Note: Descriptions are shown in the official language in which they were submitted.
Description
Pressure Balanced - Constant
Engagement Force Seal
Technical Field
This invention relates to sealing between
large diameter, relatively rotatable members and, more
particularly, to a pressure balanced, constant engage-
ment force seal arrangement.
Background Art
In earthmoving equipment and other apparatus
having large relatively rotatable structures, seal
arrangements are often utilized to retain lubricant or
coolant within the apparatus and prevent intrusion
between the structures of debris and foreign particles.
Effective sealing between relatively rotatable struc-
tures is necessary to avoid incurring expense in re-
placing the lubricant or coolant and prev~nt equipment
damage caused by intruding debris.
In the past notable success has been attained
in sealing between stationary and rotatable structures
through the use of two relatively rotatable metallic
seal rings which are urged axially together by a pair of
elastomeric torics which are arranged between a ro-
tatable seal ring and the rotatable structure and also
between a stationary sealing ring and the stationary
structure. Each of the torics engaged a seal ring and
its cooperating structure along ramped surfaces which
provided a force for biasing the seal rings together at
an interface between a pair of sealing faces, one being
associated with each seal ring. Examples of such dual
seal rings being biased together by a pair of elasto-
meric torics include U.S. Patent 4,077,634 which issued
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9~'90
to Durham on March 7, 1978, U.S. Patent 3,540,743 which
issued to E. Ashton on No~ember 17, 1970, and U.S-
Patent 3,136,389 which issued to C.F. Cummins on June 9,
1964, all of which are assigned to the assignee of the
present invention. Such seal rings have typically been
made entirely of a high grade steel alloy known in the
trade as Stellite. While the aforementioned seals have
performed admirably on relatively small diameter sealing
applications such as track rollers for crawler tractors,
larger diameter sealing rings of nearly two feet in
diameter, such as are used for sealing the wheel and
brake mechanisms on large off-highway trucks, have a
less favorable sealing history.
The large diameter elastomeric toric-biased
metal seal rings sometimes warp and prevent closure
therebetween as a result of distortion mechanisms not
fully understood. Other sets of seal rings are some-
times adversely affected by heat which caused their
deformation to an out of round configuration and reduced
the seal's effectiveness. The ramped biased surfaces on
such seal rings are believed to provide some variation
in the seal face load as the seal rings move axially
such as when the seal faces wear.
patent 4,077,634 is directed toward main-
taining a constant load on the seal faces and does so
remarkably well for small and medium size seal rings.
However, for large seal rings the face loading becomes
more variant. Additionally, force balancing of the seal
rings is difficult to achieve since the resilient torics
which provide the biasing force engage xamped seal ring
surfaces which have axial surface components. As such,
the axial surface components on opposite ends of the
seal rings are not usually uniformly exposed during
movement of the torics so as to cause the sealing force
to be affected by fluid pressure directed against those
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surfaces. Also, if, during assembly, the large torics
are not precisely positioned or are not accurately
manufactured, more or less axial area on the seal rings
become exposed to fluid pressure and thus cause the seal
rings to be unbalanced as regards fluid pressure directed
against them.
U.S. Patents 2,814,513 and 2,710,206 which
were issued November 26, 1957, and ~une 7, 1955, re-
spectively, include axial biasing means for forcing the
seal rings into axial engagement with a nonconstant
force. U.S. Patent 2,814,513 utilizes a coil spring
while U.S. Patent 2,710,206 utilizes an elastomeric O-
ring for providing the axial engagement force. Neither
of the aforementioned seal biasing means provides a
substantially constant sealing force nor are the seal
arrangements pressure balanced. Such designs perform
satisfactorily for relatively small applications such as
track rollers for endless track on crawler tractors.
