Radial lip oil seal

A shaft seal includes a rigid case and an elastomeric seal body affixed thereto. The seal body member includes a primary sealing lip and a secondary sealing lip axially spaced from one another by an intermediate flex section. The sealing surfaces of both sealing lips are lined with a singular piece of low friction material in the form of a single annular wafer having radially inner and outer liner portions covering the primary and secondary sealing lips. The wafer is formed with a weakened material section intermediate the inner and outer annular liner portions for increasing the flexibility and independent operation of each sealing lip.

TECHNICAL FIELD 
The present invention relates to a radial lip type oil seal having a 
primary sealing lip and secondary sealing lip, each lined with a low 
friction material. 
BACKGROUND OF THE INVENTION 
Radial lip oil seals having an elastomeric body portion thermally bonded to 
an annular, usually cup-shaped, metal case have been in use for many 
years. Such seals are generally used between relatively rotatable parts to 
seal oil or grease in a predetermined location for lubrication. Common 
applications for these seals include sealing vehicular engine crankshafts 
and transmission shafts. In each case, the elastomeric body portion of the 
seal is usually designed to include an annular flex portion of reduced 
cross-sectional thickness bonded to the metal case member and located 
intermediate the seal lip and metal case. The purpose of this flex section 
is to allow the seal lip to stay in continuous, intimate contact with the 
shaft it is to seal despite any lack of concentricity between the 
relatively rotating members, e.g. the rotating shaft and the stationery 
engine block into which the annular metal case member is usually press-fit 
or otherwise nonrotatably secured. 
It is also known that for certain applications, particularly off-road 
vehicular applications such as earth hauler and tractor applications, it 
is desirable that the elastomeric oil seal include at least one secondary 
seal lip, axially spaced from the primary seal lip, for the purpose of 
excluding dirt, dust and other particulate type contaminants from the 
primary seal lip. During the molding process of such "dual lip" seals, the 
anchoring portion of the annular metal case is clasped between an upper 
and lower die and extends within a molding cavity formed by the two. A 
common annular ring of elastomeric prep material is heated within the mold 
and subsequently flows within the die cavity filling it, forming the 
primary and secondary seal lips and a common flex section opposite the 
entrapped anchoring portion of the metal case. Upon cooling and stripping 
the seal from the mold, the two lips are seen to be joined to the metal 
case by the common flex section. Further, that portion of the elastomeric 
body portion intermediate the primary and secondary seal lips also 
functions as a secondary flex section. 
As a result of the common flex section, each seal lip in operation is 
relatively independent of the case member. That is, each seal lip can 
accommodate shaft eccentricity with the axis of the metal case member and 
with the bore in which it is located. Further, as a result of the second 
or intermediate flex section, the primary and secondary sealing lips are 
fairly operationally independent of one another. That is, because the 
elastomeric material is relatively soft and pliable, each seal lip can 
accommodate shaft surface irregularities appearing only at that one seal 
lip, such as some localized out of roundness, without affecting the 
performance of the other seal lip. For certain seal designs, the common 
flex section and the secondary flex section may be one and the same. 
U.S. Pat. No. 2,992,027 presents a discussion of this same operational 
characteristic and suggests that the design of the flex section itself, 
which is intermediate the primary and secondary seal lips, may be altered 
to assure independent action. 
Most recently, the wear characteristics of this general seal design have 
been enhanced by lining the sealing surface of each seal lip with a low 
friction, high wear resistant material such as polytetrafluoroethylene 
(PTFE) or the like. An example of this design is shown in U.S. Pat. No. 
4,171,561. While such a design enhances at least the long life 
characteristics of the oil seal, it has been found that the benefit of the 
relatively independent action of the primary and secondary seal lips 
relative to one another has been diminished by the stiffness of the PTFE 
liner which extends across the secondary flex section. 
Consequently, attempts have been made to economically provide an oil seal 
of this type with both seal lips lined with low-friction material but 
without sacrificing the independent flexibility of each. 
One such design includes a method of manufacture which allows the use of a 
single annular prep material piece and a single PTFE liner wafer with the 
inherent cost and molding process advantages of such a design, namely that 
shown in U.S. patent application Ser. No. 347,920, assigned to the 
assignee of the present invention. By such technique, the PTFE wafer is 
split during mold closure into two separate annular rings, one for the 
primary lip and the other for the secondary lip. Unfortunately, the 
reliability of the freed wafer being split and locating consistently in 
the final design position by the hydrodynamic force of the flowing 
elastomeric prep material can not always be assured. 
SUMMARY OF THE INVENTION 
According to the present invention, there is provided a multiple lip 
elastomeric oil seal wherein each lip sealing surface is lined with a 
low-friction, high wear resistent single liner common to each lip yet 
which provides increased flexibility and independent action to each lip. 
