CH706020B1 - Motor spring for watch movement barrel with increased running time. - Google Patents

Abstract

The invention relates to a motor spring (10) for a watch movement cylinder. According to the invention, the cylinder mainspring comprises a composite structure comprising a first portion (11) made of support material, covered, at least in part, by a second portion (12) made of diamond. The support material of the first portion may be a metalloid, such as carbon, silicon or germanium, in particular crystalline or polycrystalline silicon. Alternatively, the first support portion may be made of metallic material, in particular a metal or an alloy based on elements Fe, Ni, Co, Cr, Mn, V, Ti, Se, W, C, Si, especially an Invar ® , a Fe-Ni or Ni-Cr or Ni-Co alloy, a hard or semi-hard steel, a hardened or stainless steel, a special non or low alloy steel, titanium or Ti alloy, tungsten or a W. alloy

Description

The present invention relates to the field of timepieces, and more precisely a mainspring 1 intended to be mounted in a barrel 2 of a timepiece movement to accumulate and restore the energy necessary for running and to the movement's power reserve.

A known type of watch mechanism comprises a winding system, a clockwork movement and an hour and minute indication dial, under which there is a barrel 2 which forms a cylindrical case in which is housed a mainspring 1 which constitutes the mechanical energy reservoir of the watch.

[0003] As shown in FIG. 1A, the mainspring 1 is wound on itself in a spiral inside the cylindrical walls 3 of the barrel drum and around a barrel shaft 4 which is independent in rotation from the barrel 2.

[0004] The barrel shaft 4 is integral in rotation with a ratchet wheel which is part of the winding system. The teeth of the ratchet cooperate with a ratchet system to form a non-return mechanism, so that the winder drives the barrel shaft 4 in rotation only in the direction which makes it possible to wind and to arm the mainspring. 1.

[0005] The barrel 2 comprises a base disc, cylindrical walls forming the drum 3 of the barrel, and generally a flat cover. The barrel 2 carries at its periphery a set of teeth which drives the cogs of the watch movement proper (not shown).

[0006] Figs. 1A, 1B and 2 illustrate a well known type of mainspring 1 in cocked / disarmed positions in and relaxed out of a barrel. The mainspring 1 is formed from a steel tape wound around itself in a spiral around the barrel shaft 4, to which it is hooked by an inner end 6 provided with a notch. The other outer end 7 of the mainspring 1 is itself integral with the drum 3 of the barrel (fixing by a hook or preferably via a flange 8). The barrel 2 is generally equipped with a system limiting the arming force, such as a stop device (not shown - limiting the number of arming turns) or a disengageable device such as a return blade 9 elastic of the mainspring 1 to prevent it from breaking.

[0007] The drawback of watches with fully mechanical movements of the existing type is that their running time is limited to one or a few days. Conventionally, the metallic bands of the mainspring are calculated to provide a fixed autonomy of 36 to 40 hours, or a power reserve of 12 to 16 hours. (By convention, the reserve is equal to the running time minus 24 hours).

[0008] Now, some collector's watches have a running time (in English "Power Reserve") reaching 58 h or 60 hours, or two and a half days of autonomy and a power reserve of one day and half maximum.

[0009] A constant objective in Watchmaking has been and still remains to increase the running time (ie the autonomy of the movement, without winding) and consequently the movement's power reserve (ie the said duration of autonomy less 24 hours), without increasing the bulk of the barrel spring.

[0010] It appears that the running time is determined primarily by the maximum amount of elastic energy Wmaxque can accumulate the mainspring of the barrel.

Obviously, the maximum limit Wmax of energy accumulated by a usual metal strip of a mainspring of limited dimensions, is determined by the appearance of fracturing phenomena and / or the appearance of excessive plastic deformations in certain cases. regions of this ribbon.

[0012] The risk of fractures occurring is concentrated on the inner end portion 6 of the spiral winding of the ribbon 5 of the mainspring 1, which has a minimum radius ρ of curvature. This leads to increasing the diameter of the barrel shaft 4, and more precisely its corresponding bung radius Rb.

The risks of plasticization are concentrated at the other end 7, outside, of the mainspring 1, as well as on the external face X of the blade of the tape 5, regions most exposed to elongation stresses.

The need to store a maximum of energy in a cylinder mainspring of limited dimensions (by design and miniaturization of the watch case), is such that it leads to the use of the usual 5 mainspring ribbons 1 of barrel 2 to excessive stresses, close to the elasticity limits, without safety margin, and even beyond, in the field of permanent deformations, things unconventional in Mechanics.

[0015] The permanent deformation is such that after having been introduced into the barrel 2 using a sling and after a few daily cycles of use (arming / disarming), the spring 1 reaches a shape which no longer corresponds at all in its initial form (we say that "the spring is returned"). But above all, the returned spring loses its elastic force. This decreases the escapement pulses and the amplitude of the balance wheel oscillations. However, too low an amplitude of the balance is detrimental to the isochronism of the oscillations, and therefore detrimental to the chronometric qualities of the watch movement.

To prevent these phenomena, in a known manner, the metal strip 5 of a mainspring 1 is initially given a profile of turns excessively unwound by slipping. As illustrated in fig. 2, the turns of the metal strip 5 have an initial curvature whose increase in radius ρ accelerates; the radius ρ of curvature tends to infinity (straight portion: ref. X), then the radius ρ is reversed (curvature of opposite direction) and finally decreases to give an inverted spiral winding in the shape of the letter S as shown diagrammatically on the fig. 2or half upside down in the shape of a half letter S (not shown). The optimal profile (L) in the transverse plane of the turns of a relaxed mainspring 1 of conventional type is therefore not a uniformly curved profile in a regular spiral.

[0017] The fact remains that, in order to make the most of the amount of energy that can be stored, the metallic motor springs of the existing type work at the maximum of plastic deformation stresses or even beyond, which has the disadvantage of limiting their duration. of life to a few hundred cycles or a thousand cycles.

Theoretical modeling and comparison with practical experiments with mainsprings made it possible to express the general properties of a barrel spring strip. One can refer to the work of Léopold Defossez "General Theory of Horology", Volume 1, Chapter IV "The Motive Force" or to the collection of "Techniques of watchmaking construction for the engineer", folder "Mechanics-Theory », Ch. 2 “Energy”, published under the direction of Michel Vermot and edited by the Center de Compétences en Technologie et Design Horlogers.

[0019] It appears in particular that: - the torque or elastic moment delivered by a mainspring tape is given by the formula: M = E (h.e <3> /12.L).α or E is the coefficient of elasticity of the material (or Young's modulus) expressed in units of force per unit of section (in Newton per square meter or in Pascal and their multiples - N / mm <2> or MPa); h is the height of the coil winding of the mainspring; e is the thickness of the tape; L the length of the tape and α the winding angle of the spring; - the maximum amount of elastic energy Wmax that can accumulate a ribbon spring made of a material having a coefficient of elasticity E (Young's modulus) and a yield stress σmax (in N / mm <2>) does not depends only on its volume V and these elasticity parameters σmax and E: Wmax = (e.h.L / 6). (Σmax <2> / E) = (V / 6). (Σmax <2> / E) Modeling shows that, to achieve maximum development, the spring must occupy a volume V = e.h.L which optimally corresponds approximately to half of the available volume Vo in the barrel, namely: V = e.h.L = Vopt = Vo / 2.

