EP2725432B1 - Pneumatic winding mechanism, in particular for a timepiece comprising a source of mechanical energy - Google Patents

Description

Technical area

The present invention relates to a pneumatic mechanism, preferably for a timepiece, intended to produce mechanical energy, preferably for recharging a mechanical energy source of the timepiece, and comprising a first hermetic enclosure of variable volume, whose internal pressure can alternatively increase and decrease depending on the variations of the surrounding temperature.

The invention also relates to a timepiece comprising such a pneumatic mechanism for recharging its source of mechanical energy.

State of the art

Timepieces are already known in the state of the art in which a compound is caused to change phase according to the surrounding temperature. For example, requests JP 2003-028049 and JP 2003-120514 disclose devices for producing mechanical energy from changes in ambient temperature. They plan to use pasta phase changes, mainly composed of paraffins, to produce mechanical energy from the thermal energy generated by temperature changes. Additives are listed, which adjust the temperature of the phase change of the dough according to the specific needs of the user, by changing the base composition of a given paraffin.

To allow a reduction in the size of pneumatic winding mechanisms and possibly allow their implementation in small timepieces, the Applicant has developed a device disclosed in the patent application published under EP 2469350 A1 . This application describes a mechanism capable of recharging a source of mechanical energy, such as a cylinder, from the deformations of a hermetic enclosure filled with a mixture of reagents, comprising a metal alloy and a compound at least partially in the form of a gas in a the conditions of use of the mechanism. This compound reacts with the metal alloy, defining an equilibrium, between the gaseous and metallic phases, which is in particular dependent on the temperature. Thus, when the surrounding temperature changes, the proportion of this compound is in gaseous form is modified, so the pressure in the hermetic enclosure too, which leads to a change in its volume and therefore to the production of exploitable work .

The choice of reagents composing the mixture must take into account the temperature range of use of a timepiece and must generate sufficient work in a pressure range adapted to the introduction of the mechanism in a timepiece, possibly small, such as a pocket watch or a wristwatch.

More specifically, the reagent mixture selected for the implementation of this invention has a coefficient ΔP / ΔT substantially greater than 0.01 bar. ° C ^-1 in operating ranges in temperature, substantially between 0 and 50 ° C and, in pressure, substantially between 1 and 50 bar.

Thanks to these characteristics, larger variations in the volume of the hermetic enclosure can be obtained than with the previous mechanisms.

However, another constraint to be taken into account in the realization of such mechanisms concerns their mechanical structure. Indeed, to facilitate or even to allow an inverse variation of the volume of the chamber when the temperature varies in the opposite direction, it is preferable to provide a counter-spring acting on the movable part of the enclosure. However, the pressure in the chamber being in principle at least a few bars, the dimensions of such a counter-spring may be too large to allow the integration of the pneumatic winding mechanism in a timepiece of the wristwatch type, according to the chosen mixture of reagents.

Disclosure of the invention

A main object of the present invention is therefore to propose a pneumatic mechanism comprising a counter-spring whose dimensions are sufficiently small for the pneumatic mechanism to be able to be integrated in a timepiece such as a pendulum or a pocket watch. , to ensure the reassembly of a source of mechanical energy of this timepiece.

• la première enceinte hermétique contient un premier mélange de réactifs, de coefficient ΔP₁/ΔT, comprenant un premier alliage métallique agencé au contact d'un gaz et, susceptible de donner lieu à au moins un changement de phase en fonction des variations de la température environnante,
• caractérisé par le fait qu'il comprend une seconde enceinte hermétique de volume variable dont la pression interne peut alternativement croître et décroître en fonction des variations de la température environnante,
• que la seconde enceinte hermétique contient un second mélange de réactifs, comprenant un second alliage métallique agencé au contact d'un gaz et, susceptible de donner lieu à au moins un changement de phase en fonction des variations de la température environnante,
• que le second mélange de réactifs présente par ailleurs un coefficient ΔP₂/ΔT dont la valeur est différente d'au moins 10% de celle de ΔP₁/ΔT,
• les première et seconde enceintes hermétiques présentant entre elles une connexion mécanique telle que le volume de l'une des enceintes hermétiques augmente lorsque le volume de l'autre diminue,
• la connexion mécanique étant reliée à un organe mobile pouvant se déplacer relativement aux variations de volume des enceintes.

