Method for producing friction by leasing

Abstract

Method of making a tube (1) for a friction system comprising the tube (1) and a shaft (2), in particular a tube intended to rub around a shaft pinion, the method comprising a first step of plastic deformation of the tube, in particular a first step of controlled plastic deformation of the tube, and then a second step of hardening the tube, in particular hardening by heat treatment.

Description

[0001] The invention relates to a method for producing a tube for a friction system. It also relates to a method for producing friction between a shaft and such a tube. It further relates to a tube for producing such friction. It further relates to an assembly producing such friction. It further relates to a movement comprising such a tube or such an assembly. Finally, it relates to a timepiece, in particular a wristwatch, comprising such a tube or such an assembly or such a movement.

[0002] The driving of the hands or discs allowing the time display on a watch is generally done by means of a cannon-pinion, which is pinched and then driven onto a tiger-pinion of a central pinion. The pinching creates two bumps in the tube or barrel of the cannon-pinion which come into contact with the tiger-pinion and thus ensure, by friction of the bumps on the tiger-pinion, the transmission of the rotation of the central pinion to the cannon-pinion in normal operating mode for displaying the time.

[0003] Adjusting the diameter of the tang and the distance between the bosses ensures the transmission of a torque allowing the rotation of the minute hand. The higher this torque, the better the hands will behave in the event of shocks. In time setting mode, the rotation of the stem causes the rotation of the cannon pinion via a correction mechanism, which slides on the center pinion to position the hand in the correct place relative to the dial.

[0004] Such a structure, a roadway - central gable, constitutes, for example, a lantern.

[0005] Too high a friction torque results in a difficult adjustment feeling and also causes wear of the lantern.

[0006] It is therefore necessary that the torque transmitted by the cannon be large enough to avoid untimely slipping of the hands, but not too large so as to obtain a qualitative sensation when setting the time.

[0007] For reasons related to the materials and dimensions of the parts, it is difficult to obtain high friction torques for an internal cannon pinion diameter of around 0.3 to 1 mm with cannon pins manufactured in a traditional manner. This torque is sufficient for conventional needles, but the use of precious metal needles or large needles requires a higher tightening torque to ensure their retention, particularly in the event of impacts.

[0008] When attempting to make larger bumps to increase the torque, the material cracks and the results are uneven. It is therefore not possible to guarantee the resistance, particularly the resistance to shocks, of high inertia needles without cracking the road surface during the lantern operation.

[0009] Traditionally, the lantern operation is carried out by pinching the constriction of a tube of the cannon pinion opposite a bearing or clearance of the tigeron. This pinching is a manual task, and its result depends on the dexterity and sensitivity of the watchmaker, and is therefore random. This is inconvenient because, as seen previously, the lantern operation is intended to ensure a certain level of friction between the tigeron and the cannon pinion during normal operation of the watch in order to display the time, while manual time-setting operations by the user apply a torque greater than that of friction. The friction torque must therefore not be too high.

[0010] Correct adjustment of the friction torque is therefore delicate. Furthermore, the road surface is a fragile component, and re-fitting a lantern after dismantling often results in deterioration requiring replacement of the road surface.

[0011] Precise control of the applied clamping force is therefore important, and conventional manual clamping does not achieve this precision or the required reproducibility.

[0012] In document CH129931, the cannon-pinion is adjusted with a greasy friction on the shaft of the minute pinion, which generally has a groove ("lantern notch") to accommodate two bulges generated in the wall of the cannon-pinion. Sufficient quality of such an assembly can only be ensured by pairing the cannon-pinion and the center pinion so that the lantern is perfectly adjusted, otherwise the cannon-pinion will wobble and the hands will move unexpectedly. Document CH129931 presents a solution that has become traditional, consisting of using a pinion with a support cone ensuring the centering of the cannon-pinion on the center pinion before lantern fitting.

[0013] The lanterning of the cannon-pinion is therefore a traditional method which requires skill on the part of the watchmaker who must sometimes rework the cannon-pinion to adapt it to the pinion, or perfect mastery of the geometries or torques obtained in the case of more industrial productions.

[0014] Functional tolerances are small, as are the nominal dimensions of the components. Any change in a dimension potentially leads to a malfunction of the system, and in industrial production, it is necessary to pair batches of roadways and gables that are dimensionally compatible before assembly. This leads to significant logistical constraints.

