Lubricant Additives

208 Lubricant Additives: Chemistry and Applications

The difference in friction-modifying characteristics between organic FMs and molybdenum
dithiocarbamate suggests that it might be benefi cial to use a combination of these materials.

7.9 CONSEQUENCES OF NEW ENGINE OIL

SPECIFICATIONS AND OUTLOOK

Although initial fuel economy requirements were focused on fresh oil only, new engine oil specifi -
cations will address fuel economy longevity as well. A good example is Sequence VIB, which has
been developed for the ILSAC GF-3 specifi cation.
Sequence VIB includes aging stages of 16 and 80 h to determine fuel economy as well as fuel econ-
omy longevity. These aging stages are equivalent to 4000–6000 mi of mileage accumulation required
before the EPA metro/high-highway fuel economy test. That test is used in determining CAFE.
To obtain engine oil formations that are optimized with regard to fuel economy longevity,
high requirements are demanded for base oil selection and additive system design [3,7,22]. These
requirements are

To minimize the increase of viscosity thereby maintaining a low electrohydrodynamic fric-

tion coeffi cient

To maintain low boundary/mixed friction

A minimum increase of viscosity can be obtained by base fl uid selection (in terms of volatility,
oxidation stability, and antioxidant susceptibility) and selection of antioxidants and their treat level.
The market is already anticipating requirements by increasing the production capacity of groups II
(HIVI) and III (VHVI) base fl uids and by increased interest in groups IV (PAOs) and V (a.o. esters)
base fl uids.
To achieve low friction under BL and ML conditions, the use of effective friction-reducing addi-
tives is needed. To maintain low boundary and mixed friction over time, it is necessary to prevent
consumption of these additives by processes such as oxidation and thermal breakdown. Therefore,
selecting suitable antioxidant systems for molybdenum compounds and organic FMs and develop-
ing organic FMs with highest thermal/oxidative stability will be key for high fuel economy longev-
ity and a successful application in engine oil formulations.

FIGURE 7.13 Friction coeffi cient versus temperature—CEC RL 179/2 plus molybdenum dithiocarbamates.

0.14

0.13

0.12

0.11

0.10

0.09

0.08

0.07

0.06

40 50 60 70 80 90 100 110 120 130 140

Temperature (°C)

Friction coefficient

f (

−)

RL 179/2 + 0.5% GMO + 0.07% Mo (A) + 0.07% Mo (B)