Friction system for timepiece movement

Abstract

The invention relates to a friction system (100) for a timepiece movement, comprising a shaft (1) for mounting in a timepiece movement, on which the first, second and third fixed elements are mounted, a first fixed element (2), a second fixed element (4), a toothed member (3), a third fixed element (6) and a spring (5), the toothed member is mounted in a freely rotatable manner on the shaft between the first and second fixed elements, and the spring is mounted on the shaft and arranged between the second and third fixed elements. According to the invention, the spring takes the form of a gasket comprising an inner portion (51) close to the shaft and abutting against the third fixed element and an outer peripheral portion elastically abutting against the annular periphery of the second fixed element, the spring is elastically deformed and forms a kinematic coupling between the first fixed element and the toothed member and between the second fixed element and the toothed member until a predetermined friction torque is reached.

Description

Technical Field

[0001] The present invention relates to the field of mechanical clocks. More specifically, the present invention relates to a friction system for a watch movement. Background Art

[0002] Friction systems are generally used in watch movements in order to connect a first member to a second member to rotate therewith until a torque limit value is reached. Once this limit value is exceeded, the two members are no longer connected to rotate as one. Generally, this type of system is used in particular for the hour and minute display means located at the center wheel for driving the display hands or the display dial.

[0003] The center wheel is generally mounted on the shaft by pressing to ensure the friction between it and the arbor. The pressing includes subjecting the tube contained in the center wheel to a pressure opposite to the shoulder of the arbor. This pressure is manually applied, and its result depends on the dexterity and sensitivity of the watchmaker and is therefore unpredictable, which is regrettable because the purpose of the pressing is to ensure a certain degree of friction between the arbor and the center wheel during the normal operation of the watch, and the torque applied by the manual pointer setting operation performed by the user is greater than the frictional torque, so the frictional torque cannot be too high.

[0004] Therefore, the correct adjustment of the frictional torque is very delicate. Therefore, it is very important to precisely control the applied clamping force, and the traditional manual pressing cannot achieve this precision nor the required repeatability.

[0005] Another disadvantage is that the friction obtained via pressing cannot withstand the transmission of high torques and is sensitive to assembly / disassembly.

[0006] There are also other solutions for obtaining friction, such as metal foils, but it is difficult to ensure the manufacturing repeatability between batches.

[0007] There are also helical springs, but these springs take up too much space. Summary of the Invention

[0008] The main object of the present invention is to overcome the various disadvantages of the prior art.

[0009] Another object of the present invention is to provide a friction system that allows the transmission of high torques, is easy to manufacture, and whose friction repeatability is easy to manage.

[0010] To this end, the present invention relates to a friction system for a watch movement, which comprises:

[0011] - a shaft for mounting in a watch movement;

[0012] - a first fixed element mounted on the shaft;

[0013] - A second fixed element mounted on the shaft;

[0014] - A toothed member mounted between the first fixed element and the second fixed element in a freely rotatable manner on the shaft;

[0015] - A third fixed element mounted on the shaft;

[0016] - A spring mounted on the shaft and arranged between the second fixed element and the third fixed element.

[0017] According to the present invention, the spring is in the form of a washer, which includes an inner part and an outer peripheral part. The inner part is close to the shaft and abuts against the third fixed element, and the outer peripheral part elastically abuts against the annular periphery of the second fixed element. The spring elastically deforms and forms a kinematic connection between the first fixed element and the toothed member and between the second fixed element and the toothed member until a predetermined frictional torque is reached.

[0018] According to other advantageous alternative embodiments of the present invention:

[0019] - The washer includes at least two tabs provided at its outer periphery, and the tabs are arranged to elastically abut against the annular periphery of the second fixed element;

[0020] - The first fixed element and the toothed member each have a conical contact surface;

[0021] - The shaft includes a shoulder for mating with a flat section of the second fixed element;

[0022] - The third fixed element is in the form of a ring, which has a thickened portion near the hole through which it is passed for mounting on the shaft, and the thickened portion is arranged to abut against the spring;

[0023] - The second fixed element has a conical contact surface in contact with the tabs of the spring;

[0024] - The inner part and the tabs on the outer periphery of the spring are in two different planes.