[0015] The cannon pinion is traditionally machined from free-cutting steel (20AP or Finemac) and then hardened by heat treatment according to the supplier's specifications to achieve a hardness of 550±50 HV. This hardness represents a compromise to allow both the cannon pinion to deform without cracking during the lanterning stage and the maintenance of the torque over time. The material is put into a metallurgical state allowing the lanterning to be corrected by the watchmaker until the correct torque is obtained.

[0016] This hardening heat treatment has the effect, in addition to increasing the hardness of the road surface to make it more resistant to wear, of increasing elastic return and reducing elongation at break. However, it only changes the dimensions of the road surface in a negligible way, even on a watchmaking scale.

[0017] Given the industrial manufacturing tolerances of the carriageways and center gables, batches of carriageways must be matched with batches of center gables, so as to ensure dimensional correspondence.

[0018] The lantern stage generates a narrowing of the internal diameter of the roadway along an axis located in the plane perpendicular to the axis of the roadway, to bring the distance between bumps to a chosen theoretical value.

[0019] The parts are then assembled on the movement: the cannon pinion is driven onto the center pinion and the two bosses made during the previous step are slightly elastically separated during insertion onto the pinion, then are housed in a groove or on a cone made on the pinion, and ensure the relative positioning of the two parts along the axis of the cannon pinion, as well as the relative maintenance of the two parts in rotation up to a friction torque defined by the geometry and rigidity of the parts.

[0020] This torque is checked or measured and, if it is not sufficient, the road surface is removed and changed, or pinched again.

[0021] The material characteristics of the two components are respectively a hardness of 550±50 HV for the road surface and 650±50 HV for the pinion, both in 20AP steel.

[0022] Document EP2881803 describes a recent alternative to lantern work obtained using a shape memory alloy ring intended to tighten the roadway around the king pin. The ring is widened at low temperature (martensitic state), placed opposite the roadway area and then heated to achieve the austenitic structure allowing it to tighten and the controlled retention of the roadway on the king pin.

[0023] Document CH41140 presents a longitudinally split barrel roadway to facilitate the insertion of the roadway onto the center gable. A circular rim created on the lower part of the roadway fits into a groove located between the bearing surfaces of the center gable.

[0024] There are several problems with the known state-of-the-art solutions. First, the typical torques measured on traditionally produced pavements are limited and a high torque could only be obtained by dimensional changes, which are not always possible due to the respective dimensions of the components and the mechanical properties of the material.

[0025] Then, the control of the lantern torque is not industrializable with the known processes without resorting to pairings, because the torque depends very precisely on the internal diameters of the roadway and external diameters of the center pinion. The machining tolerances and the additional dispersion induced by the heat treatment then the pinching are such that it is necessary to pair batches to guarantee a friction torque within the required tolerances. Even with such pairing, the standard deviation of the torques measured on sets of at least 500 tubes assembled on 500 shafts is of the order of 0.3 to 0.35 mNm.

[0026] The aim of the invention is to provide a lantern friction device making it possible to overcome the drawbacks mentioned above and to improve the devices known from the prior art. In particular, the invention proposes a simple, reliable and reproducible friction device and a method for producing such a device.

[0027] According to a first aspect, a method according to the invention is defined by claim 1.

[0028] Different modes of carrying out the method are defined by claims 2 to 7.

[0029] According to a first aspect, a tube according to the invention is defined by claim 8.

[0030] According to a first aspect, a set of tubes according to the invention is defined by claim 9.

[0031] According to a first aspect, an assembly according to the invention is defined by claim 10.

[0032] Different embodiments of the assembly are defined by claims 11 and 12.

[0033] According to a first aspect, a watch movement according to the invention is defined by claim 13.

[0034] According to a first aspect, a timepiece according to the invention is defined by claim 14.

[0035] According to a first aspect, equipment according to the invention is defined by claim 15.

[0036] Various embodiments of the equipment are defined by claims 16 to 18.

