After the posts on the 2-part crank pulleys and alluminium pulleys, I
think it mught be worthwhile to go back to basic principles on this.
One has to consider the dynamic nature of the forces in the engine.
If order to dampen out movement in the crank, a weight with a large
moment of inertia is required to be fixed solidly to the crank. This
is generally called the flywheel!
Now the flywheel is attached to one end of the crank and there will
undoubtably be twisting in the crank, allowing for much less damped
(more violent) movement at the other end. The question is: why have a
damped pulley? One possible reason might be to eliminate the effects
of the sudden movements (in the crank) on the devices driven by the
pulley, but since the belts must surely stretch, this does not seem to
be a good reason.
The other reason might be to reduce the damping effect of the pulley
on the crank. Using Newton's laws of motion: "for every action there
is an equal and opposite reaction".
The effect of the damper is to 'decouple' the outer part of the crank
pulley during very short pulses from the crank (as it twists). The
inner part of the pulley turns with the crank, but the outer part
turns in a smoother fashion.
The effect of this is to make the crank pulley seem lighter -- at
least when considering the short (fast) pulses in the crank. So
perhaps an alluminium (lightweight!) crank pulley might work after
all!
I would also suggest that one reason the flywheel is attached to the
back of the engine is that you certainly want to dampen out any pulses
going into the transmission and there anr only 2 ways: 1. Have a large
moment of inertia (flywheel) or 2. have a flexible coupling
(impractical?). Since the flywheel is required for idling and low rev
operation of the engine anyway, this is what is used.
Regards,
Simon
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