Clock spiral spring

Abstract

The present invention relates to a spiral spring (1) intended to be associated with a balance wheel in a regulating organ of a watch movement and comprising a series of equidistant turns formed by a blade wound upon itself between a first inner turn (2) and a last outer turn (6). The blade has a variable cross-section chosen such that the equation ∂s∂l=C∂α∂l is satisfied at each point along the blade from at least the beginning of the third turn to at least the end of the antepenultimate turn, where ∂s∂l is the linear flexibility of the blade, C is a constant, ∂α∂l is the curvature of the blade at rest as a function of the length l of the blade, α is the winding angle at the length l of the blade. The present invention also relates to a regulating organ comprising a balance wheel and such a spiral spring (1), as well as a timepiece comprising such a spiral spring (1) or such a regulating organ.

Description

technical field

[0001] The present invention relates to a spiral spring intended to be associated with a balance wheel in a regulating organ of a watch movement and comprising a series of equidistant turns, formed by a blade wound on itself between a first inner turn, intended to be solid to a ferrule itself solid to the axis of the balance wheel, and a last outer turn, intended to be solid to a stud itself solid to the cock.

[0002] The present invention also relates to a regulating organ comprising a balance wheel and such a spiral spring, as well as a timepiece comprising such a spiral spring or such a regulating organ. State of the art

[0003] The balance spring used in watchmaking, in conjunction with a balance wheel to form the regulating organ of a watch, is an essential component, as the balance spring is primarily responsible for the accuracy of a mechanical watch movement. Consequently, balance springs have been the subject of extensive research and development. It has long been established that the flat balance spring, whether in the form of an Archimedean spiral or an involute of a circle, with a constant pitch, has the disadvantage of developing eccentrically during its expansion and contraction. In particular, balance springs are predominantly of constant cross-section, regardless of their constituent materials. A constant torque applied to such balance springs results in a curvature that is also constant at every point.Thus, the strong curvature of the inner coil and the weak curvature of the outer coil are both credited with the same additional curvature. The inner coil is therefore relatively undeformed compared to the outer coil. The outer coils of a constant-section balance spring tend to move closer together or further apart when the spring is contracting or expanding, respectively. Given their minimal relative deformation, the inner coils, on the other hand, tend to maintain their almost constant distance.

[0004] The significant deformation of the outer coils would cause a substantial displacement of the outer end of the balance spring if it were not attached to the stud. However, it is attached to the stud, resulting in a significant eccentricity in the balance spring's development. Conversely, the slight deformation of the inner coils would cause a minimal displacement of the inner end of the balance spring if it were not fixed to the ferrule. Its attachment to the ferrule results in a considerably smaller eccentricity than that caused by the outer end being fixed to the stud. This eccentricity of the balance spring disrupts the balance wheel's operation.

[0005] To achieve concentric development, a balance spring with a constant cross-section requires significant modification to its outer coil to compensate for the substantial displacement of the outer end, while the inner coils require less modification, or even none at all. Several known solutions have already been proposed to minimize the eccentricity of the balance spring's development. These include raised Breguet or Philips terminal curves, as well as Michel angles on the outer coil to compensate for the significant deformation of the outer coils. There are also less common solutions to compensate for the slight deformation of the inner coils. These include Grossmann curves and Michel angles on the inner coil.

[0006] It is therefore necessary to propose a new spiral spring for which the contraction and expansion under constant torque are better distributed between the two ends of said spiral spring so that the internal and external coils require adjustments of similar magnitude, or possibly no adjustments at all. Disclosure of the invention

[0007] For this purpose, the invention relates to a spiral spring intended to be associated with a balance wheel in a regulating organ of a watch movement and comprising a series of equidistant turns, formed by a blade wound on itself between a first inner turn and a last outer turn.

[0008] According to the invention, said blade has a variable cross-section chosen such that the equation ∂ s ∂ l = C ∂ α ∂ l is satisfied at each point along the blade from at least the beginning of the third turn to at least the end of the antepenultimate turn, Or ∂ s ∂ l is the linear flexibility of the blade, C is a constant ∂ α ∂ l is the curvature of the blade at rest as a function of length l of the blade, α is the winding angle to the length l of the blade.

