Method for manufacturing a clutch friction lining

Abstract

Method for producing a clutch friction lining (4), characterized in that it comprises the following steps: - Producing a flat friction body (6) comprising at least one hole (10) which opens only in the area of ​​a first surface (7) of the body (6), - Attaching the friction body (6) to a support (5) by adhering the first surface (7) of the body (6) to the support (5), - Machining a second surface (8) of the friction body (6), which is opposite to the first surface (7), using a milling machine, until the hole (10) opens in the area of ​​the second surface (8) of the friction body (6), wherein the material thickness removed by milling is between 0.2 and 1 mm.

Description

[0001] The present invention relates to a method for manufacturing a clutch friction lining intended for use in a friction disc of a motor vehicle clutch, in particular a dual clutch.

[0002] A dual clutch allows the shaft of the vehicle's engine to be coupled alternatively to two coaxial input shafts of a transmission, which can be of a fully automated type.

[0003] A dual-clutch transmission allows gear changes while maintaining the transmission of drive torque to the vehicle's wheels. The two clutches are each assigned to one of the even or odd gear positions. During a gear change, the first clutch disengages while the second clutch engages, thus progressively transferring the drive torque from the first to the second clutch.

[0004] Each clutch incorporates a mechanism with a diaphragm spring designed to interact with a pressure plate, which is fixed to the cover and the engine shaft. Each diaphragm spring is adjustable between a rest position and an active position by means of a corresponding release bearing. Depending on the clutch type, the active position of the diaphragm spring corresponds to either coupling or decoupling the engine and transmission shafts, and the rest position of the diaphragm spring corresponds to either coupling or decoupling these shafts. Accordingly, these are referred to as a normally open or normally closed clutch.

[0005] The release bearing is actuated by an actuator controlled by an electronic computer to exert a predetermined force on the diaphragm spring and adjust it over a given distance.

[0006] The pressure plate of each clutch, which is actuated by the corresponding diaphragm spring, is designed to press a friction disc, fitted with friction linings, against a reaction plate connected to the drive shaft. A reaction plate can be provided for each clutch. Alternatively, a single reaction plate is used, shared by both clutches and mounted between the two friction discs.

[0007] The friction linings are designed to come into contact with the counter materials of the pressure plates and the reaction plate(s).

[0008] Each friction disc is rotationally connected to an input shaft of the gearbox, and each reaction plate is rotationally connected to a flywheel connected to the motor shaft. Thus, clamping a friction disc between the corresponding pressure and reaction plates enables the transmission of torque between the drive shaft and the associated gearbox shaft.

[0009] A coating typically comprises an annular friction element composed of a fibrous material, a binder, and fillers. The friction element is attached to a carrier formed by an annular metal film, for example, by pressing or gluing.

[0010] A coating is attached to each of the radial sides of the friction disc, with the counter materials of the pressure plate and the corresponding reaction plate coming into contact with the friction elements.

[0011] The friction linings are attached to the friction disc by rivets arranged in holes in the linings, with the heads of the rivets coming into contact either with a recess formed in the friction body or with the metal film.

[0012] Each rivet can be used to fasten either one or both friction linings to the friction disc. If the rivets are used to fasten only one clutch friction lining, the other lining must also have holes opposite the rivets to allow the insertion of a riveting tool.

[0013] The following section considers the case in which the rivet heads come into contact with the metal film rather than with a countersink recessed in the friction body. This solution reduces the axial space required by the unit and is therefore particularly useful in the case of dual couplings, where available axial space is limited.

[0014] In such a case, it must be ensured that the side of the metal film located at the bottom of the hole, which serves as a support for the head of the rivet, is not covered with friction material.

[0015] Conversely, the free thickness of a rivet varies from one rivet to another, which can lead to a parallelism error of the friction linings and cause vibrations or a so-called "chattering" phenomenon when the friction disc rotates during operation.

[0016] It is known to produce a clutch friction lining by molding or hot pressing, wherein a metal film is arranged on the base of a solid part of a mold, and then a friction material consisting of fibers, a binder, and at least one filler is applied to the metal film. The assembly is then hot-pressed using a movable piston. During this process, the friction material polymerizes, forming a friction body that adheres to the metal film.

[0017] As stated above, the friction body must include holes that allow the rivet heads to be positioned or that allow the insertion of a riveting tool. The metal film must also include holes that, depending on the intended method of fastening the linings, serve either for the insertion of the rivet shank or for the insertion of the riveting tool.

