CH705299A2 - Micromechanical functional assembly for clock, has toothed gear wheels including layers, where each layer includes carbon of specific amount, and contact surfaces of layers have orientations of crystal planes on surface different from other - Google Patents

Abstract

The assembly (100) has a micromechanical part i.e. toothed gear wheel (10) including a layer (11) defining a contact surface (11a) intended to come into frictional contact with another contact surface (21a) defined by another layer (21) that belongs to the toothed gear wheel or another toothed gear wheel. Each of the layers includes carbon in an amount of 50 percent of carbon atoms, where the contact surfaces of the layers have orientations of crystal planes on a surface different from the other. The toothed gear wheels are made of monocrystalline or polycrystalline diamond. The toothed gear wheels include respective substrates made of silicon or steel or ceramic.

Description

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a functional micromechanical assembly comprising a first part comprising a first layer defining a first contact surface intended to come into contact with friction with a second contact surface defined by a second layer said second layer belonging to either said first piece, or at least a second micromechanical component constituting with said first part said assembly. It relates more particularly to a pair of micromechanical watchmaking parts cooperating mechanically with each other such as an escape wheel and pallets of anchor.

STATE OF THE PRIOR ART

[0002] The recent constructions of mechanical watch movements with a diamond-coated silicon escapement (pallets and escape wheel), and without voluntary liquid lubrication of the pallet / escape wheel contact, do not work satisfactorily. Indeed, the regulating power of such an unlubricated exhaust is lower than those of exhaust devices comprising conventional lubrication. The Applicant has found in some cases that the unlubricated exhaust stopped working after a few hours following an irreversible degradation of the tribological performance of the exhaust liners.

The only exhaust approach coated non-lubricated diamond that seems effective is to polish beforehand the diamond friction surfaces before mounting in the watch movement. However, this is laborious and incompatible with the requirements of an industrial manufacture with an acceptable cost price.

In micromechanical applications, most of the diamond layers used are of a nanocrystalline nature (grain size <50 nm, Ra <50 nm) because intuitively, the person skilled in the art believes that the smoother the surfaces, the better they rub. on each other.

The main object of the present invention is to provide a tribological solution for rubbing micromechanical components without lubrication reliably and durably, especially in watch applications and which overcomes at least the disadvantages of the prior art mentioned above .

The invention also aims to provide a functional assembly of micromechanics, particularly watchmaker, comprising moving elements with improved tribological characteristics that do not require post-processing steps such as polishing.

SUMMARY OF THE INVENTION

For this purpose, the invention relates to a micromechanical functional assembly comprising at least a first part comprising a first layer defining a first contact surface intended to come into frictional contact with a second contact surface defined by a second layer. second layer belonging either to said first piece or to at least a second micromechanical component constituting with said first part said assembly, the latter being characterized in that the first and second layers are each formed of carbon having a height of at least 50 % of carbon atoms, and in that they have at least at the level of the first and second contact surfaces orientations of crystalline planes surface different from each other.

With such an arrangement, it is possible to operate a pair of micromechanical parts, such as the pair pallets anchor / escape wheel of a watch movement without lubrication. The applicant has found that the tribological performance of such a functional assembly in this application is as good or better than that of the exhausts of the state of the art with liquid lubrication.

The first and second layers of said micromechanical parts or said arranged in such a configuration have a greater wear resistance. Furthermore, the energy losses due to friction between two contact surfaces of the layers are greatly reduced so that the micromechanical functional assembly thus has better tribological characteristics compared to pairs of antagonistic friction surfaces of the same structure. The phenomenon resulting from the friction of surfaces of identical structure, commonly referred to by the English term "interlocking", is removed by the arrangement of the present invention. According to an advantageous embodiment of the invention, at least said first layer has at least at its contact surface a microcrystalline structure, and preferably said first and second layers have at least at their contact surface each a microcrystalline structure. Typically, the grain size of said first and / or second layers at least at their respective contact surface is greater than 200 nm and less than 10 micrometers.

According to a preferred variant of this embodiment, the crystalline planes of said first and / or second layers have at least at their respective contact surface each different orientations in predetermined directions, and for example involving the direction {100} or {111} direction.

Preferably, the crystalline planes of said first layer having an orientation in the {100} direction at least at the level of the first contact surface and the crystalline planes of said second layer having an orientation in the {111} direction will be associated. at least at the second contact surface.

According to an advantageous characteristic, the average angle defined by the normals at the crystalline planes of the layers {100} and {111} at least at their respective contact surface is between 10 ° and 70 °, preferably between 40 ° and 50 °, and more preferably 45 °.

According to an advantageous embodiment, the first piece is made of solid mono or polycrystalline diamond.

