EP4003795A1

EP4003795A1 - Brake disc for a braking system

Info

Publication number: EP4003795A1
Application number: EP20750365.7A
Authority: EP
Inventors: Alberto Ferrari; Bruno Greppi; Edoardo NICOLIS
Original assignee: Ferdiam Srl
Current assignee: Ferdiam Srl
Priority date: 2019-07-26
Filing date: 2020-07-24
Publication date: 2022-06-01
Also published as: IT201900013047A1; WO2021019408A1

Abstract

A brake disc (1; 10; 100) for a braking system (9), in particular for a vehicle braking system, has a first friction surface (12) and a second friction surface (13), which are on opposite sides of the brake disc (1; 10; 100) and axially spaced from each other. The brake disc (1; 10; 100) comprises a first annular body (2) and a second annular body (3): the first friction surface (12) is on a first face (21) of the first annular body (2) and the second friction surface (13) is on a first face (31) of the second annular body (3). Each of the annular bodies (2, 3) also has a second face (22, 32) which is opposite the first face (21, 31) and faces the second face (22, 32) of the other annular body (3, 2). The first annular body (2) and the second annular body (3) are assembled together or are assembled on opposite faces (51, 52) of a central body (5) which is interposed between them. The coupling between the annular bodies (2, 3) or between at least one annular body (2, 3) and the central body (5) is a form-fit coupling by mechanical interference, thanks to a coupling with mechanical interference between the projecting teeth (41) and corresponding seats (45).

Description

BRAKE DISC FOR A BRAKING SYSTEM

DESCRIPTION

The present invention generally relates to the braking systems sector. Specifically, the present invention relates to a brake disc for a braking system, in particular for a vehicle braking system. The braking system is of the type where the brake disc frictionally engages another member of the braking system to produce a braking action thanks to the frictional force that develops between the brake disc and the other member when the braking system is actuated. For example, the brake disc rotates jointly with a wheel of the vehicle and is capable of frictionally engaging at least one brake pad which is mounted on a jaw fixed to the body of the vehicle.

As, during braking, the vehicle's kinetic energy is dissipated as heat energy that is absorbed by the brake disc, the brake disc must be able to withstand the operating temperatures and to disperse heat. In applications where braking generates very high heat outputs, a ventilated disc - also known as a "self-ventilating” disc - is used, the body of which has ventilation channels wherein a substantially radial air flow forms to cool the disc itself.

As the brake discs are subject to very high stress, another problem associated with the brake discs is wear, which can be significant during the service life of the brake disc. This requires the disc itself to be oversized to ensure that, at the end of its scheduled life, the brake disc is still of a sufficient thickness to ensure safe braking. The oversized brake disc has a high mass, leading to higher costs and greater consumption by the vehicle on which it is mounted. Moreover, the wear of the brake disc produces micrometric particulate and, therefore, is also of relevance from an environmental perspective.

Brake discs have been proposed that aim to address these issues. For example, the international patent application published under number WO 2015/159209 A1 specifically proposed a brake disc where the friction surface, which is intended to come into contact with the brake pad, is made of a composite material comprising diamond particles within a binding-material matrix, in particular a metal matrix. This solution has proven useful in greatly reducing the wear of the brake disc thanks to the mechanical resistance of this composite material and in facilitating heat dispersion thanks to the heat conductivity of the composite material.

In order to achieve greater breaking performance, there is the need to make a brake disc in which both faces (which is to say, two friction surfaces on opposite sides of the brake disc) are made of a composite material. It should be taken into account that, due to its purpose, the composite material is resistant to wear and, consequently, its surface is difficult to process mechanically. This poses some technical difficulties. Indeed, the two opposite faces - which are friction surfaces - must be parallel within very strict tolerances in order to properly operate the brake disc and to avoid vibrations during braking.

For example, if the brake disc is made by sintering, it is very difficult to ensure that the material is distributed homogeneously enough for the two opposite faces to be parallel within the tolerances permissible for brake discs.

In ordinary-metal brake discs, the faces can easily be made parallel through a mechanical grinding process which removes any non-parallel material from the faces, but this mechanical process could only be performed with great difficulty in a brake disc where the friction surfaces are made of a composite material such as that mentioned above. Moreover, the need to grind surfaces by removing material to make them parallel would require a layer of composite material with a thickness greater than that actually required by braking demands. As the composite material is a“valuable” material that is more expensive than the rest of the material of the brake disc, this would entail higher costs also for the rough brake disc, not only higher costs for the final processing.

These technical difficulties limit the actual use of brake discs with friction surfaces that are made of composite material or another hard material.

Therefore, the present invention takes up the technical problem of providing a brake disc for a braking system that enables the abovementioned drawbacks in the prior art to be overcome and/or that enables further advantages to be obtained.

This is achieved by providing a brake disc for a braking system according to independent claim 1. The technical problem is also solved by a brake disc according to independent claim 5.

It should be noted that independent claims 1 and 5 share a same inventive concept, which can be identified as a specific mode of coupling by interference. Therefore, there is unit of invention between claims 1 and 5, as will become more evident in the description below. The choice of outlining two independent claims is for clarity purposes only, as combining the respective embodiments in a single independent claim would have led to a claim expressed in terms that would be more complex and potentially less clear.

Specific embodiments of the present invention are defined in the dependent claims. The present invention also concerns a method for processing a brake disc according to claim 16.

One aspect underlying the present invention is the fact that the two friction surfaces on opposite sides of the brake disc form part of annular bodies that are made separately and which are form- fit mounted directly together (as defined in claim 1) or on a central body (as defined in claim 5). The form fit coupling is obtained by means of coupling with mechanical interference between projecting teeth and corresponding seats. Each annular body has a friction surface on a first face and coupling elements on a second face, which is opposite to the first face and facing the other annular body.

Coupling by mechanical interference, which entails a certain degree of deformation of the coupling elements involved, makes it possible to avoid having a unique intercoupling position. Indeed, depending also on the magnitude of the force applied during mounting, the parts can be intercoupled in a plurality of relative positions, in particular in terms of distance and inclination between the friction surfaces.

To make a coupling with mechanical interference, a position must be obtained - while the tooth is being inserted into the seat - whereby the cross-section of the seat is smaller than the corresponding cross-section of the tooth and, therefore, the tooth stretches the seat wider.