[0018] In one design, the holes in the friction element are created by drilling with a drill or milling machine. The aim here is to remove as much friction material as possible without damaging the metal film that serves as a support for the rivet heads.

[0019] In a second design, the holes in the friction element are formed directly during the forming or hot pressing process. In this case, the movable piston includes protruding zones designed to form the holes after hot pressing.

[0020] In both cases, however, friction material generally remains at the bottom of the hole, on the surfaces of the metal film that are intended to form supports for the heads of the rivets.

[0021] To solve this problem, document WO 2011 / 009427A1 proposes covering these areas of the metal film with an intermediate layer designed to reduce the adhesion of the friction material.

[0022] The remaining friction material at the bottom of the hole can then be removed by vaporization using a laser beam. The laser beam's power is carefully controlled to ensure that the metal film is not damaged by the generated heat. This process is relatively time-consuming and expensive.

[0023] From US 3 300 353 A, a brake pad is known which is applied to a curved pad carrier and then machined by means of a turning tool in such a way that a ridge present between two pad rings is removed.

[0024] EP 0 202 145 A1 discloses a porous friction material whose pores have small channels.

[0025] JP S62-37530A describes a method for manufacturing a brake disc in which a pad with grooves is welded to one side of a base plate. Slots are then cut into the pad, starting from the side of the pad that does not contact the base plate.

[0026] JP H02 - 286 928 A discloses a method for manufacturing a brake lining in which a plate-shaped friction material is formed from several fragments by means of connecting bridges, the friction material is connected to a metal plate and then the connecting bridges are removed.

[0027] From DE 11 2008 001 240 T5 a method for manufacturing friction elements of a dry clutch friction disc is known, in which a friction lining is glued onto an insertion part and then fastening holes for rivets are formed.

[0028] The invention is intended in particular to provide a simple, effective and economical solution to this problem.

[0029] To this end, it proposes a method for manufacturing a clutch friction lining, characterized in that it comprises steps consisting of: - to produce a flat friction body that includes at least one hole that opens only in the area of ​​a first surface of the body, - to attach the friction body to a carrier by adhering the first surface of the body to the carrier, - to machine a second surface of the friction body, opposite the first surface, using a milling machine until the said hole opens in the area of ​​the second surface of the friction body, whereby the material thickness removed by milling is between 0.2 and 1 mm.

[0030] In this way, the friction element is attached to the carrier according to the manufacturing process and includes at least one hole passing through the friction element. The coupling friction lining therefore does not include any friction material at the bottom of the hole in the area of ​​the corresponding surface of the carrier that is intended to serve as a support for the head of a rivet.

[0031] The holes to be formed in the carrier for the insertion of rivet shanks or a riveting tool can then be produced, for example, by drilling, punching, or laser cutting. Alternatively, the holes in the carrier can be made before the friction element is attached to the carrier. In this case, it is necessary to position the carrier correctly relative to the friction element before attaching it.

[0032] Of course, the invention is not limited to the technical field of dual clutches.

[0033] According to a further feature of the invention, the friction body is designed in the form of an annular friction body which is attached to an annular support.

[0034] Preferably, the friction element is produced by die casting in a mold comprising a fixed part with a first punch, and a movable piston with a second punch, wherein at least one of said punches comprises a protruding part suitable for forming the hole during casting.

[0035] For example, the temperature inside the mold during die casting can be between 150°C and 250°C, preferably between 180°C and 250°C. Furthermore, the pressure inside the mold can be progressively increased over time, with a maximum pressure of between 200 and 300 bar.

[0036] The friction body can comprise at least one fibrous material, at least one binder and at least one filler.

[0037] In this case, the shaping of the friction body can be done hot in order to at least partially polymerize the binder.

[0038] After pressure forming, the friction element must have sufficient grip to be attached to the carrier.

[0039] For example, the polymerization rate after this shaping process can be between 50 and 90%, and is preferably approximately 70%.

[0040] Furthermore, after the friction body has been shaped, the carrier can be applied to the first side of the friction body and then pressed hot against the friction body until the binder has completely polymerized and the friction body has adhered to the carrier.

[0041] For example, the temperature during this step can be between 150°C and 250°C, and preferably between 180°C and 200°C. The pressure applied to the carrier can be between 200 and 300 bar.

[0042] Alternatively, the friction element can be attached to the carrier by gluing.

[0043] In this case, the friction element can be glued to the carrier using an adhesive based on phenolic resin.

