Brakes – Wheel – Axially movable brake element or housing therefor
Patent
1998-05-04
2000-09-19
Oberleitner, Robert J.
Brakes
Wheel
Axially movable brake element or housing therefor
188218XL, 188264A, F16D 5502
Patent
active
06119820&
DESCRIPTION:
BRIEF SUMMARY
A disc brake rotor is arranged to rotate with a member, such as a wheel of a vehicle or a rotating part of a machine. Such a rotor provides two oppositely-facing annular friction surfaces which, in the operation of the brake, are engaged by blocks of friction material to decelerate the rotor and hence the member. Two of the friction material blocks are moved (usually by hydraulic means) towards one another into contact with the two friction surfaces so that frictional forces occur slowing the rotation of said rotor, and hence of said member. These frictional forces generate considerable amounts of heat which has to be absorbed by the rotor and causes its temperature to rise. If the rotor becomes too hot, the braking performance is adversely affected and the rotor wears rapidly. Thus, such rotors need to have a significant thermal capacity in order to avoid rapid temperature rises.
In order to reduce temperature rises in disc brake rotors, it is conventional to form the rotor so that it comprises a first generally disc-shaped portion which provides one of said annular surfaces, and a second generally disc-shaped portion which provides the other of said annular surfaces. Said first and second portions are of constant thickness and are arranged in spaced parallel relationship. These portions are joined by vanes between which are cooling ducts extending radially outwardly of the rotor. The cooling ducts are arranged so that, as the rotor is rotated, air passes through the ducts and acts to cool said portions of the rotor on their opposite sides to said annular surfaces. Air inlets to said ducts are provided at an inner edge of said first and second portions and the rotor functions as a centrifugal fan driving air outwardly to outlets at the outer edges of said portions. Conventionally, said vanes extend in straight lines radially of the rotor and each vane is of constant thickness along its length (see eg GB 969,845). This geometry has the advantages that it is simple to manufacture (such rotors are normally cast out of metal, usually iron) and that the rotor acts in the same way whatever the direction of rotation (with the advantage that one type of rotor can be provided on both sides of a vehicle). However, this geometry has the disadvantages that the ducts are divergent in cross-sectional area in an outward direction due to the increasing distance between adjacent vanes with increasing radius. This divergence causes deceleration of the air in the ducts which reduces cooling efficiency which is dependant on air velocity. Thus, the cooling efficiency is poor in the region where it is most required, ie in the region of the ducts opposite where the rotor is engaged by the blocks of friction material. This cooling inefficiency is further increased by the tendency in such rotors for the air to flow mainly along the leading edges (in the direction of rotation) of the vanes reducing the effective area for heat transfer to the air.
The disadvantages in cooling efficiency of the conventional rotors described above have been addressed to some extent in other designs of rotor. In some of these designs, the vanes have been curved forwardly relative to the direction of rotation so that the vanes do more work on the air increasing its velocity and hence the cooling effect (and disadvantageously increasing also the work required to rotate the rotor). In other designs, the vanes have been curved backwardly relative to the direction of rotation so that the vanes more closely follow the streamlines of the air. This decreases the work required for rotation and brings the trailing edges of the vanes more into use as heat-transferring surfaces. In other designs (see DE 43 23 782 A1 and WO 95/08727), the thickness of said first and second portions of the rotor increases uniformly in the outwards direction so that the cross-sectional area of each duct is more uniform along its length or indeed constant. This gives the air a more constant velocity along the duct thereby smoothing out the cooling effect. This has the disadvantage th
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patent: 4164993 (1979-08-01), Kobelt
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Patent Abstracts of Japan, vol. 008, No. 083 (M-290), Apr. 17, 1984 & JP 59 001825 (Jan. 7, 1984).
Fenton Marcus Brian Mayhall
Kao Tseng Kuan
Steptoe Colin
Thorpe William Anthony
Federal-Mogul Technology Limited
Lipka Pamela J.
Oberleitner Robert J.
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