Preferably, the average roughness (Rms) of one of the first or second contact surfaces is between 80 nm and 3 micrometers. The average roughness of the other of the first or second contact surface is smaller and preferably at least one and a half times smaller, typically between 50 nm and 2 micrometers.

According to an alternative embodiment of the invention, said first and / or second friction layer defining said first contact surface and / or said second contact surface covers a first and / or a second substrate to form said first and / or said second part covered with a. Typically the first and / or second substrate may be of silicon or steel or ceramic, with or without an intermediate layer of chromium, titanium, nickel type, etc. In the case of a silicon substrate, the latter may be nitrided, carburized, oxidized or crude.

According to another variant, the first and / or the second part are made of solid mono or polycrystalline diamond thus directly defining the first and / or second contact surfaces. Whether said first and / or said second layer are deposited on a substrate or solid, the thickness of these layers is at least greater than 150 nm. For massive pieces, the thickness of the first layer can reach up to 1 mm. For parts with a substrate, the first and / or second deposited layer can be up to 50 microns thick.

The functional micromechanical assembly of the present invention finds advantageous applications in the field of watchmaking. In particular, the first piece may be a pallet and the second piece an escape wheel or vice versa. In another watch application, the first piece may be an axis of a mobile and the second piece a bearing or vice versa. According to another application of this field, the first and second parts may be gear wheels. In such a pair of elements, the contact surfaces of the parts in contact with friction do not undergo irreversible degradation of their tribological performance and have good stability. It is possible to provide an operation of a mobile watchmaking system, such as a Swiss lever escapement without lubrication of the pallet / escape wheel contact, with performances at least equivalent to the standard references. The friction layers (solid or on substrate) of the present invention, in particular diamond, are immediately effective, without having to modify by post-treatment the nature of the friction surfaces (for example by polishing, surface termination, etc.). . In a horological application involving only one part according to the invention, it may be a cylinder spring formed of a blade, a front face of said blade forming said first contact surface, and the rear face of said blade forming said second contact surface. It goes without saying that in particular applications the functional micromechanical assembly of the invention, a part can come into frictional contact with two or more parts other parts. In this case, the friction surfaces of the parts coming into contact with each other will have orientations of the crystalline planes, different from one another according to the invention.

The layers of the present invention are advantageously formed by hot filament CVD technology or by microwave technology. Diamond can also be massive, with or without growth. The orientations of the desired crystalline planes (for example {100} and {111}) are obtained by varying in particular the proportions of reactive gases in the deposition chamber as well as the pressure and temperature parameters, as for example described in FIG. Y. Avigal et al publication "[100] - Textured diamond films for tribological applications" published by Elsevier in Diamond and Related Materials, Vol. 61997, pages 381-385 in particular § 3.1, in the publication of Qijin Chen et al entitled "oriented and textured growth of (111) diamond on silicon using hot filament chemical vapor deposition" published by Elsevier in the journal Thin Solid Films vol. 2741996 pages 160 - 164 and in the publicaton of M. Grujjicic and S. G. Lai published in the Journal of Materials Synthesis and Processing, Vol. No. 2, 200 pages 73 - 85 these documents being incorporated herein by reference

DESCRIPTION OF THE FIGURES

Other characteristics and advantages of the micromechanical functional assembly according to the invention will also emerge from the following detailed description of embodiments of this assembly, this description being made with the aid of the accompanying drawings, given as non-limiting examples in which: <tb> - fig. 1 <sep> is a diagrammatic representation in an enlarged view of an example of two contact surfaces of two micromechanical parts forming a micromechanical functional assembly and having respectively {111} and {100} crystalline plane orientations according to the invention; <tb> - fig. 2 <sep> is a diagrammatic representation in enlarged view of the contact surface of one of the micromechanical parts of FIG. 1 which has an orientation in the {100} direction and illustrates the tilt angle of each of the {100} crystal planes; <tb> - fig. 3 <sep> is a partial side view of a pallet having a rest plane A and a pulse plane B cooperating with the rest plane C and pulse D of an escape wheel, the planes A and B defining the first contact surface and the planes C and D defining the second contact face according to the invention; and <tb> - fig. 4 <sep> is a top view of a leaf spring leaf having a front face and a rear face respectively defining the first and second contact surfaces according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates an exemplary embodiment of a pair of micromechanical parts 10 and 20 according to the invention. The first piece 10 comprises a substrate 15 on which is deposited a diamond layer 11 having a contact surface 11a intended to come into frictional contact with a second contact surface defined by a second layer 21. The layer 11 has the the contact surface 11a of crystalline planes oriented in a predetermined direction namely the {111} direction. At least at the level of the contact surface 11a, the layer 11 is microcrystalline, with grain sizes greater than 200 nm and a roughness Rms greater than 80 nm.

