WO2015155435A1

WO2015155435A1 - Method for improved treatement of a surface of a friction member

Info

Publication number: WO2015155435A1
Application number: PCT/FR2015/050788
Authority: WO
Inventors: Isabelle Alix; Gérard Crosland; Guillaume GARESTIER; Philippe Perret
Original assignee: Valeo Materiaux De Friction
Priority date: 2014-04-11
Filing date: 2015-03-27
Publication date: 2015-10-15
Also published as: CN106457464B; CN106457464A; EP3129185A1; KR20160142313A; FR3019767B1; FR3019767A1

Abstract

The invention relates to a method for treating a surface of a friction member comprising an organic matrix containing at least one inorganic material, such as a friction member of a clutch friction device (10). At least one area of said surface, referred to as the area to be treated (27), is treated by scanning it with a LASER beam along at least one predetermined path (25). The LASER beam has an energy density between 0.05 and 1 J/cm², a frequency between 10 Hz and 10 kHz and a pulse duration between 1 ps and 1 ns.

Description

PROCESS FOR PERFECTING THE SURFACE OF AN ELEMENT

FRICTION

The present invention relates to the field of surface-treated friction linings.

Friction linings are friction elements used in particular in clutches of motor vehicles.

In a known way, in a clutch, the function of the friction elements is, when they are clamped between a pressure plate and a flywheel, to transmit the engine torque and to ensure, when starting the engine and the gearshift , the progressivity of this transmission of torque. This progressiveness contributes to driving comfort.

The gaskets are fixed by riveting on both sides of a disk called thereafter friction disk. The term "friction device" is usually understood to mean a device comprising in particular the friction disc carrying the linings.

Fittings mounted on the friction disk, clamped between the pressure plate and the flywheel or the reaction plate, transmit the torque to the gearbox. A transmission of poor quality can eventually lead to a failure of the clutch. The quality of torque transmission and resistance to centrifugal force are directly related to the mechanical strength of the materials used to make the trims and the coefficient of friction between the disc and the trims it carries. Good transmission quality requires:

on the one hand, to ensure the greatest possible coefficient of static friction between the surfaces of the friction disc and the linings and,

- On the other hand, to increase, during the usual break-in phase, the coefficient of dynamic friction between the linings and the pressure plate or the flywheel in preferred friction zones.

To optimize the quality of the transmission, it is known to treat the surface of the fittings.

For this purpose, the document FR 2 742 503 proposes a first type of surface treatment method of a lining in which, after machining the rheologically stabilized lining, the lining is superficially carbonized by over-baking of this lining at 200.degree. 300 ° C.

However, this type of process is energy intensive because the overcooking, carried out in an oven or oven, is long (it usually lasts more than 24 hours). In addition, the surface properties of a lining thus treated are relatively irregular. Indeed, over-cooking is likely to engender in the thickness of the packing an uncontrolled change gradient ranging from 50 to 300μη-ι. In addition, the effect of over-baking in the thickness of a filling may vary from one filling to the other of the same batch.

A second type of surface treatment method of a liner is proposed in particular in the document WO2009156700 or DE10 2009 002240.

In this case, it is placed on the surface of the liner to be treated a chemical effect film based on polymers, optionally crosslinked, or based on acrylates.

This second type of treatment method allows a better control of the modification gradient in the thickness of the treated lining. However, it is difficult to apply this treatment in a localized manner. Indeed, to locate the treatment it is necessary to use masks, which complicates the implementation of the method. It is therefore preferred to apply the treatment to an entire surface, in particular to irrelevant areas of this surface. Although, as disclosed in DE 10 2005 003 507, recent developments in the state of the art have led to a surface treatment process that is selectively applicable to certain areas of a lining surface, the delineation of the areas to be treated remains relatively imprecise.

Furthermore, improving the static or dynamic coefficient of friction of a liner by applying a chemical-based film based on polymers or acrylates requires controlling various parameters such as the chemical nature of the film, its thickness. and its roughness, which makes the implementation of the treatment process relatively complex.

It is therefore an object of the invention to overcome these disadvantages by providing a surface treatment method that effectively and simply applies to specific surface areas to be treated as well to improve the static coefficient of friction between the liner and friction that the dynamic coefficient of friction between the lining and the pressure plate or the flywheel in preferential areas of friction.

To this end, the subject of the invention is a process for treating a surface of a friction element comprising an organic matrix containing at least one inorganic material, such as a clutch friction device friction element, characterized in that at least one zone of this surface, called the zone to be treated, is scanned by scanning it with a LASER beam, according to at least one predetermined trajectory (25), the LASER beam having an energy density of between 0 , 05 and 1 J / cm ² , a frequency between 10 Hz and 10 kHz and a pulse duration of between 1 ps and 1 ns.

