PHYSICAL CHARACTERISTICS of ROUGHNESS in INTERNAL-COMBUSTION ENGINES 440155
EXPERIMENTS have been run to find relationships between the primary causes and the outward effects of roughness as produced by a single-cylinder engine and by an 8-in-line engine.
This was done by recording simultaneously on a multi-element oscillograph, oscillograms of the following phenomena:
Sound pressure near the engine.
Vibrations of the crankcase structure.
Lateral vibrations of the flywheel.
Lateral vibrations of the crankshaft.
Pressure development in the combustion chamber.
A study of the oscillograms reveals that the sensation of roughness in both of these engines is closely related to a shock type of excitation that is developed in the crankshaft-flywheel system.
In the single-cylinder engine this phenomenon was affected by any change in engine conditions which altered the development of the combustion pressures. Moreover, the sensation of roughness was greatly diminished by using a so-called “flexi-disc flywheel.”
In the multicylinder engine, the shock type of excitation of the crankshaft-flywheel system as well as the sensation of roughness could be affected in two different ways:
By changing the characteristics of the pressure development.
By changing piston weight and thus altering inertial forces acting on the crankshaft.