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Shaft
seals are incorporated into automotive, truck,
and off-road vehicle wheel assemblies to
contain grease and to exclude dirt, mud, and
other contaminants. The specific seal design
typically depends on how and where the seal must
function; for example, light duty versus heavy
duty, and non-driven axles versus driven axles.
The non-driven axles in light duty applications
can typically be sealed effectively with a radial
lip shaft seal such as the one shown in Figure
210.
Other
designs are possible. Figure 211 shows
a simple non-spring-loaded and
non-unitized design with a radial
exclusion lip. Studies have shown that the
most effective designs include an axial
dirt lip (Figures 212 and 213)
that contacts a vertical surface (e.g. a unitized
wear
sleeve) to exclude contaminants.
The
driven axles in light duty applications are generally
sealed with standard spring-loaded seals.
Some wheel bearings are sealed and greased for
life. These are called hub unit bearings. Figure
214 shows a hub unit application
for a driven axle. The spring-loaded seal prevents
axle oil from entering the greased hub unit bearing.
Heavy
duty wheel end seals (also called oil bath seals)
have become the focus of increasing demands of
late. Warranty periods have been lengthened, temperature
expectations raised, and contamination exclusion
concerns elevated. As shown in Figures
215 and 216, both the non-driven
and driven axles in heavy duty truck applications
often feature oil-lubricated bearings that must
be sealed. The hub rotates while the spindle is
stationary, and unitized seals are commonly used.
As
shown in Figure 217,
the external seal design features a rotating seal
sleeve in conjunction with a stationary sealing
element. Because the O.D. of
this seal is metal, tools are required for proper
installation. Figure 218 shows
an internal seal design, which features a stationary
sleeve and a rotating sealing element. With rubber
on both the seal I.D. and
O.D., this seal can be installed by hand without
tools if necessary. Note that this internal design
also features both an axial dirt lip and a flinger to
maximize exclusion of contaminants.
Heavy
duty wheel end applications lubricated with hypoid
grease can also utilize the designs shown in Figures
217 and 218. The spring-loaded, unitized
design shown in Figure 213 is
also a possibility. Note that this design features
both a metal I.D. and a metal O.D.
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