[0037] According to a second aspect, the invention is defined by the following propositions. 1. Method for producing a tube (1) for a friction system comprising the tube (1) and a shaft (2), in particular a tube intended to rub around a shafted pinion, the method comprising a first step of plastic deformation of the tube, in particular a first step of plastic deformation of the tube controlled in deformation, then a second step of hardening the tube, in particular hardening by heat treatment. 2. Method for producing a tube (1) for a friction system comprising the tube and a shaft (2), in particular a tube intended to rub around a shafted pinion, the method comprising a step of plastic deformation of the tube, controlled in deformation, the deformation step being carried out on a portion of the tube in the annealed state and / or whose elastic limit is less than 1000 MPa and / or whose hardness is less than 400 HV or less than 350 HV. 3.Method according to one of the propositions 1 and 2, characterized in that the tube is a tube of a roadway or a clutch element and / or a torque limiter element. 4. Method according to one of the propositions 1 to 3, characterized in that the deformation step is carried out by pinching the tube. 5. Method according to one of the propositions 1 to 4, characterized in that the deformation step is carried out on a tube made of 20AP alloy or Finemac alloy having a hardness less than or equal to 400 Hv, or even less than or equal to 350 Hv. 6. Method according to one of the propositions 1 to 5, characterized in that the deformation step is controlled by optical measurement of the deformation or by a template placed in the tube during the deformation step or by passing gauges. 7. Method according to one of proposals 1 to 6, characterized in that the deformation is carried out on a portion of the tube whose elongation at break is greater than or equal to 2%, or even greater than or equal to 3%. 8.Tube (1), in particular a roadway, in particular a lantern roadway, obtained by implementing the method according to one of propositions 1 to 7. 9. Set of at least 500 tubes (1) according to proposition 8, the standard deviation of the diameters of the circles centered on the axes (A) and inscribed in the cross sections of the tubes at the level of the tops of the bumps being less than 0.2 micrometers. 10. Assembly (3), in particular a center-roadway pinion assembly, comprising a shaft and a tube according to proposition 8. 11. Assembly (3) according to proposition 10, characterized in that the friction torque between the shaft (2) and the tube (1) is greater than or equal to 1.8 mNm, or even greater than or equal to 2.0 mNm. 12. Assembly (3) according to proposition 10 or 11, characterized in that the diameter of the shaft is less than or equal to 2 mm, or even less than or equal to 1 mm. 13. Watch movement (100), comprising a tube (1) according to proposition 8 and / or an assembly according to one of propositions 10 to 12. 14.Timepiece (200), in particular wristwatch, comprising a movement (100) according to proposition 13 and / or a tube according to proposition 8 and / or an assembly according to one of propositions 10 to 12.

[0038] The attached figure represents, as an example, an embodiment of a timepiece.

[0039] There figure 1 is a diagram of an embodiment of a timepiece.

[0040] An embodiment of a timepiece 200 according to the invention is described below with reference to the figure 1 . The timepiece is for example a watch or a wristwatch. The timepiece may comprise a watch movement 100, in particular a mechanical watch movement, in particular automatic, or electronic. The timepiece may also comprise a watch assembly, in particular a watch case intended to contain the movement.

[0041] The movement comprises an assembly 3 or a friction system 3 comprising a shaft 2 and a tube 1. The shaft is housed in the tube 1. For example, the tube 1 is a cannon or a cannon shaft and the shaft 2 is a center pinion, in particular a shafted center pinion.

[0042] The shaft 2 and the tube 1 each have diameters D which are equal to the ready functional clearance which allows the tube 1 to slide freely relative to the shaft 2 along an axis A and which allows the tube to rotate freely relative to the shaft 2 around the axis A. The diameters D are for example between 0.3 mm and 2 mm, or even between 0.6 mm and 1 mm. Preferably, the diameters D are less than or equal to 2 mm, or even less than or equal to 1 mm.

[0043] The assembly comprises a lantern, that is to say that the shaft 2 and / or the tube further comprise particular conformations 11, 21 in order to create friction between the tube and the shaft 2.

[0044] The shaft 2 includes a tapered groove or clearance 21.

[0045] The tube comprises at least one hump 11 or at least one hump, preferably two, three or four humps made in the same plane P perpendicular to the axis A or at least substantially in the same plane P perpendicular to the axis A. Preferably, the hump(s) are made in a portion 12 of lesser thickness of the roadway.

[0046] Advantageously, the groove or the conical clearance on the one hand, and the bump(s) on the other hand are arranged to cooperate by contact with each other when the shaft 2 is positioned in the tube 1, in particular when the tube is driven into the shaft 2 until a shoulder 22 made on the shaft 2 comes into contact against a stop surface 13 of the tube.