The object of the present is to increase the running time and the power reserve of a mechanical clockwork movement and to produce a mainspring of a barrel having an increased running energy compared to the springs. motors made of a metal strip of the existing type, without increasing the size of the barrel or reducing the maximum elastic moment (Mo).

The primary objective of the invention is therefore to achieve the manufacture of a mainspring in materials offering an increased amount of elastic energy and that this maximum amount of energy corresponds to the energy required for walking. 'a watch movement over several days.

Another objective of the invention is to find a way to manufacture such a mainspring of a cylinder with a specific form of spring winding having in particular a profile of curvature of turns in their plane, this if possible, according to a reliable, reproducible and inexpensive process.

[0023] Among other objectives, it would also be appropriate to seek to eliminate the drawbacks of the ribbon springs known from the state of the art, that is to say to avoid or at least reduce: the friction of the turns between them inside the spring; the disadvantages of lubrication; the appearance of plastic deformations limiting the energy of the spring; the loss of elastic moment over time; the delicate work of quenching, annealing or tempering steel tapes; the surface finishing of the strips of spring tape; and, provide a barrel mainspring to improve operating conditions with safety margins for long life.

The primary problem is therefore to find a material capable of storing increased energy or at least equivalent compared to existing materials, such as special steels and especially special alloys, in particular non-ferrous alloys, cobalt, nickel, chromium or molybdenum.

[0025] To this end, according to the invention, it is planned to produce a mainspring for a barrel made of diamond and more precisely of a portion made by depositing polycrystalline diamond. However, a new problem appears: the techniques available to date do not make it possible to produce a rough portion of diamond having dimensions compatible with the quantity of energy that must be stored by a mainspring of the barrel and an adequate form of winding. with curved barrel spring spiral profile.

Briefly, these objectives are achieved according to the invention by producing a mainspring for a barrel having a composite structure: the mainspring is composed of a first portion forming a support blade and constituting the core or the skeleton of the spring, this support portion preferably being made of crystalline silicon or of metal, the surface of the first portion being completely, or at least partially, directly covered with a second portion made of diamond, and preferably forming a thick layer of polycrystalline diamond matrix.

According to a first advantageous embodiment, the support material is silicon, preferably crystalline or polycrystalline silicon or optionally germanium or more generally a semiconductor support material, in particular a high temperature metalloid (HT) or refractory (ie resistant to temperatures above T1 = 500–600 ° C or preferably over T2> 800 ° C), such as the elements of column IVA and neighboring columns of the conventional table of chemical elements known as the Mendeleiev Table (IVA: C, Si, Ge, ... ie carbon, silicon, germanium etc.).

[0028] Alternatively, in other advantageous embodiments, the support material is a metallic, HT or refractory material, in particular titanium or a titanium-based alloy or advantageously a variety of Invar <®>, c ' that is to say an alloy based on iron and nickel. More generally, the metallic support material can be chosen from the families of metals and metallic alloys based mainly on iron (Fe) and / or nickel (Ni) and / or cobalt (Co) and / or chromium ( Cr) and / or titanium (Ti) and / or tungsten (W) and / or manganese (Mn) and / or carbon (C) and / or silicon (Si) with possible presence of trace elements (< 1%), and comprising in particular Fe-Ni-based alloys, Fe-Cr-based alloys, Fe-Ni-Cr and Fe-Ni-Co alloys or even Fe-Co alloys. In simplified embodiments, the support can be made of steel, specifically a steel chosen from hard or semi-hard steels, special non-alloy or low-alloy steels and / or hardenable or stainless steels.

Advantageously, according to the present invention, such a mainspring structure makes it possible to have a metal or silicon skeleton forming a blank of predefined shape of a spring winding and having a cross section, therefore an appreciable outer surface (longitudinal surface) from which the thickness of the outer diamond layer is deposited and increased, in particular by chemical vapor deposition (CVD) or more exactly in the plasma phase, which avoids cutting in the diamond and finally gives a motor spring with a composite structure having an appreciable diamond section and volume, such a diamond shell supporting most of the bending and tensile stresses of the spring with a maximum elastic stress σmax well superior to conventional steels.

[0030] The invention is carried out with a mainspring for a watch movement barrel according to claim 1.

[0031] The invention also relates to a timepiece comprising such a mainspring, according to claim 18.

[0032] The invention also provides a method of manufacturing such a mainspring according to claim 19 or according to claim 26.

[0033] Other objectives, characteristics and advantages of the invention will become apparent from the following detailed description of embodiments of the invention, given by way of non-limiting example, with reference to the accompanying drawing figures.

On the accompanying drawing boards: FIGS. 1A and 1B <sep> represent a mainspring consisting of a steel strip in the armed and disarmed position in a barrel, according to the state of the art; fig. 2 <sep> shows an optimum inverted S-shape of the turns, in a relaxed position, of a mainspring according to the state of the art; figs. 3A and 3B <sep> schematically show the stresses inside a mainspring in radial and transverse cross-sectional views of the turns of the metal tape, according to the prior art; figs. 4A and 4B <sep> illustrate operations of depositing and cutting a diamond plate to make a tiny timepiece, such as a spiral resonator, according to the state of the art; fig. 5 <sep> is a diagram of the elasticity parameters of a conventional spring steel (stress at 1 elongation e and Young's modulus E); fig. 6 <sep> is an elasticity diagram of unusual materials, diamond and silicon, implemented in a mainspring according to the invention; fig. 7 <sep> is a diagram in radial section of a coil of a mainspring with a composite structure, according to a first embodiment of the invention; fig. 8A <sep> is a dimensioned radial section of a coil of a composite structure mainspring according to another embodiment of the invention; fig. 8B <sep> is a dimensioned cross section of the composite structure of a coil of a mainspring made according to the invention; fig. 9 <sep> is a torque versus running time diagram developed by a standard steel spring and a mainspring according to the invention; figs. 10A to 10E <sep> show the process steps for manufacturing a composite structure mainspring according to the invention; fig. 11 <sep> is a detailed diagram in radial section of the first portion of the composite structure of a mainspring made according to the invention; and, fig. 12A and 12B <sep> show schematically other steps of the barrel mainspring manufacturing process according to the invention.

The first problem was therefore to find a material capable of storing an increased energy or at least equivalent compared to existing materials (called "spring steels"), such as special steels and special alloys, in particular alloys. non-ferrous, cobalt, nickel, chromium or molybdenum.

[0036] Figs. 5 and 6 show elasticity diagrams of various materials, each curve W indicating the stress level σ applied to a specimen of the material to obtain an elongation ε (ε = ΔL / L), the linear slope of the curve corresponding to the modulus of elasticity E (or Young's modulus). Fig. 5 shows an elasticity curve Wo for a conventional material, such as a spring steel used to constitute a metallic tape of a mainspring of known type. Fig. 6shows the elasticity curves W1 and W2 for unusual materials, such as diamond W2 and silicon W1, which will be used to form the composite structure of a mainspring according to the invention.

It appears, at first glance, that diamond has a high Young's modulus E2 (of the order of five or six times the modulus or the constant of elasticity E0 of the steel), which is against indicated for the production of a barrel spring (cf. the aforementioned collection TCH ch. 2.1.5 "The search for a high value of E turns out to be perfectly useless [...], not only useless, but harmful"). However, the diagram shows that diamond withstands a high maximum stress limit σ2 compared to other materials and that the elastic range W2 of diamond remains wide (high maximum elastic energy).

[0038] It was envisaged to make diamond timepieces, in particular balance springs.

