The present invention relates to a disk for disk braking systems, in particular for motorcycles. Prior art

In the field of disk braking systems, such as the braking systems for motorcycles, various solutions for dispersing the friction heat generated and for regenerating the brake pad surface have been studied. Perforated disks or disks with protrusions and recesses have been developed. These solutions, rather simple from the constructional point of view, are not completely satisfactory with regards to braking uniformity and friction force, particularly during the initial stage. Brake disks have thus been developed which are the object of Italian application MI2003A001814, having hollows on the faces, the hollows of one face being preferably offset with respect to those of the other, to ensure braking uniformity and disk strength. Being of various shape and inclination, the hollows may preferably concern at least the outer edge of the disk or extend from the inner edge to the outer edge. Machining these disks, which operation may comprise the creation of hollows by milling, is however much longer and more complex than the common perforated disks. Solutions have been suggested in which the disk consists of two half-disks linked to each other by means of rivets, but the solution was found to be difficult to be manufactured with unsatisfactory results in disk shape and inadequate behavior as a result of thermal expansion phenomena.

A brake disk which is simple to be manufactured would be desirable to allow an adequate heat exchange and an adequate force, without negative repercussions on robustness, the weight and size being equal. Summary of the invention

The above-mentioned problems have now been solved by a brake disk comprising two half-disks, each having a friction surface able to interact with a brake pad and directly linked to each other by brazing on a face opposite to said friction surface. According to preferred aspect, the weld material has a fusion temperature of at least 950 ⁰ C, preferably 1050 ⁰ C and more preferably 1100 ⁰ C. According to a preferred aspect, it is a Ni-Cu based compound, preferably a Fe-Ni based compound. Thereby, the weld material may withstand temperatures of at least 95O ⁰ C or even higher, and in all cases higher than those which may be generated by using the brake.

The two half-disks preferably have holes and/or recesses in the profile of the edges which are offset with respect to those of the other half-disk so as to form, with the other half-disk, closed or half-closed cavities in the brake disk on the disk surfaces exposed to the brake pads. According to another aspect of the invention, the two half-disks may consist of several portions; the portions of a half-disk are offset if compared to those of the other half-disk, so that once the brazing operation has been performed, a half-disk portion keeps together at least two portions of the other half-disk.

The invention further relates to a method for manufacturing a brake disk as shown above. Brief description of the drawings The present invention will now be discioseα Dy means or tne αetaneα description of preferred but not exclusive embodiments, provided by way of example only, with the aid of accompanying figures 1-4, which diagrammaticaliy illustrate brake disks for motorcycles according to various aspects of the invention. Figure 5 shows a half-disk portion for manufacturing a disk according to a particular aspect of the invention.

Detailed description of an embodiment

The figures show brake disks according to the invention. The brake disk, in particular brake disks for motorcycles, may be made of any material suitable for the purpose, preferably steel which is commonly used. The disks according to the present invention have two overlapping half-disks 1 and 2 directly linked to each other by brazing. In the figures, the dashed line shows the hidden profile of the furthermost half-disk from the observer. Similar details are shown by the same reference number. It is worth noting that, according to a particular aspect of the invention related to figures 1 and 2, the half-disks may have a pattern of the edges, in particular of the outer edges 3 and 4, but also according to a further aspect exemplified in figure 2, of the inner edges 5 and 6, which may be corrugated or ragged, different from a circular profile; the two half-disks may, have a similar or different profile. If the profile is similar, according to a preferred aspect, it is offset in joining the two disks, as shown in figures 1 and 2. The opportunity that the support connections 7 of the disk to the wheel hub, which may be of known type - e.g. of the so-called "fixed" (figure 1-3) or "floating" (figures 2 and 4) type - are provided on the two half- disks so as to mate despite the profile offsetting, is taken into account. Alternatively, the connections may also be provided on only one of the half-disks or distributed therebetween, in an alternating manner, for example. Each of the two half-disks may be provided with holes: the holes of the disk facing the observer indicated by numeral 8 and those of the disk underneath indicated by numeral 9. The holes are preferably offset. Thereby, closed hollows are created on the two disk faces. If deemed appropriate, part of the holes may be coinciding to create through holes in the disk. As exemplified in figures 3 and 4, the disk edges may also be circular and may coincide. In this case, the technique according to the present invention allows to create hollows by offsetting the holes, indicated again by reference numerals 8 and 9.