[0047] In the configuration shown in the figure 1 , the bump(s) are in contact with a portion or circle of the groove or clearance having a diameter d1.

[0048] Before placing the shaft 2 in the tube 1, the distance d2 (not shown) between bosses or the diameter d2 of the circle inscribed in the right cross-section of the tube at the tops of the bosses or in the vicinity of the tops of the bosses is less than the diameter d1.

[0049] For example, 1.01 <d1 / d2<1.1, voire 1.02<d1 / d2<1.09, voire 1.03<d1 / d2<1.08.

[0050] Once the tube 1 is inserted onto the shaft 2, the tube 1 is elastically deformed at the bumps, so that the distance between the bumps or the diameter of the circle inscribed in the cross-section of the tube at the tops of the bumps or in the vicinity of the tops of the bumps is d1. It follows that the tube 1 exerts radial or substantially radial forces on the shaft 2. Combined with the shaft-tube friction, these forces define a shaft-tube friction torque. The torque depends mainly on the stiffness of the bumps and / or the elastic deformation of the bumps and / or the coefficient of friction at the shaft-tube interface.

[0051] Preferably, the friction torque between the shaft 2 and the tube 1 is greater than or equal to 1.8 mNm, or even greater than or equal to 2.0 mNm.

[0052] As seen previously, the tube 1 may be a tube of a cannon. Preferably, a needle may be fixed on such a tube. Alternatively, a needle may be kinematically connected to such a tube. Thus, the assembly may be used for correcting one or more hands indicating horological information. Alternatively, the assembly may be used to correct any type of organ indicating horological information or information derived from the time, in particular to correct a disc. Alternatively again, the assembly may be a clutch or a torque limiter. In the case of a vertical clutch, the shaft 2 may be axially movable relative to the tube 1 between a position such as that shown in the figure 1 (engaged position) and a position in which the bumps are opposite a deeper groove in the shaft 2 in which they do not rub (disengaged position in which the tube 1 rotates freely around the shaft).

[0053] Preferably, tube 1 is made of 20AP alloy or Finemac alloy. Alternatively, tube 1 may be made of stainless steel. Alternatively, tube 1 may be made of a beryllium copper alloy such as CuBe2.

[0054] For example, shaft 2 is made of 20AP alloy or Finemac alloy.

[0055] Methods of carrying out a method for producing the tube 1 for a friction system comprising the tube 1 and the shaft 2 are described below.

[0056] According to a first embodiment, the method for producing the tube 1 comprises: a first step of plastic deformation of the tube 1, then a second step of hardening of the tube 1, in particular a second step of hardening by heat treatment.

[0057] According to a second embodiment, the method for producing the tube 1 comprises a step of plastic deformation of the tube 1, in particular a step of plastic deformation of the tube 1 controlled in deformation, the deformation step being carried out on a portion of the tube in the annealed state and / or whose elastic limit is less than 1000 MPa and / or whose hardness is less than 400 HV or less than 350 HV.

[0058] After study, it appears that controlling the pinching of the tube 1 in dimension (and not in force as known from the prior art) makes it possible to give a clearer instruction to the equipment and to partially tighten the standard deviation of the final dimensions of the tube 1, in particular the distance between bumps d2 (not illustrated).

[0059] Thus, according to a third embodiment, the method of producing the tube 1 comprises: a first step of plastic deformation of the tube 1, in particular controlled in deformation, the deformation step being carried out on a portion of the tube in the annealed state and / or whose elastic limit is less than 1000 MPa and / or whose hardness is less than 400 HV or less than 350 HV, then a second step of hardening the tube, in particular a second step of hardening by heat treatment.

[0060] Surprisingly, the applied heat treatment has almost no influence on the dimensions of the part, while it induces a modification of the response of the part to mechanical stresses. The response to torque is thus more homogeneous on parts clamped in the annealed state or in the delivery state than on parts previously hardened and then clamped.

[0061] In addition, the implementation of dimensionally controlled pinching improves the dimensional regularity of the inter-bumps. Ultimately, the dispersion induced by pinching of the uncured material is less than on the cured material. As a result, the pinching exhibits a more homogeneous and repeatable behavior than on the thermally cured material, and the dispersion of the final dimensions of tube 1, in particular of the inter-bump dimension d2, linked to the process, is significantly lower.

