Unitized exclusion seal

A static dirt exclusion element is arranged in a unitized housing to contact a rotating exclusion element so as to provide a primary barrier to dust and airborne contaminants. A secondary barrier is provided in the housing in the form of a porous filter element formed of a foam or felted material to further exclude and entrap contaminants.

BACKGROUND OF THE INVENTION 
2. Field of the Invention 
This invention relates generally to shaft seals and more particularly 
relates to a debris-excluding shaft seal with an extended life expectancy 
achieved through minimization of frictional contact between rotating 
sealing surfaces and through entrapment of abrasive contaminants within a 
porous filter element. 
2. Description of Prior Developments 
Prior debris-excluding seals have traditionally experienced various 
operational problems including the generation of excessive heat via 
frictional contact between rotating seal elements. This frictional heat is 
primarily caused by the relatively high contact forces extisting between 
the rotating seal elements. While these high contact forces were believed 
necessary to effect a reliable seal, they have been shown to cause rapid 
wear between the rotating sealing surfaces and have significantly reduced 
seal life. 
One approach to overcome this heating problem is to avoid contact between 
the rotating elements by providing a small clearance therebetween. 
However, this approach presents another problem wherein debris passes 
through, or is entrapped within the clearance space. This condition 
results in extremely rapid abrasive wear of the sealing elements as well 
as wear of the rotating shaft. 
It has generally been assumed that by providing a plurality of engagement 
points between rotating seal elements so as to form a plurality or series 
of sealing surfaces, a more effective barrier to debris would result. 
Thus, known debris excluding seals generally provide several points of 
contact between the rotating seal elements to form a series of sealing 
surfaces. However, each contact point acts as a source of frictional heat, 
which as noted above, adversely affects seal life. 
A particularly difficult sealing problem arises in those applications where 
dirt excluding seals must accommodate significant shaft runout and/or 
shaft-to-bore misalignment. Prior seals have not proven effective in these 
cases and have not been well accepted by industry. 
Another inconvenience associated with existing dirt excluding seals is the 
difficulty of properly and accurately aligning the stationary seal element 
with respect to the rotating seal element during installation of the seal 
assembly about a shaft. 
In those instances where a seal is provided with hydrodynamic features, an 
additional problem often arises. While the hydrodynamic pumping effect 
serves to prevent lubricant from passing beyond the seal lip, a vacuum is 
generated which tends to draw or suck air beneath the lip from the 
surrounding environment on the dry or air side of the seal. If the air 
contains any contaminants such as dust particles, the contaminants are 
also drawn under the seal lip. This not only accelerates lip wear and 
reduces seal life but it also results in contaminanted lubricant and/or 
wear of internal moving parts. 
When a seal produces a hydrodynamic action a surprisingly large pressure 
differential is developed across the seal lip. As noted, a vacuum effect 
is created on the air or dry side of the seal while ambient pressure is 
present within the wet or inner side of the seal. This condition can 
result in large contact forces between the lip and shaft if an air tight 
seal is formed therebetweem. This contact force can be reduced by allowing 
a small amount of air to be drawn past the seal lip so as to minimize the 
pressure differential. However, by drawing air beneath the seal lip, the 
problem of contamination arises. 
Moreover, large contact forces such as described above generate excessive 
frictional heat. In some instances this heat between the shaft and lip 
becomes so great that the lubricant which flows against and beneath the 
lip breaks down and becomes corbonized. This carbonized lubricant then 
bonds to the lip and/or shaft and forms a deposit of build-up of hardened 
carbon. This build -up then prevents continuous contact between the lip 
and shaft and results in seal leakage. 
Accordingly, a need exists for a unitized dirt-excluding shaft seal which 
minmizes the generation of frictional heat by reducing the contact force 
between rotating sealing surfaces thereby extending seal life and 
protecting shaft finish. 
A need also exists for a seal which prevents contaminants such as dust 
particles from passing beneath a seal lip, particularly in those cases 
where the seal is generating a hydrodynamic effect, yet which avoids large 
contact forces between the seal lip and the shaft. 
