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Piston Movement as a Source of Engine Noise
Published January 01, 1972 by Institution of Mechanical Engineers in United Kingdom
In current engines piston slap is only a predominant source of noise over a limited frequency range, but further attenuation of broad band sources such as combustion and exhaust noise will increase its relative importance.
Instrumentation has been developed to continuously monitor piston to cylinder clearance at a number of points over the piston skirt, from which piston to cylinder attitudes may be derived. Results from a petrol engine are presented, illustrating the cyclic incidence and intensity of piston to cylinder impact as a function of engine temperature, load and speed. The results are compared with measurements of cylinder block vibration for a wide clearance piston, an oil cushion piston and a standard piston design.
A theoretical analysis of the transverse and rotational motion of the piston is described and its predictions compared with the measured results. The analysis includes the effect of frictional forces at the gudgeon pin and piston skirt. The value of the analysis as a design aid to control the piston to cylinder approach velocities, and hence the intensity of piston slap, is indicated. A practical example is illustrated by film animation based on experimental measurements.