HK1200925B - Overmoulded horology wheel - Google Patents

Description

Overmolded timepiece wheel

Technical Field

The invention concerns a timepiece wheel overmoulded on a arbour having a pivot axis, said overmoulding being achieved by injection moulding on a metal washer fitted to said arbour, wherein the density of said washer is lower than the density of said arbour, the injected plastic material forming a peripheral overmoulded region carrying a toothing of said wheel.

The invention also relates to a timepiece escapement.

The invention relates to a timepiece movement.

The invention also relates to a timepiece.

The invention also relates to a method for manufacturing an overmoulded timepiece wheel.

The present invention relates to the field of horology, and more specifically to the field of pivotally mounted oscillating parts, which can be made by injection-coating on a metal frame.

Background

The use of an over-molded timepiece component is often advantageous in reducing manufacturing costs for mass production. Furthermore, the inertia of the parts is less than that of metal parts having the same geometry, which is advantageous for the overall efficiency of the movement. Over-molding is typically used for wheels or wheel sets that are positioned on or around a metal spindle having one or more shoulders that leave a void for mating with a pivot or the like.

However, plastic materials chosen for their tribological properties and their adhesion to their metal frame (most commonly the mandrel) have the drawback of creep/expansion. This creates problems of durability and leads to a loss of geometry of one or more toothed rings of a wheel or toothed shaft manufactured in this way.

European patent application No.0369704A2 in the name of salt jiri KOGYO discloses a stepped mandrel with an integral flange and a plastic toothing on the outer periphery of the mandrel (which is in particular moulded onto the mandrel). French patent application No.2020572A1 by WITTNER discloses a metronome escape wheel moulded with a barrel and its wheels, and in particular on the cut-out slot of a arbour, from a single piece of plastic material. U.S. patent application No.3930362A to slazick (cielas zyk) discloses a wheel whose plate and ring gear are made of a plastic material overmolded onto a spindle and right of a groove therein.

Disclosure of Invention

The invention proposes to improve the durability and accuracy of an overmoulded timepiece wheel.

The invention therefore concerns a timepiece wheel overmoulded on a arbour having a pivot axis, said overmoulding being achieved by injection moulding on a metal washer fitted to said arbour, wherein the density of said washer is lower than the density of said arbour, the injected plastic material forming a peripheral overmoulded region carrying a toothing of the wheel, characterized in that said washer has a spring-type profile and comprises elastic arms performing a damping function on the peripheral toothing.

According to one feature of the invention, the gasket comprises at least one flat surface forming a bearing and sealing surface for cooperating in a sealing manner with an injection mould for the overmoulding operation.

According to one feature of the invention, the timepiece wheel comprises a toothed shaft mounted coaxially on the arbour or integral with the arbour.

The invention also relates to a timepiece escapement including at least one overmolded escape wheel of this type.

The invention also concerns a timepiece movement including at least one overmoulded timepiece wheel of this type, and/or a timepiece escapement including at least one overmoulded escapement wheel of this type.

The invention also concerns a timepiece comprising at least one overmoulded timepiece wheel of this type, and/or a timepiece escapement comprising at least one overmoulded escapement wheel of this type.

The invention further relates to a method for manufacturing an overmoulded timepiece wheel, characterized in that the following steps are carried out:

-preparing a spindle for incorporation in the wheel by manufacturing the spindle with a shoulder forming a flange comprising at least one planar bearing and sealing surface, or by mounting a metal washer comprising at least one planar bearing surface onto the spindle;

-placing the mandrel thus obtained in an injection mould comprising complementary bearing and sealing surfaces arranged to cooperate in a sealing manner with said bearing and sealing surfaces;

-injecting a plastic overmoulding material for the mandrel into the mould.

Drawings

Other features and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the drawings in which:

fig. 1 shows a schematic perspective view of an overmoulded timepiece wheel in a particular embodiment in the form of an escape wheel including an escape pinion.

Fig. 2 shows a schematic cross-sectional view of the wheel of fig. 1 according to a plane through the pivot axis of the wheel, with a first washer variant.

