BRAKE DISK HAVING HIGH RESISTANCE TO WEAR AND THERMO-MECHANICAL STRESSES

Abstract: A brake disk (1; 40; 60; 80; 90; 100) comprising a bell (2), having an axis of rotation (3), and a braking band (4), produced as separate parts and in engagement by means of a shaped coupling (14) with tangential and axial restraints is characterized in that the brake disk comprises at least one insert (19; 41; 61; 81) which is deformable in a plastic or elastic manner in the shaped coupling (14) in order to ensure that the loads transmitted by a braking action are distributed substantially uniformly on the braking band (4) and on the bell (2).

Description: DESCRIPTION "Brake disk having high resistance to wear and thermo- mechanical stresses" In general, the present invention relates to a brake disk having high resistance to wear and thermo-mechanical stresses. In particular, the present invention relates to a brake disk comprising a substantially central bell, having an axis of rotation, and a braking band, produced as separate parts and connected to one another, by means of a restrained joint with axial and tangential restraints. It is known that a braking device of the type commonly in use in motor vehicles comprises a metal brake disk fixed to the wheel axle and, acting astride the disk, a caliper fixed to the stub axle or to the hub- carrier of the vehicle and having brake linings generally known as "pads". In particular, the brake disk comprises a braking band having a swept braking surface, and a bell fixed to the wheel axle. . The calipers, which are operated hydraulically by means of cylinder/piston units, push the pads against the swept surface of the braking band. The braking action is therefore brought about by the friction between the pads and the swept surface of the braking band of the brake disk. The friction of the pads against the braking band of the disk causes the kinetic energy of the masses to be braked to be dissipated as heat, bringing about an increase in the brake-disk temperature, which increase is particularly high in the region of the swept surface. For this reason, the braking band is required to be particularly resistant both to the wear caused by the abrasive action of the pads, and to temperature. These wear-resistance characteristics are not, however, required of the bell for which, in contrast, it is advantageous to use a material which enables a complex geometrical shape with good mechanical characteristics to be produced. For the above-mentioned reasons, it is known, particularly in high-performance braking devices, to form the brake disk in two parts, the braking band being made of wear-resistant and temperature-resistant material and the bell of material which has the above-mentioned mechanical characteristics . The materials commonly used to produce the braking band are composite materials of the carbon/silicon carbide (C/SiC) type, or metal-matrix materials (MMCs) which are distinguished by good wear resistance, a high degree of hardness and, at the same time, fragility, a low coefficient of thermal expansion, and low specific weight . Materials commonly used for the bell, on the other hand, are metals such as steel, anodized aluminium alloys, etc. In order to take account of the different thermal expansion of the materials and of the fragility of the braking band, the coupling between the bell and the braking band is often formed by a restrained joint with tangential and axial restraints and without any radial restraint so as to allow for the different radial expansions of the two parts and to prevent cracks or fissures arising in the composite material of the braking band. In particular, the tangential restraint of the above-mentioned coupling, which is essential for the transmission of the braking torque, is achieved by means of a toothed coupling between radial teeth provided along the outer surface of the bell and corresponding radial teeth provided along the inner surface of the braking band. However, a coupling of this type between the bell and the braking band has the serious disadvantage that, because of the machining tolerances of these parts, it is not possible to ensure that all of the teeth of the bell and the corresponding teeth of the braking band which are in contact are stressed tangentially in the same manner as a result of the braking action. In other words, with a coupling of this type, it is not possible to ensure that the loads transmitted by the braking action are distributed uniformly on the teeth of the bell and on the corresponding teeth of the braking band. Some pairs of radial teeth of the joint therefore often undergo a considerably greater tangential mechanical stress than other pairs, as a result of which the breaking load may be exceeded or cracks or fissures may be triggered in the fragile material of the braking band, such cracks tending to be propagated rapidly throughout the surface of the material . The technical problem upon which the present invention is based is that of providing a brake disk having structural and functional characteristics of the coupling between the bell and the braking band such as to overcome the disadvantages mentioned above with reference to the brake disks of the prior art. This problem is solved by a brake disk comprising a bell, having an axis of rotation, and a braking band, produced as separate parts and in engagement by means of a shaped coupling with tangential and axial restraints, characterized in that the brake disk comprises at least one insert which is deformable in a plastic or elastic manner in the shaped coupling in order to ensure that the loads transmitted by a braking action are distributed substantially uniformly on the braking band and on the bell. The present invention is based upon the surprising discovery that, if at least one insert made of a material which is deformable in a plastic or elastic manner is interposed in the joint between the bell and the braking band, the loads transmitted by the braking action are distributed substantially uniformly on the bell and on the braking band since the excessive tangential stresses which may arise in some joints due to the manufacturing tolerances between the bell and the braking band are absorbed by the material of the inserts of these joints by plastic or elastic deformation thereof. By virtue of the substantially uniform distribution of the loads on the bell and on the braking band which is achieved in the brake disk according to the present invention, the likelihood of cracks or fissures being triggered in the relatively fragile material of the braking band is advantageously greatly reduced since, in contrast with the prior art mentioned, the braking band is no longer substantially subject to excessive local stresses . In the brake disk according to the present invention, the material of the inserts interposed between the bell and the