Assembly for attaching a hairspring for clock movement, hairspring and method for adjusting the marking and the operation of a balance wheel-hairspring assembly

Abstract

The invention relates to an assembly (1) for the removable attachment of a balance spring (2) of a watch movement comprising a balance bridge (4), this assembly comprising the balance spring (2) on the one hand, a retaining means (8) for the balance spring (2), and a removable locking piece (10) on the other hand, the balance spring (2) comprising a winding of turns (12) extending between a first free end of a first inner turn and a second free end (18) of a last outer turn (20), the second free end (18) of the last outer turn (20) of the balance spring (2) comprising an attachment means in which the retaining means (8) is engaged to ensure the removable attachment of the balance spring (2) by its last outer turn (20), the attachment means being dimensioned such that, in its position natural resting statethe spiral spring (2) not being in contact with the retaining means (8) engaged in this fastening means, the locking piece (10) for ensuring the removable fixing of the second free end (18) of the last coil outside (20) of the spiral spring (2) being engaged on the retaining means (8) to lock the fastening means.

Description

Technical field of the invention

[0001] The present invention relates to an assembly for fixing a spiral spring for a watch movement. The present invention also relates to an adjustment method for such a fixing assembly. Technological background

[0002] In the field of watchmaking, a hairspring, combined with a balance wheel, forms a regulating organ commonly called a hairspring balance for mechanical timepieces. At first glance, the hairspring appears as a very thin spring that coils around itself in turns when no stress is exerted on it. In the assembled state, a first end of the hairspring, called the first turn on the inside, is attached to a collet fitted to a balance staff, and a second end of the hairspring, called the last turn on the outside, is attached to a stud, which is a part generally attached by means of a stud holder in a balance bridge, also called a balance cock.

[0003] More specifically, the time base for mechanical timepieces, also called an oscillating system, comprises a balance-spring assembly and an escapement. The balance consists of a balance staff pivoted between a first and a second bearing and connected to a balance rim by means of radial arms. The balance spring is attached via its first coil on the inside to the balance staff, for example by means of a collet, and it is attached via its last coil on the outside to a fixed attachment point such as a stud carried by a stud holder.

[0004] As for the escapement, in a very widespread embodiment, it comprises a double-plate system consisting of a large plate which carries a plate pin and a small plate in which a notch is formed. The escapement also comprises an anchor whose anchor rod is pivoted between a first and a second bearing. The anchor consists of a rod which connects a fork to an input arm and an output arm. The fork consists of an input horn and an output horn and carries a pin. The travel of the fork is limited by an input limiting pin and an output limiting pin which can be made in one piece with an anchor bridge. The input arm and the output arm carry an input pallet and an output pallet respectively.Finally, the anchor cooperates with an escapement wheel comprising an escape wheel and an escape pinion, this assembly formed by the wheel and the escape pinion being pivoted between a first and a second bearing.

[0005] A hairspring is a spring that, as its name suggests, takes the form of a spiral when at rest. Wound in a plane parallel to the plane of the clockwork, the hairspring serves only one function: to make the balance wheel oscillate around its equilibrium position, also called dead center, at the most constant frequency possible. When the balance wheel leaves its equilibrium position by pivoting in a given direction, the hairspring contracts. This creates a restoring torque in the hairspring that has the effect of returning the balance wheel to its equilibrium position. During this beat, the hairspring relaxes. However, as the balance wheel has acquired a certain speed, and therefore kinetic energy, it passes its equilibrium position in the opposite direction to the previous one until the restoring torque exerted by the hairspring on the balance wheel stops the latter again and forces it to rotate in the other direction.

[0006] The hairspring therefore relaxes and contracts alternately: it is said to breathe. However, many factors contribute to preventing a hairspring from developing isochronously during the expansion and contraction phases. In particular, the hairspring must resist oxidation and magnetism, which stick the coils together and tend to disrupt the accuracy of the watch, or even stop it completely. The influence of atmospheric pressure, on the other hand, is weak. For a long time, temperature was the heart of the problem, because heat expands the metal, while cold shrinks it. The hairspring must also be elastic to deform and yet always return to its shape.

[0007] The material used to make spiral springs is usually steel. Ductile, the steel used must be corrosion-resistant. For two decades now, developments have also been made to make spiral springs from silicon. Silicon spiral springs, particularly because they are insensitive to magnetism, allow for greater operating precision than their steel predecessors. However, their cost is higher and, being fragile, they are more difficult to assemble.