For this purpose, the present invention relates more particularly to a pneumatic mechanism, intended to produce mechanical energy from variations in the surrounding temperature, of the type mentioned above and in which

• the first hermetic enclosure contains a first reagent mixture, with a coefficient ΔP ₁ / ΔT, comprising a first metal alloy arranged in contact with a gas and capable of giving rise to at least one phase change as a function of the variations in the temperature surrounding,
• characterized in that it comprises a second hermetic enclosure of variable volume whose internal pressure can alternatively increase and decrease depending on the variations of the surrounding temperature,
• the second hermetic enclosure contains a second reagent mixture, comprising a second metal alloy arranged in contact with a gas and capable of giving rise to at least one phase change as a function of the variations in the surrounding temperature,
• the second mixture of reagents furthermore has a coefficient ΔP ₂ / ΔT whose value is at least 10% different from that of ΔP ₁ / ΔT,
• the first and second hermetic enclosures having between them a mechanical connection such that the volume of one of the hermetic enclosures increases when the volume of the other decreases,
• the mechanical connection being connected to a movable member movable relative to the volume changes of the speakers.

The second hermetic enclosure plays the role of counter-spring, and helps the first chamber to regain its initial state when the temperature varies in the opposite direction, while ensuring a smaller footprint with a conventional metal spring.

Preferably, the pneumatic mechanism is intended to recharge a mechanical energy source of a timepiece, the first reagent mixture having a coefficient ΔP ₁ / ΔT substantially greater than 0.01 bar. ° C ^-1 in ranges operating temperature, substantially between 0 and 50 ° C and, in pressure, substantially between 1 and 50 bar, the coefficient ΔP ₂ / ΔT having a different value of at least 10% of that of ΔP ₁ / ΔT in these operating ranges. In addition, the movable member is advantageously connected to a conversion mechanism of the energy that can be connected to the source of mechanical energy.

Moreover, each of the first and second gases preferably comprises dihydrogen or dideuterium capable of reacting with the corresponding metal alloys to form an alloy of the metal hydride type, by phase change between the gaseous and solid phases.

More particularly, each of the first and second metal alloys preferably corresponds to a general formulation of the type AB ₅ , AB ₂ or AB, wherein A is a metal or a metal mixture, and B is a metal or a metal mixture. A may advantageously comprise at least one element chosen from the group comprising Ce, La, Mn, Nd, Pr, Ti, while B may advantageously comprise at least one element chosen from the group comprising Co, Ni, Sn, Fe, Mn.

In general, to these two main elements A and B it will be preferred to add complementary elements in a smaller proportion. In other words, at least one of the two metal alloys may comprise a third metal or weakly substituted metal alloy. proportion to A or B. For example, we can choose for one of the two hydrides a formulation of the type TiFe _0.9 Mn _0.1

As a further nonlimiting example, it can be provided that each of the first and second metal alloys is selected from the group consisting of (La, Ce) (Ni, Co) ₅ , (La, Ce) (Ni, Co) _{5+ ε} , (La, Ce) (Ni, Sn) _{5 + ε} , the two alloys being different from each other.

Thanks to these characteristics, the preferred reagents ensure that the pressure variations in the hermetic enclosures make it possible to provide sufficient work to recharge the source of mechanical energy when the surrounding temperature varies.

Advantageously, the predicted value difference between the respective ΔP / ΔT coefficients allows one of the speakers to reduce its volume when that of the other speaker increases significantly.

• en température, comprise sensiblement entre 15 et 40°C, plus préférablement entre 15 et 35°C,
• en pression, comprise sensiblement entre 1 et 30 bars, plus préférablement entre 1 et 10 bars.

According to a preferred embodiment variant, the coefficient ΔP ₁ / ΔT of the reagent mixture in the first sealed enclosure is substantially equal to or greater than 0.5 bar. ° C ^-1 in a preferred operating range,

• at a temperature substantially between 15 and 40 ° C, more preferably between 15 and 35 ° C,
• in pressure, substantially between 1 and 30 bar, more preferably between 1 and 10 bar.

In this way, the pneumatic mechanism has thermodynamic properties suitable for use in the watchmaking field.

