HK1237894B - Clock balance/hairspring assembly - Google Patents

Description

Balance wheel and hairspring assembly of a watch

Technical Field

The invention relates to a balance with hairspring assembly, the balance wheel of which has a device for adjusting inertia.

The invention also relates to a timepiece movement including such an assembly and to a timepiece equipped with such a movement.

Background Art

Patent CH 705 238 discloses a clamped flyweight balance that allows adjustment of inertia and/or balance. The balance has two arms, each comprising a stem for receiving a flyweight and a housing that clamps the stem in place. Depending on the orientation of the balance assembly on the movement, access to the flyweights positioned on the countersunk side of the balance can be difficult or even impossible, necessitating disassembly. Furthermore, if the distance between the stud and the inner diameter of the wheel rim is too small, the flyweights can strike the stud, thereby disrupting the proper functioning of the balance.

Summary of the Invention

The object of the present invention is to remedy several disadvantages of the known prior art.

More precisely, one object of the invention is to provide a balance wheel making it possible to realize a compact timepiece movement.

Another object of the present invention is to provide a balance-spring system that allows simple access to the flyweights for adjusting the inertia after they have been mounted.

The invention also has the object, at least in one particular embodiment, of providing a balance-spring system that is easy to implement and not very expensive.

These and other objects will subsequently emerge more clearly and are achieved by means of a balance-spring system comprising at least one balance wheel and at least one hairspring, the at least one balance wheel oscillating about a pivot axis via a balance shaft mounted between the bottom plate and the bridge and aligned with said pivot axis, an inner coil of the at least one hairspring fixed to the balance shaft or to an inner stud mounted integrally with the balance shaft, an outer coil of the at least one hairspring fixed to an outer stud integral with the bridge supporting the balance shaft, the balance wheel comprising a balance hub, a rim, at least one arm, a front face and a back face, the at least one arm connecting the hub to the rim, the front face having a countersunk hole, the at least one arm comprising a cavity for receiving and retaining a flyweight (30), the hairspring being mounted facing the front face of the balance wheel.

According to the present invention, the flyweight is mounted on the at least one arm of the balance wheel on the back side thereof, and the distance between the bottom of the countersunk hole on the front side of the balance wheel and the hairspring is a predetermined interval between 0.05 mm and 1.50 mm.

According to other advantageous variants of the invention:

- the value of the predetermined interval is between 0.10 mm and 0.70 mm;

- said at least one flyweight comprises a head and a stem, the head resting on the back of the balance wheel, the stem being housed in the cavity;

- the head of said at least one flyweight comprises a control structure so as to adjust said at least one flyweight from the back of the balance wheel;

- said stem is flush with the bottom of said countersunk hole on the front face of the balance wheel, so that said countersunk hole has no protruding elements;

- the diameter of the shaft of the at least one flyweight is at least equal to the width of the cavity;

- said at least one arm, said rim and said hub form a unitary element.

The invention also relates to a timepiece movement including an oscillating balance-spring system according to the invention.

The invention also relates to a timepiece comprising a timepiece movement according to the invention.

The subject matter of the present invention thus makes it possible, through the various functional and structural aspects of the invention described above, to obtain a timepiece movement comprising a balance-spring system whose structure, close to the regulating inertia, is particularly simple.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will appear more clearly on reading the following description of a particular embodiment of the invention, given by way of illustrative and non-limiting simple example and the accompanying drawings, in which:

- FIG. 1 a is a view from below of a balance wheel according to the invention;

- FIG1 b is a sectional view of the balance wheel according to the invention, taken along line A-A of FIG1 ;

- Figure 2 is a cross-sectional view along the line A-A of Figure 1 of the balance-spring system according to the invention, equipped in a timepiece movement.

DETAILED DESCRIPTION

A balance spring assembly according to one embodiment will be described below with reference to FIGS. 1 a , 1 b and 2 simultaneously.

The invention therefore concerns a timepiece balance-spring system intended to be incorporated in an oscillating mechanism in the middle of a timepiece movement and comprising at least one balance wheel 1 oscillating about a pivot axis P via a balance staff 40 aligned with this axis P and at least one balance spring 2 .

As can be seen in FIG2 , a balance staff 40 is mounted between bottom plate 13 and bridge 9 and has, at each end, a conical pivot portion 41 that allows it to pivot about pivot axis P while limiting friction. The inner coil of balance spring 2 (not visible in the figure) is fixed to balance staff 40 or to collet 7 , which may be integral with balance spring 2 and is mounted integrally with balance staff 40 , while the outer coil 21 of balance spring 2 is fixed to collet 8 , which is integral with bridge 9 .

While the invention is described herein in the specific case of a single balance wheel and a single balance spring regulating element, a person skilled in the art will be able to extrapolate the invention to the case of multiple balance wheels and/or multiple balance springs.

As can be seen in the figure, the balance wheel 1 comprises a hub 3 supporting the balance staff 40, a rim 4, at least one arm 5 connecting the hub 3 to the rim 4, a front face 10 having a countersunk hole 11, and a flat back face 12. The arm 5 comprises a cavity 6 for receiving and retaining at least one flyweight 30, and the hairspring 2 is mounted opposite the front face 10 of the balance wheel 1, which receives the countersunk hole 11.

1a and 1b , balance 1 comprises a rigid part formed by a hub 3, a rim 4 and an arm 5 connecting rim 4 to hub 3. Cavity 6 is delimited on the one hand by the rigid part of balance 1 and on the other hand by an elastically deformable part 61.

