Pad with variable particle size

Abstract

The invention relates to a brake pad (10) comprising a backing plate (1) and a friction lining (2), the lining (2) being defined by a friction surface (26) intended to come into contact with a brake rotor, a surface for attachment to the backing plate, a rear edge (21) and a front edge, the lining (2) comprising: a collection groove (3) for collecting brake particles, the groove (3) being open on the friction surface (26) and being able to be placed in fluid communication with a vacuum source, the collection groove (3) having a trailing edge (32); a first friction material, having a first grain size, and occupying a first volume (V1) of the friction lining (2); and a second friction material, having a second grain size larger than the first grain size, and occupying a second volume (V2) of the friction lining (2) separate from the first volume (V1), the second volume (V2) extending at least from the trailing edge (32) of the groove (3) to the rear edge (21) of the friction lining (2).

Description

Description Title: Variable grain size plate Technical field

[0001] This disclosure relates to the field of friction brakes and in particular the linings used in such brakes. These brakes find applications in particular in road vehicles (cars, buses, heavy goods vehicles) and rail vehicles (trains, trams, metros). Prior art

[0002] Document FR 3 087 238 A1 describes a friction lining for disc or drum brakes, equipped with a groove for collecting brake particles. The groove is connected to a vacuum source whose function is to suck up and collect the particles in order to limit their spread in the environment. An air inlet hole, of a suitable size to obtain sufficient vacuum levels and flow rates, is provided in the lining. The vacuum level and flow rate are therefore maintained constant (at the same suction power) throughout the life of the pad.

[0003] In application FR2212695, filed on 02.12.2022 and entitled “Inclined air inlet drilling”, the hole is arranged in an inclined manner in order to maximize the speed of the air flow at the disc and also in order to encourage an air flow in the opposite direction to the direction of movement of the disc.

[0004] The Applicant is concerned with constantly improving suction performance to maximize particle capture while limiting the energy expended to generate suction. Summary

[0005] Thus, the present disclosure contributes to improving suction performance.

[0006] A brake pad is provided comprising a base and a friction lining, the lining being delimited by a friction surface intended to come into contact with a brake rotor, a surface for attachment to the base, a rear edge and a front edge, the lining comprising: a groove for collecting braking particles, the groove being open on the friction surface and being capable of being placed in fluid communication with a source of vacuum, the collection groove having a trailing edge; a first friction material, having a first grain size, and occupying a first volume of the friction lining; and a second friction material, having a second grain size greater than the first grain size, and occupying a second volume of the friction lining, distinct from the first volume, the second volume extending at least from the trailing edge of the groove to the rear edge of the friction lining.

[0007] The inventors have in fact demonstrated that when a pad has manufacturing imperfections, there is no seal at the trailing edge of the groove, between the pad and the disc. This lack of seal has surprisingly led to an improvement in the suction performance. However, since these manufacturing imperfections fade as the pad wears, the sealed contact between the disc and the pad is quickly restored, which eliminates the benefit of imperfections on suction performance. The inventors have shown that using a larger grain size on a rear area of ​​the pad makes it possible to reproduce the effects obtained with a manufacturing imperfection on improving suction performance, and this, over a greater part of the life of the pad: the larger grains form a profile irregularity and therefore a non-adherence of the trailing edge of the groove to the disc, whatever the state of wear of the pad.

[0008] By definition, the terms "front" and "back" refer to the direction of movement of the rotor: a given point on the rotor sees, as it moves, first a "front" edge, then the "back" edge.

[0009] By "trailing edge" is meant the inner surface of the groove located on the rear side of the groove.

[0010] By "grain size" is meant the usual definition of grain size in the study of the granulometry of the material. It can be, in a section plane of the material, an arithmetic mean of the equivalent diameters (the diameter that a circular grain of identical section would have) of a statistically relevant number of grains.