[0039] Document WO2004 / 029 733 generally describes the use of diamond for the production of mechanical timepieces, a use which in fact applies in a limited manner to the production of a balance spring made of diamond. synthetic.

Now, we know how to produce polycrystalline diamond plates by deposition and epitaxial growth of diamond microcrystals (on a substrate).

[0041] Unfortunately, the manufacture (growing and obtaining) of a thick diamond plate is exceedingly difficult, slow and expensive.

[0042] Figs. 4A and 4B show schematically the steps in the production of a balance spring made of diamond, according to the state of the art. The production steps consist in obtaining such a diamond plate Q by epitaxial growth and then in cutting or cutting concentric turns in the raw diamond plate Q obtained.

[0043] While the plane dimensions P of the part consisting of a diamond deposit can reach dimensions of less than one centimeter, at most a few centimeters, its fineness f is limited to a few tens of micrometers.

[0044] In addition, deep incision and notch operations in diamond which use plasma structuring techniques to cut the shape of a part, are extremely hard and expensive. They are limited to tiny surfaces.

As a result, the operations of depositing and growing a plate made of polycrystalline diamond and then the techniques of engraving and cutting in the diamond by plasma make it possible to produce only tiny parts, of insignificant volume, of microscopic thickness, not not exceeding a fineness of the order of a tenth of a millimeter (volume hardly exceeding one cubic millimeter).

Thus, these techniques for producing a monolithic plate made of diamond and then sculpting or chiseling a part in the rough diamond plate make it possible to produce only tiny parts intended to store no motive energy and / or to Above all, do not absorb mechanical energy, for example a spiral resonator (in English "Hairspring", litt. Spring-Hair).

These techniques are not suitable for the production of mainsprings which must all the same store an energy of the order of a tenth of a Joule to a few Joules and whose volume (V) must be substantial to store a maximum. energy (Wmax = V / 6.σmax <2> / E), so that their dimensions must clearly exceed one cubic millimeter (typically more than an order of magnitude). The volume Vo of a barrel varies, of course, depending on the type of watch, its surface and its fineness, but generally remains of the order of an area of one square centimeter and a volume of around one hundred cubic millimeters. . The height h of the barrel springs is generally of the order of one millimeter. The thickness e is of the order of a tenth of a millimeter. But above all, as to the longitudinal dimension of a mainspring, the length L of the turns of the deployed spring largely reaches one or more decimeters. How to register such a length of spring in a plate of millimeter dimensions (at most centimeter)?

The invention solves this problem of manufacturing a mainspring of a mainspring from a material for storing a high operating energy and to achieve a mainspring for a mainspring from a material such as diamond.

[0049] FIG. 7 shows that, according to the invention, there is obtained a mainspring 10 for a barrel making it possible to store an increased operating energy, from a first portion 11 of a spring made of a support material other than diamond, said first portion 11 can advantageously take a three-dimensional shape corresponding to a skeleton or to a blank of the final shape of the spring, then by covering, completely or partially, said first portion 11 with a second portion 12 made of diamond.

The support material 11 can be chosen from materials resistant to high temperatures (of the order of 800–900 ° C) to which a diamond deposition takes place by chemical vapor deposition (CVD) processes. or more exactly in a plasma (CVD-plasma).

The support material is a body, in particular a metal or a metalloid resistant to such temperatures. The support material may in particular be a metal or an alloy, a metalloid, or else a chemical compound body (eg silicon carbide).

According to an advantageous alternative embodiment, the support portion is a ribbon or a leaf spring blank made of metal or a metal alloy resistant to high temperatures such as temperatures of more than T1 = 600 ° C or at minimum greater than T1 = 500–600 ° C, preferably greater than T2 = 800 ° C, approximately. The metallic material forming the support portion is preferably chosen from metals and alloys having a low coefficient of thermal expansion.

Indeed, diamond has a coefficient of thermal expansion αDia of approximately one micrometer per meter and per degree at room temperature (precisely between αDia = 0.9.10 <-> <6> / K and 1.1.10 <-> <6> / K at T0 = 25 ° C). More precisely, the coefficient of thermal expansion of diamond αDias increases with temperature in the range T0 to T2 = 800 ° C and remains of the order of: αDiA = 1 to 4. 10 <-> <6> / K

Such a coefficient of expansion is particularly low. The production of a diamond deposit on a metallic support risks inducing a problem of cohesion between the metallic support and the outer diamond layer in the face of expansion / contraction stresses, after the deposition of the diamond layer at high temperature T1 / T2, when tempering at room temperature T0. To produce a composite spring comprising an outer portion made of diamond deposited on a portion of a metallic support, according to the invention, it is preferable to choose metallic materials whose thermal expansion coefficient is as close as possible to the very low coefficient of expansion. αDiA diamond, while resisting high temperatures T1 or T2. The metallic material is preferably chosen from the families of materials composed of the following materials: - first of all, the materials called Invar <®>, which are ferric nickel alloys, also called nickel steels; one can choose for example an Invar such as the Fe 36 Ni alloy (64% iron and 36% nickel), Invar N42 (58% Fe 42% Ni), Invar N93 and all other Fe- alloys. Ni in any proportions, especially Fe-Ni-Cr and Fe-Ni-Co alloys, as well as Fe-Cr alloys, or even Fe-Co alloys; their coefficient of expansion is approximately one to two micrometers per meter and per degree at room temperature: αInv = 1.5 to 2. 10 <-> <6> / K at T0 = 25 ° C; - secondly, titanium or titanium-based alloys, as well as tungsten or tungsten-based alloys; - alternatively in the context of simplified embodiments, the first portion of support material can be formed from a steel strip blade blank, in particular a steel chosen from the families of hard or semi-hard steels, hardenable or stainless steels , and special steels considered to be unalloyed or low alloyed (content of non-ferric elements, in particular manganese less than 1% or less than 5%).

Thus, in such embodiments, the first support portion is preferably formed from a metallic material chosen from the families of metals and alloys offering good mechanical properties, from the point of view of flexibility, of resistance. expansion, temperature resistance (melting point greater than T1 = 500 ° C – 600 ° C, or even more than T2 = 800 ° C) and exhibiting a low coefficient of expansion a, to avoid delamination due to shear stress at the diamond / metal interface caused by different elongations of the substrate of metallic support material and the outer diamond layer, when the temperature returns to room, after deposition. It is preferable to choose a metallic material having a coefficient of expansion close to and as low as that of diamond. In fact, the subsequent diamond deposition will be carried out by CVD in the vapor or plasma phase at temperatures compatible with the sublimation / condensation of carbonaceous particles, under the effect of a plasma torch, i.e. at temperatures of the order of T1 = 500 to 600 ° C or at T2 = 800 ° C or even more.

With a support portion of metal or metal alloy having a low coefficient of thermal expansion as close as possible to that of diamond, one can advantageously obtain a composite spring structure according to the invention having a good quality of manufacture, good cohesion and good mechanical strength at the end of manufacture, once returning to ambient temperature.

In the other advantageous embodiment, the support portion is a ribbon or a three-dimensional blade made of semiconductor material or metalloid, HT or refractory, allowing cutting or deep engraving operations, in particular engraving DRIE (“Deep Reactive Ion Etching”), using lithography or chemical ablation techniques on semiconductor materials (silicon or germanium, or even carbon). Silicon has a coefficient of expansion of approximately: αSi = 2 to 3.10 <-> <6> / K at T0 = 25 ° C which is particularly close to the coefficient of expansion of diamond.

