PHYSICAL CHARACTERISTICS of ROUGHNESS in INTERNAL-COMBUSTION ENGINES

LLOYD WITHROW; ARTHUR S. FRY

doi:10.4271/440155

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:

1.
Sound pressure near the engine.
2.
Vibrations of the crankcase structure.
3.
Lateral vibrations of the flywheel.
4.
Lateral vibrations of the crankshaft.
5.
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:

1.
By changing the characteristics of the pressure development.
2.
By changing piston weight and thus altering inertial forces acting on the crankshaft.

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PHYSICAL CHARACTERISTICS of ROUGHNESS in INTERNAL-COMBUSTION ENGINES 440155

SAE MOBILUS