Bearing seal for sensing angular velocity

A seal for an antifriction bearing having a fixed inner race and a rotating outer race includes inner and outer seal cases which are pressed over cylindrical mounting surfaces on the inner and outer races, respectively. To this end, the seal cases have extended axial walls which actually fit over the mounting surfaces in the bearing races and radial walls, connected to the extended axial walls. The radial walls of the two cases are spaced apart so that an annular chamber exists between the two radial walls. Each seal case has an elastomeric seal element supported by its radial wall remote from its extended axial wall and that seal element establishes a fluid barrier along the other seal case, so that the two seal elements isolate the chamber from the interior of the bearing and from the environment at the exterior of the bearing. The inner case carries a sensor having a head that is located in the annular chamber between the two axial walls. The radial wall of the outer case carries means for exciting the sensor such that it produces a pulsating signal when the outer case rotates relative to the inner case, and the frequency of the signal reflects the angular velocity.

BACKGROUND OF THE INVENTION 
This invention relates in general to bearing seals and more particularly to 
seals which have the capacity to sense angular velocity. 
Antilock brake systems, which are found on many automotive vehicles of 
current manufacture, require devices at the wheels for sensing the angular 
velocities of the individual road wheels. On any vehicle so equipped, the 
speed sensing devices generate signals which are monitored by an 
electronic processor that in turn controls the braking forces applied to 
the wheels, the object being to keep all four wheels rotating at the same 
velocity, even though one of the wheels may be rolling over a surface that 
offers considerably less frictional resistance than the surface over which 
the others are rolling. Some automobiles also have traction control 
systems that minimize slip at the drive wheels and thereby maximize the 
tractive effect. These systems rely on speed sensing devices as well, and 
indeed when a vehicle is equipped with both an antilock braking system and 
a traction control system, the speed sensing devices at the drive wheels 
may serve both systems. 
The typical speed sensing device includes an encoder ring which rotates 
with the wheel to which the device is assigned and a sensor which monitors 
the encoder ring in the sense that it produces a pulsating electrical 
signal the frequency of which reflects the angular velocity of the ring. 
To this end, the ring, which is formed from a ferrous metal, has 
discontinuities in the form of teeth or apertures that disrupt a magnetic 
flux upon rotation of the ring. The sensor responds to the periodic 
disruptions and delivers a signal, the frequency of which is proportional 
to the angular velocity of the ring and vehicle wheel. In order for the 
sensor to operate effectively, the head of the sensor must be quite close 
to the rotating ring. 
While the typical sensing device is located in the region of the bearing 
for the wheel that it monitors, it still lies outside the sealed 
environment of the bearing which is often supplied as a package. As such, 
the sensing device is exposed to water and much worse corrosive road 
chemicals. It is also exposed to grit and to stone impingement. 
To be sure, others have placed encoder rings within the sealed environments 
of bearing packages. Indeed, where the inner races of the bearings rotate, 
as holds true at the front wheels for most front wheel drive automobiles, 
the bearing assemblies will accommodate speed sensing devices. Sometimes 
enough space exists between the two rows of rolling elements in such a 
package to accept an encoder ring which rotates with the inner races, 
while the outer races or housing in which the outer races fit accommodates 
the sensor. The sensor head, the encoder ring, and the gap which lies 
between them all exist within an environment isolated by seals which 
protect the raceways and rolling elements of the bearing. U.S. Pat. No. 
5,085,519 shows such an arrangement. 
But when the outer races of the bearing assemblies rotate around stationary 
inner races, as holds true for some designs used at the nondriven front 
wheels of rear wheel drive automobiles, the bearing assemblies do not 
easily accept a sensing device. The problem resides in mounting the sensor 
and accommodating its electrical leads. Relatively little space exists in 
the sealed environment for the somewhat bulky sensor, and the spindle must 
undergo additional machining to provide bores for the leads. For this 
reason, in most bearing assemblies which have both rotating outer races 
and sensing devices, the sensors are located outside of the bearing 
assemblies. In this regard, see U.S. Pat. Nos. 4,884,901 and 4,795,278. 
While others have attempted to incorporate the sensing devices into the 
seals, the arrangements are cumbersome and diminish the effectiveness of 
the seals. Moreover, the sensors are arranged such that they are not 
easily removed and replaced. 