[0011] Friction materials for use in brake pad linings generally include a friction modifier to promote the coefficient of friction (this includes one or more abrasive materials and / or one or more solid lubricants), a fibrous material for reinforcement, a filler to provide consistency to the material, and a binder. The friction modifiers may include inorganic friction modifiers, for example, alumina, silica, magnesia, zirconia, chromium oxide, quartz, etc., and organic friction modifiers, for example, synthetic rubber, cashew resin, etc. The friction modifiers may also include solid lubricants such as, for example, graphite, molybdenum disulfide, etc. The fibrous material may include metal fibers, inorganic fibers, and / or organic fibers.The filler material may include barium sulfate, calcium carbonate, metal powder, vermiculite, mica and the like. The filler is thus mineral and / or metallic.

[0012] In one aspect, the first material comprises a first metallic filler and the second material comprises a second metallic filler distinct from the first metallic filler, and the difference in grain size between the first and second materials is provided by a difference in grain size of their metallic fillers. In another aspect, the first material comprises a first mineral filler and the second material comprises a second mineral filler distinct from the first mineral filler, and the difference in grain size between the first and second materials is provided by a difference in grain size of their mineral fillers.

[0013] In another aspect, the second grain size is at least three times larger than the first grain size. Optionally, the second grain size is at least 5 times, or at least 10 times, or even at least 15 times larger than the first grain size. Optionally, the second grain size is less than 50 times, or less than 20 times, or less than 15 times or less than 10 times the first grain size.

[0014] In another aspect, the groove has a leading edge and the second volume includes the leading edge. In this embodiment, the entire groove is contained within the second volume. This leaves a significant air suction potential at the interface between the groove and the disc.

[0015] In another aspect, the first volume is at least three times larger than the second volume. Indeed, it may be advantageous for the material having the smaller grains to remain in the majority in the overall composition of the lining in order to provide a large contact surface between the lining and the disc (on a microscopic scale).

[0016] In another aspect, the second volume extends from the friction surface to the attachment surface. This configuration allows the benefits of using a coarse-grained material to be retained over the entire life of the pad.

[0017] In another aspect, an underlay separates the attachment surface from the first and second volumes. The material forming the underlay may have a different hardness than the first and second friction materials.

[0018] In another aspect, the groove is a first groove, the liner comprising a second groove forward of the first groove, the second groove having a second trailing edge, the first material occupying a third volume extending from the second trailing edge to the first groove.

[0019] In another aspect, the liner includes a conduit extending from the groove to a free end, at the inner or outer edge of the liner, or the attachment surface. This conduit can, synergistically, multiply the improvement in suction performance obtained by the integration of the coarse-grained material into the liner.

[0020] The invention also relates to a method for manufacturing a brake pad comprising: placing a first friction material, of a first grain size, in a first volume of a mold; placing a second friction material, of a second grain size greater than the first grain size, in a second volume of the mold, the second volume being distinct from the first volume and extending to a rear side of the mold; sintering the friction materials on a base; and producing a braking particle collection groove by molding or machining, the groove being at least partially located in the second volume. The groove can in particular be obtained during the sintering of the friction materials. Brief description of the drawings

[0021] Other features, details and advantages will become apparent upon reading the detailed description below, and upon analyzing the attached drawings, in which:

[0022] [Fig. 1] Figure 1 is a perspective view of a brake pad.

[0023] [Fig. 2] Figure 2 is a sectional view of the plate of Figure 1, along line 11-11 identified in Figure 1.

[0024] [Fig. 3] illustrates a brake pad.

[0025] [Fig. 4] illustrates a brake pad.

[0026] [Fig. 5] illustrates a brake pad.

[0027] [Fig. 6] illustrates a brake pad. Description of the embodiments

[0028] The figures represent different elements schematically. They are not necessarily drawn to scale. The cylindrical reference frame is used: the axial direction corresponds to the axis of rotation of the rotor (disc or drum), the radial direction is perpendicular to the axial direction, and the tangential or circumferential direction is perpendicular to the radial direction.

[0029] As illustrated in Figures 1 and 2, a brake pad 10 comprises a base 1, also called a base. The base 1 is for example made of a metallic material. The base 1 is a flat plate of substantially constant thickness (for example between 3 and 5 mm) whose general shape in its main plane is trapezoidal with straight or curved edges. It may include ears intended for guiding it in a caliper or a yoke. The base 1 comprises an internal face 13 on which a lining 2 is fixed, and an external face 14 which is opposite and parallel to the internal face 13. These two faces are joined by a lateral edge 11.

