Rail wheel

A rail wheel with a wheel body and wheel brake discs connected thereto with fastening elements on both sides is designed in such a way that at least in the respective contact regions of the wheel brake discs a mechanically and thermally highly resilient intermediate layer is arranged on the wheel body.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of priority to International Patent Application No. PCT/EP2008/010931 filed 19 Dec. 2008, which further claims the benefit of priority to German Patent Application No. 10 2008 003 923.3 filed 11 Jan. 2008, the contents of which are incorporated herein by reference in their entirety.

BACKGROUND

The invention relates to a rail wheel.

In the known rail wheels, the wheel brake disks connected to the wheel body on both sides are fastened to the wheel body by a plurality of fastening elements, primarily throughbolts, distributed over the circumference.

In this case, the wheel brake disks bear with integrally formed cooling ribs, centering and fastening eyes directly against the wheel body, to be precise against a circumferential wheel web which connects a wheel hub to an outer race.

However, considerable operationally induced problems arise due to the direct contact of the wheel brake disks with the wheel body.

For example, during a braking operation, as a result of the axial temperature gradients which occur, considerable excessive rises in the surface pressure occur radially on the outside of the wheel brake disk between the wheel web and the contact regions. (If the respective brake disk were not bolted to the wheel body, it would assume the shape of a Belleville spring).

In addition, the annular wheel brake disks have the tendency to deform in an opposed plate-like manner due to internal tensile stresses in the frictional surfaces, which stresses occur due to high thermal loading.

Excessive rises in the surface pressures in the radially inner contact regions then occur in the cold state.

Due to a thermally induced “breathing” of the wheel brake disk, i.e. a radial contraction and expansion at intervals, a “frictional sliding” occurs in the contact regions during every braking operation.

Due to the above-mentioned excessive rises in the surface pressures, especially at high braking powers, scoring occurs between the wheel brake disks and the wheel body in the region of the contact regions or local plastic deformation occurs in the wheel web, and this may lead in the long term to damage, such as the formation of cracks, in the wheel.

SUMMARY

The invention is based on the object of developing a rail wheel of the generic type in such a manner that an operationally induced overstressing is prevented with structurally very simple means and, as a result, the service life as a whole is increased.

This object is achieved by a rail wheel as claimed.

Scoring phenomena and, therefore, wheel damage are avoided by arranging a mechanically and thermally highly loadable intermediate layer at least in the respective contact region between the wheel brake disks and the wheel body.

The thermally induced radial deformations of the wheel brake disk, which are referred to as “breathing” in the prior art and occur during braking, are now ineffective, since the intermediate layer acts as it were as a sliding layer on which either the wheel brake disk correspondingly slides, when the intermediate layer is held on the wheel body in a radially secured manner, or the intermediate layer together with the connected wheel brake disk moves in a sliding manner thereon relative to the wheel body.

The planar dimension of the intermediate layer is expediently the same size or larger than the associated dimension of the contact region of the wheel brake disks, and therefore a low surface pressure is effective.

The above-mentioned scoring phenomena or plastic deformations in the wheel web are, therefore, prevented, and therefore the formation of cracks arising as a consequence thereof is also effectively avoided.

This, of course, results in a significant increase in the service life of the entire rail wheel and in a noticeable improvement in operational reliability.

For this purpose, it is also expedient to produce the intermediate layer from a metal sheet, the hardness of which is significantly greater than the hardness or strength of the wheel web.

A metal sheet made of stainless steel with polished surfaces, which is customarily present in the form of rolled stock, is ideally suited for this purpose, wherein the tensile strength of a metal sheet of this type should be >1000 N/mm2and the thickness approximately 1 mm. However, in principle, other metal sheet thicknesses are also usable.

According to at least one implementation, the intermediate layers each consist of circular ring portions which are lined up in a row next to one another in the circumferential direction.

In this case, circular ring portions of 30°, 60°, 120° or 180° are conceivable. In principle, of course, the intermediate layer may be designed as a single-part sheet metal ring. The circular ring portions are fastened in the radial direction in a form-fitting or frictionally engaged manner. The form-fitting connection can take place either at the wheel web or on the contact side of the wheel brake disk.

By contrast, a frictional connection is achieved by corresponding distortion by means of the bolted connection through which the wheel brake disks are fastened to the wheel web or to the wheel body.

Further implementation details of the invention are characterized in the dependent claims.

DETAILED DESCRIPTION

FIG. 1illustrates a partial region of a rail wheel, specifically of one of the regions in which wheel brake disks2are connected on both sides to a wheel body1.

In this case, a wheel web3of the wheel body1, which wheel web forms two circumferential, radially extending contact surfaces, has a bore14through which a bolt6is guided, with which the wheel brake disks2are fixedly connected to the wheel body1.

