Brakes – Elements – Brake wheels
Reexamination Certificate
1999-12-23
2001-10-16
Schwartz, Christopher P. (Department: 3613)
Brakes
Elements
Brake wheels
C188S01800A
Reexamination Certificate
active
06302246
ABSTRACT:
The present invention relates to a brake unit comprising at least one disk brake and at least one brake pad having at least one friction lining. More specifically, the brake unit includes a brake rotor made of a ceramic-metal composite (CMC) whose outer surface or surfaces at least partially form a friction surface for the at least one friction lining, and a disk brake cup that is mounted on the disk brake by way of one or more mounting elements.
SUMMARY OF RELATED ART
In high-performance brake units used both for motor vehicles and for rail vehicles, outstanding braking properties, excellent braking smoothness, and at the same time the longest possible service life are required. Conventional brake units having cast-iron disk brakes, however, have comparatively unfavorable wear rates in braking operation. In high-performance brake units, in addition to brake related wear, so-called “stroking wear,” is particularly significant. This type of wear creates geometrical defects on the brake rotor and promotes rubbing phenomena, therefore degrading braking smoothness. The same effect results from thermal distortion of the brake rotor, which occurs when the brake rotor is heavily loaded and high temperatures thereby occur. Lastly, the cast-iron disks commonly used are not designed for extremely high brake loads, since in such a situation heat stress cracks occur on the friction surface and render the friction surface unusable. Until now these defects could be remedied only by costly replacement of the disk brakes in question.
Another frequent reason for costly replacement of disk brakes is corrosion damage to the brake rotors. So-called “idle spots,” in particular, which can occur if the vehicle is not driven for some time, can cause rubbing vibrations that adversely affect braking smoothness and reduce braking performance.
With brake units having conventional cast-iron disk brakes, it is also possible for high-frequency sounds, in the range from approximately 1500 to 6500 Hz, to occur. Preventing this noise necessitates replacement of the disk brake.
With the development of disk brakes and disk brake friction surfaces made of ceramic-metal composites (CMC disk brakes), attempts were made to eliminate these disadvantages. German Patent 43 22 113, for example, discloses a brake rotor for disk brakes, in particular for use as a shaft or axle disk brake of rail vehicles, which has a metal support member equipped with a layer of microscopically or macroscopically organized regions of at least two different materials. One region is formed from a ceramic material, and the other region from a metallic, sintered metal, or sintered metal-ceramic material. Besides the complex methods of fabrication required for a multiple-part disk brake of this kind, the design does not solve the problem of the wear lifetime and braking smoothness of a brake unit, in particular for motor vehicles but also for rail vehicles applications.
German Patent Application 196 23 425 A1 discloses a reaction-bonded ceramic for ceramic composite materials that includes mullite as the principal constituent, and corundum and thortveitite or cerianite as secondary constituents used substantially as thermal protection material. This patent does not address the problem of the braking smoothness and service life of brake units.
German Patent Application 42 37 655 A1 discloses a brake rotor for the disk brake of a motor vehicle that has an inner and an outer friction ring between which cooling channels are arranged. The outer friction ring is made of a composite fiber material and the inner friction ring of a gray cast iron material. The two friction rings are immovably joined to one another. The material of the friction surfaces of the brake pads can correspondingly also be adapted to the material of the friction surfaces of the disk brake. Although this does result in improved frictional behavior and a reduction in friction vibrations of the disk brake, the manufacture of multiple-part disk brakes with different friction linings for the brake pads is very complex. No mention is made in this patent concerning the service life of the brake unit.
SUMMARY OF THE INVENTION
The present invention is a brake unit that offers great braking smoothness and a long service life, and can nonetheless be manufactured easily and economically.
In one aspect, the invention is a brake unit having at least one disk brake, that includes a brake rotor made of a ceramic-metal composite, having a friction surface with a hardness of between about 1600 and 2500 HV, at least one brake pad having a friction lining adapted to contact the friction surface of the brake rotor, the friction lining having a coefficient of friction of between about 0.3 and 0.5, and a disk brake cup mounted on the brake rotor by at least one mounting element, the disk brake cup being formed of a noncorroding material and the mounting elements being formed at least in part from a noncorroding material, thus forming a corrosion-inhibiting attachment of the disk brake.
The brake unit according to the invention has a friction surface of the disk brake with an hardness of approximately 1600 to 2500 HV. At least one friction lining has a coefficient of friction of approximately 0.3 to 0.5, and the disk brake cup and/or the mounting elements are configured such that a corrosion-inhibiting attachment to the disk brake exists, so that the brake unit can be operated in corrosion-free fashion over a service life of at least approximately eight to ten years, or approximately 200,000 to 300,000 km.
Friction surfaces made of ceramic-metal composite material for brake rotors, and brake rotors made of ceramic-metal composite material, in combination with friction linings having a coefficient of friction of approximately 0.3 to 0.5 and a corrosion-inhibiting attachment of the disk brake cup to the brake rotor, make it possible to significantly extend both braking smoothness and the service life of the brake unit, according to the present invention, as compared to conventional brake units. A wide variety of wear tests on test stands and vehicles have shown that service lives of approximately eight to ten years, or 200,000 to 300,000 km can be achieved without difficulty, because the wear rates for brake operation are lesser, by orders of magnitude, than with the presently widespread technology using cast iron disks.
The wear components resulting from “stroking wear” are reduced to such an extent that geometrical defect formation plays no further role. As a result, practically no further rubbing phenomena occur, so that braking smoothness is no longer disadvantageously influenced by the defects. In addition, thermal distortion of the brake rotor is no longer observed at temperatures up to 1200° C., and thermal stress cracks in the friction surface also no longer occur, so that premature disk brake replacement is no longer necessary.
Extensive corrosion tests have shown that the corrosion-free attachment of the CMC disk brake to the disk brake cup can effectively prevent corrosion on the disk brake, particularly “idle spots.” In addition, the irritating sounds at 1500 to 6500 Hz produced by conventional brakes no longer occur when CMC disk brakes are used, due to the advantageous material properties of the ceramic-metal composite material. This is due to the high vibration damping properties of these materials. These reasons for premature disk brake replacement in conventional brakes are thus also eliminated.
The combination according to the present invention of a brake rotor made of ceramic-metal composite material, corrosion-optimized attachment of the disk brake cup to the disk brake, and suitable friction linings, permits the brake unit according to the present invention to achieve a service life, during which the brake unit can be operated in corrosion-free fashion, which is superior to that of previously known brake units. This is the case even if free carbon is present, for example, in the material of the disk brake. Operating costs, availability, and customer satisfaction are thereby conside
Naumann Emil
Rebstock Kolja
Riedel Hans-Georg
Ross Karl-Heinz
Wolfsried Stephan
Daimler-Chrysler AG
Kenyon & Kenyon
Schwartz Christopher P.
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