[0062] This results in a more ductile material that is less subject to variation than thermally hardened material. The plastic deformation step is, for example, carried out on the material as delivered, slightly work-hardened or in the annealed state. It allows for plastic deformations of greater amplitude, which then allows for higher friction torques, for example, beyond 1.6 mNm. Combined with pinch control in terms of size and no longer in terms of force, this solution also reduces dispersion within road lot sizes and avoids pairing tubes 1 and shafts 2.

[0063] In the various embodiments, the step of plastic deformation of the tube 1 comprises the production of at least one bump in the tube. This deformation is preferably carried out by pinching.

[0064] In the various execution modes and depending on the type of alloy, the tube hardening step may include a quenching treatment followed by stress relief annealing and, if necessary, a tempering treatment, or a structural hardening annealing treatment.

[0065] By proceeding according to the execution methods described above, a higher friction torque can be obtained for the tube-shaft assembly. To do this, the manufacturing range of the tubes is modified, and the bosses are made on the tubes before the hardening heat treatment. The higher the friction torque, the greater the risk of the minute hand slipping relative to the center pinion, particularly in the event of an impact. If the hand is heavy (made of precious metals) or large, the risk of slipping in the event of an impact is high, for a given friction torque.

[0066] By proceeding according to the execution methods described previously, a different microstructure is obtained at the level of the bumps than when proceeding according to the state-of-the-art ranges, for example with carbides of a slightly larger size for the Finemac alloy but without impact on the behavior of the assembly.

[0067] Preferably, the plastic deformation of the tube 1 to form the bumps is carried out not by controlling the force of a clamp pressing on the tube, but by controlling and / or measuring the displacement of the material inside the tube 1. Alternatively, the distance between the bumps can be measured and / or controlled during the production or formation of the latter.

[0068] When the bosses are made on the tube 1 on a portion of material in the annealed state or more generally before hardening, the forces required are lower, the elastic return of the material is less and the material is more ductile, it is therefore possible to avoid cracking and to create bosses of larger dimensions, i.e. a smaller inter-bom dimension d2.

[0069] On the contrary, according to the prior art, the tube pinching is carried out on the hardened material (for example Rp0.2[20AP] > 1800 MPa and Rp0.2[Finemac] > 1600 MPa after hardening heat treatment). This limits the admissible deformation to approximately 3%, while requiring a significant force. A greater deformation in this state of material generates cracking of the tube.

[0070] Thus, according to the prior art, when a machined and finished, thermally hardened roadway is traditionally clamped, the deformation necessary to obtain a sufficiently high torque to prevent the slippage of large mass needles cannot be obtained without the risk of cracking the roadway wall. In addition, given the natural dispersion of the diameters of the cones of the center pinions, it is necessary to pair the batches of lantern roadways and the batches of pinions to guarantee the torque, and also to correct the pinching during the assembly step. The production method according to the prior art is therefore complex and requires repeating the torque measurements throughout the process to validate the pairing of the two batches during assembly. Above all, it limits the tightening torque if one wants to avoid cracks appearing on the roadways.High friction torques are only accessible with the production method known from the prior art manually, by processing the assemblies one by one.

[0071] In the different execution modes, the deformation step is for example carried out by pinching the tube 1.

[0072] In the various embodiments, the deformation step is for example carried out on a portion 12 of the tube whose elongation at break is greater than or equal to 2%, or even greater than or equal to 5%.

[0073] In the various embodiments, the deformation step can be controlled by optical measurement of the deformation. Alternatively, in the various embodiments, the deformation step can be controlled by a template arranged in the tube during the deformation step or by passing gauges. In such a case, during the action of the clamp, the tube is deformed until the bumps formed in the tube come into contact with the template. The template is chosen with a diameter smaller than the diameter d2, so that after the elastic shrinkage of the material at the end of the deformation action, the distance between the bumps or the diameter of the circle inscribed in the cross-section of the tube at the tops of the bumps or in the vicinity of the tops of the bumps is d2.

[0074] An embodiment of a tube according to the invention is obtained by implementing the method described above.

