Dial for a timepiece

Abstract

Dial plate (1) for a timepiece intended to be mounted on a connecting ring (2), having a first lower surface (12) intended to be oriented towards the interior of a timepiece and a second upper opposite surface (13) intended to be visible, and comprising a third surface (11) connecting the first and second surfaces and forming a peripheral contour of the dial plate, characterized in that said third peripheral contour surface (11) comprises a section passing through a plane perpendicular to the second surface (13) comprising a first part (11a) extending from the first lower surface (12) towards the second upper surface (13) of the dial plate (1), in a direction not perpendicular to said first lower surface (12).

Description

Introduction

[0001] The present invention relates to a dial plate, a connecting ring for such a dial plate, and a dial itself comprising the assembly of a dial plate and a connecting ring. It also relates to a timepiece incorporating such a dial, such as a wristwatch. State of the Art

[0002] A dial for a timepiece, according to a first prior art solution, is described in document EP3339970. Such a dial comprises feet welded beneath a dial plate, intended for securing the dial plate to a timepiece frame, for example, with screws. This solution has the disadvantage of requiring a weldable material to form the dial, while also necessitating time-consuming manufacturing and assembly operations, including welding the feet and then screwing them into a frame. Furthermore, there is a risk of creating a statically indeterminate situation if the assembly precision is imperfect. Finally, this solution is incompatible with certain timepieces where the available space is very limited, restricting the number of screws that can be inserted to secure the dial, for example, wristwatches equipped with multiple mechanical functions.

[0003] Other solutions, such as the one described in document CH696987, require welding or gluing two superimposed plates, which retains the disadvantage of a tedious manufacturing process while increasing the thickness of the dial over its entire surface.

[0004] Ultimately, existing solutions do not provide a satisfactory result, and the general objective of the invention is to propose a dial solution for watch parts that avoids the drawbacks of the prior art. More specifically, the invention seeks to achieve all or some of the following objectives.

[0005] A first objective of the invention is to offer a dial solution suitable for any type of material, more particularly for a fragile material, such as a ceramic.

[0006] A second object of the invention is to offer a dial solution that combines simple manufacturing, user-friendly integration into a timepiece, and compatibility with all timepieces, including wristwatches with a small available volume.

[0007] Finally, a third object of the invention is to propose a dial solution enabling reliable and robust fixing of the dial on a blank or frame of a watch part. Brief description of the invention

[0008] To this end, the invention is based on a dial plate defined by independent claim 1.

[0009] Other forms of execution are defined in the dependent claims. Brief description of the figures

[0010] These objects, features and advantages of the present invention will be described in detail in the following description of a particular embodiment, given by way of non-limiting example, with reference to the accompanying figures, among which: There figure 1 represents a top-down perspective view of a dial according to one embodiment of the invention. figure 2 represents a cross-sectional view of a dial plate according to the embodiment of the invention. figure 3 represents a perspective view of a dial connecting ring according to the embodiment of the invention. figures 4 to 6 These images represent cross-sectional views to illustrate the assembly of a dial plate with a connecting ring according to the embodiment of the invention. figure 7 illustrates an enlarged view of details of the dial assembly on a blank according to the embodiment of the invention. figure 8illustrates a cross-sectional view of the arrangement of a dial within a timepiece according to the embodiment of the invention.

[0011] The invention is based on a dial 10 illustrated by the figure 1 , obtained by the mechanical assembly of two distinct components, a dial plate 1 and a connecting ring 2. The connecting ring 2 extends under the dial plate 1, in the peripheral part of the dial plate 1, and has the function of forming a removable fixing component of the dial 10 on a blank of a watch part.

[0012] By convention, we define the horizontal direction as any direction in a plane parallel to a horizontal plane, in particular to the surface of the dial plate 1, which may be flat or substantially flat. The vertical direction z is conventionally defined as the direction perpendicular to a horizontal plane, oriented from the dial plate towards the side intended to be visible to the wearer of a watch incorporating the dial plate. In an embodiment where the dial plate 1 is not flat, the horizontal direction will be defined from a plane substantially tangent to the upper surface of the dial plate and perpendicular to the vertical direction z.With this convention, which simplifies the following description, the adjectives "upper" and "lower" will characterize elements respectively intended to be oriented vertically on the visible side of a timepiece and on the opposite side. For example, the upper surface of the dial plate will refer to the surface visible to the wearer of a wristwatch, and the lower surface of the dial plate to the invisible surface, facing inward toward the inside of the watch, on the side closest to the wearer's wrist. Those skilled in the art will understand that these terms, as defined, can be used regardless of the shape of the dial plate, which is not necessarily circular. Furthermore, throughout this description, we use the term "dial" to mean any indicator intended to be permanently mounted within a watch case.Thus, within the framework of the invention, a counter for an indication derived from the time (a chronograph counter, for example) can be considered as a dial.