[0009] By choosing a linear flexibility proportional to the curvature of the spiral spring according to the invention, the shape of said spiral spring subjected to a homogeneous torque is advantageously always an involute of a circle. Its pitch decreases or increases depending on the direction of the applied torque, but it remains constant along the entire length of the coil. Consequently, the inner coils move apart and together at exactly the same rate as the outer coils. Thus, the contraction and expansion of the spiral spring of the invention under constant torque are advantageously better distributed between the two ends of said spiral spring.

[0010] The present invention also relates to a regulating organ comprising a balance wheel and a spiral spring as defined above.

[0011] The present invention also relates to a timepiece comprising a regulating organ or a spiral spring as defined above. Brief description of the drawings

[0012] Other features and advantages of the present invention will become apparent from the following detailed description of various embodiments of the invention, given by way of non-limiting examples, and made with reference to the accompanying drawings in which: there figure 1 is a schematic plan view of a spiral spring according to an embodiment of the invention, in its rest position; the figure 2 is a curve that represents the thickness (h) of the blade as a function of the length ( l ) of the blade for a preferred embodiment of the invention; the figures 3 to 5are plan views of a spiral spring according to other embodiments of the invention, in its rest position; figures 6a to 6c represent a spiral spring of constant cross-section respectively at rest, in expansion and in contraction, the displacements at the ferrule and the stud being highlighted; and the figures 7a to 7c represent a spiral spring of variable section according to the invention respectively at rest, in expansion and in contraction, the displacements at the ferrule and the pin being highlighted. Embodiments of the invention

[0013] With reference to the figure 1The present invention relates to a spiral spring 1 intended to be associated with a balance wheel in a regulating organ of a watch movement. The spiral spring 1 comprises a series of turns formed by a single blade wound on itself between a first inner turn 2, the free end 2a of which is intended to be fixed to a ferrule 4, which is itself fixed to the balance staff (not shown), and a final outer turn 6, the free end 6a of which is intended to be fixed to a stud 8, itself fixed to the balance cock or bridge (not shown).

[0014] The spiral spring 1 is in the shape of an undeformed involute of a circle when at rest, so that its pitch is represented on the figure 1 is constant or substantially constant. The turns are therefore equidistant, with the possible exception of the first and last turns, as will be described in more detail below.

[0015] The spiral spring 1 can be made of various suitable materials, preferably materials whose rigidity is substantially insensitive to temperature variations, such as silicon-based materials.

[0016] The blade has a cross-section, preferably rectangular, of height b and thickness corresponding to the dimension represented by the reference h on the figure 1 .

[0017] According to the present invention, the blade has a variable cross-section chosen such that the equation ∂ s ∂ l = C ∂ α ∂ l is satisfied at each point along the blade from at least the beginning 10a of the third turn 10 to at least the end 12a of the antepenultimate turn 12, starting from the center towards the outside of the spiral 1, Or ∂ s ∂ l is the linear flexibility of the blade, C is a constant, ∂ α ∂ l is the curvature of the blade at rest as a function of length lof the blade, α is the winding angle to the length l of the blade.

[0018] An example of calculating the constant C will be described below.

[0019] The linear flexibility of the blade is defined as follows: a blade of length L of any shape is subject only to a couple M (without applying force F). Then the relationship between the torque Met and the angular deflection Θ The length of the blade is given by: M = KΘ , Or K is rigidity (or stiffness).

[0020] For a blade with constant inertia cross-section and (isotropic) Young's modulus E, The rigidity is given by: K = EI L .

[0021] Conversely, we have Θ = S . M , S = L EI , Or S is the flexibility or compliance of the blade.

[0022] An element of infinitesimal length dl the blade is subjected to a bending moment µdue, for example, to a couple, a force F is put. µ is then the sum of the torque and the moment of the force at the point considered. The length element will then undergo an infinitesimal angular deflection d ϑ given by dϑ = dsμ Or ds is the (infinitesimal) flexibility of the length element dl. For an infinitesimal flexibility varying according to the curvilinear abscissa l From the blade, we can write: ds = ∂ s ∂ l dl Or ∂ s ∂ l is linear flexibility. The integration of linear flexibility between two curvilinear abscissas l 1, l 2 gives the flexibility of the blade segment delimited by the two abscissas. In particular, the integration of the curvilinear abscissa over the entire length of the blade gives ∫ 0 L dl ∂ s ∂ l = S , that is, the flexibility of the blade.

