Friction system for clockwork

Description

Technical field of the invention

[0001] The invention relates to the field of mechanical watchmaking. More specifically, it concerns a friction system for a watch movement. Technological background

[0002] Friction systems are commonly used in watch movements. They allow one component to rotate with a second component until a certain torque limit is reached. Once this limit is exceeded, the two components are no longer rotated together. This type of system is generally used for hour and minute displays, particularly in the movement of the hands or display discs.

[0003] Typically, the rotor is fitted with a lantern pinion to ensure friction between it and a spring bar. This fitting involves pinching a tube within the rotor opposite a bearing or clearance point on the spring bar. This pinching is a manual task, and its result depends on the watchmaker's dexterity and sensitivity, making it unpredictable. This is unfortunate because the lantern pinion is intended to ensure a certain level of friction between the spring bar and the rotor during normal watch operation, while manual time-setting operations by the user apply a torque greater than that of friction, which therefore must not be excessive.

[0004] Correctly adjusting the friction torque is therefore a delicate process. Precise control of the applied clamping force is thus important, and conventional manual adjustment does not allow for this precision or the required reproducibility.

[0005] Another disadvantage is that the lantern frictions cannot withstand the transmission of high torque and are sensitive to assembly / disassembly.

[0006] There are other solutions for obtaining friction such as shims, but these have manufacturing repeatability that is difficult to guarantee from one batch to another.

[0007] There are also coil springs, but these are too bulky.

[0008] JP S53 21249 U discloses a sliding mechanism using a spring attached to a toothed member. US 3 731 481 A discloses a friction system for engaging / disengaging a watch comprising a toothed member, a locking cam, and a spring attached to the axis of the seconds hand. Summary of the invention

[0009] The invention aims in particular to overcome the various drawbacks of the prior art.

[0010] The invention also aims to provide a friction system that allows the transmission of high torque, is easy to manufacture, and whose friction repeatability is easily manageable.

[0011] To this end, the present invention relates to a friction system for clockwork movements comprising: an axis arranged to be mounted in the watch movement; a first fixed element, mounted on the axis; a second fixed element, mounted on the axis; a toothed member, mounted freely in rotation on the axis between the first fixed element and the second fixed element; a third fixed element, mounted on the axis; a spring mounted on the axis and arranged between the second fixed element and the third fixed element.

[0012] According to the invention, the spring is in the form of a washer comprising an inner part near the axis bearing against the third fixed element, and an outer peripheral part of the washer resting in elastic support against an annular element of the second fixed element, the spring being elastically deformed and forming a kinematic link both between the first fixed element and the toothed member, and between the second fixed element and the toothed member up to a predefined friction torque.

[0013] In accordance with other advantageous variants of the invention: The washer comprises at least two lugs arranged on its outer periphery, the lugs being arranged to rest in elastic support against the annular element of the second fixed element; the first fixed element and the toothed member each have a conical contact surface; the shaft comprises a bearing surface arranged to cooperate with a flat of the second fixed element; the third fixed element is in the form of a ring, the ring having an overthickness near the hole through which it is mounted on the shaft, the overthickness being arranged to bear against the spring; the second fixed element has a conical contact surface with the lugs of the spring; the lugs on the outer periphery of the spring and the inner part are in two different planes.

[0014] The invention also relates to a watch movement comprising a friction system according to the invention. Brief description of the figures

[0015] Other features and advantages of the invention will become apparent from the following detailed description, given by way of non-limiting example, with reference to the accompanying drawings in which: there figure 1 represents a perspective view of a friction system according to the invention; the figure 2 represents an exploded view of a friction system according to the invention; the figure 3 represents a cross-sectional view along axis AA of a friction system according to the invention. Detailed description of the invention

[0016] With reference to the figure 1 A friction system 100 according to the invention is shown. This system comprises a shaft 1 arranged to be mounted in a clockwork movement; the shaft may comprise parts with cross-sections 10, 11 of different diameters.