Fig. 3 shows a schematic cross-sectional view according to a plane through its pivot axis of another washer variant incorporated in the wheel.

Fig. 4 shows a block diagram of a timepiece including a movement which in turn includes an escapement mechanism having an escape wheel according to the invention.

Figure 5 shows a variation of the wheel in a similar manner to figure 2 in which the overmoulded region is confined to the periphery of the wheel surrounding the washer but does not make any contact with the spindle on which the washer is mounted.

Fig. 6 shows a top view of a wheel according to the invention comprising a collar (cut washer) with arms forming a damping spring.

Detailed Description

The present invention relates to the field of horology, and more specifically to the field of pivotally mounted oscillating parts, which can be made by injection-coating on a metal frame.

The invention more particularly proposes to make a wheel pair that has a very low sensitivity to temperature and maintains its stability and accuracy despite expansion. Preferably, the invention aims to limit the deformations caused by the expansion of the operating region of the wheel (i.e. its crown).

The invention concerns more particularly a timepiece wheel 1 overmoulded on an arbour 2 having a pivot axis D.

According to the invention, the overmoulded timepiece wheel 1 is injection-moulded on a washer 3, preferably of metal, mounted on or integral with the arbour 2. Injection molding involves a peripheral region and therefore the crown of the wheel, which ensures a lower sensitivity to any expansion.

In particular, according to the invention, the wheel 1 is a wheel with reduced inertia, the material of the washer 3 therefore being different from that of the spindle 2 and its density preferably being lower than that of the spindle 2. The use of a washer 3 made of light aluminium or a similar alloy considerably reduces the inertia of the wheel compared to a wheel overmoulded on a steel mandrel comprising a support flange also made of steel. Preferably, the inertia of the washer 3 is lower than the inertia of the spindle 2.

The injected plastic material forms a peripheral overmoulded area 11 which carries a toothing 13 of the wheel 1. Preferably, the inertia of the peripheral overmoulded region 11 is lower than the inertia of the mandrel 2. The inertia of the peripheral over-moulded region 11 is lower than that of the gasket 3, if possible.

As shown in fig. 5, which constitutes a preferred variant of the invention, this peripheral over-moulding region 11 is located at the periphery of the wheel 1, away from the spindle 2 and not in contact with the spindle 2, and therefore without tension which causes stress in the ring gear.

In the case of a wheel forming part of the escapement, in particular the escapement wheel, a low inertia, in particular a small variation of inertia with temperature, is advantageous for the regularity of the operation, which is an important advantage of the invention.

As regards the manufacturing costs, a considerable saving of material is achieved and a simple rod can be used as the spindle 2, only the pivot shaft needs precision machining and a collar or a stamped washer can be used for the washer 3.

In an advantageous variant, the washer 3 is not circular, but has a spring-type profile and comprises, for example, elastic, in particular curved arms 31, which perform a damping action on the peripheral toothing, as shown in fig. 6.

In a particular embodiment, the gasket 3 comprises at least one planar bearing surface 4 forming a bearing and sealing surface 40 for cooperating in a sealing manner with an injection mould for the overmoulding operation.

In the embodiment in the form of a timepiece wheel set, the overmoulded timepiece wheel 1 includes at least one toothed shaft 5, the toothed shaft 5 being mounted coaxially on the arbour 2 or integral with the arbour 2, by: the mandrel 2 is manufactured or fixedly secured by using adhesives, brazing, welding, deforming, bonding, screws, pressing or other means.

Advantageously, the toothing of the toothed shaft 5 traverses the entire length of the toothed shaft 5, which allows the use of the entire exposed portion of the toothed shaft and reduces the height of the movement.

Preferably, the toothed shaft 5 is mounted against the washer 3 or is integral with the washer 3.

When selecting an overmolded wheel, it is desirable to obtain low inertia. The gasket 3 is therefore advantageously perforated with holes or openings 12 to reduce its inertia with respect to the axis D.