Each bolt6, of which a plurality is furthermore distributed at an equal angular spacing on a circumferential circle, is guided through a fastening eye5in the respective wheel brake disk2, the end side of said eye likewise forming a contact region in relation to the wheel web3, such as cooling ribs4of the wheel brake disk.

An intermediate layer7assigned to each wheel brake disk2is arranged between the contact regions of the fastening eye5and the cooling ribs4and the wheel web3, and therefore the wheel web3and the contact regions of the wheel brake disk2bear against said intermediate layer.

Said intermediate layers7are composed of a mechanically and thermally highly loadable material, e.g., of a hard-rolled metal sheet, the hardness or strength of which is greater than that of the wheel web3.

As can be seen particularly clearly inFIG. 4, the intermediate layers7consist of circular ring portions which are distributed uniformly over the circumference, wherein the number of circular ring portions can vary. For example, for twelve bolts6, the same number of circular ring portions is provided, said portions accordingly each enclosing an angle of 30°.

For radial securing purposes, the intermediate layers7may be held in a form-fitting manner, to which end, in the example shown inFIG. 1, the wheel web3has steps8in which the intermediate layers7are located in a manner substantially secured against displacement in the radial direction.

The intermediate layers7have corresponding openings for the passage of the bolts6.

In the example shown inFIG. 2in which, as inFIGS. 3 and 5, an enlarged illustration in the contact region of the intermediate layers7is reproduced; the radial securing takes place in both directions, i.e., to the outside and to the inside, by means of a sleeve9, which is inserted into the bore14and is held in an axially secured manner there. The sleeve9protrudes over the wheel web3on both sides at least by the thickness of the intermediate layers7.

The outside diameter of the sleeve9approximately corresponds to the clear diameter of a central recess in the intermediate layer7such that the latter can easily be attached and is held in a manner secured against lateral displacement.

In the variant embodiments according toFIGS. 1 and 2, the intermediate layers7are, therefore, locked on the wheel web3. By means of the visible extensive contact of the intermediate layers7with the wheel web3, the outside radius of which is determined by the radial width of the cooling ribs4which virtually form outer contact regions, the production of significant temperature differences between the metal sheet and wheel web are avoided and therefore so too are thermally induced distortions of the intermediate metal sheets in relation to the wheel. The metal sheets do not slide on the wheel web.

By contrast, the wheel brake disk2which is supported on the respective intermediate layer slides in the radial direction on the intermediate layer7in the event of a thermally induced changing shape such that scoring or damage of the wheel web is prevented.

In the sense mentioned above, the intermediate layers7are also locked on the wheel web3in the example shown inFIG. 5.

For this purpose, the intermediate layers7have flanges13in the region of the bores14in the wheel web3, the flanges being in the form of collars and projecting into the bore14, and corresponding in the outside diameter thereof approximately to the clear diameter of the bore14such that radial securing in both directions is ensured.

FIG. 3illustrates a further example of fixing the intermediate layers7.

Here, the wheel brake disk2, in the contact regions thereof which face the wheel web3, has steps10in each of which one of the intermediate layers7is located and secured radially.

During a temperature-induced expansion and contraction of the wheel brake disks2, in the radial direction, the respective intermediate layer7moves at the same time by the same amount such that the intermediate layers7virtually slide on the wheel web3.

As can be seen inFIG. 4, there is a further type of radial fixing of the intermediate layers7in that punched-out portions are made in said intermediate layers in the region of overlap with sliding blocks11, which are arranged between the wheel web3and the wheel brake disks2, said punched-out portions corresponding in the basic contour dimensions thereof to the sliding blocks11, wherein the sliding blocks11pass through the associated punched-out portions, thus resulting in form-fitting positional fixing on the wheel web3.

Since temperature differences occur between the wheel brake disk2and the intermediate layer7during each braking operation, the intermediate layer7is designed in such a manner that differences in curvature do not result in any distortion.

The intermediate layer7is configured such that the intermediate layer7is provided on the outer and inner borders with contact portions12which bear against the associated edges of the steps8,10(FIG. 4).

In principle, a single-part intermediate layer in the form of a ring is capable of functioning. However, due to the large diameter of the wheel brake disks2for rail wheels, it is substantially more cost effective to use circular ring portions, wherein the latter are punched or cut by laser beam or water jet.

In the example shown inFIG. 4, 60° circular ring portions are selected, and each intermediate layer7is provided on the outer border with two contact portions12and on the inner border with one contact portion12which is located in the center while the two outer contact portions are arranged, with respect to the length, in the outer border regions, thus resulting in three-point contact by means of which, as mentioned, distortion in the event of differences in curvature is prevented.

LIST OF REFERENCE NUMBERS