Moreover, at least one or each of the hermetic enclosures may advantageously have at least one generally deformable bellows wall as a function of the variations in internal pressure due to changes in the surrounding temperature.

Finally, the invention relates to a timepiece comprising a pneumatic mechanism, according to the above characteristics, arranged to recharge a source of mechanical energy, as well as a system for energy conversion associated at least indirectly with firstly, to the first and second hermetic enclosures and, on the other hand, to the source mechanical energy to recharge the latter from the volume variations of the first and second hermetic enclosures.

Brief description of the drawings

• - la figure 1 représente un schéma bloc illustrant le principe de la présente invention;
• - les figures 2a et 2b représentent l'évolution de la pression en fonction de la température pour des couples d'alliages d'hydrures métalliques suivant des variantes de réalisation préférées de la présente invention;
• - la figure 3 représente une vue de face simplifiée des enceintes hermétiques selon un premier mode de réalisation;
• - la figure 4 représente une vue de face simplifiée des enceintes hermétiques selon un second mode de réalisation de l'invention;
• - les figures 5a et 5b représentent des vues en coupe des enceintes hermétiques selon un troisième mode de réalisation de l'invention pour différentes températures;
• - la figure 6 représente une courbe illustrant la relation entre une caractéristique géométrique particulière du mécanisme pneumatique selon l'invention et la valeur de la variation de température auquel le mécanisme est soumis.

Other features and advantages of the present invention will appear more clearly on reading the detailed description of preferred embodiments which follows, made with reference to the accompanying drawings given as non-limiting examples and in which:

• - the figure 1 represents a block diagram illustrating the principle of the present invention;
• - the Figures 2a and 2b represent the evolution of the pressure as a function of temperature for pairs of metal hydride alloys according to preferred embodiments of the present invention;
• - the figure 3 represents a simplified front view of the hermetic enclosures according to a first embodiment;
• - the figure 4 represents a simplified front view of the hermetic enclosures according to a second embodiment of the invention;
• - the figures 5a and 5b show sectional views of hermetic enclosures according to a third embodiment of the invention for different temperatures;
• - the figure 6 represents a curve illustrating the relationship between a particular geometrical characteristic of the pneumatic mechanism according to the invention and the value of the temperature variation to which the mechanism is subjected.

Mode (s) of realization of the invention

In the remainder of the description, the same numerical references will be used in relation to different variant embodiments to designate elements of the same function, for the sake of simplification of the understanding.

The figure 1 illustrates the general principle of the invention using a block diagram.

According to a preferred embodiment of the present invention, the pneumatic winding mechanism comprises a source of energy primary 1 for recharging a secondary energy source 3, through a conversion mechanism 2, the secondary energy source 3 being arranged to supply a watch movement 4 in mechanical energy.

The primary energy source 1 comprises a first hermetic enclosure (numerical reference 5, visible on the figures 3 and 4 ) having a volume that can alternately grow and decrease depending on variations, in one direction and the other, of the surrounding temperature. Indeed, the first hermetic enclosure contains a mixture of reagents, comprising a metal alloy arranged in contact with a gas and, likely to give rise to at least one phase change depending on the variations in the surrounding temperature, this phase change having an impact on the amount of gas present in the first sealed chamber and thus on the internal pressure of the latter.

By way of illustrative and nonlimiting example, the reagent mixture placed in the first chamber 5 has a coefficient ΔP ₁ / ΔT substantially greater than 0.01 bar. ° C ^-1 , preferably greater than 0.5 bar. ^° C ^-1 , in operating ranges, in temperature, substantially between 0 and 50 ° C and, at pressure, substantially between 1 and 50 bar, preferably between 1 and 20 bar.

The primary energy source 1 also comprises a second hermetic enclosure (reference numeral 6 on the figures 3 and 4 ) playing the role of counter-spring. Like the first hermetic enclosure (5), the second hermetic enclosure (6) comprises a mixture of reagents comprising a metal alloy and a gas, the mixture having the particularity of undergoing at least one phase transition when the surrounding temperature varies. The phase transition causes a change in the amount of gas in the second chamber, and therefore a change in the volume occupied by the latter.