More specifically, the invention contemplates a seal for sealing fluids 
around a shaft, wherein the seal comprises a seal case and an elastomeric 
seal body mounted to the seal case and including a primary seal lip and a 
secondary seal lip. A fluorinated resin seal lip liner is bonded to the 
seal body and covers the primary and secondary seal lips. The liner is 
formed with a weakened material section located between the primary and 
secondary lips for increasing flexibility therebetween, i.e. across the 
secondary flex section. 
It is therefore one object of the present invention to provide an 
elastomeric oil seal having at least one primary sealing lip and at least 
one secondary sealing lip, each being bonded to a metal case member by a 
common elastomeric flex section and each being lined by a common liner 
wafer formed of low-friction material 
It is another object of the present invention to be able to produce the 
above-described type seal by a molding technique used to form single lip 
type seals having a low-friction material liner. 
It is a further object of the present invention to provide the 
above-described type seal wherein each seal lip shall be relatively 
uninfluenced by the operational characteristics of the other. 
The objects, features, and advantages of the present invention are readily 
apparent from the following detailed description for carrying out the 
invention when taken in connection with the accompanying drawings.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring now to the drawings, in FIG. 1 there is shown a shaft seal which 
is known in the prior art. It includes an annular seal body portion, 
generally designated 1, bonded to a radial flange member 2 forming a 
portion of an annular cup shaped case described below. The annular seal 
body portion 4 includes a flexible neck portion 6 nearest the anchored 
portion of the seal body. The remainder of the seal body 4 includes a 
primary seal lip 8 and a secondary seal lip 10. 
At the primary sealing lip 8 there is provided a spring retention groove 12 
for retaining an annular spring which holds the primary seal lip in light 
compression upon the shaft on which it is to be mounted for purposes of 
maintaining intimate sealed contact with the shaft. Both the primary 
sealing lip 8 and the secondary sealing lip 10 are formed by a respective 
pair of converging sidewalls 14, 16, and 18, 20 meeting at an apex 
defining the static sealing band for each such lip. Further, it will be 
seen that the sealing lips are provided with a liner 22 of low friction 
material such as filled or unfilled polytetrafluoroethylene (PTFE) or the 
like. 
Liner 22 is of one-piece construction and is of generally uniform 
cross-sectional thickness with the exception of the one sidewall of the 
primary sealing lip, namely the air side 24 which is seen to include a 
series of hydrodynamic groove configurations 26. Generally these groove 
configurations are in the form of a single spiral groove hydrodynamically 
coined in a known fashion into the PTFE liner during the molding process 
in which the elastomeric seal body member and the polytetrafluoroethylene 
liner are bonded to one another and the seal body member bonded to the 
flange 2. 
That portion of the seal body 4 which lies intermediate the primary and 
secondary seal lips constitutes, in effect, a second flex section, 
generally designated 28. It is important that sufficient flexibility be 
maintained in this section such that the primary or secondary seal lip can 
accommodate localized shaft surface irregularities such as an out-of-round 
condition without affecting the performance of the other seal lip. 
Unfortunately, since the polytetrafluoroethylene liner material is 
considerably stiffer than the elastomeric material of the seal body, a 
great deal of the flexibility otherwise present between the two seal lips 
is lost. 
Looking now principally at FIGS. 2, 3, 5 and 6, the principal features of 
the present invention will be understood. Like reference numerals are used 
when referring to the same seal components shown and described in 
connection with FIG. 1. 
It will be seen that the shaft seal of the present invention includes an 
annular elastomeric seal body member 4 bonded to an annular cup-shaped 
rigid, preferably metal, case member 30. The case member 30 includes a 
cylindrical wall member 32 and a radial flange 2 extending therefrom. The 
elastomeric seal body member is bonded to the flange 2 at its free end. 
The sealed body 4 includes, in axially progressing order, an anchor 
portion 34, a flexible neck portion 6, a secondary seal lip portion 36, an 
intermediate flex portion 28, and a primary seal lip portion 38. 
Each primary and secondary seal lip portion 36, 38 includes a sealing lip 
8, 10 formed by generally radially converging sidewalls 14, 16, 18 and 20 
respectively. Radially opposite the primary seal lip is located a spring 
retention groove 12 in which there is adapted to be retained an annular 
coil spring 39 (FIG. 5) for purposes of assuring that the primary seal lip 
is held with adequate consistent compressive load upon the shaft. The 
primary and secondary seal lips 36 and 38 are each covered with a liner 40 
of low friction fluorinated resin material such as polytetrafluoroethylene 
or the like. Further, it is preferred for some applications that the 
primary sealing lip include hydrodynamic configurations 26 within the 
polytetrafluoroethylene liner 40. 