[0044] To improve the adhesion between the friction element and the carrier, the side of the carrier on which the friction element is to be attached is prepared by sandblasting or chemical attack and / or coated with an adhesion primer.

[0045] Preferably, the second surface of the friction body is machined by grinding until the hole opens into the area of ​​the second surface of the friction body.

[0046] Machining by grinding the entire second surface of the friction body can be done simply, quickly and cost-effectively.

[0047] Especially if the friction body includes several holes, all holes in the area of ​​the friction surface can be ground in a single grinding step.

[0048] Finally, after processing the second surface of the body, any particles that may be present in the hole can be removed, for example by suction.

[0049] The invention also relates to a clutch friction lining manufactured according to the method described above, comprising a friction body intended to be mounted on a carrier, wherein said friction body comprises at least one groove which has no material on the groove bottom and no machining marks on the bottom and walls of the grooves.

[0050] The invention becomes more understandable and further details, features and advantages of the invention emerge from the following description, which is given as a non-limiting example with reference to the accompanying drawings, wherein: Fig. 1. A perspective exploded view of a friction disc according to the state of the art is, the Fig. 2 to Fig. Seven schematic views are shown, illustrating the various steps of the method for manufacturing a clutch friction lining according to the invention.

[0051] Fig. Figure 1 represents a prior art friction disc 1 comprising a grooved hub 2 extending along axis A and designed to be coupled to an input shaft of a transmission, and connected to a flange 3 extending radially outward from the grooved hub 2. Annular friction linings 4 are mounted on both sides of the flange 3 in the region of its radially outer periphery.

[0052] Each clutch friction lining 4 comprises a carrier formed by an annular metal film 5, i.e. a composite foil or a film of a thin metallic material with a thickness typically between 0.2 and 1 mm.

[0053] Ring-shaped friction elements 6 are mounted on the surfaces of the metal films 5 opposite the flange 3. These elements 6 are conventionally composed of a fibrous material, a binder, and fillers, as is known in particular from document FR 2 941 758 A1 on behalf of the applicant.

[0054] Each friction body 6 comprises a radial mounting surface 7 facing the side of the corresponding metal film and a radial friction surface 8 facing away from the mounting surface 7.

[0055] The fastening surfaces 7 are, for example, glued onto the corresponding metal films 5, and each of the metal films 5 is fastened to the flange 3 by rivets 9.

[0056] The friction surfaces 8 are designed to interact with a pressure plate and a reaction plate of a clutch mechanism, in particular a dual clutch, to transmit a torque from a driving element, such as a crankshaft of an internal combustion engine, to a driven element, such as an input shaft of a transmission.

[0057] As mentioned above, holes 10 are formed in the friction bodies and serve to accommodate the heads of the rivets.

[0058] Furthermore, holes 19 and 20 in the metal films 5 are excluded and serve to guide the shanks of the rivets 9 or a riveting tool (not shown), as is known per se. The holes 19 have a smaller diameter than the holes 20.

[0059] Thus, the heads of the rivets 9 come into contact with the metal films 5 around the holes 19, which serve to guide the shanks of the rivets 9, and the heads are also arranged in the holes 10 of the friction bodies 6.

[0060] For the reasons stated above, efforts are being made to produce friction bodies 6 with holes 10 in a simple and cost-effective manner, which pass completely through the friction bodies 6, i.e., which have no friction material at the bottom of the hole 10 on the metal films 5.

[0061] The invention proposes the following method for this purpose, which, with reference to the Fig. 2 to Fig. 7 is described. These figures represent only one cross-section B ( Fig. 2) of a ring-shaped coating 4.

[0062] The process includes a first step of manufacturing a friction body 6 which has holes 10 that open only in the area of ​​the mounting surface 7 of the body 6.

[0063] As in Fig. As shown in Figure 1, the friction element 7 is produced in particular by die casting in a mold comprising a fixed annular part 11 with a first punch, and a movable annular part 12 with a second punch having projecting cylindrical parts 13 suitable for forming the holes 10 during the mold casting process. As in the prior art, the friction element 6 comprises at least one fibrous material, at least one binder, and at least one filler.

[0064] The molding of the friction body 6 is carried out hot in order to at least partially polymerize the binder.

[0065] The temperature inside the mold during die casting can be between 150°C and 250°C, preferably between 180°C and 200°C. Furthermore, the pressure inside the mold can be progressively increased over time, with a maximum pressure of between 200 and 300 bar. The polymerization rate after this forming process can be between 50 and 90%, and is preferably on the order of 70%.