The present invention resides in a seal which contains a speed sensing 
device, with the encoder ring and the head of the speed sensing device 
being located in a region isolated from the surrounding environment by the 
seal. Moreover, the seal has excellent sealing characteristics and 
accommodates the sensing device such that the sensing device does not 
significantly enlarge the bearing assembly or render it unacceptable for 
traditional bearing mountings. The seal comes preassembled, and is 
designed for use in preassembled bearing packages where the air gap 
between the encoder ring and the sensor head of the seal are preset. Yet 
in several embodiments the sensor may be removed quite easily from the 
seal, should it require replacement.

DETAILED DESCRIPTION 
Referring now to the drawings, A (FIG. 1) designates an antifriction 
bearing which couples a road wheel B of an automotive vehicle to a spindle 
C that is attached to and projects from the suspension system of the 
vehicle, all to enable the road wheel B to rotate about an axis X of 
rotation which is of course the axis of the spindle C. The bearing A is 
fitted with seals D and E at its inboard and outboard ends, respectively, 
to isolate its interior from the surrounding environment. The inboard seal 
D further produces a signal which reflects the angular velocity of the 
wheel B--indeed, a wheel speed input signal for enabling the effective 
operation of an antilock braking system or a traction control system. 
The bearing A includes (FIG. 1) an outer race in the form of a double cup 
2, an inner race in the form of two cones 4 and 6, and rolling elements in 
the form of tapered rollers 8 arranged in two circular rows between the 
cup 2 and the two cones 4 and 6. At its outboard .end the cup 2 has an 
outwardly directed flange 10 to which the wheel B is bolted. At its 
inboard end, it has a machined cylindrical surface 12 which faces 
outwardly and an annular groove 13 which opens out of the surface 12 near 
its end. The cup 2 also has two raceways 14 which taper downwardly from 
its ends to its midportion. The two cones 4 and 6 lie essentially within 
the cup 2 and fit over the spindle C, to which they are clamped such that 
they cannot shift axially. Each cone 4 and 6 has an outwardly presented 
raceway 16 that is tapered and a thrust rib 18 which projects radially 
outwardly beyond the large end of the raceway 16. The thrust rib 18 has a 
cylindrical surface 20 which runs out to the end of its cone 4 or 6, that 
is, to the so-called cone back face against which the clamping force is 
applied. The two cones 4 and 6 abut at their opposite ends, that is, at 
their front faces, and when so arranged, their raceways 16 lie within and 
face the raceways 14 of the cup 2. The cone raceways 16 likewise taper 
downwardly toward the midportion of the bearing A where the two cones 4 
and 6 abut. The rollers 8 lie in circular rows between the opposed 
raceways 14 and 16 of the cup 2 and the cones 4 and 6, with their tapered 
side faces contacting the raceways 14 and 16. The large end faces of the 
rollers 8 bear against the thrust ribs 18 for the cones 4 and 6, and 
indeed, the ribs 18 prevent the rollers 8 from being expelled from the 
annular space between the cup raceways 14 and the cone raceways 16, that 
is from the interior of the bearing A. 
The seal D fits around the cup 2 and the thrust rib 18 of the inboard cone 
to close one end of the annular space between the cup and cone raceways 14 
and 16. The seal E fits into the outboard end of the cup 2 and around the 
thrust rib 18 of the outboard cone 6, closing the other end of the annular 
space that exists between the raceways 14 and 16. Thus, the seals D and E 
isolate the annular interior of the bearings A from the surrounding 
environment. 
The inboard seal D includes (FIG. 2) an outer seal case 26 formed from 
steel as a stamping. It has an extended axial wall 28 which fits over the 
cylindrical surface 12 at the inboard end of the cup 2, there being an 
interference fit between the wall 28 and surface 12. The surface 12 thus 
provides a mounting for the outer case 26, and the case 26 establishes a 
static fluid barrier at the surface 12. Initially, the axial wall 28 forms 
a continuous cylinder, but once the wall 28 is fitted over the surface 12, 
a short section of the wall 28 is rolled inwardly into the groove 13 of 
the cup 2, to produce an annular locking segment 29 which mechanically 
unites the outer case 26 and cup 2. The axial wall 28 projects beyond the 
end of the cup 2, and at a bend merges into a short axial wall 30 which 
extends back toward the end face of the cup 2. The short axial wall 30 
lies within the extended wall 28 and at its opposite end merges into a 
radial wall 32 which extends radially inwardly toward the thrust rib 18 of 
the inboard cone 4, terminating at an inner margin located slightly 
outwardly from the cylindrical surface 20 on the rib 18. The portion of 
the radial wall 32 that lies nearest to the short axial wall 28 abuts the 
end face of the cup 2, thereby locating the outer case 26 axially with 
respect to the cup 2. The remaining portion of the radial wall 32, which 
lies inwardly from the end face of the cup 2, contains elongated apertures 
34 arranged in a circular row at equal circumferential intervals, with 
their major axes directed radially, that is to say radially with respect 
to axis X to which the circular row is concentric (FIG. 3). The apertures 
34 form discontinuities in the wall 32. 