After the two annular bodies are initially mounted together, and if the friction surfaces are not parallel to each other as required, then a correction can be made by using a suitable press and pressing the brake disc between two parallel pressing surfaces which, each acting on a respective friction surface, move the annular bodies relative to each other (with the teeth moving in the corresponding seats) until each friction surface is parallel to the respective pressing surface and, therefore, to the other friction surface.

In other words, in a brake disc according to the present invention, the mode of coupling between the parts allows their relative position to be adapted or adjusted in order to make the friction surfaces parallel. This adjustment does not require material to be removed from the friction surfaces, as it affects only the coupling elements that are on the other face of the annular bodies. This is particularly useful for brake discs in which the friction surfaces are made of a composite material which is difficult to process using tools and/or in which the friction surfaces are formed from a thin layer of material.

Specifically, the form-fit coupling by mechanical interference takes place without any abutting contact between the annular body and the body coupled to it (i.e. the other annular body or the central body) and/or the projecting teeth are not in an end-of-stroke position within the seats in which they are inserted. This is useful because any significant abutting contact or end-of-stroke position could interfere with (or even prevent) the movement of the bodies into a different coupling position to achieve parallelism between the friction surfaces.

According to one embodiment for obtaining the mode of coupling described above, each projecting tooth has a tapered shape with a cross-section that diminishes away from the face from which the tooth projects; alternatively or in combination, each seat has a cavity for receiving the corresponding tooth: the cavity opens up onto the mouth of the seat and has a cross-section which diminishes away from the mouth. Therefore, in this configuration the interference increases as the tooth advances in the seat. For example, the projecting tooth and/or the seat cavity have a truncated-conical shape. To engage with a truncated-conical shaped projecting tooth, the seat cavity can, for example, be cylindrical or truncated-conical shaped; to engage with a truncated- conical shaped seat, the projecting tooth can, for example, be cylindrical or truncated-conical shaped.

In some embodiments, each seat is obtained in a protrusion which projects out from the respective face of the annular body or the central body. Basically, the seat is a cavity (for instance, a hole) which is made in the protrusion and which opens onto the top of the protrusion. Rather than making the seat directly in the thickness of the body - for instance in the thickness between the friction surface and the opposite face of the annular body - making the seat in a protrusion is useful because it allows a greater height for the seat and therefore more space to make the coupling with the tooth without reaching an end-of-stroke position. Morover, it prevents the body portion from being damaged or weakened where the friction surface is made.

In some embodiments, each annular body is not a single piece but is formed by a plurality of modules, each corresponding to an angular sector of the respective annular body; each module has a respective portion of the friction surface and, on the other side, respective coupling elements. This can make it easier to make, as smaller moulds are required.

In particular, if the two annular bodies are directly coupled to each other, the modules forming the first annular body can be arranged with an angular offset relative to the modules forming the second annular body, so that each module acts as a bridge and a structural link between two adjacent modules of the other annular body.

In preferred embodiments, the friction surfaces are made of a composite material comprising diamond particles. In particular, the annular bodies or the modules forming them have, on the friction surface side, a layer of composite material comprising diamond particles.

In any case, it should be noted that the present invention, although developed with reference to brake discs having friction surfaces made of composite material, is also similarly applicable to brake discs made of another material. Indeed, in general, the present invention avoids a grinding process in which material is removed from the friction surfaces to make them parallel. Although the advantage of the present invention is particularly relevant for brake discs having friction surfaces made of hard, difficult-to-work materials, the advantage of avoiding this process also exists for brake discs having friction surfaces made of a more workable material.

Further advantages, features, and methods of use of the present invention will become clear from the following detailed description of its embodiments, which are presented here for exemplifying and non-limiting purposes.

Reference will be made to the figures in the accompanying drawings, wherein:

- Figure 1 is a perspective view of a first embodiment of a brake disc according to the present invention, showing a first face of the brake disc;

- Figure 2 is a perspective view of the brake disc according to Figure 1 , showing a second face of the brake disc;

- Figure 3 is a perspective view of an inner face of a first component of the brake disc according to Figure 1 ;

- Figure 4 is a perspective view of an inner face of a second component of the brake disc according to Figure 1 ;

- Figure 5 is a close-up view of a detail of the second component in Figure 4, shown in cross- section;

- Figure 6 is a close-up view of a detail of the brake disc according to Figure 1 , shown in cross- section;

- Figure 7 is a close-up cross-sectional view of a detail of the brake disc according to Figure 1 ;

- Figure 8 is a simplified view of a detail of Figure 7;

- Figure 9 is a simplified view of a braking system comprising a brake disc according to the present invention;

- Figures 10 and 11 are simplified illustrations of the processing of a brake disc according to the present invention, to make the friction surfaces parallel;

- Figures 12 and 14 are simplified illustrations of three successive steps for making a component of a brake disc according to the present invention;

- Figure 15 is a perspective view of a second embodiment of a brake disc according to the present invention, showing a first face of the brake disc;

- Figure 16 is a perspective view of the brake disc according to Figure 15, showing a second face of the brake disc;

- Figure 17 is a perspective view of the brake disc according to Figure 15, with some parts removed;

- Figure 18 is a perspective view of the brake disc according to Figure 15, with some parts separated from each other;

- Figure 19 is a perspective view of a component of the brake disc according to Figure 15;

- Figure 20 is a perspective view, with some components of the brake disc according to Figure

15 being assembled to each other;

- Figure 21 is a perspective view of a third embodiment of a brake disc according to the present invention, showing a first face of the brake disc;

- Figure 22 is a front view of the first face of the brake disc according to Figure 21 ;

- Figure 23 is a perspective view of the brake disc according to Figure 21 , showing a second face of the brake disc;

- Figure 24 is a front view of the second face of the brake disc according to Figure 21 ;

- Figure 25 is a side view of the brake disc according to Figure 21 ;

- Figure 26 is a first perspective view of an inner component of the brake disc according to Figure 21 ;

- Figure 27 is a second perspective view of an inner component of the brake disc according to Figure 21 ;

- Figure 28 is a close-up view of a detail of the inner component according to Figures 26 and 27;

- Figures 29 and 30 are perspective views of inner faces of components of the brake disc according to Figure 21 ;

- Figures 31 and 32 are partially-broken perspective views of the brake disc according to Figure 21 , with some parts removed.

