Brake disk for vehicles

A brake disk for a disk brake, which consists of a brake disk chamber and at least one friction ring connected to the brake disk chamber by rivets, wherein a jacket of the brake disk chamber is provided with sections having reduced wall thickness and/or through-holes, which are axially directed material cut-outs located on the outer periphery of the brake disk chamber jacket, which material cut-outs are used to at least partially place the axially directed rivets. The friction ring and the brake disk chamber are centered with respect to each other exclusively by the rivets. The friction ring has at least one fastening extension directed inward from the friction surface, to which fastening extension a collar of the brake disk chamber jacket is connected by the rivets in that the side of the friction ring directed toward the brake disk chamber has an axially directed depression for accommodating the collar of the brake disk chamber, which depression is designed in such a way that there is radial play between the brake disk chamber and the friction ring.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to composite brake disks for motor vehicles. Brake disks are constituent parts of a motor-vehicle braking system which are installed coaxially with a wheel and have a friction ring and a brake-disk hub. The brake-disk hub here serves to fasten the brake disk on a wheel hub, whereas the friction ring is brought into tribological contact with the brake pads of the braking system during braking operation. This dissipates the kinetic energy of the motor vehicle in the form of friction heat, and the vehicle is braked.

Such brake disks can be produced in one or more parts, the material of the friction ring being subjected to the greatest amount of stress. Friction rings are therefore usually designed in the form of castings, in particular using GG-15 or GG-25. In order for the heat which is produced during braking operation to be dissipated from the friction ring, such friction rings are often configured in the form of internally ventilated friction rings, that is to say they are provided with channels or bores which have air flowing through them in order thus to improve the dissipation of heat from the friction ring.

Such a brake disk, in the case of which the friction ring or the (usually joined-together) friction rings is or are produced separately from the brake-disk hub and then connected thereto in a suitable manner, has the advantage that the friction ring(s), on the one hand, and the brake-disk hub, on the other hand, can be produced from the materials which are most suitable for the respective requirements. This means that for example, on the one hand, it is possible to achieve a reduction in weight and, on the other hand, advantageous decoupling between the friction ring and brake-disk hub is thus possible.

DE 100 32 972 A1 describes a composite brake disk, in the case of which the essentially conventionally formed brake-disk hub has a lateral surface which is circular and cylindrical in relation to the axis of rotation of the disk brake and in which through-passages or at least reduced-wall-thickness portions are provided. This brake-disk hub therefore has a certain elasticity which is beneficial for essentially unimpeded thermal friction-ring expansion, i.e. the unavoidable friction-ring expansion is thus not impeded to any significant extent by the brake-disk hub, and therefore stressing is not built up and undesirable friction-ring deformation is ruled out. The material proposed by said document for the brake-disk hub is a higher-strength steel material or the like.

It is an object of the present invention to provide a brake disk in the case of which a suitable connection between the friction ring and brake-disk hub allows the amount of space required for attaching the brake disk to the wheel hub to be kept small. In addition, the intention is to provide a connection between the brake-disk hub and friction ring which, when braking operation creates heat, builds up the lowest possible level of stressing in the brake disk and, in addition, can also transmit very high braking force.

This and other objects are achieved according to the invention by a brake disk for a disk brake, which comprises a brake-disk hub and at least one friction ring, which is connected to said brake-disk hub via rivets, wherein a lateral surface of the brake-disk hub is provided with reduced-wall-thickness portions and/or through-passages, which are axially directed material cutouts, which are located on the outer circumference of the lateral surface of the brake-disk hub and serve for the at least partial placement of the axially directed rivets. The friction ring and the brake-disk hub are centered in relation to one another exclusively via the rivets. The friction ring has at least one fastening extension, which is directed inward from the friction surface and to which a collar of the lateral surface of the brake-disk hub is connected by the rivets, that side of the friction ring which is directed towards the brake-disk hub having an axially directed depression, which is intended for accommodating the collar of the brake-disk hub and is configured such that an amount of radial play is present between the brake-disk hub and friction ring.

