EP3542225B1 - Watch escapement with optimized draft - Google Patents

Description

Technical area

The present invention relates to the field of watchmaking. It relates, more particularly, to an exhaust with optimized draft.

State of the art

A conventional escapement, such as a Swiss lever escapement, English lever escapement, Daniels escapement, or the like, has an anchor which intermittently blocks an escape wheel, and transmits energy from the finishing gear to the gear. regulating organ when the wheel is released. Oscillations of the regulating member, such as a sprung balance, actuate the anchor in order to effect this periodic release of the escape wheel, and again provide an impulse to the regulating member to maintain its oscillations.

To this end, the anchor has at least two vanes, one - input - located upstream with respect to the direction of rotation of the escape wheel, the other - output - located downstream. At each alternation of the regulating member, the pallet which is engaged with the escape wheel is raised, releasing the escape wheel and transmitting an impulse to the regulating organ via the impulse faces located on pallets. At the same time, the other pallet is moved in the path of the teeth of the escape wheel, and blocks it. Then the cycle begins again for the other pallet.

In order to prevent the anchor from moving unintentionally, for example during an impact, a “pull” is provided. This draft is conventionally generated by the angle made by the rest plane of each pallet with the center distance between the anchor and the escape wheel when the latter is blocked. This angle is chosen so that the interaction between the escape wheel and the anchor applies a torque to the latter, which tends to keep it in its rest position. In doing so, in order to raise the anchor, the escape wheel must perform a small angular displacement in the opposite direction of its direction of travel, before being released. The anchor must therefore work against the finishing gear during the pallet release phase.

This work carried out by the anchor on the escape wheel during release is energy intensive, and reduces the efficiency of the escapement. The effect is particularly pronounced with regard to the entry vane, for which the pulling force typically increases during the release phase due to the geometry of the system.

Several attempts have been made to eliminate such a draft generated between the teeth of the escape wheel and the resting planes of the pallets.

For example, documents EP 2 431 823 and GB 667 885 reveal escapements in which the pallet rest planes follow an arc of a circle having its geometric center on the axis of rotation of the anchor. In doing so, the pull is eliminated, but a retention force is still necessary in order to prevent the anchor from being released unintentionally during an impact. These documents therefore propose to provide a retention force by means of magnets, friction, or the like. The use of magnets near the regulating member is not desirable at first glance, and the means for generating friction, such as for example elastic blades which come into contact with the anchor, are difficult to adjust for optimize the retention force, and require additional attachment points on the frame.

Moreover, the document CH702689 describes an improved escapement which nevertheless comprises a straight and therefore planar rest face 101, which also implies a pulling angle on the inlet pallet which increases along the release phase. This form of pallet is represented by the figure 6 , and clearly illustrates the end of the rest face 101. Indeed, the moment the tooth of the escape wheel exceeds the point indicated by the reference 103, the pulse phase starts thanks to the radius of curvature of this sub -part of the impulse face 102.

The object of the present invention is therefore at least partially to overcome the drawbacks mentioned above.

Disclosure of the invention

To this end, the invention relates to an escapement for a timepiece comprising an escapement wheel mounted to pivot about a first axis of rotation and intended to be driven by a source. motor, and an anchor pivotally mounted about a second axis of rotation and arranged to cooperate with a regulating member arranged to perform oscillations with a predetermined periodicity. The anchor comprises an entry pallet and an exit pallet, each pallet comprising a rest face arranged to alternately and sequentially block said escape wheel, that is to say one at a time and the one after the other.

The anchor is adapted to transmit impulses received from the escape wheel to the regulating member, and to release said escape wheel periodically under the control of said regulating member.

In order to keep the anchor in its blocking position and thus to avoid any untimely release, the rest face of the input pallet is arranged such that, when it blocks a tooth of the escape wheel, a pulling force is generated by the interaction between said rest face and said tooth so as to apply a torque which tends to maintain the anchor in the rest position. Retention of the anchor at rest is thus ensured by the interaction between the pallet and the escape wheel, without recourse to other retention means.