Of course, according to the invention, the area to be treated can be scanned by several beams. In addition, each beam can impact one or more zones predetermined.

The LASER beam makes it possible to benefit from perfectly parameterizable operating conditions, allowing a very precisely localized chemical treatment of the area to be treated.

The LASER beam is used to precisely select the area to be treated and to save unnecessary costs caused by the treatment of irrelevant areas.

The method according to the invention also makes it possible to chemically modify, in a perfectly controlled manner, the surface structure of the treated zones.

Conventionally, a friction lining is composed of asbestos-free synthetic fibers such as glass fibers for example. These fibers are spun, possibly twisted with copper wire and then impregnated with an organic matrix called binder matrix, consisting of thermosetting resins and / or elastomers. These binder matrix wrapped fibers are rolled to form a preform and baked in a mold to form the liner.

After cooking, the liner is conventionally machined to remove a molding skin which covers it with irregularities.

The use of a LASER beam makes it possible to modify in a perfectly controlled manner, over a controlled depth of between 10 and 300 μm, the molecular nodes within the meshes of the three-dimensional network formed by the thermoset resins or the crosslinked vulcanized elastomers. the organic matrix.

The method according to the invention thus modifies the density of the three-dimensional structure of the matrix, for example by a controlled modification of the molecular structure of the organic binders and a surface oxidation of the metallic elements, such as copper. On the other hand, the LASER beam treatment does not degrade the junctions between the mechanical reinforcing elements such as continuous glass fibers or reinforcing fillers, and the binding matrix of the lining.

The method according to the invention can also make it possible to remove locally certain chemical compounds to create a specific surface topology, such as for example a modification of the roughness according to the desired function, in particular the modification of static friction or dynamic friction.

In addition, a localized treatment makes it possible to respect the initial geometry of the friction element, which was previously produced by hot pressing and machining of the thermoset material.

By using the LASER beam according to the method of the invention, it is possible to locate a surface treatment much more easily than with a chemical effect film, while controlling the treatment in the thickness of the lining at least as much. although with a chemical effect film. Preferably, the energy density of the LASER beam applied to the area to be treated is less than 0.3 J / cm ² . Preferably also the section of the LASER beam impacting the area to be treated is between 20 and Ι ΟΟμηη, preferably equal to about 35μη "ΐ. Preferably, the wavelength of the LASER beam applied to the area to be treated is between 550 and 1200 nm Preferably, still, the frequency of the LASER beam applied to the area to be treated is greater than 100 Hz, the duration of pulsing is greater than 100ps and the wavelength is between 634 and 1064 nm.

Since a LASER beam is perfectly configurable, the treatment according to the method of the invention can, depending on the energy domain (wavelength), the length of the water used, the focal length, and the energy density. , to the controlled modification of organic binders. This modification occurs at the level of the macromolecular structure, for example by the departure of carbon and heteros elements in a controlled manner. This leads to a physicochemical modification of the surface structure of the treated zone, resulting in a surface tension and a surface topology different from those of the untreated surface in the treated zone.

The treatment according to the teaching of the invention makes it possible to act practically solely on the organic matrix, so that it is avoided to degrade the junction between the mechanical reinforcements and the matrix in the volume of the material.

The LASER source used can be chosen indifferently among, inter alia, an excimer laser, a YV04 laser (to have the processing flexibility in the near IR, the visible, see the UV), or a YAG laser.

The surface of a friction element such as a lining being between 50 and 1000 cm ² , to achieve a global and industrial treatment, several LASER beams can be used at a time, in particular from a bundle of optical fibers such as means of transporting the beam from the source to the target adapted to the industrial configuration.

Advantageously, the LASER beam is controlled according to a law allowing a predetermined variation of the effect in depth of the treatment of the area to be treated.

An area to be treated may be located on an outer face, said friction, of the friction element, the latter forming annular clutch friction device lining.

The scanning of the LASER beam on the surface to be treated thus makes it possible to modify, in a controlled micrometric thickness, the roughness or the surface chemistry of the surface of the material of the zone to be treated in order to increase on the one hand the coefficient of static friction between the lining and the friction disk and the coefficient of dynamic friction between the lining and the pressure plate or the flywheel in preferred friction zones in the running-in phase. The scanning of the LASER beam on the surface to be treated also allows an adaptation of the friction device in a dry clutch for manual gearbox (single clutch) or for robotic gearbox (double and single dry clutch).