braking band may be selected, for example, from drawing steel and copper alloys, each of the materials mentioned having plastic or elastic deformation characteristics adequate for absorbing the excessive tangential stresses due to the manufacturing tolerances between the bell and the braking band. The material of the inserts is preferably drawing steel. The material used for the production of the bell, on the other hand, is selected from metals having good mechanical characteristics such as, for example, steel, hard anodized aluminium alloys, sintered steel, and cast iron. In contrast, the materials used for the production of the braking band are composite materials of the carbon/silicon carbide (C/SiC) type or metal-matrix materials (MMCs) such as, for example, aluminium alloys reinforced with ceramic particles such as silicon carbide, alumina, titanium boride, etc. Further characteristics and advantages of the brake disk according to the present invention will become clearer from the following description of some preferred embodiments of the brake disk, the description being given by way of non-limiting example with reference to the appended drawings, in which: Figure 1 is an exploded perspective view of an embodiment of the brake disk according to the present invention, Figure 2 is a front view of the brake disk of Figure 1, Figures 3 and 3a are respective views of a section of the brake disk of the present invention extended in a plane, taken along a cylindrical drawing surface III-III of Figure 2, Figure 4 is a perspective view of a detail of the brake disk of Figure 1, Figure 5 is an exploded perspective view of another embodiment of the brake disk according to the present invention, Figure 6 is a front view of the brake disk of Figure 5 , Figures 7 and 7a are respective views of a section of the brake disk of the present invention extended in a plane, taken along a cylindrical drawing surface VII-VII of Figure 6, Figure 8 is an exploded perspective view of a further embodiment of the brake disk according to the present invention, Figure 9 is a front view of the brake disk of Figure 8, Figures 10 and 10a are respective views of a section of the brake disk of the present invention extended in a plane, taken along a cylindrical drawing surface X-X of Figure 9, Figure 11 is an exploded perspective view of a further embodiment of the brake disk according to the present invention, Figure 12 is an exploded perspective view of a further embodiment of the brake disk according to the present invention, Figure 13 is a front view of the brake disk of Figure 12, Figures 14 and 14a are respective views of a section of the brake disk of the present invention extended in a plane, taken along a cylindrical drawing surface XIV-XIV of Figure 13, Figure 15 is an exploded perspective view of a further embodiment of the brake disk according to the present invention, Figure 16 is a front view of the brake disk of Figure 15, Figures 17 and 17a are respective views of a section of the brake disk of the present invention extended in a plane, taken along a cylindrical drawing surface XVII- XVII of Figure 16, Figure 18 is a schematic section through a portion of a detail of the brake disk of Figure 15. In the drawings, for each embodiment of the brake disk according to the present invention described below, the same reference numerals are attributed to common and functionally equivalent structural elements. With reference now to Figures 1-4, a brake disk according to the present invention, generally indicated 1, comprises a bell 2, having an axis of rotation 3, and a braking band 4, provided with a swept braking surface 5. Preferably, the bell 2 is made of hard anodized aluminium alloy or of sintered steel, whereas the braking band 4 is made of a composite carbon/silicon carbide material . The bell 2 has an outer set of teeth constituted by a plurality of radial teeth 6 which are preferably spaced uniformly and have sides 7 joined by respective straight or curved head surfaces 8. Each radial tooth 6 of the bell 2 has an axial through-hole 15 through which fixing means described in the following part of the description can extend in order to achieve the axial restraint between the bell 2 and the braking band 4. The braking band 4, on the other hand, has an inner set of teeth constituted by a plurality of radial teeth 11, and corresponding recesses 9 between the teeth 11. Preferably, the radial teeth 11 of the braking band 4 are spaced uniformly and the number of radial teeth 11 is equal to the number of radial teeth 6 of the bell 2. In particular, each recess 9 is delimited by facing sides 10 of two neighbouring teeth 11 of the braking band 4, the sides 10 converging towards the axis of rotation of the disc 3, and by a base surface 12 having an elliptical shape such as not to interfere with the swept braking surface 5 in order to limit the transmission of heat from the braking band 4 to the bell 2. The opposite sides 10 of each tooth 11 of the braking band 4 are joined by a straight or curved head surface 13. The sides 7 of the teeth 6 also converge towards the axis of rotation 3 of the bell 2 with the same inclination as the sides 10 which delimit the recesses 9. According to the invention, tangential restraint is achieved in the brake disk 1 by means of a toothed coupling 14 with clearance between the teeth 6 of the bell 2 and the teeth 11 of the braking band 4, after the interposition of inserts 19 between them. Each insert 19 is constituted by a substantially "L" -shaped plate-like element having unequal limbs 20 and 21, the limbs being joined to one another by a curved portion 26 disposed outside the plane containing the second limb 21 and having its concave side facing towards the first limb 20. The second limb 21 also has an open hole 29 in its free end. Moreover, a greater part of the length of the second limb 21, containing the above-mentioned open hole 29, extends at an inclination to the perpendicular to the plane containing the first limb 20 so that, during the assembly of the brake disk 1, the hole 29 is aligned with a respective hole 15 of a successive tooth 6 of the bell 2, the limb approximating to an arcuate shape equivalent to a circular sector covered by two adjacent teeth. In this embodiment, a first circumferential series 22 of first plate-like elements 19a is disposed on one side of the toothed coupling 14 between the bell 2 and the braking band 4 and a corresponding, second circumferential series 23 of second plate-like elements 19b is disposed on the opposite side of the toothed coupling 14 so that, in the region of each tooth 11 of the braking band 4, there are two associated plate-like elements, that is, a first plate-like element 19a and a second plate-like element 19b, disposed opposite one another, that is, situated on opposite sides of the tooth 11 of the braking band 4. In