According to the invention, the rest face has a profile shaped such that the draw angle (γ) at the point of contact of said face with a tooth of the escape wheel is constant or decreasing along the stroke. clearance of the entry pallet.

Since the pulling angle of the entry vane does not increase during the corresponding release phase, the pulling force and torque does not increase either. The oscillations of the regulating member are consequently less disturbed when disengaging the inlet pallet than usual, which improves the efficiency and isochronism of said regulating member. Moreover, this is achieved without having to provide a pallet having a rest face in the form of an arc of a circle and additional means for generating a retention force for the anchor. The escapement thus proposed is consequently more efficient than a conventional escapement in terms of the isochronism of the regulating member, and is significantly simpler than the non-draft escapements mentioned above.

For this purpose, the rest face of the input pallet can be convex.

dans lequel :

• - γ est l'angle de tirage ;
• α_orientation est l'angle fait par une tangente à la face de repos de la palette d'entrée à son point de contact avec la roue d'échappement et l'entraxe entre l'ancre et la roue d'échappement ;
• α est l'angle fait par une ligne joignant ledit point de contact et l'axe de rotation de la roue d'échappement et ledit entraxe ;
• R est la longueur de ladite ligne joignant ledit point de contact et l'axe de rotation de la roue d'échappement ; et
• Axe est la longueur dudit entraxe.

Advantageously, the shape of said rest face observes the equation $$90-\gamma -{\alpha }_{\mathit{orientation}}={\tan }^{-1}\left(\raisebox{1ex}{$R\ast \sin \left(\alpha \right)$}\!\left/ \!\raisebox{-1ex}{$\mathit{Axis}-R\ast \cos \left(\alpha \right)$}\right.\right)$$

in which :

• - γ is the draw angle;
• α _orientation is the angle made by a tangent to the rest face of the input pallet at its point of contact with the escape wheel and the center distance between the anchor and the escape wheel;
• α is the angle made by a line joining said point of contact and the axis of rotation of the escape wheel and said center distance;
• R is the length of said line joining said point of contact and the axis of rotation of the escape wheel; and
• Axis is the length of said center distance.

The value of γ can either be substantially constant, or can decrease along at least part of the release stroke. The draft can thus be optimized by choosing the value and / or the progression of γ during the release.

For example, the value of γ can be in a range of between 5 ° and 20 °, preferably between 10 ° and 15 °.

Advantageously, at least one of said pallets may have come integrally with at least part of the anchor, which facilitates the manufacture of the anchor and, if the input pallet is integral with the anchor, ensures that the shape of the rest face of this pallet has the desired shape with respect to the axis of rotation of the anchor.

Finally, the invention relates to a timepiece movement comprising an escapement as defined above, as well as to a timepiece comprising such a movement.

Brief description of the drawings

• la figure 1 représente une vue schématique en plan d'un échappement selon l'invention ;
• la figure 2 représente une vue schématique en plan de la palette d'entrée d'un échappement selon l'invention, à échelle agrandie ;
• la figure 3 représente la forme de la face de repos de la palette d'entrée de la figure 2 en comparaison avec des lignes droites ;
• la figure 4 représente un modèle géométrique générique utile pour calculer la forme de la face de repos de la palette d'entrée de la figure 2 ;
• la figure 5 représente une vue simplifiée de la géométrie illustrée dans la figure 4 ;
• la figure 6 représente une vue d'une partie d'un échappement selon l'art antérieur représenté par le document CH702689 ; et
• la figure 7 représente un graphique illustrant l'évolution de l'angle de tirage au cours du dégagement selon l'art antérieur et selon l'invention.

