EP3511780B1 - Method for lubricating an escapement - Google Patents

Description

Technical area

The present invention relates to the field of watchmaking, particularly mechanical watchmaking. It relates to a method of lubricating an escapement.

In the field of mechanical watches, the escapement makes it possible to regulate the supply of energy supplied by the barrel and to maintain the oscillations of the regulating organ.

The most common mechanisms are said to be Swiss anchor and make an anchor mounted pivoting interact, with in particular an escapement wheel that the anchor comes to block alternately by an entry pallet and by an exit pallet, which it includes.

Traditionally, the pallets are made of rubies, while the escape wheel is made of steel. The optimization of the tribological conditions between the pallets of the anchor and the escape wheel leads to lubricating the contact zones between them so as to reduce energy losses by friction and increase the efficiency of energy transmission.

This lubrication is delicate and complex, and is the subject of much research, know-how and innovation. Indeed, the speeds of relative movement between the pallets and the teeth of the escapement wheel are high, of the order of 70mm/s during the impulse phase and the lubricant used must therefore have a suitable viscosity to be effective. at these speeds.

Lubricants meeting these specifications are generally quite fluid. To be effective, it is imperative to maintain sufficient lubricant used in the contact area without impeding the movement of moving components. It must also remain in place during the operation of the escapement and in the event of shocks so as not to impair the contact and soil the components inside the movement. This is obtained by applying an epilame which contributes to the complexity general and overall lubrication of an escapement. Indeed, the epilame forms a film on the surface of the lipophobic type paddles. It is advisable to operate the escapement dry so that the contact of the toothing of the escapement wheel is free of epilame, so as to form a trench, in which the oil will then be applied and contained. , due to the lipophobic properties of epilame.

In order to constitute a reservoir of lubricant making it possible to supply the contact and to reduce the contact surfaces, the teeth constituting the escape wheel can be bevelled.

More recently, watchmakers have explored the use of silicon to make the lever and the escape wheel, because this material offers, in addition to freedom in the production of complex geometry, reduced coefficients of friction, in particular for silicon interactions. -Silicon. Quite quickly, the use of SiO ₂ obtained by thermal oxidation or of diamond obtained by CVD deposition became essential in order to improve the mechanical resistance and the tribological properties. Watchmakers have long argued that silicon components thus coated would make it possible to overcome the lubrication difficulties known until then. However, in practice, it is generally found that, to obtain the expected levels of performance and reliability, the use of lubrication with traditional lubricants used for steel/ruby escapements is also necessary with a silicon escapement.

This is all the more constraining since the parts produced in silicon are more fragile than the steel parts, and since the current industrial epilaming processes are not applicable to the silicon parts. Indeed, the use of a bulk epilaming treatment would inevitably damage the silicon parts given the fragility of the silicon. Piece by piece epilaming would be tedious, costly and inefficient.

Similarly, the production of a bevel like steel parts to constitute a reservoir, complicates and increases the manufacturing costs of the silicon parts.

The watchmakers also explored the use of lithography techniques known as LIGA to make the lever and the escape wheel. These techniques make it possible to reproduce given shapes with great precision. The parts are made of nickel or a nickel alloy, in particular of NiP, by growth in structures defined by lithography.

Despite the complex shapes that the LIGA makes it possible to obtain, favoring geometric optimization and greater theoretical performance, it is nevertheless still necessary to lubricate the surfaces of the contact members of the exhaust, with a waxing step and the application of an oil of the prior art to obtain the expected performance and guarantee the reliability of the exhaust.

State of the art

The document US 3,496,003 discloses a solid lubricant comprising particles of PTFE (among others) mixed with an oil present in an amount sufficient to form a film on the surface of the particles to cause them to cling well to the surface of the substrate on which they are have been filed.

The document US 2005/014658 discloses a grease thickened with soap and containing PTFE particles.

The document EP2120105 discloses a solution for lubricating a micromechanical part, in particular a silicon escape wheel, the lubricant possibly being a grease. A hydrophilic coating acting as an epilame is interposed between the part and the lubricant to retain the lubricant in the friction zone.