If, then, the internal diameter of the depression is greater than an external diameter of the collar, and therefore the friction disk is centered in relation to the brake-disk hub exclusively by the rivets, this has the advantage that, with it being possible for the support of the brake-disk hub on the friction disk to be machined to best possible effect, it is possible to provide a centering rivet connection between the two parts which, on the one hand, allows high braking forces to be transmitted and, on the other hand, as far as the transmission of heat from the friction disk to the brake-disk hub is concerned, provides for the best possible insulation effect with, at the same time, a high degree of freedom from warping. In addition, it is advantageous if the depression fully accommodates the collar of the brake-disk hub and/or if a bore for accommodating the rivet in the collar of the brake-disk hub, said bore corresponding to a bore in the fastening extension for accommodating the rivet, has a planar depression at its end which is directed away from the friction disk, said planar depression serving to accommodate the manufactured head of the rivet to some extent or to the full extent. The manufactured head and brake-disk-chamber collar thus form an essentially planar surface form, and the amount of dirt and brake-lining dust adhering can therefore be reduced.

It is thus advantageously possible for the extension of the friction-disk surface in the inward direction as far as the lateral surface of the brake-disk hub to be of essentially planar configuration. This makes it difficult for dirt to accumulate and for water to penetrate into the connection between the brake-disk hub and friction disk.

Centering of the brake-disk hub and friction ring in relation to one another exclusively via the rivets also has the advantage that, in case of heating and of different coefficients of expansion of the materials, it is not possible for stressing to occur on account of the two parts being otherwise fixed in relation to one another. In order for it to be possible to ensure an optimum contact pattern of the rivets, specifically in the relevant cross section, these should then be formed in a specific manner, with geometrical provision made in order to compensate for a force-transmission loss which occurs in standard rivets according to the prior art due to the latter, as they deform, forming a tapering barrel shape with a relatively poor contact pattern. Tests have shown that, during the operation of setting the rivet, a leading clearance directly at the manufactured head, for example a cone over a sub-region of the rivet stem, prevents the barrel shape brought about by the riveting process according to the prior art and optimizes the contact pattern of the rivet in the vicinity of the manufactured head. It is thus advantageous if, starting from a manufactured head, at least over a sub-region of its stem in the region of the brake-disk hub, each rivet, prior to being deformed, has a cone, of which the diameter decreases in the direction of a rivet-closing head.

Furthermore, the brake disk can advantageously be configured such that its friction ring has at least one fastening extension, which is directed inward from the friction surface and to which a collar of a lateral surface of the brake-disk hub is connected by the rivets. The fastening extension creates a support surface for the collar of the brake-disk hub, it being possible for said support surface, like the brake-disk hub prior to the joining operation, to be provided, for example by machine, with a surface quality which is advantageous for the joining pairing. The support surface for the collar of the brake-disk hub and friction ring can be optimized in terms of heat transmission such that the heat transmission, when the friction disk is heated, results in the lowest possible level of stressing in joining partners.

For this reason, an advantageous embodiment of the brake disk has indents on the internal diameter of the friction ring, on the depression thereof and support surface of the collar of the brake-disk hub, wherein a respective rivet is placed between the indents. In the case of a preferred embodiment, as seen in the radial direction, the indents have a maximum depth bounded by a reference circle of interconnected longitudinal axes of the rivets. They therefore extend as far as the rivet center point, obviously in a state in which they are offset in relation to the same circumferential direction.

Further advantageous embodiments of the invention provide for use to be made of an internally ventilated brake disk having two adjacent friction disks, which are connected to one another by radially running, regularly arranged webs, wherein the webs run from an outer-circumference periphery to an inner-circumference periphery of the friction disks, and the latter are connected by the webs such that the interspaces thereof form identically sized cooling channels through which cooling air can flow and which are subdivided by further, relatively shorter webs such that, in a radial region relatively close to the inner-circumference periphery of the friction disks, a respectively relatively shorter web is located centrally between the webs, and the relatively shorter webs project radially inward beyond the webs and extend as far as the fastening extension, where, in alignment therewith in the radially inward direction, a respective rivet connects the fastening extension to the collar.

This achieves an even more stable embodiments of the brake disk, which can transmit even more braking force, in particular when eighteen rivets are arranged at regular spacings on the reference circle for rivet-connection purposes.