[0013] According to the embodiment illustrated in the figures, the dial plate 1 has a disc shape, comprising a small thickness (also called height, as it is oriented vertically according to the chosen convention) between a first lower flat surface 12 intended to face the inside of a watch and a second upper flat surface 13, opposite and parallel, intended to be visible. This dial plate 1 has a central vertical axis A passing through its center. Alternatively, the first lower surface 12 and / or the second upper surface 13 may be non-planar, but for example curved. It may have a vertex at its center. It may be convex or concave. Furthermore, the dial plate could have a non-circular shape, as will be discussed later.

[0014] There figure 2corresponding to the invention as claimed, represents a cross-sectional view of the dial plate 1 passing through a vertical median plane, that is to say, a vertical plane comprising the axis A of the dial plate or, more generally, a vertical plane passing through the center of the dial plate 1. This figure 2This allows us to represent, more specifically, a section of a third surface 11 of the dial plate 1, forming a peripheral contour surface of the dial plate 1. This third surface 11 connects the first lower surface 12 and / or the second upper surface 13. It forms an assembly surface of the dial plate 1, as will be detailed later. This section of the third surface 11 has the particularity of not being oriented along the vertical direction z. In other words, it is not perpendicular or substantially perpendicular to the dial plate 1, and more specifically to either of the first and second surfaces 12, 13.

[0015] More specifically, the section of the third surface 11 has a particular and advantageous shape, including in particular: a first part 11a extending from the first lower surface 12 in a direction not perpendicular to said first lower surface 12, i.e. not aligned with the vertical direction z. This first part 11a advantageously extends over at least one quarter of the thickness of the dial plate (in other words, one quarter of the height considered along the vertical direction z between the two first and second surfaces 12, 13), and a second part 11b extending from the second upper surface 13 in a direction not perpendicular to said second upper surface 13, i.e. not aligned with the vertical direction z, and a third part 11c connecting between the first and second parts, forming a peripheral connecting zone of the dial plate 1 suitable for cooperation with a dial connecting ring 2, which will be described below.

[0016] According to the embodiment, the first part 11a and the second part 11b of the third surface 11 are therefore inclined outwards from the dial plate 1, that is to say in a direction comprising a horizontal component which moves away from the first and second surfaces 12, 13 of the dial plate 1.

[0017] According to this embodiment, the first part 11a of the section of the third surface 11 has an inclination of first angle α1 relative to the first surface 12 and / or relative to a horizontal plane. This first angle α1 is advantageously between 50° and 70°, or even between 60° and 70°.

[0018] The second part 11b of the third surface 11 has a second inclination angle α2 relative to the upper second surface 13 and / or relative to a horizontal plane. This second angle α2 is advantageously between 60° and 80°, or even between 65° and 75°.

[0019] According to the embodiment, the first angle α1 is advantageously smaller than the second angle α2.

[0020] The third part 11c has a vertex, that is, an area furthest from the second upper surface 13. This vertex is approximately positioned in the middle of the thickness of the dial plate 1 or slightly below the horizontal median plane of the dial plate 1. This vertex consists of a point according to the embodiment.

[0021] Advantageously, the third connecting portion 11c is a rounded section, specifically with a radius between 0.1 mm and 0.5 mm. It connects the two portions 11a and 11b to form a continuous curve. This rounded curve is advantageously smooth.

[0022] The first part 11a and the second part 11b are inclined linear parts in the embodiment, but could alternatively have other shapes not necessarily linear.

[0023] Preferably, the third peripheral contour surface 11 extends around the entire perimeter of the dial plate 1. Alternatively, it could extend along one or more sectors around the perimeter of the dial plate 1. In the described embodiment, the dial plate is a surface of revolution with axis A. All sections obtained by a vertical median plane, that is, a plane perpendicular to the upper second surface 13 including its axis and / or center, advantageously have the same shape. In other words, the dial plate preferably has no discontinuity on its peripheral contour, which has a horizontal section of well-defined geometry, for example, circular, rectangular, polygonal, etc., and particularly without truncation.

