Torsional damper and clutch disc

Abstract

A torsional damper for equipping a vehicle powertrain, the damper comprising: a first element rotatable about an axis of rotation; a second element rotatable relative to the first element about an axis of rotation, the second element comprising first and second transverse washers mounted to be rotationally coupled about the axis and axially spaced apart from each other, the first element comprising an intermediate disc axially arranged between the first and second transverse washers; a spring mounted between the first and second elements so as to be compressed to allow relative rotation between the first and second elements about an axis; comprising a first friction washer provided with at least one fixed portion fixed to the first or second element in a rotationally rigid manner and having a friction portion arranged between the first transverse washer and the first element; the first elastic gasket is axially arranged between the first element and the friction part of the first friction gasket; bk second friction means of a second friction washer provided with at least one fixed portion fixed to the first or second element in a rotationally rigid manner and having a friction portion arranged between the second transverse washer and the first element; and a second spring washer axially disposed between the first element and the friction portion of the second friction washer.

Description

Technical Field

[0001] The present invention relates to a torsional damper for a vehicle powertrain. More precisely, the present invention is intended for use in a vehicle, such as a clutch disc of a truck.

[0002] A clutch disc generally includes a friction disc having a rotational axis X, the friction disc being provided with friction linings, a hub configured to drive a gearbox input shaft to rotate about the axis X, and a torsional damper kinematically arranged between the friction disc and the hub. The torsional damper generally includes a spring inserted between a first element and a second element of the damper so as to be compressed, allowing relative rotation about the rotational axis X between the first element and the second element, and a friction device configured to dissipate the energy stored in the spring by friction.

[0003] To this end, the friction device used in a clutch disc generally includes a friction washer that is rotationally locked to the first element of the damper by a coupling element such as teeth or splines or a folded protrusion inserted into a complementary groove of the first element.

[0004] An advantage of such a friction device is that it allows the friction washer to move axially along the axis X when the friction member becomes thinner due to wear.

[0005] However, in order to allow axial movement of the friction washer relative to the first element, the above-mentioned coupling elements (teeth, splines, protrusions) must be fitted with a minimum angular clearance. In the absence of angular clearance, due to the axial friction between the teeth / splines, the axial movement of the friction washer will be difficult or even impossible.

[0006] The presence of angular clearance means that the friction washer and the first element are not strictly rotationally coupled to each other, especially since when the friction device operates, the plastic deformation phenomenon caused by the impact between these coupling elements tends to amplify the initial angular clearance. Specifically, the vibrations passing through the damper generate impacts between the aforementioned coupling elements and the support members. The degree of impact is such that these coupling elements may plastically deform or shear.

[0007] This may lead to premature wear and reduced performance of the friction device. Summary of the Invention

[0008] The damper according to the present invention aims to solve the technical problems posed by the prior art by explicitly eliminating the problem of plastic deformation while proposing a cost-reducing solution.

[0009] According to the present invention, this object is achieved by a torsional damper for equipping a vehicle powertrain, the damper comprising:

[0010] - a first element rotatable about a rotational axis X,

[0011] - A second element rotatable relative to a first element about a rotation axis X,

[0012] The second element includes a first lateral washer and a second lateral washer. The first lateral washer and the second lateral washer are mounted for rotationally coupled about the axis and axially spaced from each other, and the first element includes an intermediate disk axially disposed between the first and second lateral washers.

[0013] - A spring mounted between the first element and the second element so as to be compressed to allow relative rotation about the axis X between the first element and the second element,

[0014] - A first friction device including a first friction washer provided with at least one fixed portion fixed to the first element or the second element in a rotationally rigid manner. The first friction washer has a friction portion disposed between the first lateral washer and the first element; and a first elastic washer axially disposed between the first element and the friction portion of the first friction washer.

[0015] - A second friction device including a second friction washer provided with at least one fixed portion fixed to the first element or the second element in a rotationally rigid manner. The second friction washer has a friction portion disposed between the second lateral washer and the first element; and a second elastic washer axially disposed between the first element and the friction portion of the second friction washer.

[0016] Thus, rotation between the first or second element and the two friction washers without angular clearance can be prevented, while allowing the friction portion to move relative to the first or second element, so that wear on the friction surface can be compensated and the problem of plastic deformation can be eliminated. In addition, placing the friction devices on either side of the first element enables a more flexible system, and the two elastic washers independently withstand axial pulsations passing through the damper. Therefore, the service life of the damper according to the present invention is increased.