According to further preferred embodiments of the invention, directed radially outward from the relatively shorter web, the cooling channels divide up into at least three flow channels, two first further relatively shorter webs being arranged in each cooling channel, in a state in which they are offset radially outward in relation to each relatively shorter web in the circumferential direction.

Such an arrangement and configuration of cooling channels between the friction disks gives rise to a high rib density. The higher this density, the greater the cooling surface area and therefore the better the extent to which it is possible to compensate for temperature peaks which occur, and this results in an optimized cooling of the brake disk. The cooling-channel arrangement, which increases the surface area provided for cooling the brake disk, thus advantageously enhances the cooling performance.

It is also advantageous if the friction disk which is directed towards the brake-disk hub is extended inwards in the direction of the fastening extension, and thus forms the latter.

Further advantageous embodiments of the invention are distinguished by the rivet geometry being further optimized. For example, a transition provided from the rivet stem to the manufactured head of the rivet is provided with an axial undercut on the manufactured head of the rivet. An undercut of 88 degrees between the rivet stem and the underside of the manufactured head of the rivet is preferred. Tests have shown that this even further optimizes the contact pattern between the rivet and brake-disk hub, and therefore the connection is suitable for an even greater amount of force transmission over a longer service life. This advantage is also increased, in addition, if the rivets consist of an austenitic, stainless steel. It is possible here for the brake-disk hub to consist of a light metal or of steel or of a non-metal material, that is to say suitable materials for the chamber are preferably higher-strength high-strength light metals (inter alia magnesium) or a high-strength, thin-walled sheet steel or aluminum and other non-ferrous or non-metal materials. The brake-disk hub can therefore be produced, for example, by casting or forging or by extrusion. If use is made of a brake-disk hub according to the invention made of a lightweight material, it is possible to use steel wheels in addition to aluminum wheels.

If the brake-disk hub and the friction ring are connected to one another by means of orbital riveting, it is possible for a surface pressure of the rivets even on the gray-cast-material of the friction ring to be kept to as low a level as possible.

DETAILED DESCRIPTION OF THE DRAWINGS

The brake disk1illustrated in the figures has a brake-disk hub3and a friction ring2and is provided for installation on a wheel hub (not shown) in order to rotate therewith, during operation, about the axis of rotation D. The single-piece, internally cooled friction ring2, which is produced from gray cast iron, includes two friction disks2′,2″ with webs2′″ which are located therebetween, and connect the friction disks to one another, for cooling-air guidance. The annular friction disk2′, which is located closer to the brake-disk hub3in the axial direction, i.e. as seen in the direction of the axis of rotation D, extends radially R (as seen in relation to the axis of rotation D), by way of a so-called fastening extension9, a certain amount further in the direction of the axis of rotation D than the other friction disk2″, which is further away from the brake-disk hub3in the axial direction.

In the region of overlap between the aforementioned fastening extension9of the friction disk2′ and a collar3b, which projects outward in the radial direction R from the free end of the lateral surface3aof the brake-disk hub3, said lateral surface being circular-cylindrical in relation to the axis of rotation D, the brake-disk hub3is connected to the friction disk2′ and thus to the friction ring2, via axially extending rivets5. In this regard, the text here (and in particular in the introductory part of the description) refers to a connection between the brake-disk hub3and the friction ring2.

In the lateral surface3aof the brake-disk hub3, and to some extent also in the base3cof the brake-disk hub3, cutouts7are distributed uniformly over the circumference of the brake-disk hub3. The rivets5project into the cutouts, i.e. the rivets5are placed at least to some extent therein. Each of these cutouts7, which also form reduced-wall-thickness portions7, extends in the axial direction around the respectively associated, likewise oriented rivet5and serves to accommodate the latter to some extent and/or to accommodate the set rivet5during installation, i.e. the connection of the brake-disk hub3to the friction ring2, as can be seen in the axial direction. The cutouts7here are essentially in the form of a semicircular cylinder and are formed in the lateral surface3aof the brake-disk hub3during casting or forging, and therefore, although said lateral surface3ais weakened in the region of the cutouts7, it still forms a closed wall on the inside, i.e. as seen from the axis of rotation D. Of course, through-passages in the form of bores are also provided, pretty much as an extension to the cutouts7, in the collar3bof the brake-disk hub3, and the rivets5are fitted through these. These cutouts7therefore allow the rivets5to be arranged closer to the axis of rotation D.