[0025] The present invention also relates to a watch movement including a friction system according to the present invention. Description of the Drawings

[0026] According to the following detailed description given by way of example with reference to the accompanying drawings and without any limitation, other features and advantages of the present invention will become apparent, wherein:

[0027] - Figure 1 A perspective view of the friction system according to the present invention is shown;

[0028] - Figure 2 An exploded view of the friction system according to the present invention is shown;

[0029] - Figure 3 Shows a cross-sectional view of the friction system according to the present invention along axis A-A. Detailed Description

[0030] Figure 1 Shows a friction system 100 according to the present invention. The friction system includes a shaft 1, which is arranged to be mounted in a watch movement, and the shaft may include sections 10, 11 with different diameters.

[0031] The shaft 1 carries a toothed member 3, which is a pinion in this example and is mounted to be rotatable freely on the shaft 1. Alternatively, the toothed member 3 may be a wheel disc. The shaft 1 may also carry a plurality of toothed members, and various known shapes may be adopted according to the needs of those skilled in the art.

[0032] As Figure 2 shown, the friction system includes a first fixed element 2, such as a flange, which is press-fitted onto the shaft 1 and extends perpendicular to the shaft 1. The flange 2 has a first conical contact surface 20, and the first conical contact surface 20 serves as the first friction surface between the toothed member 3 and the flange 2.

[0033] The friction system 100 further includes a second fixed element 4. The toothed member is located between the first fixed element 2 and the second fixed element 4 and rotates around the shaft 1. The second fixed element 4 is in the form of a retaining ring, and it includes an annular rib 42 on the face facing the toothed member 3. The annular rib 42 forms an annular contact surface between the toothed member 3 and the second fixed element 4.

[0034] The retaining ring 4 has an annular periphery 40 forming a skirt on its other face, so that a gap 43 extends between the annular periphery 40 of the retaining ring 4 and the center. As Figure 3 shown, the annular periphery 40 is beveled to form a conical contact surface.

[0035] Advantageously, the shaft 1 includes a shoulder 12, which is arranged to cooperate with the flat section 41 of the second fixed element 4. This arrangement enables the second fixed element 41 to be slid onto the shaft while ensuring its correct positioning and retention on the shaft after installation.

[0036] The friction system further includes a third fixed element 6, which is mounted or press-fitted onto the shaft 1. The third fixed element is in the form of a ring 6, and the ring 6 has a thickened portion 60 near the hole 61 through which it is mounted on the shaft 1. The diameter of the thickened portion 60 is smaller than the diameter of the ring 6 and forms an annular contact surface 62 for the spring 5.

[0037] The spring 5 is mounted so as to be able to move or not move about the shaft 1 and is arranged between a second fixed element and a third fixed element.

[0038] The spring 5 is in the form of a flat washer and includes an inner part 51 and an outer peripheral part. The inner part is adjacent to the shaft 1 and abuts against the third fixed element 6, more precisely against the thickening 6, and the outer peripheral part elastically abuts against the conical contact surface 40 of the skirt 4.

[0039] At rest, the spring 5 is in the form of a flat washer and will undergo elastic deformation when the spring 5 is compressed between the second fixed element 4 and the third fixed element 5. Using a flat washer is particularly advantageous because using flat components makes it easier to replicate, especially compared to, for example, dome-shaped elements.

[0040] According to an embodiment of the present invention, the spring 5 includes at least two tabs 50 which are arranged at the outer periphery of the washer and are intended to elastically abut against the conical contact surface 40 of the second fixed element 4. Thus, when all the components are assembled, the spring 5 allows a kinematic coupling to be formed between the first fixed element 2 and the toothed member 3 and between the second fixed element 4 and the toothed member 3 until a predetermined frictional torque is reached.

[0041] Preferably, as shown in the figure, the spring 5 has three tabs for improving the distribution of the force and facilitating the deformation of the spring.

[0042] The tabs 50 are distributed on the washer 5 at the same angular pitch in order to obtain a good distribution of the bearing capacity on the annular periphery 40 of the retaining ring 4. In the example shown, the three tabs are arranged at 120° to each other. If the number of tabs is larger, for example in the case of five tabs, they will be arranged at 72° to each other.

[0043] According to a particularly advantageous aspect, the frictional torque can be adjusted very well by precisely pressing the ring 6 onto the shaft 1 against the spring 5, and the elastic force exerted by the spring 5 on the second fixed element 4 makes it possible to obtain a very precise frictional torque.

[0044] When the friction system is assembled, as Figure 3 shown, the tabs 50 on the outer periphery of the spring 5 and the inner part 51 are in two different planes, and the spring 5 is bent during assembly to press it between the ring 6 and the retaining ring 4.