The reagent mixture placed in the second chamber (6) has characteristics different from those of the mixture introduced into the first chamber (5). For temperature conditions included substantially between 0 and 50 ° C and, and pressure substantially between 1 and 50 bar, the coefficient ΔP ₂ / ΔT preferably has a value different from at least 10% of that of the mixture of reactants of the first chamber.

This property allows the second chamber 6 to be compressed when the first chamber 5 expands due to an increase in the surrounding temperature, if ΔP ₁ / ΔT is greater than ΔP ₂ / ΔT or to be expanded if ΔP ₂ / ΔT is greater than ΔP ₁ / ΔT.

In the remainder of the discussion, we will consider the case where ΔP ₁ / ΔTT is greater than ΔP ₂ / ΔT for the sake of simplification of the disclosure and without limitation. The skilled person will not encounter any particular difficulty to achieve a mechanism according to the following teaching adapted to the opposite case, that is to say when ΔP ₁ / ΔT is greater than ΔP ₁ / ΔT

The Figures 2a and 2b For this purpose, the evolution of the pressure as a function of temperature is presented for two examples of two reagent mixtures each comprising a metal hydride and dihydrogen. In the first mixture of reagents, the MnNi ₅ is used in the first chamber, and the LaNi ₅ in the second, for illustrative and not limiting. In the second mixture, LaNi ₅ is replaced by MnNi _4.15 Fe _0.85 .

To know more in detail the properties of these hydrides, one can advantageously refer to the patent application EP 2469350 A1 , whose teaching is incorporated in this application by reference.

From a structural point of view, in a first preferred embodiment, the pneumatic mechanism is arranged in the form of a double piston, such as that presented in FIG. figure 3 .

More specifically, it comprises a first hermetic enclosure 5 having the general shape of a piston chamber of volume V ₁ . The first hermetic enclosure 5 is provided with a movable surface 8 of area S ₁ and, inside, there is a first hydride under a pressure P ₁ .

A second hermetic enclosure 6, also having the shape of a piston chamber, of volume V ₂ , also has a movable wall 9 of area S ₂ and contains another hydride under a pressure P ₂ .

The two walls 8 and 9 are connected by a rigid rod 7. Thus, as the surrounding temperature increases, the amount of gas increases in both chambers, increasing their respective internal pressures. Since ΔP ₁ / ΔT is greater than ΔP ₂ / ΔT, the increase of the pressure P ₁ in the first sealed enclosure 5 is faster than the pressure P ₂ in the second enclosure and causes an increase in its volume V ₁ by displacement of the movable wall 8. The rod 7, secured to the movable wall 8, pushes the movable wall 9 towards the inside of the second chamber and therefore causes a decrease in its volume V ₂ .

Moreover, the rod 7 is connected to a mechanism for converting energy 2, comprising a movable member 10 in translation, integral with the rod 7. A pawl 12, intended to lock the secondary energy source 3 in the direction its discharge, is provided to prevent it from discharging into the pneumatic mechanism when the surrounding temperature decreases.

For example, it is possible to provide that the source of mechanical energy is a barrel 11; loaded via a ratchet secured to a bung, itself secured to an inner end of a barrel spring, while the other end of the barrel spring is secured to a barrel drum meshing with a clockwork wheel. These elements, well known to those skilled in the art, are not represented. Therefore, the energy conversion mechanism can be associated with a pawl 12, conventional, arranged to lock the ratchet only in the direction of rotation corresponding to the discharge of the mainspring, in a conventional manner.

Alternatively, an inverter device can be inserted into the conversion mechanism, so that the increase in the volume of the second hermetic enclosure 6, when the temperature decreases, also allows to recharge the mainspring spring 11.

A second preferred embodiment of the invention is shown in FIG. figure 4 . Here, the first hermetic enclosure 5 comprises a fixed wall 13, and at least one deformable wall 14, for example a bellows, carrying a movable wall 8. The second hermetic enclosure 6 comprises also a fixed wall 15 and at least one deformable wall 16 carrying a movable wall 9.

The movable walls 8 and 9 are integral with a rod 7 connected to a power conversion mechanism 2, operating in a similar manner to that which has just been exposed. An inverter device can also be provided so that the secondary energy source 3 can be recharged at a time when the temperature increases and when it decreases.

