Organic Friction Modifi ers 199
In Sequence VIA, which is prescribed for ILSAC GF-2, EHL is dominating, leading to a sub-
stantial effect of engine oil viscosity on fuel economy. Effects of FMs will be small due to the low
presence of BL and ML conditions, which is due to the application of roller followers. Hence, the
Sequence VIA test engine is often indicated as “a very expensive viscometer.”
This characterization of the Sequence VIA engine will be addressed by Sequence VIB, to be
used for ILSAC GF-3, for which an engine, a bucket tappet sliding valve train will be used, leading
to an increase of the BL and ML regimes [3].
In Europe, the M111 engine is used for the CEC L-54-T-96 fuel economy test, which is pre-
scribed in the ACEA A1 and B1 engine oil specifi cations. Similar data as aforementioned are not
available to the authors, but data given in a Shell paper [15] indicate the frictional loss occurring in
this engine, which can be translated to lubrication regimes (Table 7.2).
On the basis of the relatively high amount of frictional loss in the valve train and piston
assembly, the M111 engine should be sensitive to FMs. This is due to the use of four valves per
cylinder to improve combustion effi ciency and so to obtain more power from a given amount
of fuel.
However, compared to other engine designs, the frictional loss in the M111E valve train will be
higher. Provided that the higher-power output obtained from the four-valve assembly is signifi cantly
higher than that is lost by higher valve train friction, this approach is favorable with regard to fuel
economy.
7.3 FRICTION MODIFIERS VERSUS ANTIWEAR/
EXTREME-PRESSURE ADDITIVESA point of debate is often about the difference between FMs and antiwear/extreme-pressure (AW/EP)
additives, especially when it is about FMs active at BL conditions. For a good understanding, this
should be clarifi ed; therefore, this section deals with the principal difference between these two addi-
tive categories [16].
AW/EP additives are types of compounds that provide good BL. Such materials have the capac-
ity to build strong BL layers under severe load conditions. Hence, AW/EP additives protect closely
approaching metal surfaces from asperities damaging the opposite surface. On the contrary, most
AW additives have little friction-modifying properties.
The crucial differences between AW/EP and FM fi lms are their mechanical properties. AW/EP
fi lms are semiplastic deposits that are diffi cult to shear off. Thus, under shearing conditions, their
coeffi cient of friction is generally moderate to high. Conversely, FM lubricant fi lms are built up of
orderly and closely packed arrays of multimolecular layers, loosely adhering to one another and
with the polar head anchored on the metal surface. The outer layers of the fi lm can be easily sheared
off, allowing for a low coeffi cient of friction.
TABLE 7.2
Lubrication Regimes in the DB M111E Engine
Frictional Loss (%) Main Lubrication Regime
Valve train 25 Boundary lubrication
Piston assembly 40 Mixed lubrication
Bearings 35 Elasto-hydrodynamic
lubrication