A first embodiment of a brake disc according to the present invention is shown in Figures 1 to 8. The brake disc is indicated with the reference number 1 and has a central axis 11 , which is to say an axis passing through the centre of the disc-like shape and perpendicular to the faces of the disc-like shape, and two friction surfaces 12, 13 which are on opposite sides of the brake disc 1 and are axially spaced from each other. In the present description, the terms“axial” and“axially” should be understood as referring to the central axis 11 or lines parallel to the central axis 11. The two friction surfaces 12, 13 are annular shaped with their centre on the central axis 11. In other words, the brake disc 1 has two opposite faces, which are perpendicular to the central axis 11 , and a thickness between the two opposite faces; the friction surfaces 12, 13 are on the opposite faces.

When in use, the central axis 11 is a rotational axis of the brake disc 1 and each of the two friction surfaces 12, 13 is intended to come into contact with a respective member of the braking system, in particular with a brake pad, to produce a braking action thanks to a frictional force between the friction surface and the respective member.

By way of illustration, Figure 9 shows a braking system 9 that includes a brake disc according to the present invention. The braking system 9 is a braking system for a vehicle such as an automobile, a car, a lorry, a train, a motorcycle, a bicycle. It should be noted that the braking system according to the present invention differs from known braking systems in what relates to the brake disc, whereas the other components of the braking system are known per se.

The braking system 9 comprises a brake disc 1 which rotates jointly with a wheel 90 of the vehicle. The brake disc 1 and the wheel 90 are fixed together, for instance by bolts 91 , and are mounted rotationally relative to the body of the vehicle so as to rotate jointly about a single rotational axis corresponding to the central axis 11 of the brake disc 1. For example, the brake disc 1 and the wheel 90 are mounted on a single shaft 92.

The braking system 9 further comprises a jaw 95 which is fixed to the body of the vehicle or to a part thereof (for instance, to a fork of a motorcycle or to the frame of a car) and houses a peripheral region of the brake disc 1.

As the vehicle travels, the wheel 90 and the brake disc 1 rotate about the rotational axis 11 , thus having an angular motion relative to the jaw 95.

The jaw 95 comprises at least one braking member 96, which is intended to engage the brake disc 1 to produce a braking action. In particular, the jaw 95 comprises two braking members 96, which are brake pads and which are on opposite sides relative to the brake disc 1 : each brake pad 96 is intended to come into contact with a respective friction surface 12, 13 of the brake disc 1.

When the vehicle travels without the brake on, the brake pads 96 are not in contact with the brake disc 1 and thus do not interfere with the rotation of the wheel 90. When the braking system 9 is actuated, the brake pads 96 are pushed against the brake disc 1 , for example by means of a hydraulic command, to produce a braking action thanks to a friction force (in particular, a kinetic friction force) between the friction surfaces 12, 13 and the brake pads 96.

In the embodiment shown in Figures 1 to 8, the brake disc 1 comprises a first annular body 2 and a second annular body 3, which are assembled together with each other.

The first friction surface 12 is on a first face 21 of the first annular body 2, the second friction surface 13 is on a first face 31 of the second annular body 3. The first faces 21 , 31 are facing in opposite directions and are outer faces of the brake disc 1. Substantially, the annular bodies 2, 3 are friction rings.

Each annular body 2, 3 also has a second face 22, 32 which is opposite the first face 21 , 31 and is facing the second face 32, 22 of the other annular body 3, 2. The second faces 22, 32 are therefore inner faces of the brake disc 1.

The second faces 22, 32 of the annular bodies 2, 3 are provided with coupling elements to fix the annular bodies 2, 3 together. Overall, the coupling elements on the first annular body 2 and the coupling elements on the second annular body 3 are shaped and arranged so as to be mutually corresponding and couplable.

The coupling elements are shaped in such a way that there is not a unique intercoupling position between the two annular bodies 2, 3 in terms of distance and inclination between their first faces 21 , 31 and so that the coupling position can be adjusted during assembly.

Specifically, the coupling elements are projecting teeth 41 and seats 45 shaped to receive corresponding projecting teeth 41. For example, each seat 45 has a cavity for receiving the corresponding tooth 41 and the cavity opens onto a mouth of the seat 45, the mouth facing the other annular body.

In particular, the second face 22 of the first annular body 2 has a plurality of projecting teeth 41 projecting towards the second annular body 3 and a plurality of seats 45 with mouth facing the second annular body 3; the second face 32 of the second annular body 3 has a plurality of seats 45 with mouth facing the first annular body 2 and a plurality of projecting teeth 41 projecting towards the first annular body 2. The seats 45 on one annular body are positioned so as to receive the projecting teeth 41 of the other annular body. Specifically, the projecting teeth 41 and the seats 45 extend along respective axial lines parallel to the central axis 11.

For example, on each second face 22, 32 the projecting teeth 41 and the seats 45 mutually alternate both along substantially radial lines and along substantially annular paths. In the particular embodiment shown, triads of coupling elements are arranged along respective substantially radial lines (or at a slight incline relative to an exactly radial line) and each triad comprises a projecting tooth 41 interposed between two seats 45 or a seat 45 interposed between two projecting teeth 41 ; three annular or circumferential paths, concentric to each other, are defined relative to the central axis 11 , on each of which the projecting teeth 41 and the seats 45 mutually alternate.

As can be seen in Figure 5, the projecting tooth 41 has, on its lateral surface, an axial recess 43 which extends up to the entire height of the tooth 41 ; this axial recess 43 has the purpose of facilitating the discharge of air from the seat 45 as the tooth 41 is inserted into the seat 45.

Specifically, each seat 45 is made in a protrusion 47 which projects out from the second face 22, 32 towards the other annular body 3, 2. The seat 45 is a cavity (for instance, a hole, in particular a blind hole) made in the protrusion 47; the cavity opens onto the top of the protrusion 47, forming the mouth of the seat 45, and extends axially towards the second face 22, 32.

The second faces 22, 32 may also be provided with reliefs or ribs 48 which are in relief relative to the surface of the respective second face. These ribs 48 extend substantially radially relative to the central axis 11 or at a slight incline relative to an exactly radial line, if appropriate. The ribs 48 are interposed between triads of coupling elements. The ribs 48 are positioned and directed in such a way that, in the brake disc 1 , the ribs 48 of the first annular body 2 extend in a way that corresponds to the ribs 48 of the second annular body 3 and the ribs 48 of the two annular bodies 2, 3 are facing each other, even if they are not touching.