[0058] Preferably, the support material is a material which can be shaped into a three-dimensional shape of a leaf spring.

[0059] But especially preferably according to the invention, the support material is a material which can be, prior to the diamond deposition, shaped as a spring coil curved into a spiral.

[0060] A material is preferably chosen which enables a mainspring winding preform to be machined with an accuracy compatible with the sizing and accuracy of the desired spring.

The support material is preferably silicon, in particular crystalline silicon and more precisely monocrystalline silicon.

[0062] Silicon offers the advantage of being able to be easily engraved and cut into three-dimensional shape in semiconductor wafers of macroscopic dimensions and which can reach dimensions largely suitable for a watch spring or a watch movement. Other materials, including a metalloid such as germanium could be suitable.

[0063] Crystalline silicon also exhibits interesting elasticity parameters, as shown on the elasticity diagram of FIG. 6. Silicon has a high elongation limit ε1 and above the elastic elongation limit ε2 of diamond, which makes it a flexible and stretchable material, without registering permanent plastic deformation or fracturing.

Advantageously, the silicon of the first support portion 11 can thus withstand all the stress deformations of the outer diamond portion 12, while remaining within its elastic range (without breaking).

[0065] The diagram of FIG. 6 indicates, however, that silicon supports maximum stresses σ1 much lower than the maximum stresses σ2 of diamond.

However, as the silicon forms the first portion 11 which is disposed at the heart of the composite structure 10 or on the internal face 11.1 of the turns 10 of the mainspring of the barrel, according to the invention, the silicon is exposed to stress levels (in tension) much lower than the outer portion 12 made of diamond, even at almost zero stresses (neutral fibers in the median axis NN of the turns), which corresponds to its aptitudes and its elastic limits .

In the diagram of FIG. 7 which shows a sectional view of a non-dimensioned spring coil 10, the first portion 11 of support material appears in the center and concentric with the second portion 12 of diamond. The first portion 11 preferably has a rectangular section h ́.t, as shown schematically on this transverse sectional plane (radial with respect to the turns). Longitudinally, the first support portion preferably forms a lace or a blade of curved profile, following a specific spiral winding of a mainspring as described below.

The blade of rectangular section of support material which forms the first portion, has a height h '(greater than one or two tenths of a millimeter) and a thickness t (greater than ten micrometers, possibly a few micrometers).

Advantageously, the volume and the surface developed by the first portion 11 offer a three-dimensional support for the deposition and the growth of the diamond, which makes it possible to obtain an outer portion 12 made of diamond having a section surface and a appreciable volume to withstand the stresses and energy stored by the spring.

In addition, the first support portion 11 offers a blank or a primer of three-dimensional shape to the diamond deposit, which makes it possible to foresee the possibility of obtaining, after the diamond deposit, a completed form of spring. motor 10 composed of diamond, avoiding subsequent extremely harsh cutting or cutting operations.

Preferably therefore, the layer 12 of thickness d of diamond covers the entire surface of the first support portion 11 and forms a shell 12 around the core of support material. The diamond shell 12 supports most of the mechanical stresses and protects the support material 11 therefrom. According to the embodiment of FIG. 7, the first portion 11 has a substantially rectangular section (square vent) and the thick diamond layer 12 completely covers the four transverse faces 11.1, 11.2, 11.3 and 11.4 of the first support portion 11.

Alternatively, the thick diamond layer 12 can cover only certain faces of the first support portion 11, in particular the internal 11.1 and external 11.2 faces of the turns of the mainspring 10 which support most of the forces F and bending, tensile and possibly compressive stresses in the thickness of the mainspring 10, as shown in FIG. 8B.

According to another alternative (not shown), the thick diamond layer 12 can cover only one face of the first support portion, in particular all or part of the outer face 11.2 of the turns of the mainspring 10 which supports most of the work and tensile stresses of the spring (the outer face of conventional springs is the most exposed and the most subject to the phenomena of plasticization and the appearance of fractures, then to rupture). The composite structure of the mainspring 10 according to the invention then appears to be formed of a first strip of support material joined to an outer strip 12 formed by depositing a thick layer of polycrystalline diamond on the external face 11.2 of the first strip. 11.

[0074] Thus, the first portion 11 forms a support which makes it possible to obtain a second portion 12 made of diamond, the effective section and volume of which can be considerably developed.

[0075] The composite structure then makes it possible to achieve a considerable diamond cross section in the mainspring turns, according to the invention. In fact, the diamond section area A reaches values of approximately: A = 2. (H.d + t.d) (or at least one side A = h ́.d) where d is the thickness of the deposited crystalline diamond layer; H is the height (overall) of the composite structure of the turns of the spring, including the diamond thickness d at the end edges (H = h ́ + 2.d); t is the thickness (horizontal or radial dimension) of the first portion of support material, h ́ being the height (vertical) of the first portion.

[0076] The composite structure according to the invention makes it possible to produce a spring composed of diamond reaching macroscopic dimensions compatible with the amounts of mechanical energy that a mainspring must store, as shown below.

[0077] FIG. 8A shows a dimensioned embodiment of a mainspring 10 of a barrel having a composite structure, according to the invention.

The following examples of mainspring sizing are given as an indication and are not limitative (in particular in the context of a common application to a standard type of mechanical barrel watch model).

The height h ́ of the first portion 11 of support material can reach a value of the order of a tenth of a millimeter to a few millimeters, rarely more than a centimeter, typically between 0.5 mm and 1, 5 mm.

The thickness d of the diamond deposit 12 is generally greater than five micrometers and can typically reach between 10 μm and 60 μm.

[0081] The thickness t of the first portion 11, measured perpendicular to the turns (in a plane transverse to the winding), is generally of the order of a few micrometers to around a hundred micrometers. Preferably, the thickness t is chosen of the same order as the thickness d of the diamond layer 12, between 10 μm and 60 μm.

The mainspring 10 of the cylinder obtained according to the invention is thus composed mainly of diamond 12, the proportion of diamond relative to the volume of the spring varying from 17% to 99%, typically between 33% and 67%, and preferably greater than 50% (majority diamond portion 12 by volume relative to the total volume of mainspring 10 and majority diamond in effective area occupied relative to the total section of a turn).

The description which follows gives a few examples of embodiments and results of implementation of mainsprings corresponding to standard barrels.

Such embodiments of a mainspring 10 are intended for a barrel 2, the dimensions of which are as follows: Height of the barrel: <sep> Hb = 0.7 mm Radius of barrel drum: <sep> Rt = 5, 25 mm Bung radius: <sep> Rb = 1.2 mm = 58 mm <3> Either an available volume in the barrel: <sep> Vo; = 0.55 V = 32 mm <3> The optimum volume of the spring will be <sep> Vopt.

For such barrel dimensions, by way of comparison reference, a ribbon 5 of a mainspring 1 made of conventional spring steel has optimum dimensions of the following values: Strip thickness: <sep> e = 95 μm; Ribbon height: <sep> h = 700 µm;

Length L of the tape to obtain maximum development and maximum running time: L = 480 mm.

[0087] This mainspring 1 made of conventional steel tape provides the following dynamic parameters to the watch movement: = 3.5.10 <-3> Maximum elastic moment: <sep> M0 N.m (or exact. 348 g.mm) = 2.9. 10 <-3> Elastic moment at 24 hours: <sep> M24 Nm (Newton-meter) Number of turns in 24 hours: <sep> Nb = 4.4 turns Or loss of moment in 24 hours: <sep> ΔM0 –24 / M0 = (M0 – M24) / M0 = 17%

And for the watch movement in question, this ribbon 5 of the mainspring 1 provides a maximum operating time of 58 hours after N = 10.5 turns (power reserve of 34 h).