[0024] Alternatively, the dial plate could be not circular, but for example polygonal, square, or rectangular. In all cases, it is advantageous that all or nearly all sections by a vertical median plane have the same shape.

[0025] The dial plate 1 may be ceramic-based, in particular zirconia or alumina, a fluorescent and / or phosphorescent ceramic, or a composite ceramic based on yttria-treated zirconia and Dy / Eu-doped strontium aluminate. It may advantageously be made of "luminescent zirconia," for example, as described in patent application EP2730636. Alternatively, it may be composite-based. As a further alternative, it may be made of a stone, in particular onyx, opal, turquoise, or sapphire, or of mother-of-pearl. The expression "made of a certain material" means that the dial plate comprises at least 50%, or even at least 80%, by weight of said material.

[0026] The dial plate 1 can be coated with a layer of varnish, for example a varnish with fluorescent and / or phosphorescent properties, so as to modulate the day and night appearance of the dial plate. Alternatively, the dial 10 can include a second solid plate with fluorescent and / or phosphorescent properties fixed beneath the first lower surface 12 of the dial plate 1.

[0027] According to the embodiment, the dial 10 further includes a connecting ring 2, more particularly represented by the figures 3 And 7This connecting ring 2 is intended for assembly with the dial plate 1 described previously. Its function is to assemble the dial 10 onto a watch movement blank or a watch component, as will be detailed later. The connecting ring 2 is preferably made of metal or a metal alloy. It can be made of brass or steel, particularly Nivaflex®.

[0028] The connecting ring 2 includes a connecting portion 21 in its upper part, having a connecting surface 210 for cooperating with the third peripheral contour surface 11 of the dial plate 1. The connecting portion 21 is therefore intended for securing the dial plate 1. According to the embodiment, the connecting surface 210 has a frustoconical shape and is suitable for elastic deformation. Alternatively, the connecting portion 21 could have another shape suitable for elastic deformation. Advantageously, the connecting portion includes at least one section passing through a vertical plane having an inclination with respect to the vertical direction, such that its upper end is offset towards the dial plate 1 or towards the center of the connecting ring with respect to a vertical direction.Thus, at least a portion of the connecting section is inclined towards the center of the connecting ring relative to a direction perpendicular to the plane of the connecting ring. As will be detailed later, this connecting section 21 serves to hold a dial plate in its assembled position. At least a portion of its contact surface 210 therefore remains in direct or indirect contact with the dial plate in its assembled position, exerting a holding force on this dial plate. Naturally, this holding force is preferably reversible, and this connecting section therefore contributes to a removable retention of the dial plate. Furthermore, the connecting section is adapted to bear against the peripheral contour of a dial plate.By such support, it is able to exert a force comprising at least one component directed towards the center of the dial plate, particularly a radial component in the case of a circular dial plate.

[0029] The connecting portion 21 further includes a horizontal or substantially horizontal support surface 211 intended to receive the support of a lateral part, or peripheral part, of the first lower surface 12 of the dial plate 1.

[0030] The connecting ring 2 further includes a lower fixing portion, which extends below the connecting portion 21, and which is intended for fixing the connecting ring 2 to a watch blank, and thus for fixing a dial within a watch. According to the embodiment, this lower fixing portion has the form of a skirt 22 which extends substantially in a direction opposite to the connecting surface 210, relative to the support surface 211. In other words, the connecting portion 21 and the lower fixing portion form portions arranged substantially in the vertical direction, which are distributed on either side of the horizontal or substantially horizontal support surface 211.

[0031] The skirt 22 of the embodiment extends in a vertical direction. It comprises at least one elastic element 220. Preferably, this elastic element 220 extends partially along the height h of the skirt 22. The elastic element 220 advantageously takes the form of a blade embedded in the wall of the skirt 22. It may, for example, take the form of a blade embedded at both ends. Such a blade may extend in a substantially horizontal direction. It may be formed by at least one through slot 221, or cutout, extending in a horizontal plane and formed in the wall of the skirt 22. Preferably, the skirt 22 comprises several elastic elements. According to the embodiment, the skirt 22 comprises three identical elastic elements 220, 220', 220". These three elements are advantageously equally distributed around the circumference of the connecting ring 2.