U.S. Patent 4,212,475 which issued July 15,
1980, illustrates a seal arrangement in which an elasto-
meric toric is disposed between two radially facing
surfaces, one of which is on a seal ring. Application
of a precise sealing force on the seal rings is diffi-
cult since the sealing force is provided by a spring
having a force level dependant on its deformation. The
problems encountered in applying a precise sealing force
are accentuated by fluid pressure forces acting non-
uniformly on the seal rings since such seal ring is not
pressure balanced.
For large diameter applications the afore-
mentioned seal arrangements have at least one of the
following disadvantages; lack pressure balancing for
seal ring moVement; have a biasing means whose force
varies with the position of the seal rings; and have
biasing means for urging the seal faces together which
is affected by fluid pressure exerted thereon.
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Summary of the Invention
In accordance with the present invention, a
seal arrangement is provided for sealing between first
and second relatively rotatable structures, the second
relatively rotatable structure having a radially facing
seal surface, wherein the seal arrangement has a first
and a second annular seal ring respectively having
first and second axially opposably disposed engageable
sealing face portions, the second seal ring having a
radially facing seal surface, a first axially facing
surface, and a second axially facing surface opposably
arranged relative to and having a smaller axial area
than said first axially facing surface; means for
sealing between the second seal ring and the second
relatively rotatable structure, the sealing means being
in exclusive contact with the radially facing seal
surfaces and having a pressure balancing surface which
is in fluid communication with the first and second
axially facing surfaces, a portion of the pressure
balancing surface acting in concert with the second
axially facing surface to counterbalance the axial
force exerted on said first axially facing surface by a
fluid; and means for axially biasing the second seal
ring toward the first seal ring with a substantially
constant force for axial movements of the second seal
ring within a predetermined range.
By providing a seal ring which is pressure
balanced for practical axial operational positions and
a sealing force which is substantially constant for
varying axial displacements of the engaged seal rings,
a precise sealing force can be applied so as to obtain
an effective, highly reliable seal.
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Brief Description of the Draw~
The invention will be more fully understood
from the following detailed description of a preferred
embodiment, taken in connection with the accompanying
drawing, in which Fig. 1 is a transverse vertical
section of an embodiment of the present invention seal
arrangement illustrated in a disc brake assembly from
an off-highway truck.
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Best Mode for Carrying Out the Invention
The present invention is concerned primarily
with sealing between lar~e diameter, relatively ro-
tatable structures. Accordingly, in the description
which follows, the invention is shown embodied in a disc
brake arrangement 10 whlch is typically found in large,
off-highway trucks. It should be understood, however,
that the invention may be utilized as a sealin~ arrange-
ment for relatively rotatable structures in any device.
Referring now to the drawing in detail, disc
brake arrangement 10 includes a rotatable drive train
structure 12 and a stationary foundation structure 14.
While only one half of the disc brake arrangement 10 is
shown, it is to be understood that such arrangement is
actually annularly disposed about an axis of rotation 16
which symbolizes the center line of a vehicle axle (not
shown). All surfaces and directions hereinafter de-
scribed will be related to the axis of rotation 16.
Drive train structure 12 includes a radially
arranged wheel rim 18 and brake disc support portion 20,
which is axially adjacent rim 18. The brake disc
support portion 20 is joined for rotation with wheel rim
18 by a plurality of teeth 26 which are integral with
disc support portion 20 and which mesh with internal
spline 28 which is integral with wheel rim 18.
plurality of brake discs 30 are each keyed on a plural-
ity of external teeth 32 which extend radially outwardly
from disc support portion 20.
Stationary foundation structure 14 constitutes
a connecting shell 34 which has a plurality of radially
directed internal teeth 36 formed thereon and a plurality
of brake plates 38 which are interleaved with annular
brake discs 30 and keyed to internal teeth 36.