Therefore, each annular body 2, 3 has: a first face 21 , 31 which is flat and defines the respective friction surface 12, 13; a second face 22, 32 which is substantially parallel to the first face; a thickness between the first face and the second face; coupling elements on the second face, in particular teeth 41 projecting from the second face itself and/or seats 45 formed in protrusions 47 projecting from the second face itself; reliefs or ribs 48, if appropriate.

In the brake disc 1 in its assembled conditions, the projecting teeth 41 of an annular body are inserted in the corresponding seats 45 of the other annular body and there is a mechanical interference coupling of the projecting teeth 41 to the corresponding seats 45. If we take a single pair of projecting tooth 41 and corresponding seat 45, their shapes and dimensions are such that the lateral surface of the projecting tooth 41 engages with the inner lateral surface of the seat 45 when the tooth 41 is inserted in the seat 45.

This is a mechanical interference coupling in the sense that the projecting tooth 41 is not coupled in the seat 45 with any clearance, but rather it is, at least in some sections, transversally larger than the seat 45, so that for the projecting tooth 41 to be advanced into the seat 45 an axial force must be applied that deforms the seat 45 and/or the tooth 41. The extent to which the tooth 41 is inserted into the seat 45 depends on the force applied: a greater force means a greater insertion of the tooth 41.

The teeth 41 and the seats 45 are sized and shaped in such a way that, in the brake disc in its assembled condition and with the desired distance between the friction surfaces 12, 13, the teeth 41 are not inserted in the seats 45 at the end of the stroke and, therefore, the teeth could be advanced further if adequate force is applied.

In particular, each projecting tooth 41 has a tapered shape with a cross-section that diminishes away from the face 22, 32 from which the tooth 41 projects; alternatively or in combination, the cavity of each seat 45 has a cross-section which diminishes away from the mouth. With these tooth and/or seat configurations, the further the tooth is inserted into the seat, the greater the interference between them.

For example, the projecting tooth 41 has a truncated-conical shape, or the cavity of the seat 45 has a truncated-conical shape, or (as in the embodiment shown) both the projecting tooth 41 and the cavity of the seat 45 have a truncated-conical shape. The conicities are appropriately selected so as to obtain the coupling described above.

Thanks to the interaction between the projecting teeth 41 and the seats 45, the first annular body 2 and the second annular body 3 are form-fit coupled to each other by mechanical interference. Moreover, in this condition there is no abutting contact between the first annular body 2 and the second annular body 3.

“Abutting contact” refers to when, at a specific mutual position as one body moves relative to the other, a portion of the body’s surface has come into contact with a portion of the other body’s surface in such way as to prevent further movement in that direction, for instance because the surface portions in contact are substantially perpendicular to the movement direction. In other words, an abutting contact defines an end of the stroke for the movement, due to a body-against- body position that occurs at a specific stopping point.

Conversely, as can be seen particularly in Figures 7 and 8, the teeth 41 are not inserted in the seats 45 at the end of the stroke. Indeed: the ends of the teeth 41 are not in abutting contact with the bottom of the seats 45; the necks at the top of the seats 45 are not in abutting contact with the surface from which the teeth 41 project; the ribs 48 of one annular body are not in abutting contact with the ribs 48 of the other annular body.

Figures 10 and 11 give a simplified illustration of the advantage of this coupling mode.

The two annular bodies 2, 3 are produced as separate pieces and are then coupled to each other. As shown in an extremely accentuated manner in Figure 10, in an initial coupled positioned the first two faces 21 , 31 and, therefore, the two friction surfaces 12, 13 can be non-parallel or can deviate from a parallel alignment beyond a permissible tolerance.

In the example shown, the non-parallel alignement is also due to the fact that the faces 21 and 22 in the first annular body 2 are not parallel to each other due to inaccuracies in their manufacture: as largely accentuated in Figures 10 and 11 , the first annular body 2 has a thickness between the faces 21 and 22, the thickness being greater at the top of the figure than at the bottom of the figure. Consequently, the distance of the first face 21 from the coupling elements (i.e. from the teeth 41 and from the protrusions 47) is not constant across the entire friction surface 12.

In Figure 10, there is an inclination of several degrees between the friction surfaces 12, 13, but this is illustrative only: in a real scenario, the deviation from a parallel alignment could be in the order of a few tenths of a degree and the tolerance (referring to the difference between the maximum distance and the minimum distance between the surfaces) could be in the order of 3 hundredths of a millimetre.

Since the coupling is by mechanical interference and, in particular, has no abutting contact (i.e. it is not in an end-of-stroke position), any non-parallel alignment (i.e. the deviation from a parallel alignment) can be corrected: the brake disc 1 is placed in a press 60 between two pressing surfaces 61 , 62 that are parallel and facing each other (for example, the pressing surfaces 61 , 62 are the faces of two planes 63, 64 movable relative to each other), with each friction surface 12, 13 facing a respective pressing surface 61 , 62; adequate force is exerted by approaching the pressing surfaces 61 , 62 towards each other and then pressing the annular bodies 2, 3 between the two pressing surfaces 61 , 62. By action of the press 60, the two annular bodies 2, 3 move relative to each other and the projecting teeth 41 are further inserted into the seats 45 where the distance between the first faces 21 , 31 is greater, until each first face 21 , 31 is completely in contact with (and parallel to) the respective pressing surface 61 , 62, as shown in Figure 11. In this way, it is possible to obtain the parallel alignment between the friction surfaces 12, 13 on the first faces 21 , 31.

In other words, in order to correct a non-parallel alignment between the friction surfaces 12, 13, a processing method is applied whereby the brake disc 1 is pressed between two parallel pressing surfaces 61 , 62, which press on the first face 21 of the first annular body 2 and on the first face 31 of the second annular body 3, respectively, with a pressing direction which is parallel to the central axis 11.

This is possible because interference coupling, without abutting contact, leaves a margin of correction to compensate for the inaccuracies in the making and assembly of the annular bodies 2, 3. Instead of correcting any deviation from a parallel alignment by removing material from the first faces 21 , 31 (as would be the case if the procedures for known brake discs are carried out), the present invention allows the first faces 21 , 31 to be left intact and a correction to be implemented by affecting the coupling distance between the parts. This is particularly useful when the friction surfaces 12, 13 are made of a difficult-to-work material or are made of a low-thickness noble material.