[0032] The portion for attaching the connecting ring, i.e. the skirt 22 in the embodiment, has a shape designed to cooperate with a blank of a watch part, as will be detailed later with reference to the figure 7 This design therefore includes the shape and additional elements for the connecting ring's fixing portion to enable the fastening function. This fixing is removable. Depending on the embodiment, this fixing can be done without tools. It is of the clip-on or spring-fit type.

[0033] THE figures 4 to 6These figures illustrate more precisely the assembly of a dial plate 1 with a connecting ring 2. Depending on the embodiment, the assembly is achieved by pressing or clipping, i.e., by elastic interlocking. This assembly is therefore not necessarily tool-based. It also does not require any tedious operations such as welding or gluing. Furthermore, it can be reversible and removable.

[0034] There figure 4illustrates an approach phase of the dial plate 1 above the connecting portion 21 of the connecting ring 2. The first part 11a of the cross-section of the third surface 11 of the dial plate 1 comes to rest on the upper end of the connecting surface 210 of the connecting ring 2. The dimensions of the frustoconical connecting surface 210 are such that the downward pressure exerted on the dial plate 1 then induces a progressive elastic deformation of the connecting portion 21 of the connecting ring 2 with which the third surface 11 cooperates. Throughout this assembly phase, the third surface 11 of the dial plate 1 therefore cooperates with the connecting surface 210 by contact.According to the embodiment, the connecting portion 21, which is inclined on the side of the dial plate with respect to a vertical direction in its rest position, is therefore moved away in the direction of the vertical by the contact of its connecting surface 210 with the dial plate 1.

[0035] The assembly movement continues until the first lower surface 12 of the dial plate 1 comes to rest against the support surface 211 of the connecting ring 2, as shown in the figure 5In this final assembly configuration, only the rounded portion 11c of the cross-section of the third surface 11 is in contact with the connecting surface 210 of the connecting ring 2. Due to the deformation of the connecting portion 21, the latter exerts a holding force on the dial plate 1, ensuring its reliable and robust retention. Furthermore, the connecting surface 210 of the connecting portion 21 of the connecting ring 2 has the advantageous characteristic of directing the holding force downwards, that is, exerting a force that tends to press the lower first surface 12 of the dial plate 1 against the support surface 211 of the connecting ring 2. It thus resists the withdrawal of the dial plate 1 and promotes its stable retention. In the final assembly configuration, the connecting surface 210 therefore remains in contact with the dial plate 1 to ensure its retention.Furthermore, the connecting portion 21 remains in a deformed position in the final configuration, so that it exerts an elastic restoring force on the dial plate, thus fulfilling its holding function. Advantageously, this restoring force includes at least one component directed towards the center of the dial plate.

[0036] As a point of interest, the stresses exerted by this holding force are concentrated on portion 11c, which advantageously minimizes stresses within the dial plate material while ensuring adequate holding force of the dial plate on the ring. In this embodiment, the contact area of ​​the third surface 11 is effectively reduced to a single point, which is the aforementioned vertex of the third portion 11c. Consequently, the contact between the third surface 11 and the connecting surface 210 is linear or substantially linear.

[0037] The figure 6illustrates a phase of dissociation of the dial plate 1 from the connecting ring 2. For this, a pivoting of the dial plate 1 is carried out, for example by levering on an area of ​​the dial plate 1. The aforementioned linear or substantially linear contact between the third surface 11 of the dial plate 1 and the connecting surface 210 of the connecting ring 2 makes it possible to facilitate this disassembly of the dial plate 1, by defining an advantageous pivoting area P of the dial plate 1 at the level of its third part 11c of its third surface 11, which pivots against the connecting surface 210 of the connecting portion 21 of the connecting ring 2. The latter deforms elastically during this operation.Thus, the solution according to the embodiment also allows the dial plate 1 to be disassembled from the connecting ring 2, which is particularly advantageous for after-sales service, for example, if it becomes necessary to replace the connecting ring 2 or the dial plate 1. The dial plate 1 and the connecting ring 2 therefore remain two separate components that can be removably assembled, according to the embodiment. Alternatively, it might be preferable to create an assembly that is more difficult to remove without departing from the scope of the invention, for example, by modifying the geometries of surfaces 11 and 210.