~ seal arrangement 40 cooperates with the
drive train structure 12 and foundation structure 14 to
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seal coolant in a space 42 defined thereamong. A supply
of such coolant is circulated through the interleaved
brake discs and plates 30 and 38, respectively, to cool
the same. The drive train structure 12 and foundation
structure 14 respectively include a first and a second
seal retainer structure 44 and 46 which are respectively
joined to wheel rim 18 and the stationary connecting
shell 34 by a plurality of threaded fasteners such as
capscrews 47. The second or stationary retainer struc-
ture 46 includes an end plate 48 and a seal retainer 50
which is connected to end plate 48 by a plurality of
threaded fasteners 52 (only one of which is shown~.
Seal retainer 50 has a radially inwardly facing seal
surface 54 and a radially outwardly facing surface 56
which is sealed to end plate 48 by an O-ring 58 which is
placed in an annular notch 60 formed on the radial
interior of annular end plate 48. End plate 48 has a
radially inwardly facing assembly surface 57 which is
radially separated from seal surface 54. The seal
surface 54 intersects with a retaining ramp surface 55
which extends, at a predetermined angle, toward axis 16
for reasons to be later discussed.
Seal arrangement 40 includes first and second
annular seal rings 62 and 64 which are respectively
sealed to the rotatable seal retainer structure 44 and
the stationary seal retainer 50 by an O-ring 66 and
elastomeric toric 68. The annular seal ring 64 has a
radially inwardly facing inner periphery 64a and a
radially outwardly facing outer periphery 64b coaxially
arranged relative to the axis of rotation 16. The
rotatable seal ring 62 has an axially facing sealing
face portion 70 while stationary seal ring 64 has an
axially facing sealing face portion 72 which is axially
engageable with sealing face portion 70. Sealing face
portions 70 and 72 preferably constitute hard facing
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alloys from the Aerospace Material S~ecification 4775B
such as Co].monoy 6 or Haynes Stellite 43 as they are
commonly known in the trade. Such material is metal-
lurgically bonded to the body portions 74 and 76 of seal
rings 62 and 64, respectively. Each of the seal ring
body portions 74 and 76 make up the major portion of the
seal rings and is a readily available material which is
commonly joined to other materials and constitutes, by
example, ordinary low carbon steel. The seal ring 62
includes a first axially facing surface 78 and an
opposably arranged, smaller second axially facing
surface 80 while the seal ring 64 has a first axially
facing surface 82 which extends radially to the seal
face portion 72 and a second axially facing surface 84
which is smaller in area than and opposably arranged
relative to the axially facing surface 82. The outer
periphery 64b of the seal ring 64 further includes a
radially outwardly facing seal surface 86 which is
juxtaposed relative to radially inwardly facing seal
surface 54 of stationary seal retainer 50 and is in
concentric relationship therewith. The sealing surface
86 intersects with a retaining ramp surface 89 which
extends, at a predetermined angle, away from axis 16.
Elastomeric toric 68 constitutes a vulcanized
rubber material which is in exclusive contact with the
radially facing seal surfaces 54 and 86. Toric 68 has
an outside diameter of about 21 inches by example and an
exemplary diametral thickness of 1/2 inch which is
compressed approximately 25~ when it is assembled in the
illustrated position. The compression of toric 68
increases the frictional engagement between it and
seal ring 64 and between it and seal retainer 50 so as
to prevent relative circumferential movement thereamong.
Axial mo~ement of seal rin~ 64 is accommodated by a
rolling motion of toric 68 about its circular center
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line 68a. Such rolling produces a substantially zero
axial force component on the seal xing 64.
A Belleville spring 88 having a first axially
facing surface 88a and a second axial facing surface 88b
is disposed axially between surface 84 and a retainer
surface 90 which extends substantially radially inwardly
and is a part of end plate 48. A plurality (preferably
at least three) of retaining tabs 91 are joined to the
axially facing surface 84 at selected circumferential
positions at or near the inner periphery 64a of the seal
ring 64. Axial surfaces 88a and 88b are in respective
contact with surfaces 84 and 90. The Belleville spring
88 is stressed during assembly of seal arrangement 40
preferably to at least a radial configuration where its
force level is substantially constant (varies only about
25% for axial spring positions within a range of 0.160
inches. Although only a single Belleville spring 88 is
illustrated, it is to be understood that a plurality of
such Belleville springs can be grouped together to
provide the desired constant force effect. By judiciously
choosing the maximum axial operational displacement of
seal ring 64, at least one belleville sprlng 88 can be
designed to operate in that displacement range with
substantially constant force application.