SUMMARY OF THE INVENTION 
The present invention has been designed to fulfill the needs noted above 
and therefore has as a primary object the provision of a unitized 
dirt-excluding shaft seal having extended life expectancy and improved 
performance, particularly in those applications where extremely dusty and 
dirty operating conditions prevail. Typical applications include front 
crankshaft seals for off-road engines as well as drive shaft and axle 
seals for earth moving machinery. 
Another object is to provide a dirt-excluding shaft seal which minimizes 
the contact forces between rotating seal elements so as to minimize the 
production of frictional heat and correspodingly reduce the frag force of 
the seal on the shaft. 
Still another object is to provide a dirt-excluding shaft seal which 
employs a single line of contact between a stationary seal case and a 
rotating seal lip so as to further reduce frictional heat. 
Another object is to prevent airborne particles from contacting a seal lip 
and to prevent such particles from being drawn under the lip, particularly 
in those cases where the particles are drawn toward the lip by a vacuum 
created by hydrodynamic effects. 
Yet another object of the present invention is to facilitate the handling, 
installation and alignment of a dirt excluding shaft seal about a shaft. 
Another object is to provide a dirt-excluding seal which effectively 
accommodates significant amounts of shaft runout as well as singnificant 
misalignment between the seal bore housing and the shaft. 
The present invention is generally directed to a unitized dirt-excluding 
seal which includes a static exclusion element arranged in limited contact 
with a rotating exclusion element. The rotating element is pressed or 
bonded to a shaft so as to rotate with the shaft. These coacting sealing 
elements provide an initial or primary barrier to exclude contaminants 
such as dust and abrasive particles from the interior of the seal. The 
contaminants are thus prevented from passing from the environment 
surrounding the seal to an interior region within the seal, wherein 
lubricant or bearing surfaces are located. 
A secondary barrier may be incorporated with the seal to further prevent 
the passage of contaminants therethrough. The secondary barrier may take 
the form of a foam or felted filter that contacts or nearly contacts an 
interior portion of the rotating element. Additional sealing lips may be 
provided on the interior of the primary and/or secondary barrier to serve 
as conventional lubricant seals. These conventional seal elements may 
allow small amounts of ambient air to pass beyond the seal lips so as to 
prevent excessive loading between the lip and shaft yet without allowing 
passage of contaminants past the lip. This is possible because of the 
presence of the filter which traps the airborne contaminants before they 
contact the seal lip so that only clean filtered air reaches the interior 
seal lip. 
Various other objects, features and attendent advantages of the present 
invention will be more fully appreciated from the following detailed 
description when considered in connection with the accompanying drawings, 
in which the same reference numbers designate the same or corresponding 
parts throughout.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As seen in FIG. 1, a conventional one-piece dirt excluding shaft seal (1) 
includes a dirt exclusion lip (3) and an oil sealing lip (5) each engaging 
a rotating shaft (7). This traditional design depends on dynamic 
intereference between the lips and shaft to maintain an adequate seal. The 
exclusion lip (3) is intended to run on an oil film which tends to attract 
dust particles from the air. When the oil and dust particles mix, an 
abrasive slurry is formed which accelerates seal wear and leads seal 
failure. 
In use, heat is generated by friction between the seal lips (3), (5) and 
the shaft. The frictional heat produced by the exclusion lip (3) is 
transferred along the shaft and raises the shaft temperature to a value 
above that which would result from the sole use of the oil sealing lip (5) 
in the absence of dirt exclusion lip (3). Moreover, frictional heat 
generated by the oil sealing lip is transferred to the shaft and raises 
shaft temperature adjacent the exclusion lip as well. This increased shaft 
temperature adversely affects the life of each lip and correspondingly 
reduces the effective life of the seal. Heat from the frictional contact 
with the shaft causes the elastomeric or polymeric lip material to become 
hard and brittle and eventually chip and break, thereby causing a leak. 
As seen in FIG. 2, a basic embodiment of the present invention is directed 
to a two-piece unitized shaft seal (9) which is mounted over shaft (7) and 
press fit within the bore of a seal housing (11). The unitized seal 
includes an annular case member (13) and an annular shaft engaging member 
(15). Typically, the shaft engaging member is pressed onto or bonded to 
the shaft and rotates with the shaft, while the case member remains static 
within the metallic housing or bore (11). 