[0038] Preferably, as described in the embodiment, the third surface 11 of the dial plate 1 is an outer peripheral surface of the dial plate 1. In this particular case of a disc-shaped dial plate, the vertex of the third part 11c belongs to a circle centered on the axis A, whose radius R, visible on the figure 2 , defines the largest radius of the dial plate 1.

[0039] Thanks to this achievement, dial plate 1 has the advantage of being able to be made of a fragile material, in particular a material that does not exhibit plastic deformation under stress, as has been specified.

[0040] Next, when a dial 10 formed by the assembly of a dial plate 1 and a connecting ring 2 is obtained, as illustrated by the Figures 1 And 5 Dial 10 is ready to be mounted within a timepiece. figure 7This figure illustrates more specifically a phase of fixing the dial 10, and more precisely the connecting ring 2, according to the embodiment on a blank 3 of a timepiece. In this figure, the dial 10 is in an approach phase over a blank. This blank 3 includes protruding protrusions 31, shaped to cooperate with the elastic elements 220, 220', 220" of the connecting ring 2. As the dial 10 continues its descent, each blade 220 is pushed apart by a protrusion 31, deforming elastically. This movement continues until the first lower surface 12 of the dial plate 1 comes abutting against the blank 3.

[0041] Optionally, the skirt 22 of the connecting ring 2 also includes a vertically or substantially vertically oriented surface 222, which is designed to abut against a surface 33 of the blank 3, also oriented vertically or substantially vertically. These elements serve to ensure angular indexing of the dial on the blank. Alternatively or additionally, the connecting ring 2 can directly cooperate with a case 4 or any component of a timepiece, so as to allow the angular positioning of the dial 10 within a timepiece.

[0042] As can be seen from the preceding description, the connecting ring 2 in this embodiment also has the advantage of allowing the dial 10 to be mounted on a watch movement without requiring assembly screws or feet, for which spaces would need to be provided within the watch movement. It thus remains compatible with the integration of a dial within a watch movement that leaves little free space for dial positioning.

[0043] THE figure 8This illustrates the final positioning of a dial according to the embodiment of the invention within a timepiece. In this position, the connecting ring 2 is fixed to a blank 3 of the watch movement 30, as described previously. The lower first surface 12 of the dial plate 1 bears against the support surface 211 of the connecting ring 2 on its periphery, and against an upper surface 32 of the blank 3 in the central part of its surface. Alternatively, it could be positioned against any other stop arranged to prevent the vertical movement of the dial 10 towards the interior of the timepiece.

[0044] Furthermore, in this embodiment, it appears that the connecting ring 2 comprises one or more specific surfaces designed to cooperate with a case 4 of a watch case 40 of the timepiece, in order to limit the axial play of the dial 10, and in particular to mitigate the effect of any shocks. To this end, the connecting ring 2 may include a horizontal or substantially horizontal surface 212 arranged at the upper end of its connecting portion 21, which is positioned against a horizontal or substantially horizontal surface 410 of the case 4. Note that this stop or support may intentionally have some clearance. According to the embodiment, the horizontal surface 212 of the connecting ring 2 is concealed by a flange 41 of the case 4, the corresponding horizontal surface 410 of which is formed beneath the flange 41.On the other hand, the connecting ring 2 includes a vertical or substantially vertical surface 213, which cooperates with a vertical or substantially vertical surface 411 of the case 4. This cooperation between said two vertical surfaces 213, 411 allows the dial 10 to be guided within the watch case 40. This cooperation is achieved through contact. It may include some clearance. In this way, the dial can be mounted directly between the dial 10 and the case 40, independently of the watch movement 30 comprising the blank 3 on which the dial 10 is mounted. Such a solution is therefore particularly advantageous in terms of the precision of dial assembly within a watch case, thus reducing the number of tolerances involved in the assembly.

[0045] Naturally, the invention is not limited to the embodiment described and the dial according to the embodiment of the invention remains compatible for mounting in any timepiece, according to the extent as defined by the attached claims.

Claims

1. A dial plate (1) for a timepiece which is designed to be mounted on a connection ring (2), which plate has a first, lower surface (12) designed to be positioned on the interior side of a timepiece, and an opposite second, upper surface (13) designed to be on view, and comprising a third surface (11) which connects the first and second surfaces, and forms a peripheral contour of the dial plate, said third surface (11) of peripheral contour comprising a section which passes via a plane perpendicular to the second surface (13), characterized in that said third surface (11) of peripheral contour also comprises : - a first part (11a) extending from the first, lower surface (12) to the second, upper surface (13) of the dial plate (1), in a direction which is non-perpendicular to said first, lower surface (12), and in particular is inclined towards the exterior of the dial plate (1), - a second part (11b) extending from the second, upper surface (13), to the first, lower surface (12), in a direction which is non-perpendicular to said second, upper surface (13), and in particular is inclined towards the exterior of the dial plate (1).