A plurality of openings, only one of which is
indicated by the reference numeral 92, extend from the
radially inwardly facing periphery 64a to the radially
outwardly facing periphery 64b of seal ring 64 so as to
provide fluid communication and thus pressure trans-
mission to a cavity 94 defined by the stationary struc-
ture 46, elastomeric toric 68, seal xing 64, and Belle-
ville spring 88. Since the coolant communicates with
both axial sides of Belleville spring 88, that spring is
pressure balanced so as to be unaffected by any changes
in pressure occurring in the coolant. A portion of the
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g
axial load (one-half) exerted by the coolant on a
pressure balancing surface 96 of torie 68 is transmitted
to seal ring 64 so as to act in concert with the axial
foree exerted by the eoolant on axially faeing surface
84 to counterbalance the foree exerted on axially faeing
surfaee 82. Such eounterbalaneing makes seal ring 64
pressure balaneed, and, thus, insensitive to pressure
ehanges in the eoolant whieh ean result from varying
operating conditions and temperatures.
A pair of annular notches 98 and 100 are
individually formed in juxtaposed radially facing
surfaces of seal ring 62 and retainer ring 44, respec-
tively, so as to cooperatively form an enclosure within
which O-ring 66 is housed. As can be seen, an axially
facing side lOOa of notch 100 is radially larger than an
axially facing side 98a of noteh 98 and an axially
facing side 98b of notch 98 is radially larger than an
axially facing side lOOb of notch 100. Such structure
restrains O-ring 66 within the cooperating notehes and
faeilitates assembly of retaining ring 44 and sealing
ring 62 into a eonfiguration whieh is relatively stiff
and amenable to subassembly.
The seal surfaee 54 whieh is engaged with the
sealing torie 68 and the assembly surface 57 whieh is in
elosely spaeed relation with the Belleville spring 88
are radially separated to faeilitate assembly through
the use of a two eomponent stationary strueture 46 and
to provide greater flexibility in separately designing
the sealing torie 68 and belleville spring 88. While
surfaees 78,80,82,84,88a, and 88b have been referred to
as axially faeing surfaees, it is to be understood that
sueh surfaees need not entirely faee the axial direetions
to fall within the seope of the present invention. It
is only neeessary for the heretofore deseribed axially
faeing surfaees to have an axial surfaee eomponent to
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come within the present invention's purview. Such axial
surface components will provide the present invention
with the hereafter described features when those surface
components conform to the limitations set forth herein.
Radially facing surfaces 54 and 86 must, however, be
true radial surfaces ha~ing no axially facing surface
components.
Industrial ~pplicability
The seal arrangement 40 provides a highly
effective and reliable seal for large diameter appli-
cations such as those having a diameter of ten inches or
more. O-ring 66 frictionally links and seals rotatable
seal ring 62 to retainer ring structure 44 so as to
cause simultaneous rotation thereof. The sealing face
portions 70 and 72 of the respective seal rings 62 and
64 are lapped according to well known machining pro-
cedures which facilitate sealing between the two en-
gageable sealing faces. Since the body portions 74 and
76 of the seal rings, by example, constitute upwards of
90~ of the seal rings' weight and volume, the relatively
expensive alloying material which is needed only for the
sealing face portions 70 and 72 is minimized. In
addition to the body portions 74 and 76 being less
costly, the composite seal rings' utilizing body and
seal face portions are more rigid and more easily
machined than seal rings made entirely of the sealing
face portions' material.