particular, for each tooth 11, the first platelike element 19a has a first limb 20a having an inner surface 24a bearing on one of the two opposite sides 10 of the tooth 11 and an outer surface 25a coupled with clearance with a side 7 of a first tooth 6a of the bell 2 adjacent the tooth 11 of the braking band 4. The second plate-like element 19b disposed opposite the first plate-like element 19a, on the other hand, has a respective limb 20b having an inner surface 24b bearing on the other of the two opposite sides 10 of the tooth 11 and an outer surface 25b coupled with clearance with a side 7 of a second tooth 6b of the bell 2 neighbouring the first tooth 6a and adjacent the above-mentioned tooth 11 of the braking band 4. The first limbs 20a and 20b preferably extend so as to bear on the two opposite sides 10 of the tooth 11 substantially throughout the greater part of the axial length thereof . Moreover, again for each tooth 11 of the braking band 4, the first plate-like element 19a has a second limb 21a which is joined to the first limb 20a by a curved portion 26a, and the second plate-like element 19b has a second limb 21b which is joined to the first limb 20b by a curved portion 26b. The second limb 21a of the first plate-like element 19a extends circumferentially on one side of the toothed coupling 14 between the bell 2 and the braking band 4 and comprises a first portion 27a which extends from the curved portion 26a, in contact with the tooth 11, and a second portion 28a in contact with the second tooth 6b. Similarly, the second limb 21b of the second platelike element 19b extends circumferentially on the opposite side of the toothed coupling 14 and in the opposite direction to the second limb 21a of the first plate-like element 19a. In particular, the second limb 21b comprises a first portion 27b which extends from the curved portion 26b, in contact with the tooth 11 of the braking band 4, and a second portion 28b in contact with the first tooth 6a neighbouring the second tooth 6b and adjacent the tooth 11 of the braking band 4. As is clear from Figures 3 and 3a, the two curved joining portions 26a and 26b extend or project from respective opposite sides of the toothed coupling 14. This advantageously prevents the opposed plate-like elements 19a and 19b associated with a tooth 11 of the braking band 4, which closely follow the corners of the tooth 11, from stressing them mechanically. The curved joining portions 26a and 26b also favour the correct insertion of the limbs 20a and 20b in the axial direction so that these limbs can advantageously interact with the respective sides 10 of a tooth 11 throughout the greater part of the axial length or depth thereof . Each of the plate-like elements 19a of the first series 22 has an open hole 29a formed in the second portion 28a of the second limb 21a and, similarly, each of the plate-like elements 19b of the second series 23 has a hole 29b formed in the second end portion 28b of the second limb 21b. In particular, for each tooth 6 of the bell 2 there is an associated pair of opposed holes 29a and 29b belonging, respectively, to a first plate-like element 19a and to a second plate-like element 19b which are associated with two adjacent teeth 11 of the braking band 4. Each pair of opposed holes 29a and 29b is aligned with the through-hole 15 formed in the respective tooth 6 of the bell 2 to permit the insertion of fixing means which restrain the bell 2 and the braking band 4 axially, in association with the plate-like elements 19a and 19b. In this embodiment, the fixing means take the form, for each tooth 6, of a bolt assembly 32 composed of a bolt 33 having a head 34 and a shank 35 which extends through the hole 15 in the tooth 6 and a pair of opposed holes 29a and 29b associated with the tooth 6, a nut 36, and two washers 37 associated with the shank 35 and arranged on opposite sides of the tooth 6 so as to be in contact with the head 34 and with the nut 36, respectively. Each bolt assembly 32 associated with a tooth 6 of the bell 2 thus restrains on the tooth 6 a pair of end portions 28a, 28b of corresponding plate-like elements 19a and 19b associated, respectively, with neighbouring teeth 11 of the braking band 4, and consequently restraining the bell 2 and the braking band 4 axially. According to a preferred embodiment of the invention which is shown in deliberately accentuated manner in Figure 3a in order to make its characteristics clear, the axial length or depth of the teeth 6 of the bell 2 is slightly greater than the axial length or depth of the teeth 11 of the braking band 4, by an amount of the order, for example, of a few tenths of a millimetre, and the first portions 27a and 27b of the first plate-like element 19a and of the second plate-like element 19b associated with a tooth 11 of the braking band 4 are curved in a manner such as to have concave sides facing away from the respective first limbs 20a and 20b of the plate-like elements 19a and 19b. In this embodiment, the first portions 27a and 27b axially preload the respective tooth 11 of the braking band 4, that is, they constantly act or, in other words, exert axial forces thereon. In particular, this preloading takes place in a predefined region of contact between respective sections of the first portions 27a and 27b and corresponding surface portions of the tooth 11. Free relative movements, due to the clearances, between the bell 2 and the braking band 4 are thus advantageously prevented by resilient forces directed axially or tangentially. Naturally, the first portions 27a and 27b of the first plate-like element 19a and of the second plate-like element 19b associated with a tooth 11 of the braking band 4 may be curved so that each has more than one section in contact with a corresponding surface of the tooth 11 in order to exert the axial preloading. Alternatively, the above-mentioned axial preloading function may also be performed by making the axial length or depth of the teeth 11 of the braking band 4 slightly greater than the axial length or depth of the teeth 6 of the bell, by an amount of the order, for example, of a few tenths of a millimetre, without curvature of the above-mentioned first portions 27a and 27b of the first plate-like element 19a and of the second plate-like element 19b. The axial preloading on each tooth 11 of the braking band 4 associated with a first plate-like element 19a and with a second plate-like element 19b would in fact thus be exerted entirely by the first portions 27a and 27b of the plate-elements 19a and 19b, once the axial restraint between the bell 2 and the braking band 4 had been achieved. In order to assemble the brake disk 1, each first plate-like element 19a of the first series 22 is inserted in a corresponding recess 9 from one side of the braking band 4 so as to arrange the inner surface 24a of the first limb 20a bearing on one of