[0008] A balance spring must be isochronous. No matter how far the balance wheel rotates, it must always take the same amount of time to oscillate. If the balance spring contracts by only a few degrees, it stores little energy and returns slowly to its equilibrium position. If the balance spring is moved far from its equilibrium position, it moves very quickly in the opposite direction. The important thing is that these two movements take the same amount of time. The underlying idea is that the energy available to the balance spring is not constant and that it must still function whether the watch is fully wound or is in its last hours of power reserve.

[0009] Due to their small size, hairsprings are difficult to assemble. However, the way in which the two ends of a hairspring are attached also greatly influences the rate accuracy of the watch movement. In most mechanical watch movements, the two ends of the hairspring are inserted into a drilled part and are immobilized by means of a pin manually forced in place using pliers. This can cause the hairspring to rotate slightly, which is detrimental to the rate accuracy of the movement.

[0010] Another technique is to fix the ends of the spiral springs using glue. However, this technique has also shown its limitations. It has been observed that due to its viscosity, the glue exerts a tensile force on the spiral spring by capillarity and can press the ends of the spiral spring against the walls of the stud in which these ends are engaged. The resulting deformation of the spiral spring induces mechanical stresses in it which are detrimental to the regularity of its operation.

[0011] To overcome these problems, the Applicant has already proposed a method for fixing a hairspring consisting of gluing the last coil to the outside of a hairspring in a stud using a drop of fluid glue which can be polymerized, for example, by means of ultraviolet radiation. Thus, even if, at the time of depositing the drop of glue, for example using a syringe-type glue dispenser, the free end of the last coil of the hairspring moves a little under the effect of the weight of the drop of glue, which induces unwanted mechanical stresses in the hairspring, the glue is, before hardening, sufficiently fluid to allow the free end of the last coil of the hairspring to spontaneously return to its rest position.The mechanical stresses induced in the spiral spring at the time of depositing the drop of liquid glue therefore disappear by themselves, so that the regularity of the running of the spiral spring is not affected by the operation of gluing the latter.

[0012] The above solution thus makes it possible to fix a hairspring by the free end of its last coil on the outside in a stud, eliminating completely or at least for the most part the mechanical stresses which are usually induced in such a hairspring during its assembly. The regularity of operation of the hairspring is thus greatly improved. In use, the Applicant has nevertheless realized that the hardened glue dot formed when the drop of liquid glue used to fix the free end of the last coil to the outside of the hairspring polymerizes sometimes tends to separate from the stud, which, of course, leads to the immediate breakdown of the clockwork movement in which this hairspring is installed. Such a situation is notably due to problems with the surface condition of the stud which prevent the glue dot from adhering perfectly to the stud as well as to the creep and aging of the glue dot over time.Furthermore, when the ambient temperature increases, most glues soften, which has the effect of changing the active length, and therefore the stiffness of the hairspring, and therefore negatively influencing the running of the clockwork movement.

[0013] Finally, it should be noted that, particularly in the case of high-end watch movements, the use of glues or synthetic products that are hardly compatible with the high degree of finishing and know-how required by such watch movements is avoided as much as possible.

[0014] European patent application EP1515200A1 discloses a hairspring for a balance-spring assembly of a mechanical watch movement, a free end of a last coil on the outside of which has an opening capable of elastically deforming to receive and tighten a fixing element of the stud type. Preferably, the fixing element has a cylindrical shape with a circular section comprising flats with which the free end of the last coil on the outside of the hairspring is in contact to prevent this free end from rotating around the fixing element during operation of the movement. The fixing element makes it possible to fix the free end of the last coil to the outside of the hairspring, avoiding the use of auxiliary fixing means such as pins or glue.On the other hand, by adjusting the position of the free end of the last coil on the outside of the balance spring relative to the fixing element, it is possible to adjust the height of this free end on the fixing element. This is made possible by the fact that the free end of the last coil on the outside of the balance spring is frictionally engaged on the fixing element. This is however problematic because there is a risk that in the event of an impact, for example, the free end of the last coil on the outside will change position relative to its fixing element, or even become detached from this fixing element, which at best will impair the accuracy of the balance-spring assembly or, at worst, cause the timepiece to fail.It may also be noted that since the attachment of the last coil to the outside of the spiral spring is ensured by the friction forces which arise from the elastic contact between the opening provided in the free end of the last coil to the outside of the spiral spring and the fixing element, this does not guarantee the truly durable nature of the spiral spring to the extent that, with time and wear, these friction forces will tend to relax, so that the friction forces between the edges of the opening provided in the free end of the last coil to the outside of the spiral spring and the fixing element quickly become insufficient to guarantee the immobilization of the spiral spring on this fixing element. Summary of the invention

[0015] The present invention aims to overcome the problems mentioned above and others by providing a mechanical assembly allowing the perfectly reliable fixing of a spiral spring for a watch movement without elastic deformation of the last coil on the outside and without the use of glue, thanks to which the spiral spring can, if necessary, be disassembled and then reassembled without risk of damaging it.