The calculations according to the invention of motor springs with a composite structure intended for such a barrel, are carried out while maintaining the height H and above all, taking care to preserve the maximum elastic moment M0 (the torque of torsion applied to the movement is limited to avoid rebound phenomena, detrimental to the isochronism of the movement and detrimental to the behavior of the exhaust parts).

As a reminder, the maximum elastic moment M0 of a spring is proportional to the square or the cube of its thickness e. More precisely, M0 is proportional to the modulus E and the cube of the thickness e, but M0 is also proportional to the maximum stress limit a and to the square of the thickness e, as indicated by the following classical formulation:

However, diamond has a modulus of elasticity E2 and a yield strength σ2 considerably higher than conventional spring steels (of the order of double to tenfold, typically fivefold or sixfold). It is already announced that the diamond thickness d / 2d and the total thickness T of the coils of the mainspring 10 with a composite structure according to the invention can be reduced (from about a quarter to more than half, typically one third) with respect to the thickness e of the steel tape 5 of a conventional mainspring 1. Consequently, the section (S = HT) of the coils of the composite diamond spring according to the invention being less bulky that the section (R = he) of conventional spring steel tape, it is possible to consider increasing the length L ́ and the number of turns Nb of the winding in the mainsprings designed according to the invention and of the suddenly increase the running time of the movement.

It is therefore a matter of producing, according to the invention, motor springs 10 for such a barrel 2, the turns of which must finally reach overall dimensions fixed at a total height H of 700 micrometers and a reduced total thickness T one third, ie a total thickness T of 62 micrometers.

In the following embodiments of the mainspring according to the invention, the second portion 12 is then formed of a diamond thickness d varying between 10 micrometers and 25 micrometers. The first support portion 11 is formed of a lace or a strip of rectangular section (h ́.t) whose thickness t varies in a complementary manner between 42 micrometers and 12 micrometers, such dimensions having no value. limiting.

Thus, for such a barrel, with the same maximum elastic moment M0 = 0.5 Nm and the same number of revolutions in 24 hours Nb = 4.4 revolutions, the examples of motor springs with a composite structure 10 produced according to invention, can take the following dimensions: With a diamond thickness d = 10 µm, the maximum development length of the spring reaches L ́ = 600 mm, and provides a maximum running time D-74 hours after N = 13.5 turns. With a diamond thickness d = 15 µm, the maximum spring development length is L ́ = 700 mm, and provides a maximum running time D-86 hours after N = 15.7 turns. With a diamond thickness d = 20 µm, the maximum development length of the spring is L ́ = 722 mm, and provides a maximum running time D-92 hours after N = 16.7 turns. With a diamond thickness d = 25 µm, the maximum development length of the spring reaches L ́ = 736 mm, and provides a maximum running time of D-94 hours after N = 17 turns, (power reserve of 70 h.)

Thus, thanks to the invention, a mainspring with a composite structure 10 comprising a second portion 12 of diamond can provide a period of operating autonomy significantly greater than that of a ribbon 5 of a mainspring 1 in conventional steel: placed under the same conditions, a mainspring composed of diamond according to the invention can achieve a running time that is one third, half, two thirds, or even nearly double and possibly more than that, a ratio greater than twice the running time of a ribbon 5 of a mainspring 1 made of conventional steel.

It should be noted that advantageously, the greater the relative thickness of diamond d / T and the proportion of diamond in the composite structure of the mainspring according to the invention, the greater the gain in power reserve. .

Overall, in the four previous embodiments of a mainspring, according to this example indicative of dimensions, the diamond portion occupies, relative to the total section of a turn (S = HT), a diamond surface (A = 2d.H + 2d.t) greater than one sixth (17%), one third (33%), half (50%) and two thirds (67%) of the total sectional area of the coil (first portion + second portion).

Advantageously, it therefore appears that in order to obtain the same value of maximum elastic moment M0 (so that the barrel applies the same maximum torque to the movement and avoid rebating) while retaining the same barrel and the same movement, a mainspring 10 with a composite structure 11/12 according to the invention requires thicknesses 2d of diamond and coil T much less than the thickness e of a steel strip 5 of a conventional mainspring 1 under conditions equivalent.

Such a refinement of the turns composed of diamond, relative to the ribbon; spring steel, can allow the choice according to the invention: increase the length L ́, the number of turns Nb and the running time D of the motor spring with a composite structure, considering that its volume V must reach half of the volume Vo of the fixed barrel (V ≈ Vo / 2) ; and or, to reduce the overall size V = THL ́ of the winding of the motor spring with a composite structure compared to the existing springs and consequently reduce the size V0 of the barrel, therefore the dimensions of the movement and those of the timepiece ;

[0100] FIG. 9 shows and makes it possible to compare the shape of the evolution curves, as a function of time, of the elastic moment M of the preceding mainsprings placed under the same conditions (same standard barrel, same movement). The elastic moment M is equivalent to the torque applied by the barrel to the watch movement. The solid line curve represents the change in the moment delivered by the conventional steel tape mainspring according to the previous basic comparison example, during its operating time D. The line in lines represents the change of the moment delivered by the mainspring with a composite structure according to the last exemplary embodiment, during its operating time D ́.

[0101] It is clear that the mainspring according to the invention initially delivers (fully armed) the same maximum moment value M0 (which has been capped to avoid rebuff), the same moment at 24 hours M24, therefore substantially the same loss of moment ΔM0–24 / M0 after one day J. However, thanks to the decrease in thickness T, to the increase in spring length L ́ allowed by the invention, the development α ́ ( total winding angle) and the operating time D ́ of the composite-structure mainspring increase considerably, compared to the operating time D of the conventional steel mainspring, placed under the same operating conditions (same dimensioning of standard barrel, same movement).

[0102] In general, during the construction of a watch movement, the setting of the parameters of the mainspring of the barrel is carried out as follows: Mo, the value of the maximum elastic moment, spring loaded, is fixed (taking into account the torque necessary for the movement and the gear ratios); ΔM = (M0 – M24) / M0, the variation of elastic moment in 24 hours is limited according to the tolerated margin of variation of oscillations.

[0103] However, for a composite spring with a composite structure, according to the invention, the maximum elastic moment is:

[0104] And the loss of moment in 24 hours is worth:

[0105] Thus, for a maximum elastic moment M0 given initially, given the relationship between the elasticity limits σ2 of diamond and those σ0 of conventional steels, a mainspring of a barrel made of diamond according to the invention, can have a total thickness of diamond 2d significantly less than the thickness e of a conventional ribbon placed under equivalent conditions. Compared to this reference thickness e of spring steel, the 2d thickness of diamond can decrease from a quarter to a half and even better (2d <e / 2); typically the thickness of 2d diamond is about a third less than the thickness e of conventional spring steel.

[0106] As a result, the total thickness T of the turns of the mainspring according to the invention is reduced, and since, optimally, a mainspring occupies a volume Vopt of approximately half of the available volume V0 of the barrel. : V = T.H.L, = Vopt ≈ 0.5.V0

[0107] The length L ́ of the spring can be increased consecutively by an elongation of one third to double, or even more; Typically, the length L ́ of the diamond mainspring can be extended by half the length L ́ of the equivalent conventional steel mainspring tape.

