Brakes – Elements – Cooling and lubricating
Patent
1998-11-23
2000-09-12
Oberleitner, Robert J.
Brakes
Elements
Cooling and lubricating
188218XL, 19211323, F16D 6510
Patent
active
061163872
DESCRIPTION:
BRIEF SUMMARY
This invention is concerned with disc brake rotors.
A disc brake rotor is arranged to rotate with a member, such as a wheel hub 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 two blocks of friction material which are moved (usually by hydraulic or pneumatic 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.
In order to reduce temperature rises in disc brake rotors caused by the frictional forces, it is conventional to form the rotor so that it comprises a first generally annular friction portion which provides one of said annular friction surfaces, and a second generally annular friction portion which provides the other of said annular friction surfaces. Said first and second friction portions are conventionally of constant thickness so that they have substantially equal thermal capacity at all points thereof. Said friction portions are arranged in spaced parallel relationship. These friction 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 friction portions. Air inlets to said ducts are provided at an inner edge of said first and second friction portions and the rotor functions as a centrifugal fan driving air outwardly to outlets at the outer edges of said friction portions.
The most common type of disc brake rotor used on vehicles is the so-called "top hat" type. In addition to first and second friction portions, as mentioned above, this type of rotor comprises an annular mounting portion arranged to engage the member with which the rotor rotates and be secured thereto. The rotor also comprises a generally cylindrical connecting portion which extends axially and joins said mounting portion to said first friction portion. The first friction portion is, thus, displaced axially relative to the mounting portion and is supported by the connecting portion. The second friction portion is supported by said vanes.
Most rotors of the "top hat" type have their first friction portion nearer to the mounting portion than their second friction portion. This means that there is free access for the cooling air between the inner edges of the first and second friction portions. However, this design is subject to the problem known as "coning". Coning occurs when the friction portions become hot and expand while the connecting portion, which is not so hot, expands less. The connecting portion, thus, is pulled into a slightly conical form by the first friction portion, expansion of the second friction portion enhancing this effect. This results in the friction portions bending out of their initial planes. This bending causes greater pressures to occur during braking at some parts of the friction portions so that more heat is generated. These portions of the friction portions, thus, have to absorb greater amounts of heat than other portions thereof. This causes temperature differentials which affect the performance of the brake and also affect the wear of the rotor and the brake pads. Such differentials can also result in cracking of the rotor.
The problem of coning is discussed in U.S. Pat. Nos. 3,378,114 and 4,651,851. The latter of these proposes the solution of attaching the first friction portion to the connecting portion further from the mounting portion than the distance between the mounting portion and the second friction portion. This design partially counteracts the problem of coning as expansion of the second friction portion opposes rather than enhances the inclination caused by expansion of the first friction portion. Furthermore, the connecting portion is longer so that a given expansion causes less inclination. This design is partially successful in evening out the pressure across the friction surfaces and there
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Patent Abstracts of Japan, vol. 008, No. 083 (M-290), Apr. 17, 1984 & JP 59 001825 A (Akebono Brake), Jan. 7, 1984 (see abstract; Figure 1).
Kao Tseng Kuan
Thorpe William Anthony
Nguyen Lan
Oberleitner Robert J.
T&N Technology Limited
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