FR2677721A1 - Progressive friction disc for a dry friction clutch - Google Patents

Abstract

A progressive friction disc of a dry clutch, according to the invention, includes two friction linings (1, 5; 6, 10) in the form of a ring, between which is inserted a progressiveness device (2, 4; 7) formed of a deformable fibrous material. The said deformable fibrous material exhibits, in the free state, a porosity lying between 20% and 95% allowing, under the effect of compressive stresses, the decrease in thickness of the material and, when such stresses cease, return to the original thickness.

Description

 The invention relates to a friction disc for a dry friction clutch.

 Such a disc is, generally, formed of a metallic veil comprising axially defodmable parts, which form a progressive device, on which are attached, on either side, two friction linings in the form of crowns.

 The role of the progressivity device is, on the one hand, to allow the progressive and smooth transmission of the engine torque during a clutch operation and, on the other hand, to compensate for geometric defects in the surfaces of the 'clutch.

 The friction linings are fixed to said web in the usual manner by riveting.

 As a result, the useful thickness of each liner is limited to its portion which is located above the heads of the fixing rivets.

 As a result, the friction disc is unnecessarily heavy and its inertia is increased. This leads to difficulties in achieving synchronism during clutch release operations and gear change.

 In order to eliminate the fixing of the linings by riveting, it has already been proposed to glue the linings on flat metal plates, with the interposition, in discrete zones, of elastic arms made of elastomeric material.

 Such a construction is for example described in patents US-A-2,253,316, FR-B-2,450,977.

 In another type of construction, described in patent application EP-A-0252583, the friction linings are fixed to a flat metallic web, by means of concentric circular beads made of elastomeric material.

 These known solutions using arms or cords made of elastomeric material, however, have the disadvantage of a non-homogeneous distribution of the elastomer which results in a defect in the uniformity of the progressiveness at the level of the friction linings.

 The object of the present invention is to produce a progressive friction disc free from the aforementioned drawbacks.

 According to the invention, a dry clutch progressive friction disc has two friction linings and is characterized by at least one progressive device made of deformable fibrous material.

Said deformable fibrous material according to the invention has a porosity of between 20% and 95%.

 Such a progressive device according to the invention is inserted between said linings to ensure a certain deformability, by reducing thickness, under the effect of compression stresses, and, by returning to its original thickness, when such stresses cease .

 The fibrous material comprises mineral fibers and / or organic fibers. It can also include a binder.

 The mineral fibers are advantageously chosen from the group formed by glass fibers, ceramic fibers, carbon fibers. The organic fibers are advantageously chosen from the group formed by aramid fibers, thermoplastic fibers, such as polyester fibers, polyamide fibers and polyetheretherketone fibers.

 Continuous fibers and / or short fibers, for example less than a millimeter, can be used.

 The fibers can be either in an ordered form such as a woven, and / or in a disordered form, such as a mat, felt, paper or tablecloth.

 In the free state, that is to say in the absence of compression constraints, the materials according to the invention have a minimum porosity rate, as indicated above. When these materials are subjected to compressive stresses, thanks to the porosity present, there is a reduction in the thickness of said materials.

 In preferred variants, the fibrous material is used in the form of continuous rings to best ensure the uniformity of the deformation of the friction disc.

 However, discontinuous shapes can be used, such as stars or openwork crowns for example.

 According to a first embodiment of the invention, said crown of fibrous material is placed between a lining and a metallic support or web.

 As a variant, between each lining and a metal support or veil is placed such a ring made of fibrous material.

 According to another embodiment of the invention, said crown of fibrous material is arranged between two metal supports or webs, joined together, on each of which is attached, in particular by gluing, a friction lining.

 According to an advantageous arrangement of the invention, said crown of fibrous material is bonded, on either side, to the elements, veil or lining, with which it is in contact.

 By allowing continuous contact on a flat support, the linings can themselves be fixed by gluing.

 It follows that the useful thickness of said linings, that is to say that which can be worn in operation, is practically constituted by the thickness itself of the lining.