[0016] To this end, the present invention relates to an assembly for the removable attachment of a spiral spring of a watch movement comprising a balance bridge, this assembly comprising the spiral spring on the one hand, a means for retaining the spiral spring and a removable locking part on the other hand, the spiral spring comprising a winding of turns which extends between a first free end of a first turn on the inside and a second free end of a last turn on the outside, the second free end of the last turn on the outside of the spiral spring comprising an attachment means in which the retaining means is engaged to ensure the removable attachment of the spiral spring by its last turn on the outside, the attachment means being dimensioned so that, in its natural rest position, the spiral spring is not in contact with the retaining means engaged in this attachment means,the locking part for ensuring the removable fixing of the second free end of the last coil outside the spiral spring being mounted on the retaining means, to lock the attachment means.,

[0017] According to a particular embodiment of the invention, the attachment means is an opening provided in the second free end of the last coil outside the spiral spring.

[0018] According to a particular embodiment of the invention, the second free end of the last coil outside the spiral spring in which the opening is formed is made in one piece with the entire spiral spring.

[0019] According to another particular embodiment of the invention, the opening is formed by a curved portion of the second free end of the last coil outside the spiral spring.

[0020] According to yet another particular embodiment of the invention, the second free end of the last coil outside the spiral spring is provided with a plate in which the opening is formed.

[0021] According to yet another particular embodiment of the invention, the plate is secured to the second free end of the last coil outside the spiral spring.

[0022] According to yet another particular embodiment of the invention, the plate is fixed by welding to the second free end of the last coil outside the spiral spring.

[0023] According to yet another embodiment of the invention, the opening is oblong in shape.

[0024] According to yet another embodiment of the invention, the oblong opening has a major axis in the extension of the last turn on the outside.

[0025] According to yet another particular embodiment of the invention, the retaining means comprises a tenon arranged to engage in the opening provided in the second free end of the last coil outside the spiral spring.

[0026] According to yet another particular embodiment of the invention, the tenon is made in one piece with the balance bridge of the clockwork movement.

[0027] According to yet another particular embodiment of the invention, the retaining means comprises a support piece formed from a stud surmounted by the tenon.

[0028] According to yet another particular embodiment of the invention, the support piece is arranged in a housing provided in the balance bridge.

[0029] According to yet another particular embodiment of the invention, the support piece is arranged in the greasy friction housing.

[0030] According to yet another particular embodiment of the invention, the support piece is screwed into the housing.

[0031] According to yet another particular embodiment of the invention, to prevent untimely unscrewing of the support piece, a holding piece is arranged between the balance bridge and the support piece.

[0032] According to yet another particular embodiment of the invention, the holding part is a spring-effect washer.

[0033] According to yet another embodiment of the invention, the locking part is a washer fixed to the tenon in a removable manner.

[0034] According to yet another embodiment of the invention, the washer is driven onto the tenon.

[0035] According to yet another particular embodiment of the invention, a flexible element arranged to modify the stiffness of the spiral spring is arranged between the second free end of the last coil outside the spiral spring and a lever bypassing the winding of coils and ending in a plate in which the opening is formed.

[0036] The invention also relates to a method for adjusting the rate of a balance-spring assembly fixed by means of the fixing assembly according to the invention, in which the attachment means comprised by the second free end of the last coil outside the balance spring is engaged on the tenon of the support piece, the support piece being, if necessary, pivoted in one direction or the other until the tenon is no longer in contact with the attachment means of the balance spring, after which the reference mark of the balance-spring assembly is adjusted by pivoting this balance-spring assembly around the balance staff until the pin of the balance plate is aligned with an escapement line passing through the balance staff and an anchor staff, then, once the reference mark of the balance-spring assembly has been adjusted, it is ensured once again that the tenon of the support piece is not in contact with the attachment means of the spiral spring and, if so,the support piece is turned again so as to move the tenon away from the means of attachment of the spiral spring, then the removable locking piece is fixed on the tenon to lock the second free end of the last coil outside the spiral spring.

[0037] The invention also relates to a method for adjusting the rate of a balance-spring assembly whose balance spring is fixed by means of the fixing assembly according to the invention, in which, after fixing the removable locking piece on the tenon to block the second free end of the last coil outside the balance spring, the support piece is pivoted clockwise or counterclockwise, thereby driving the second free end of the last coil outside the balance spring.