[0017] The damper may include one or more of the following features:

[0018] The first friction washer and the second friction washer are identical and symmetrically positioned relative to the first element. Thus, due to the standardization of parts, the production of the damper is simple and inexpensive.

[0019] The first elastic washer and the second elastic washer are identical and symmetrically positioned relative to the first element. Thus, due to the standardization of parts, the production of the damper is simple and inexpensive.

[0020] The first friction device further includes a first shim washer axially disposed between the first element and the first elastic washer. Thus, the first elastic washer is optimally positioned and retains its position over time. Moreover, it enables the load characteristics of the first elastic washer to be optimized.

[0021] The second friction device further includes a second shim washer axially disposed between the first element and the second elastic washer. The first shim washer and the second shim washer are identical and symmetrically positioned with respect to the first element. Thus, the second elastic washer is optimally positioned and retains its position over time. Moreover, due to the standardization of the parts, the production of the damper is simple and inexpensive.

[0022] The first friction washer includes only two fixing portions, each fixing portion being connected to the friction portion by a flexible element. Thus, the presence of only two fixing portions allows the first friction washer to have a stiffness that is almost zero. Moreover, the first friction washer is simple to manufacture and inexpensive.

[0023] Each fixing portion is connected to the friction portion by a single flexible element. Thus, the first friction washer is simple to manufacture and inexpensive.

[0024] The second friction washer includes only two fixing portions, each fixing portion being connected to the friction portion by a flexible element. Thus, the presence of only two fixing portions allows the second friction washer to have a stiffness that is almost zero. Moreover, the second friction washer is simple to manufacture and inexpensive.

[0025] Each fixing portion is connected to the friction portion by a single flexible element. Thus, the second friction washer is simple to manufacture and inexpensive.

[0026] The flexible element is a flexible protrusion.

[0027] The two fixing portions are arranged 180 degrees from each other. Thus, the first and / or second friction washer is simple to manufacture and inexpensive.

[0028] The two fixing portions are arranged between 50 degrees and 110 degrees from each other. The two fixing portions are preferably arranged 90 degrees from each other. Thus, the first and / or second friction washer can adapt to various ergonomic constraints of the damper while maintaining an almost zero stiffness.

[0029] The first friction washer includes at least three fixing portions, each fixing portion being connected to the friction portion by a flexible element that includes at least one corrugated portion having a series of regions that are axially offset in pairs in the radial direction. Thus, the first friction washer is more robust while having an almost zero stiffness.

[0030] The second friction washer includes at least three fixing parts, each fixing part being connected to the friction part by a flexible element which includes at least one corrugated part having a series of regions axially offset in pairs in the radial direction. Thus, the second friction washer is more robust while having a stiffness that is almost zero.

[0031] Each fixing part is connected to the friction part by a single flexible element. Thus, the first and / or second friction washers are simple and inexpensive to manufacture.

[0032] The first element includes an annular member, such as a disc or washer, whose center is arranged on the rotation axis X.

[0033] Each fixing part of the friction washer is fixed to the first element or the second element by a support element.

[0034] The torsional damper is capable of transmitting torque from the vehicle's engine to the vehicle's drive wheels.

[0035] According to one embodiment, the first element is intended to be driven in rotation by the vehicle's engine, while the second element is intended to drive in rotation an input member of the vehicle's gearbox, such as a shaft.

[0036] According to a variant, the second element is intended to be driven in rotation by the vehicle's engine, and the first element is intended to drive in rotation an input member of the vehicle's gearbox, such as a shaft.

[0037] The first elastic washer is axially arranged between the first element and the friction part of the first friction washer so as to axially press the friction part of the first friction washer against the friction surface of the second element.

[0038] Each fixing part is axially locked to the first or second element.

[0039] Each fixing part is mounted in rotationally coupled relation to the first or second element without angular clearance.

[0040] In particular, the mounting of the fixing part is non-removable to avoid angular mounting clearances. In other words, the fixing part is fixed to the first or second element in a non-removable manner.

[0041] The fixing part is connected to the first or second element by an embedded connection, such as a riveted or welded connection. The term "embedded connection" is understood to mean a connection without degrees of freedom.