[0030] According to the present disclosure, the lining 2 is made of at least two distinct friction materials. The lining 2 is delimited by a friction surface 26 (“rubbing” surface), a fixing surface 20 opposite the friction surface 26 and fixed on the sole 1, an inner edge 23, an outer edge 24, a rear edge 21 and a front edge 22. The outer edges 24, rear 21, and front 22 are convex or rectilinear, the inner edge 23 is concave or rectilinear.

[0031] The thickness of the lining 2 (measured vertically in Figure 1, perpendicular to the plane H) decreases as the pad wears. The friction surface 26 therefore gradually moves closer to the base 1 as the lining 2 wears. In operation, the lining 2 (and the rotor, not shown) release(s) particles due to the friction between the lining 2 and the rotor. The path of the particles 28 along the friction surface 26 is shown in dotted lines in Figure 1.

[0032] The lining 2 is provided with at least one collecting groove 3 open on the friction surface 26, and which is located near the rear edge 21. The groove 3 may be distant from the rear edge 21 by a distance less than 20% of the circumferential width of the lining 2. For example, the portion of the friction surface 26 which is located between the rear edge 21 and the groove 3 may be less than 10% of the entire friction surface 26.

[0033] The depth of the groove(s) 3 may be less than the height of the lining 2 (measured perpendicular to the plane of the friction face 26), that is to say that some lining material 2 may remain between the bottom of each groove 3 and the internal face 13 of the sole 1. The distance between the bottom of each groove 3 and the internal face 13 (measured perpendicular to this internal face 13) is called “residual height” and is for example equal to at least 1%, or at least 5% or at least 10% or at least 20% of the initial height (before wear) of the lining 2.

[0034] Alternatively, the depth of the groove(s) 3 is equal to the height of the lining 2, that is to say that the bottom of the groove(s) 3 coincides with the internal face 13 of the sole 1.

[0035] The collection groove 3, or at least one of the collection grooves 3, extends at least partly along the rear edge 21, and is rectilinear or follows the curvature of the rear edge 21. The smallest dimension of the groove 3 is its width, measured in the plane H of the wafer 10, substantially in the tangential direction T.

[0036] The lining 2 is for example provided with a single continuous groove, substantially rectilinear or having one or more bends between two or more substantially rectilinear portions.

[0037] Alternatively, the lining 2 is provided with a plurality of collection grooves 3 which are two by two disjointed. By disjointed grooves, it is to be understood that the grooves do not communicate with each other other than, possibly, by a conduit internal to the lining.

[0038] In the example illustrated, the groove 3 has a blind end 31 which does not open onto the outer surface 24. On the inner surface 23 side, the groove has a hole, one end 91 of which opens onto the inner surface 23.

[0039] Various examples of holes can be envisaged, perpendicular to the sole or to the internal edge, or inclined, according to all the configurations described by means of the angles p, 5 and 0 in application FR2212695, filed on 02.12.2022 and unpublished.

[0040] One of these examples is illustrated in Figure 2 which is a sectional view of the plate 10 along the direction noted ll:ll in Figure 1. It shows the leading edge 33 of the groove 3, that is to say the internal surface of the groove which is “seen” first by a point of the disc during its rotation.

[0041] An air flow is generated in the collection groove 3 by a vacuum source (suction system), connected to the groove by means of a conduit 40. At the blind end 31, the sole 1 has a through suction hole 17 which opens into the groove 3. Thus, the particles 28 sucked into the groove 3 pass into the suction hole 17 then into the conduit 40.

[0042] The hole 90 opens at one of its ends outside the friction face 26, either onto a peripheral surface 21, 22, 23, 24, or through the sole 1, or into another groove. In the example illustrated, one of the ends 91 of the hole 90 opens onto the internal surface 23, and the other end 92 opens into the collection groove 3. This hole provides additional suction. Indeed, thanks to a sudden increase in section at the end 92, there exists, during operation, a depression between the end 91 and the collection groove 3. The hole 90 is inclined at an angle p in a vertical plane.

