To assist in more precise control of engine
functions, sealing suppliers have developed seals incorporating high ferrite content rubber that can essentially be used as
part of a position indicator system that can
assist in enhanced timing of the combustion process.
The seal incorporates a hydrodynamic pumping helix feature molded
into the lip while running against a
metal sleeve, which is augmented by
the dynamic slinger effect of the rotating inner sleeve. An added benefit is
that centrifugal force helps to keep the
soot that can build up in lube oil away
from the sealing surface. On the exterior side, an integral excluder dust lip
made of PTFE impregnated nonwoven
polyester is designed to allow positive
contact to the shaft at a very low load,
thus preventing dirt ingress without
high wear or heat build-up.
The introduction of direct-injection
technologies has provided engine manufacturers the ability to more precisely
manage fuel, thereby reducing emissions. To further augment this advantage, sealing suppliers have developed
encoder units, which allow for 20%
higher precision and 100% higher
repeatability over the traditional tone
wheel or gear tooth-type configuration.
By magnetizing special rubber with
high ferrite content, the elastomer-
ic encoder essentially becomes the
magnet and position indicator in the
system, allowing for smaller sensors
that are more precise and not as sen-
sitive to shock. These encoders are
designed to allow for more precise
timing of the combustion process, thus
decreasing the waste in the exhaust
and eliminating costly gear machining.
They can also be incorporated into
the crankshaft seal system rather than
bolting on a separate tone wheel. The
design also enables them to indicate a
zero-speed condition, as they do not
rely on the movement of a slotted or
toothed surface across the front of the
magnet to create a signal. Essentially,
since the rubber itself is magnetized,
the encoder is always on.
TECHNOLOGY
that older style or nondiesel-specific
valve stem seals can contribute up to
4% of overall internal oil consumption.
Another development has been the
“Plug-n-Seal” concept that is designed
to replace the tube connectors that
were sealed with O-rings installed in
grooves. Rubber is essentially over-molded onto the tube and special
inside diameter or outside diameter
sealing beads are added to the ends.
This development allows for improved
sealing of joints, easier installation of
the tube and accommodation of some
misalignment. This ensures the joint
will not only assemble correctly, but
stays sealed under misalignment and
temperature cycling. This concept
has been applied not only in engine
cooling systems, but also in air intake
components and turbochargers.
Seals often are a forgotten component in the engine system, but
sealing technology has been evolving
to meet the challenges of next-generation clean diesel engines. Small
changes have demonstrated the ability to create a big impact, and in many
cases these changes can be obtained
without major reconfigurations to the
existing application. Working with
experienced sealing suppliers can be
critical to making that happen. dp
“Plug-n-Seal” concepts, designed to replace
the tube connectors that were sealed with
O-rings installed in grooves, involve over-molding rubber onto the tube and adding
special inside diameter or outside diameter
sealing beads to the ends. This configuration can provide improved sealing of joints,
easier installation of the tube and accommodation of some misalignment.
100 DIESEL PROGRESS NORTH AMERICAN EDITION June 2011