[0023] Linear flexibility allows for the introduction at each point l of the blade a specific inertia section I ( l), possibly a modulus of elasticity E ( l ) also variable. Linear flexibility then becomes ∂ s ∂ l = 1 EI l

[0024] More generally, one can disregard the material(s) composing the blade and choose a linear flexibility. ∂ s ∂ l l as needed.

[0025] In summary, given a linear flexibility blade ∂ s ∂ l l subjected to a bending moment µ ( l Given, then its angular deflection at any point is given by the differential equation ∂ ϑ ∂ l = ∂ s ∂ l μ l , the solution ϑ of the differential equation fully defining the shape of the deformed blade.

[0026] To determine C , according to the invention, we have equality ∂ s ∂ l = C ∂ α ∂ l .

[0027] By integrating along the entire length of the spiral spring, we have s2 - s 1 = C(α2 - α1), where S2 is the linear flexibility for the winding angle α2 and s 1 is the linear flexibility for the winding angle α 1 , with α 2 - α 1 = 2π N,N being the number of turns of winding of the spiral spring between its two ends.

[0028] And on the other hand, s 2 − s 1 = S = 1 K = 1 Jω 2 where S is the flexibility of the spiral, i.e., the inverse of its rigidity K = Jω 2< , J being the inertia of the pendulum and ω its angular frequency. We therefore obtain the expression C = 1 2 πJNω 2 as a constant governing the proportionality between curvature and linear flexibility, in accordance with the invention.

[0029] The variable linear flexibility of the blade according to the invention can be obtained at least by a variation of the thickness h of the blade, a variation of the height of the blade, and a local variation of the elastic modulus of the material of the blade.

[0030] In the case where the blade material is homogeneous and isotropic or substantially homogeneous and isotropic, the linear flexibility as defined above is such that ∂ s ∂ l = 1 E I Or E is the Young's modulus of the blade material and I is the inertia of the blade section, with I = bh 3 12 Or b is the height of the blade and h is the thickness of the blade.

[0031] For this reason ∂ s ∂ l = 12 Ebh 3

[0032] Furthermore, for a spiral spring at rest in the shape of an involute of a circle, its winding angle α as a function of its length l (or its curvilinear abscissa) is given by α l = 2 l a where a is the radius of the developed circle. The derivative of the winding angle with respect to the length, i.e., the curvature of the spring at rest, is given by ∂ α ∂ l = 1 2 al = a α

[0033] However, according to the invention ∂ s ∂ l = C ∂ α ∂ l

[0034] Therefore, 12 Ebh 3 = C a α

[0035] Hence h = 12 α abCE 1 3

[0036] Hence h = 12 2 l a abCE 1 3 = 12 2 a abCE 1 3 . l 1 6

[0037] Therefore, in a preferred embodiment in which the blade material is homogeneous and isotropic or substantially homogeneous and isotropic, the variable section of the blade is obtained by a variation in the thickness h of the blade, said thickness h varying along the blade proportionally to the sixth root of the length l of the blade, as depicted on the figure 2 .

[0038] According to a first embodiment, the blade can have a variable cross-section chosen such that the equation ∂ s ∂ l = C ∂ α ∂ l is satisfied at every point along the entire length of the blade. This means that the blade does not include any cross-sectional area larger or smaller than the cross-sectional areas of the blade on either side of said larger or smaller cross-sectional area, as shown in the figure 1 For example.

[0039] According to other embodiments, the spiral spring according to the invention has, on at least one of its inner 2 and outer 6 coils, an eccentricity correction feature, such as at least one local softening zone, a zone of increased stiffness, or a specific terminal curve. Preferably, the inner 2 and outer 6 coils each have an eccentricity correction feature.

