ABSTRACT
Crankshafts drive many accessories such as fuel injection
pumps, camshafts, oil- and water pumps, compressors, fans,
alternators etc. by using either gears or belts. Since crankshaft
rotational speed fluctuates and engine accessories have
moments of inertia, belts slip on pulleys and gears hit other
gears, which results in noise and wear.
This paper describes the mechanism of the rotational
speed fluctuations of crankshafts by separating rotational speed
fluctuations into those for a rigid and those for a torsional
crankshaft for a V-type six-, eight- and ten-cylinder diesel
engine. After that, crankshaft rotational speed fluctuations at
crankshaft locations are discussed.
1. INTRODUCTION
A V-type six-, eight- and ten-cylinder naturally-aspirated
diesel engine was used for calculation. The V-type six-cylinder
naturally-aspirated diesel engine was used for measurement. A
generally-used model was employed for calculation, in which
the individual crankshaft moments of inertia were connected to
the respective crankshaft torsional stiffness, to calculate the
rotational speed fluctuations at the individual masses [1].
Another model was used to calculate the rotational speed
fluctuations for the rigid crankshaft, in which the moments of
inertia of the total crankshaft were combined into one. The
rotational speed fluctuations were calculated by the dynamic
stiffness matrix method.
First, rotational speed fluctuations at the flywheel for the
V-type six-cylinder engine were calculated in the time domain,
and compared with the measured ones to verify the
appropriateness of the calculation model. Then, the authors
calculated the rotational speed fluctuations for the rigid
crankshafts on the V-type six-, eight- and ten-cylinder engine,
to separate the rotational speed fluctuations into those for the
rigid and those for the torsional crankshaft (caused by the
torsional vibrations). Finally, the rotational speed fluctuations
at the pulley were compared with those at the flywheel for
those engines.
The authors find that, at low speeds, the rotational speed
fluctuations at the flywheel are larger than those at the pulley.
This is because, for the flywheel, the rotational speed
fluctuations for the rigid crankshaft are almost in the same
phase as those caused by the torsional vibrations, whereas, for
the pulley, the rotational speed fluctuations for the rigid one are
almost in the reverse phase to those caused by the torsional
vibrations