This teaching therefore leads to the difficulty of epilaming the parts of the escapement, including for the silicon parts, which remains a disadvantage in terms of industrialization.

The object of the present invention is to propose a method for lubricating an escapement, at least partially overcoming the aforementioned drawbacks.

Disclosure of Invention

More specifically, the invention relates to a lubrication method as proposed in the claims.

Brief description of the drawings

• la figure 1 représente des essais comparatifs de performance pour trois mouvements d'un premier calibre, avec différentes configurations de lubrifications, après 24h de rodage,
• les figures 2a et 2b montrent respectivement, en termes d'amplitude et de rendement, des mesures effectuées pour 10 mouvements d'un second calibre et trois lubrifiants,
• les figures 3a, 3b et 3c montrent des comparaisons d'amplitude, tandis que les figures 4a, 4b et 4c montrent des comparaisons de rendement, pour 3 lubrifiants, par rapport à un lubrifiant A de référence ; les mesures sont effectuées sur des jeux de mouvements d'un troisième calibre,
• la figure 5 montre une comparaison des rendements de l'échappement pour des lubrifiants selon l'invention, obtenus avec différentes huiles de base.

Other details of the invention will appear more clearly on reading the following description, made with reference to the appended drawing, in which:

• there figure 1 represents comparative performance tests for three movements of a first caliber, with different lubrication configurations, after 24 hours of running-in,
• THE figures 2a and 2b show respectively, in terms of amplitude and efficiency, measurements taken for 10 movements of a second caliber and three lubricants,
• THE figures 3a, 3b and 3c show amplitude comparisons, while the figures 4a, 4b and 4c show performance comparisons, for 3 lubricants, compared to a reference lubricant A; the measurements are carried out on sets of movements of a third caliber,
• there figure 5 shows a comparison of exhaust efficiencies for lubricants according to the invention, obtained with different base oils.

Embodiment of the invention

• le rendement des échappements,
• la stabilité dans le temps des lubrifiants, tant en termes de performance qu'en terme de composition (stabilité chimique),
• leur mise en oeuvre pour faciliter l'industrialisation de l'étape de lubrification.

As explained in detail in the introduction to this application, the issue of the lubrication of escapement mechanisms is a permanent subject of research for watchmakers, with the aim of improving:

• exhaust efficiency,
• the stability over time of lubricants, both in terms of performance and in terms of composition (chemical stability),
• their implementation to facilitate the industrialization of the lubrication stage.

The applicant has identified, after extensive research, particularly interesting effects in the use of specific lubricants to lubricate an exhaust.

More particularly, the subject of the invention is a method for lubricating a watch escapement mechanism comprising a wheel set intended to receive a driving force and a stopper member intended to cooperate with the wheel set to block or leave its alternate rotation. The mobile and the stop member respectively have first and second contact members intended to cooperate with each other. At least the first or the second contact members are made based on silicon, or based on nickel or a nickel alloy (in particular NiP) by a LIGA type technology.

Advantageously, the escapement mechanism is a so-called Swiss lever mechanism. The mobile is an escape wheel intended to be pivotally mounted and the stopper is an anchor also intended to pivot on its axis. The anchor is provided with an input pallet and an output pallet, intended to cooperate with the toothing of the escape wheel. The pallets on the one hand, and the teeth of the escape wheel on the other hand, define contact members, since they are intended to interact with each other, during the successive stages of the escapement. This type of mechanism is well known and does not need to be described in detail.

Preferably, the lever on the one hand, and the escape wheel on the other hand are made in one piece based on silicon, optionally covered by a surface layer, for example of oxide, natural or made by a step of oxidation. Those skilled in the art can also consider other coatings or surface treatments on the contact members.

It is also possible to envisage other configurations in which only one of the lever or of the escapement wheel is silicon-based, or only the contact members are silicon-based.

Alternatively, the lever on the one hand, and the escape wheel on the other hand are made of a nickel-based part or a nickel alloy, obtained by LIGA-type technology. The nickel or nickel alloy used may also contain additives of the doping or solid lubricant type (hBN, talc, etc.). Those skilled in the art can also consider other coatings or surface treatments on the contact members.