[0017] Axle 1 carries a toothed element 3, here a pinion, mounted freely for rotation on the shaft 1. Alternatively, this toothed element 3 can be a wheel. The shaft 1 can also carry several toothed elements and can take on a large number of known shapes according to the needs of those skilled in the art.

[0018] As illustrated in the figure 2 The system includes a first fixed element 2, such as a flange, driven onto the axis and extending perpendicularly to the axis 1. This flange 2 has a first conical bearing surface 20 and serves as the first friction surface between the toothed member 3 and the flange 2.

[0019] The system 100 also includes a second fixed element 4, the toothed element being positioned and rotating around the axis 1, between the first fixed element 2 and the second fixed element 4. The second fixed element 4 is in the form of a collar comprising an annular rib 42 on its face oriented towards the toothed element 3 forming an annular bearing surface between the toothed element 3 and the second fixed element 4.

[0020] The collar 4 has on its other face an annular peripheral rim 40 forming a skirt, an empty space 43 thus extending between the annular peripheral rim 40 and the center of the collar 4. As can be observed at the figure 3 , the peripheral annular rim 40 is beveled so as to form a conical bearing surface.

[0021] Advantageously, the axis 1 includes a bearing 12 arranged to cooperate with a flat 41 of the second fixed element 4. Such an arrangement allows the second fixed element 41 to slide on the axis while ensuring its correct position and secure retention on the axis once mounted.

[0022] The system also includes a third fixed element 6 which is mounted or driven onto the shaft 1. This third fixed element is in the form of a ring 6, the ring 6 having a raised section 60 near the hole 61 through which it is mounted on the shaft 1. The raised section 60 has a diameter smaller than that of the ring 6 and forms an annular bearing surface 62 for a spring 5.

[0023] The spring 5 is mounted fixed or movable around the axis 1 and is arranged between the second fixed element and the third fixed element.

[0024] The spring 5 is in the form of a flat washer comprising an inner part 51 in the immediate vicinity of the axis 1 which bears against the third fixed element 6, and more precisely against the overthickness 6, and an outer peripheral part in elastic support against the conical surface 40 of the skirt 4.

[0025] At rest, the spring 5 is in the form of a flat washer, which then deforms elastically when constrained between the second fixed element 4 and the third fixed element 5. The use of a flat washer is particularly advantageous because the use of a flat part makes it easier to reproduce the latter, especially compared to a domed element for example.

[0026] According to one embodiment of the invention, the spring 5 comprises at least two lugs 50 arranged on the outer periphery of the washer and are arranged to rest in elastic support against the conical support surface 40 of the second fixed element 4. Thus, when the set of parts is assembled, the spring 5 makes it possible to form a kinematic link both between the first fixed element 2 and the toothed member 3, and between the second fixed element 4 and the toothed member 3 up to a predefined friction torque.

[0027] Preferably, and as illustrated in the figures, the spring 5 has three lugs to provide better distribution of forces and also facilitate deformation of the spring.

[0028] The lugs 50 are distributed on the washer 5 at identical angular distances to ensure good distribution of the bearing force on the annular peripheral rim 40 of the collar 4. In the illustrated case, the three lugs are arranged at 120° to each other. If there were more lugs, for example five, they would be arranged at 72° to each other.

[0029] According to a particularly advantageous aspect, the friction torque can be perfectly adjusted by precisely driving the ring 6 on the axis 1 against the spring 5, the elastic force exerted by the spring 5 on the fixed element 4 allowing a very precise friction torque to be obtained.

[0030] When the system is assembled, as illustrated in the figure 3, the lugs 50 located on the outer periphery of the spring 5 and the inner part 51 are in two different planes, the assembly causing the spring 5 to bend in order to constrain it between the ring 6 and the collar 4.

[0031] The constraint of the spring 5 can therefore be modified by acting on the gap between the planes of the bearing surfaces 62 and 40, by moving the ring 6 on the axis 1, and consequently the frictional torque that the system can undergo before the toothed member 3 pivots relative to the axis 1. Such an arrangement thus allows an extremely simple and easily reproducible adjustment.