The force exerted on the brake disc 1 in the press 60 is much higher than the force exerted on the brake disc 1 by the jaw 95 during use; therefore, the coupling position reached in the press 60 is unchanged by the braking system 9 during use. Indeed, the jaw 95 is not capable of exerting enough force to move the two annular bodies 2, 3 relative to each other any further.

In the assembled condition, substantially radial ventilation channels 16 are present between the second faces 22, 32 of the annular bodies 2, 3 and are defined by the empty spaces between the ribs 48 and the coupling elements (in particular the protrusions 47). Basically, the ventilation channels 16 are bordered by projecting elements, such as the teeth 41 and the protrusions 47, and/or by the ribs 48.

As the brake disc 1 rotates about the central axis 11 , an air flow forms in the brake disc 1 itself and is sucked centrally and forced towards the periphery, passing through the ventilation channels 16 between the two annular bodies 2, 3. This helps cool the friction surfaces 12, 13 and the entire brake disc 1. This is taken into account when selecting the incline of the ribs 48 relative to the radial line, so as facilitate the air flow. In other words, the brake disc 1 acts like a centrifugal fan as regards the flow of air inside of it.

To further facilitate the cooling of the brake disc 1 during use, the annular bodies 2, 3 can have a plurality of through-bores 49 which pass through the thickness between the first face and the second face.

A flange or cup 19 is fixed to one of the two annular bodies, in particular to the second annular body 3, to allow the brake disc 1 to be connected to the wheel 90 (or to another member rotating jointly with the wheel 90) by bolts 91. For this purpose, the second annular body 3 comprises fixing seats 37 for the flange 19.

In the embodiment shown, both annular bodies 2, 3 comprise both projecting teeth 41 and seats 45. In an alternative embodiment, an annular body comprises only teeth and the other annular body comprises only seats.

As for the shape of the teeth 41 and the seats 45, although they have a truncated-conical shape in the example shown, other shapes are possible such as pyramidal or prismatic shapes.

Aspects such as the number of teeth 41 and seats 45, their sizes and their arrangement on the second faces of the annular bodies are non-binding for the present invention and can be selected on a needs basis.

The outer surface of the protrusions 47 can be equipped with fins or other elements which increase its surface area; this is useful for enhancing and increasing the heat exchange with the air flow in the ventilation channels 16.

As regards the material of the annular bodies 2, 3, in the preferred embodiment each annular body has, on the first face 21 , 31 and on the friction surface 12, 13, a layer 40 of composite material comprising diamond particles, such as diamond powder or granules. For example, the layer 40 of composite material has a thickness of less than 5 mm. The rest of the annular body can be made of a metal material without diamond particles.

For example, the composite material includes a binding matrix in which the diamond particles are embedded and incorporated. Even more particularly, the composite material has a metal binding matrix and then it is of the "metal matrix composite" (MMC) type.

In an exemplary embodiment, the metal binder is a mixture of carbonyl iron, tin, and phosphorous iron (indicative quantities: carbonyl iron at approximately 90% by weight; tin at approximately 2- 3% by weight; phosphorous iron for the remainder). The diamond particles are added in quantities comprised between 10% and 20% of the volume of the metal binder. For example, diamond particles have a particle size in the order of microns.

For further details as an example, reference is made to publication WO 2015/159209 A1 , whose teachings regarding the composite material and its production also apply to the present invention. Preferably, the annular body is made by sintering, using processes pertaining to powder technology.

One process for making it is described below in combination with Figures 12, 13 and 14, which schematically show the steps of the method.

A layer 71 of metal powder is distributed, through a hopper, into a mould 75 in a cold moulding press 70. For example, the metal powder used is iron powder, specifically Hoganas ASC300 "standard grades", with a particle size of d90 = 45 microns.

This first layer 71 will form the annular body 2, 3 part that is provided with coupling elements, which is to say the annular body part that has the teeth 41 and/or the seats 45 and that is not the layer 40 of composite material forming the friction surface.

The mould 75 (of which an extreme simplification is shown in the figures) is equipped with movable planes and, thanks to the movement of punches inside the mould itself, is able to create the elements necessary for the interference coupling of the annular body.

A metal powder mixture is prepared, in which carbonyl iron constitutes approximately 90% of its weight, tin constitutes approximately 2-3% of its weight and phosphorous iron constitutes the remainder. Diamond particles, with a particle size in the order of microns, are added to the mixture in a quantity comprised between 10% and 20% of the metal powder mixture. The mixture thus obtained is appropriately mixed to ensure that the diamond particles are homogenous and dispersed uniformly in the metal powders.

The mixture obtained is distributed in the mould 75, through a hopper, on top of the first layer 71 of metal powder, thus forming a second layer 72 which will form the layer 40 of the annular body and the friction surface made of composite material. For example, if the desired thickness for the composite layer 40 is 5 mm, the second layer 72 of mixture in the mould will have a greater height to take into account the compaction and shrinkage of material in transitioning from the powder state to the solid compact state.

The cold moulding press 70 is sized so as to exert a specific pressure of approximately 4 MPa on the powders. The press 70 has an upper movable plane 76 with a flat face 77 which, by pressing the top of the second layer 72, compresses the powders and creates a flat face on the second layer 72, which corresponds to the first face 21 , 31 (with friction surface 12, 13) of the annular body 2, 3.

After compressing, the piece obtained is removed from the press 70 and inserted into a sintering oven. The sintering cycle involves a step of heating the piece to a temperature of between 940°C and 980°C, with a temperature gradient of approximately 2.5°C/minute, followed by a step of maintaining the maximum temperature for about 30 minutes and, finally, a step of cooling the piece, which is left in the oven. During the heating step, a constant flow of hydrogen can be activated, which has a beneficial effect on sintering quality. Through this process, the annular bodies 2, 3 can be obtained, each having a surface layer 40 which is made of a composite material with diamond particles and which has a flat outer face, which is the friction surface, while the rest of the annular body is made of metal. If the first annular body 2 is different from the second annular body 3, as in the example shown in the Figures, then two different moulds 75 are used.

Although not shown in the figures, the mould 75 and the upper movable plane 76 are shaped so as to also obtain other details of the annular bodies, such as the circular cavity in the centre of the annular body, any through-bores 49 and any fixing seats for the flange 37.