It is also possible to envisage other configurations in which only one of the lever or the escape wheel is made of nickel or of a nickel alloy, or only the contact members are made of nickel. or a nickel alloy.

According to the invention, the lubrication of the exhaust comprises a step of applying a grease comprising particles of PTFE (polytetrafluoroethylene) dispersed in a base oil, the PTFE load being adjusted with respect to the specific surface of the particles so as to obtain a grease having a grade of between 3 and 1, preferably a grade 2 according to the NLGI scale (National Lubricating Grease Institute), given below.

Preferably, the base oil is of the PFPE (Perfluoropolyether) type. Preferably again, the application step is carried out without an epilaming step.

There figure 1 shows pendulum amplitude measurements. These measurements were carried out on three watch movements of the same type, with a standard geometry of the lever and the escapement wheel. The graph represents the average values of the amplitude readings in 6 positions, at 0h of operation (barrel loaded to the maximum excluding sliding flange) after running in for 24h, measured for each movement. A line represents, for each lubricant, the average of the measurements of the three movements. Between each lubricant, the movements are disassembled and degreased, then lubricated with the next lubricant.

The reference measurement is a standard escapement, with a steel escape wheel (with beveled teeth) and ruby pallets, epilame and lubricated according to state-of-the-art methods. The following 7 measurements relate to silicon escapements, with geometries identical to the standard reference escapement but without bevel on the teeth of the escape wheel. The ^1st measurement corresponds to dry operation, without lubrication. Measurement A corresponds to lubrication according to the state of the art, that is to say with epilaming and lubrication as in the reference escapement.

Measurement B relates to the grease used according to the method of the invention. Measurements C to F relate to different types of lubricants tested, with or without epilame, depending on the consistency and flow of the grease.

It can be seen that grease B makes it possible to obtain higher efficiencies than the other solutions, with a significant improvement in the amplitude of the balance wheel of 24° compared to the reference, and of at least 22° compared to the alternatives tested. In addition, this level of performance is obtained without the application of epilame and with a simplified geometry of the escapement wheel teeth (without bevel), which represents an industrial advantage.

On the picture 2 , the performance of other lubricants has been studied on an escapement with an escapement and an escape wheel in NiP whose teeth are not bevelled. 10 movements of a second caliber (different from the one used on the figure 1 ) were used for the measurements. The graph represents the average values of the amplitude readings ( fig. 2a ) in 6 positions, at 0h of operation (barrel loaded to the maximum excluding sliding flange) after running in for 24h, and the outputs ( fig. 2b ) measured for each movement, in a low horizontal position. A line represents, for each lubricant, the average of the measurements of the different movements. Between each lubricant, the movements are disassembled and degreased, then lubricated with the next lubricant. Lubricant A is a reference lubricant from the state of the art, B is the lubricant according to the invention and C is another lubricant tested.

There is a gain in amplitude of 25° and a gain of 9 efficiency points in the low horizontal position, for the grease according to the invention compared with the reference.

On the picture 3 , other lubricants have been studied on an escapement with an anchor and an escape wheel in NiP whose teeth are not bevelled, on series of movements of the same caliber of a second type. The graph represents the average values of the amplitude readings in 6 positions, at 0h of operation (barrel loaded to the maximum excluding sliding flange) after a 24h running-in period. A line represents, for each lubricant, the average of the measurements of the different movements. For each comparison, the measurements are carried out on different batches, which is why the results are presented 2 by 2 and not all on the same graph. Lubricant A is a reference lubricant of the state of the art recognized for its performance, B is the lubricant according to the invention and G and H are other lubricants tested.

A gain in amplitude of 16° was observed for the grease according to the invention compared to the reference, which is a significant improvement compared to the amplitudes obtained with G and H.

On the figure 4 , are represented the efficiencies corresponding to the amplitudes measured at the picture 3 .

A yield gain of 6 points is observed, i.e. 14% for the grease according to the invention compared to the reference, which is a significant improvement compared to the yields obtained with G and H.

The improvements obtained are considerable (between 6 and 9 performance points) compared to the low optimizations generally observed, which are of the order of those obtained with the other lubricants tested (between 0 frequently and 3 points for a single lubricant).

