Balance wheel for a watch movement

Abstract

To provide a balance wheel with optimized characteristics. [Solution] The balance wheel 1 includes a hub 2 connected to a ferro 3 by an arm 4, wherein the ferro is made of an electrically insulating material having a relative permeability of less than 1.01 and a density exceeding 6.5.

Description

Technical Field

[0001] The present invention relates to a balance wheel for a timepiece and a center shaft / balance wheel assembly.

Background Art

[0002] The adjusting member of a timepiece usually includes a flywheel called a balance wheel. This component determines the quality of the operation of the timepiece. More specifically, the combination of the balance wheel and the hairspring forms an oscillator that adjusts the movement at a specific frequency.

[0003] Currently, in the balance wheels of wristwatch movements, the rims and arms are made from copper-based alloys, particularly copper-beryllium, brass, nickel silver, or Dekralfor. The mainly used copper-beryllium provides an advantageous combination of qualities including particularly non-magnetism, excellent chemical stability, and sufficient mechanical characteristics. The density of these alloys usually exceeds 8.

[0004] The problems caused by magnetic fields are well known to watch manufacturers and are becoming increasingly encountered. Magnetic fields are spreading more and more in daily life, interfering with the operation of mechanical wristwatches and causing large drifts in mechanical wristwatches.

[0005] To solve this problem, all the solutions considered so far have centered around non-magnetic materials for the hairspring (Si or Nb-based alloys), pivot points (balance wheel center shaft, anchor lever stem, escape wheel pinion), wheel plates, and anchor lever plates.

[0006] The materials used for the balance wheel rims are usually non-magnetic such as brass, nickel silver, or copper-beryllium, but these also have excellent electrical conductivity.

[0007] Despite all combinations of these non-magnetic materials, the movement still drifts significantly in a magnetic field.

[0008] This drift is generally recognized as being due to the presence of ferromagnetic elements in movement components other than the escapement and oscillator, such as the balance spring studs and winding stem.

[0009] Therefore, even if these components were replaced with components made from materials that do not contain ferromagnetic elements, drift at this rate would still be observed.

[0010] The inventors discovered that this drift may be due to the influence of eddy currents. Eddy currents occur when a conductive material is moving within a magnetic field gradient, or when a balance wheel is rotating within a constant magnetic field parallel to the balance wheel's ferro, and they also affect the balance wheel's rate.

[0011] Some watchmakers also produce balance wheels made from ceramic or diamond materials. However, while these materials are non-magnetic, they are extremely difficult to machine into balance wheels, resulting in very high manufacturing costs.

[0012] Therefore, one object of the present invention is to provide a balance wheel without known limitations by using a specific alloy having a density greater than 6.5 that is nonmagnetic, unaffected by eddy currents, and can be incorporated into the available space for a given movement. As is often the case with ceramics, if the density is too low, the balance wheel becomes too large for a given inertia and cannot be accommodated in the movement. [Overview of the Initiative] [Problems that the invention aims to solve]

[0013] The present invention solves the aforementioned drawbacks by providing a balance wheel made from a non-magnetic, electrically insulating material having a density greater than 6.5. [Means for solving the problem]

[0014] To achieve this objective, the present invention relates to a balance wheel including a hub connected to a ferro by at least one arm, wherein at least the ferro is made of a material having a relative permeability of less than 1.01, a density greater than 6.5, and is not conductive.

[0015] According to other advantageous alternative embodiments of the present invention, - The material preferably has an electrical conductivity of 2.5 MS / m or less, more preferably less than 1.5 MS / m. - The materials are selected from metals or metal alloys, ceramics, composites of ceramics and metals, and non-magnetic hard metals. - The material is an alloy containing chromium, iron, nickel, and / or cobalt as its main components. - The material has a face-centered cubic crystal structure, - The material is an austenitic alloy, - The austenitic alloy preferably has a chromium content of more than 10%, preferably more than 15%. - The austenitic alloy is selected from 316L steel, 904L steel, Finox, or MP35N.

[0016] The present invention relates to an assembly comprising a balance wheel according to the present invention and a central shaft disposed to receive the balance wheel, wherein the central shaft is also made of an electrically insulating material having a relative permeability of less than 1.01 and a density greater than 6.5.

[0017] The present invention further relates to a watch movement comprising a balance wheel according to the present invention.