When the temperature increases, the increase in the quantity of gas in the first chamber 5 causes an increase in the volume V ₁ , by deformation of the wall 14, and displacement of the movable wall 8. The movement of the latter causes a displacement of the movable wall 9, and a contraction of the wall 16, so that the volume V ₂ of the second hermetic enclosure decreases.

In a third embodiment presented to figures 5a and 5b the pneumatic mechanism, also of piston type, is arranged in a cylindrical frame 17. Inside the latter is a first hermetic enclosure 5 having the general shape of a ring, and comprising an annular mobile wall 19 whose section section is U-shaped, and a fixed wall 20 of annular shape and integral with the frame 17.

The frame 17 also comprises a second hermetic enclosure 6, of cylindrical shape, and arranged inside the first enclosure 5 being coaxial with the latter. Like the first chamber 5, the second chamber 6 is delimited by a movable wall 22 in the form of an open cylinder, inside which is arranged a fixed wall 23, disc-shaped and secured to the frame 17.

The two movable walls 19 and 22 are connected by four belts 24 guided by pulleys 25 with which the belts cooperate without slipping.

At a first predetermined temperature, the pneumatic mechanism is in the visible configuration on the figure 5a . The volume V ₁ of the hermetic enclosure 5 is minimal, and the volume V ₂ of the hermetic enclosure 6 is maximum.

When the surrounding temperature increases, the pressure in the first chamber 5 increases more rapidly than that of the second chamber 6. As a result, the volume V ₁ of the hermetic enclosure 5 increases and generates a torque on the system pulleys-belts, of so that the volume V ₂ of the hermetic enclosure 6 decreases.

As in the previous embodiments, the frame 17 is connected to a mechanism for converting the energy 2 (not shown), in order to transmit a portion of the energy generated by the increase of the volume V ₁ of the hermetic enclosure 5 to the secondary energy source 3, for reloading. Advantageously, the internal movements of the pneumatic mechanism can be exploited from the rotation of the pulley axes during changes in the surrounding temperature.

Alternatively, an inverter device may also be provided so that the secondary energy source 3 recharges when the volume V ₂ of the hermetic enclosure 6 increases, that is to say when the surrounding temperature decreases.

Whatever the embodiment chosen for the counter-spring, the second chamber 6 must succeed in providing sufficient work, to replace the first chamber 5 in its initial configuration when the surrounding temperature decreases.

Also, the Applicant has examined what are the relevant parameters to be taken into account for a good operation of the pneumatic mechanism according to the invention.

• où dx est un déplacement élémentaire de la surface d'aire S₂ selon un axe orthogonal à la surface;
• x₀ est la position d'équilibre de la paroi mobile de la première enceinte, lorsque la température est égale à une température de référence
• T₀, par exemple T₀ = 18°C pour correspondre sensiblement à la température ambiante ;
• et x(T) est la position de la paroi mobile de la première enceinte hermétique à une température quelconque T.

From a thermodynamic point of view, the work done by the second speaker at the first speaker can be expressed as follows: $${\mathrm{<figure-callout\; id="2"\; label="W"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">W</figure-callout>}}_{2\to 1}={\int }_{x\left(T\right)}^{x_0}{P}_2\left(\mathrm{<figure-callout\; id="2"\; label="T\; S"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">T\; </figure-callout>},\right)S_{}{}_2\mathit{dx}$$

• where dx is an elementary displacement of the surface area S ₂ along an axis orthogonal to the surface;
• x ₀ is the equilibrium position of the movable wall of the first enclosure, when the temperature is equal to a reference temperature
• T ₀ , for example T ₀ = 18 ° C to substantially correspond to the ambient temperature;
• and x (T) is the position of the movable wall of the first hermetic enclosure at any temperature T.

Since the internal pressure P ₂ varies little with temperature, and the deformable wall can move only over a limited distance, it is important that the area S ₂ is large enough so that the force exerted on the movable wall of the first enclosure is sufficient.