[0032] The invention also relates to a watch movement comprising a friction system according to the invention.

[0033] The invention also relates to a method for assembling a friction system according to the invention, the method comprising the following steps: provide an axis 1; drive a first fixed element 2 onto the axis 1 into a predetermined position; slide a toothed element 3 onto the axis 1 until it reaches the first fixed element 2; slide the second fixed element 4 onto the axis 1, orienting the second fixed element 4 relative to the axis by means of a flat 41 cooperating with a bearing surface 12 formed on the axis 1; place a spring 5 equipped with at least three lugs 50 arranged on the outer periphery of the spring 5, the lugs 50 resting against the second fixed element 4; progressively drive a third fixed element 6 onto the axis 1, so as to compress the spring 5 between the second fixed element 4 and the third fixed element 6, to obtain a kinematic link both between the first element and the toothed element, and between the second fixed element and the toothed element until a predetermined friction torque is obtained.

[0034] Of course, the present invention is not limited to the illustrated example and is susceptible to various variants and modifications which will appear to a person skilled in the art, without departing from the scope of the invention as defined by the claims.

Claims

1. Friction system (100) for a horological movement, which friction system comprises: - a staff (1) intended to be mounted in the horological movement; - a first stationary element (2) mounted on the staff; - a second stationary element (4) mounted on the staff; - a toothed member (3) mounted to rotate freely on the staff between the first stationary element and the second stationary element; - a third stationary element (6) mounted on the staff; - a spring (5) mounted on the staff (1) and arranged between the second stationary element (4) and the third stationary element (6); the spring (5) taking the form of a flat washer comprising an inner part (51) close to the staff (1) bearing against the third stationary element (6), and an outer, peripheral part of the washer bearing resiliently against an annular element of the second stationary element (4), the spring being arranged to be stressed in order to resiliently deform between the second stationary element (4) and the third stationary element (6), and to form a kinematic link both between the first stationary element (2) and the toothed member (3), and between the second stationary element (4) and the toothed member (3) up to a predefined friction torque.

2. System according to claim 1, characterised in that the washer comprises at least two catches (50) disposed at its outer periphery, the catches (50) being arranged to resiliently bear against the annular element of the second stationary element (4).

3. System (100) according to claim 1 or 2, characterised in that the first stationary element (2) and the toothed member (3) each have a conical contact surface (20, 30).

4. System (100) according to one of claims 1 to 3, characterised in that the staff (1) comprises a shoulder (12) arranged to cooperate with a flat section (41) of the second stationary element.

5. System (100) according to one of claims 1 to 4, characterised in that the third stationary element (6) takes the form of a ring, the ring having an excessive thickness (60) in the vicinity of the hole (61) through which it is mounted on the staff (1), the excessive thickness (60) being arranged so as to bear against the spring (5).

6. System (100) according to one of claims 1 to 5, characterised in that the second stationary element (4) has a conical contact surface (40) with the catches (50) of the spring (5).

7. System (100) according to one of claims 1 to 6, characterised in that the catches (50) on the outer periphery of the spring (5) and the inner part (51) lie in two different planes.

8. Method for assembling a friction system according to the invention, the method comprising the following steps of: - providing a staff (1); - driving a first stationary element (2) onto the staff (1) into a predetermined position; - sliding a toothed member (3) onto the staff (1) as far as the first stationary element (2); - sliding a second stationary element (4) onto the staff (1), while orienting the second stationary element (4) relative to the staff (1) by means of a flat section (41) cooperating with a shoulder (12) formed on the staff (1); - placing a spring (5) on the staff (1); - gradually driving a third stationary element (6) onto the staff (1), so as to compress the spring (5) between the second stationary element (4) and the third stationary element (6), in order to obtain a kinematic link both between the first element and the toothed member, and between the second stationary element and the toothed member until a predefined friction torque is obtained.