[0042] Each first or second element and each fixing part include at least one opening, each fixing part opening being arranged opposite an opening in the first or second element, and each fixing part being fixed to the corresponding first or second element in a rotationally rigid manner by at least one fixing element, such as a rivet or a pin.

[0043] Each fixed part is also axially locked to the first or second element by a fixing element.

[0044] In particular, the fixing element can be a rivet, which includes a shank for engaging in an opening of the fixed part and the first or second element, and also includes a head widened relative to the shank at each end.

[0045] The fixed part is arranged radially outside the spring.

[0046] The spring is a helical spring, which extends circumferentially or tangentially around the axis X at the mean installation radius, and the fixed part is arranged radially outside the mean installation radius.

[0047] The mean installation radius is taken from the middle region of the spring length and the main axis around which the turns are wound.

[0048] Each flexible element can be elastically deformed axially.

[0049] The load applied by the first elastic washer is greater than the load applied by the flexible element of the first friction washer.

[0050] Each flexible element has a linear axial stiffness.

[0051] Each flexible element is arranged circumferentially between two springs.

[0052] The first element includes a hole for receiving the spring and a support element arranged circumferentially between two adjacent holes. Each flexible element is rigidly fixed to the support element of the first element.

[0053] The friction part consists of a plurality of friction pads spaced apart from each other.

[0054] The friction part consists of a single circular friction pad.

[0055] Each fixed part is arranged to receive one or two rivets.

[0056] Each fixed part is arranged circumferentially between two adjacent springs.

[0057] According to one embodiment, the first friction washer is cut from a metal sheet.

[0058] According to one embodiment, the first friction washer is flat before being installed in the torsional damper.

[0059] In appropriate cases, the deformation of the first friction washer during its installation enables the axial load of the flexible element to be generated, particularly in a direction opposite to the direction of the force applied by the first elastic washer.

[0060] The second element includes first and second lateral washers, the first and second lateral washers being mounted for rotationally coupled about axis X and axially spaced from each other; and the first element includes an intermediate disk axially disposed between the two lateral washers.

[0061] The invention also relates to a clutch disk for a vehicle powertrain, the clutch disk being equipped with a damper as described above and a friction disk carried by the first element and provided with friction linings.

[0062] The hub is rotationally coupled to the first and second lateral washers. In other words, the second element includes the hub.

[0063] The hub is provided with a collar, and the first and second lateral washers axially abut on either side of the collar.

[0064] The hub is riveted to the first and second lateral washers.

[0065] According to a first variant, especially in the case without a pre-damper, the hub is an output hub capable of driving the input shaft of the gearbox.

[0066] According to a second variant, the hub is an intermediate hub that is angularly spaced from the output hub, and the clutch disk further includes a pre-damper provided with a pre-damping spring kinematically arranged between the output hub and the second element.

[0067] The clutch disk includes an output hub driven in rotation directly or indirectly (e.g., through a pre-damper) by the first element.

[0068] The friction disk and the first friction washer are fixed to the first element with the same fixing elements, such as the same rivets.

[0069] The friction disk, the first element (especially the central disk), the first friction device and the second friction device together form a pre-assembled sub-assembly that can be inserted between the first and second lateral washers.

[0070] This sub-assembly is mounted on the hub without axial locking. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] With reference to the drawings described in detail below, other features and advantages of the invention will become apparent upon reading the following description.

[0072] Figure 1 is a partial perspective view of a clutch disk according to the invention, the clutch disk including a first friction washer according to a first embodiment.

[0073] Figure 2 is Figure 1 a partial cross-sectional view of the torsional damper of the clutch disk of

[0074] Figure 3 is a side view of a first friction washer according to the second embodiment.

[0075] Figure 4 is Figure 3 a close-up of.

[0076] For greater clarity, in all the figures, identical or similar elements are identified by the same reference numerals. Detailed Description

[0077] Of course, the embodiments shown in the figures presented above are given only as non-limiting examples.

[0078] In the description and claims, the terms "outer" and "inner" and "axial" and "radial" orientations are used to denote elements of the damper according to the definitions given in the description. By convention, the "radial" orientation is orthogonal to the rotational axis X of the damper, the "axial" orientation is determined, and moving away from the rotational axis from the inner side to the outer side, the "circumferential" orientation is circular about the axis X, and the tangential orientation is orthogonal to the rotational axis of the damper and orthogonal to the radial direction. The terms "outer" and "inner" are used to define the relative position of one element with respect to another, with reference to the rotational axis X of the damper, and the element closer to the axis is thus called the inner element, as opposed to the outer element located radially at the periphery.

