1944-01-01

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:
  1. 1.
    Sound pressure near the engine.
  2. 2.
    Vibrations of the crankcase structure.
  3. 3.
    Lateral vibrations of the flywheel.
  4. 4.
    Lateral vibrations of the crankshaft.
  5. 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. 1.
    By changing the characteristics of the pressure development.
  2. 2.
    By changing piston weight and thus altering inertial forces acting on the crankshaft.

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