[0038] Thanks to these characteristics, the present invention provides an assembly making it possible to fix a spiral spring of a watch movement without the aid of glue, in a removable, repositionable manner, while guaranteeing the immobilization of the free end of the last coil outside the spiral spring without inducing mechanical stress in this spiral spring, in particular in a plane in which the winding of the coils of this spiral spring extends, so that the regularity of operation of the watch movement is not affected. Brief description of the figures

[0039] Other characteristics and advantages of the present invention will emerge more clearly from the following detailed description of an embodiment, this example being given purely for illustrative and non-limiting purposes only, in conjunction with the appended drawing in which: there figure 1is a general perspective view of an assembly for the removable attachment of a spiral spring of a clockwork movement in its simplified execution variant; figure 2 is a general perspective view of an assembly for the removable attachment of a spiral spring of a clockwork movement in its improved execution variant; figure 3 is a top view of a silicon spiral spring including first and second flexible arms for use in the attachment assembly of the figure 2 ; there figure 4 is a perspective view of a spiral spring whose last turn on the outside is provided with a plate made from the same material and in which the opening is made to receive the tenon; the Figure 5 is a perspective view of a spiral spring provided with a plate attached to the free end of the last coil on the outside of this spiral spring and in which the opening is provided to receive the tenon; figure 6 is a perspective view of a spiral spring whose last coil on the outside is curved to form the opening receiving the tenon; the figure 7 is a schematic view which illustrates the case in which the tenon is made of a single piece with the balance bridge of the clockwork movement; the figure 8 is a schematic view which illustrates the case in which the retaining means comprises a support piece formed of a stud surmounted by a tenon and arranged with greasy friction in a housing provided in the balance bridge; figure 9 illustrates the case in which the retaining means comprises a support piece formed from a stud surmounted by a tenon and arranged in a housing made in the balance bridge by screwing with the interposition of a washer between the balance bridge and the support piece to prevent any untimely unscrewing; figure 10is a perspective view of a spiral spring whose last coil on the outside is curved to form a hook receiving the tenon; the Figures 11 and 12 illustrate respectively in the assembled state and in the dissociated state the case in which the retaining means is arranged in the manner of a support piece arranged in a housing provided in the balance bridge, the last coil outside the balance spring being capped by a locking piece provided with a tenon which is received in an opening provided in the support piece. Detailed description of the invention

[0040] The present invention proceeds from the general inventive idea which consists of providing a mechanical assembly allowing the fixing without glue of the second free end of the last coil to the outside of a hairspring for a balance-spring assembly of a watch movement. By making it possible to do without the use of glue, the present invention makes it possible to avoid the problems linked to such materials, in particular in terms of aging and creep, as well as in terms of image; indeed, in particular in the field of high-end watch parts, it is understood that one will seek as much as possible to avoid having to resort to assemblies of mechanical parts ensured by means of glue.According to another of its advantages, the mechanical assembly according to the invention allows the second free end of the last coil to be fixed to the outside of the balance spring in a removable manner, whereby the positioning of the balance spring can be readjusted if necessary when the timepiece is returned to the workshop. According to yet another of its advantages, the mechanical assembly according to the invention allows the second free end of the last coil to be fixed to the outside of a balance spring for a watch movement without inducing mechanical stress in this second end, in particular in the plane in which the winding of coils which forms the balance spring extends, which is very favorable with regard to the running accuracy of the balance-spring assembly.

[0041] Designated as a whole by the general numerical reference 1, the fixing assembly according to the invention is intended for the removable fixing of a spiral spring 2 of a clockwork movement comprising a balance bridge 4.

[0042] More precisely, and as visible on the figure 1 , this fixing assembly 1 comprises, in addition to the spiral spring 2, a retaining means 8 as well as a removable locking part 10.

[0043] As it emerges from the figure 1, the spiral spring 2 comprises a winding of turns 12 which extends between a first free end 14 of a first turn on the inside 16 and a second free end 18 of a last turn on the outside 20. According to the invention, the second free end 18 of the last turn on the outside 20 of the spiral spring 2 comprises an attachment means which, in a preferred and non-limiting embodiment of the invention, is in the form of an opening 22 in which the retaining means 8 is engaged to ensure the removable fixing of the spiral spring 2 by its last turn on the outside 20. The opening 22 is dimensioned so that, in the natural rest position of the spiral spring 2, the edges 24 of this opening 22 are not in contact with the mechanical fixing means 8 engaged in this opening 22.In this way, the fixing of the spiral spring 2 by means of the fixing assembly 1 according to the invention does not induce in this spiral spring 2 any stress in an XY plane in which the spiral spring 2 extends, and therefore has no influence on the precision of the operation. As for the removable locking part 10, intended to ensure the removable fixing of the second free end 18 of the last coil to the outside 20 of the spiral spring 2, it is engaged, preferably by driving, on the retaining means 8, following the spiral spring 2.

