Radiation efficiency as a factor in the design of engine components

Abstract

The importance of radiation efficiency as a factor in the design of engine components is shown. The sound power reduction of a two‐piece engine gear cover was the goal. In the past, the action taken was to reduce the vibration amplitude. This ignores the role of radiation efficiency, often assumed to be one. Wallace [C. E. Wallace, J. Acoust. Soc. Am. 51, 926–945 (1972)] has shown how to analytically calculate radiation efficiency. Three models of the gear cover were developed. The standard gear cover comprises the flat steel plate attached to the block and an aluminum shell covering the gears. The first model, ♯1, greatly stiffened the shell; the second model, ♯2, greatly stiffened the flat plate; and the third model, ♯3, reversed the units, i.e., an aluminum shell was attached to the block and thin steel cover was used to enclose the gears. The model showed decreasing sound power levels from ♯1 to ♯3. A prototype part made up to the specifications of number ♯3 showed sound power measurements, using acoustic intensity methods, in close agreement with predictions.