[0108] The reduction of the thickness T and the lengthening of the length L 'of the mainspring of the barrel according to the invention opens up at least two areas for improving the characteristics of watch movements.

[0109] First axis, the lengthening of the length L ́ of the mainspring according to the invention makes it possible to increase the number of revolutions of the barrel (Nb) therefore to increase the number of hours of operation D ́ of the movement , all the other parameters of the clockwork movement and of the size of the barrel remaining unchanged elsewhere.

[0110] The invention thus makes it possible to increase the running time D 'in the same gear and in particular to achieve a running time increased by a third to double or even more, typically half more.

[0111] Another axis, the reduction of the thickness T (as well as the increase in the running time D ') of the mainspring according to the invention, can make it possible to reduce the loss of elastic moment in 24 hours:

[0112] However, the increase in the length L 'is generally associated with a corresponding increase in the number of turns or the number of development turns Nb of the barrel spring. Nevertheless, the reduction of the diamond thickness 2d, therefore of the thickness T, and the increase in the running time D ́ could make it possible to reduce the loss of elastic moment in 24 hours ΔM0–24 / M0.

[0113] However, the loss of moment in 24 hours determines the weakening of the pulses of the escapement and the variation in amplitude of the balance. Advantageously, the reduction in the thickness T of the turns of the mainspring composed of diamond together with the increase in the operating time D ́ and in the length L ́ of the turns of the mainspring of the barrel according to the invention , makes it possible to preserve the amplitude of the oscillations of the balance and therefore to improve the chronometric precision of the timepiece.

[0114] For its fixing, the mainspring according to the invention is preferably hung in the corresponding barrel by hooks formed at the ends of the mainspring 10 which are blocked in the notches of the barrel 2.

[0115] More specifically, the mainspring has angled outer and inner ends, the two elbows being fixed respectively in two notches provided in the shaft and the drum of the barrel, in a conventional manner per se. Elbows are formed or preformed during etching and cutting operations of the first portion in a silicon wafer, as discussed below.

[0116] Furthermore, the invention advantageously makes it possible to initially give the first portion 11 or support blade, a three-dimensional winding shape of turns of the desired mainspring having a profile of spiral curvature or an inverted shape.

[0117] A profile (L) of curvature of the spring winding 1, such as that of FIG. 2, develops in the plane of the coil (horizontal plane, transverse to the spring) on a two-dimensional surface, and the shape of the spring extends into three-dimensional space.

To obtain a first portion 11 of support material, having an initial three-dimensional shape with a two-dimensional curvature profile, the invention advantageously provides for cutting the shape of the first portion 11 in a plate of material of support by etching processes, in particular so-called “lithography” processes, as described below.

As already indicated, the support material is preferably silicon.

[0120] Silicon offers particularly advantageous properties for producing the first portion 11 which forms the supporting skeleton of a mainspring 10 of the barrel according to the invention.

An interesting property of silicon is that it has a high melting point, greater than 1400 ° C, which allows it to be compatible with high temperatures (of the order of 800 ° C to 1000 ° C). ) to which is subjected a support on which grows a deposit of polycrystalline diamond by a process of vapor deposition (CVD).

[0122] And above all, etching operations in a crystalline silicon substrate plate make it possible to obtain simply and inexpensively a first support portion 11 constituting a blank of the final shape of the mainspring 10 of the barrel according to the invention and already having a specific three-dimensional preform of the winding of the mainspring according to the invention. In particular, provision is made to cut a first portion with a profile of spiral curvature or an inverted shape.

The invention thus provides a method for manufacturing a mainspring 10 of a barrel having a composite structure formed of a first portion 11 made of a support material, advantageously of crystalline silicon, covered at least in part with a second portion 12 in polycrystalline diamond, the first portion 11 being obtained by steps of vertical etching in depth (considered here as the height h ́) of a plate of the support material, preferably a silicon substrate, according to a plane profile of preform of curvature of the coil of the mainspring, followed by stages of deposition and growth of polycrystalline diamond from carbon (or carbonaceous compounds) by chemical vapor deposition (CVD) or plasma (CVD) operations -plasma), to make the second portion 12 in Diamond which forms a thick layer on all or part of the surface of the first portion 11.

[0124] Figs. 10A to 10E show schematically the important steps of such a method of manufacturing a mainspring of the barrel according to the invention.

At the start of manufacture, there is a wafer 100 or silicon wafer (English "silicon wafer") formed of a thick layer 101 of crystalline silicon (in particular monocrystalline) deposited or attached to a base-support 102 called a substrate, generally with the interposition of a layer 103 of silicon oxide. Such crystalline silicon substrate wafers 100 are commonly available from silicon suppliers and smelters for the requirements of the manufacture of integrated circuits.

[0126] The height h ́ (vertical dimension, perpendicular to the plate, horizontal) of the useful layer 101 of crystalline silicon can be chosen. In the present case, it is appropriate to choose a height h ́ corresponding to the height H of the coils of the mainsprings 10 of the barrel desired. The height h ́ generally reaches in the order of a hundred micrometers to a few millimeters, for example h ́ = 500 µm or h ́ = 700 µm or h ́ = 1 mm or h ́ = 1.2 mm, typically.

[0127] To cut out one or more samples of the first portion 11 in silicon having the shape of a spring blank, masking and substantially vertical etching operations are carried out in depth (height h ') in the silicon wafer 100.

[0128] As shown schematically in FIGS. 10A and 10B, a masking layer 104 is deposited on the surface of the silicon wafer. The masking layer is in particular a layer 104 of photosensitive resin. There are multiple masking and etching techniques known in the field of etching semiconductor materials and other equivalent techniques can be implemented. The masking layer 104 is exposed through a pattern of rib (s) and the photosensitive resin layer 104 is revealed and then treated to form the etching mask 105. The revealing and processing of the exposed resin removes the resin layer 104 at the locations of the mask openings and leaves one or more masking resin ribs 105 implanted depending on the pattern used.

[0129] According to the invention, the ribs 105 have a profile in the plane of the plate 100 (horizontal plane, transverse to the projected spring winding), the profile of each rib 105 being wound in a spiral curvature or an inverted form.

[0130] A form of winding with a spiral profile, such as that shown in FIG. 10D, is advantageous for reasons of size with respect to the surface of the silicon wafer ("wafer") and makes it possible to implant a plurality of windings on the plate and to obtain a series of first portions of springs. motors from a single wafer.

[0131] FIG. 10B shows the ribs 105 (studs) formed by a spirally wound rib, taken in radial section with respect to the winding.

[0132] The next step, shown schematically in FIG. 10C, consists in performing a substantially vertical etching through the openings of the resin etching mask 105.

Preferably, a deep reactive ionic etching is carried out (abbreviated DRIE for "Deep Reactive Ion Etching") using a gas flow excited (ionized) by plasma (RF) or a flow of ion plasma. Such an etching process makes it possible to achieve an etching depth corresponding to the desired height h ’of the turns.

[0134] Such an etching hollows out the layer 101 of crystalline silicon in depth in the vertical direction h ', leaving, under each rib 105, an intact island 11 of silicon in the form of a lace or of a wall wound in a spiral, the wall having sides offering good verticality.

[0135] The etching can be stopped by a layer 103 of silicon oxide interposed between the useful layer 101 of silicon and the substrate 102 of the wafer 100, intended to be removed.