[0043] This configuration is given as an example, other inclinations being possible as described in the unpublished document FR2212695.

[0044] Figure 3 shows (in part) a pad 10 comprising a friction lining 2 fixed to a sole 1. A particle collection groove 3 is adjacent to a rear edge 21 of the lining. The groove 3 comprises one or more blind ends 31, a leading edge 33 and a trailing edge 32.

[0045] The friction lining 2 is formed from two distinct materials, one having a smaller grain size than the other. Thus, a first material occupies a volume V1 and a second material, with a larger grain size than the first material, occupies a volume V2. A dotted line describes the interface between the two materials. In the present disclosure, it is understood that the first volume V1 is entirely occupied by the first material and that the second volume is entirely occupied by the second material.

[0046] The volume V2 extends at least between the trailing edge 32 and the rear edge 21. Thus, when particles are torn off in the area of ​​the friction surface 26 between the trailing edge 32 and the rear edge 21, an asperity is formed which, during suction, allows an air leak to be created at the interface between the disc and the friction surface 26. It is thus possible, in the same way as with the optional hole 90 discussed above, to increase the suction capacity of the groove and thus to increase the suction performance of the device.

[0047] In the example of Figure 3, the leading edge 33 of the groove 3 is located in the volume V1 and is therefore formed from the first material, with smaller grains.

[0048] As described in Figure 4, groove 3 can, however, be entirely included in volume V2. Asperities at the leading edge have the same effect as those formed on the trailing edge and increase the suction performance accordingly.

[0049] Figure 4 also illustrates the end 91 of the hole 90. This end 91 can open into the first or second volume. In the version illustrated here, the hole 90 is entirely included in the second volume V2.

[0050] If in the examples of figures 3 and 4, the volume V2 extends from the friction surface 26 to the sole 1, figure 5 shows a variant in which the interface between the two materials (dotted line) is inclined and does not reach the sole. This figure also shows that a sub-layer 27 can be provided below the two materials. The sub-layer can be formed from a third material, in particular having a hardness different from that of the first and second materials.

[0051] Volumes V1 and V2 can, together, form the entirety of trim 2.

[0052] The volume V1 can be at least three times, preferably at least 5 times larger than the volume V2. This ensures that the friction surface 26 (regardless of the wear condition) provides a large contact area with the disc. A volume V1 that is too small would reduce braking performance and increase wear due to a grain size that is generally too large over too large a portion of the friction surface. The article “Size effect of zircon particles in brake pads on the composition and size distribution of emitted particulate matter”, (Park et al., Tribology International, 03 / 2021, DOI 10.1016 / j.triboint.2021.106995) describes the adverse effects of a friction material with too large a grain size.

[0053] Apart from their grain size, the first and second materials may be substantially identical. A The first material may differ from the second material in the grain size of the filler, whether mineral or metallic, and / or in the size of the abrasive elements, the remainder of the composition of the two materials being identical.

[0054] The following table shows two examples of first material and second material (mass percentages of each element).

[0055] It is understood that these materials are given by way of example and that a person skilled in the art would know how to vary the composition of each of these materials to obtain a desired grain size. A third example may be given by way of illustration, in which the first material has small zircon grains and small mica grains, and in which the second material has large zircon grains and large mica grains.

[0056] The grain size of the second material may be between three times and fifteen times the grain size of the first material. In absolute value, the grains of the first material may have a size between 60 pm and 120 pm, preferably between 90 pm and 110 pm, more preferably about 100 pm. The grains of the second material may have a size between 300 pm and 800 pm, preferably between 350 pm and 600 pm, more preferably about 400 pm. These orders of magnitude may correspond to example 2. In a variant which may correspond to example 1, the grains of the first material may have a size between 0.5 pm and 20 pm, preferably between 1 pm and 15 pm, more preferably about 2 pm. The grains of the second material may have a size between 25 pm and 150 pm, preferably between 30 pm and 120 pm, more preferably approximately 100 pm.