The micromechanical part 20 comprises a substrate 25 on which is deposited the diamond layer 21 having a contact surface 21a in opposition to the surface 11a of the micromechanical part 10. The layers 11 and 21 thus form friction layers.

At least at the level of the contact surface 21a the layer 21 has its crystalline planes oriented in a predetermined direction namely the direction {100}. In practice these crystal planes are substantially inclined with respect to the friction direction F because of unavoidable growth defects specific to the conventional method for obtaining the layer 21. At least at the level of the contact surface 21a, the layer 21 is microcrystalline, and has grain sizes greater than 200 nm.

At least at the contact surfaces 11a and 21a intended to come into contact with friction with each other the layers 11 and 21 therefore have different orientations of crystalline planes and in this example, these two orientations are along the {100} and {111} directions. Referring to FIG. 1 we see that it is also possible to define the difference in orientation of the crystalline planes of the surfaces 11a and 21a by the angle β which is the average angle formed by the normals N11 and N21 to the crystalline planes of the contact surfaces 11a and 21a β is between 10 ° and 70 °, preferably between 40 ° and 50 ° and more preferably equal to 45 °. The angle βmax corresponds to the average of the angular differences of crystalline orientations p of the two contact surfaces 11a and 21a. This angle is easily calculated by the skilled diamond because it is an important criterion in the control of the diamond deposition process.

FIG. 2 again shows the micromechanical part 20, considered in isolation, so as to illustrate the angle of "tilt" α. This angle is measured between the local normal to the surface 21a on the one hand and on the other hand to the normal NF to the theoretical friction plane PF (dashed in the figure) which is defined by the direction of friction F and a straight line G belonging to the theoretical surface defining the surface 21a.

The angle α is calculated relative to the theoretical friction plane PF. It represents the average of the angles αi between the normal N25 and the normal on the planes <100> N21 in fig. 2. The angle αmoy is preferably less than 30 °, and more preferably less than 10 °.

Typically, the layers 11 and 21 have a thickness of at least 150 nm and preferably about 2.5 micrometers in order to obtain orientations of homogeneous crystalline planes.

More generally, the layers 11 and 21 defining the surfaces 11a and 21a each comprise carbon having at least 50% carbon atoms. For example, these layers can be formed of diamond, graphite diamond like carbon (DLC) or a combination of these materials.

According to an alternative embodiment not shown the surfaces 11a and / or 21a are at least partially covered with a covering layer of a material other than that constituting the layers 11 and / or 21. These cover layers may for example example be made of a film of gold, nickel or titanium. These cover layers should preferably not have a thickness greater than 100 nm. In this case, the surface texture of the first and second contact surfaces advantageously has the orientations of the crystalline planes on the surface, different from each other according to the invention.

The layers 11 and 21 of the micromechanical parts 10 and 20 are depositable on substrates made of all types of materials suitable for deposition of diamond layer, DLC (Diamond Like Carbon), or graphite. For example, the substrates 15 and 25 may be chosen from the set of materials comprising ceramics, silicon, deoxidized silicon, oxidized silicon, nitrided silicon, silicon carbide and steels.

The realization of the contact surfaces 11a and 21a of the invention can also be envisaged without using a substrate for one and / or the other of the micromechanical parts. Indeed the surfaces 11a and / or 21a may according to one embodiment of the invention be from monocrystalline solid diamond or polycrystalline.

FIG. 3 shows an example of application of the invention to the realization of a watch exhaust in which an anchor 30 comprises a pallet 31 which cooperates with a tooth 40 of an escape wheel 41. The pallet 31 has a plane of rest A and a pulse plane B which cooperate with the rest planes C and pulse D of the tooth 40. The resting planes A and B pulse have for example a contact surface conforming to the surface 11a and the planes C and D then have a contact surface conforming to the surface 21a respectively described in connection with FIG. 1 and 2. These planes A, B, C, D correspond to highly stressed areas and subject to high levels of friction and / or contact. According to a variant, the anchor 30 can come from material with the pallet 31.

In FIG. 4, we see another watch application of the invention in which a leaf spring blade 50 has a front face 50a and a rear face 50b which respectively conform to the contact surfaces 11a and 21a described in connection with FIGS. 1 and 2.

Nevertheless, it is obvious to a person skilled in the art that the invention can be extended to other embodiments not shown in which, for example, the micromechanical parts 10 and 11 consist of a mobile axis such that a pivot and a bearing such as a stone or a pair of gear wheel teeth, or any other pair of elements highly subject to intense mechanical stress tribological or not.