 Therefore, it is possible, thanks to the invention, to use linings whose thickness is limited vis-à-vis a lining which would be fixed by rivets, for the same possible wear thickness.

 By reducing the thickness of the friction linings, the mass of the friction disc and consequently its inertia is reduced.

 This significantly improves the operating conditions of the transmission chain fitted to the clutch.

 The invention also makes it possible to improve the progressive characteristics of a dry clutch friction disc.

 The fibrous material used according to the invention allows self-adaptation, almost point by point, to the local differences in the tightening of the clutch friction disc between a pressure plate and a reaction plate.

 The friction linings can thus more easily adapt and compensate for the flatness irregularities of such pressure and reaction plates, in particular when these are caused to deform under the effect, in particular, of heating.

 As a result, the useful surface of contact of the linings with said pressure and reaction plates is practically identical to the total surface of said linings, which allows a homogeneous distribution of the wear of the linings and, thus, improving the longevity of these.

Other characteristics and advantages of the invention will appear on reading the description of exemplary embodiments of the invention, with reference to the appended drawings in which
- Figure 1 shows, in section, a subset of clutch friction disc according to a first embodiment of the invention;
- Figure 2 shows, in section, a subset of clutch friction disc according to a second embodiment of the invention
- Figure 3 shows, in section, a subset of clutch friction disc according to a third embodiment of the invention.

 The clutch friction disc sub-assembly shown in FIG. 1 comprises a metallic web 3 forming a support for a set of two friction linings 1 and 5, in the form of crowns, attached on either side of said web 3.

 According to the invention, each friction lining 1 and 5 is secured to said web 3 with the interposition of a crown made of deformable fibrous material 2.4, forming a progressive device, adhered by any means suitable for said web 3, on the one hand, and to the corresponding trim 1.5, on the other hand.

 Such a sub-assembly is intended to be associated with an internally splined hub, intended to come into engagement on a splined shaft, in practice a gearbox input shaft of a motor vehicle.

The association of said sub-assembly with said hub can be done via the metallic veil 3, either directly as described for example in the patent
FR-849.990, either by means of a torsion damping device comprising elastic means interposed in rotation between said web 3 and one or more against-webs integral with the hub, as described for example in patent application FR-2.624 . 237.

 For further details, reference is made to the description given in the aforementioned documents.

 These well known arrangements will not be described below.

 As a variant, not shown, one of the friction linings is directly adhered to said metallic veil 3, while, in accordance with the invention, a ring made of fibrous material is interposed between the other lining and said veil.

 The production of the sub-assembly described above with reference to FIG. 1 is carried out using the components below.

 The friction linings 1.5 are in the form of rings with an outside diameter of 200 mm and an inside diameter of 137 mm; their thickness is 1.6 mm.

 They are made of material sold under the reference F202 by the company VALEO.

The web 3 is in the form of a disc with a diameter of 200 mm and a thickness of 0.6 mm, made of steel
XC70.

 The crowns of 2.4 deformable fibrous material have an outside diameter of 200 mm and an inside diameter of 137 mm with a thickness of 1.5 mm.

 They are made of a mixture of glass fibers and fusible polyamide-type fibers. This type of material is commonly called T.R.E. (thermo plastic reinforced stampable).

The crowns of deformable fibrous material 2,4 are produced for example in the following manner
- the mixture of glass fibers and polyamide fibers is in the form of veils which are superimposed.

The stack of these sails is heated to the melting point of the polyamide fibers. Then we press the sails between the plates. The sails are thus compacted, the press plates being at room temperature, the cooling of the polyamide binds the glass fibers very firmly. A sheet is thus obtained.

 According to the invention, the compaction of the material is limited by limiting the travel of the press plates to obtain a porosity of between 20 and 95%, thanks to which the fibrous material is deformable.

 Subsequently, in the sheets of fibrous materials thus produced, parts in the form of crowns are cut.

 In this example, the composition of the TRE material is by mass, 40% glass fibers, 60% polyamide fibers.

 The thickness after compaction is 1.5 mm with a porosity rate of 60%.

 The porosity being defined by the vacuum rate, that is to say the ratio of the volume of vacuum occupied by the air in the material, to the total volume of this material.

