In many studies the torsional load is neglected for the
load analysis of the crankshaft, and this is because
torsional load is less than 10 percent of the bending load
[10]. In this specific engine with its dynamic loading, it is
shown in the next sections that torsional load has no
effect on the range of von Mises stress at the critical
location. The main reason of torsional load not having
much effect on the stress range is that the maxima of
bending and torsional loading happen at different times
(see Figure 4). In addition, when the peak of the bending
load takes place the magnitude of torsional load is zero.
Figure 5 compares the magnitude of maximum torsional
and bending loads at different engine speeds. As can be
seen in this figure, the maximum of total load magnitude,
which is equal to the maximum of bending load
decreases as the engine speed increases. The reason
for this situation refers to the load sources that exist in
the engine at 355 degree crank angle. At this crank
angle these two forces act in opposite directions. The
force caused by combustion which is greater than the
inertia load does not change at different engine speeds
since the same pressure versus crankshaft angle is
used for all engine speeds. The load caused by inertia
increases in magnitude as the engine speed increases.
Therefore, as the engine speed increases, a larger
magnitude of inertia force is deducted from the
combustion load, resulting in a decrease of the total load
magnitude.