[0044] According to a special embodiment of the invention, the opening 22 provided in the second free end 18 of the last outer coil 20 of the spiral spring 2 is preferably but not exclusively oblong in shape, with a major axis 26 which extends in the extension of the last outer coil 20 (see figure 3 ).

[0045] In the embodiments illustrated in figures 4 to 6 , the opening 22 is oblong in shape with a radius of curvature R centered on the center 27 of the winding of turns 12.

[0046] The opening 22 can be materialized according to different forms of execution.

[0047] According to one embodiment of the invention, the second free end 18 of the last outer coil 20 of the spiral spring 2 in which the opening 22 is formed is made in one piece with the entire spiral spring 2. The last outer coil 20 of the spiral spring 2 can thus be provided with a plate 28 made of the same material and in which the opening 22 is formed ( Figure 4 ). Conversely, the plate 28 can be attached to the second free end 18 of the last coil on the outside 20 of the spiral spring 2, for example by joining such as welding ( Figure 5). It is also possible to form the opening 22 by means of a curved portion 30 of the second free end 18 of the last coil on the outside 20 of the spiral spring 2 ( Figure 6 ).

[0048] The retaining means 8 comprises a tenon 32 arranged to engage in the opening 22 formed in the second free end 18 of the last coil on the outside 20 of the spiral spring 2.

[0049] According to a first embodiment, the tenon 32 is made in one piece with the balance bridge 4 of the clockwork movement ( Figure 7 ).

[0050] According to another embodiment of the invention, the retaining means 8 comprises a support piece 34 formed by a stud 36 surmounted by the tenon 32. This support piece 34 is arranged in a housing 38 formed in the balance bridge 4. The support piece 34 is arranged in the housing 38 either with greasy friction ( figure 8 ), or by screwing ( figure 9). In the case where the support piece 34 is screwed into the housing 38, the support piece 34 is externally threaded and the housing 38 is provided with a complementary thread on an internal side wall 40. To prevent accidental unscrewing of the support piece 34, a holding piece 42 such as a spring washer may be arranged between the balance bridge 4 and the support piece 34 ( Figure 9 ).

[0051] The removable locking part 10 is a washer fixed to the tenon 32 in a removable manner, typically by driving it out.

[0052] In its simplified embodiment, the fixing assembly 1 according to the invention allows the adjustment of the reference mark of a balance-spring assembly 44. Furthermore, in its preferred embodiment, the fixing assembly 1 according to the invention allows not only the adjustment of the reference mark of the balance-spring assembly 44, but also the adjustment of the rate of such a balance-spring assembly 44.

[0053] As already described above, the assembly of the fixing assembly 1 according to the invention begins by engaging the opening 22 provided in the second free end 18 of the last coil on the outside 20 of the hairspring 2 on the tenon 32 of the support piece 34. Normally, the entire mechanical assembly formed by the hairspring 2, the balance-spring assembly 44 equipped with such a hairspring 2 and the retaining means 8 is dimensioned so that, when the tenon 32 of the support piece 34 is engaged in the opening 22 of the hairspring 2, the edges 24 of the opening 22 of the hairspring 2 are not in contact with the tenon 32 engaged in this opening 22. In the rare event that this is not the case, however, the present invention advantageously allows the support piece 34 to be pivoted slightly in one direction or in the other. the other until the tenon 32 is no longer in contact with the edges 24 of the opening 22 of the spiral spring 2.After which, the reference mark of the balance-spring assembly 44 is adjusted by pivoting this balance-spring assembly 44 around a balance staff 46 until a pin 48 of a balance plate 50 is aligned with an escapement line passing through the balance staff 46 and an anchor staff (not shown in the drawing). Once the reference mark of the balance-spring assembly 44 has been adjusted, it is again ensured that the tenon 32 of the support piece 34 is not in contact with the edges 24 of the opening 22 of the hairspring 2; as previously, in the extremely rare event that this should not be the case, the present invention makes it possible to turn the support piece 34 again so as to move the tenon 32 away from the edges 24 of the opening 22 of the spiral spring 2, then to drive the washer onto the tenon 32 to block the second free end 18 of the last coil on the outside 20 of the spiral spring 2.Otherwise, that is to say if no contact is observed between the edges 24 of the opening 22 of the spiral spring 2 and the tenon 32 of the support piece 34, the spiral spring 2 can be directly blocked by fixing the washer on the tenon 32.

[0054] It will of course be understood that the support piece 34 cannot be pivoted if it is made of one piece with the balance bridge 4.