[0040] More specifically, according to another embodiment, and with reference to the figure 3 The blade can have a variable cross-section chosen so that the equation ∂ s ∂ l = C ∂ α ∂ l is satisfied at every point along the entire length of the blade, at least with the exception of the inner turn 2 and / or the outer turn 6, which have an eccentricity correction feature, namely a zone of increased stiffness Ci, Ce respectively, whose cross-section is larger than the cross-section of the blade in the vicinity of said zone of increased stiffness Ci, Ce. This means that a zone of increased stiffness Ci, Ce has a stiffness greater than, or even much greater than, the stiffness of the areas of the blade on either side of said zone of increased stiffness Ci, Ce. Such zones of increased stiffness Ci, Ce constitute angles. Such angles were proposed by Messrs. Emile and Gaston Michel and are known to those skilled in the art. For example, the zone of increased stiffness Ci begins at approximately 60° from the end 2a intended to be fixed to the ferrule 4 of the first turn 2 and extends over a spiral segment with an angle of approximately 60°.The increased stiffness zone Ce starts at approximately 45° from the end 6a intended to be fixed to the pin of the last turn 6 and extends over a spiral segment with an angle of approximately -90°, as shown on the . figure 3 The spiral spring 1 having a variable section according to the invention can comprise either an angle bracket Ci on its inner coil 2, or an angle bracket Ce on its outer coil 6, or preferably an angle bracket Ci on its inner coil 2 and an angle bracket Ce on its outer coil 6.

[0041] According to another embodiment, and with reference to the figure 4 The blade can have a variable cross-section chosen so that the equation ∂ s ∂ l = C ∂ α ∂ l is satisfied at every point along the entire length of the blade, at least with the exception of an eccentricity correction feature, namely at least one local easing zone provided on at least one of the turns, said at least one local easing zone having a cross-section smaller than the blade cross-section in the vicinity of said local easing zone. This means that a local easing zone has a cross-section smaller than the cross-sections of the blade zones on either side of said local easing zone.

[0042] Preferably, said at least one local softening zone extends over a spiral segment with an angle Δα between approximately 8° and 100°, and preferably less than approximately 90°.

[0043] Preferably, said at least one local softening zone has a thickness (h) between 0.5H and 0.9H, where H is the thickness of the blade in the vicinity of said at least one local softening zone.

[0044] Advantageously, the number of local relaxation zones is between 1 and 4, and is preferably equal to 4.

[0045] Said at least one local slackening zone may be provided on at least one of the first, second, penultimate and last turns.

[0046] More in particular, said at least one local easing zone may be provided centered at ¾ turn of the first inner turn 2 from its free end 2a, then possibly at ¾ turn of the last outer turn 6 from its free end 6a, then possibly at 5 / 4 turn of the last outer turn 6 from its free end 6a, ¾ turn of the first inner turn 2 from its free end 2a and / or at 5 / 4 turn of the first inner turn 2 from its free end 2a.

[0047] In a preferred embodiment, the spiral spring blade 1 has a variable cross-section according to the invention and comprises a first local softening zone e1 centered approximately ¾ of a turn from the last outer coil 6 of its free end 6a, a second local softening zone e2 centered approximately ¾ of a turn from the first inner coil 2 of its free end 2a, a third local softening zone e3 centered approximately 5 / 4 of a turn from the last outer coil 6 of its free end 6a, and a fourth local softening zone e4 centered approximately 5 / 4 of a turn from the first inner coil 2 of its free end 2a, as shown in the figure 4 .

[0048] In other embodiments not shown, the blade includes only the first two and second local softening zones e1, e2 or only the first two and third local softening zones e1, e3.

[0049] It is specified that, throughout this description, the position indicated for the local softening zones is the position indicated when the spiral spring is at rest, the blade being undeformed.

[0050] Local softening zones can correspond to rectangular notches formed equally on either side of the spiral spring leaf 1, or to other shapes. More generally, a local softening zone can be defined as a more or less abrupt decrease in the leaf thickness followed by a substantially constant thickness, and finally a more or less abrupt increase in thickness until it returns to a thickness substantially equal to the initial thickness. Furthermore, local softening zones can be created indifferently, notably by thinning the leaf, symmetrically on either side of the leaf as shown in the diagram. figure 4, or only on one side or the other of the blade, or even distributed asymmetrically on either side of said blade.

[0051] Advantageously, in order to guarantee no contact between the coils of the spiral spring 1 during its contraction and expansion, it is possible to slightly modify the first inner coil 2 and / or the last outer coil 6 by providing bends (cf. figure 4For example, it is possible to provide on the outer coil 6 at least one bend C0 positioned approximately 1 / 4 turn from its free end 6a and a bend C1 at the level of the first local flexibility zone e1. Another bend C3 can be provided at the level of said third local flexibility zone e3. Similarly, the blade can have, on its first coil 2, at least one bend C5 positioned approximately 1 / 4 turn from its free end 2a and a bend C2 at the level of the second local flexibility zone e2. Another bend C4 can be provided at said fourth local flexibility zone e4.