The seal D also has an inner case 36 (FIG. 2) that includes an extended 
axial wall 38 which fits over the cylindrical surface 20 on the thrust rib 
18 for the inboard cone 4. As such, it lies immediately inwardly from the 
radial wall 32 of the outer case 26. An interference fit exists between 
the axial wall 38 and the cylindrical surface 20 of the rib 18, so the 
cylindrical surface 20 provides a mounting for the inner case 36 and 
establishes a static fluid barrier along it. At its end closest to inboard 
row of rollers 8, the wall 38 turns outwardly in the form of a slight 
radial lip 40 that serves to unitize the seal D. At its opposite end the 
axial wall 38 merges into a radial wall 42 which projects outwardly from 
the thrust rib 18, generally flush with the back face of the cone 4. But 
the radial wall 42 terminates short of the axial walls 28 and 30 on the 
outer case 26, and indeed merges into a short axial wall 44 which is 
directed toward the radial wall 32 of the outer case 26. The axial wall 44 
lies partially within the short axial wall 30 of the outer case 26, but 
its free end is spaced from the radial wall 32 of the outer case 26. 
The two cases 26 and 36 are configured and positioned such that their 
respective radial walls 32 and 42 are spaced from each other, and these 
walls coupled with the axial walls 30, 38 and 44 of the two cases 26 and 
36 enclose an annular chamber 46. The radial wall 42 of the inner case 36 
has a circular opening 48 (FIG. 4) which opens into the chamber 46. 
In addition to the two cases 26 and 36, the seal D has an inner seal 
element 50 (FIG. 2}which is formed from an elastomer and thus possesses a 
measure of flexibility. The inner seal element 50 is bonded to the radial 
wall 32 of the outer case 26, with the region of bonding taking the form 
of a flat annular segment 52 which extends outwardly beyond the row of 
apertures 34, so that the elastomer completely fills the apertures 34 and 
renders the wall 32 impervious. At the inner margin of the radial wall 32 
the inner seal element 50 flares axially, taking the form of a pumping 
labyrinth 54 having a cylindrical surface 56 which lies around, but is 
spaced slightly away from the extended axial wall 38 of the inner case 36. 
The labyrinth 54 also has a front face 58 which is presented toward the 
lip 40 on the inner case 36. The labyrinth 54 contains pumping cavities 60 
which open out of the cylindrical surface 56 and the front face 58, 
interrupting the edge at which those surfaces intersect. The side surfaces 
of the cavities 60 lie oblique to the direction of relative movement 
between the pumping labyrinth 54 and the extended axial wall 38 on the 
inner case 36 so as to direct any lubricant that enters the cavities 60 
back toward the lip 40 and the interior of the bearing A. The seal element 
50 also includes a contact lip 62 which projects generally axially away 
from the labyrinth 54 toward the radial wall 42 of the inner case 36, yet 
considerable space remains between the end of the lip 62 and the radial 
wall 42. The lip 62 has converging surfaces which meet at an edge where 
the lip 62 contacts the extended axial wall 38 of the inner case 36. 
Indeed, immediately behind the edge 64, the lip 62 has a groove which 
contains a garter spring 66 that urges the lip 62 toward the axial wall 38 
to ensure that the edge 64 remains in contact with the wall 38. Thus, the 
pumping labyrinth 54 and contact lip 62 establish fluid barriers along the 
extended wall 38 of the inner case 36. 
Another fluid barrier exists between the short axial wall 30 of the outer 
case 26 and the short axial wall 44 of the inner case 36, it being 
established by an elastomeric outer seal element 68 (FIG. 2) which is 
carried by the axial wall 44. The seal element 68 includes a base 70, 
which is bonded to the inside and outside faces of the wall 44 as well as 
along its end edge, and a lip 72 which projects from the base 70, first 
radially toward the short axial wall 30 of the outer case 26 and then 
obliquely away from the radial wall 32 of the inner case 26. The obliquely 
directed portion of the lip 70 contacts the short axial wall 44 of the 
outer case 26. Being formed from an elastomer, the lip 70 possesses a 
measure of flexibility. 