[0136] Each portion 11 of the silicon support thus obtained according to the invention is detached from the substrate 102.

[0137] Such a silicon portion 11 forms a blade of substantially rectangular section but has a profile wound in a spiral curvature, as illustrated in FIG. 10D or an inverted form. This spirally wound silicon blade which forms the first portion 11 of the composite structure according to the invention is then subjected to operations for depositing and growing a thick layer 12 of polycrystalline diamond.

[0138] The first portion 11 made of silicon can be subjected to a surface treatment before the deposition operations to promote the nucleation of the diamond, that is to say the germination of diamond crystals. In particular, it is possible to deposit a coating of microcrystalline or nanocrystalline nucleation diamond in order to then initiate the growth of polycrystalline diamond, according to the teaching of document US Pat. No. 6,037,240.

[0139] The surface 11.1–11.2–11.3–11.4 of crystalline silicon, in particular monocrystalline, is preferably pickled and purged of all traces of oxidation. In the event that a layer of silicon oxide (SiO2) has formed, it is removed for example by pickling in an acid bath or by plasma treatment in a chamber containing 100% hydrogen gas H2 or ionized H <+> at low pressure, according to the teaching of US Pat. No. 6,037,240 or of document WO-94/08 076.

[0140] Alternatively, as stated above, the first support portion can be formed of a metal strip strip on which a thick layer of polycrystalline diamond will be deposited, to form the second outer diamond portion. It is preferable that the metal support material of the first portion has a low coefficient of thermal expansion close to that of diamond in order to ensure good cohesion of the composite structure spring according to the invention. The metallic material can in particular be chosen from the families of metals and alloys composed of Invars (iron and nickel alloys or nickel steels), Fe-Ni-based alloys, in particular Fe-Ni-Cr or Fe-Ni- Co, Fe-Cr base alloys, Fe-Co alloys, alloys based mainly on iron and mainly on elements such as C, Si, Ni, Co, Mn, Cr, Va, Ti, Se, W of hard or semi-hard steels, hardenable or stainless steels and / or special so-called non-alloy or low-alloy steels, titanium, tungsten and their alloys. Such a metal support portion consisting of a strip strip advantageously wound in a spiral spiral or reversed in the shape of a letter S or half reversed in the shape of half of the letter S (depending on the elastic properties of the outer layer: Modulus elasticity and elastic limit), can be obtained in a conventional manner by rolling and slitting operations with, where appropriate, quenching operations,

[0141] The diamond deposition is carried out according to techniques classified among chemical vapor deposition (abbreviated CVD, from the English Chemical Vapor Phase Deposition). In fact, it is a deposit of polycrystalline diamond from carbon or more precisely from carbon compounds (eg acetylene, acetone, carbon fluoride or other carbon radicals, methane and its hydrocarbon radicals CH4, CH2 **, CH ***, C ****) generally introduced in a gaseous state and then ionized in the form of a flow of plasma, emitted by a filament overheated or excited by radio frequencies (microwaves). The ionized and superheated carbon is deposited by crystallizing in the form of polycrystalline diamond, in particular microcrystals or nanocrystals, on the relatively cold surface (800 ° –1000 ° to 1400 °) of each first portion 11 of crystalline silicon support.

[0142] It has been observed that the smaller the size of the crystals, the higher the maximum stress limit σ2 'of the synthetic diamond deposit and tends to approach the maximum limit of single crystal diamond (natural or artificial).

[0143] In the present, the expression "polycrystalline diamond" includes the deposit of microcrystalline diamond, composed of crystals of micrometric dimensions and nanocrystalline diamond, composed of crystals of nanometric dimensions.

[0144] The outer portion of the spring according to the invention may advantageously be composed of microcrystalline diamond or preferably of nanocrystalline diamond; or even crystals of size below a nanometer, the smaller the size of the crystals, the more resistant the diamond to high yield stress σ2 ́.

[0145] Further details on the deposition and growth operations of a 12-thick layer of diamond by CVD can be found in EP-0 732 635 filed in the name of CSEM, to which reference should be made.

[0146] As shown in FIGS. 10Det 10E, the deposit 12 of polycrystalline diamond forms over the entire surface 11.1 to 11.4 of the first portion 11 and grows regularly until it forms a thick outer layer 12 of diamond which coats the first portion 11.

[0147] Advantageously, such a method makes it possible to form an outer layer 12 or diamond gangue of regular thickness and simply reaching a thickness greater than five or ten micrometers and preferably greater than 20 μm or 30 μm.

[0148] FIG. 11 however shows, in detail, a cross-sectional view of a first portion 11 made of silicon as obtained at the end of the etching step (FIG. 10C) on which it appears that the lateral flanks 11.1 and 11.2 of the first portion 11 are not strictly parallel but have a slight angle δ with respect to the vertical, angle δ which has been exaggerated on this representation. The angle "called" draft angle ", inherent in engraving techniques, is very small in the order of 1 ° –2 ° and often even less. However, on a first portion 11 having a height h 'of the order of 0.5 to 1.5 mm and an initial thickness t of 30 μm at the level of the rib 105, it leads to a terminal thickness t' thinned by half or worse without thickness (triangular section or bevel cut). To avoid such a defect, it is proposed according to one embodiment of the method according to the invention to perform two almost vertical etchings, from the two opposite faces of a wafer 100 of silicon substrate and through two etching masks. 104 and 114 symmetrical with respect to the mid-plane 0–0 of plate 100, as shown schematically in figs. 12A and 12B. The support portion 11 'thus obtained has a transverse thickness t which decreases slightly towards the median plane 103, but remains acceptable over the height h1 + h2 of this first portion 11.

[0149] Such a method makes it possible in particular to use conventional silicon wafers formed from a height h1 of a layer 101 of silicon deposited on a substrate 102 of silicon (itself having a height h2 of the order of a hundred from micrometers to a few millimeters), the layer 101 and the substrate 102 being separated or not by an intermediate layer 103 of silicon oxide.

[0150] Thus, according to such an alternative method of manufacturing a mainspring 10 of a barrel according to the invention, two masking layers 104 and 114 are deposited on two opposite faces of a plate 100 of substrate 102 comprising at the at least one layer 101 of crystalline silicon (greater than a hundred micrometers in height); two etching masks comprising at least one pair of ribs 105/115 substantially symmetrical with respect to a median plane 103 of the plate are cut out in the masking layers 104 and 114, respectively, and at least one quasi-vertical etching is carried out, preferably by deep reactive ionic etching, through the two opposite masks, over the total height of the silicon substrate wafer 100.

The following steps consist in extracting at least a first portion 11 of silicon thus obtained, then in depositing and growing on at least a surface part of such a first portion 11, a thick outer layer 12 of polycrystalline diamond. by chemical vapor deposition (CVD) of carbon or carbonaceous compounds or by plasma decomposition in a radiofrequency field (CVD-plasma) of carbonaceous gases crystallizing in polycrystalline diamond.

[0152] Advantageously, such diamond deposition and growth operations regularize the total thickness T of the mainspring 10 finally obtained.

In general, an advantageous characteristic of the invention is to have a first portion 11 which forms a support vertically (by convention here in the direction of the height h '), which allows a deposit to grow. of thick diamond layer 12 in the horizontal direction corresponding to the thickness (T; d / t / d) of the coils of the mainspring (ie in the radial directions), this over the entire height h ́ of the first portion- support 11 instead of seeking to conventionally grow a diamond deposit vertically, by seeking to reach a desired height of the mainspring turns of the barrel.