[0052] According to other embodiments, it is possible to provide, as an eccentricity correction feature, a specific terminal curve on the inner and / or outer coil. Thus, the spiral spring 1, which is shown flat on the Figures 1 , 3 And 4The outer coil 6 may not be flat, as it may have a raised terminal curve of the Breguet or Philips type. This specific terminal curve constitutes an eccentricity correction feature. It is also possible to provide an inner Grossmann curve on the inner coil, this specific terminal curve also constituting an eccentricity correction feature. The balance spring 1, having a variable cross-section according to the invention, may comprise either an inner Grossmann curve on its inner coil 2, or a raised terminal curve of the Breguet or Philips type on its outer coil 6, or both, as shown in the figure. figure 5 .

[0053] All the different embodiments of eccentricity correction arrangements described above can be combined with the variable-section spiral spring according to the invention. Preferably, only one type of eccentricity correction arrangement is provided for each of the inner 2 and outer 6 coils. Thus, the spiral spring 1 according to the invention has a variable section as defined above and can have, on its inner coil 2, one or two local softening zones e2, e4 or an increased stiffness zone Ci or an inner Grossmann curve, and on its outer coil 6, one or two local softening zones e1, e3 or an increased stiffness zone Ce or a raised terminal curve of the Breguet or Philipps type.For example, the spiral spring 1 according to the invention has a variable section as defined above and may further have areas of local softening on its inner coil 2 and outer coil 6, or areas of local softening on its inner coil 2 and an area of ​​increased stiffness Ce on its outer coil 6, or areas of local softening on its inner coil 2 and a raised terminal curve on its outer coil 6, or an area of ​​increased stiffness Ci on its inner coil 2 and areas of local softening on its outer coil 6, or an inner Grossmann curve on its inner coil 2 and areas of local softening on its outer coil 6, etc.

[0054] With reference to Figures 6 and 7 , are represented the behavior of a spiral spring with a constant cross-section from the prior art ( figures 6a to 6c ) and the behavior of a spiral spring with a variable cross-section according to the invention ( figures 7a to 7c ).

[0055] On the figures 6a and 7aThe radial displacement of end 2a of the inner coil 2, intended to be fixed to the ferrule, and the radial displacement of end 6a of the outer coil 6, intended to be fixed to the pin, of a spiral spring with a constant cross-section and / or variable cross-section, respectively, subjected to a constant torque, are shown. For the spiral spring with a constant cross-section shown in the figure 6a The displacement of end 2a is small and the displacement of end 6a is large. For the spiral spring with variable cross-section according to the invention, the displacement of end 2a is increased and the displacement of end 6a is decreased.

[0056] THE figures 6b and 7b represent the constant section spiral spring of the figure 6a , respectively the spiral spring with variable cross-section according to the invention of the figure 7a, in expansion (one turn). It is observed that the coils of the spiral spring with constant section tend to spread out more on the outside than on the inside, whereas those of the spiral spring with variable section according to the invention remain equidistant.

[0057] THE figures 6c and 7c represent the constant section spiral spring of the figure 6a , respectively the spiral spring with variable cross-section according to the invention of the figure 7a , in contraction (one turn). It is observed that the outer coils of the spiral spring with constant section tend to get closer together than the inner coils, whereas the coils of the spiral spring with variable section according to the invention are again equidistant.

[0058] The spiral spring of the invention advantageously always has the shape of an involute of a circle when subjected to a constant torque. Its pitch decreases or increases depending on the direction of the applied torque, but it remains constant along the entire length of the blade. Consequently, the inner coils move apart and together at exactly the same rate as the outer coils. Furthermore, the trajectory of the end of the spiral spring intended to be fixed to the pin is advantageously shorter than that of a similar spiral spring with a constant cross-section. Thus, the spiral spring of the invention exhibits an eccentricity that is better distributed between its inner and outer ends. This advantageously allows, where necessary, for the provision of eccentricity correction features on the inner and outer coils, such as angle brackets, specific raised curves, or localized flexing zones, which are of similar magnitude.

