Wristwatch Comprising A Monocoque Case

Abstract

A timepiece, especially a wristwatch, having a one-piece (monocoque) case and a novel means for accurately centering the dial relative to the central axis of the case. The centering means comprises three separately located abutment means on the dial and on the case, two of which are diametrically opposed to each other while the third is on a radius perpendicular to the diameter of the first two.

Description

The object of the present invention is a wristwatch comprising a monocoque case provided with a groove for the glass, a glass whose shoulder is engaged in the glass groove, a movement and a dial held in place by the shoulder of the glass, and maintaining the movement securely in the watchcase.

Wristwatches of this type are already known in which the monocoque case is made of a plastic material which is sufficiently rigid to satisfy the conditions imposed upon objects of this type. In order to simplify and rationalize the manufacture of these watches, it has also been contemplated to make the dial in a single piece of injected or molded plastic and to use this dial to hold the movement in place within the monocoque case, the dial being itself fastened to the inside of the case by the shoulder of the glass. However, these embodiments encountered a difficulty which resulted from the fact that it is difficult to effect the manufacture of a part such as a watch dial in plastic with sufficiently narrow tolerances with respect to the dimensions for the use contemplated. It is known, as a matter of fact, that when a dial provided with an hour circle is not accurately centered with respect to the periphery of the glass, when it is mounted on the movement and placed within the case, the eccentricity of the hour circle with respect to the periphery of the glass is immediately apparent even if it is very slight. It is therefore important that the dial be centered with a high degree of precision. Ordinarily the dial is fastened to the movement, although its peripheral part extends beyond the periphery of the latter, and it is the movement which is centered with respect to the case, possibly by means of a casing ring.

The object of the present invention is to produce a wristwatch of the above-mentioned type, the parts of which can be encased rapidly while assuring a proper centering of the dial and the movement with respect in particular to the glass.

For this purpose the wristwatch of the invention is characterized by the fact that the dial is centered with respect to the glass groove by guide members located on its periphery, on the one hand at the two ends of a diameter and on the other hand on a radius perpendicular to said diameter, the case having on its inner face guide elements which have a shape which is the reverse of that of the guide elements of the dial, but arranged in the same manner.

The accompanying drawing shows by way of example one embodiment of the watch of the invention.

FIG. 1 is a partial axial section thereof.

FIG. 2 is a top plan view of the case on a smaller scale, and

FIG. 3 is a bottom plan view of the dial.

The drawing shows a monocoque case 1 which comprises a main cup-shaped part of rigid plastic material, for instance a plastic reinforced with fiber glass, and a metal clamping ring 2 intended to secure the glass 3. The latter has a shoulder 4 which engages, with the interposition of a thin sheet 5 of L-shaped profile, into the glass groove 6 which is formed by the inner face of a peripheral rib 7 located on the upper part of the case.

Below the glass groove 6, the case has a groove 8 of circular shape, the upper part of which is limited by a cylindrical face and the lower part by a portion of slightly frustoconical surface. The bottom 9 of this groove is flat. As can be noted in particular from FIG. 2, the groove 8, 9 is interrupted at three places on the periphery of the case by ribs 10 which protrude into the lower part of the groove and are limited by the flat upper faces 11. Of these three ribs, two are diametrically opposite, while the third is located at the end of a radius perpendicular to the diameter which defines the first two. They are symmetrical with respect to said diameter and said radius and their side faces are parallel two by two. It will furthermore be noted that one of the ribs is located in the axis of the winding stem.

The case described contains a movement 13 whose frame element opposite the dial has at its periphery a protruding collar 14 of circular shape. This collar is engaged in an annular recess in the case 1 in such a manner that it is fastened in height and centered within the case. The side face of the collar 14 is adapted in diameter to the inner side face 15 which limits said recess.

In order to hold the movement in place, there is used the dial 16 which is made of one piece of rigid plastic. The hour circle, as well as the central hole 19 of the dial, are arranged in the same manner as in an ordinary movement. On its back, the dial 16 has a cylindrical wall 17 which extends slightly recessed from the periphery. The latter therefore extends beyond the wall 17. In its lower face it has three pairs of spurs 18 which are located, like the ribs 10, on opposite sides of a diameter and on opposite sides of a radius perpendicular to said diameter. The distance between the spurs 18 with flat side face is, for instance, 2.6 mm and corresponds to the width of the ribs 10. The result is that when the dial is put in place on the movement, slight variations in dimensions do not prevent precise centering. As a matter of fact, the two pairs of diametrically opposite spurs force the center of the dial to position itself on the diameter of the case which is defined by the ribs 10. Moreover, the third pair of spurs, by engaging on the third rib 10, has the effect of bringing the center of the dial immediately into the axis of the case and therefore into the axis of the movement.

It will furthermore be noted that the wall 17 is split at the location of the winding stem so as to permit the passing of said member.

Upon the casing of the movement, it is sufficient to engage the shoulder 4 of the glass, which has been previously provided with a tension ring 20, into the glass groove 6. Said tension ring rests against the periphery of the dial which has a cut of slight depth, which maintains the assembly consisting of the dial and the movement in position in the case. Finally, the unit is locked by means of the ring 2 which is force-fitted on the rib 7.

In another embodiment, the dial could be cut from a metal plate or plate of other material with three notches on its periphery corresponding to the spurs of the case.

Claims

What is claimed is:

1. A timepiece comprising a monocoque case defining a movement-receiving compartment and an annular space in which is fitted a glass through which the watch dial is viewable, a movement fitted in said compartment, a watch dial fitted in said case axially between said glass and said movement, said dial bearing axially against said movement whereby said dial holds said movement against any axial movement thereof in said case, said case comprising three radially projecting abutment means which engages three corresponding radially projecting abutment means on said dial, two of said abutment means being diametrically opposed to each other relative to the central axis of said annular space and the third of said abutment means being located on a radius from said axis perpendicular to the diameter interconnecting said two abutment means.

2. The timepiece of claim 1, each of said abutment means comprising a rib extending radially between two circumferentially spaced shoulders whereby said rib and shoulders are locked against any circumferential movement relative to each other.

3. The timepiece of claim 1, said glass being secured in said case by a tension ring which bears axially against the outer circumferential portion of said dial and thereby secures said dial movement in said case.

4. The timepiece of claim 1, said movement being centered within said compartment, a winding stem extending from said movement radially through said case, a sealing tube in said case surrounding said stem.

5. The timepiece of claim 1, said dial comprising an axially extending circumferential wall projecting axially adjacent to said abutment means and a radially projecting circumferential shoulder radially overlapping said abutment means.

6. The timepiece of claim 5, a circumferential shoulder on said movement, said wall of said dial bearing axially against said shoulder to hold said movement against any axial displacement thereof.