An area to be treated may be located on an internal face, said support, of the friction element, the latter forming annular clutch friction device lining. The area to be treated of the bearing face is intended to bear on at least one complementary face of a progressivity blade of a clutch friction disc.

Preferably, the zone to be treated is 2 to 3 times greater than that of the complementary face of the progressivity blade.

Advantageously, the area of the bearing face to be treated is provided with an orifice for the passage of a rivet for fixing the annular seal on the progressivity blade of the friction disc.

Preferably, the zone to be treated extends around the rivet passage orifice and the surface of the zone to be treated is preferably 2 to 3 times greater than that of the orifice.

This allows an improvement of the static friction and a reduction of the risk of separation following the localized slip in the fixing zones. Indeed, the micrometric wear of the friction material around the riveted junctions and pressure zones with the friction disc causes micro-shear and eventually generates slips. These slips can cause the rupture of the riveted junction and degrade the operation of the clutch. This can result in a loss of reliability resulting in some degree of discomfort and dissatisfaction of the user.

Advantageously, the area to be treated is located on the radially outer half of the friction face or the bearing face of the annular liner.

The scanning path of the LASER beam may be formed by paths, possibly discontinuous, curved and substantially parallel to each other, of the LASER beam.

In particular, the scanning path of the LASER beam may be formed by paths, possibly discontinuous, substantially circular and concentric, of the LASER beam.

In a variant, the scanning path of the LASER beam may be formed by paths, possibly discontinuous, substantially rectilinear and parallel to each other, of the LASER beam.

The scanning of the LASER beam on the area to be treated thus follows a predetermined path for cooperation of the area to be treated perfectly adapted to the complementary areas of the elements intended to come into contact with the friction element. The subject of the invention is also a friction element forming an annular lining intended to be carried by a friction disk, characterized in that it comprises a surface treated according to a method as defined above.

The invention further relates to a friction device for a motor vehicle clutch, of the type comprising a friction element forming an annular lining carried by a friction disc, characterized in that the friction element is as defined above .

The invention finally relates to a clutch for a motor vehicle, of the type comprising a friction device equipped with a friction element forming an annular lining carried by a friction disk, characterized in that the friction element is as defined above.

The clutch can be a single clutch having a single friction disc to be clamped between a pressure plate and a reaction plate. Or, the clutch can be a double clutch, that is to say a clutch having two friction discs, a first friction disc being intended to be clamped between the pressure plate and the flywheel or a plate of reaction, and a second friction disc being adapted to be clamped between another pressure plate and the flywheel or the reaction plate.

The invention will be better understood on reading the appended figures, given by way of examples and having no limiting character, in which:

FIG. 1 is a perspective view, with a partial sectional view showing the arrangement of the assembly, of a friction device for clutch showing a zone of friction element forming an annular lining treated according to a first embodiment of the method; according to the invention;

- Figure 2 is a front view of the outer face, said friction, the annular lining friction element having treated areas according to a second embodiment of the method according to the invention;

Figures 3 to 5 are views similar to Figure 2 illustrating third to fifth embodiments of the method according to the invention;

- Figure 6 is a front view of the inner face, said support, the friction element forming annular seal showing treated areas according to a sixth embodiment of the method according to the invention;

Figure 7 is a view similar to Figure 6 according to a seventh embodiment of the method according to the invention.

There is shown in Figure 1 a friction device 10 for clutch, according to the invention. This device 10 comprises a friction disk 12 and two identical friction linings 14 carried respectively by the two faces of the disc 12. gaskets 14 each have a generally flat ring shape. The disk 12 has a conventional structure and provides, in the example described, a progressivity function. It thus comprises progressivity blades (not shown in Figure 1) deformable axially and elastically. Each liner 14 includes orifices 16, hereinafter referred to as lined holes 16, forming each passing seat for a fastening rivet 18 for fastening the liner 14 to the progressivity blades of the friction disk 12. Each lining 14 also includes orifices 16A. , subsequently called sagging holes 16A. Each flared hole 16A is positioned opposite a lamed hole 16 of the liner 14 of the opposite face of the friction disk 12. A flared hole 16A conventionally allows the passage of a tool for the mounting of a rivet 18.

The lining 14 has two faces, an outer face 20, said friction, and an inner face 22, said support. The friction face 20 is the face which, once the friction device 10 mounted in the clutch, frictionally engages with the pressure plate, the flywheel or a reaction plate. The friction face 20 can also frictionally cooperate with the pressure plate or the reaction plate when the clutch is a double clutch, that is to say a clutch with two friction disks each connected to a shaft of the clutch. gearbox input. In this case, a friction face 20 of a first friction disc located on the motor side frictionally engages with a first pressure plate or with a central reaction plate, and another friction face 20 with a second friction disk. located at a remote side of the engine which frictionally engages with a second pressure plate or with the central reaction plate. The bearing face 22 is the face which bears against the progressivity blades of the friction disc 12.