The invention will be better understood on reading the following description of an embodiment, given by way of example and made with reference to the drawings in which:

• the figure 1 represents a schematic plan view of an exhaust according to the invention;
• the figure 2 represents a schematic plan view of the inlet pallet of an exhaust according to the invention, on an enlarged scale;
• the figure 3 represents the shape of the rest face of the entry pallet of the figure 2 in comparison with straight lines;
• the figure 4 represents a generic geometric model useful for calculating the shape of the rest face of the entry pallet of the figure 2 ;
• the figure 5 represents a simplified view of the geometry shown in the figure 4 ;
• the figure 6 shows a view of part of an exhaust according to the prior art represented by the document CH702689 ; and
• the figure 7 represents a graph illustrating the evolution of the draw angle during release according to the prior art and according to the invention.

Mode (s) for carrying out the invention

The figure 1 illustrates an exhaust 1 according to the invention. This escapement 1 takes the general form of a Swiss lever escapement, in which each blade participates in providing an impulse to the regulating organ.

As generally known, the escapement comprises an escape wheel 3, arranged to be driven by a driving source, not illustrated. This driving source can be, for example, a mainspring or an electric motor, which is in kinematic connection with the escape wheel 3 by means of a finishing gear (also not shown).

The escape wheel 3 is pivotally mounted on a shaft (not shown), the theoretical axis of which is indicated by the reference sign 5, and which corresponds to a first axis of rotation. In the illustrated variant, the teeth of the escape wheel 7 each have a rest face 7a, which interacts with the paddles when the escape wheel 3 is blocked, and an impulse face. However, the invention applies to other forms of escapement wheel, for example with pointed teeth (English lever escapement), or less conventional forms.

The teeth 7 of the escape wheel 3 interact in a known manner with an anchor 9, which pivots around a theoretical axis of rotation 11. In the illustrated variant, this theoretical axis 11 coincides with a shaft (not illustrated), but an anchor of the “suspended” type as described in the document. CH708113 , or any other suitable type is also possible. This axis 11 corresponds to a second axis of rotation.

The general shape of the anchor 9 illustrated is conventional. To this end, it comprises a rod 9a extending from the axis of rotation 11 and terminating in a fork 9c, which interacts with a regulating member (not shown) in a known manner and which should not be described here in detail. . Furthermore, a pair of arms 9b extend on either side of the axis of rotation 11 in directions substantially perpendicular to the rod 9a, and terminate in pallets 13, 15. It goes without saying that d 'Other less usual forms of anchor can also be used within the scope of the invention.

Each of these pallets 13, 15 is arranged to block and to release the escape wheel periodically, the latter being blocked by one of the pallets 13, 15, then re-blocked by the other, in sequence.

Pallet 13 shown on the right on the figure 1 is the input pallet, located upstream with respect to the direction of rotation of the escape wheel 3 indicated by the arrow, and the pallet 15, located downstream, is the output pallet.

In the illustrated variant, the pallets 13, 15 come in one piece with the anchor 9, but the invention also applies to pallets attached to the arms 9b in a conventional manner. Each pallet 13, 15 comprises, as generally known, a rest face 13a respectively 15a, and an impulse face 13b respectively 15b. The rest faces 13a, 15a are used to block the escape wheel 3 during rest phases, and the impulse faces 13b, 15b cooperate with the teeth 7 to transmit an impulse to the anchor and thus to the regulating organ. Even if already implicit in the above, the rest face 13a extends to the point where the contact between the pallet 13 and the tooth 7 no longer ensures the locking of the escape wheel 3, at which point the contact between these elements begins to generate the transmission of force between tooth 7 of escape wheel 3 and vane 13. The figure 6 clearly illustrates this point of transition between these two faces.