Apart from closing the annular space between the cup 2 and the inboard cone 
4, the seal D carries a sensor 74 (FIGS. 2 & 4) which reacts to the 
rotation of the outer seal case 26 with the cup 2 and wheel B, 
specifically to the disruption in a magnetic flux--a disruption which 
results from the apertures 34 in the radial wall 32 of the inner case 26 
moving past the sensor 74. Discontinuities other than apertures may also 
serve to stimulate the sensor 74. For example, circumferentially spaced 
ridges or alternating pole--no pole or alternating north--south poles on 
the radial wall 32 will create the necessary disruptions in the flux. 
Several varieties of sensing devices have the capacity to sense 
discontinuities, whether those discontinuities be apertures or ridges or 
alternating magnetic poles, and the sensor 74 may operate on the principle 
utilized by any of those types. Irrespective of the principle of 
operation, the sensor 74 has a head 76 which projects from a flange 78 and 
contains a ferromagnetic core which terminates at an end face 80. When the 
head 76 contains only a single core, it is preferably cylindrical in 
configuration, but when it has two cores, it preferably takes on an 
elongated configuration. The head 74 projects through the opening 48 and 
into the sealed chamber 46 where the end face 80 of its core is presented 
toward the radial wall 32 of the outer case 26--indeed, toward the ring of 
apertures 34 in the wall 32. Yet a small air gap exists between the face 
78 and the radial wall 32. The flange 78 fits snugly against the radial 
wall 32 or a gasket or seal may be interposed between it and the wall 42. 
The sensor 74 is secured to the inner case 36 by two machine bolts 82 (FIG. 
5) which pass through the flange 78 of the sensor 74, through the radial 
wall 42 of the case 36, and into an arcuate retainer 84 (FIG. 6) that is 
located within the chamber 46. Actually, the bolts 82 thread into inserts 
86 that are embedded within the retainer 84, and between the two inserts 
86, the retainer 84 has a cylindrical hole 88 which aligns with the 
opening 48 in the case 36 and receives the head 76 of the sensor 74. 
Preferably the inserts 86 are made from metal, and the remainder of the 
retainer 84 is molded from a polymer. 
The retainer 84 does not lie loosely in the chamber 46. On the contrary, 
its radial dimension is essentially that of the spacing between the two 
axial walls 38 and 44 of the inner case 36, so the sensor 74 fits snugly 
between those walls. Thus, the axial walls 38 and 44 resist torque applied 
to the bolts 82. Furthermore, the retainer 84 is actually bonded to the 
inner case 36 with the elastomer from which the outer seal element 68 is 
formed. To this end, the base 70 of the outer seal element 68 extends 
along the inside face of the axial wall 44 for the inner case 36 and is 
bonded to the exposed face of the retainer 84, forming pads 90 on each 
side of the hole 88. More of the elastomer exists in bands 92 formed along 
the edges at the opposite face, indeed within rabbets along those edges. 
And while all of the bands 92 are bonded to the retainer 84, the outer 
bands 92 are bonded to the short axial wall 44 and radial wall 42 of the 
inner case 36, whereas the inner band 92 is bonded to the extended axial 
wall 38 and radial wall 42 of the case 36. Still more of the elastomer is 
bonded to the surface of the hole 88 where it forms a gasket 94 having an 
inner diameter slightly less than the diameter of the head 76 for the 
sensor 74. Actually, the gasket 94 extends axially beyond the cylindrical 
hole 88 in the retainer 84 and also lines the opening 48 in the radial 
wall 42 of the inner seal case 36, it being bonded to the radial wall 42 
as well. The head 76 of the sensor 74 fits snugly into the gasket 94 which 
effects a fluid-tight seal between the head 76 and the retainer 84 and 
inner case 36. 
Finally, the sensor 74 beyond its flange 78 has an electrical cable 96 
extended from it. Through the cable 96 signals reflecting the angular 
velocity of the outer case 26 pass to an electronic processor. 