[0018] The present invention further relates to a wristwatch equipped with a movement having a balance wheel according to the present invention. [Modes for carrying out the invention]

[0019] The present invention relates to a balance wheel including a central axis made of a non-magnetic material. The central axis supports a balance wheel having a ferrule and at least one arm integrally formed with the ferrule. The arm extends from a hub at the center of the balance wheel, and therein, the central axis is pressed against a shoulder. Conventionally, the central axis also supports a collet for attaching a hairspring (not shown).

[0020] According to the present invention, the ferrule is made of a non-magnetic electrically insulating material having a density exceeding 6.5.

[0021] For the purposes of the present invention, the non-magnetic material is understood to mean a material having a relative permeability of less than 1.01.

[0022] The electrically insulating material is understood to mean a material having a low or very low conductivity.

[0023] According to the present invention, the material making up the ferrule has a conductivity of 2.5 MS / m or less, preferably 1.5 MS / m or less. Such conductivity enables the restriction of the influence of eddy currents, making it possible for the rate drift of a wristwatch when in a magnetic field.

[0024] The balance wheel is made of a material selected from metal, metal alloy, ceramics such as ytterbium oxide, europium(III) oxide, dysprosium oxide, cerium(IV) oxide, or neodymium oxide, a composite of ceramics and metal, or non-magnetic hard metal such as tungsten carbide using a nickel binder.

[0025] In a preferred embodiment of the present invention, the balance wheel is made of an alloy mainly containing iron, chromium, nickel, and / or cobalt and has a face-centered cubic crystal structure.

[0026] Even more preferably, the balance wheel is made of an austenitic alloy selected from 316L steel, 904L steel, FInox, or MP35N. It will be apparent to those skilled in the art that other austenitic alloys having similar properties can be used without particular difficulty.

[0027] Such austenitic alloys preferably have a chromium (Cr) content exceeding 10%, preferably exceeding 15%.

[0028] For example, the alloy used to make the balance wheel is 316L steel consisting of a maximum of 0.02% carbon (C), a maximum of 1% silicon (Si), a maximum of 2% manganese (Mn), a maximum of 0.04% phosphorus (P), a maximum of 0.03% sulfur (S), 16% to 18% chromium (Cr), 2% to 2.5% molybdenum (Mo), and 10.5% to 13% nickel (Ni).

[0029] Depending on the needs of those skilled in the art, the balance wheel is coated by electroplating, PVD, or CVD with a layer, particularly a decorative layer.

[0030] The present invention further relates to an assembly of a central shaft and a balance wheel, wherein the central shaft that receives the balance wheel is made of the same type of material as the material from which the balance wheel is made, i.e., a material having a relative permeability of less than 1.01, a density exceeding 6.5, and being electrically insulating. For example, a 316L steel balance wheel can be attached to a 904L steel central shaft.

[0031] The central shaft can be coated with a layer, particularly chemical NiP or NiB, to improve its properties, particularly its hardness and resistance to wear and friction.

[0032] The present invention further relates to a timepiece movement and a timepiece provided with a balance wheel according to the present invention.

Claims

1. An assembly comprising a balance wheel including a hub (2) connected to a fellow (3) by at least one arm (4), wherein at least the fellow is made of a material having a relative permeability of less than 1.01, a density greater than 6.5, and being electrically insulating; and a central shaft disposed to receive the balance wheel, the central shaft being made of a material having a relative permeability of less than 1.01, a density greater than 6.5, and being electrically insulating.

2. The assembly according to claim 1, characterized in that the material preferably has an electrical conductivity of 2.5 MS / m or less, more preferably less than 1.5 MS / m.

3. The assembly according to claim 1 or 2, characterized in that the material is selected from metals, metal alloys, ceramics, composites of ceramics and metals, or non-magnetic hard metals.

4. The assembly according to any one of claims 1 to 3, characterized in that the material is made from an alloy mainly composed of iron, chromium, nickel, and / or cobalt.

5. The assembly according to any one of claims 1 to 4, characterized in that the material has a face-centered cubic crystal structure.

6. The assembly according to any one of claims 1 to 5, characterized in that the material is an austenitic alloy.

7. The assembly according to claim 6, characterized in that the austenitic alloy has a chromium content of more than 10%, preferably more than 15%.

8. The assembly according to claim 6 or 7, characterized in that the austenitic alloy is selected from 316L steel, 904L steel, Finox, or MP35N.

9. A movement comprising the assembly according to any one of claims 1 to 8.