In a usual escapement of the kind which has just been defined, the rest faces 13a, 15a are typically planes, the angle of which is chosen such that, during the rest phases, the force F resulting from the contact between the rest face 13a, 15a comprises a component which tends to keep the pallet 13 or 15, where appropriate, engaged with the escape wheel 3. This force F exerts a torque around the axis of rotation 11 of the anchor 9, which tends to keep it engaged with the teeth of escape wheel 3, that is to say which tends to cause the anchor to pivot counterclockwise (depending on the orientation of the figure 1 ) when the input pallet 13 is engaged, and clockwise when the output pallet 15 is engaged. It should be noted that only friction between, for example a rest face in an arc of a circle centered on the axis of rotation of the anchor and the escape wheel does not exert such a torque, since no force can generate a torque around the axis of rotation of the anchor 9 is exerted between the elements concerned when they are at rest and in the absence of a dynamic force tending to move the anchor. In other words, the pulling force is applied statically.

However, in a conventional escapement, the angle that the rest face 13a of the inlet vane 13 presents to a tooth 7 of the escape wheel increases along the release phase, which represents the part of the movement of the escapement. the anchor between its initial position at rest and the moment when the tooth 7 makes the transition from the rest face 13a to the impulse face 13b of the pallet. This results from the fact that, when the anchor 9 pivots about its axis 11, this angle is modified according to the geometry of the anchor and of the entry pallet 13. In fact, the slope of the rest face 13a becomes steeper with respect to tooth 7. Consequently, the force, and the torque, required to overcome the pulling increase along the stroke of the release phase of the input vane 13. This is detrimental to the efficiency. and the efficiency of the escapement, and disturbs the oscillations of the regulating organ, which is detrimental to isochronism.

The same drawback does not occur at the level of the exit pallet 15, since the angle which its rest face 15a makes with the tooth 7 decreases along the path of the undercut, since the exit pallet 15 is on the side. 'other side of the axis of rotation 11 of the anchor 9 relative to the entry pallet 13.

The invention therefore relates to the shape of the rest face 13a of the input pallet 13. Since the active faces 13a, 13b, 15a, 15b of the pallets do not have to be planar, the terminology of "face" is used. Instead of the usual wording "plan of ...".

In particular, the rest face 13a of the input pallet 13 is formed such that the angle it makes with a tooth 7 of the escape wheel 3 remains constant, or decreases along the stroke. clearance.

The figure 2 illustrates, on an enlarged scale, the shape of an inlet pallet 13, the rest face 13a of which has a shape calculated such that the angle of the pulling force is constant when it is used in an escapement having the geometry of that of the figure 1 .

On the figure 2 , the edge joining the rest face 7a to the impulse face 7b of a tooth 7 of the escape wheel 3 has been shown in two positions, one - on the right - being at the start of the phase of release, the other - on the left - just before the end of the release phase and before the transition to the impulse phase. The rest face 13a of the pallet 13 is convex and curved so that the direction of the force F resulting from the contact between the tooth 7 and the pallet 13 remains oriented substantially in the same direction when the anchor 9 is pivoted during the phase clearance.

The figure 3 schematically illustrates the difference between this curvature and conventional rest 13c and 13d pulse planes, represented by straight lines.

This figure clearly shows that when the profile of the rest face 13a crosses the line A, it deviates from the line 13c representing a rest plane B, which represents the start of the transition between the rest face 13a and the impulse face 13b. To line B, the profile joins an arc of a circle of which it is tangential, this arc of a circle also being tangential to the face pulse 13b, in order to make this transition continuously. In the illustrated variant, the pulse face 13b is straight and therefore represents a conventional pulse plane. However, a curved pulse face 13b is also possible.

The figures 4 and 5 schematically illustrate a geometric model which makes it possible to calculate the shape of the rest face 13a of the input pallet, and this independently of the shape of the anchor. This model represents schematically the interaction between the escape wheel 3 and the anchor 9. In the figure 4 , the anchor 9 and several teeth 7 are illustrated schematically, while in figure 9 the model is illustrated in a minimalist manner.

In this model, the center distance O _R O _A between the axis of rotation 5 of the wheel 3 and the axis of rotation 11 of the anchor 9 acts as a reference for the geometry. The point of contact C between a tooth 7 of the escape wheel 3 and the rest face 13a of the input pallet 13 traces the profile of said rest face 13a during the release phase, and can be expressed as Cartesian coordinates like C = (X _C , Y _C ) . These coordinates X _C , Y _C are respectively perpendicular and parallel to the center distance O _R O _A.