In terms of composition, different greases from the above family have been tested, with comparable results. Thus, the base oil (PFPE) can have a viscosity, measured at 40° C., of between 5 and 330 cSt, preferably between 10 and 310 cSt. The PTFE particles dispersed in the base oil are micron to submicron and the density can be adjusted by those skilled in the art, so as to obtain a grease which, in the end, has a grade between 3 and 1, preferably a grade 2. In practice, the PTFE load is adjusted in relation to the specific surface of the particles according to the grade targeted. Typically, the particles have a size between 50 nm and 10 μm. Preferably, the particle size is between 1 µm and 7 µm. These particles form agglomerates whose size is less than 150 μm. As the lubricant interacts with the contact surfaces of the exhaust, the aggregates are broken up and the particles redistribute into other aggregates.

This grade corresponds to a fairly consistent grease, qualified according to the NLGI table (National Lubricating Grease Institute) below. NLGI consistency index ASTM worked (60 cycles): penetration at 25°C in tenths of a millimeter Appearance of lubricating grease Consistency of analogue food product 000 445-475 Very fluid Ketchup 00 400-430 Fluid Applesauce 0 355-385 Semi-fluid Mustard 1 310-340 very soft Double tomato concentrate 2 265-295 Soft Peanut butter 3 220-250 medium-hard Margarine 4 175-205 Hard frozen yogurt 5 130-160 Very hard Fudge 6 85-115 Extremely hard cheddar cheese

This type of grease can be deposited using an oil pick, usually used, or using other equipment or automatic or semi-automatic dispensers, allowing at least partial automation of the dispensing of the lubricant on the functional surfaces of the contact elements.

Obtaining this level of performance for a grease of this consistency is particularly surprising. In fact, given the speeds relative displacement of the contact elements, the use of a grease is a priori not indicated, because its response to a shearing stress, such as undergone during contact with the exhaust, is not sufficiently fast. However, it has been observed that the mechanical resistance of this type of grease drops suddenly when it is subjected to a shearing stress, in other words, it quickly becomes fluid during the friction undergone in operation. On the other hand, the flow threshold also returning rapidly to its normal level after the end of the application of a mechanical stress, the grease advantageously remains in place on the contact members, despite the absence of epilame.

• stabilité chimique : afin de ne pas se dégrader dans le temps ;
• maintien dans les zones de contact : afin de ne pas être dispersé en cas de choc ou lors du fonctionnement du mécanisme et venir souiller le mouvement ;
• maintien de la performance mécanique : la répétition des sollicitations ne doit pas avoir d'incidence (aussi faible que possible) sur le comportement du lubrifiant.

In the context of a traditional escapement, in particular with a Swiss lever, with interactions between ruby pallets and a steel escape wheel, the grease according to the invention has significant advantages. In terms of performance, these are improved by a few points compared to a reference exhaust. It can however be noted that the traditional escapements have been optimized in a very important way as historical evolutions have progressed. In addition, the lubricant according to the invention makes it possible to simplify the geometries and therefore the industrial process. Moreover, the durability of the lubricant according to the invention is improved according to the following criteria:

• chemical stability: so as not to degrade over time;
• support in the contact zones: so as not to be dispersed in the event of an impact or during operation of the mechanism and soil the movement;
• maintenance of mechanical performance: repeated stresses must have no effect (as small as possible) on the behavior of the lubricant.

Thus, even for an escapement with ruby/steel interactions, the lubricant according to the invention has advantageous effects.

Other base oils can be considered. For better compatibility with PTFE particles, a synthetic base oil is preferred, and without metallic soap in the composition of the grease. In In fact, a grease comprising a metallic soap cannot in general contain more than 10% by mass of PTFE. Now, preferably, the advantageous performances of the grease are obtained with contents (mass percentage) of PTFE comprised between 10 and 55%.

As shown on the figure 5 , good results in terms of improved performance were obtained with an ester-type base oil, with performance improvements of 4 points compared to a traditional lubrication given as a reference. More particularly, di-ester or polyol-ester type esters are indicated.

Good results have also been obtained with a base oil of the PAO (Polyalphaolefin) type, with performance improvements of 6 points compared to traditional lubrication. On this batch of movements, a base oil of the PFPE type makes it possible to obtain an improvement of 8 points compared to the reference.

