Intermet Study Reveals the Advantages of Cast Ductile Iron Crankshafts
4 March 1999
Intermet Study Reveals the Advantages of Cast Ductile Iron Crankshafts
Significant Cost and Weight Savings With Positive
NVH Characteristics
TROY, Mich., March 4 -- Intermet Corporation
will present a paper today to the Society of Automotive Engineers that
demonstrates the lower-cost, weight-saving, and positive NVH (noise, vibration
and harshness) characteristic advantages of utilizing cast ductile iron
crankshafts in an aluminum block, V-6 engine.
The results of the joint study conducted by Intermet Corporation, Ricardo
Inc. and Simpson Industries Inc., found that the NVH characteristics of a
modern, aluminum block, V-6 engine were as good or better when a cast ductile
iron crankshaft with a multi-mode damper was substituted for the production,
forged steel crankshaft with conventional, single torsional mode damper.
Dr. Alan P. Druschitz, Intermet corporate director of materials
development, says that the recent trend in automotive crankshaft design to
replace cast ductile iron with forged steel has often been based on an
anticipated NVH benefit brought on by the higher elastic modulus (stiffness)
of steel. However, not only do cast ductile iron crankshafts weigh and cost
less due to their lower material, production and machining costs, they also
produce comparable NVH performance to steel forged crankshafts when certain
key system elements are addressed.
Much of the long-standing perception that steel components perform better
than those cast in ductile iron has to do with the belief that there will be
greater torsional and bending vibrations in the iron component. Druschitz
says, though, that this claim ignores the effects of rotating mass and
vibration dampers. "To begin with, a cast ductile iron crankshaft of
identical design will have less rotating mass with which to develop torsional
vibrations, since ductile iron is less dense than steel," he explains. In
addition, a ductile iron crankshaft can be cast with hollow pins, mains and
counterweights, which allow further reductions in rotating mass.
Torsional vibration dampers are commonly used to reduce the effect of
critical vibrations by absorbing and dissipating torsional vibration energy.
However, dampers can also be designed to reduce bending vibrations.
Druschitz says that none of the previous studies in this area took into
account the significant effect dampers can have on NVH characteristics. The
Intermet study, for the first time, included suitably designed dampers for
each crankshaft as part of its comparison.
Results of the new study concluded:
* Sound pressure measurements for an engine with a cast ductile iron
crankshaft with a multi-mode damper tuned to torsional frequencies of 209 and
309 Hz produced similar noise levels over an rpm range of 1000-6500 compared
to the same engine with production, forged steel crankshaft and a single
torsional mode damper.
* Bedplate acceleration measurements using the cast ductile iron
crankshaft also produced very similar or even slightly lower accelerations
over a rpm range of 1000-6500 compared to the production part.
* And, engine mount acceleration measurements produced similar results
over the same rpm range.
Druschitz presented his findings on the influence of crankshaft material
and design on the NVH characteristics of a modern aluminum block, V-6 engine
at this week's 1999 Society of Automotive Engineers Expo at Cobo Conference
and Exposition Center in Detroit, Michigan. The presentation was one of two
given this year by Intermet at the annual SAE event.
With headquarters in Troy, Michigan, Intermet Corporation and its
subsidiaries design and manufacture precision iron and aluminum cast
components for automotive and industrial equipment manufacturers worldwide.
Intermet also produces precision-machined components and manufactures cranes
and specialty service vehicles. The company has more than 6,900 employees at
19 operating locations in North America and Europe. The company's Internet
address is http://www.intermet.com.