 The development of the subset includes the steps described below.

 First of all, the web 3 is cleaned by abrasion and then degreasing using a chlorinated solvent such as trichlorethylene.

 The rear attachment faces of the friction linings 1.5 are coated with phenolic resin adhesive.

 The faces of the crowns made of fibrous material TRE 2.4 coming into contact with the web 3 are also coated with the same adhesive.

 Inside a cylinder, the inside diameter of which corresponds to the outside diameter of the various elements of the sub-assembly, are successively arranged a first lining 5, a ring made of fibrous material 4, the web 3, a second ring made of fibrous material 2 , a second friction lining 1.

 The cylinder is then closed by means of a piston on which a pressure of 2 bar is applied.

The whole is then brought to a temperature of 1800C to ensure the polymerization of the glue.

 It has been determined that the sub-assembly thus obtained has a deformation capacity of 0.5 mm under a load of 3500 N corresponding to the calibration of a clutch mechanism.

 It has also been determined that the inertia, compared to a standard embodiment where the linings are fixed using rivets on corrugated metal supports, is reduced by 18%.

 Bench tests have shown comparable results, in terms of friction and wear, compared to a standard friction disc.

 The sub-assembly shown in FIG. 2 is formed by two adjacent metallic webs 8, 9, on an external face of each of which is joined by adhesion a friction lining 6, 10 in the form of a crown.

 At least one veil 8 or 9, and preferably, as shown, each of the veils 8,9 has a flat central part 8a, 9a and a flat peripheral part 8b, 9b on which the linings 6,10 are fixed.

 The peripheral part 8b, 9b of each of the webs 8, 9 is axially offset with respect to the corresponding central part 8a, 9a by virtue of an offset respectively 8c, 9c.

 The webs 8a and 9a are placed in such a way that their central part 8a, 9a is in contact and that the recesses 8c and 9c are placed in opposition, so that the peripheral parts 8b and 9b are spaced apart, leaving a space between them. in the shape of a crown.

 According to the invention, said crown-shaped spacing is filled with a deformable fibrous material 7 shaped as a crown and adhered at least partially to at least one of the webs 8, 9, on the peripheral part 8b, 9b of said webs, on a opposite side to that on which is fixed a lining respectively 6.10, forming a progressive device.

 In this exemplary embodiment, the radial dimension of the crown of deformable fibrous material 7 is identical to the corresponding radial dimension of the friction linings 6,10, and a radially internal portion of the space between said peripheral parts 8b, 9b 8,9 sails are provided empty of deformable fibrous material 7.

 As in the case of FIG. 1, the friction linings 6, 10 are located in line with the crown of deformable fibrous material 7.

 As a variant, not shown where the sub-assembly has the same shape as in FIG. 2, the deformable fibrous material in the form of a crown can be of a radial dimension different from that of the friction linings.

 It will be noted that according to the exemplary embodiments of FIGS. 2 and 3, the torque is transmitted during a clutch operation, directly from a lining to the adjacent web, which avoids any shear stress on said crown made of fibrous material. .

 The elements making up the sub-assembly described with reference to FIG. 2 have the characteristics described below.

 The friction linings 6.10 are each in the form of a crown, the outside diameter of which is 200 mm and the inside diameter of 137 mm, with a thickness of 1.6 mm.

 They are made with a material sold under the reference F202 by the company VALSE.

 The sails 8 and 9 are each made of steel of the XC70 type, and have a thickness of 0.3 mm and an outside diameter of 200 mm.

 The deformable fibrous material 7 is in the form of a crown, the outside diameter of which is 200 mm and the inside diameter of 137 mm, with a thickness of 2 mm.

This ring of fibrous material is cut from a ceramic fiber paper such as the paper sold under the reference K60 by the Company
Kerlane, with a porosity of 90%, defined as above.

 The development of the sub-assembly from the above elements is carried out as indicated below.

 First, a chemical pickling, for example using acid, 8.9 sails, then a passivation followed by drying.

 The linings 6.10 are then coated with a glue based on phenolic resin.