To install the sensor 74 on the inner case 36, one simply aligns its head 
76 with the gasket 94 that lines the opening 48 in the case 36 and the 
cylindrical hole 88 in the retainer 84 and urges the head 76 through the 
gasket 94 until the flange 78 comes against the radial wall 42. The bolts 
82 are fitted through the flange 78 on the sensor 74 and threaded into the 
metal inserts 86 in the retainer 84. The sensor 74 is removed from the 
seal case 36 as easily as it is installed. The ease of installation and 
removal facilitate replacement of the sensor 74 after the bearing is 
placed in service, all without any further disassembly of the bearing A. 
The seals D and E come with the bearing A which they serve to unitize, thus 
enabling the bearing A to be sold as a preassembled package. To install 
the seal D, which itself is unitized by its lip 40, on the bearing A, the 
extended axial wall 28 of the outer case 26 is pressed over the 
cylindrical surface 12 of the cup 2, while the extended axial wall 38 of 
the inner case 36 is concurrently pressed over the cylindrical surface 20 
on the thrust rib 18 of the inboard case 4. The advancement of the outer 
case 26 over the cup 2 ends when its radial wall 32 abuts the end of the 
cup 2. The inner case 36 is advanced over cone thrust rib 18 to a position 
which will provide a proper gap between the end face 80 of the sensor 74 
and the radial wall 32 of the outer case 26. The sensor 74 may be on the 
inner case 36, when it is pressed over the thrust rib 18 or it may be 
installed afterwards. In any event, once the outer and inner cases 26 and 
36 reach the proper positions on the cup 2 and cone 4, the axial wall 28 
of the outer case 26 is rolled inwardly opposite the groove 13 in the cup 
2 to create the annular locking segment 29 which unites the outer case 26 
with the cup 2. 
In operation, the outer case 26 and its seal element 50 rotate with cup 2 
which is attached to the road wheel B. The inner case 36 and its seal 
element 68, on the other hand, remain fixed in position on the inboard 
cone 4 which in turn is on the spindle C, it being clamped firmly on the 
spindle C with the outboard cone 6. The spindle C, of course, is fixed in 
the sense that it does not rotate about the axis X. The head 76 of the 
sensor 74 produces a magnetic flux which passes through the radial wall 32 
of the outer case 26 in the region of the apertures 34 in that wall. Being 
nonuniform in the region of its apertures 34, the ferrous radial wall 32 
disrupts the magnetic flux as the wall 32 rotates, and the sensor 74 
delivers, through the leads of the cable 96, a pulsating or sinusoidal 
signal, the frequency of which is proportional to the angular velocity of 
the outer case 26. Actually, the radial segments between the apertures 34 
in the rotating radial wall 32 cause changes in the magnetic flux, and the 
sensor 74 detects these changes, producing a pulsating signal. Other forms 
of discontinuities may be used to excite the sensor 74 as well. For 
example alternating ridges and valleys will serve that purpose as will 
alternating magnetic poles. 
Since the air gap is located within the chamber 46, it is isolated from the 
surrounding environment which at times can be quite severe. As such, the 
head 76 of the sensor 74 does not see a continuous spray of moisture 
during inclement weather, nor is it subject to attack from road chemicals 
used to thaw ice. Moreover, sand and grit cannot lodge in the air gap and 
perhaps damage the sensor 74 or the encoder ring formed by the radial wall 
32 of the inner seal case. 
Should the sensor 74 fail to function properly, it is easily removed and 
replaced, since only the two bolts 82 hold it in place, and they are 
easily withdrawn. 
Despite the presence of the sensor 74, the seal D remains quite 
compact--and the same holds true with regard to the packaged bearing A. 
The seal D, with its pumping labyrinth 54 and contact lip 62 on the inner 
seal element 50 and its lip 72 on the outer seal element 68, provides 
highly effective barriers which prevent lubricant from leaving the 
interior of the bearing A and contaminants from entering. 
