Crankshaft Damping

Abstract

The author attempts to give a correct physical explanation of natural damping by torsional vibrations, and also to obtain approximate formulae for pre-calculation of the damping in any given case. The paper describes experimental work with a single-cylinder engine driven by external power, and excited to torsional vibrations by a spring-loaded cam disk. In this way the damping from the moving parts could be investigated separately, and it was found that the damping was almost entirely due to hysteresis in the crankshaft, and oil damping, due to lateral shaft movements in the main and crankpin bearings, which was directly proportional to the bearing clearance. The paper also gives a simple and practical method for the calculation of damped vibrations in arbitrary elastic systems, and the calculation of hysteresis and bearing damping in a single-cylinder engine. Formulae are given for the total damping in multi-cylinder engines, with or without heavy flywheels, and the results are compared with the measured damping of oil engines in service.