The friction linings 14 being identical, in what follows, only one of the liners 14 will be described.

The liner 14 comprises, in a manner known per se, an organic matrix containing at least one inorganic material.

A friction liner typically comprises:

20 to 45% by volume (preferably 35%) of thermosetting resins forming a first part of the binder matrix, such as, for example, phenoplast, melamine formaldehyde, epoxy, polyamide imide, bismaleimide or polyimide resins;

10 to 25% by volume (preferably 15%) of prevulcanized or sulfur vulcanized elastomers, forming a second part of the binder matrix;

- 0.5 to 10% by volume (preferably 3%) of copper, distributed in son or powder in the friction element;

the 100% volume complement of other inorganic components as per Examples include glass, barium sulfate, friction modifier fillers, and organic components such as graphite lubricants, carbon black, or organic friction modifier fillers.

The friction face 20 of the liner 14 is treated according to a first exemplary method according to the invention.

The treatment can take place before or after riveting the gaskets 14 on the friction disc 14.

According to this method, at least one zone of the friction face 20 has been scanned by a LASER beam executing a predetermined trajectory 25. During the treatment, the LASER beam has been adjusted preferentially so that its energy density is less than 0.3 J / cm ² , that its frequency is greater than 100 Hz, that the duration of pulsing is greater than 100ps, that the wavelength is between 634 and 1064 nm and that the cross section of the beam is equal to approximately 35 μm. ι.

The above preferential choices of the energy density, the frequency, the puise duration, the section and the wavelength allow an efficient and perfectly localized chemical treatment of the treated zone. LASER beam can advantageously be controlled according to a law allowing a predetermined variation of the effect in depth of the treatment of the treated zone 27.

Although a scan path of the LASER beam has been shown on the face 20 of the liner 14 to allow visualization of a treated area 27, it is not visible to the naked eye. On the other hand, this trajectory can be visualized by confocal microscopy or by scanning electron microscopy.

It will be noted that the trajectory 25 diagrammatically represented on the friction face 20 of the lining 14 (see FIGS. 1 to 5) is for a purely illustrative purpose and does not correspond in particular to the number of passes of the LASER beam for the real trajectory 25. used to effectively obtain the treated area 27 according to the invention.

In FIG. 2 it can be seen that this trajectory 25 may be discontinuous so as to form several treated zones 27 on the same face 20 of a liner 14. It can also be seen that the trajectory 25 may be parallel to a direction substantially corresponding to the width of the treated area 27. More generally, the scan path 25 of the LASER beam may be formed by paths, possibly discontinuous, substantially rectilinear and parallel to each other.

FIGS. 3 and 4 illustrate the fact that the same type of treated zones 27 coming from the same type of trajectories 25 may differ in their positioning with respect to the orifices 16. It is also seen that, unlike the treated zones 27 of the FIG. 2, the trajectory 25 can be parallel to a corresponding direction substantially the length of the treated area 27.

In FIG. 5 it can be seen that the treated zone 27 can be curved, for example parabolic, the scanning trajectory 25 being formed by paths, possibly discontinuous, curved and substantially parallel to each other.

FIGS. 1, 3, 4 and 5 also illustrate that the treated zone 27 is preferably located on the radially outer half of the friction face 20 of the lining 14.

Note that the trajectory 25 diagrammatically shown on the bearing face 22 of the lining 14 (see FIGS. 6 and 7) is for a purely illustrative purpose and does not correspond in particular to the number of passes of the LASER beam for the trajectory 25. actual used to effectively obtain the treated area 27 according to the invention.

As the transmission of the driving torque of the lining 14 to the friction disc 12 is done by the rivets 18, each treated zone 27 of the bearing face 22, as can be seen in FIGS. 6 and 7, preferably extends around the orifice 16 for passing the rivet 18. The surface of the treated zone 27 is advantageously two to three times greater than that of the orifice 16.

As in FIG. 1, FIG. 6 shows that the scan trajectory 25 is formed by paths, possibly discontinuous, substantially circular and concentric, of the LASER beam.

Each treated zone 27 of the bearing face 22 of the lining 14 comes to bear on at least one corresponding face of a progressiveness blade of a friction disk 12. The treated zone 27 is preferably, as illustrated in FIG. FIG. 7, two to three times greater than that of the corresponding face of the progressivity blade of the friction disk 12, to take account of the elastic deformation of the blade when the friction device 10 is clamped between the pressure plate and the flywheel.

