14

22 17

I b

a_•18 18 2.8 20 2•5 •' 24

to prevent their axial vibration, thereby suppressing noise emission from the cylinder block.•CHA

and a porous ceiling, spaced away from the underside of the bridge. Several configurations are shown and graphs are presented showing a decrease of the order of 10 dB in the air vibration at frequencies of 4, 12, and 31 Hz.i CHA

4,445,594

43.50.Gf DISC BRAKE NOISE REDUCTION

Charles T. Hoffman, Jr., assignor to General Motors Corporation 1 May 1984 {Class 188/73.37); filed 30 October 1981

A disc brake pad assembly has clench tabs extending through rubber- like grommets in openings in a caliper housing leg, so that the grommets are

4,453,848

43.50.Gf NOISE REDUCING PLATEN

James W. Adkisson and Paul A. Ishman, assignors to Florida Data Corporation

12 June 1984 (Class 400/661); filed 24 May 1982

The patent states that, "it is believed that the vibrations generated along the longitudinal channels are at a frequency above the audible

204 range..." Also, "the openended nature substantially prevents undesired re- verberations." No data is given, for reasons that appear obvious.•CHA

retained in the openings and the brake pad assembly is retained on the housing !eg. The grommets provide a noise damping action.iCHA

4,449,869

43.50.Gf DEVICE FOR THE MANUFACTURE OF GEAR WHEELS FOR LOW NOISE GEARINGS

Kurt Maier, assignor to BHS-Dr. Ing. Hofier Maschinenbau GmbH 22 May 1984 {Class 409/11); filed in Germany 21 December 1979

The patent relates to a method and a device for the manufacture of quiet gear wheels. The procedure involves first minimizing errors in the gear cutting process and then, by specific adjustments, superimposing upon the residual error additional small errors of higher frequency. It is stated that when one gear engages with another, the resultant overall noise level lies outside the range of hearing. This certainly is "an unexpected novel effect." If it is truly significant for a new gear, it may fade with wear.iCHA

4,450,931

43.50.Gf STRUCTURE FOR DECREASING LOW- FREQUENCY AIR VIBRATION

Mitsuyasu Yamashita, Hiroshi Igarashi, and Shosuke Koga, assignors to NGK Insulators, Limited and the Institute of Physical Research

29 May 1984 (Class 181/198); filed in Japan 9 March 1981 A structure for decreasing low-frequency air vibrations emanating

from an elevated road or railway is constructed as an "absorption resonant" system with dense (steel, concrete) walls surrounding the bridge columns

4,455,971

43.50.Gf WATER-COOLED INTERNAL COMBUSTION ENGINE WITH A SOUND-ABSORBING COVER

Karl Kirchweger and Franz Knopf, assignors to Hans List, Graz, Aus- tria

26 June 1984 (Class 123/41.7); filed in Austria 14 July 1981

This patent describes an enclosure which has, within it, a duct separat- ing the exhaust system from the rest of the enclosure. This duct has an acoustidally muffled inlet opening penetrating the top of the enclosure and a lower, muffled exit through the side of the enclosure so as to allow air from

the engine fan to sweep into the inlet and through the duct when the engine is operating. When the engine is stopped, residual heat in the exhaust system causes a counter flow of air by gravity and prevents overheating of the enclosure.iCHA •

779 J. Acoust. Soc. Am. 77(2), Feb. 1985; 0001-4966/85/020779-01500.80; ¸ 1985 Acoust. Soc. Am.; Patent Reviews 779

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