Abstract:
Wheel-mounted brake disks which are arranged on both sides of a wheel base of a railway wheel and are fastened by through bolts, the bolt head of every through bolt lying in a countersink of one wheel-mounted brake disk and a nut screwed onto the through bolt lying in a countersink of the other wheel-mounted brake disk, each resting either directly or indirectly on the bottom of the countersink. The wheel-mounted brake disks are designed so that every countersink has an undercut portion that extends down to the bottom.

Description:
PRIORITY CLAIM 
     This patent application is a U.S. National Phase of International Patent Application No. PCT/EP2012/059599, filed 23 May 2012, which claims priority to German Patent Application No. 10 2011 102 518.2, filed 26 May 2011, the disclosures of which are incorporated herein by reference in their entirety. 
     FIELD 
     Disclosed embodiments relate to wheel brake disks. 
     SUMMARY 
     Disclosed embodiments develop wheel brake disks of the generic type such that, with an optimization of the friction surface area, the service life of the through bolts is increased and thus the operational reliability of the rail wheel as a whole is improved. 
     The flexibility of the bolted components is improved, that is to say increased, whereby the bolt loading is considerably reduced and the service life of the through bolts is lengthened, without these having the disadvantages associated with the use of spring washers or other elements. 
     The bore diameter of the depression on the friction surface can, like before, be kept very small, and is determined exclusively by the diameter of the bolt head or of the nut. 
     The ratio of half of the diameter difference between the depression in the region of the undercut and through bore to the base thickness may be selected to be greater than 1, wherein the base thickness may be reduced to such an extent that the region can still permanently withstand the thermal and mechanical loading of the wheel brake disk. To minimize a notch effect, the transition from the base of the depression to the cylindrical part of the undercut should be realized with a radius which should be selected to be as large as possible. 
     As mentioned, during a braking operation, the known wheel brake disk bulges outward in the center, with a tensile load being exerted on the through bolts, or deformation into a dish/shield shape occurs, with tensile and bending loads being exerted on the through bolts. The now flexible base can bend elastically and, in functional terms, acts in the manner of a spring element. Even in the case of high loads, the bolted region of the wheel brake disk remains substantially in contact with the wheel body. 
     Owing to the increased flexibility, the additional force in the bolt is considerably reduced, and the service life of the bolted connection is lengthened. Furthermore, the additional force generated by the thermal expansion of the bolted region is reduced owing to the relatively thin base. The overall result is thus a noticeable lengthening of service life, and an improvement in operational reliability. 
     Furthermore, the disclosed embodiments can be realized with little outlay in terms of manufacturing, wherein a minimization of costs is attained by virtue of the fact that additional components, such as spring washers or spring elements, can be omitted. 
     Furthermore, the disclosed embodiments can be used for all types of wheel brake disks, even in conjunction with brake linings with small friction elements. 
     According to at least one disclosed embodiment, the base thickness may be partially reduced, wherein for this purpose, the base has a concentric recess on the inner and/or outer side. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Exemplary embodiments of the invention will be described below on the basis of the appended drawings, in which: 
         FIG. 1  shows a partial detail of a rail wheel in a cross section; and 
         FIGS. 2-4  show, in each case in cross section, an exemplary embodiment of the wheel brake disk. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows, in a partial detail, a rail wheel having a wheel body  1  which has a radially inwardly extending web  10 , to both sides of which wheel brake disks  2  are fastened by means of through bolts  3 . To receive the bolt head  4  on one side and a nut  5  on the other side, a depression  6  for each through bolt  3  is provided in each wheel brake disk  2 , the depression  6  merging into a through bore  12  facing toward the web  10 , wherein the base of the depression  6  delimits a base  9 , which on the other side forms an abutment surface  11  which bears against the web  10  of the wheel body  1 . 
     According to at least one disclosed embodiment, each depression  6  has an undercut  8  which extends as far as the base and which merges, at the side averted from the wheel body  1 , into a cylindrical region  7  which forms an insertion opening for the through bolt  3  and which proceeds from a friction surface  16  of the wheel brake disk  2 . 
     The diameter of the cylindrical region  7 , which is smaller than the diameter of the undercut  8 , is selected to be as small as possible, and is determined exclusively by the associated dimension of the bolt head  4  or of the nut  5  and/or of a tool by means of which the through bolt  3  can be tightened. 