[0055] In the preferred embodiment of the invention illustrated in perspective in figure 2, it is possible not only to adjust the reference of the balance-spring assembly 44, but also to adjust the rate of this balance-spring assembly 44. The operation of adjusting the rate of the balance-spring assembly 44 occurs after the second free end 18 of the last coil on the outside 20 of the hairspring 2 has been blocked by fixing the washer on the tenon 32. At this moment, the support piece 34 is pivoted clockwise or counterclockwise, thereby driving the second free end 18 of the last coil on the outside 20 of the hairspring 2.

[0056] More precisely, we see in fact at the figure 3that the spiral spring 2 comprises a flexible element 52 which consists of a pivot 54 comprising first and second uncrossed flexible blades 56, 58 and a rigid part 60. The first and second flexible blades 56, 58 are joined, on the one hand laterally to an elongated fixed support 62, and on the other hand to the pivot 54 by approaching each other. Thus, the flexible blades 56, 58 move closer from the fixed support 62 to the pivot 54. The fixed support 62 is attached to a fixing part 62a secured to the bridge 4. The second free end 18 of the last outer turn 20 of the balance spring 2 is joined to the pivot 54. In the figure, the variable torque is applied to an additional blade 63 which connects the last outer turn 20 to the rigid part 60, so that the stiffness of this additional blade is modified and, therefore, the stiffness of the balance spring 2 and therefore the rate of the balance-spring assembly 44.For this purpose, the spiral spring 2 is extended, beyond its flexible element 52, by a lever 64 bypassing the coil winding 12 and terminated by a plate 28 in which the opening 22 according to the invention is provided. Via the lever 64 and the flexible element 52, the torque is transmitted to the spiral spring 2. For a complete description of the spiral spring 2 used in the context of this improved embodiment of the present invention, reference should be made to European patent application EP21202213.1 in the name of the Applicant.

[0057] It goes without saying that the present invention is not limited to the embodiment which has just been described and that various simple modifications and variants can be envisaged by those skilled in the art without departing from the scope of the invention as defined by the appended claims.

[0058] The tenon 32 can be made in one piece with the balance bridge 4. In the case where the support piece 34 is a separate piece mounted by greasy driving in a housing 38 machined in the balance bridge 4, it can be pivoted in the clockwise or counterclockwise direction. By pivoting the support piece 34, the tenon 32 is likewise pivoted, so that this tenon 32 is in no way in contact with the edges 24 of the contour of the opening 22 made in the free end 18 of the last coil on the outside 20 of the balance spring 2. The balance spring 2 can thus spontaneously place itself in its natural rest position, free from any mechanical stress, which is the most favorable solution for the running precision of the balance-spring assembly 44.

[0059] Generally speaking, the spiral springs 2, in particular when they are made of silicon, are manufactured with very strict tolerances, so that the position of the geometric center of the opening 22 made in the free end 18 of the last coil on the outside 20 of the spiral spring 2 is known in advance very precisely, which makes it possible to precisely position the tenon 32 on the balance bridge 4, or the support piece 34 corresponding to the assembly formed by the stud 36 and the tenon 32 in the housing 38 provided for this purpose in the balance bridge 4.

[0060] In the case where the spiral spring 2 is made of silicon, the free end 18 of the last coil on the outside 20 of the spiral spring 2 in which the opening 22 is formed is made in one piece with the whole of the spiral spring 2. In the case where the spiral spring 2 is made of a metal alloy, the opening 22 intended to receive the tenon 32 of the support piece 34 can be formed by simply bending the free end 18 of the last coil on the outside 20 of the spiral spring 2. It is also possible to envisage fixing, typically by welding, on the free end 18 of the last coil on the outside 20 of the spiral spring 2, a plate 28 in which an opening 22 is formed to receive the tenon 32 of the support piece 34.

[0061] In the extremely rare case where, after fitting the hairspring 2 and engaging the tenon 32 in the opening 22 formed in the free end 18 of the last coil on the outside 20 of the hairspring 2, it is observed that the edges 24 of this opening 22 come into mechanical contact with the tenon 32 at any location, the present invention advantageously makes it possible to pivot the support piece 34 until no more mechanical contact can be observed. Thus, whatever the circumstances, the present invention makes it possible to guarantee immobilization of the free end 18 of the last coil on the outside 20 of the hairspring 2 without any stress being induced in the XY plane in which the hairspring 2 extends, which is very favorable for the running precision of the balance-hairspring assembly 44.

[0062] In the simplified variant of the invention, there is a single point of attachment of the free end 18 of the last coil on the outside 20 of the spiral spring 2, namely the tenon 32 of the support piece 34 engaged in the opening 22 formed in the free end 18 of the last coil on the outside 20 of the spiral spring 2 which plays the role of a stud and only the reference of the balance-spring assembly 44 can therefore be adjusted.