the opposite sides 10 which delimit the recess 9. Then, in order to achieve the tangential restraint in the brake disk 1., the radial teeth 6 of the bell 2 are inserted in the respective recesses 9, forming the toothed coupling 14 between the bell 2 and the braking band 4, and each second plate-like element 19b of the second series 23 is inserted in the corresponding recess 9 from the opposite side of the braking band 4 so as to arrange the inner surface 24b of the first limb 20b bearing on the other side 10 delimiting the said recess 9. Finally, the first plate-like elements 19a and the second plate-like elements 19b are anchored to the respective teeth 6 of the bell by means of the bolt assemblies 32, thus achieving the axial restraint between the bell 2 and the braking band 4. Another embodiment of the brake disk according to the present invention, generally indicated 40, will now be described with reference to Figures 5-7. In the brake disk 40, the inserts interposed between the bell 2 and the braking band 4 are constituted by a circumferential series of plate-like elements 41 of substantially U-shaped profile, each of the plate-like elements 41 comprising a base 42, as well as a first limb 43a and a second limb 43b which . are substantially identical to one another and are joined to corresponding ends of the base 42 by curved portions 44a and 44b, respectively. The curved portions 44a and 44b are disposed outside the respective planes containing the first limb 43a and the second limb 43b and both have their concave sides facing towards the base 42. In this embodiment, a plate-like element 41 is associated with each tooth 11 of the braking band 4 in a manner such that the base 42 has an inner surface 45 bearing on that side 10 of the tooth 11 which has its surface facing in the opposite direction to the direction of rotation R of the braking band 4 in use, the base 42 having an outer surface 46 coupled with clearance with a side 7 of a first tooth 6a of the bell 2 adjacent the tooth 11 of the braking band 4. The base 42 preferably extends so as to bear on the side 10 of the tooth 11 substantially throughout the axial length thereof . The other of the two opposites sides 10 of the tooth 11, that is, the side 10 having its surface facing in the direction of rotation R of the braking band 4, is coupled with clearance, without the interposition of inserts, with a second tooth 6b neighbouring the first tooth 6a and adjacent the tooth 11 of the braking band 4, . Moreover, again for each tooth 11, the first limb 43a and the second limb 43b of the plate-like element 41 extend circumferentially on opposite sides of the toothed coupling 14 between the bell 2 and the braking band 4. In particular the first limb 43a has a first portion 48a which extends from the curved portion 44a, so as to be in contact with the tooth 11, and a second portion 49a in contact with the second tooth 6b of the bell 2. Similarly, the second limb 43b has a first portion 48b which extends from the curved portion 44b, so as to be in contact with the tooth 11, and a second portion 49b in contact with the second tooth 6b of the bell 2. For each plate-like element. 41, both the second portion 49a of the first limb 43a and the second portion 49b of the second limb 43b, which are in contact with a tooth 6 of the bell 2, have respective open holes 50a and 50b aligned with a through-hole 15 formed in the tooth 6. In order to achieve the axial restraint in the braking disk 40, a bolt assembly 32 is associated with each tooth 6 of the bell, enabling the opposed portions 49a and 49b of a plate-like element 41 to be restrained on the tooth 6, and consequently achieving axial restraint of the bell 2 and the braking band 4. According to a preferred embodiment of the invention shown in Figure 7a, the axial length or depth of the teeth 6 of the bell 2 is slightly greater than the axial length or depth of the teeth 11 of the braking band 4, by an amount of the order, for example, of a few tenths of a millimetre, and the first portions 48a and 48b of a plate-like element 41 associated with a tooth 11 of the braking band 4 are curved so as to be concave on the side of the plate-like element 41 facing away from the base 42 . Each tooth 11 of the braking band 4 is thus preloaded axially by the first portions 48a and 48b of a respective plate-like element 41 associated therewith. In order to assemble the brake disk 40, each platelike element 41 is produced with one of the two limbs 43a or 43b open and is inserted in a corresponding recess 9 in a manner such that the inner surface of the base 42 is arranged bearing on that one of the two sides 10 delimiting the recess which has its surface facing in the opposite direction to the direction of rotation R of the braking band 4 in use. The radial teeth 6 of the bell 2 are then inserted in the respective recesses 9, forming the toothed coupling 14 between the bell 2 and the braking band 4, and the open limb 43a or 43b of each plate-like element 41 is bent so as to be disposed on one side of the toothed coupling 14. Finally, the plate-like elements 41 are anchored to the respective teeth 6 of the bell 2 by means of the bolt assemblies 32. Another brake disk according to the present invention, generally indicated 60, will now be described with reference to Figures 8-10. In the brake disk 60, the inserts interposed between the bell 2 and the braking band 4 are constituted by a circumferential series of substantially C-shaped platelike elements 61 each having a profile which is substantially complementary to that of a tooth 6 of the bell 2 and comprises a base 65 and two substantially identical limbs 62a and 62b, each plate-like element 61 being able to be fitted in a corresponding recess 9 with each of the limbs 62a and 62b interfering with a respective one of the opposed sides 10 delimiting the recess 9. In particular, each recess 9 of the braking band 4 is associated with a plate-like element 61 in which the limbs 62a. and 62b have respective inner surfaces 63a and 63b each coupled with clearance with one of the two opposite sides 7 of a tooth 6 of the bell 2 which engages the recess 9, and respective outer surfaces 64a and 64b each in contact with one of the two facing sides 10 of two neighbouring teeth 11a and lib defining the recess 9. The base 65 of each plate-like element 61 associated with a recess 9, however, is coupled with clearance with the head surface 8 of a tooth 6 of the bell 2 which engages the recess 9. Preferably, each of the limbs 62a and 62b extends substantially throughout the axial length of a respective side 10 delimiting the recess 9 and the base 65 extends substantially throughout the axial length of the head surface 8 of a respective tooth 6 of the bell 2. The brake disk 60 also has a first plurality 66 of plates 68 arranged in a circumferential series on one side of the toothed