Search

EP-4741947-A1 - HAIRSPRING FOR CLOCK RESONATOR

EP4741947A1EP 4741947 A1EP4741947 A1EP 4741947A1EP-4741947-A1

Abstract

The spiral for a watch resonator according to the invention comprises a ferrule (2) having a geometric axis (A) and an integer number N, greater than or equal to 2, of coplanar elastic blades (3, 4) wound in spirals from and around the ferrule (2) and extending to external extremities (7, 8). The N elastic blades (3, 4) are arranged with rotational symmetry of order N about the geometric axis (A). The spiral is characterized in that, for each of the elastic blades (3, 4), on at least a portion of the blade extending from a first point located on the second turn of the blade counted from the ferrule (2) to a second point (11, 12) located on the outer turn of the blade, the stiffness of the blade is constant and the pitch is increasing, and on a portion (9, 10) of the outer turn of the blade located between the second point (11, 12) and the outer end (7, 8) of the blade, the stiffness of the blade is greater than on said portion of the blade, this portion (9, 10) of the outer turn being arranged to make the development of the blade more concentric during the oscillations of the spiral.

Inventors

  • Chabloz, David
  • SAROUFIM, Elie

Assignees

  • PATEK PHILIPPE SA GENEVE

Dates

Publication Date
20260513
Application Date
20241107

Claims (13)

  1. Spiral (1; 1';1") for a clockwork resonator, comprising a ferrule (2) having a geometric axis (A) and an integer number N, greater than or equal to 2, of coplanar elastic blades (3, 4) wound in spirals from and around the ferrule (2) and extending to external extremities (7, 8), the N elastic blades (3, 4) being arranged according to a rotational symmetry of order N about the geometric axis (A), characterized in that , for each of the elastic blades (3, 4): - on at least a portion of the blade extending from a first point located on the second turn of the blade counted from the ferrule (2) to a second point (11, 12; 13, 14; 15, 16) located on the outer turn of the blade, the rigidity of the blade is constant and the pitch is increasing, - on a portion (9, 10) of the outer loop of the blade located between the second point (11, 12; 13, 14; 15, 16) and the outer end (7, 8) of the blade, the rigidity of the blade is greater than on said portion of the blade, this portion (9, 10) of the outer loop being arranged to make the development of the blade more concentric during the oscillations of the spiral.
  2. Spiral (1; 1") according to claim 1, characterized in that the pitch has a first constant value over at least several complete turns counted from the first point.
  3. Spiral (1; 1") according to claim 2, characterized in that the pitch has the first constant value also of the ferrule (2) at the first point.
  4. Spiral (1) according to claim 2 or 3, characterized in that the pitch has a second constant value, greater than the first constant value, on at least one complete turn after said several complete turns counted from the first point.
  5. Spiral (1) according to claim 4, characterized in that the pitch has the second constant value at least up to the second point (11, 12).
  6. Spiral (1") according to claim 2 or 3, characterized in that the pitch is strictly increasing at least over several complete turns after said several complete turns counted from the first point and at least up to the second point (15, 16).
  7. Spiral (1') according to claim 1, characterized in that the pitch is strictly increasing at least on said portion of the blade.
  8. Spiral (1') according to claim 7, characterized in that the pitch is strictly increasing at least from the ferrule (2) to the second point (13, 14).
  9. Spiral (1; 1';1") according to any one of claims 1 to 8, characterized in that the pitch is increasing at least from the ferrule (2) to the second point (11, 12; 13, 14; 15, 16).
  10. Spiral (1; 1';1") according to any one of claims 1 to 9, characterized in that the rigidity of the blade is constant at least from the ferrule (2) to the second point (11, 12; 13, 14; 15, 16).
  11. Spiral (1; 1';1") according to any one of claims 1 to 10, characterized in that the second point (11, 12; 13, 14; 15, 16) is located in the two-thirds of the outermost turn closest to the outer end (7, 8), preferably in the half of the outermost turn closest to the outer end (7, 8), in angular length measured from the geometric axis (A).
  12. Clock resonator comprising a balance wheel and a balance spring (1; 1'; 1") according to any one of claims 1 to 11.
  13. Timepiece comprising a clockwork resonator according to claim 12.