Member (15) may be formed of any non-metallic engineering material such as 
an elastomeric or thermoplastic material. Preferred materials include 
carboxylated nitrile and materials which are highly resistant to abrasion, 
can withstand high operating temperatures, are easily molded and have good 
resistance to chemical attack. The case member (13) is preferably formed 
of a metallic material for efficiently conducting heat from member (15) 
towards housing (11) where it is dissipated without raising the 
temperature of the shaft. 
Member (15) is provided with an annular unitizing channel (17) which not 
only prevents disengagement of members (13) and (15) prior to installation 
but also aids in the installataion of the unitized seal. That is, channel 
(17) serves to axially align the shaft engaging member (15) with respects 
to the radial flange (19) of the case member. The radial inner extremity 
(20) of the flange is properly and automatically disposed between the 
mutually confronting radially extending walls (21) of the channel upon 
installation. Little, if any additional adjustment is required once the 
unitized seal is seated within its housing. 
An important feature of the unitized seal is the relative axial widths of 
the channel (17) and the flange (19). In order to minimize or prevent 
unwanted contact between the internal walls (21) of the channel and the 
surfaces of the flange, the width A of the flange should be less than the 
width B of the channel. Moreover, a clearance C should be maintained 
between the radial innermost end face of the flange and the floor of the 
channel to prevent contact therebetween in the event of excessive radial 
shaft runout and/or excessive radial shaft whip. 
In order to prevent disassembly of the shaft engaging member (15) from the 
case member (13), channel (17) is bounded by annular radial ridges or 
projections (23). These projections, while preferably formed of a 
resilient material, are radially short and axially thick to resist axial 
deflection upon contact with the radial inner extremity of flange (19). 
Such contact may occur during handling and installation of the seal, but 
once the seal is correctly installed, this contact is avoided or minimized 
by the dimensioning noted above. 
The shaft engaging member (15) is further provided with a radially 
outwardly projecting lip element (25). As seen as FIG. 3, the lip element 
may be formed with a relatively thin and resilient end portion (27). The 
tip (29) of the end portion is axially extended toward and over channel 
(17) to an extent which ensures a proper contact pressure range between 
the tip and an outer surface portion of the flange. This contact pressure 
should range from approximately 0.5 oz. to 25.0 oz. for most practical 
applications. 
An additioal advantage is gained by this dimensioning of the flange, 
channel and tip. By ensuring a biased interference fit between tip (29) 
and flange (19) over an axial extent X as shown in FIG. 3, axial end play 
of shaft (7) will not result in a loss of contact between the tip (29) and 
flange (19) within a tolerance of X. The degree of interference X may be 
varied depending upon the acceptable limits of contact force and shaft end 
play. 
In the event of shaft runout or shaft whip, contact will be maintained 
between tip (29) and flange (19) since relative radial movement between 
these seal members does not affect the axially directed sealing contact 
force therebetween. This is not the case, however, for conventional seals 
such as shown in FIG. 1 which rely upon radial sealing forces. The axial 
widths D and E of the lip element (25) and the end portion (27), 
respectively, should be generally less than the thicknesses F, G of either 
of the radial projections (23) so that the specified light contact 
pressure range is maintained between the tip (29) and the flange (19). 
A definite advantage is gained by providing a single circumferential line 
or band of continuous contact between tip (29) and flange (19) in that the 
frictional heat generated along this annular contact line is limited to a 
single source and location and is thus adequately controlled and 
significantly reduced. Little if any heat is transferred from this contact 
area to the shaft. Moreover, this contact needs no lubricant so that 
attraction and accumulation of airborne particulate contaminants by oil or 
the like is avoided. 
Installation of the unitized seal is simplified by its design. The seal is 
simply pressed axially into housing (11) in a conventional manner after 
the shaft engaging member has been radially stretched over the shaft. The 
radial prejections (23) of the shaft engaging member prevent its 
disengagement from the case member during installation due to the 
relatively stiff resistance to deflection provided by the short height and 
wide axial width of the projections. Once seated within housing bore (11), 
either the case or the shaft engaging member may be axially shifted if 
desired, to attain single point contact therebetween at tip (29). Thus, 
the radially inner end portion or extermity 20 of shaft (19) may be 
aligned without contact within channel (17) during use. 