coupling 14 of the brake disk 60 and a second plurality 67 of plates 68 arranged in a circumferential series on the opposite side < of the toothed coupling 14. Each plate 68 has two opposed holes 70 in alignment with respective. holes 15 of two neighbouring teeth 6 and, moreover, the plates 68 of the first plurality 66 alternate with the plates 68 of the opposed second plurality 67. Each tooth 11 of the braking band 4 is thus preloaded axially by a respective plate 68 of the first plurality 66 or of the second plurality 67. According to a preferred embodiment of the invention shown in Figure 10a, the axial length or depth of the teeth 6 of the bell 2 is slightly greater than the axial length or depth of the teeth 11 of the braking band 4 by an amount of the order, for example, of a few tenths of a millimetre, and each plate 68 of the first plurality 66 and of the second plurality 67, which plate 68 extends over two neighbouring teeth 6 of the bell 2, is curved so that a portion thereof is in contact with a corresponding surface portion of a tooth 11 of the braking band 4 interposed between the neighbouring teeth 6 of the bell 2. In order to achieve the axial restraint in the brake disk 60, each plate 68 of the first plurality 66 and of the second plurality 67 is restrained on two neighbouring teeth 6 of the bell 2 by means of bolt assemblies 32. In order to assemble the brake disk 60, each platelike element 61 is inserted in a corresponding recess 9 so that the outer surfaces 64a and 64b of the limbs 62a and 62b interfere with respective facing sides 10 of two neighbouring teeth 11 delimiting the recess 9. The radial teeth 6 of the bell 2 are then inserted in the respective recesses 9, forming the toothed coupling 14 between the bell 2 and the braking band 4. Finally, the plates 68 of the first plurality 66 and of the second plurality 67 are arranged in circumferential series on respective opposite sides of the toothed coupling 14 and the plates 68 are anchored to the respective teeth 6 of the bell 2 by means of the bolt assemblies 32. Another embodiment of the brake disk according to the present invention, generally indicated 80, will now be described with reference to Figure 11. The brake disk 80 of this embodiment differs from the brake disk 60 described above and illustrated in Figures 8-10 in that the plate-like elements 61 are joined together to form a ring 81 by respective portions 82, each of the portions 82 joining the free ends of two facing limbs 62 belonging to two neighbouring plate-like elements 61. Each portion 82 also has a surface coupled with clearance with a corresponding head surface 13 of a tooth 11 of the braking band 4 and preferably extends throughout the axial length of the head surface 13. This embodiment has the advantage that the insert interposed between the teeth 6 of the bell 2 and the teeth 11 of the braking band 4 is formed as a single part, thus facilitating the assembly of the brake disk 80. Another embodiment of the brake disk according to the present invention, generally indicated 90, will now be described with reference to Figures 12-14. In the brake disk 90, the inserts interposed between the bell 2 and the braking band 4 are constituted by plate-like elements 61 joined to form a ring 81 as described above for the brake disk 80 shown in Figure 11. However, for the axial restraint between the bell 2 and the braking band 4, the brake disk 90 has two annular plates 91 disposed on opposite sides of the toothed coupling 14 between the bell 2 and the braking band 4 and both having a plurality .of circumferential holes 93 in alignment with corresponding holes 15 provided in the teeth 6 of the bell 2. The two annular plates 91 are restrained on the teeth 6 of the bell 2 by means of suitable rivets 94, each rivet 94 being associated with a tooth 6 of the bell 2. Another, particularly preferred embodiment of the brake disk according to the invention, generally indicated 100, will now be described with reference to Figures 15-18. The brake disk 100 of this embodiment differs from the brake disk 90 described above and illustrated in Figures 12-14 in that the bell 2 has an annular band 101 formed integrally with or welded to a peripheral portion of the bell comprising the radial teeth 6. Each tooth 6 of the bell 2 therefore has an axial blind hole, and an annular plate 91, restrained on the teeth 6 of the bell 2 by means of rivets 102, for example, of the "fast" type, is provided for achieving the axial restraint between the bell 2 and the braking band . According to a preferred embodiment of the invention shown in Figure 14a with reference to the brake disk 90 and in Figure 17a with reference to the brake disk 100, the axial length or depth of the teeth 6 of the bell 2 is slightly greater than the axial length or depth of the teeth 11 of the braking band 4 by an amount of the order, for example, of a few tenths of a millimetre, and each annular plate 91 has a curved portion 103, as shown in Figure 18, for preloading each tooth 11 of the braking band 4 axially by interaction or contact of the portions 103 with corresponding surface portions of the teeth 11 of the braking band 4. In the brake disk according to the present invention, there is generally a coupling with clearance between the radial teeth of the bell and the inserts interposed between the bell and the braking band. In this coupling, each insert interposed in a respective recess 9 bears on at least one of the two facing sides 10 of two corresponding neighbouring teeth 11 of the braking band 4, and is coupled with clearance with at least one of the two sides 7 of a corresponding tooth 6 of the bell 2 forming a toothed coupling with the two neighbouring teeth 11 of the braking band 4. In particular, each side 10 of each tooth 11 lies in a respective radial plane extending through the axis of rotation 3 of the brake disk 1 and each side 7 of each tooth 6 facing a corresponding side 10 lies in a respective plane parallel to the corresponding radial plane, and the distance between each pair of facing sides of a tooth of the bell and of a tooth of the braking band is preferably equal to the thickness of the insert interposed between the teeth, preferably plus half of the clearance . Moreover, as will be described below, each insert can also be interposed in a respective recess 9 in a manner, such as to bear on or to interfere with at least one of the two facing sides 10 of two corresponding neighbouring teeth 11 of the braking band 4 and on or with at least one of the two sides 7 of a corresponding tooth 6 of the bell 2 forming a toothed coupling with the two neighbouring teeth 11 of the braking band 4. The main advantage of the brake disk according to the present invention is that the inserts enable the loads transmitted by the braking action to be distributed substantially uniformly on the bell and on the