A modified seal F (FIG. 7) is very similar to the seal D, particularly 
insofar as its outer case 26, inner case 36 and seal elements 50 and 68 
are concerned. However, the outer case 26, at the end of its extended 
axial wall 28 has an outwardly directed ring 100 which facilitates 
stripping the case 26 from the cylindrical surface 12 over which its axial 
wall 28 fits. On the other hand, the extended wall 38 of the inner case 
36, beyond the inner seal element 50 contains an offset 102 which 
positions that portion of the axial wall 38 away from the cylindrical 
surface 20 of the cone thrust rib 18. The radial wall 42 of the inner case 
36 contains a similar offset 104, and indeed the extended axial wall 38 
and the radial wall 42 merge at their respective offsets 102 and 104. Here 
the two walls 38 and 42 have an elastomeric drive element 106 bonded to 
them. When unrestrained the drive element 106 projects radially inwardly, 
slightly past the inner surface of the remainder of the axial wall 38, and 
here it presents an undulating surface. Indeed, as the inner case 36 is 
advanced over the thrust rib 18, the drive element 106 is compressed 
between the offset 102 in the wall 38 and the cylindrical surface 20 of 
the rib 18. As such the drive element 106 increases the friction between 
the inner seal case 36 and the cone rib 18, thereby further assuring that 
the case 36 will not rotate on the rib 18. 
Apart from that, the radial wall 42 is solid throughout, and as such is 
completely devoid of openings. The short axial wall 44, however, in the 
region beyond the bend that represents the merger of the two axial walls 
28 and 30 in the outer case 26 contains an aperture 108. The outer seal 
element 68 at the free end of the short axial wall 44 on the inner case 36 
is molded integral with a grommet 110 that occupies the aperture 108 and 
with a carrier 112 that encapsulates a sensor 114 having an end face 116 
that is presented toward the radial wall 32 of the outer case 26--indeed, 
toward the ring of apertures 34 in that case. The outer seal element 68, 
the grommet 110, and the carrier 112 are all united into a single 
elastomeric molding which is bonded to both the inside and outside faces 
of the short axial wall 30 and to the inside face of the radial wall 42. 
Another modified seal G (FIGS. 8 & 9) also closely resembles the seal D. 
However, the radial wall 32 of its outer case 26 contains no apertures 34 
and thus does not constitute an encoder ring. Instead, it carries an 
encoder ring 120 which projects axially from the radial wall 32 into the 
annular chamber 46 so as to lie close to the short axial wall 44 of the 
inner case 36. The ring 120 has teeth 122 (FIG. 9) which project axially, 
giving a serrated configuration to the ring 120. 
The inner case 36, on the other hand, carries an annular sensor 124 which 
is likewise located in the annular chamber 46. It includes a coil 126 
which lies along the radial wall 42 of the inner case 36, its windings 
extending circumferentially, and a ferrous block 128 that encircles the 
contact lip 62 of the inner seal element 50 and lies within encoder ring 
120. The block 128 carries an annular magnet 130 which has alternating 
north and south poles and is presented toward the teeth 122 of the ring 
120, there being an air gap between the two. The coil 126 has leads which 
are contained within a cable 96 that passes through the inner case 36 at 
its short axial wall 44. 
When the cup 2 and outer seal case 26 rotate, the encoder ring 120 revolves 
around the magnet 130 and the teeth 122 disrupt the magnetic field 
produced by the magnet 130. The disruption is such that it induces an 
alternating current voltage across the leads of the coil 126 and that 
voltage has a frequency which is proportional to the angular velocity of 
the cup 2 and thus provides an accurate reflection of that angular 
velocity. 
In the seal G, the size of the air gap does not depend on the relative 
axial positions of the two seal cases 26 and 36, so the case 36 for the 
seal G may be positioned with less precision than the corresponding seal 
cases 36 on the seals D and F. 
Still another modified seal H (FIGS. 10 & 11) fits a slightly modified 
bearing assembly I. The seal H also resembles the seal D. However, the 
extended axial wall 28 of its outer case 26 merges directly into the 
radial wall 32, there being no axial projection of the extended wall 28 
with a return in the form of a short axial wall 30. The extended axial 
wall 28 at its opposite end has an outwardly directed ring 100 to 
facilitate stripping the outer case 26 for the cup 2. 
The inner case 36, on the other hand, has its radial wall 42 extended 
outwardly beyond the extended axial wall 28 of the outer case 26 so that 
its short axial wall 44 has a diameter greater than the extended axial 
wall 28 of the outer case 26. The outer seal element 68, while being 
bonded to the free end of the short axial wall 44, takes on a slightly 
altered configuration. It has a lip 140 which projects obliquely inwardly 
toward the extended axial wall 28 of the outer case 26 and contacts that 
wall along its outwardly presented surface. 
This invention is intended to cover all changes and modifications of the 
example of the invention herein chosen for purposes of the disclosure 
which do not constitute departures from the spirit and scope of the 
invention.