According to the invention, the angle γ, which represents the predetermined draw angle, is constant or decreasing along the path of the release. This angle γ is measured between on the one hand the tangent T to the rest face 13a of the entry pallet at its point of contact C with the escape wheel 3, and on the other hand the normal to the line O _A C joining the axis of rotation of the anchor and the point of contact between the rest face 13b of the input pallet 13 and a tooth 7 of the escape wheel 3.

After having chosen γ (or its development) beforehand, as well as the geometry of the escape wheel 3 and of the anchor 9, the geometry can be solved as follows. Note that, in the notation used below, a term such as "CF", "O _A F" or the like means the length of a straight line joining the points concerned.

First of all, we see that: $$\mathit{CF}=R.\mathit{sin}\left(\alpha \right)$$

dans lequel Axe est la longueur de l'entraxe O_RO_A.in which R is the distance between the axis of rotation O _R of the wheel 3 and the point of contact C between the tooth 7 and the rest face 13a, and α is the angle that O _R C makes with the center distance O _R O _A. Thereafter $$O_{\mathrm{AT}}F=\mathit{Axis}-R.\mathit{cos}\left(\mathrm{\alpha }\right)$$

in which Axis is the length of the center distance O _R O _A.

For completeness, we note that the angle θ formed by the line O _A C with the center distance O _R O _{A is} expressed as $$\theta ={\mathit{tan}}^{-1}\left(\mathit{CF}/O_{\mathrm{AT}}F\right)$$

dans lequel α_orientation est l'angle que fait la tangente de la face de repos 13a de la dent 7 avec l'entraxe O_AO_R. Cette équation peut être réorganisée comme suit $$90°-\gamma -{\alpha }_{\mathit{orientation}}={\mathit{tan}}^{-1}\left(X_C/Y_C\right)$$

The draw angle γ is measured between a line orthogonal to O _A C and the tangent T of the rest face 13a at point C. Therefore $$90°=\gamma +{\alpha }_{\mathit{orientation}}+{\mathit{tan}}^{-1}\left(X_{\mathrm{VS}}/Y_{\mathrm{VS}}\right)$$

in which α _orientation is the angle formed by the tangent of the rest face 13a of the tooth 7 with the center distance O _A O _R. This equation can be rearranged as follows $$90°-\gamma -{\alpha }_{\mathit{orientation}}={\mathit{tan}}^{-1}\left(X_{\mathrm{VS}}/Y_{\mathrm{VS}}\right)$$

By redefining X _C and Y _C in polar coordinates, we obtain: $$90-\gamma -{\alpha }_{\mathit{orientation}}={\tan }^{-1}\left(\raisebox{1ex}{$R\ast \sin \left(\alpha \right)$}\!\left/ \!\raisebox{-1ex}{$\mathit{Axis}-R\ast \cos \left(\alpha \right)$}\right.\right)$$

The profile of the rest face 13 can thus be plotted by calculating the value of α _orientation at the contact point C for each position of the anchor along the release phase, while observing the above relationship. In the case where γ varies, a function representing this variation can be used in the calculation.

Indeed, one can calculate α _orientation for a plurality of angular positions of the anchor, and then join the associated tangents in a continuous manner in order to arrive at the desired profile.

The value of γ can, for example, lie within a range of values between 5 ° and 20 °, preferably between 10 ° and 15 °, and can decrease along at least part of the release phase, while remaining within this range. Furthermore, γ can also have a tolerance of +/- 10%.

The result of this pulling is that the anchor 9 can be retained in engagement with a tooth 7 of the escape wheel, and that the resistance to clearance of the inlet pallet 13 does not increase. Consequently, the oscillations of the regulating member are less disturbed during these releases.