The Applicant's work therefore consisted in establishing a relationship between the area of the deformable wall of the second hermetic enclosure, and the other relevant parameters of the device.

où P_a est la pression atmosphérique.At the equilibrium state, the pneumatic mechanism obeys the relation: $$\left(P_1\left(T_0\right)-P_{\mathrm{at}}\right){\mathrm{<figure-callout\; id="1"\; label="S"\; filenames="imgf0004.png"\; state="\{\{state\}\}">S</figure-callout>}}_1=\left(P_2\left(T_0\right)-P_{\mathrm{at}}\right){\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">S</figure-callout>}}_2$$

where P _a is the atmospheric pressure.

• où ΔH_hyd,i représente l'enthalpie de formation de l'hydrure présent dans la première enceinte (respectivement dans la seconde enceinte) ;
• ΔS_hyd,i représente l'entropie de formation de l'hydrure présent dans la première enceinte (respectivement dans la seconde enceinte) ;
• P₀ est une pression de référence, par exemple P₀ = 1 bar ;
• et R représente la constante des gaz parfaits.

This is a thermodynamic equilibrium, which is established between the two hermetic enclosures, where the hydrides they contain have an internal pressure P _i which can be written: $${\mathrm{<figure-callout\; id="0"\; label="P\; i\; T"\; filenames="imgf0001.png,imgf0004.png"\; state="\{\{state\}\}">P\; </figure-callout>}}_i\left(T_{}\right)\left({}_0\right)={\mathrm{<figure-callout\; id="0"\; label="P"\; filenames="imgf0001.png,imgf0004.png"\; state="\{\{state\}\}">P</figure-callout>}}_0\exp \left[\mathrm{\Delta }{H}_{\mathit{hyd},i}/{\mathit{RT}}_0-\mathrm{\Delta }{S}_{\mathit{hyd},i}/R\right]\mathrm{with\; i}=1,2$$

• where ΔH _{hyd, i} represents the formation enthalpy of the hydride present in the first chamber (respectively in the second chamber);
• ΔS _{hyd, i} represents the formation entropy of the hydride present in the first chamber (respectively in the second chamber);
• P ₀ is a reference pressure, for example P ₀ = 1 bar;
• and R represents the constant of perfect gases.

When the surrounding temperature varies, the hermetic enclosures exert a force F on the source of mechanical energy thanks to their variations of volume. This one expresses itself in the form: $$F\left(T\right)=S_1{P}_1\left(T\right)-S_2{P}_2\left(\mathrm{T}\right)-P_{\mathrm{at}}\left(S_1-{\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">S</figure-callout>}}_2\right)$$

It is the work relating to this force F which makes it possible to recharge the source of mechanical energy.

Equations (2) and (4) allow to deduce the expression of the area S ₂ : $${\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">S</figure-callout>}}_2=\left|\frac{F\left(T\right)\left(P_1\left(T_0\right)-P_{\mathrm{at}}\right)}{\left(P_2\left(T_0\right)-P_{\mathrm{at}}\right)\left(P_1\left(T\right)-P_{\mathrm{at}}\right)-\left(P_2\left(T\right)-P_{\mathrm{at}}\right)\left(P_1\left(T_0\right)-P_{\mathrm{at}}\right)}\right|$$

Note that the absolute value comes from the fact that the force can be positive or negative depending on whether the temperature is lower or higher than To.

• où K_b est la raideur du ressort de barillet ;
• d(T) = x(T)-xo est le déplacement relatif de la paroi mobile de la première enceinte hermétique.

The secondary energy source 3, which is for example a barrel, exerts a force which opposes that of the pneumatic mechanism. This can be expressed as follows: $$F_b\left(T\right)=-K_{b}d\left(T\right)$$

• where K _b is the stiffness of the mainspring;
• d (T) = x (T) -xo is the relative displacement of the movable wall of the first hermetic enclosure.