[0079] Figure 1 A perspective view of a clutch disc for a vehicle powertrain is shown. The clutch disc is equipped with a damper 100 and a friction disc 6 provided with a friction lining 7.

[0080] The torsional damper 100 includes a first element 1 capable of rotating about a rotational axis X, and a second element capable of rotating about the axis X relative to the first element 1. The torsional damper 100 is capable of transmitting torque from the vehicle's engine to the vehicle's drive wheels.

[0081] A spring may be mounted between the first element 1 and the second element so as to be compressed to allow relative rotation about the axis X between the first element 1 and the second element.

[0082] The second element may include a first lateral washer and a second lateral washer, which are mounted for rotational connection about the axis X and are axially spaced apart from each other. The first element 1 may include an intermediate disc 1a axially disposed between the two lateral washers.

[0083] The friction disc 6 may be carried by the intermediate disc 1a at its outer periphery.

[0084] The clutch disc may further include an output hub 40 which is indirectly driven to rotate via a first lateral washer by a second element via a pre-damper. The output hub 40 may be angularly clearance-coupled to the second element. The pre-damper may be provided with a pre-damping spring which is kinematically arranged between the output hub 40 and the second element.

[0085] The output hub 40 may include a collar, with the first lateral washer and the second lateral washer axially adjacent to either side of the collar.

[0086] The intermediate disc 1a may include a support element 13. Alternatively, the first lateral washer and the second lateral washer may include the support element 13.

[0087] The damper 100 may include a first friction device 10a which includes a first friction washer 11a. The first friction washer 11a may be provided with two separate fixing portions 12 which are rigidly rotationally fixed to the first element 1 or the second element. More specifically, each of the two fixing portions 12 may be fixed to the support element 13 of the intermediate disc 1a. Alternatively, each of the two fixing portions 12 may be fixed to the support element 13 of the first lateral washer or the second lateral washer.

[0088] The first friction washer 11a has a friction portion 15. The friction portion 15 may have a friction track 16 and a back surface 17.

[0089] Each of the two fixing portions 12 of the first friction washer 11a may be connected to the friction portion 15 by a flexible element 14 which allows the back surface 17 to move axially relative to the first element 1. Thus, rotation without angular clearance between the first element and the first friction washer 11a can be prevented, while allowing the back surface 17 of the friction portion 15 to move relative to the first element 1, so that wear on the friction surface can be compensated for.

[0090] The flexible element 14 may be a flexible protrusion. It may be integrally formed with the friction portion 15 and the fixing portion 12. Thus, the first friction washer 11a is advantageously made of a single metal plate.

[0091] Each support element 13 and each fixing portion 12 may each include at least one opening 21. Each fixing portion opening 12 is arranged opposite the support element opening 13.

[0092] Thus, each fixing portion 12 may be fixed to the corresponding support element 13 in a rotationally rigid manner by at least one fixing element, such as a rivet 20.

[0093] Each fixing portion 12 is also axially locked to the support element 13 by the rivet 20.

[0094] The friction part 15 is formed radially inside the first friction washer 11a, and each fixing part 12 is formed radially outside the first friction washer 11a.

[0095] As can be seen from the figure, the clutch disc may further include a spring. The spring may be a helical spring that extends circumferentially or tangentially around the axis X at the average installation radius. The fixing part 12 is arranged radially outside the average installation radius. The average installation radius is taken from the middle region of the spring length and the main axis around which the spring coils are wound.

[0096] The first friction washer 11a may include two separate fixing parts 12, and the first element 1 or the second element may include a plurality of support elements 13, and a part of the support elements 13 receives the fixing parts 12.

[0097] Each flexible protrusion 14 can be elastically deformed axially.

[0098] The first friction device 10a may further include a first elastic washer 18a. The first elastic washer 18a may be arranged axially between the first element 1 and the first friction washer 11a. More specifically, the first elastic washer 18a may be arranged axially between the intermediate disc 1a and the back surface 17 of the friction part 15.