Indeed the graph of the figure 7 illustrates a comparison between the evolution of the pull angle along the release phase for a conventional planar pallet (such as that in document CH702689 ), shown in dashed lines, and for a pallet having a rest face shaped according to the invention, shown in solid lines. From the results of this modeling, it is clear that the draw angle, and thus the resistance to release, no longer increases in the context of a rest face according to the invention.

The anchor 9 and / or the escape wheel 3 described above can, for example, be manufactured by micromachining processes, such as LIGA, 3D printing, masking and etching from a plate of material, stereolithography or the like. Suitable materials can, for example, be chosen from monocrystalline, polycrystalline or amorphous metals (such as steel, nickel-phosphorus, brass or the like), non-metals such as silicon, its oxide, its nitride. or its carbide, alumina in all these forms (for example ruby), diamond (including adamintine carbon), these non-metallic materials being monocrystalline or polycrystalline. All these materials can optionally be coated with another hard and / or anti-friction material, such as adamantine carbon, alumina or silicon oxide.

Although the invention has been described above in connection with specific embodiments, additional variants are also conceivable without departing from the scope of the invention as defined by the claims.

Claims (9)

1. Escapement (1) for a timepiece comprising:

   - an escapement wheel (3) mounted in a pivotable manner about a first axis of rotation (5) and destined to be driven by a power source;

   - a pallet fork (9) mounted in a pivotable manner about a second axis of rotation (11), said pallet fork comprising an entry pallet (13) and an exit pallet (15), each pallet (13, 15) comprising a rest surface (13a, 15a) arranged to block said escapement wheel (3) alternately and sequentially, the pallet fork (9) being adapted to transmit impulsions received from the escapement wheel (3) to a regulating member arranged to produce oscillations, and to release said escapement wheel (3) periodically under the control of said regulating member,

   in which the rest surface (13a) of the entry pallet (13) is arranged in such a way that, when it blocks a tooth (7) of the escapement wheel (3), a draw force is generated by the interaction between said rest surface (13a) and said tooth (7) in such a way as to apply a torque which tends to retain the pallet fork (9) in the rest position,
   characterized in that said rest surface (13a) is configured in such a way that the draw angle (γ) at the point of contact (C) of said surface (13a) with a tooth (7) of the escapement wheel (7) is constant or decreasing during disengagement of the entry pallet (13).
2. Escapement (1) according to Claim 1, in which said rest surface (13a) is convex.
3. Escapement (1) according to Claim 2, in which said rest surface (13a) is configured according to the equation: $$90-\gamma -{\alpha }_{\mathit{orientation}}={\tan }^{-1}\left(\raisebox{1ex}{$R\ast \sin \left(\alpha \right)$}\!\left/ \!\raisebox{-1ex}{$\mathit{Axe}-R\ast \cos \left(\alpha \right)$}\right.\right)$$

   

   in which:

   yis the draw angle;

   α_orientation is the angle between a tangent (T) to the rest surface (13a) of the entry pallet (13) at its point of contact (C) with the escapement wheel (3) and the centre-to-centre line (O_AO_R) between the pallet fork (9) and the escapement wheel (3);

   α is the angle between a line (R) joining said point of contact (C) and the axis of rotation (11, O_R) of the escapement wheel (3) and said centre-to-centre line (O_AO_R) ;

   R is the length of said line joining said point of contact (C) and the axis of rotation (11, O_R) of the escapement wheel; and

   Axe is the length of said centre-to-centre line (O_AO_R).
4. Escapement (1) according to Claim 3, in which γ is substantially constant.
5. Escapement (1) according to Claim 3, in which γ diminishes along at least a part of the disengagement travel.
6. Escapement (1) according to Claim 4, in which the value of γ lies in a range between 5° and 20°, preferably between 10° and 15°.
7. Escapement (1) according to one of the preceding claims, in which at least one of said pallets (13, 15) is integral with at least a part of the pallet fork (9).
8. Timepiece movement comprising an escapement (1) according to one of the preceding claims.
9. Timepiece comprising a movement according to Claim 8.

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