Claims

1. Spiral spring (1) intended to be associated with a balance wheel in a regulating organ of a watch movement and comprising a series of equidistant turns formed by a blade wound on itself between a first inner turn (2) and a last outer turn (6), characterized in that the blade has a variable cross-section chosen such that the equation ∂ s ∂ l = C ∂ α ∂ l is satisfied at each point along the blade from at least the beginning (10a) of the third turn (10) to at least the end (12a) of the antepenultimate turn (12), where ∂ s ∂ l is the linear flexibility of the blade, C is a constant, ∂ α ∂ l is the curvature of the blade at rest as a function of length l of the blade, α is the winding angle to the length l of the blade.

2. Spiral spring according to claim 1, characterized in that the blade has a variable cross-section chosen such that the equation ∂ s ∂ l = C ∂ α ∂ l is satisfied at each point along the entire length of the blade at least with the exception of the inner turn (2) and / or the outer turn (6) which have an increased stiffness zone (Ci, Ce) whose section is greater than the section of the blade in the vicinity of said increased stiffness zone (Ci, Ce).

3. Spiral spring according to one of claims 1 and 2, characterized in that the blade has a variable cross-section chosen such that the equation ∂ s ∂ l = C ∂ α ∂ l is satisfied at each point along the entire length of the blade at least with the exception of at least one local easing zone (e1, e2, e3, e4) provided on at least one of the turns, said at least one local easing zone (e1, e2, e3, e4) having a cross-section smaller than the cross-section of the blade in the vicinity of said local easing zone (e1, e2, e3, e4).

4. Spiral spring according to claim 3, characterized in thatsaid at least one local easing zone (e1, e2, e3, e4) is provided on at least one of the first, second, penultimate and last turns.

5. Spiral spring according to any one of claims 3 to 4, characterized in that said at least one local easing zone (e1, e2, e3, e4) extends over a spiral segment with an angle Δ α between approximately 8° and 100°, and preferably less than approximately 90°.

6. Spiral spring according to any one of claims 3 to 5, characterized in that said at least one local softening zone (e1, e2, e3, e4) has a thickness (h) between 0.5H and 0.9H, where H is the thickness of the blade in the vicinity of said at least one local softening zone (e1, e2, e3, e4).

7. Spiral spring according to any one of claims 3 to 6, characterized in that The number of local relaxation zones (e1, e2, e3, e4) is between 1 and 4, and is preferably equal to 4.

8. Spiral spring according to any one of claims 3 to 7, characterized in that said at least one local easing zone (e1, e2, e3, e4) is provided centered at at least one of the positions chosen from among 3 / 4 turn of the last outer turn (6) from its free end (6a), 5 / 4 turn of the last outer turn (6) from its free end (6a), 3 / 4 turn of the first inner turn (2) from its free end (2a), and 5 / 4 turn of the first inner turn (2) from its free end (2a).

9. Spiral spring according to claim 1, characterized in that the blade has a variable cross-section chosen such that the equation ∂ s ∂ l = C ∂ α ∂ l is satisfied at every point along the entire length of the blade.

10. Spiral spring according to any one of claims 1 to 9, characterized in thatThe variable linear flexibility of the blade is obtained at least by a variation in the thickness (h) of the blade, a variation in the height of the blade, and a local variation in the elastic modulus of the material of the blade.

11. Spiral spring according to any one of claims 1 to 10, characterized in that the blade material is homogeneous and isotropic or substantially homogeneous and isotropic, so that the linear flexibility is such that ∂ s ∂ l = 1 E I Or E is the Young's modulus of the blade material and I is the inertia of the blade section.

12. Spiral spring according to claim 11, characterized in that the variable section of the blade is obtained by a variation in the thickness (h) of the blade, said thickness (h) varying along the blade proportionally to the sixth root of the length ( l ) of the blade.

13. Spiral spring according to any one of the preceding claims, characterized in thatthe blade has at least one bend (C0, C1, C2, C3, C4, C5).

14. Regulator comprising a balance wheel and a spiral spring according to any one of claims 1 to 13.

15. Watch movement comprising a regulating organ according to claim 14 or a balance spring according to any one of claims 1 to 13.

16. Timepiece comprising a watch movement according to claim 15 or a regulating organ according to claim 14 or a balance spring according to any one of claims 1 to 13.

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