Another embodiment of the invention is shown in FIG. 4 wherein case member 
(13) is radially and axially stepped at (31) to provide an annular 
mounting ridge (33) against which a polytetrafluoroethylene (PTEF) lip 
element (35) is clamped in a known fashion. A sealing gasket (37) is 
provided between the lip element and the clamping member (39) to prevent 
leakage in a conventional gasket arrangement. 
FIG. 5 depicts another embodiment wherein an elastomeric seal lip (41) is 
bonded to the case member in a common configuration. In both FIGS. 4 and 
5, it can be appreciated that the frictional heat developed by the dirt 
exclusion portion of the seal is limited to the flange (19). This heat is 
transferred from the metal flange to the seal housing (11) where it is 
dissipated without adversely affecting either seal lip element (35) or 
(41). 
Since most elastomers and thermoplastic resist heat transfer, little if any 
heat is transferred through lip element (25) of the shaft engaging member 
to the shaft. This significantly enhances the life of the seals and 
protects the shafts. Moreover, the light contact pressure between the 
contelevered tip (29) of lip element (25) and the flange (19) even further 
reduces frictional heating of the seals. 
A further refinement of the invention is shown in FIG. 6. Although the seal 
shown in FIG. 6 appears similar to that shown in FIG. 4, a significant 
improvement is incorporated in the desigh of FIG. 6. While this embodiment 
includes a primary dust excluding portion composed of annular shaft 
engaging member (15) and flange (19) as described above, a secondary 
porous annular filter element (45) is clamped between step (33) of metal 
case (13) and lip element (35) with the inner case or clamping member 
(39). One or more gaskets (47) may be clamped between the filter and case 
and/or between the filter and lip element. The gaskets, preferably rubber 
washers , prevent lubricant from passing between the radial outermost tip 
of the lip (35) and casing (13). This in turn prevents the lubricant from 
wicking through the foam filter element and reducing its effectiveness. 
As a secondary barrier to dust and other particulate contaminants, the 
filter (45) is arranged to be in contact with the rotating shaft engaging 
member (15) or at least in near contact therewith. Filter (45) is 
preferably formed of a felted polyurethane foam since polyurethane foam 
has excellent resistance to abrasion an ensures a long operational life. 
The mesh or pore size of the foam is preferably within the range of 1 to 
500 microns. 
As further seen in FIG. 6, lip element (35) is provided with spiral grooves 
or slits (49) for generating a hydrodynamic pumping action which tends to 
pump lubricant inwardly in the direction of arrow (51). This pumping 
action tends to create a vacuum around the outer side of the lip as at 
(53). This vacuum in turn tends to draw in particulate airborne 
contaminants past the dirt and dust excluding elements 15 and 19. 
By arranging filter (45) between the dust excluding elements 15 and 19 and 
the lip element (35), all particulate matter drawn past the first 
contaminant excluding barrier (15,19) is embedded within the pores of the 
filter (45) and is prevented from reaching the lubricant sealing lip (35). 
This significantly increases seal life and allows contact forces between 
lip element (35) and shaft (7) to be reduced. 
That is, in order to prevent contaminants from being drawn past lip element 
(35), prior designs have maintained large contact forces between the lip 
and shaft so as to form an air-tight seal. This approach often failed 
because at high rotative speeds the lip was unable to maintain contact 
with the shaft and contaminants would thus gain entry to the luburicant 
side of the seal. Furthermore, the high contact forces augmented by the 
hydrodynamically induced pressure differential carbonized the lubricant as 
discussed above. 
The seal shown in FIG. 6 need not and preferably does not maintain an 
air-tight seal but rather maintains a light contact to allow a small 
amount of filtered air to flow past lip element (35). This air flow tends 
to neutralize any hydordynamically induced pressure differential and 
thereby prevents excessive lip-to shaft contact forces. 
As shown in FIG. 7, the two-stage seal may be used without the lip seal 
(35) so as to serve only as a dust guard. Morever, the filter (45) may be 
used with any of the embodiments shown in FIGS. 2, 4 or 5 as well. It is 
also possible to bond the filter (45) to the rotating elements (15) 
instead of clamping or bonding the filter to the metal case (13). 
Obviously, numerous modifications and variations of the present invention 
are possible in light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims, the invention may 
be practiced otherwise than as specifically described herein.