[0154] Advantageously, as illustrated in FIG. 10E, the outer portion 12 of polycrystalline diamond has edges 13 and 14 which are softened or rounded without ridge, with a radius of curvature r.

[0155] More generally, the mainspring 10 of the barrel according to the invention advantageously has an outer surface of diamond which offers a surface roughness (Ra <1 μm) and a low coefficient of friction. In addition, the roughness can be reduced by CVD formation of nanocrystals or by plasma polishing treatment, which further weakens any source of friction.

As an alternative to polishing or depositing nanocrystals, it is possible to add an external coating of dry lubrication, in particular a teflon coating, deposited for example by CVD, or a coating of molybdenum disulphide, which adheres well. on the surface crystals of the diamond portion.

[0157] Advantageously, the mainspring 10 obtained according to the invention makes it possible to practically eliminate the friction previously existing between a conventional mainspring and the barrel 2. In addition, the mainspring 10 of the barrel according to the The invention hardly exhibits any internal friction between its turns during its unwinding. This point is particularly favorable to the regularity of the torque delivered to the clockwork movement, therefore to the regularity of the amplitude of the balance and makes it possible to put an end to the lubrication problem (see the aforementioned work by L. Defossez “Theory general watchmaking ”, chapter IV“ Motive force ”, Fig. 52 Factors influencing the efficiency of a spring). The mainspring 10 with an outer thickness layer 12 of diamond, according to the invention, no longer requires lubrication, nor any work on softening or rounding the edges (nor, of course, annealing work, quenching, tempering and baking like metal tapes in conventional spring steel).

[0158] An important advantage of the mainspring 10 composed of diamond according to the invention is that it hardly loses elastic force during operation, since the diamond does not undergo plastic deformation. Thus the elastic moment and the maximum amount of energy accumulated by the mainspring of the barrel according to the invention remains constant over time and no longer presents a fatigue problem, which contributes to ensuring the operating time and the reserve. of the clockwork movement.

[0159] And adding to the absence of deformation, the hardness of the diamond enables it to resist wear phenomena, so that the motor springs 10 composed of diamond according to the invention promise to have a long life. life, the diamond being renowned for its longevity.

Claims (26)

1. Motor spring (10) for a watch movement cylinder, characterized in that it comprises a composite structure comprising a first portion (11) made of support material, covered, at least in part, by a second portion (12) made of diamond. 2. The cylinder engine spring according to claim 1, characterized in that the support material of the first portion (11) is a metalloid, such as carbon, silicon or germanium. 3. cylinder engine spring according to claim 1 or 2, characterized in that the support material of the first portion is crystalline silicon. 4. The cylinder engine spring according to claim 1, characterized in that the support material constituting the first portion (11) is a metallic material. 5. A cylinder engine spring according to claim 1 or 4, characterized in that the first portion (11) is in a support material selected from the families of metals and metal-based alloys, composed of one or several elements among the elements Fe, Ni, Cr, Co, Cu, Mn, V, Ti, Se, W, with possible addition of C and / or Si, said families of metallic materials including Fe-Ni based alloys , Fe-Cr-based alloys, Fe-Co-based alloys, Fe-Ni-Cr or Fe-Ni-Co-based alloys, hard and medium-hard steels, hardenable or stainless steels, special steels classified as unalloyed or low alloyed, as well as titanium and / or titanium alloys, tungsten or tungsten alloys. 6. cylinder engine spring according to one of claims 1 to 5, characterized in that the second portion (12) is formed of at least one layer (12.2) of polycrystalline diamond, greater than ten micrometers thick. 7. cylinder engine spring according to one of claims 1 to 6, characterized in that the first portion (11) is disposed in the heart of the second portion (12) of diamond. 8. cylinder engine spring according to one of claims 1 to 7, characterized in that the first portion (11) and the second portion (12) have substantially rectangular concentric sections. 9. cylinder engine spring according to one of claims 1 to 8, characterized in that the second portion (12) diamond has a thickness (d) greater than one tenth of the thickness (t) of the first portion (11). 10. The cylinder engine spring according to one of claims 1 to 9, characterized in that the second portion (12.2) covers at least one side (11.2) of the first portion (11). Barrel cylinder spring according to one of claims 1 to 10, characterized in that the second portion (12) has a thickness (d) perpendicular to the surface (11.1-11.4) of the first portion (11). ) of diamond greater than one sixth or, preferably, one third of the thickness (t) of the first portion (11). Barrel cylinder spring according to one of claims 1 to 11, characterized in that each turn of the mainspring has a diamond cross-sectional area greater than the cross-sectional area of the first portion (11). 13. cylinder engine spring according to one of claims 1 to 12, characterized in that it is composed mainly of diamond volume relative to the total volume of the mainspring. 14. The cylinder engine spring according to one of claims 1 to 13, characterized in that it has a thickness of turns (T) greater than ten micrometers and a height of turns (H) greater than a hundred of micrometers. Barrel cylinder spring according to one of claims 1 to 14, characterized in that the expanded mainspring (10) has a spiral shape or an inverted shape. 16. A cylinder engine spring according to one of claims 1 to 15, characterized in that the second portion (12) is directly in contact with the surface (11.1-11.4) of the first portion (11). 17. A cylinder engine spring according to one of claims 1 to 15, characterized in that an intermediate coating of nucleation or seed crystal is interposed between the first portion (11) and the second portion (12) of diamond . 18. Timepiece characterized in that it comprises at least one mainspring (10) barrel according to one of the preceding claims for actuating a clockwork movement. 19. A method of manufacturing a mainspring (10) of a barrel having a composite structure comprising a first portion (11) made of support material, covered, at least in part, by a second portion (12) made of diamond, the process comprising steps of: - Have a plate (100) made of support material (101); Performing an etching (106), substantially vertical (h), in the support material (101), through an etching mask (105); Extracting at least a first portion (11) obtained from a support material; - Deposit on each first portion (11), a second portion (12) of diamond. 20. Method according to the preceding claim, wherein the support material plate is a plate (100) having at least one layer (101) of crystalline silicon. 21. Method according to the preceding claim, wherein the surface of each first portion (11) of silicon is preserved from any oxidation, or if necessary, such a layer of silicon oxide is pickled. 22. Method according to one of claims 19 to 21, wherein the etching (106) is carried out by substantially vertical deep reactive ion etching in the height (h) of the plate (100). 23. Method according to one of claims 19 to 22, wherein the etching mask comprises at least one rib (105) having, parallel to the plane of the plate, a winding profile forming a spiral or inverted curvature. 24. Method according to one of claims 19 to 23, wherein the second portion (12) is formed by deposition of at least one layer (12.2) of polycrystalline diamond, thickness (d) greater than ten micrometers . 25. The method of claim 24, wherein the deposit (12) of diamond forming the second portion on the first portion (11) is made perpendicular to the plane formed by the turns (10) and / or height (h). of the first portion (11). 26. A method of manufacturing a mainspring (10) of a barrel having a composite structure comprising a first portion (11) made of support material, covered, at least in part, by a second portion (12) made of diamond, the process comprising steps of: - having a plate (100) made of supporting material (101) Performing two etchings, substantially vertical, through two symmetrical etching masks (104, 114) (105, 115) disposed on two opposite faces of the plate (100), the etchings being performed on the total height of the plate (100); ); Extracting at least a first portion (11) obtained from a support material; - Deposit on each first portion (11) a second portion (12) of diamond.