Description

The present invention relates to a spiral, or spiral spring, for a watch resonator, that is to say a spiral intended to serve as a return spring for a balance wheel of a watch part. In a mechanical timepiece, the balance wheel and hairspring assembly is the timekeeping base. The balance wheel oscillates at a specific frequency, being periodically returned to an equilibrium position by the hairspring. Its oscillations are sustained by an escapement. The oscillation frequency of the balance wheel depends on its moment of inertia and the stiffness of the hairspring. Thus, to obtain the desired frequency, a balance wheel with a specific moment of inertia is paired with a hairspring of a specific stiffness during assembly, an operation called "matching." It is known that the development of a classic balance spring (in the shape of an Archimedean spiral) during the oscillations of the balance wheel is eccentric. In other words, the center of gravity of the balance spring shifts during the oscillations of the balance wheel. This affects the accuracy of the resonator. Indeed, the eccentric development generates lateral forces between the pivots of the balance staff and the bearings in which they rotate, lateral forces that vary according to the amplitude of oscillation and modify the frequency. Furthermore, the eccentric development adds a perturbation in the vertical positions, related to the weight of the balance spring and the shifts in the center of gravity. This perturbation also varies with the amplitude of oscillation and differs depending on the vertical position of the resonator. Several solutions have been proposed to make the development of a balance spring more concentric, namely equipping the spring with a terminal curve that extends beyond the plane of the spring to bring the center of gravity back onto the axis of rotation (Breguet spring), and stiffening a portion of the outer coil of the spring (patent). EP 1473604 ) or vary the rigidity and pitch of the spiral along its blade (patent EP 2299336 These solutions make it possible to reduce, but not eliminate, the eccentricity of the spiral's development. Other solutions do not aim to make the spiral concentric but rather to compensate for the lateral forces exerted by the spiral on the balance staff by superimposing another identical spiral wound in the opposite direction or offset by 180° onto the spiral. The patent FR 2447571 This describes an arrangement in which the two balance springs are Breguet springs offset by 180°. Mounting two superimposed balance springs on the balance staff produces forces or bending moments on the latter that do not cancel each other out. Furthermore, matching the balance wheel to achieve the desired frequency is difficult because it requires managing the combination of two stiffnesses. Finally, the superposition of two balance springs, like the terminal curve of a Breguet spring, increases the overall height of the resonator. The drawbacks of the two-superimposed spiral arrangement have been resolved in the prior art by replacing the two spirals with a double-planar spiral made of two identical coplanar blades wound one inside the other and offset by 180°, or more generally with a multiple-planar spiral comprising N coplanar blades wound one inside the other and arranged with rotational symmetry of order N. Examples of such double or multiple spirals can be found in patents. CH 700812 And EP 2154583 in particular. The difficulty, however, with these spirals is ensuring that the different blades do not touch during the spiral's development. For this, the patent EP 2154583 Two solutions are proposed. One, in the context of a double spiral, consists of placing the points where the outer ends of the two blades are fixed outside the plane of the spiral so that the blades form two symmetrical cones on either side of the spiral plane, which negates most of the advantages of the double spiral. The other proposed solution, for a double or multiple spiral, consists of varying the pitch of the turns and the blade thickness along the entire length of each blade. Varying the blade thickness modifies the stiffness of the spiral, which requires a significant increase in the external diameter of the spiral, making it impossible to create a compact resonator. The present invention aims to remedy, at least in part, the aforementioned drawbacks of the prior art, and to this end provides a spiral according to claim 1, a watch resonator according to claim 12 and a watch part according to claim 13. Particular embodiments are defined in the dependent claims. Other features and advantages of the present invention will become apparent from the following detailed description, made with reference to the accompanying drawings, in which: there figure 1 represents a spiral according to a first embodiment of the invention; there figure 2 represents a spiral according to a second embodiment of the invention; there figure 3 represents a spiral accor