It should be noted that, in the procedure described, the second layer 72 of powder with diamond is arranged on top of the first layer 71 , which is still in powder state. Therefore, during the subsequent pressing and sintering, the two layers 71 , 72 are intimately interlinked; this is useful to prevent the surface layer 40 from delaminating from the rest of the annular body.

The coupling of the annular bodies 2, 3 with each other and the step of processing in the press 60 to correct any non-parallel alignment between the friction surfaces 12, 13 lead to the finished brake disc 1.

A second embodiment of a brake disc according to the present invention is shown in Figures 15 to 20 and is referred to by the reference number 10.

The brake disc 10 differs from the brake disc 1 according to the first embodiment in that each annular body 2, 3 is made of several pieces instead of a single piece: the first annular body 2 is formed by a plurality of modules 28 (for example, six mutually identical modules 28) and the second annular body 3 is formed by a plurality of modules 38 (for example, six mutually identical modules 38).

Each module 28, 38 corresponds to an angular sector of the respective annular body 2, 3 and is provided with a respective part of the friction surface 12, 13 on its first face 21 , 31 and with respective teeth 41 and/or seats 45 on its second face 22, 32.

The modules 28 of the first annular body 2 are form-fit coupled by mechanical interference with the modules 38 of the second annular body 3, by modes entirely analogous to those described above for the first embodiment. Therefore, also for the brake disc 10 any non-parallel alignment between the friction surfaces 12, 13 can be corrected using a press 60. Pressing using the press 60 also enables the correction of any misalignments or non-coplanarity of the modules on a same face, thus leading to a friction surface that is flat and parallel to the other friction surface.

For each annular body 2, 3, the modules 28, 38 are arranged side by side with their sides 29, 39 lining up to each other. In the embodiment shown, the sides 29, 39 of the modules 28, 38 have a direction which is inclined relative to the radial line and basically corresponds to the incline of the ventilation channels 16 in the brake disc 10.

The modules 28 of the first annular body 2 are angularly offset relative to the modules 38 of the second annular body 3, as is particularly clear from Figure 20: the sides 29 of the modules 28 do not correspond with the sides 39 of the modules 38, but are instead about halfway between the sides 39 of the modules 38 (and vice versa). Consequently, each module 28 on one face of the brake disc 10 bridges two modules 38 on the other side of the brake disc 10. This allows all the modules to be interconnected and enables a structure to be obtained that does not require other means for interconnecting the modules of each annular body.

In the particular embodiment shown, each module 28, 38 comprises four radial pairs formed by a projecting tooth 41 and a seat 45. Two annular or circumferential paths, concentric to each other, are defined relative to the central axis 11 , on each of which projecting teeth 41 and seats 45 alternate.

In the case of modules bridging between the modules on the other face, this corresponds to four coupling regions (in radial pairs) between opposite modules; therefore, there is a strong coupling and the stress is well-distributed. A different number of coupling elements is obviously possible. In each radial pair, a relief element 44 is interposed between the projecting tooth 41 and the seat 45. In the assembled condition, the relief elements 44 of the modules 28 are facing the relief elements 44 of the modules 38, but they are not touching. The relief elements 44 help to delimit the ventilation channels 16.

The modules 28, 38 illustrated do not have the ribs 48 shown for the first embodiment; however, ribs 48 could also be made on the modules 28, 38. Furthermore, the brake disc 10 may comprise fixing seats 37 for the flange 19 (although they are not shown in the figures).

Moreover, it should be noted that the modules 28, 38 do not have the through-bores 49 shown for the first embodiment. However, in one variant embodiment, these through-bores 49 could be present in the modules 28, 38.

Each module 28, 38 can be obtained through the sintering process described above, with the use of a corresponding mould 75. The materials used may be the same and, therefore, each module 28, 38 may have a surface layer 40 made of a composite material with diamond particles.

From a manufacturing perspective, the modular manufacturing of the annular bodies 2, 3 is useful because the individual modules 28, 38 - being smaller in size than the whole annular body - can be made more easily and using smaller equipment. Moreover, in a sintering process, a homogenous material is easier to make in a small body than in a large body.

Furthermore, it should be taken into account that any manufacturing defect would require the whole annular body to be discarded if it is a single body, even when the defect only affects a small part of the annular body, whereas only one module would be discarded if the annular body is modular.

Figures 21 to 32 show a third embodiment of a brake disc according to the present invention, which is referred to by the reference number 100.

The third embodiment differs from the other embodiments described above in that the two annular bodies 2, 3 are not directly coupled to each other, but are coupled on a central body 5 which is positioned between the first annular body 2 and the second annular body 3.

For example, the central body 5 is disc-shaped (or, alternatively, ring-shaped) and comprises the flange or cup 19 so as to enable the connection of the brake disc 100. In the embodiment shown, the flange 19 is made in a single piece with the remainder of the central body 5. The central body 5 is made of metal, such as aluminium.

The central body 5 comprises a first face 51 , which faces the first annular body 2, and a second face 52, which is opposite the first face 51 and faces the second annular body 3.

The annular bodies 2, 3 are mounted on the respective opposite faces 51 , 52 of the central body 5. At least one of the two annular bodies 2, 3 (but preferably both) is form-fit coupled to the central body 5 by mechanical interference, by modes analogous to those described for the brake disc 1 and for the brake disc 10.

For instance, if we take the first annular body 2, then - in the same way as described above - its second face 22 has a plurality of projecting teeth 41 projecting towards the first face 51 of the central body 5. In turn, the first face 51 of the central body 5 has a plurality of seats 45 with mouth facing the first annular body 2. The projecting teeth 41 of the first annular body 2 are inserted in the corresponding seats 45 of the first face 51 of the central body 5 and there is a mechanical interference coupling of the projecting teeth 41 to the corresponding seats 45.

In particular, the form-fit coupling of the first annular body 2 to the central body 5 takes place without any abutting contact between the first annular body 2 and the central body 5; the projecting teeth 41 are not in an end-of-stroke position within the seats 45 in which they are inserted.

Preferably, the second annular body 3 is also form-fit coupled to the central body 5 by mechanical interference, just as with the first annular body 2. The second face 32 of the second annular body 3 has a plurality of projecting teeth 41 projecting towards the second face 52 of the central body 5, which in turn has a plurality of seats 45 with mouth facing the second annular body. The projecting teeth 41 of the second annular body 3 are inserted in the corresponding seats 45 of the second face 52 of the central body 5 and there is a mechanical interference coupling of the projecting teeth 41 to the corresponding seats 45.