The reference signs in the claims are not limiting in nature. The verbs "understand" and "include" do not exclude the presence of elements other than those listed in the claims. The word "a" preceding an element does not exclude the presence of a plurality of such elements.

Claims (23)

A micromechanical functional assembly (100) comprising at least a first part (10) having a first layer (11) defining a first contact surface (11a) for frictional contact with a second contact surface (21a) defined by a second layer (21), said second layer belonging to either said first piece (10) or at least a second micromechanical piece (20) constituting with said first piece (10) said assembly (100) characterized in that that the first and second layers (11, 21) each comprise carbon having at least 50% carbon atoms and that they have at least at the first and second contact surfaces (11a, 21a). ) orientations of crystalline planes at the surface different from each other. 2. Functional micromechanical assembly according to claim 1, characterized in that at least said first layer (11) has a microcrystalline structure at least at the first contact surface. 3. Functional micromechanical assembly according to claim 2, characterized in that said first and second layers (11, 21) each have a microcrystalline structure at least at their respective contact surface. 4. Functional micromechanical assembly according to one of the preceding claims, characterized in that the crystalline planes of at least said first layer have, at least at the first contact surface, an orientation in a predetermined direction. 5. Functional micromechanical assembly according to claim 4, characterized in that the crystalline planes of said first and second layers have, at least at their respective contact surface, each of the different orientations in predetermined directions. 6. Functional micromechanical assembly according to one of the preceding claims, characterized in that the crystalline planes of at least said first layer have an orientation in the direction {100} at least at the first contact surface. 7. Functional micromechanical assembly according to one of claims 1 to 5, characterized in that the crystalline planes of at least said first layer have an orientation in the direction {111} at least at the first surface of contact. 8. Functional micromechanical assembly according to one of claims 1 to 4, characterized in that the crystalline planes of said first layer have an orientation in the direction {100} at least at the first surface of contact and in that the crystal planes of said second layer have an orientation in the {111} direction at least at the second contact surface. 9. The micromechanical functional assembly according to claim 8, characterized in that the average angle defined by the normals at the crystalline planes respectively of the layers {100} and {111} at least at said first and second contact surfaces is between 10 ° and 70 °, preferably between 40 ° and 50 ° and more preferably 45 °. 10. Functional micromechanical assembly according to any one of the preceding claims, characterized in that the size of the grains of at least said first layer (11) is greater than 200 nm at least at the first surface of contact. 11. functional micromechanical assembly according to any one of claims 1 to 9, characterized in that the grain size of said first and second layers (11) is greater than 200 nm at least at their respective contact surface. 12. Functional micromechanical assembly according to any one of the preceding claims, characterized in that at least one of the first or second layers is at least partially covered with a cover layer of another material. 13. Micromechanical functional assembly according to claim 12, characterized in that the cover layer is less than 100 nm. 14. functional micromechanical assembly according to any one of the preceding claims, characterized in that said second layer belongs to said second piece (20) and in that the first and / or second piece are made of solid mono or polycrystalline diamond . 15. Functional micromechanical assembly according to any one of the preceding claims, characterized in that the average roughness (Rms) of one of the first or second contact surfaces is greater than 80 nm. 16. Functional micromechanical assembly according to any one of claims 1 to 15 when it does not depend on the 14, characterized in that said first and / or a second layer defining said first contact surface and / or said second contact surface covers a first substrate to form said first part 17. functional micromechanical assembly according to any one of claims 1 to 15 when it does not depend on the 14, characterized in that said second layer belongs to said second piece (20) and in that said first and / or a second layer defining said first contact surface and / or said second contact surface covers a first substrate and / or a second substrate to form said first and / or said second part. 18. Micromechanical functional assembly according to claim 16 or 17, characterized in that the first and / or second substrate is made of silicon or steel or ceramic. 19. Functional micromechanical assembly according to one of claims 16 to 18, characterized in that said first and / or second friction layer have a thickness of at least 150 nm. 20. Functional micromechanical assembly according to any one of claims 1 to 19, characterized in that said second layer belongs to said second part (20) and in that the first part is a pallet (30) and in that the second piece is an escape wheel (40) or vice versa. 21. functional micromechanical assembly according to any one of claims 1 to 19, characterized in that said second layer belongs to said second part (20) and in that the first part is an axis of a mobile and in that the second piece is a landing or vice versa. 22. functional micromechanical assembly according to any one of claims 1 to 19 characterized in that said second layer belongs to said second part (20) and in that said first and second parts are gear wheel teeth. 23. functional micromechanical assembly according to any one of claims 1 to 18, characterized in that said second layer belongs to said first piece (10) and in that the first piece is a barrel spring formed of a blade and in that a front face of said blade forms said first contact surface and in that the rear face of said blade forms said second contact surface.