When the system has reached a mechanical equilibrium, the forces F (T) and F _b (T) oppose exactly, so that the work supplied to the barrel by the pneumatic mechanism can thus be written: $${\mathrm{<figure-callout\; id="1"\; label="W"\; filenames="imgf0004.png"\; state="\{\{state\}\}">W</figure-callout>}}_{1+2\to b}\left(T\right)=\frac{F_b^2\left(T\right)}{2K_b}=\frac{K_b{d}^2\left(\mathrm{<figure-callout\; id="2"\; label="T"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">T</figure-callout>}\right)}{2}$$

These last two equations make it possible to deduce the expression of the force F (T): $$F\left(T\right)=\frac{2{\mathrm{<figure-callout\; id="1"\; label="W"\; filenames="imgf0004.png"\; state="\{\{state\}\}">W</figure-callout>}}_{1+2\to b}\left(T\right)}{d\left(T\right)}$$

Finally, the surface S _{2 is} written: $${\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">S</figure-callout>}}_2=\left|\frac{2{\mathrm{<figure-callout\; id="1"\; label="W"\; filenames="imgf0004.png"\; state="\{\{state\}\}">W</figure-callout>}}_{1+2\to b}\left(T\right)\left(P_1\left(T_0\right)-P_{\mathrm{at}}\right)}{d\left(T\right)\left(P_2\left(T_0\right)-P_{\mathrm{at}}\right)\left(P_1\left(T\right)-P_{\mathrm{at}}\right)-d\left(T\right)\left(P_2\left(T\right)-P_{\mathrm{at}}\right)\left(P_1\left(T_0\right)-P_{\mathrm{at}}\right)}\right|$$

Equation (9) shows that the area S ₂ necessary for the proper functioning of the pneumatic mechanism depends on the surrounding temperature, but also on the work done by the pneumatic mechanism on the source of mechanical energy, as well as the relative displacement of the mobile wall of the first hermetic enclosure.

The Applicant has therefore determined the evolution of the area S ₂ as a function of the surrounding temperature, by using relevant values of W _{1 + 2 → b} and d, and using different mixtures of reagents, so that the device can be inserted into a small timepiece, such as a wristwatch.

As a nonlimiting illustrative example, to recharge a timepiece of this type, it is assumed that the energy required is of the order of 0.2 J / day. This corresponds generally to a barrel spring delivering a torque of 8 N.mm making four revolutions per day.

It is also considered that the movable wall of the first sealed enclosure may have a maximum displacement of 10 mm, for example, in order to have acceptable conditions from a point of view of the bulk of the mechanism.

In these circumstances, and for the embodiments described in figures 3 and 4 as well as for the reagent mixtures presented in figure 2a , the area S ₂ knows an evolution according to the temperature such as that presented on the figure 6 . Note that in this representation, ΔT = T-To, where To = 18 ° C.

For an increase in temperature of the order of 10 ° C, which corresponds to a surrounding temperature of 28 ° C, that of a pocket watch or a worn watch, it is noted that the area S ₂ must be of the order of 700 mm ² . This area corresponds to a disc of about 15 mm radius, and makes the introduction of the pneumatic mechanism possible in a small timepiece.

The Applicant has made the same calculations for the embodiment presented to the figures 5a and 5b , and for the reagent mixtures presented at figure 2b . It follows that for a temperature increase of 10 ° C compared to the initial temperature, the necessary area S ₂ , so that the work provided by the second hermetic enclosure 6 to the second hermetic enclosure 5 is sufficient, is to the order of 450 mm ² , which corresponds to an enclosure of 12 mm radius.

It follows from the above that the pneumatic mechanism comprising a counter-spring comprising a hermetic enclosure containing a metal hydride alloy according to the present invention has a small footprint, making it particularly suitable for timepieces of small sizes, such as wristwatches for example.

The foregoing description attempts to describe particular embodiments as non-limiting illustrations and the invention is not limited to the implementation of certain particular characteristics which have just been described, such as, for example, the chemical compounds mentioned, or the embodiments presented.

Other reagents can meet the conditions set and be implemented in a pneumatic mechanism for reassembly of the mechanical energy source of a timepiece, without departing from the scope of the present invention. It is conceivable to use other metal alloys as long as a phase change is involved in the operation of the pneumatic mechanism to present sufficient values of the respective ΔP / ΔT coefficients, with a difference of at least 10% between them.

Moreover, the skilled person will not encounter any particular difficulty to adapt the various embodiments presented according to his own needs, and implement a pneumatic winding mechanism in part to meet the characteristics that have just been exposed, without departing from the scope of the present invention.

In particular, it will be noted that the ranges of values proposed for the relevant parameters are relatively broad, notably because the conditions to be respected differ substantially according to the dimensions of the timepiece to be produced.