The invention is not limited to the exemplary embodiments presented and other exemplary embodiments will become apparent to those skilled in the art.

It is in particular possible to adapt the shape of the treated zone to any form of stress experienced by the friction or bearing surfaces of the friction lining and to treat each friction or support face of each lining of a liner. same friction device for clutch independently of one another. It is also possible that the treated areas of the same face vary with respect to each other.

Indeed, once the lining riveted on the friction disk, it appears that each friction face is subject to specific constraints and it is then relevant to apply to each a specific treatment independent of that applied to the other side of friction. Moreover, some friction discs being of the type with several rows of rivets, it is understood that the treatment method according to the invention is adaptable to this type of disc also.

It is also possible to use the same method for treating surface areas of friction elements other than friction linings, such as brake pads.

Claims

1. A method of treating a surface of a friction element (14) comprising an organic matrix containing at least one inorganic material, such as a clutch friction device (10) friction element, characterized in that at least one zone of said surface, said zone to be treated (27), is scanned by scanning it by a laser beam, according to at least one predetermined trajectory (25), the laser beam having an energy density of between 0.05 and and 1 J / cm ² , a frequency between 10 Hz and 10 kHz and a pulse duration of between 1 ps and 1 ns.

The method of claim 1, wherein the energy density of the LASER beam applied to the area to be treated (27) is less than 0.3 J / cm, and / or the frequency of the LASER beam applied to the area to be treat (27) is greater than 100 Hz, and / or the duration of pulsation of the LASER beam applied to the area to be treated

(27) is greater than 100 ps.

3. The method of claim 1 or 2, wherein the section of the LASER beam impacting the area to be treated (27) is between 20 and Ι ΟΟμηη, preferably equal to about 35μη "ΐ.

4. Method according to any one of claims 1 to 3, wherein the wavelength of the LASER beam applied to the area to be treated (27) is between 550 and 1200 nm, preferably between 634 and 1064 nm.

A method according to any one of the preceding claims wherein the friction device friction member (10) is obtained by molding and wherein the LASER beam processing step is preceded by a machining step for to the elimination of a molding skin.

6. Method according to any one of claims 1 to 5, wherein the LASER beam is controlled according to a law allowing a predetermined variation in the effect in depth of treatment of the area to be treated (27).

7. Method according to any one of claims 1 to 6, wherein a zone to be treated (27) is located on an outer face, said friction (20), of the friction element, the latter forming a seal device ring (14) (10) clutch friction.

8. Method according to any one of claims 1 to 7, wherein an area to be treated (27) is located on an inner face, said support (22), the friction element, the latter forming a annular lining (14) of clutch friction device (10), the area to be treated (27) of the bearing face (22) being intended to bear on at least one corresponding face of a progressivity blade a friction disk (12) clutch.

The method of claim 8, wherein the surface of the area to be treated

(27) is two to three times greater than that of the face corresponding to the progressivity blade.

10. The method of claim 8 or 9, wherein the area to be treated (27) of the bearing face (22) is provided with an orifice (16) for the passage of a rivet (18) fixing the the annular seal (14) on the blade.

1 1. A method according to claim 10, wherein the area to be treated (27) extends around the rivet passage opening (16) (18), the area of the area to be treated (27) being preferably two to three times greater than that of the orifice (16).

12. A method according to any one of claims 1 to 11, wherein the area to be treated (27) is located on a half (28) radially outer of the friction face (20) or the bearing face (22). ) of the annular seal (14).

13. A method according to any one of claims 1 to 12, wherein the scanning path (25) of the LASER beam is formed by paths, possibly discontinuous, curved and substantially parallel to each other, the LASER beam.

14. The method of claim 13, wherein the scan path (25) of the LASER beam is formed by paths, possibly discontinuous, substantially circular and concentric, LASER beam.

15. Method according to any one of claims 1 to 12, wherein the scan path (25) of the LASER beam is formed by paths, possibly discontinuous, substantially straight and parallel to each other, the LASER beam.

16. Annular lining friction element (14) intended to be carried by a friction disk (12), characterized in that it comprises a surface treated according to a method according to any one of claims 1 to 15.

17. Device (10) for friction clutch of a motor vehicle, of the type comprising a friction element forming an annular lining (12) carried by a friction disc (14), characterized in that the friction element is according to the claim 16.

Clutch for a motor vehicle, of the type comprising a friction device equipped with a friction element forming an annular lining (12) carried by a friction disc (14), characterized in that the friction element is according to the claim 16.