braking band, thus greatly reducing the likelihood of the triggering of cracks or fissures in the relatively fragile material of the braking band due to excessive local stresses. A further advantage of the brake disk according to the present invention is that it is easy and inexpensive to produce. In the description given above, reference is made to an insert made of material which is deformable in a plastic or elastic manner. In particular, "material deformable in a plastic or elastic manner" is intended to define a material which, when subject to a load such as, for example, the braking action undergone by the braking band, deforms in an "elastoplastic" manner, or in an elastic manner. This elastoplastic or elastic deformation constitutes a compliance of the connection between the teeth of the bell and of the braking band which enables all of the teeth to be brought to a working condition in which the above-mentioned load is distributed uniformly or substantially uniformly. In particular, if the material deforms in an elastoplastic manner, when the load is applied to the braking band for the first time, an at least partial permanent deformation of the inserts is brought about and takes up the manufacturing tolerances of the. coupling between the teeth of the bell and of the braking band once and for all . Subsequent loads applied to the disk will therefore be transmitted substantially uniformly to all of the teeth. If the material deforms in an elastic manner, it is appropriate to distinguish between two situations of use of the inserts . If the inserts are disposed between the teeth of the bell and of the braking band without preloading, upon the application of the load, during a first stage, the clearance present between the teeth will be taken up and the band will rotate relative to the bell without transmitting the load. When the smallest of the clearances present between the teeth has been taken up and a portion of an insert present therein comes to bear on the tooth of the bell, it will start to undergo elastic deformation under load. As the relative rotation between the braking band and the bell continues, a portion of a second insert in turn will come to bear on the respective second tooth of the bell . This will continue in the same manner until all of the teeth come to bear in order to work simultaneously until the total load is reached. Between the first tooth and the last tooth to come to bear there will be a load difference which will correspond to the elastic reaction of the insert which came to bear first and will be equal to the product of the elastic constant of the insert with the greatest tolerance (that is, the difference between the greatest clearance provided between the teeth of the bell and of the braking band and the smallest of these clearances, or the difference due to the manufacturing tolerances) . This load difference will be smaller the smaller is the ratio between the difference in the dimensions of the teeth and the deformation which the insert undergoes (from the time at which all of the teeth are bearing) to reach to the total load. Alternatively, the inserts are arranged between the teeth of the bell and of the braking band with preloading, for example, because the inserts are mounted between the teeth of the bell and of the braking band with a predetermined interference (or force fitting) which brings about preloading thereof . In this case the load differences between the various teeth will be given by the differences in the preloading of the various inserts due to the manufacturing tolerances of the distances between the facing teeth. The greatest of these preloading differences will correspond to the maximum load difference present at the same moment between the teeth. Precisely because a preloading is provided, in this situation, there is no clearance to be taken up between the facing teeth and, when the load due to the braking action is applied, all of the inserts deform simultaneously by the same amount, all increasing the load by the same amount. In other words, the tooth which had the greatest preloading will be that which is loaded most, purely by an amount equal to its greater preloading. This difference in preloading which, in comparison with the overall load, will be equal only to a small fraction thereof, will be the sole lack of uniformity in the distribution of the load on the teeth of the bell and of the braking band. In order to satisfy contingent and specific requirements, an expert in the art may apply modifications, adaptations and replacements of elements with other functionally equivalent elements to the above- described brake disk without thereby departing from the scope of protection of the invention as defined by the following claims.

Claims: CLAIMS 1. A brake disk (1; 40; 60; 80; 90; 100) comprising a bell (2), having an axis of rotation (3), and a braking band (4) , produced as separate parts and in engagement by means of a shaped coupling (14) with tangential and axial restraints, characterized in that the brake disk comprises at least one insert (19; 41; 61; 81) which is deformable in a plastic or elastic manner in the shaped coupling (14) in order to ensure that the loads transmitted by a braking action are distributed substantially uniformly on the braking band (4) and on the bell (2) . 2. A brake disk (1; 40; 60; 80; 90; 100) according to Claim 1 in which the bell (2) has a plurality of radial teeth (6) formed along its outer surface and each having an axial hole (15) , the braking band (4) has a plurality of radial teeth (11) and corresponding recesses (9) between the teeth (11) , which are formed along its inner surface, and the number of which is equal to the number of radial teeth (6) of the bell (2), and the tangential restraint is achieved by toothed coupling (14) between the radial teeth (6) of the bell (2) and the radial teeth (11) of the braking band (4) , after the interposition of the at least one insert (19; 41; 61; 81) in the recesses (9) of the braking band (4) . 3. A brake disk (1; 40; 60; 80; 90; 100) according to Claim 2 in which each tooth (6) of the bell (2) comprises two opposite radial sides (7) joined by a head surface (8) , and each tooth (11) of the braking band (4) comprises two opposite radial sides (10) joined by a head surface (13) , the facing sides (10) of a pair of neighbouring teeth (11) defining the sides of a corresponding recess (9) . 4. A brake disk (1; 40; 60; 80; 90; 100) according to Claim 3 in which, in each of the recesses (9) , the at least one insert (19; 41; 61; 81) bears on at least one of the two facing sides (10) of two corresponding neighbouring teeth (11) of the braking band (4) and is coupled with clearance with at least one of the two sides (7) of a corresponding tooth (6) of the bell (2) , forming a toothed coupling with the two neighbouring teeth (11) of the braking band (4) . 