[0063] In the improved embodiment of the invention, there are two attachment points and the balance spring 2 is preferably made of silicon; in this case, there are two attachment points and both the reference mark and the rate of the balance-spring assembly 44 can be adjusted. Furthermore, it is understood that, thanks to the invention, the rate of the balance-spring assembly 44 can be finely adjusted in different ways: by modifying the inertia of the balance, for example, by adding or removing material, or by screwing or unscrewing weights. It is also possible to adjust the rate of the balance-spring assembly 44 by modifying the stiffness of the balance spring 2 according to the invention. Some balance-spring assemblies can even be adjusted in both ways at the same time.

[0064] The stud 36 of the support piece 34 can be threaded to allow fine adjustment of the height along a Z axis perpendicular to the support surface provided by the support piece 34. To prevent the threaded support piece 34 from unscrewing involuntarily, it is possible to provide a holding piece 42, for example of the elastic washer type, between the threaded support piece 34 and the surface of the balance bridge 4 in order to block the threaded stud 36. Thanks to the invention, by modifying the stiffness of the balance spring 2 fixed on the balance staff 46 by means of a collet 66, it is possible to adjust the rate of the balance-spring assembly 44, which is much simpler than adjusting the rate of a balance-spring assembly by modifying the inertia of the balance, for example by adding or removing material, or by means of weights, or screws, etc. that are moved.

[0065] According to a special embodiment of the invention illustrated in the figure 10, the attachment means may have an open geometry, for example shaped as a hook 68, in which the retaining means 8 is engaged to ensure the removable fixing of the spiral spring 2 by its last turn to the outside 20. This fixing means 8 of the type of a tenon 32 is arranged in the interior space delimited by the hook 68 and held in place by the holding part 42. Normally, when putting the spiral spring 2 in place, no mechanical contact should be observed between the hook 68 and the tenon 32. If this were not the case, however, it would be possible to pivot the support part 34 until no more mechanical contact can be observed.

[0066] According to a special embodiment of the invention, the retaining means 8 comprises a support piece 70 arranged in a housing 72 formed in the balance bridge 4. The support piece 70 is arranged in the housing 72 either by greasy friction or by screwing. The free end 18 of the last coil on the outside 20 of the balance spring 2 comes to bear on this support piece 70 and is capped by a blocking piece 74 provided, on the underside, with a tenon 76 which is received in an opening 78 formed in the support piece 70. Nomenclature

[0067] 1. Fixing assembly 2. Hairspring 4. Balance bridge 8. Retaining means 10. Removable locking piece 12. Winding of coils 14. First free end 16. First coil inside 18. Second free end 20. Last coil outside 22. Opening 24. Edges 26. Major axis 27. Center 28. Plate 30. Curved portion 32. Tenon 34. Support piece 36. Stud 38. Housing 40. Inner side wall 42. Holding piece 44. Balance-hairspring assembly 46. Balance staff 48. Pin 50. Balance plate 52. Flexible element 54. Pivot 56. First Flexible blade 58.Second flexible blade 60.Rigid part 62.Fixed support 62a.Fixing piece 63.Additional blade 64.Lever 66.Ferrule 68.Hook 70.Support piece 72.Housing 74.Locking piece 76.Tenon 78.Opening

Claims

1. Assembly (1) for the removable attachment of a spiral spring (2) of a timepiece movement comprising a balance bridge (4), this assembly comprising the spiral spring (2) on the one hand, a retaining means (8) for the spiral spring (2), as well as a removable locking part (10) on the other hand, the spiral spring (2) comprising a winding of turns (12) which extends between a first free end (14) of a first turn on the inside (16) and a second free end (18) of a last turn on the outside (20), the second free end (18) of the last turn on the outside (20) of the spiral spring (2) comprising an attachment means in which the retaining means (8) is engaged to ensure the removable attachment of the spiral spring (2) by its last turn on the outside (20), the attachment means being dimensioned so that, in its natural rest position, the attachment means is not in contact with the retaining means (8) engaged in this attachment means,the locking part (10) for ensuring the removable fixing of the second free end (18) of the last coil to the outside (20) of the spiral spring (2) being mounted on the retaining means (8) for locking the attachment means, ., 2. Fixing assembly (1) of a spiral spring (2) according to claim 1, characterized in that the attachment means is an opening (22) provided in the second free end (18) of the last coil on the outside (20) of the spiral spring (2).

3. Fixing assembly (1) of a spiral spring (2) according to claim 2, characterized in that the opening (22) is oblong in shape and has a major axis (26) in the extension of the last turn on the outside (20).

4. Fixing assembly (1) of a spiral spring (2) according to claim 1, characterized in thatthe second free end (18) of the last coil on the outside (20) of the spiral spring (2) in which the opening (22) is formed is made in one piece with the entire spiral spring (2).