FIG. 5shows, on the inside of the friction disk2′ of the brake disk1, a combination of webs1aand relatively shorter webs1b,1cof the internally ventilated brake disk1which is repeated in a geometrically regular manner in the circumferential direction over the circular-ring surface of said friction disk. The friction disks2′,2″ of the friction ring2are connected to one another via the webs1aand the relatively shorter webs1b,1c, wherein the webs1a, at the same time, bound cooling channels20, which are repeated in a likewise geometrically regular manner in the circumferential direction over the circular-ring surfaces of the friction disks2′,2″. The cooling channels20each extend from an inner-circumference periphery14of the friction disks2′,2″ at the beginning of the webs1aas far as an outer-circumference periphery15of the friction disks2′,2″ of the brake disk1.

As seen in the circumferential direction, centrally in each cooling channel20between the respectively equal-length webs1awithin the friction disks2′,2″, the shorter web1bextends in each case from the vicinity of the inner-circumference periphery14of the friction disks2′,2″, in the direction of the outer-circumference periphery15of the latter, as far as a first diameter12of the friction disks2′,2″. Proceeding therefrom, two first further shorter webs1c, which are offset in the circumferential direction in relation to the shorter web1bwithin the cooling channel20, extend further outward in the radial direction as far as the outer-circumference periphery15, one offset to the left, and the other offset to the right. The first further shorter webs1cdivide up the cooling channels20, in the radially outward direction from the relatively shorter web1c, into three flow channels1c′,1c″,1c′″. All the webs1a,1b,1chave essentially the same web width and are rounded at the front and rear. The radially outer ends of the respective webs1a,1chere are located on the same circle circumference in the vicinity of the outer-circumference periphery15, and the radially inner ends of the respective webs1aare located on the same circle circumference in the vicinity of the inner-circumference periphery14, of the brake disk1. Moreover, starting from each of the relatively shorter webs1b, the friction disk2′, which is directed toward the brake-disk hub3, is extended in the radially inward direction and, level with the collar3bof the brake-disk hub3, is provided in the axial direction with a bore21which serves to accommodate the rivet5, which fastens the friction disk2′ on the brake-disk hub3. Closing heads5″″ of all the rivets5are located on the visible side of the fastening extension9of the friction disk2′, whereas the manufactured heads5″ of the rivets5are fully recessed in a planar depression23of the collar3bof the brake-disk hub3, as illustrated inFIG. 2. The friction disk2′, which is directed toward the brake-disk hub3, likewise has an axially directed depression27, which is intended for supporting the collar3bof the brake-disk hub3and of which the internal diameter is greater than an external diameter of the collar3b. Therefore, friction disk2′ and the brake-disk hub3are centered in relation to one another exclusively by way of the rivets5. That side of the friction ring2which is directed toward the brake-disk hub3therefore has an axially directed depression27, which is intended for accommodating the collar3bof the brake-disk hub3and is configured such that an amount of radial play25is present between the radially-outward facing projections of brake-disk hub3and corresponding indents30of friction ring2.

FIG. 3shows a view of part of a rivet5designed in the form of semitubular rivets, measuring 5 mm×13 mm, with a manufactured head5″ and a stem5′. In the direction of the manufactured head5″, the rivet stem5′ is designed to be conical with an increasing diameter. In the direction of the rivet stem5′, the manufactured head5″ has an undercut, and therefore the angle designated by a double arrow F measures essentially 88 degrees. The extent of a radius R between the cone5′″ of the rivet stem5′ and the undercut of the manufactured head5″ is not defined and is established by manufacturing. The cone5′″ has a length of at least 1.5 mm and at most 4 mm, the diameter of the cone5′″ at the manufactured head5″ being 5.33 mm. Tests have found that this rivet geometry, along with self-centering of the rivet during the operation of setting the rivet5, results in an advantageous contact pattern with a 100% amount of contact, which gives rise to optimum centering and force transmission. In addition, the conical rivet stem5′ and the undercut F of the manufactured head5″ provide for perfect sealing of the rivet connection and, consequently, protection against corrosive media.