[0099] As Figure 2 shown, the first elastic washer 18a is arranged axially between the intermediate disc 1a and the back surface 17 of the friction part 15 of the first friction washer 11a so as to axially press the friction part 15 against the friction surface of the first lateral washer.

[0100] The first elastic washer 18a may be one-piece. The first elastic washer 18a may be continuous and extend circumferentially. The first elastic washer 18a may have a corrugated shape. The corrugated shape has a series of regions that are axially offset in pairs in the radial direction.

[0101] The first friction device 10a may further include a first spacer washer 30a. The first spacer washer 30a may include a continuous and circumferentially extending body. The first spacer washer 30a may include a plurality of protrusions 31 that extend axially from the body. The plurality of protrusions 31 may be adapted to hold the first elastic washer 18a.

[0102] The first spacer washer 30a may be arranged axially between the first element 1 and the first friction washer 11a. More specifically, the first spacer washer 30a may be arranged axially between the first element 1 and the first elastic washer 18a.

[0103] Each flexible protrusion 14, the first elastic washer 18a, and the first spacer washer 30a may be configured such that in operation, for at least one compression state of the first elastic washer 18a, each flexible protrusion 14 applies an axial load in a direction opposite to the direction of the load applied by the first elastic washer 18a on the friction portion 15.

[0104] The flexible protrusion 14 and the first elastic washer 18a may be configured such that the load applied by the first elastic washer 18a remains greater than the load applied by the flexible protrusion 14 of the first friction washer 11a.

[0105] Generally, the compression state of the first elastic washer 18a may depend on the initial preload of the first elastic washer 18a and the wear state of the first friction device 10a.

[0106] The two separate fixing portions 12 may be arranged 180 degrees from each other. Optionally, the two separate fixing portions may be arranged between 50 degrees and 110 degrees from each other, preferably 90 degrees from each other.

[0107] Figure 1 It is shown that each flexible protrusion 14 may be circumferentially arranged between two springs. The first element 1 may include holes for receiving the springs, and each support element 13 is circumferentially arranged between two adjacent holes.

[0108] The friction portion 15 may consist of a single friction plate. The friction plate may extend annularly around the axis X. The friction plate may be continuous. Alternatively, the friction portion 15 may consist of a plurality of friction pads spaced apart from each other. Each friction pad 15 may be associated with a single flexible protrusion 14.

[0109] The friction portion 15 forms a radial inner ring of the first friction washer 11a, which extends around the rotation axis X and radially expands.

[0110] The first friction washer 11a may further include a radial outer ring 23, and each flexible protrusion 14 connects the friction portion 15 and the radial outer ring 23. The radial outer ring 23 extends around the rotation axis X and radially expands.

[0111] The fixing portion 12, the flexible protrusion 14, the friction portion 15, and the radial outer ring 23 may be formed as a single piece from a cut metal plate.

[0112] There may be a space between two adjacent flexible protrusions 14, especially to allow the arrangement of springs. In other words, each flexible protrusion 14 is arranged between two springs.

[0113] The radial outer ring 23 is arranged against the radial outer edge of the first element 1.

[0114] Each fixing part 12 can be formed on the flared opening that extends the flexible protrusion 14 and connects the flexible protrusion 14 to the radially outer ring 23. Each fixing part 12 can be designed to receive two rivets 20.

[0115] According to Figure 3 and 4 In a second embodiment of the first friction washer 11a as shown, the first friction washer may include a plurality of fixing parts 12. The plurality is at least three fixing parts 12. Each flexible protrusion 14 connecting the fixing part 12 to the friction part 15 can be corrugated. Each corrugated flexible protrusion 14 can have a series of regions that are axially offset in pairs in the radial direction.

[0116] The damper can include an even number n of springs, such as four springs, which are circumferentially disposed between the intermediate disk 1a and the second element. The first friction washer 11a can include n fixing parts 12, such as four fixing parts, and n flexible elements, such as four flexible elements. Thus, the first friction washer 11a can have a relatively small axial stiffness. Each fixing part 12 can be circumferentially arranged between two adjacent springs.

[0117] The damper 100 can further include a second friction device 10b. The second friction device 10b can be independent of the first friction device 10a. The second friction device 10b is designed to withstand axial pulsations related to engine torque transmission independently of the first friction device 10a. The second friction device 10b includes a second friction washer 11b. The second friction washer 11b can be the same as the first friction washer 11a. The first friction washer 11a and the second friction washer 11b can be positioned symmetrically about the center with respect to the first element 1.