2. The dial plate (1) for a timepiece as claimed in the preceding claim, characterized in that the section of said third surface (11) of peripheral contour additionally comprises: - a third part (11c), for connection between the first and the second part, forming a peripheral connection area of the dial plate (1), which can cooperate with the dial connection ring (2).

3. The dial plate (1) for a timepiece as claimed in one of the preceding claims, characterized in that the first part (11a) of the section of the third surface (11) extends over a height representing at least a quarter of the thickness of the dial plate (1).

4. The dial plate (1) for a timepiece as claimed in the preceding claim, characterized in that the first part (11a) of the third surface (11) has an inclination with a first angle α1 relative to the first, lower surface (12), in that the second part (11b) of the third surface (11) has an inclination with a second angle α2 relative to the second, upper surface (13), and in that the first angle α1 is between 50° and 70°, or between 60° and 70°, and in that the second angle α2 is between 60° and 80°, or between 65° and 75°.

5. The dial plate (1) for a timepiece as claimed in one of claims 2 to 4, characterized in that the third part (11c) has a top furthest from the upper, second surface (13), which top is substantially positioned in the middle of the thickness of the dial plate (1).

6. The dial plate (1) for a timepiece as claimed in one of the preceding claims, characterized in that the third part (11c) is a rounded portion, in particular with a radius of between 0.1 mm and 0.5 mm.

7. The dial plate (1) for a timepiece as claimed in one of the preceding claims, characterized in that it is based on ceramic, in particular a zircon or an alumina, a fluorescent and / or phosphorescent ceramic, or a composite ceramic based on yttriated zircon and Dy / Eu-doped strontium aluminate, or in that it is based on composite material, or in that it is based on a stone, in particular onyx, opal, turquoise or sapphire, or in that it is based on mother-of-pearl.

8. A connection ring (2) comprising a connection portion (21) with a connection surface (210) which can undergo elastic deformation, and configured to cooperate by contact with a third surface (11) of peripheral contour of said dial plate (1) as claimed in one of the preceding claims, so as to ensure its retention in an assembly configuration with the connecting ring and comprising a skirt (22) comprising at least one elastic element (220) in the form of an embedded tongue.

9. The connection ring (2) for a dial plate (1) as claimed in the preceding claim, characterized in that the connection portion (21) has a connection surface (210) with a frusto-conical form and / or a part of the connecting potion having an inclination towards the center of the connecting ring relatively to a perpendicular direction to the connecting ring plane.

10. The connection ring (2) for a dial plate (1) as claimed in claim 8 or 9, characterized in that said skirt (22) extends substantially in a direction opposite the connection surface (210) relative to a support surface (211).

11. A dial for a timepiece, characterized in that it comprises the assembly of a dial plate (1) as claimed in one of claims 1 to 7 with a connection ring (2) as claimed in one of claims 8 to 10, and in that said assembly is carried out by driving, inducing an elastic deformation of the connection portion (21) of the connection ring (2) with which the third surface (11) of the dial plate (1) cooperates.

12. The dial for a timepiece as claimed in the preceding claim, characterized in that the third surface (11) of the dial plate has a linear or substantially linear contact with the connection surface (210) of the connection portion (21).

13. A timepiece, in particular a wristwatch, characterized in that it comprises a dial as claimed in one of claims 11 or 12.

14. The timepiece as claimed in the preceding claim, characterized in that the connection ring (2) of the dial is fastened on a blank (3) of a timepiece movement (30).

15. The timepiece as claimed in claim 13 or 14, characterized in that it comprises a middle (4), and in that the connection ring (2) comprises a surface (212) which is horizontal or substantially horizontal and / or a surface (213) which is vertical or substantially vertical, and in that the middle (4) comprises a surface (410) which is horizontal or substantially horizontal, which can be supported on said horizontal surface (212) of the connection ring (2), and / or in that the middle (4) comprises a surface (411) which is vertical or substantially vertical, which can be in contact with said vertical surface (213) of the connection ring (2)

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