 The friction linings 6.10 are then bonded to their respective web forming a support 8.9, by hot pressing at a temperature of 1800C.

 The faces of the webs 8, 9 opposite those to which the friction linings have been glued, are abraded using an emery disc, then cleaned with a chlorinated solvent such as trichlorethylene.

 The two faces of the crown are coated with fibrous material 7 with an adhesive based on phenolic resin.

 In a suitable assembly, not shown, the various elements 9 and 10, 7, 6 and 8 are positioned successively.

 The sub-assembly 9 and 10 is first deposited at the bottom of the assembly which comprises a cylinder whose internal diameter corresponds to the external diameter of 9 and 10, and of the crown 7 which is thus positioned correctly.

 The centering of the sub-assembly 6.8 with respect to the sub-assembly 9 and 10 is carried out by a cylindrical part whose external diameter corresponds to the internal diameters 8d and 9d of the elements 8 and 9.

 The friction disc elements are pressed under 2 bars and the assembly is heated to a temperature of 1800C to assemble the sub-assembly by gluing.

 This sub-assembly thus obtained has an inertia reduced by 26% compared to a standard solution with cambered blades and riveted fittings.

 With this type of refractory materials, the stability of the physical and mechanical properties, under high temperature rises, is particularly remarkable.

 On the other hand, tests of axial gymnastics of the sub-assembly, simulating the successive operations of lifting and lowering the pressure plate of the clutch in operation, show very good resistance to fatigue of the material after more than 5 × 105 cycles (compression and return to free state). This number of cycles is representative of the number of clutch operations performed during the total lifetime of a running vehicle.

 Test benches and vehicles show levels of friction equivalent to a conventional solution and lower and more homogeneous wear in high energy levels always in comparison with a conventional solution.

 As a variant, as shown in FIG. 3, the two metallic webs used are flat, flexible and are kept apart from one another, in particular by a rigid spacer 11.

 In a variant not shown, the crown made of fibrous material 2 and / or 4.7 is made up of a set of elementary sub-layers stacked and advantageously secured to each other.

 In addition, with fibrous materials which have damping characteristics depending on the nature of the binders and / or fibers used, it is possible to obtain that on loosening the friction disc does not immediately resume its initial thickness, which is favorable for a frank release.

 The different metallic sails 3; 8 and 9 can advantageously have cutouts intended to lighten them, to increase their flexibility or to avoid stresses and deformations due to possible heating in service.

Claims (11)

 1) Dry clutch progressive friction disc, comprising two friction linings (1,5; 6,10), characterized by at least one progressivity device (2,4; 7) formed from a deformable fibrous material.  2) Friction disc according to claim 1, characterized in that said deformable fibrous material has, in the free state, a porosity between 20% and 95%.  3) Friction disc according to one of the preceding claims, characterized in that said deformable fibrous material comprises mineral fibers.  4) Friction disc according to claim 3, characterized in that said mineral fibers are chosen from the group formed by glass fibers, ceramic fibers, carbon fibers.  5) Friction disc according to any one of the preceding claims, characterized in that said deformable fibrous material comprises organic fibers.  6) Friction disc according to claim 5, characterized in that said organic fibers are chosen from the group formed by aramid fibers, thermoplastic fibers, such as polyester fibers, polyamide fibers and polyether-etherketone fibers .  7) Friction disc according to any one of the preceding claims, characterized in that said deformable fibrous material is in an ordered form such as a woven.  8) Friction disc according to any one of claims 1 to 6, characterized in that said deformable fibrous material is in a disordered form such as a mat, felt, paper or web.  9) Friction disc according to any one of the preceding claims, characterized in that said progressiveness device (2,4) is glued between a lining (1,5) and a metallic support or web (3).  10) Friction disc according to any one of claims 1 to 8, characterized in that said progressive device (7) is disposed between two supports or webs (8,9) integral with each other, on each of which is attached, in particular by gluing, a friction lining (6,10).  11) Friction disc according to any one of the preceding claims, characterized in that said progressiveness device (2,4; 7) is in the form of a crown.