[0118] The second friction device 10b can further include a second elastic washer 18b. The second elastic washer 18b can be the same as the first elastic washer 18a. The first elastic washer 18a and the second elastic washer 18b can be positioned symmetrically about the center with respect to the first element 1. The second elastic washer 18b enables the second friction washer 11b to be axially squeezed independently with respect to the first friction washer 11a.

[0119] The second friction device 10b can also include a second spacer washer 30b. The second spacer washer 30b can be the same as the first spacer washer 30a. The first spacer washer 30a and the second spacer washer 30b can be positioned symmetrically about the center with respect to the first element 1.

[0120] The presence of the two independent friction devices 10a and 10b, which are identical to each other and axially symmetrically positioned with respect to the first element 1, enables the problem of plastic deformation to be ultimately eliminated, thereby increasing the service life of the damper 100.

Claims

1. A torsional damper (100) for equipping a vehicle powertrain, the damper comprising: - a first element (1) rotatable about an axis of rotation (X), - a second element rotatable relative to the first element (1) about an axis of rotation (X), The second element comprises a first transverse washer and a second transverse washer mounted so as to be coupled in rotation about an axis (X) and axially spaced from each other, and the first element (1) comprises an intermediate disk arranged axially between the first and second transverse washers, - a spring mounted between the first element (1) and the second element so as to be compressed to allow relative rotation between the first element (1) and the second element about the axis (X), - a first friction device (10a), comprising a first friction washer (11a), the first friction washer being provided with at least one fixing portion (12) fixed in a rotationally rigid manner to the first element (1) or the second element, the first friction washer (11a) having a friction portion (15) arranged between the first transverse washer and the first element (1); and a first elastic washer (18a) being arranged axially between the first element (1) and the friction portion (15) of the first friction washer, - A second friction device (10b), comprising a second friction washer (11b) provided with at least one fixing portion (12) fixed to the first element (1) or the second element in a rotationally rigid manner, the second friction washer (11b) having a friction portion (15) arranged between the second transverse washer and the first element (1); and a second elastic washer (18b) arranged axially between the first element (1) and the friction portion (15) of the second friction washer.

2. The torsional damper (100) according to claim 1, wherein: The first friction washer (11a) and the second friction washer (11b) are identical and are symmetrically positioned relative to the first element (1).

3. The torsional damper (100) according to any one of the preceding claims, wherein: The first elastic gasket (18a) and the second elastic gasket (18b) are identical and are symmetrically positioned relative to the first element (1).

4. The torsional damper (100) according to any one of the preceding claims, wherein: The first friction device (10a) further comprises a first gasket washer (30a) arranged axially between the first element (1) and the first elastic washer (18a).

5. The torsional damper (100) according to the preceding claim, wherein The second friction device (10b) further comprises a second shim washer (30b) arranged axially between the first element (1) and the second elastic washer (18b), the first shim washer (30a) and the second shim washer (30b) being identical and symmetrically positioned relative to the first element (1).

6. The torsional damper (100) according to any one of the preceding claims, wherein: The first friction washer comprises only two fixed parts (12), each fixed part (12) being connected to the friction part (15) via a flexible element (14).

7. Torsional damper (100) according to the preceding claim, wherein The two fixing parts (12) are arranged at 180 degrees to each other.

8. The torsional damper (100) according to claim 6, wherein: The two fixing parts (12) are arranged between 50 and 110 degrees to each other, preferably at 90 degrees to each other.

9. The torsional damper (100) according to any one of claims 1 to 5, wherein: The first friction washer comprises at least three fixed parts (12), each fixed part (12) being connected to the friction part (15) via a flexible element (14), the flexible element comprising at least one corrugated part having a series of regions in a radial direction which are axially offset in pairs.

10. The torsional damper (100) according to any one of claims 1 to 5, wherein: Each fixed portion (12) is connected to the friction portion (15) via a flexible element (14), allowing the friction portion (15) to move axially relative to the supporting element (13) of the first element (1).

11. A clutch disc for a vehicle powertrain, equipped with a damper according to any of the preceding claims and having a friction disc (6) carried by a first element (1) and provided with a friction lining (7).

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