[0066] After retracting the movable piston 12 ( Fig. 3) The method includes a second step of attaching the friction body 6 to a support, which in this case is an annular metal film 5 with a thickness between 0.2 and 1 mm.

[0067] For this purpose, the ring-shaped metal film 5, as in Fig. 4 shows the piston engaging in the fixed part 11 of the mold and resting on the mounting surface 7 of the friction body 6. The preceding piston 12 is replaced by an annular piston 14, which has a substantially flat surface 15 facing the metal film 5.

[0068] The metal film 5 is now pressed hot by the piston 14 against the friction body 6 until the binder is completely polymerized and the friction body 6 adheres to the metal film 5.

[0069] To improve adhesion, the surface of the metal film 5 on which the friction body 6 is to be attached can be prepared by sandblasting or chemical treatments and / or coated with an adhesion primer before hot pressing.

[0070] In a variant not shown, the friction body 6 is attached to the metal film 5 by gluing with the help of an adhesive based on phenolic resin.

[0071] After removing the clutch friction lining 4 from the mold ( Fig. 5), the friction surface 8 of the friction body 6, which is opposite the mounting surface 7, is machined by chip removal ( Fig. 6), until the holes 10 open into the area of ​​the friction surface 8 of the friction body 6 ( Fig. 7).

[0072] For this purpose, the metal film 5 is placed on a magnetic table 16 to hold the clutch friction lining 4 in position, while the friction surface 8 of the friction body 6 is machined using a milling cutter 17. The material thickness removed is between 0.2 and 1 mm, preferably between 0.3 and 0.5 mm. After machining, the friction body 6 has a thickness between 1.5 and 5 mm. Any friction material particles present in the holes are then removed, for example, by vacuuming.

[0073] The holes in the carrier, which allow the insertion of rivet shanks or a riveting tool, can then be produced, for example, by drilling, punching, or laser cutting. Alternatively, the holes in the carrier can be produced before the friction element is attached to it. In this case, it is necessary to correctly position the carrier relative to the friction element before attaching it.

Claims

[1] Method for producing a clutch friction lining (4), characterized by that it includes the following steps: - Producing a flat friction body (6) comprising at least one hole (10) which opens only in the area of ​​a first surface (7) of the body (6), - Attaching the friction body (6) to a support (5) by adhering the first surface (7) of the body (6) to the support (5), - Machining a second surface (8) of the friction body (6), which is opposite to the first surface (7), using a milling machine, until the hole (10) opens in the area of ​​the second surface (8) of the friction body (6), wherein the material thickness removed by milling is between 0.2 and 1 mm. [2] Method according to claim 1, characterized by , that the friction body (6) is designed in the form of an annular friction body (6) which is attached to an annular support (5). [3] Method according to claim 1 or 2, characterized by, that the friction body (6) is produced by die casting in a mold which has a fixed part (11) comprising a first punch, and a movable piston (12) comprising a second punch, wherein at least one of the punches comprises a projecting part (13) which is suitable for forming the hole (10) during casting. [4] Method according to claim 3, characterized by , that the friction body (6) comprises at least one fibrous material, at least one binder and at least one filler. [5] Method according to claim 4, characterized by , that the shaping of the friction body (6) is carried out hot in order to at least partially polymerize the binder. [6] Method according to claim 5, characterized by, that the carrier (5) is applied to the first surface of the friction body (6) after the friction body (6) has been formed and is then hot-pressed against the friction body (6) until the binder has fully polymerized and the friction body (6) has adhered to the carrier (5). [7] Method according to any one of claims 1 to 6, characterized by , that the friction element (6) is attached to the carrier (5) by gluing. [8] Method according to claim 7, characterized by , that the friction body (6) is glued to the carrier (5) by means of an adhesive based on phenolic resin. [9] Method according to any one of claims 1 to 8, characterized by , that the surface of the carrier (5) on which the friction body (6) is to be attached is prepared by sandblasting or chemical treatment and / or coated with an adhesion primer. [10] Method according to any one of claims 1 to 9, characterized by, that after processing the second surface (8) of the body (6), any particles that may be present in the hole (10) are removed from it, in particular by suction. [11] Clutch friction lining (4) for a clutch, characterized by that it is obtained by the method according to any one of claims 1 to 10. [12] Clutch friction lining (4) according to claim 11, comprising a friction body intended to be mounted on a carrier (5), wherein the friction body comprises at least one groove (10) which has no material on the groove bottom and no machining marks on the groove bottom and on the groove walls.

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