In particular, the form-fit coupling of the second annular body 3 to the central body 5 takes place without any abutting contact between the second annular body 3 and the central body 5; the projecting teeth 41 are not in an end-of-stroke position within the seats 45 in which they are inserted.

For the purposes of the present invention, it may be sufficient for only one of the annular bodies 2, 3 to be coupled to the central body 5 in these ways; however, the solution whereby both annular bodies are coupled in this way allows for greater possibilities in correcting any non-parallel alignment between the friction surfaces 12, 13.

The central body 5 is undulatingly shaped along a ring or circumferential path around the central axis 11 : as can be seen in the figures, each face 51 , 52 of the central body 5 has alternating radial depressions 55 and radial reliefs 57. The radial depressions 55 on one face correspond to the radial reliefs 57 on the other face.

Part of the seats 45 are situated at the radial depressions 55 and a remainder of the seats 45 are situated at the radial reliefs 57. For example, the seats in the radial depressions 55 are radially offset relative to the seats in the radial reliefs 57. Specifically, each radial depression 55 or radial relief 57 is equipped with at least three seats 45.

Each seat 45 in the radial depressions 55 is made in a protrusion 47 projecting out from the respective face 51 , 52 of the central body 5, in particular from the bottom of the radial depression 55. The seat 45 is a cavity (for instance, a hole) which is made in the protrusion 47 and which opens onto the top of the protrusion 47.

Each seat 45 in the radial reliefs 57 is a cavity (for instance, a hole) which extends into the thickness of the radial relief 57 and opens out towards the respective annular body, where a neck 46 may be present.

In the particular embodiment shown, the seats 45 in the radial reliefs 57 of one face 51 , 52 correspond to the seats 45 in the radial depressions 55 of the other face 52, 51. The cavities in the protrusions 47 are open at both ends, so that at one end they define seats 45 for the teeth 41 of the first annular body 2 and at the other end they define seats 45 for the teeth 41 of the second annular body 3. For example, the cavities in the protrusions 47 are cylindrical holes and the teeth 41 are truncated-conical shaped.

The spaces between the radial depressions 55 and the second face 22, 32 of the respective annular body 2, 3 define radial ventilation channels 16.

In the embodiment shown for the brake disc 100, each annular body 2, 3 is formed by a plurality of modules 28; 38, each of which corresponds to an angular sector of the respective annular body 2, 3 and is provided with a respective part of the friction surface 12, 13 and with respective projecting teeth 41.

In particular, each module 28, 38 comprises a plurality of radial triads of teeth 41. For example, each module 28, 38 comprises at least fifteen teeth 41 , distributed in a substantially regular way. The modules 28 forming the first annular body 2 can be angularly offset relative to the modules 38 forming the second annular body 3. The sides 29 of the modules 28 do not correspond with the sides 39 of the modules 38 but are instead about halfway between the sides 39 of the modules 38 (and vice versa). In the embodiment shown, the sides 29, 39 have a curved profile.

In a variant embodiment, each annular body 2, 3 could be a single ring-shaped piece, instead of being formed by modules 28, 38.

It should be noted that, in the embodiment shown, the annular bodies 2, 3 have only projecting teeth 41 and the central body 5 has only corresponding seats 45. In variant embodiments, the arrangement of teeth and seats can be inverted or each body can comprise both teeth and seats, in the same way as described above for the first two embodiments. The shape and sizes of the teeth 41 and of the seats 45 can also be varied and selected according to need.

The materials and procedure for making the annular bodies 2, 3 or their modules 28, 38 can be the same as described above for the other embodiments 1 , 10.

It should be noted that, in the embodiments here described, the projecting teeth 41 and the protrusions 47 for the seats 45 form a single piece with the respective body 2, 3, 5; which is to say, they are not fixing elements added during the assembly step.

The form-fit coupling by mechanical interference which is used for the present invention makes the respective bodies integral with each other and prevents relative movements under normal conditions of use within the braking system. At the same time, the form-fit coupling by mechanical interference allows small relative movements of the bodies when, in order to correct any non parallel alignment of the friction surfaces, the brake disc is pressed in a press 60 which applies a much higher pressure than that exerted under normal conditions of use within the brake system. Many modifications and variations can be made to the invention as designed herein, without departing from the scope of the present invention as defined in the accompanying claims.

All details can be replaced by other technically equivalent details and any materials, shapes and sizes of the various components may be used according to requirements.

Claims

1. A brake disc (1 ; 10) for a braking system (9), in particular for a vehicle braking system (9), the brake disc (1 ; 10) having a central axis (11), a first friction surface (12) and a second friction surface (13), said friction surfaces (12, 13) being on opposite sides of the brake disc (1 ; 10) and being axially spaced from each other,

wherein, when in use, the central axis (11) is a rotational axis of the brake disc (1 ; 10) and each of said friction surfaces (12, 13) is intended to come into contact with a respective member (96) of the braking system (9) to produce a braking action thanks to a frictional force between the friction surface and the respective member,

the brake disc (1 ; 10) comprising a first annular body (2) and a second annular body (3), the first friction surface (12) being on a first face (21) of the first annular body (2) and the second friction surface (13) being on a first face (31) of the second annular body (3), each of the annular bodies (2, 3) also having a second face (22, 32) which is opposite the first face (21 , 31) and is facing the second face (22, 32) of the other annular body (3, 2),

wherein the first annular body (2) and the second annular body (3) are assembled together with each other,

the second face (22) of the first annular body (2) having a plurality of projecting teeth (41) projecting towards the second annular body (3) and/or a plurality of seats (45) with mouth facing the second annular body (3),

the second face (32) of the second annular body (3) having a plurality of seats (45) with mouth facing the first annular body (2) and/or a plurality of projecting teeth (41) projecting towards the first annular body (2),

the projecting teeth (41) of one annular body (2, 3) being inserted in corresponding seats (45) of the other annular body (3, 2) and there being a mechanical interference coupling of the projecting teeth (41) to the corresponding seats (45),

whereby the first annular body (2) and the second annular body (3) are form-fit coupled to each other by mechanical interference.

2. The brake disc (1 ; 10) according to claim 1 , wherein the form-fit coupling of the first annular body (2) to the second annular body (3) takes place without any abutting contact between the first annular body (2) and the second annular body (3).