[0057] Figure 6 shows another example, in which more than one groove is provided. The first groove 3 is preceded by a second groove 4. A volume V3 between the two grooves is occupied by the first material. Variants with more than two grooves and more than two materials are also conceivable.

[0058] It is understood that the different aspects presented in Figures 3 to 6 can be combined: for example, an underlay can be provided under the three materials of Figure 6, or an interface between the two materials may not reach the sole in the example of Figure 3 where this interface crosses the groove.

[0059] The present disclosure also relates to a method of manufacturing a wafer 10. The method may comprise a number of steps. The method is essentially distinguished from a conventional method by the fact of placing two distinct materials in the mold to sinter the two materials at the sole in such a way as to obtain a wafer with two distinct volumes occupied by the two materials, as described in the examples above.

[0060] Thus, a first volume of the mold can correspond to the volume V1 of the wafer and can be filled with a first small-grain material, and a second volume of the mold can correspond to the volume V2 of the wafer and can be filled with a larger-grain material.

[0061] After sintering, the wafer can undergo the usual operations of heat treatment, chamfer grinding, scorching, lacquering, quality controls, etc.

[0062] The method may comprise a machining step in which the particle collection groove is machined, for example by milling. In this case, the groove is machined such that the trailing edge of the groove lies in the second volume, i.e. the volume occupied by the coarse-grained material. Alternatively, the groove may be obtained by molding.

Claims

Claims

1. Brake pad (10) comprising a shoe (1) and a friction lining (2), the lining (2) being delimited by a friction surface (26) intended to come into contact with a brake rotor, a surface (20) for fixing to the sole, a rear edge (21) and a front edge (22), the lining (2) comprising: a collection groove (3) for braking particles, the groove (3) being open on the friction surface (26) and being capable of being placed in fluid communication with a source of depression, the collection groove (3) having a trailing edge (32); a first friction material, having a first grain size, and occupying a first volume (V1) of the friction lining (2); and a second friction material, having a second grain size greater than the first grain size, and occupying a second volume (V2) of the friction lining (2) distinct from the first volume (V1), the second volume (V2) extending at least from the trailing edge (32) of the groove (3) to the rear edge (21) of the friction lining (2).

2. The wafer of claim 1, wherein the first material comprises a first metal filler and the second material comprises a second metal filler distinct from the first metal filler, and the difference in grain size between the first and second materials is provided by a difference in grain size of their metal fillers.

3. The wafer of claim 1, wherein the first material comprises a first mineral filler and the second material comprises a second mineral filler distinct from the first mineral filler, and the difference in grain size between the first and second materials is provided by a difference in grain size of their mineral fillers.

4. A wafer according to any preceding claim, wherein the second grain size is at least three times greater than the first grain size.

5. A plate according to any preceding claim, wherein the groove (3) has a leading edge (33) and the second volume (V2) includes the leading edge (33).

6. A plate according to one of the preceding claims, wherein the first volume (V1) is at least three times larger than the second volume (V2).

7. A pad according to one of the preceding claims, wherein the second volume (V2) extends from the friction surface (26) to the fixing surface (20).

8. Plate according to one of claims 1 to 6, in which an underlayer (27) separates the fixing surface (20) from the first and second volumes (V1, V2).

9. A plate according to any preceding claim, wherein the groove (3) is a first groove (3), the lining comprising a second groove (4) in front of the first groove (3), the second groove (4) having a second trailing edge (42), the first material occupying a third volume (V3) extending from the second trailing edge (42) to the first groove (3).

10. Plate according to one of the preceding claims, in which the lining (2) comprises a conduit (90) extending from the groove (3) to a free end (91), at right angles to the inner (23) or outer (24) edge of the lining (2), or to the fixing surface (20).

11. A method of manufacturing a brake pad (10) comprising: placing a first friction material, of a first grain size, in a first volume of a mold; placing a second friction material, of a second grain size larger than the first grain size, in a second volume of the mold, the second volume being distinct from the first volume and extending to a rear side of the mold; sintering the friction materials on a base; and forming a brake particle collection groove by molding or machining, the groove being at least partially located in the second volume.

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