5. Fixing assembly (1) of a spiral spring (2) according to claim 1, characterized in that the opening (22) is formed by a curved portion (30) of the second free end (18) of the last coil on the outside (20) of the spiral spring (2).

6. Fixing assembly (1) of a spiral spring (2) according to claim 1, characterized in that the second free end (18) of the last coil on the outside (20) of the spiral spring (2) is provided with a plate (28) in which the opening (22) is formed.

7. Fixing assembly (1) of a spiral spring (2) according to claim 6, characterized in that the plate (28) is secured to the second free end (18) of the last coil on the outside (20) of the spiral spring (2).

8. Fixing assembly (1) of a spiral spring (2) according to claim 7, characterized in that the plate (28) is fixed by welding on the second free end (18) of the last coil on the outside (20) of the spiral spring (2).

9. Fixing assembly (1) of a spiral spring (2) according to one of claims 1 to 8, characterized in that the retaining means (8) comprises a tenon (32; 76) arranged to engage in the opening (22) provided in the second free end (18) of the last coil on the outside (20) of the spiral spring (2).

10. Fixing assembly (1) of a spiral spring (2) according to claim 9, characterized in that the tenon (32) is made in one piece with the balance bridge (4) of the clockwork movement.

11. Fixing assembly (1) of a spiral spring (2) according to claim 9, characterized in that the retaining means (8) comprises a support piece (34) formed of a stud (36) surmounted by the tenon (32).

12. Fixing assembly (1) of a spiral spring (2) according to claim 11, characterized in that the support piece (34) is arranged in a housing (38) provided in the balance bridge (4).

13. Fixing assembly (1) of a spiral spring (2) according to claim 12, characterized in that the support piece (34) is arranged in the housing (38) with greasy friction.

14. Fixing assembly (1) of a spiral spring (2) according to claim 12, characterized in that the support piece (34) is screwed into the housing (38).

15. Fixing assembly (1) of a spiral spring (2) according to claim 14, characterized in that , to prevent accidental unscrewing of the support piece (34), a holding piece (42) is arranged between the balance bridge (4) and the support piece (34).

16. Fixing assembly (1) of a spiral spring (2) according to claim 15, characterized in that the retaining part (42) is a spring washer.

17. Fixing assembly (1) of a spiral spring (2) according to one of claims 9 to 16, characterized in that the locking part (10) is a washer fixed on the tenon (32) in a removable manner.

18. A spiral spring fixing assembly according to claim 17, characterized in that the washer is driven onto the tenon (32).

19. Fastening assembly according to claim 9, characterized in that the retaining means (8) comprises a support piece (70) arranged in a housing (72) provided in the balance bridge (4) and capped by a locking piece (74) provided with a tenon (76) which is received in an opening (78) provided in the support piece (70).

20. A spiral spring fixing assembly according to one of claims 1 to 19, characterized in thata flexible element (52) arranged to modify the stiffness of the spiral spring (2) is arranged between the second free end of the last coil outside the spiral spring and a lever (64) bypassing the winding of coils (12) and in a free end of which the opening (22) is provided.

21. Method for adjusting the reference mark of a balance-spring assembly comprising a balance spring (2) fixed by means of the fixing assembly according to one of claims 1 to 9 and 11 to 20, in which the attachment means comprised by the second free end (18) of the last coil on the outside (20) of the balance spring (2) is engaged on the tenon (32) of the support piece (34), the support piece (34) being, if necessary, pivoted in one direction or the other until the tenon (32) is no longer in contact with the attachment means of the balance spring (2), after which the reference mark of the balance-spring assembly (44) is adjusted by pivoting this balance-spring assembly (44) about a balance shaft (46) until the pin (48) of the balance plate (50) is aligned with a escapement line passing through the balance shaft and an anchor shaft, then, once the balance-spring assembly mark (44) has been adjusted,it is ensured that the tenon (32) of the support piece (34) is not again in contact with the means of attachment of the spiral spring (2) and, if this is the case, the support piece (34) is turned again so as to move the tenon (32) away from the means of attachment of the spiral spring (2), then the removable locking piece (10) is driven onto the tenon (32) to lock the second free end (18) of the last coil outside (20) of the spiral spring (2)., 22. Method for adjusting the rate of a balance-spring assembly (44) whose balance spring is fixed by means of the fixing assembly according to one of claims 1 to 20, in which, after driving the removable locking piece (10) onto the tenon (32) to lock the second free end (18) of the last coil outside (20) of the balance spring (2), the support piece (34) is pivoted clockwise or counterclockwise, thereby driving the second free end (18) of the last coil outside (20) of the balance spring (2).

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