5. A brake disk (1; 40; 60; 80; 90; 100) according to Claim 3 in which, in each of the recesses (9) , the at least one insert (19; 41; 61; 81) bears on or interferes with at least one of the two facing sides (10) of two corresponding neighbouring teeth (11) of the braking band (4) and bears on or interferes with at least one of the two sides (7) of a corresponding tooth (6) of the bell (2) forming a toothed coupling with the two neighbouring teeth (11) of the braking band (4) . 6. A brake disk (1) according to Claim 4 or Claim 5 in which the at least one insert (19) comprises a first circumferential series (22) of first plate-like elements (19a) and a second circumferential series (23) of second plate-like elements (19b), the circumferential series (22, 23) being arranged on opposite sides of the toothed coupling (14) in a manner such that two opposed plate- like elements, that is, a first plate-like element (19a) and a second plate-like element (19b) , are associated with each tooth (11) of the braking band (4). 7. A brake disk (1) according to Claim 6 in which each first or second plate-like element (19a, 19b) is substantially L-shaped and comprises a first limb (20a, 20b) and a second limb (21a, 21b) , the limbs (20a, 20b; 21a, 21b) being joined to one another by a curved portion (26a, 26b) outside the plane containing the second limb (21a, 21b) and having a concave side facing towards the first limb (20a, 20b) . 8. A brake disk (1) according to Claim 7 in which, for each pair of opposed first and second plate-like elements (19a, 19b) associated with a tooth (11) of the braking band (4) , the first limb (20a) of the first plate-like element (19a) has an inner surface (24a) bearing on one of the two opposite sides (10) of the tooth (11) and an outer surface (25a) coupled with clearance with a side (7) of a first tooth (6a) of the bell (2) adjacent the tooth (11) of the braking band (4) , and the second limb (20b) of the opposed, second plate- like element (19b) has an inner surface (24b) bearing on the other of the two sides (10) of the tooth (11) of the braking band (4) and an outer surface (25b) coupled with clearance with a side (7) of a second tooth (6b) of the bell (2) neighbouring the first tooth (6a) and adjacent the tooth (11) of the braking band (4) . 9. A brake disk (1) according to Claim 8 in which the first limbs (20a, 20b) of each pair of opposed first and second plate-like elements (19a, 19b) extend so as to bear on the opposite sides (10) of the tooth (11) of the braking band (4) , substantially throughout the axial length thereof . 10. A brake disk (1) according to Claim 8 or Claim 9 in which, for each pair of opposed first and second plate-like elements (19a, 19b) associated with a tooth (11) of the braking band (4) , the second limb (21a) of the first plate-like element (19a) extends circumferentially on one side of the toothed coupling (14) and the second limb (21b) of the opposed, second plate-like element (19b) extends circumferentially on the opposite side of the toothed coupling (14) , in the opposite direction to the second limb (21a) of the first plate-like element (19a) . 11. A brake disk (1) according to Claim 10 in which, for each pair of opposed first and second plate- like elements (19a, 19b) associated with a tooth (11) of the braking band (4) , the second limb (21a) of the first plate-like element (19a) comprises a first portion (27a) which extends from the curved portion (26a) so as to be in contact with the tooth (11) of the braking band (4) and a second portion (28a) in contact with one of the first and second teeth (6a, 6b) of the bell (2) , and the second limb (21b) of the opposed plate-like element (19b) comprises a first portion (27b) which extends from the curved portion (26b) so as to be in contact with the tooth (11) of the braking band (4) and a second portion (28b) in contact with the other of the first and second teeth (6a, 6b) of the bell (2) . 12. A brake disk (1) according to Claim 10 in which the axial length or depth of the teeth (6) of the bell (2) is greater than the axial length or depth of the teeth (11) of the braking band (4) and, for each pair of opposed first and second plate-like elements (19a, 19b) associated with a tooth (11) of the braking band (4) , the first portions (27a, 27b) are curved so as to have concave sides facing away from the first limbs (20a, 20b) , and are in contact with respective corresponding surface portions of the tooth (11) of the braking band (4). 13. A brake disk (1) according to Claim 11 or Claim 12 in which each of the first and second plate-like elements (19a, 19b) of the first and second series (22, 23) has a hole (29a, 29b) formed in the second portion (28a, 28b) of the second limb (21a, 21b) , the holes (29a, 29b) being arranged in a manner such that, for each tooth (6) of the bell (2) , a pair of opposed holes (29a, 29b) belonging to a first plate-like element (19a) and to a second plate-like element (19b) associated with two adjacent teeth (11) of the braking band (4) , respectively, is associated and aligned with a through hole (15) formed axially in the tooth (6) . 14. A brake disk (1) according to Claim 13 in which the axial restraint between the bell (2) and the braking band (4) is achieved by the restraint of the first and second plate-like elements (19a, 19b) on the teeth (6) of the bell (2) by fixing means (32; 94; 102) extending through the holes (15) in the teeth (6) of the bell (2) and the opposed holes (29a, 29b) of the first and second plate-like elements (19a, 19b) . 15. A brake disk (40) according to Claim 4 or Claim 5 in which the at least one insert (19; 41; 61; 81) comprises a circumferential series of substantially U- shaped, plate-like elements (41) , each of the plate-like elements (41) being associated with a respective tooth (11) of the braking band (4) and comprising a base (42) , as well as a first limb (43a) and a second limb (43b) disposed opposite one another, the limbs (43a, 43b) being joined to the base (42) by respective curved portions (44a, 44b) outside the respective planes containing the first and second limbs (43a, 43b) and having concave sides facing towards the base (42) . 16. A brake disk (40) according to Claim 15 in which, for each plate-like element (41) associated with a tooth (11) of the braking band (4) , the base (42) has an inner surface (45) bearing on a side (10) of the tooth (11) having its surface facing in the opposite direction to the direction of rotation (R) of the braking band (4) in use, and an outer surface (46) coupled with clearance with a first tooth (6a) of the bell (2) adjacent the tooth (11) of the braking band (4) , and the first and second limbs (43a, 43b) extend circumferentially on opposite sides of the toothed coupling (14) . 