Preferably, the diameter of the washer 3 is greater than half the maximum diameter of the wheel 1 located on the peripheral over-moulded region 11.

In order to ensure that the peripheral overmoulded area 11 is held fixed on the metal frame, in particular on the gasket 3, this gasket comprises at least one first peripheral protruding or recessed profile 6 or groove 7 revolving about the axis D, or a shoulder 8 revolving about the axis D, so as to axially fix the overmoulded plastic material after the overmoulding operation. Advantageously, the gasket 3 comprises at least one second peripheral protruding or recessed profile 9 for fixing the overmoulded plastic material in angular direction after the overmoulding operation. The two peripheral profiles 6 and 9 can be combined, as in the example of fig. 1.

In one particularly advantageous embodiment, shown in the figures, the overmoulded timepiece wheel 1 is an escape wheel, the teeth of which are formed during overmoulding onto arbour 2 and washer 3, and which comprises an escape pinion mounted against washer 3 or integral with washer 3.

The invention also relates to a timepiece escapement 10 comprising at least one overmolded escape wheel 1 of this type.

The invention also relates to a timepiece movement 100 comprising at least one overmoulded timepiece wheel 1 of this type, and/or a timepiece escapement 10 of this type comprising at least one overmoulded escapement wheel 1 of this type.

The invention also concerns a timepiece 1000 comprising at least one overmoulded timepiece wheel 1 of this type, and/or an escapement mechanism 10 comprising at least one overmoulded escapement wheel 1 of this type.

The invention also relates to a method for manufacturing an overmoulded timepiece wheel 1. According to the invention, the method performs the following steps:

preparing a spindle 2 for incorporation in the wheel 1 by making it with a shoulder forming a flange comprising at least one planar bearing and sealing surface 40, or by fitting a metal washer 3 comprising at least one planar bearing surface 4 onto the spindle 2;

placing the mandrel thus obtained in an injection mould comprising complementary bearing and sealing surfaces arranged to cooperate in a sealing manner with the above-mentioned bearing and sealing surfaces 40;

-injection coating the plastic material distal from the mandrel in the mould.

In a variant embodiment of the method, during the preparation of the mandrel 2, the toothed shaft 5 is made together with the mandrel or the toothed shaft 5 is attached, mounted onto the mandrel 2 and against the washer 3, and during the overmoulding in the mould, a part of the toothed shaft 5 is immobilized by the plastic material used for the overmoulding.

In short, the introduction of a rigid, intermediate, preferably metallic, gasket minimizes the effects of creep/expansion. The invention can of course be used with non-metallic gaskets if they are substantially more rigid than the over-moulded plastics material. The use of a silicon or quartz washer 3 is particularly advantageous because of the low inertia of the material and its great elasticity, especially in the case of washers 3 with damping arms 31. It should be noted that damping means such as slots, pockets or other means may be used in addition to the arms without departing from the invention.

The use of a gasket having a planar bearing surface facilitates sealing in an injection mold. In fact, when the wheel set is made with a toothed shaft (the toothing of which extends over the entire length of the toothed shaft), without a planar bearing surface, the sealing would have to be achieved by the toothing of the toothed shaft, which is practically impossible.

The wheel according to the invention has a very stable behaviour with temperature: very low distortion, low inertia and very little change in inertia. The wheel remains accurate and does not interfere with operation.

Claims (19)

1. An overmoulded timepiece wheel (1), the wheel (1) being overmoulded on a spindle (2) having a pivot axis (D) by injection moulding on a metal washer (3) mounted on the spindle (2), wherein the density of the washer (3) is lower than the density of the spindle (2), the injected plastic material forming a peripheral overmoulded area (11) carrying a peripheral toothing (13) of the wheel (1), characterized in that the washer (3) has a spring-type profile and comprises elastic arms (31) performing a damping function on the peripheral toothing (13).

2. Overmoulded timepiece wheel (1) according to claim 1, wherein the peripheral overmoulded area (11) is remote from the arbour (2) and is not in contact with the arbour.

