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November - December 2015
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lubricant's objective is to reduce friction and wear. However, there
are many situations in which a certain amount of traction friction is
required for equipment to operate properly. The friction modifiers
used in these applications are not intended to increase or decrease
friction but to act differently under specific shear conditions. This
essentially smooths the transition from a dynamic condition to a
static condition, such as during a gear change in a transmission or
the engagement of a clutch.
The vast majority of friction modifiers in use today are designed
to reduce friction or increase lubricity for better fuel economy.
Recently, the U.S. government increased fuel economy standards
with the goal of raising the Corporate Average Fuel Economy (CAFE)
to 54.5 miles per gallon. This number, which is double the current
standard, is for gasoline engines only, but there is a similar push for
diesel engines as well. One way to achieve this goal would be to
reduce the viscosity of the engine oils in use. The challenge is
lowering the viscosity while maintaining a sufficient lubricant film to
reduce wear and friction.
Great strides have been made in engineering to lower the friction
generated in an engine. This has increased fuel economy. There have
also been many advances in lubricant technology, including in the
development of friction modifiers.
Friction modifiers are most efficient under boundary conditions
or where metal-to-metal contact occurs. Organic friction modi-
fiers have long, soluble chains and a polar head. The polar head
attaches to the metal surfaces. The soluble chains line up
beside each other much like fibers in a carpet. The polar heads
may be comprised of phosphoric or phosphonic acids, amines,
amides or carboxylic acids. The soluble chains form dense mono
layers or thick, reacted viscous layers. These layers shear easily and
create a relatively slippery surface.
Organic Friction Modifiers
Mechanical types of friction modifiers form layers of platelets that
align with one another, providing a reduction in friction. The most
common of these is molybdenum dithiocarbamate (MoDTC). These
additives reduce friction by forming nano-sized single sheets
dispersed
Friction Modifiers
Oil
Oil
Oil
Oil
Oil
Oil Oil
Oil
Oil
Strong anti-compressive
behavior helps to
separate surfaces
Polar head attracted to surface