17. A brake disk (40) according to Claim 16 in which, for each plate-like element (41) associated with a tooth (11) of the braking band (4) , each of the first and second limbs (43a, 43b) has a first portion (48a, 48b) which extends from a respective curved portion (44a, 44b) in contact with the tooth (11) of the braking band (4) and a second portion (49a, 49b) in contact with a second tooth (6b) of the bell (2) neighbouring the first tooth (6a) and adjacent the tooth (11) of the braking band (4) . 18. A brake disk (40) according to Claim 17 in which the axial length or depth of the teeth (6) of the bell (2) is greater than the axial length or depth of the teeth (11) of the braking band (4) and, for each plate- like element (41) associated with a tooth (11) of the braking band (4) , the first portions (48a, 48b) are curved so as to have concave sides facing away from the base (42) and are in contact with respective corresponding surface portions of the tooth (11) of the braking band (4) . 19. A brake disk (40) according to Claim 17 or Claim 18 in which, for each plate-like element (41) associated with a tooth (11) of the braking band (4) , the second end portion (49a, 49b) of each of the first and second limbs (43a, 43b) has a hole (50a, 50b) , the holes (50a, 50b) being disposed opposite one another and aligned with a through-hole (15) formed axially in the second tooth (6b) of the bell (2) . 20. A brake disk (40) according to Claim 19 in which the axial restraint between the bell (2) and the braking band (4) is achieved by restraint of the platelike elements (41) on the teeth (6) of the bell (2) by fixing means (32; 94; 102) extending through the holes (15) in the teeth (6) of the bell (2) and the opposed holes (50a, 50b) in the plate-like elements (41) . 21. A brake disk (60) according to Claim 4 or Claim 5 in which the at least one insert (19; 41; 61; 81) comprises a circumferential series of plate-like elements (61) having a profile substantially complementary to that of a tooth (6) of the bell (2) , each of the plate-like elements (61) being associated with a respective recess (9) of the braking band (4) and comprising a base (65) joined at its opposite ends to two opposed limbs (62a, 62b) . 22. A brake disk (60) according to Claim 21 in which each of the opposed limbs (62a, 62b) of a platelike element (61) associated with a recess (9) of the braking band (4) has an inner surface (63a, 63b) coupled with clearance with one of the opposite sides (7) of a tooth (6) of the bell (2) in engagement in the recess (9) , and an outer surface (64a, 64b) bearing on one of the facing sides (10) of the recess (9) . 23. A brake disk (60) according to Claim 22 in which each base (65) of a plate-like element (61) associated with a recess (9) of the braking band (4) is coupled with clearance with the head surface (8) of the tooth (6) of the bell (2) which engages the recess (9) . 24. A brake disk (60) according to Claim 23 in which the opposed limbs (62a, 62b) of the plate-like elements (61) extend substantially throughout the axial lengths of the sides (10) of the teeth (11) of the braking band (4) and the bases (65) of the plate-like elements (61) extend throughout the axial lengths of the head surfaces (8) of the teeth (6) of the bell (2) . 25. A brake disk (80; 90; 100) according to Claim 24 in which the plate-like elements (61) are joined together to form a ring (81) by respective portions (82) , each of the portions (82) joining the free ends of two facing limbs (62) belonging to two neighbouring plate- like elements (61) . 26. A brake disk (80; 90; 100) according to Claim 25 in which each of the portions (82) has a surface coupled with clearance with a head surface (13) of a respective tooth (11) of the braking band (4) . 27. A brake disk (60; 80) according to any one of Claims 23 to 26, in which the axial restraint between the bell (2) and the braking band (4) is achieved by means of a first plurality (66) of plates (68) disposed in a circumferential series on one side of the toothed coupling (14) and a second plurality (67) of plates (68) disposed in a circumferential series on the opposite side of the toothed coupling (14) , alternating with the plates (68) of the first plurality (66) , each of the plates (68) of the first and second pluralities (66, 67) being restrained on two neighbouring teeth (6) of the bell (2) by fixing means (32; 94; 102) . 28. A brake disk (60; 80) according to Claim 27 in which the axial length or depth of the teeth (6) of the bell (2) is greater than the axial length or depth of the teeth (11) of the braking band (4) , and each plate (68) of the first plurality (66) and of the second plurality (67) is curved so as to have a concave side facing away from the opposed limbs (62a, 62b) of the plate-like elements (61) and is in contact with a surface portion of a respective tooth (11) of the braking band (4) . 29. A brake disk (90) according to Claim 25 or Claim 26 in which the axial restraint between the bell (2) and the braking band (4) is achieved by at least one annular plate (91) disposed on one side of the toothed coupling (14) , the at least one annular plate (91) having a plurality of holes (93) each aligned with a corresponding hole (15) in a tooth (6) of the bell (2) and being restrained on the teeth (6) of the bell (2) by fixing means (32; 94; 102) extending through the holes (15) in the teeth (6) and the holes (93) in the at least one annular plate (91) . 30. A brake disk (90) according to Claim 29, comprising two annular plates (91) disposed on opposite sides of the toothed coupling (14) . 31. A brake disk (100) according to Claim 29 in which the axial restraint between the bell (2) and the braking band (4) is achieved by at least one annular plate (91) disposed on one side of the toothed coupling (14) and an annular band (101) disposed on the opposite side of the toothed coupling (14) , the annular band (101) being formed integrally with or welded to the bell (2) in the region of a peripheral portion thereof comprising the radial teeth (6) . 32. A brake disk (90; 100) according to any one of Claims 29 to 31 in which the axial length or depth of the teeth (6) of the bell (2) is greater than the axial length or depth of the teeth (11) of the braking band (4) and the at least one annular plate (91) has curved portions (103) , each of the portions (103) being in contact with a corresponding surface portion of a tooth (11) of the braking band (4) . 33. A brake disk (1; 40; 60; 80; 90; 100) according to any one of Claims 14 to 32 in which the fixing means (32; 94; 102) are selected form the group comprising bolt assemblies (32) and rivets (94; 102) .

Inventors: PACCHIANA GIOVANNI PAOLO, PERICO PAOLO, PACCHIANA, GIOVANNI, PAOLO, PERICO, PAOLO
Applicants: BREMBO ENGINEERING S P A, PACCHIANA GIOVANNI PAOLO, PERICO PAOLO, BREMBO ENGINEERING S.P.A., PACCHIANA, GIOVANNI, PAOLO, PERICO, PAOLO
Application year: 2000
Main classification: F16D65
IPC codes: F16D65