Stock material or miscellaneous articles – Self-sustaining carbon mass or layer with impregnant or...
Reexamination Certificate
1998-09-15
2001-07-24
Speer, Timothy M. (Department: 1775)
Stock material or miscellaneous articles
Self-sustaining carbon mass or layer with impregnant or...
C428S469000, C428S698000, C188S25100R, C188S25100R
Reexamination Certificate
active
06265071
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a brake unit including a brake disc of a material having a high thermal loading capacity and a brake pad that cooperates with it in tribological fashion.
RELATED TECHNOLOGY
A new generation of brake pads is made of material having a high thermal loading capacity. Among these are ceramic materials, in particular short-fiber reinforced C/SiC ceramic materials, as described in German Patent Document No. 197 11 829.1. Another brake pad is known from German Patent Document No. 43 22 113. Its brake disc has a bearing member of a steel, cast iron or aluminum material, on whose exterior ring sections is applied in each case a concentrically disposed layer of a thermally highly-loadable material, i.e., of a ceramic material or a metal material, metal sintered material, or of a metal-ceramic sintered material. This material is temperature-resistant up to over 1500° C. To prevent the brake pad from being damaged by excessive heating during braking maneuvers, provision is made for the ceramic material to have a heat-conducting metal filling to dissipate the heat to the metal bearing member, and for the brake disc to have a ventilated brake pad design.
Combining brake discs of this kind with a suitable brake pad is problematic. German Patent Document No. 43 06 721, for example, describes a conventional inorganic brake pad. However, brake pads of this kind are not stable enough.
Unpublished German Patent Document No. 197 11 830.5 describes a sintered brake pad made of powdered metal, primary carbon and, optionally, of additives, for a short-fiber reinforced C/SiC brake disc.
SUMMARY OF THE INVENTION
The object of the present invention is to devise a brake unit including a brake disc of a material having a high thermal loading capacity and a brake pad that cooperates with it in tribological fashion, the brake unit being stable over higher temperature ranges, but is relatively simple to manufacture.
This object is achieved by providing a brake unit having the features of claim
1
.
The present invention provides for the brake pad to be made of a metal-ceramic material or a standard sintered metal pad.
In prior methods, sintered metal pads were only used in commercial vehicles or for the railroad. In the passenger car sector, they were not suited for use in conjunction with the gray cast iron brake discs that have been customary until now, since they did not offer adequate performance in terms of comfort (judder, squealing, stuttering). It now turns out surprisingly and, for one skilled in the art, unexpectedly that the usual disadvantages associated with known methods when commonly used gray cast iron brake discs are combined with sintered metal brake pads do not occur when ceramic brake discs are used. It also turns out that, when a ceramic brake disc is combined with a sintered metal pad, one can attain excellent coefficients of friction of from 0.3 to 0.5 and a temperature stability of from 900 to 1000° C.
The same holds true for brake pads having an at least partially ceramic binding phase. In response to temperatures of less than 1200° C., an only partially converted binding phase with an inorganic and an organic constituent arises during the heat treatment, depending on the polymers used.
The brake unit of the present invention constitutes an optimal combination with respect to an elevated thermal loading capacity on the part of the ceramic brake disc, in view of a reasonable service life of the brake pad, and in light of other tribological requirements, such as friction coefficient level or temperature dependence of the friction coefficient. Because of its material constitution, the brake unit of the present invention has a higher thermal loading capacity and is also more resistant to wear than conventional brake units.
The ceramic binding phase arises preferably through pyrolysis of at least one preceramic polymer. For example, conventional pad mixtures for organically bound, standard passenger-car pads may be used, the conventional organic binding agent being replaced by a preceramic polymer. The composition of these conventional, standard pads is well known to one skilled in the art. In this context, the composition may be a C-precursor, such as vinyl resins, or silicon-containing polymers. The binding phase may be introduced by a so-called polymer-pyrolysis method (PP method) and produced. The individual components are mixed, compacted and pyrolyzed at temperatures of up to 1200° C. for about 60 minutes and, if indicated, undergo a final processing. The ceramic binding phase resulting from the pad mixture and binding agent is mostly amorphous, i.e., vitreous. Depending on the type, it is temperature-stable up to 1600° C.
The metal constituent of the brake pad is selected, for example, from the group including copper and copper alloys, as well as iron and iron alloys. The metals are applied in the form of shavings, metal wool, or metal powder as an embedding phase. Advantageously contained, in addition, in the friction pad are carbon, coke or graphite, solid lubricants, such as SbS
3
, MoS
2
, CaF
2
and fillers, such as of ceramic, aluminum oxide, glass, mica dust, heavy spar, and/or iron oxide, which are used as scouring agents.
The brake disc is advantageously made of a ceramic material, in particular of oxide ceramic or of fiber-reinforced ceramic, such as C/C ceramic, SiC/SiC ceramic or C/SiC ceramic. The fibers are preferably isotropically oriented, since this achieves a uniformly high thermal conductivity in the brake pad's cross-section as well. This promotes lowering of the surface temperature in response to a stress loading.
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Dollhopf, V. et al., “Entwicklung integraler Leichtbaustrukturen aus Faserkeramik,” VDC Berichte Nr. 1080, 1994, pp. 473-483. (no month).
Mühlratzer, Aug., “Fasterverbundkeramik -Entwicklung und Einsatzmöglichkeigten,” MAN -Forschen -Planen -Bauen, Aug. 12, 1993, pp. 48-55.
Gross Gerhard
Haug Tilmann
Naumann Emil
Rebstock Kolja
Scheydecker Michael
Daimler-Benz Aktiengesellschaft
Kenyon & Kenyon
Speer Timothy M.
Young Bryant
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