The holes of a half-disk may also partially overlap the holes or recesses of one edge of the other disk, so as to create through holes 10, as shown in figures 1 and 2, at hollows created as shown above in order to increase ventilation and heat dispersion.

According to a further aspect of the invention, the half-disks may in turn consist of several portions. These portions may be substantially shaped as a circular crown sector, may be three on each half-disk, for example, and may correspond to an arc of substantially equal width. They may have an interlocking conformation at the ends thereof, for facilitating their positioning thus creating a joint. By arranging the portions of a half-disk so that the joints between the various portions are offset between the two half-disks, brazing the two half-disks will allow to keep the various portions of a half-disk together. A portion of a half-disk will keep the two portions of the other half-disk together, thus making direct joining systems between the two portions unnecessary. An advantage related to this type of construction is related to that the steel brake disks are commonly obtained by shearing or cutting (e.g. laser cutting) metal sheets which mav have a certain preferential orientation of the crystals in a direction due to machining. Such an orientation will be kept to a certain extent by the disk obtained, despite the usual tempering treatment. Such an orientation may lead to anisotropy in the mechanical behavior and thermal expansion, thus favoring deformation and strain. Therefore, the crystals in the finished disk could desirably be everywhere oriented in the same manner with respect to the radial direction, e.g. precisely in such a direction, which is obviously impossible with a disk cut in one piece from a metal sheet. By cutting several appropriately oriented portions from the metal sheet, and then assembling them, the orientation may be made more uniform with respect to the radial direction, the higher the number of portions. Disks consisting of several portions assembled by means of an interlocking system have already been suggested. However, the present invention provides a further advantage in that a complete disk, ready to be assembled without further complications, is provided. Figure 5 shows one of the half-disk portions from which a disk may be obtained as described above. If required, the complementary ends 11 and 12 may be shaped so as to couple with the corresponding ends of the adjacent portions, thus facilitating a correct positioning. In the illustrated case, three portions may form a half-disk. The second half-disk is similarly formed, by carefully placing the joints so as to be offset with respect to those of the first half-disk: a joint of the second half- disk may be where indicated by arrow A in figure 5, for example.

The invention refers to a method of production of brake disks, preferably made of steel, comprising: obtaining two half-disks preferably made of steel from a metal sheet by cutting or shearing, laying the weld material for brazing at a temperature of at least 950 ⁰ C, preferably at least 1050 ^Q C, more preferably at least 1100 ⁰ C, the relative positioning of the half-disks on a face of at least one of the half-disks, the heating at a temperature suitable to the brazing.

The obtained disk is cooled and the usually treatments, such as grinding, follow. It should be noted that the temperatures indicated above are such to allow steel tempering, if the disks are made of such a material. The brazing and subsequent cooling operations may thus be conducted, according to a possible aspect of the invention, so as to simultaneously allow such a phenomenon. The half-disks may be obtained from the metal, sheet with the desired profile and holes.

If the half-disks consist of several portions, the method may comprise the steps of assembling one of the half-disks, e.g. by simply arranging the portions side-by- side in an appropriate manner, laying the weld material on one of the faces of the half-disk, assembling the second half-disk on the face of the first disk which receives the weld material. The steps of brazing and the subsequent operations follow. If deemed appropriate, placing the weld material on the faces of the portions of one or both of the half-disks and then assembling the disk is further possible. The weld material may be laid on the face of one of the half-disks in a known manner. Techniques such as deposition according to techniques similar to printing, e.g. by ink jet, may be used if the weld material is a compound which contains metal powder (e.g. Ni - Cu or Fe-Ni) and other appropriate components, such as binders. It has been found that a very advantageous technique because of its machining simplicity, laying uniformity and material dispensing is the screen printing process. The machines commonly used for screen printing and for printing images on objects have been found suitable for the purpose. The half-disks or portions may be obtained from metal sheet by shearing or cutting, according to the same techniques used for common disks.