The arm 5 comprises a stem 32 for receiving a flyweight 30 and a cavity 6 for holding this stem 32 in place. This flyweight 30 comprises a head 31 having a control structure, for example an adjustment profile 33 designed to cooperate with a tool such as a screwdriver. Thus, the flyweight 30 can be adjusted from the back 12 of the balance 1. The stem 32 of the flyweight 30 extends the head 31, which has a larger diameter than the stem 32.

The diameter of the shank 32 of the flyweight 30 is selected to have a greater width than the cavity 6 in order to retain the shank 32 by means of the elastically deformable portion 61 , which exerts a restoring force.

Advantageously, the length of stem 32 does not exceed the thickness of arm 5 , so that stem 32 does not protrude and the arrangement of the parts situated at the center of the movement is thus optimized, increasing compactness.

This simple configuration of flyweight 30 formed only by head 31 and stem 32 is advantageous for fitting the flyweight to balance 1 from its bottom.

Once flyweight 30 is clamped in cavity 6, it can be angularly oriented via the bias of the tool, without being hampered by balance spring 2 or the small available space. Flyweight 30 includes an unbalance generated by a flat portion 34 provided on head 31, as can be seen in FIG1 a, to allow the inertia of balance wheel 1 to be adjusted.

According to the present invention, the flyweight 30 is mounted on the back face 12 of the balance wheel 1, with the head 31 resting on the back face 12 of the balance wheel 1 below the arm 5. The distance between the bottom of the countersunk hole in the front face 10 of the balance wheel 1 and the hairspring 2 is a predetermined distance V between 0.05 mm and 1.50 mm. More preferably, the predetermined distance V is between 0.10 mm and 0.70 mm. This arrangement allows for a compact design and, therefore, a reduction in the volume of the timepiece movement.

Particularly advantageously, stem 32 is flush with the bottom of countersunk hole 11 of face 10 of balance wheel 1 , so that countersunk hole 11 has no protruding elements, stud 8 thus being able to be arranged closest to rim 4 , stud 8 even being able to be positioned closest to the bottom of countersunk hole 11 .

Arm 5 , rim 4 and hub 3 form one and the same integral element, balance 1 being able to be manufactured in metal material.

The invention also relates to a timepiece movement and a timepiece equipped with a balance-spring system according to the invention.

Thanks to said aspects of the invention, it is possible to obtain a compact balance-spring system which makes it possible to reduce the thickness of the timepiece movement and, implicitly, of the watch case, so as to provide a thinner watch.

Of course, the present invention is not limited to the examples shown and may be subject to various modifications and variations that will be apparent to those skilled in the art.

Parts List

1. Balance wheel

2. Hairspring

21. Outer ring

3. Hub

4. Rim

5. Arms

6. Cavity

61. Elastic part

7. Inner pile

8. External pile

9. Bridge

10. Positive

11. Countersink

12. Back

13. Bottom plate

30. Flying Hammer

31. Head

32. Rod

33. Adjust the outline

34. Flat part

40. Oscillating shaft

41. Pivot

P, pivot axis

V. Predetermined value

Claims (8)

1. A balance wheel and hairspring system (100) comprising at least one balance wheel (1) and at least one hairspring (2), the at least one balance wheel (1) oscillating about a pivot axis (P) via a balance shaft (40) mounted between a base plate (13) and a bridge plate (9) and aligned with the pivot axis (P), an inner coil of the at least one hairspring (2) being fixed to the balance shaft (40) or to an inner stud (7) integrally mounted with the balance shaft (40), and an outer coil of the at least one hairspring (2) being fixed to an outer stud (8) supporting the balance shaft. The bridge plate (9) of (40) is integral. The balance wheel (1) includes a hub (3), a rim (4), at least one arm (5), a front (10), and a back (12). The at least one arm (5) connects the hub (3) to the rim (4). The front (10) has a countersunk hole (11). The at least one arm (5) includes a cavity (6) for receiving and holding at least one flyweight (30). The at least one flyweight (30) includes a head (31) and a rod (32). The hairspring (2) is mounted facing the front (10) of the balance wheel. The feature is that at least one flyweight (30) is mounted on the back (12) of the balance wheel (1) on at least one arm (5) of the balance wheel (1), the head (31) rests on the back (12) of the balance wheel (1), the rod (32) is flush with the bottom of the countersunk hole (11), and the distance between the bottom of the countersunk hole on the front (10) of the balance wheel (1) and the hairspring (2) is a predetermined interval (V) between 0.05 mm and 1.50 mm. 2. The system (100) according to claim 1, wherein the value of the predetermined interval is between 0.10 mm and 0.70 mm. 3. The system (100) according to claim 1 or 2, wherein the rod (32) is disposed in the cavity (6). 4. The system (100) according to claim 1 or 2, wherein the head (31) of the at least one fly hammer (30) includes a control structure for adjusting the at least one fly hammer (30) from the back (12) of the balance wheel (1). 5. The system (100) according to claim 1 or 2, wherein the diameter of the rod (32) of the at least one flying hammer (30) is at least equal to the width of the cavity (6). 6. The system (100) according to claim 1 or 2, wherein the at least one arm (5), the rim (4) and the hub (3) form an integral element. 7. A watch movement comprising a balance wheel and hairspring system (100) according to any one of claims 1 to 6. 8. A timepiece comprising the movement according to claim 7.