Different base oils can be mixed, particularly ester type base oils and PAO type base oils.

It is these associations between particles of PTFE and a base oil, with a viscosity measured at 40°C between 5 and 330 cSt, preferably between 10 and 310 cSt, making it possible to incorporate these particles of PTFE to achieve a grade NLGI between 1 and 3, which give surprising and advantageous performances, within the framework of a horological escapement. Thus is proposed a process for lubricating an escapement, making it possible to lubricate an escapement whose main parts, namely the escapement wheel and the lever can be made of silicon or based on silicon, while improving the efficiency by compared to a standard exhaust or a conventionally lubricated Silicon or LIGA exhaust. In addition, the identified family of grease makes it possible to dispense with epilame and therefore makes it possible to simplify the process and increase industrial performance.

Claims (18)

1. Method of lubricating a horological escapement mechanism comprising a mobile intended to receive a driving force and a stop organ intended to cooperate with the mobile to alternately block or liberate the rotation thereof, said mobile and said stop organ respectively having first and second contact organs intended to cooperate with one another,
   the method comprising a step of application of a grease to at least one of the first and second contact organs, said grease comprising particles of PTFE (polytetrafluoroethylene) dispersed in a base oil, the loading of PTFE being tuned with respect to the specific surface of the particles so as to obtain a grease exhibiting a grade of between 3 and 1, preferably a grade of 3 or 2 according to the NLGI (National Lubricating Grease Institute) scale.
2. Method of lubricating according to Claim 1, characterized in that said base oil is a synthetic oil and in that said grease is free of metallic soap.
3. Method of lubricating according to one of Claims 1 and 2, characterized in that said grease comprises between 10 and 55% (percentage by mass) of PTFE.
4. Method of lubricating according to one of Claims 1 to 3, characterized in that said base oil is of PFPE (perfluoropolyether) type.
5. Method of lubricating according to one of Claims 1 to 3, characterized in that said base oil is of ester type.
6. Method of lubricating according to one of Claims 1 to 3, characterized in that said base oil is of PAO (polyalphaolefin) type.
7. Method of lubricating according to one of Claims 1 to 3, characterized in that said base oil is a mixture comprising base oils of ester type and base oils of PAO type.
8. Method of lubricating according to one of the preceding claims, characterized in that said base oil exhibits a viscosity measured at 40°C of between 5 and 330 cSt, preferably between 10 and 310 cSt.
9. Method of lubricating according to one of the preceding claims, characterized in that the particles of PTFE have a size of between 50 nm and 10 µm, preferably between 1 µm and 7 µm, forming agglomerates of a size less than 150 µm.
10. Method according to one of the preceding claims, characterized in that said application step is performed without an epilamization step.
11. Method of lubricating according to one of the preceding claims, characterized in that the mobile is an escapement wheel intended to be mounted to be rotationally mobile and the stop organ is a pallet assembly also intended to pivot on its axis.
12. Method of lubricating according to Claim 11, characterized in that the pallet assembly is provided with an entry-pallet and an exit-pallet, intended to cooperate with toothing comprised by the escapement wheel.
13. Method of lubricating according to one of the preceding claims, characterized in that at least the first or second contact organs are formed based on nickel or on a nickel alloy.
14. Method of lubricating according to Claim 11 or Claim 12, and according to Claim 13, characterized in that one and/or the other of the pallet assembly and the escapement wheel is/are formed in a single piece based on nickel or on a nickel alloy.
15. Method of lubricating according to Claim 12, characterized in that the contact organs of the stop organ are made of ruby, and in that the contact organs of the mobile are made of steel.
16. Method of lubricating according to one of Claims 1 to 12, characterized in that at least the first or second contact organs are based on silicon.
17. Method of lubricating according to Claim 11 or according to Claim 12, and according to Claim 16, characterized in that one and/or the other of the pallet assembly and the escapement wheel is/are formed in a single piece based on silicon.
18. Method of lubricating according to one of the preceding claims, characterized in that the grease is applied using an oil-pike or a semi-automatic or automatic dispenser.

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