Brakes – Elements – Brake wheels
Reexamination Certificate
1999-09-30
2001-09-11
Oberleitner, Robert J. (Department: 3613)
Brakes
Elements
Brake wheels
C188S2640AA
Reexamination Certificate
active
06286639
ABSTRACT:
This invention relates generally to brake drums and more particularly to a brake drum so constructed as to substantially reduce, if not entirely eliminate, brake drum noise.
BACKGROUND OF THE INVENTION
A symmetrically round object such as a brake drum has two similar primary vibrational modes displaced 45° away from one another. If the difference in frequency of vibration between these two modes is very small, a brake drum will be more likely to howl or squeal when the brakes are applied. It has been discovered that this problem, sometimes referred to as an instability problem, can be alleviated if the difference in frequency of these two modes can be increased to over about 50 Hertz (Hz). Hz is a measure of vibration frequency in cycles per second.
It has been proposed to solve this instability problem by adding symmetrically placed stabilizing sections around the periphery of the brake drum. The stabilizing sections add mass but also increase stiffness considerably. If four stabilizing sections are oriented at 90° intervals, they will affect one of the two similar primary modes of vibration much more than the other and thus separate the vibration frequency of one mode relative to the other sufficiently to solve the instability problem. However, the stabilizing sections, while solving the instability problem, cause another problem and that is, as the brake shoes expand to apply the brakes, the weaker sections of the drum between the stabilizing sections deflect more than the stabilizing sections, distorting the brake drum. Accordingly, the frictional force at the stabilizing sections will be higher than that between the stabilizing sections, producing a variation in brake torque four times per revolution. Also, where the frictional force is higher, there is local heating (hot spots) which distorts the drum even more. This produces roughness and noise, both of which are objectionable.
What is needed is a brake drum construction which deals with the noise instability problem without causing distortion of the brake drum.
SUMMARY OF THE INVENTION
In accordance with the present invention, the stabilizing sections are serrated, that is notched or slotted, so that while mass is significantly increased, stiffness is increased only slightly. Therefore when the brakes are applied by expansion of the brake shoes, the load is applied in a more uniform manner creating less torque variation and less local heating. Also, the increased surface area produced by the serrations improves heat dissipation and hence there is less thermal distortion. An increase in mass lowers natural frequency while an increase in stiffness raises it. Thus the increased mass of the stabilizing sections will lower the frequency of one of the two similar primary modes of vibration more effectively since the serrations provide less increase in stiffness for a given mass, but will still separate the vibration frequencies of the modes in question sufficiently to solve the noise instability problem.
One object of this invention is to provide a brake drum having the foregoing features and capabilities.
Another object is to provide a brake drum which is of simple construction, is rugged and durable in use and highly effective in the performance of its intended function.
These and other objects, features and advantages of the invention will become more apparent as the following description proceeds, especially when considered with the accompanying drawings.
REFERENCES:
patent: 1990746 (1935-02-01), Nelson
patent: 2288438 (1942-06-01), Dach
patent: 3016269 (1962-01-01), De Lorean
patent: 3043631 (1962-07-01), Swoboda
patent: 3113647 (1963-12-01), Tuttle
patent: 5383537 (1995-01-01), White
patent: 5538113 (1996-07-01), White et al.
patent: 5823304 (1998-10-01), Wagg
patent: 5826684 (1998-10-01), Hester
patent: 5957249 (1999-09-01), Yamazaki et al.
patent: 5652633 (1981-05-01), None
patent: 57208329 (1982-12-01), None
patent: 5850332 (1983-03-01), None
Calcaterra Mark P.
DaimlerChrysler Corporation
Oberleitner Robert J.
Siconolfi Robert A.
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