Brakes – Elements – Brake wheels
Reexamination Certificate
1999-09-02
2001-11-27
Oberleitner, Robert J. (Department: 3613)
Brakes
Elements
Brake wheels
C188S073100
Reexamination Certificate
active
06321885
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to brake elements produced by composite casting, such as a brake drum, brake disk or the like, and to a composite casting process for the production of such brake elements. In particular, the invention relates to the composite casting of brake elements, such as brake drums, brake disks or the like suitable for vehicles, the brake elements comprising a hub and a flange for the attachment to vehicle wheels. Preferably, a brake disk may consist of two brake ring disks that are united with each other by connecting bridges produced by casting, while leaving space for cooling or ventilation channels.
BACKGROUND OF THE INVENTION
Brake drums and brake disks of the type used in many cases in passenger cars and trucks by the motor vehicle industry are subjected to severe dynamic and mechanical stresses produced especially by high thermal shock stress. For instance, when driving motor vehicles down a long gradient with full braking in the mountains, temperatures of up to 800° C. are reached on the brake disks, which may lead with subsequent quick cooling to substantial stresses and thereafter to stress cracks. In practice, therefore, it is advisable to select for the brake disk or brake drum a cast iron material with lamellar graphite, exhibiting a high thermal and temperature conductivity as well as a low thermal expansion coefficient.
Such a high-carbon gray cast iron is described, for instance, in DE 37 40 912 A1. A disadvantage, however, is that this type of cast iron with lamellar graphite exhibits a low modulus of elasticity and a low tensile strength between 100 N/mm
2
and 150 N/mm
2
. As a result, such materials are less suited for the area of the hub and the forming of the flange. According to W. Keiner,
Designing and Casting
15 (1990), No. 4, pages 4-14, the cross-section of heavy brake drums in these areas, especially at the junction to the flange, must be executed with a greater thickness of material and be reinforced by a few millimeters. The brake elements are, as a result, more or less weight-loaded.
Moreover, the hub and the flange are subjected to great dynamic stresses as a result of shocks and impacts, whereby the flange, as a result of thread tapping and the associated wheel bolts, exhibits already a lower strength, resulting, together with the notch effect emanating from the screws, in a reduction of the reverse bending strength.
In order to meet these requirements, it is common to produce brake drums or brake disks of high-grade iron-carbon alloys or other especially suited materials.
In order to reduce the expense in the production of a brake disk composed of various materials, it was suggested in DE 22 63 654 A1, to produce the concentric brake body arranged around the wheel hub in the form of a brake disk or a brake drum as a composite part in a uniform casting. For this purpose, the production of the hub starts with a drop forging of steel or with a cast iron part of spheroidal graphite. In order to improve the bond, a connecting bridge with recesses is provided which is designed as a revolving flange with a thin wall. A complete welding of the metal to the bridge is not envisioned in order to leave a small slot with a sound-absorbing effect between the sheet and the casting metal. On the other hand, a great quenching effect with respect to the cast iron flowing through and the formation of cementite is apparent in a thicker, revolving bridge. Subsequent annealing is therefore required, resulting in an increase of production costs. Furthermore, the smaller cross-section leads to a reduced transmission of power at the junction between the hub and the brake body, causing a substantial limitation in the area of application of the brake disk or the brake drum.
According to the proposed method, this brake element has a revolving parting line located between the brake body and the hub, which leads to heat accumulation during braking and prevents the flow of heat from the brake body towards the hub. The disadvantage is the resulting considerably greater expansion of the brake body in a radial direction which may eventually lead in the course of time to a destruction of the union of the hub with the brake body.
In order to increase the width of application of a brake disk or brake drum produced by composite casting, a durable composite cast union is necessary between the hub and the brake disk or the brake drum or the like, in order to transmit a maximal torque to the brake jaws when running down a long gradient with full braking.
JP A 60 024263 discloses an integrated rotor hub, in which a melting zone structure with good mechanical properties is to be developed at the border area between the rotor part and the hub part. In this production process, the two components are cast in a common mold but with different types of steel. The brake disk consists of cast iron with flaky graphite and with thermally favorable properties, although the hub part consists of a cast iron with spheroidal graphite and high mechanical strength. As a result of the common casting, the separation of the two casting materials is not distinct, and can lead to thermally or mechanically faulty stresses at the components of the brake element. The possible consequences are deformations and cracks presenting a safety risk.
SUMMARY OF THE INVENTION
The present invention concerns in particular brake drums, brake disks or the like for vehicles produced by composite casting, which resist thermal cracks and stresses and are of light weight. In preferred embodiments, the invention provides a brake element that is reliable in operation and of a cast iron material exhibiting high resilience to thermal stresses or thermal conductivity respectively, while exhibiting at the same time high mechanical strength and a high modulus of elasticity.
This invention provides a composite casting process for the production of brake elements, specifically brake drums, brake disks or the like, which comprise a hub and a flange for fastening, as well as the corresponding friction surfaces. If need be, a brake disk consists of two brake rings joined to each other by way of connecting bridges, while leaving space for cooling or ventilation channels. Typically, the friction surfaces comprising a brake ring (
1
) or a brake drum body, which interact with brake jaws, are made of a cast iron material with lamellar graphite with a tensile strength of between 100 N/mm
2
and 150 N/mm
2
with a high resistance to thermal shocks, and the hub (
2
) and the flange (
4
) are comprised of a cast iron material with a higher-grade tensile strength greater than 170 N/mm
2
. In the present invention, the hub (
2
) is connected with the brake ring (
1
) or brake drum body by composite casting, forming a material union (
5
) which is formed by casting one melt of one cast iron material on a solid body of the other cast iron material placed into the mold cavity (a) by casting and cooling or (b) by inserting a solid body and heating. After the casting of the melt at the material union (
5
), which forms the contact surface between the cast iron materials, a temperature is provided which lies at least 10° C. above the solidus temperature of the solid one of the adjoining cast iron materials of the hub (
2
) or the brake ring (
1
) or of the brake drum body. Prior to the casting of the melt, the open-lying sections of the solid body located in the mold cavity, i.e., the material union (
5
) earmarked for the cast-on, is coated with a non-metallic mixture of a reducing compound containing boron which protects against oxidation.
Certain preferred brake elements produced of a composite cast according to a casting process in accord with the present invention can be characterized by the fact that the hub (
2
) and the junction (
12
) are dimensioned in the area of the hub (
2
) so that the section modulus of torsion is stable with respect to the admissible stresses in the hub (
2
), depending on the stresses to be expected during braking and acceleration against torsion. Other preferred brake element
Dike, Bronstein, Roberts & Cushman, IP Practice Group of Edwards
Kramer Devon
Neuner George W.
Oberleitner Robert J.
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