Various Methods of Analyzing Intake-Silencer Problems 340091
INTRODUCTION of the closed body made the car silencing problem more difficult by adding “drumming” as another type of noise, it being a low-frequency noise periodic in character and associated with resonance phenomena. Studies on engine balance, engine mountings, intake and exhaust silencing, and related studies, were made by the General Motors Research Laboratories to determine the sources of the noises and provide means for their suppression.
Sources of periodic excitation of the body may be due (a) to vibration of the engine on its mountings and the transmission of such vibration to the body; (b) mechanical out-of-balance of any part of the drive train, the cooling fan and the tires; and (c) exhaust and intake-system resonance. After much previous research work, major attention was directed to the silencing of the intake and exhaust systems. An extensive laboratory investigation was conducted on “power roar”; but, after the noise sources in the intake system had been determined, their elimination seemed impracticable and it remained to develop a satisfactory type of silencer to be added to the conventional type of carburetor and manifold.
A description of this development is given, together with that of an exhaust silencer which also utilizes the principle of resonance silencing. In conclusion it is stated that the intake silencer has permitted a gain to be made in specific power per cubic inch of cylinder displacement as, by its use, the silencer has made possible a wider choice of valve timing without restriction by noise limitations.