[0075] All tubes 1 of a batch delivered in the annealed condition can be deformed repeatably. A contrariodispersions induced by the heat treatment on the response to plastic deformation, this heat treatment applied after plastic deformation has a small influence on the dimensions of the tube 1, and the tolerances are tightened. It is therefore possible to obtain, according to the methods described, a set of at least 500 tubes whose standard deviation of the diameters of the circles centered on the axes A and inscribed in the cross sections of the tubes at the level of the peaks of the bumps is less than 0.2 µm for a nominal value of 0.758 mm. In the case of a tube with two opposite bumps relative to the axis A, it is the standard deviation of the dimensions between the peaks of the bumps which is less than 0.2 µm for a nominal value of 0.758 mm. Thus, according to the methods described, it is possible to obtain a set of at least 500 tubes assembled on 500 shafts, presenting an average standard deviation of the measured torques of 0.20 mNm for a nominal value of 2.0 mNm.

[0076] An embodiment of a method for producing friction between the shaft 2 and the tube 1 comprises a phase of implementing the method for producing a tube 1 described previously and a step of placing the shaft 2 in the tube 1.

[0077] According to the solution described above, the change in range compared to the prior art has revealed a surprising behavior of the material in that the response to pinching is more homogeneous on a work-hardened material than on a hardened material and in that the hardening heat treatment does not influence the dimensions of the part. The change in range thus makes it possible to increase the deformation of the tube and to generate, at equal initial dimensions, larger and more homogeneous bumps which will induce a higher final torque. This therefore makes it possible to ensure a sufficiently high torque between the tube and the shaft, capable of subsequently supporting heavier needles. In addition, the rework rate is significantly lower.

Claims

1. Method for producing a tube (1) for a friction watch system comprising the tube and a shaft (2), the tube being designed to rub around a shaft pinion, the method comprising a step of plastic deformation of the tube, controlled in deformation.

2. Method according to the preceding claim, characterized in that the deformation step is carried out on a portion of the tube in the annealed state and / or whose elastic limit is less than 1000 MPa and / or whose hardness is less than 400 HV or less than 350 HV.

3. Method according to one of the preceding claims, characterized in that the deformation step is controlled by optical measurement of the deformation or by a template placed in the tube during the deformation step or by passing gauges.

4. Method according to one of the preceding claims, characterized in that the tube is a tube of a roadway or a clutch element and / or a torque limiter element.

5. Method according to one of the preceding claims, characterized in that the deformation step is carried out by pinching the tube.

6. Method according to one of the preceding claims, characterized in that the deformation step is carried out on a tube made of 20AP alloy or Finemac alloy having a hardness less than or equal to 400 Hv, or even less than or equal to 350 Hv.

7. Method according to one of the preceding claims, characterized in that the deformation is carried out on a portion of the tube whose elongation at break is greater than or equal to 2%, or even greater than or equal to 3%.

8. Watch tube (1), in particular cannon pinion, in particular lantern cannon pinion, obtained by implementing the method according to one of claims 1 to 7.

9. Set of at least 500 tubes (1) according to claim 8, the standard deviation of the diameters of the circles centered on the axes (A) and inscribed in the straight sections of the tubes at the level of the tops of the bumps being less than 0.2 micrometers.

10. Clock assembly (3), in particular a center-pinion assembly, comprising a shaft and a tube according to claim 8.

11. Assembly (3) according to the preceding claim, characterized in that the friction torque between the shaft (2) and the tube (1) is greater than or equal to 1.8 mNm, or even greater than or equal to 2.0 mNm.

12. Assembly (3) according to claim 10 or 11, characterized in that the shaft diameter is less than or equal to 2 mm, or even less than or equal to 1 mm.

13. Watch movement (100), comprising a tube (1) according to claim 8 and / or an assembly according to one of claims 10 to 12.

14. Timepiece (200), in particular wristwatch, comprising a movement (100) according to the preceding claim and / or a tube according to claim 8 and / or an assembly according to one of claims 10 to 12.

15. Equipment comprising means for implementing the method according to one of claims 1 to 7.

16. Equipment according to the preceding claim, characterized in that it includes an optical means of measuring the deformation.

17. Equipment according to claim 15, characterized in that it includes a template intended to be placed in the tube during the deformation step or in that It includes gauges.

18. Equipment according to one of claims 15 to 17, characterized in that It includes a clamp.

Images