The elastomeric toric 68 may, since it contacts
only the radially facing surfaces 54 and 86, roll about
its circular center line 68a and move in an unrestrained
manner in either axial direction for axial movements of
the seal ring 64 during its assembly and operation. Due
to its propensity to roll, the toric 68 provides sub-
stantially no biasing force in the axial direction on
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such engaged seal ring 64. The toric 68 has an axially
facing surface 96 which, when exposed to fluid pressure,
contributes to the axial force acting on the engaged
seal ring 64 in an axial direction tending to engage the
seal face portions. Axially facing surfaces 82 and 84
on the engaged seal ring 64 act, when exposed to fluid
pressure, to provide a net force in a direction tending
to disengage the sealing face portions 70 and 72. Such
net force is exactly counterbalanced by the pressure
induced axial force exerted on the seal ring 64 by the
elastomeric toric 68. When the elastomeric toric 68
rolls about its circular center line 68a, it exposes no
more or no less axially facing surface area on the
engaged seal ring 64 than was exposed to the fluid
pressure prior to its rolling. Such is the case because
the radially facing surfaces 54 and 86 have no axially
facing area components. Frictional forces between the
radially facing surface 54 and toric 68 and between the
radially facing surface 86 and the toric 68, prevent
rotation of seal ring 64. Since the axial surface 78 of
the seal ring 62 is greater than the axial surface 80 of
the seal ring 62, the seal ring 62 is biased axially
outwardly toward the seal retainer 44 and all seal ring
engagement force is supplied by forces acting Gn the
seal ring 64. As such, the seal ring 64 is pressure
balanced and held in a nonrotative manner.
The retaining tabs 91 secure the Belleville
spring 88 in a closely spaced annular configuration with
the seal ring 64 and the stationary structure 46 during
assembly of the seal ring 64, toric 68, and the Belle-
ville spring 88 with the stationary structure 46.
Moreover, pxoper sizing of the tabs 91 ensures that the
Belleville spring 88 is assembled in the intended
orientation in which the spring's axial surfaces 88a and
88b face the illustrated directions. Reversal of the
~59 r~o
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Belleville spring's axial surfaces preclude retention of
the spriny 88 by the retaining tabs 91 which prevents
application o~ undesired biasing forces on the seal ring
64. The retaining ramp surfaces 55 and 89 cooperate,
when juxtaposed, to prevent the escape of the toric 68
from between the seal ring 64 and seal retainer 50
during manipulation thereof preparatory to their assem-
bly with the end plate 48.
The Belleville spring 88 provides substan-
tially constant engagement force between the sealingface portions 70 and 72 so as to enable attainment of
any optimum sealing force for typical axial positions of
the seal rings 62 and 64. Also, since equal axially
opposed areas of the Belleville spring 88 are subjected
to the same coolant pressure which is transmitted
through the openings 92, the Belleville spring 88 is
also pressure balanced. Due to the pressure balancing,
the force applied by the Belleville spring 88 is inde-
pendent of the pressure of the coolant to which it is
exposed. Such pressure balancing feature is extremely
important since fluid pressures may vary substantially
within space 42 depending on parameters such as outside
temperature, coolant characteristics, severity of
service, and effectiveness of the coolant handling
apparatus.
It will now be apparent that an improved
sealing arrangement 40 has been provided between rela-
tively rotatable structures 12 and 14 which obstructs
debris and foreign matter intrusion into and escape or
leakage of coolant out of the sealed apparatus. The
instant sealing arrangement 40 is precisely pressure
balanced and engaged with constant force for any opera-
tional position of seal ring 64. As such, the present
invention is most useful for sealing applications of
large diameter but also performs effectively for sealing
11594~0
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applications having relatively small diameters. During
static and dynamic operation of seal rings 62 and 64,
excellent contact sealing obtains from engagement of
sealing face porti.ons 70 and 72 with optimum force.