Unlike the prior art, it will be noted from FIG. 2 that the intermediate 
flex section 28 is not completely covered by the liner material. Rather it 
will be seen particularly from FIGS. 2 and 3 that the liner 40 is 
substantially devoid of material intermediate the annular end portions 
covering the primary and secondary seal lips. As seen in FIGS. 3 and 5 the 
annular liner end portions are connected by axially extending web members 
42. The web members 42 each are of minor circumferential length, in the 
order of 3 to 5 arc degrees. 
The liner, prior to molding, is shown in FIG. 6. It includes an outer 
annular liner portion 44 which will cover the primary seal lip and an 
inner annular liner portion 46 which covers the secondary seal lip. The 
web portions 42 should be at least two in number, but any suitable number 
may be used. The weakened liner section does not affect the flexibility of 
the otherwise all elastomeric flex section 28. However, since the web 
portions maintain the inner and outer annular liner portions as a single 
liner 40, the molding operation for the shaft seal can be as economically 
designed and performed as with the prior art design shown and described in 
connection with FIG. 1. 
FIG. 4 shows the mold used to produce a shaft seal in accordance with the 
present invention. It includes a lower die 48 and an upper die 50, each 
held firmly to respective relatively reciprocal mold members (not shown) 
by bolts 52 and 54 respectively. The lower die 48 includes an upper land 
56, a lower land 58 and an intermediate frustoconical portion 60 
therebetween. The upper die portion likewise includes an upper land 62, a 
lower land 64 and an intermediate portion 66 therebetween. The two 
intermediate portions 60 and 66 define the mold cavity and resulting seal 
lip configuration. 
At the beginning of the mold step, the cup shaped metal case member 30 is 
first placed on the lower land 58 of the lower die and the PTFE liner 40 
and an annular ring of prep material 69 (shown in phantom) is placed on 
the upper land 56 of the lower die in sequential order. The lower lands of 
each die member act to hold the metal case member in place throughout the 
closure of the mold by spring loaded rod members, not shown (or the like). 
The upper land 56 of the lower die member 48 may be provided with a series 
of serrations or teeth in order to grip the PTFE liner and hold it in 
place throughout the closure of the mold. Such an arrangement is shown in 
U.S. Pat. No. 4,464,322, assigned to the assignee of the present 
invention, the disclosure of which is incorporated herein by reference. 
As the mold is heated and closed, the elastomeric prep is softened 
considerably and caused to flow within the mold cavity from the upper 
lands towards the lower lands, bending and conforming the PTFE liner 40 to 
shape as it flows by virtue of the hydrodynamic force caused by the 
substantially liquid elastomer. 
Once the mold is completely closed and the elastomer has consequently 
completely filled the mold cavity, the elastomer is then cured. The seal 
is then cooled and the mold members opened and the seal thereafter lifted 
from the mold. It is conventional that a certain amount of flash will be 
left at the mold juncture defining the primary sealing lip. This flash is 
removed from the seal by slicing it with a knife. This basically completes 
the molding and trimming operation and produces the finished product. 
Alternative configurations for the polytetrafluoroethylene liner 40 can be 
provided, as shown in FIGS. 7a through 7d. For example, as shown in FIG. 
7a, the liner 40 can include a first inner annulus 70 and a radially 
outwardly extending weakened section formed by a series of narrow slots or 
slits 72 producing a plurality of liner web portions 74. 
Likewise as shown in FIG. 7b, there can be provided an inner annular 
portion 70 and an intermediate weakened section 76 formed by a series of 
triangular or trapezoidal web portions 78 extending radially outward 
therefrom. It is preferred that the depth of the cuts or cut out portions 
forming the web portion 78 be such that the uninterrupted inner annular 
liner portion will not extend beyond the axial extremities of the primary 
sealing lip. In other words, it is desirable that the PTFE material within 
the intermediate flex section 28 of the elastomeric seal body member 4 be 
maintained at a minimum. 
Another alternative embodiment is that shown in FIG. 7c wherein the outer 
annular liner portion is uninterrupted and the web portions 78 extend 
radially inwardly so that the primary seal lip will include a static 
sealing band that is alternately PTFE liner material and elastomeric 
material. 
Finally, in FIG. 7d, there is shown a fourth embodiment wherein the 
weakened material section of the liner includes an annular groove 80 
separating the inner and outer liner portion 46 and 44. The intermediate 
portion is of substantially reduced cross-sectional thickness thereby 
providing a great deal of flexibility between the inner and outer annular 
liner portions, as seen particularly in FIG. 8. 
Referring again to the embodiment shown in FIG. 7d and FIG. 8, the 
intermediate weakened material section 80 of reduced cross-section can be 
formed any number of ways, for example by removing the material, or 
coining it prior to the molding operation, or hydrodynamically coining it 
during the molding operation. 
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.