base (30) of the first element and the friction member (31).

6. Winding crown (1) according to the preceding claim, each spring (33) of the plurality of springs being housed in a blind hole (34) of the base (30).

7. Winding crown (1) according to one of claims 5 and 6, the friction member (31) being rotationally fixed with the base (30) and movable relative to the base (30) in a direction essentially parallel to the axis of rotation (10).

8. Winding crown (1) according to the preceding claim, the friction member (31) comprising at least one stud (32) extending parallel to the axis of rotation, each stud (32) being intended to be inserted into a corresponding housing in the base (30) to guide the movements of the friction member (31) relative to the base (30).

9. Winding crown (1) according to claim 7, the friction member (31) comprising at least one lug (32') extending radially with respect to the axis of rotation, each lug (32') being intended to be inserted into a corresponding slot (35) in the base (30) to guide the movements of the friction member (31) with respect to the base (30).

10. Winding crown (1) according to any one of the preceding claims, the friction member (31) and the friction surface (41) being configured so that the torque limiting device limits the torque transmitted between the driving element (3) and the driven element (4) in a first direction of rotation of the winding crown (1) and does not limit the torque in a second direction of rotation opposite to the first.

11. Mechanical watch part comprising a winding crown (1) according to any one of the preceding claims.

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