3. Overmoulded timepiece wheel (1) according to claim 1, characterized in that the wheel comprises at least one toothed shaft (5) mounted coaxially on the arbour (2) or integral with the arbour (2).

4. Overmoulded timepiece wheel (1) according to claim 3, wherein the toothing of the toothed shaft (5) traverses the entire length of the toothed shaft (5).

5. An overmoulded timepiece wheel (1) according to claim 3, wherein the toothed shaft (5) is mounted in abutment on the washer (3) or is integral with the washer (3).

6. Overmoulded timepiece wheel (1) according to claim 1, wherein the washer (3) is pierced with a hole (12) to reduce the inertia of the washer with respect to the pivot axis (D).

7. Overmoulded timepiece wheel (1) according to claim 1, wherein the gasket (3) comprises at least one planar bearing surface (4) forming a bearing and sealing surface (40) for cooperating in a sealing manner with an injection mould for the overmoulding operation.

8. Overmoulded timepiece wheel (1) according to claim 1, wherein the diameter of the washer (3) is greater than half the maximum diameter of the wheel (1).

9. Overmoulded timepiece wheel (1) according to claim 1, wherein the washer (3) comprises at least one first peripheral protruding or recessed profile (6) or groove (7) pivoted about the pivot axis (D) or a shoulder (8) pivoted about the pivot axis (D) in order to axially secure the overmoulded plastic material after the overmoulding operation and/or the washer (3) comprises at least one second peripheral protruding or recessed profile (9) for angularly securing the overmoulded plastic material after the overmoulding operation.

10. Overmoulded timepiece wheel (1) according to claim 1, wherein the inertia of the washer (3) is lower than the inertia of the spindle (2).

11. An overmoulded timepiece wheel (1) according to claim 1, wherein the injected plastic material forms a peripheral overmoulded area (11) carrying a peripheral toothing (13) of the wheel (1), and the inertia of the peripheral overmoulded area (11) is lower than the inertia of the arbour (2).

12. An overmoulded timepiece wheel (1) according to claim 1, characterized in that the wheel is an escape wheel, the teeth of which are formed during overmoulding onto the arbour (2) and the washer (3), and the wheel comprises an escape pinion mounted against the washer (3) or integral with the washer (3).

13. Timepiece escapement (10) comprising at least one overmolded timepiece wheel (1) according to claim 12.

14. A timepiece movement (100) comprising at least one overmoulded timepiece wheel (1) according to claim 1.

15. A timepiece movement (100) comprising a timepiece escapement mechanism (10), the timepiece escapement mechanism (10) comprising at least one overmolded timepiece wheel (1) according to claim 12.

16. Timepiece (1000) comprising at least one overmoulded timepiece wheel (1) according to claim 1.

17. Timepiece (1000) comprising a timepiece escapement mechanism (10), the timepiece escapement mechanism (10) comprising at least one overmolded timepiece wheel (1) according to claim 12.

18. A method of manufacturing an overmoulded timepiece wheel (1), characterized in that the following steps are performed:

-preparing a spindle (2) for incorporation in a wheel (1) by manufacturing the spindle with a shoulder forming a flange comprising at least one planar bearing and sealing surface (40), or by mounting a metal washer (3) containing at least one planar bearing surface (4) onto the spindle (2), wherein the density of the washer (3) is lower than the density of the spindle (2), the washer (3) having a spring-type profile and comprising resilient arms (31) performing a damping function;

-placing the mandrel thus obtained in an injection mould comprising complementary bearing and sealing surfaces arranged to cooperate in a sealing manner with said bearing and sealing surfaces (40);

-injecting a plastic overmoulding material for the mandrel (2) away from the mandrel (2) into the mould.

19. Method of manufacturing an overmoulded timepiece wheel (1) according to claim 18, characterised in that during the preparation of the arbour (2), the arbour is made with a toothed shaft (5) or a toothed shaft (5) is affixed, mounted onto the arbour (2) and against the washer (3), and in that during the overmoulding in the mould a portion of the toothed shaft (5) is fixed by the plastic material used for the overmoulding.