Claims (11)

1. Pneumatic mechanism (1) intended to produce mechanical energy from variations in the surrounding temperature and comprising a first hermetic chamber (5) of variable volume of which the internal pressure can alternately increase and decrease according to the variations in the surrounding temperature,
   the said first hermetic chamber (5) containing a first mixture of reactants, of coefficient ΔP₁/ΔT, comprising a first metal alloy arranged in contact with a first gas and capable of giving rise to at least one change of phase according to the variations in the surrounding temperature,
   characterized in that the pneumatic mechanism (1) comprises a second hermetic chamber (6) of variable volume of which the internal pressure can alternately increase and decrease according to the variations in the surrounding temperature,
   the said second hermetic chamber (6) containing a second mixture of reactants comprising a second metal alloy arranged in contact with a second gas and capable of giving rise to at least one change of phase according to the variations in the surrounding temperature,
   the said second mixture of reactants having a coefficient ΔP₂/ΔT of which the value is different by at least 10% from that of ΔP₁/ΔT,
   the said first and second hermetic chambers having a mechanical connection (7) between them such that the volume of one of the said hermetic chambers increases when the volume of the other decreases,
   the said mechanical connection (7) being connected to a mobile member which can move relatively to the variations in volume of the said chambers.
2. Pneumatic mechanism (1) according to Claim 1, characterized
   in that it is intended to reload a mechanical energy source (3) of a timepiece,
   in that the said first mixture of reactants has a coefficient ΔP₁/ΔT substantially greater than 0.01 bar.°C^-1 in operating ranges, in temperature, substantially between 0 and 50°C and, in pressure, substantially between 1 and 50 bar, the said coefficient ΔP₂/ΔT having a value different by at least 10% from that of ΔP₁/ΔT in the said operating ranges, and
   in that the said mobile member is connected to an energy conversion mechanism (2) which can be connected to the said mechanical energy source (3).
3. Mechanism (1) according to Claim 1 or 2, characterized in that each of the said first and second gases comprises dihydrogen or dideuterium capable of reacting with the said corresponding metal alloy to form an alloy of the metal hydride type by a change of phase between the gas and solid phases.
4. Mechanism (1) according to Claim 3, characterized in that each of the said first and second metal alloys has a general formula of the type AB₅, AB₂ or AB, in which A is a metal or a mixture of metals and B is a metal or a mixture of metals.
5. Mechanism (1) according to Claim 4, characterized in that A comprises at least one of the elements chosen from the group comprising Ce, La, Mn, Nd, Pr and Ti.
6. Mechanism (1) according to Claim 4 or 5, characterized in that B comprises at least one of the elements chosen from the group comprising Co, Ni, Sn, Fe and Mn.
7. Mechanism (1) according to any one of Claims 4 to 6, characterized in that at least one of the said first and second metal alloys comprises a third metal or metal alloy substituted in a low proportion for A or for B.
8. Mechanism (1) according to any one of the preceding claims, characterized in that the said coefficient ΔP₁/ΔT of the said first mixture of reactants in the said first hermetic chamber (5) is substantially equal to or greater than 0.5 bar.°C^-1 in a preferred operating range, in temperature, substantially between 15 and 40°C, more preferably between 15 and 35°C.
9. Mechanism (1) according to any one of the preceding claims, characterized in that the said coefficient ΔP₁/ΔT of the said first mixture of reactants in the said first hermetic chamber (5) is substantially equal to or greater than 0.5 bar.'C^-l in a preferred operating range, in pressure, substantially between 1 and 30 bar, more preferably between 1 and 10 bar.
10. Mechanism (1) according to any one of the preceding claims, characterized in that at least one wall (14, 16) of each of the said hermetic chambers (5, 6) has the general shape of a bellows which is deformable according to the variations in internal pressure due to the changes in the surrounding temperature.
11. Timepiece comprising a pneumatic mechanism (1) according to any one of the preceding claims for reloading a mechanical energy source (3), characterized in that it comprises an energy conversion system (2) associated at least indirectly, on the one hand, with the said first and second hermetic chambers (5, 6) and, on the other hand, with the said mechanical energy source (3) in order to reload the latter from the variations in volumes of the said first and second hermetic chambers (5, 6).

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