3. The brake disc (1 ; 10) according to claim 1 or 2, wherein the seat (45) is made in a protrusion (47) which projects out from the second face (22, 32) of one annular body (2, 3) towards the other annular body (3, 2), the seat (45) being a cavity made in the protrusion (47) and opening onto a top of the protrusion (47).

4. The brake disc (1 ; 10) according to any of claims 1 to 3, wherein substantially radial ventilation channels (16) are present between the second faces (22, 32) of the annular bodies (2, 3) and are bordered by projections (41 , 44, 47) and/or by ribs (48) projecting out from the second face (22, 32) of one annular body (2, 3) towards the other annular body (3, 2).

5. A brake disc (100) for a braking system (9), in particular for a vehicle braking system (9), the brake disc (100) having a central axis (11), a first friction surface (12) and a second friction surface (13), said friction surfaces (12, 13) being on opposite sides of the brake disc (100) and being axially spaced from each other,

wherein, when in use, the central axis (11) is a rotational axis of the brake disc (100) and each of said friction surfaces (12, 13) is intended to come into contact with a respective member (96) of the braking system (9) to produce a braking action thanks to a frictional force between the friction surface and the respective member,

the brake disc (100) comprising a first annular body (2) and a second annular body (3), the first friction surface (12) being on a first face (21) of the first annular body (2) and the second friction surface (13) being on a first face (31) of the second annular body (3), each of the annular bodies (2, 3) also having a second face (22, 32) which is opposite the first face (21 , 31) and is facing the second face (22, 32) of the other annular body (3, 2),

the brake disc (100) also comprising a central body (5) which is positioned between the first annular body (2) and the second annular body (3),

wherein the first annular body (2) and the second annular body (3) are assembled on opposite faces of the central body (5), on a first face (51) and a second face (52) of the central body (5), respectively,

the second face (22) of the first annular body (2) having a plurality of projecting teeth (41) projecting towards the first face (51) of the central body (5) and/or a plurality of seats (45) with mouth facing the first face (51) of the central body (5),

the first face (51) of the central body (5) having a plurality of seats (45) with mouth facing the first annular body (2) and/or a plurality of projecting teeth (41) projecting towards the first annular body (2),

the projecting teeth (41) of the first annular body (2) being inserted in corresponding seats (45) of the first face (51) of the central body (5) and/or the projecting teeth (41) of the first face (51) of the central body (5) being inserted in corresponding seats (45) of the first annular body (2), there being a mechanical interference coupling of the projecting teeth (41) to the corresponding seats (45),

whereby the first annular body (2) and the central body (5) are form-fit coupled to each other by mechanical interference.

6. The brake disc (100) according to claim 5, wherein the second face (32) of the second annular body (3) has a plurality of projecting teeth (41) projecting towards the second face (52) of the central body (5) and/or a plurality of seats (45) with mouth facing the second face (52) of the central body (5),

the second face (52) of the central body (5) having a plurality of seats (45) with mouth facing the second annular body (3) and/or a plurality of projecting teeth (41) projecting towards the second annular body (3),

the projecting teeth (41) of the second annular body (3) being inserted in corresponding seats (45) of the second face (52) of the central body (5) and/or the projecting teeth (41) of the second face (52) of the central body (5) being inserted in corresponding seats (45) of the second annular body (3), there being a mechanical interference coupling of the projecting teeth (41) to the corresponding seats (45),

whereby the second annular body (3) and the central body (5) are form-fit coupled to each other by mechanical interference.

7. The brake disc (100) according to claim 5 or 6, wherein the form-fit coupling of the annular body (2, 3) to the central body (5) takes place without any abutting contact between the annular body (2, 3) and the central body (5).

8. The brake disc (100) according to any of claims 5 to 7, wherein the seat (45) is made in a protrusion (47) which projects out from the respective face (22, 32, 51 , 52) of the annular body (2, 3) or of the central body (5), the seat (45) being a cavity made in the protrusion (47) and opening onto a top of the protrusion (47).

9. The brake disc (100) according to any of claims 5 to 8, wherein the central body (5) is undulatingly shaped along a ring path around the central axis (11), both the first face (51) and the second face (52) of the central body (5) having alternating radial depressions (55) and radial reliefs (57),

wherein said radial depressions (55) form ventilation channels (16) which are positioned between the central body (5) and the annular bodies (2, 3).

10. The brake disc (1 ; 10; 100) according to any of claims 1 to 9, wherein, when coupled, the projecting teeth (41) are not in an end-of-stroke position within the seats (45) in which they are inserted.

11. The brake disc (10; 100) according to any of claims 1 to 10, wherein each annular body (2, 3) is formed by a plurality of modules (28, 38), each module (28, 38) corresponding to an angular sector of the respective annular body (2, 3) and being provided with a respective part of the friction surface (12, 13) and respective projecting teeth (41) and/or seats (45).

12. The brake disc (10; 100) according to claim 11 , wherein the modules (28) forming the first annular body (2) are angularly offset relative to the modules (38) forming the second annular body (3).

13. The brake disc (1 ; 10; 100) according to any of claims 1 to 12, wherein the annular bodies (2, 3) or the modules (28) forming the annular bodies (2, 3) have, on the first face (21 , 31) and on the friction surface (12, 13), a layer of composite material comprising diamond particles.

14. The brake disc (1 ; 10; 100) according to any of claims 1 to 13, wherein each projecting tooth (41) has a tapered shape with a cross-section that diminishes away from the face from which the tooth (41) projects and/or wherein each seat (45) has a cavity to receive the corresponding tooth and the cavity opens onto the mouth of the seat (45), the cavity having a cross-section which diminishes away from the mouth.

15. A braking system (9), in particular a vehicle braking system (9), comprising a brake disc (1 ; 10; 100) according to any of claims 1 to 14 and a jaw (95) which houses a peripheral region of the brake disc (1 ; 10; 100), the jaw (95) being equipped with respective members (96) intended to come into contact with the friction surfaces (12, 13) to produce a braking action.

16. A method for processing a brake disc (1 ; 10; 100) according to any of claims 1 to 14, wherein, in order to correct a non-parallel alignment between the friction surfaces (12, 13), the brake disc (1 ; 10; 100) is pressed between two parallel pressing surfaces (61 , 62), which press on the first face (21) of the first annular body (2) and on the first face (31) of the second annular body (3), respectively, with a pressing direction which is parallel to the central axis (11) of the brake disc (1 ; 10; 100).