[0045] Therefore, by moving the ring 6 on the shaft 1, by acting on the distance between the planes of the contact surfaces 62 and 40, the stress of the spring 5 can be changed, and thus the frictional torque that the friction system can withstand before the toothed member 3 pivots relative to the shaft 1 can be changed. This arrangement makes the adjustment very simple and easy to repeat.

[0046] The invention also relates to a timepiece movement comprising a friction system according to the invention.

[0047] The invention also relates to a method for assembling a friction system according to the invention, the method comprising the following steps:

[0048] - Providing a shaft 1;

[0049] - Press-fitting a first fixed element 2 into a predetermined position on the shaft 1;

[0050] - Sliding a toothed member 3 on the shaft 1 until it reaches the first fixed element 2;

[0051] - Sliding a second fixed element 4 on the shaft 1 while orienting the second fixed element 4 relative to the shaft 1 by means of a flat section 41 that cooperates with a shoulder 12 formed on the shaft 1;

[0052] - Placing a spring 5, the spring 5 being provided with at least three tabs 50, the tabs 50 being arranged on the outer periphery of the spring 5 and the tabs 50 abutting against the second fixed element 4;

[0053] - Gradually press-fitting a third fixed element 6 onto the shaft 1 so as to compress the spring 5 between the second fixed element 4 and the third fixed element 6 in order to obtain a kinematic connection between the first fixed element and the toothed member and between the second fixed element and the toothed member until a predetermined frictional torque is obtained.

[0054] It goes without saying that the invention is not limited to the examples shown and that various alternatives and modifications that are obvious to a person skilled in the art can be made thereto, while still remaining within the scope of the invention as defined by the claims.

Claims

1. A friction system (100) for a watch movement, the friction system comprising: - a shaft (1) for mounting in said timepiece movement; - a first fixed element (2) mounted on said shaft; - a second fixed element (4) mounted on said shaft; - a toothed member (3) mounted between the first fixed element and the second fixed element in a freely rotatable manner on the shaft; - a third fixed element (6) mounted on said shaft; - a spring (5) mounted on the shaft (1) and arranged between the second fixed element (4) and the third fixed element (6); The spring (5) is in the form of a flat washer comprising an inner portion (51) close to the shaft (1) and abutting against the third fixed element (6), and an outer peripheral portion elastically abutting against the annular periphery of the second fixed element (4), the spring being arranged to be stressed so as to elastically deform between the second fixed element (4) and the third fixed element (6) and to form a kinematic connection between the first fixed element (2) and the toothed member (3) and between the second fixed element (4) and the toothed member (3) until a predetermined friction torque is reached.

2. The friction system according to claim 1, characterized in that: The flat washer comprises at least two lugs (50) arranged at its outer periphery, the lugs (50) being arranged to elastically abut against the annular rim of the second fixed element (4).

3. The friction system (100) according to claim 1 or 2, characterized in that: The first fixed element (2) and the toothed member (3) each have a conical contact surface (20, 30).

4. The friction system (100) according to any one of claims 1 to 3, characterized in that: The shaft (1) comprises a shoulder (12) arranged to cooperate with a flat section (41) of the second fixed element.

5. The friction system (100) according to any one of claims 1 to 4, characterized in that: The third fixed element (6) is in the form of a ring having a thickening (60) near the hole (61) through which it passes for mounting on the shaft (1), the thickening (60) being arranged to abut against the spring (5).

6. The friction system (100) according to any one of claims 1 to 5, characterized in that: The second fixed element (4) has a conical contact surface (40) that contacts the tab (50) of the spring (5).

7. The friction system (100) according to any one of claims 1 to 6, characterized in that: The inner portion (51) and the tabs (50) on the outer periphery of the spring (5) are located in two different planes.

8. A method for assembling a friction system according to any one of claims 1 to 7, the method comprising the following steps: - providing a shaft (1); - press-fitting the first fixed element (2) onto the shaft (1) at a predetermined position; - sliding the toothed member (3) on the shaft (1) until it reaches the first fixed element (2); - sliding a second fixed element (4) on the shaft (1) while orienting the second fixed element (4) relative to the shaft (1) by means of a flat section (41) cooperating with a shoulder (12) formed on the shaft (1); - placing a spring (5) on the shaft (1); - gradually pressing the third fixed element (6) onto the shaft (1), thereby compressing the spring (5) between the second fixed element (4) and the third fixed element (6) in order to obtain a kinematic connection between the first fixed element and the toothed member and between the second fixed element and the toothed member until a predetermined friction torque is obtained.

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