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12 DesIGnInG WItH PoLYMeRs
333 important factor in transmissions—in a fast turning
transmission, extremely small toothed gear flanks are
subject to strong forces and significantly higher pressures
than in the engine. Consequently, comb polymers
have to stand up to high shear forces while
retaining optimal viscosity values over a wide range
of temperatures.
Fuel consumption reduced once again
After many years of development work, chemists at
Evonik have developed four comb-polymer-based
high-performance additives that meet all the demands
of today’s engines and transmissions. Most importantly,
these developments also help reduce fuel consumption
and emissions. In a comparison with a standardized
reference oil (RL 191), conventional PAMA
additives have been shown to reduce fuel consumption
by 3.5 percent—comb polymers in the engine oil,
on the other hand, lower fuel consumption by 4.4
percent. In combination with gear oils, which also
contain comb polymers, the savings increases to a
total of about 1.5 percent.
At first glance, a 1.5 percent reduction in fuel consumption
does not seem particularly high. Comparison
in absolute figures reveals the actual weight of
this relatively small percentage: the International
Energy Agency (IEA) estimates that, worldwide, road
traffic emits about five billion metric tons of carbon
dioxide per year. Of this figure, 1.5 percent corresponds
to a savings of 75 million metric tons. According
to EU standards, average CO 2 emissions per
vehicle and per kilometer must be reduced by about
elements35 Issue 2|2011
Additives are supposed to keep
the viscosity of lubricating oils
constantly within an optimal
range over the widest possible
range of temperatures. The
viscosity index (VI) plays a
decisive role. Changing temperatures
have a greater impact
on the viscosity of oils with a
low VI than on the viscosity of
oils with a high VI