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 groove (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 groove (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 makes it possible to couple the shaft of the vehicle's engine with one or the other of two coaxial input shafts of a transmission, which may 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] It is essential that only one of the clutches transmits torque. Otherwise, there is a risk of the gearbox locking up, and consequently, a risk of the wheels locking.

[0010] A friction material is conventionally composed of an annular friction element made of a fibrous material, a binder, and fillers. The friction element is attached to a carrier, which is formed by an annular metal film, for example by pressing or gluing.

[0011] A lining 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 bodies of the linings.

[0012] During operation, the friction linings are subjected to severe thermal and mechanical stresses. Furthermore, differential thermal expansion can occur between the friction element and the metal film that serves as its support. This can lead to the clutch friction lining detaching or shattering, with the fragments breaking off and potentially blocking one or even both clutch mechanisms of the dual-clutch transmission. In this case, the clutches can simultaneously transmit torque to both input shafts of the gearbox, resulting in a locking of the gearbox and the wheels.

[0013] To avoid this, patent application FR 2 927 966 A1 proposes a friction lining whose annular body comprises a first radial wall attached to a metal film and a second radial wall opposite the first wall, in which grooves are recessed. These are manufactured individually by mechanical machining or laser processing, which is relatively time-consuming and expensive.

[0014] The grooves are designed in such a way that, in the event of a breakage, the fragments of the friction body have relatively small dimensions, and that there is no risk of them causing a blockage of one of the clutch mechanisms of the dual clutch.

[0015] The grooves machined into the friction element also allow for the generation of aerodynamic forces during operation, which facilitate the separation of the friction disc from the pressure plate and the reaction plate during the decoupling phase. The geometry of the grooves can be adapted depending on the aerodynamic forces to be generated.

[0016] These grooves can also serve to more easily remove particles generated by the wear of the friction body or to improve heat exchange in order to reduce the temperature of the friction body and / or the carrier.

[0017] The grooves generally also contribute to reducing the deformation of the linings and ensuring their flatness, thus reducing the risk of premature deterioration and increasing the performance of the clutch.

[0018] The studies carried out by the applicant have shown that, with regard to the non-deformation and flatness of the covering, the grooves are globally more effective if they open both outwards and towards the carrier, i.e., if they completely traverse the friction body.

[0019] However, the state of the art does not propose any simple and cost-effective method that makes it possible to produce a covering without friction material on the groove bottom, i.e., whose grooves open opposite the corresponding carrier.

[0020] 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.

[0021] EP 0 202 145 A1 discloses a porous friction material whose pores have small channels.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] The invention is intended in particular to provide a simple, effective and economical solution to this problem.

[0026] 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 groove which 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 groove opens into the area of ​​the second surface of the friction body, whereby the material thickness removed by milling is between 0.2 and 1 mm.

[0027] In this way, the friction element is attached to the carrier according to the manufacturing process and comprises at least one groove that opens on the outside, i.e., in the area of ​​the second surface, and another that opens onto the carrier, i.e., in the area of ​​the first surface. The clutch friction lining does not include any friction material at the bottom of the groove, which allows its deformation to be limited and its flatness to be improved during operation.

[0028] Of course, the invention is not limited to the technical field of dual clutches.

[0029] 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.

[0030] 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 projecting part suitable for forming the groove during molding.

[0031] 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.

[0032] The friction body can comprise at least one fibrous material, at least one binder and at least one filler.

[0033] In this case, the shaping of the friction body can be done hot in order to at least partially polymerize the binder.

[0034] After pressure forming, the friction element must have sufficient grip to be attached to the carrier.

[0035] For example, the polymerization rate after this shaping process can be between 50 and 90%, and is preferably approximately 70%.

[0036] 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.

[0037] 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.

[0038] Alternatively, the friction element can be attached to the carrier by gluing.

[0039] In this case, the friction element can be glued to the carrier using an adhesive based on phenolic resin.

[0040] 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.

[0041] Especially when the friction element comprises multiple grooves, all grooves in the area of ​​the friction surface can be ground in a single grinding step. It should be noted that, in contrast, prior art methods require each groove to be individually machined by mechanical or laser processing.

[0042] Finally, after processing the second surface of the body, any particles that may be present in the groove can be removed, for example by suction.

[0043] The invention also relates to a clutch friction lining comprising a friction body intended to be mounted on a carrier, wherein said friction body comprising at least one groove which has no material on the groove bottom and no machining marks on the bottom and walls of the grooves, wherein the groove is produced by the method described above.

[0044] 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.

[0045] 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 gearbox, 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.

[0046] Each clutch friction lining 4 comprises a carrier formed by an annular metal film 5, that is, a foil made of a thin metallic material with a thickness typically between 0.2 and 1 mm. The carrier can also be made of plastic or a composite material.

[0047] 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.

[0048] 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.

[0049] The fastening surfaces 7 are, for example, glued onto the corresponding metal films 5, and the metal films 5 are attached to the flange 3 by rivets 9.

[0050] 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.

[0051] As mentioned above, grooves 10 are formed in the friction surfaces 8 of the friction elements 6. The number, arrangement and cross-section of the grooves 10 can be adapted depending on the requirements.

[0052] For the reasons stated above, the aim is to produce friction bodies 6 with grooves 10 in a simple and cost-effective manner, which open onto both the friction surface 8 and the mounting surface 7, i.e. grooves 10 which pass through the friction bodies 6.

[0053] 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.

[0054] The process comprises a first step of manufacturing a friction body 6 which has at least one groove 10 which opens only in the area of ​​the mounting surface 7 of the body 6.

[0055] 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 at least one projecting part 13, which is suitable for forming at least one groove 10 during the mold casting. As in the prior art, the friction element 6 comprises at least one fibrous material, at least one binder and at least one filler.

[0056] The molding of the friction body 6 is carried out hot in order to at least partially polymerize the binder.

[0057] 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%.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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 groove 10 opens into the area of ​​the friction surface 8 of the friction body 6 ( Fig. 7).

[0064] 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 grooves are then removed, for example, by vacuuming.

[0065] Although not shown in the drawings, the holes for the passage of the rivets 9 and / or the riveting tool can be made in the same way as the grooves 10, or if necessary by drilling.

[0066] In the described embodiments, the grooves are ring-shaped. However, they could have any other shape, and the number of grooves can also vary depending on requirements.

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 groove (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 groove (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 groove (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 groove (10) are removed from it, in particular by suction. [11] Clutch friction lining (4) 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, wherein the clutch friction lining is obtained by the method according to any one of claims 1 to 10.

Images