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of the cooling gallery permit high heat
flows. Steel’s low thermal conductivity
in comparison with that of aluminum,
and the resulting higher piston crown
surface temperatures, require increased
oil supply, good quality of the cooling
oil jet, and minimum wall thicknesses
between the cooling gallery and combustion
bowl.
Peak cylinder pressures of over 230 bar
combined with experience from advanced
and series development, have led to the
development of the KS Monobloc steel piston
with internal cooling gallery. A second
cooling chamber has been created beneath
the combustion bowl by introducing an intermediate
floor, � (m). The required
quantity of cooling oil flows from the outer
cooling gallery via connecting bores into
the inner cooling chamber and is then
discharg ed via drainage bores above the
connecting rod, thus ensuring a controlled
supply of oil to the connecting rod small
end. A reduction in the combustion bowl
surface temperature of about 25 °C is a
significant advantage. The connection of
the ring zone to the skirt not only improves
the piston’s structural rigidity, but
also permits a further temperature reduction
at the bowl lip of about 20 °C as a result
of the optimized shaping of the outer
cooling gallery. KS Monobloc steel pistons
are manganese phosphated, which permits
the use of uncoated steel pins and also
protects the piston from corrosion.
KS SPINTEKS FOR
COMMERCIAL VEHICLES
In developing the Spinteks piston, � (r),
KS Kolbenschmidt has realized a completely
new production method for
Monobloc steel pistons. The patented solution
consists of only one forged part
whose ring zone is reshaped after premachining,
by “spin bending” at raised
temperature to yield a closed cooling gallery.
The ring zone and skirt are welded
together. Alongside applications in the
United States, this solution is also used
in European products for extremely low
compression heights.
STEEL MATERIALS
In the production of KS Monobloc steel pistons,
a choice of two materials is currently
available. Heat treated steel 42CrMo4 is
considered an excellent compromise for
this application in terms of malleability,
machinability, strength, scaling resistance
and cost. For applications with a thermally
and mechanically limited load micro-alloyed
steels are used by economic reasons.
LOCAL MATERIALS ENGINEERING
ON THE RING GROOVE
For extreme heavy-duty engine operating
conditions, wear resistance requirements
are very high. An effective way of reduc-
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100 Years of Kolbenschmidt Pierburg
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ing top ring groove wear is to laser-harden
the lower edge. Hardened grooves show
significantly lower rates of wear in radionuclide
tracer measurements than their
unhardened counterparts, �. During engine
running-in, when the greatest wear is
experienced, laser hardening yields a
markedly reduced wear rate.
SUMMARY AND OUTLOOK
PISTON SYSTEMS
Over the last 100 years, pistons have been
subject to ever tougher requirements.
During this period, KS Kolbenschmidt
has consistently responded to these challenges
and developed optimized solutions
for higher thermal and mechanical loadings,
whilst at the same time achieving
lower weight designs. Future development
work in the automotive industry is focused
on engines with further reduced exhaust
emissions and improved fuel economy.
KS Kolbenschmidt will continue to
address all the issues and requirements
with competent strategies and innovative,
market driven products.
REFERENCES
[1] Hanke W., Buschbeck R., Letourneau S.,
Sinclair D., Skiadas A., Urabe M., Takiguchi M.:
Power Cylinder System Friction and Weight
Optimization in High Performance Gasoline
Engines, SAE 2009-01-1958, 2009
[2] Thiel N., Weimar H.-J., Kamp H.: Advanced
Piston Cooling Efficiency: A Comparison of
Different New Gallery Cooling Concepts,
SAE 2007-01-1441, 2007
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