     As can be seen very clearly in the figures, a transition  13  between the base  9  and the wall of the undercut  8  is highly rounded to eliminate or minimize a notch effect. 
     While  FIG. 2  shows, as a detail, a cross section through a wheel brake disk  2  as shown in  FIG. 1  in the assembled position,  FIGS. 3 and 4  show in each case a further exemplary embodiment of a wheel brake disk. Here, the base  9  has concentric recesses  14 ,  15 , wherein, in the variant shown in  FIG. 3 , the recess is provided on the inner side, that is to say on the side facing toward the undercut  8 , whereas the recess  15  is formed as an annular groove into the abutment surface  11  on the outer side. 
     In the case of known rail wheels, the wheel brake disks connected to both sides of the wheel body are fastened by means of a multiplicity of circumferentially distributed through bolts, wherein the through bolts pass through the wheel body, the head of the respective through bolt lies in a depression of one wheel brake disk, and a nut that is screwed onto the respective through bolt lies in a depression of the other wheel brake disk. The connection of the wheel brake disks to the wheel body may be realized in the region of a wheel hub, of a wheel web or of a wheel rim. 
     In the case of high-performance modern wheel brake disks, the direct bolted connection of the two wheel brake disks to the wheel web has become established. For the configuration of the bolted connection, a maximum possible bolt length is desired, this being achieved using sleeves under the bolt head, or under the bolt head and under the nut. 
     It is also known, instead of or in addition to the sleeves, to use spring washers in the form of plate springs, which serve to improve the flexibility of the braced parts to compensate braking-induced deformations of the bolted parts and briefly occurring shocks. 
     The effect, however, comes at the cost of negative effects that can considerably shorten the service life of the connection. When using the spring washers, the number of bolted joints, and thus possible settling rates, is multiplied. 
     Furthermore, the spring washers restrict the usage temperature of the wheel brake disks, because the spring washers must not be heated beyond their annealing temperature. The spring washers would otherwise lose their resilient action, reducing the service life of the bolted connection. Also, the use of spring washers leads to an increase in the number of components to be assembled, whereby the risk of incorrect assembly is considerably increased. 
     Furthermore, the use of spring washers requires a relatively large diameter of the depression, which restricts the possibilities for use of rigid or flexible sintered linings with small friction elements, in particular because the friction elements can become caught on the bore edge and be destroyed. 
     To minimize the bore diameter, although it has already been proposed to insert press-in bushings into the depression, it is then the case that the brake disk can only be subjected to low thermal loading, for which reason the design has not been proven, that is to say become established, in practice. 
     Aside from the bolted connection itself, most wheel brake disks have elements for centering on the wheel body, for example in the form of sleeves held in the through bores of the wheel body, which sleeves have peg-shaped ends which engage into grooves of the friction disks. 
     The diameter of the respective depression should basically be as small as possible, the diameter being just large enough that a tool for tightening the bolted connection can be inserted and that the spring washers, if they are used, can expand. By means of an opening which is small in relation to the friction surface area, it is the intention for the friction behavior to be impaired as little as possible, and for the catching of lining elements to be prevented. 
     The base of the depression is generally formed, where possible, with a high stiffness, that is to say the base thickness is selected so as to be large in relation to the diameter of the through bore of the respective wheel brake disk. Here, the ratio of half of the diameter difference between the cylindrical depression and through bore to the base thickness in the case of connections without spring washers or spring elements may be less than 1, whereby a rigid abutment surface is provided which practically cannot bend. 
     During braking, owing to the heating at the surface, the respective wheel brake disk undergoes bulging in cross section, which bulging leads to tensile loading of the through bolt. In the case of the conventional design with a rigid base, the loading directly gives rise to an additional force in the bolt as a result of the deformation and clamping length. The bulging may be so great that the abutment surface by which the wheel brake disk bears against the wheel body is lifted. Aside from the tensile force generated by the bulging, an additional force is also exerted on the through bolt by a deformation of the wheel brake disk into a dish/shield shape that arises during the course of the braking operation or owing to internal stresses. 
     LIST OF REFERENCE NUMERALS 
     
         
           1  Wheel body 
           2  Wheel brake disk 
           3  Through bolt 
           4  Bolt head 
           5  Nut 
           6  Depression 
           7  Cylindrical region 
           8  Undercut 
           9  Base 
           10  Web 
           11  Abutment surface 
           12  Through bore 
           13  Transition 
           14  Recess 
           15  Recess 
           16  Friction surface