Note: Descriptions are shown in the official language in which they were submitted.
CA 02371537 2002-03-22
Jeff Baehl
ELASTOMER ENERGIZED ROD SEAL WITH INTEGRATED BACKUP RING
BACKGROUND OF THE INVENTION
1. Field of the invention.
The present invention relates to an improved sealing element
which includes an energizer element, a seal element, and an
integrated backup ring with controlled flex.
2. Description of the related art.
Seal elements are commonly utilized in machines having parts
which move relative to each other and which include fluid which
is to be retained in a specific portion of the machine. Seal
elements may additionally be utilized between static members of
machines in situations in which a fluid is to be kept within a
certain portion of the machine. One of the machine parts
typically includes a gland which is designed to house the sealing
element. Examples of such seals include the annular seals
utilized in hydraulic mechanisms to seal between the piston and
the cylinder of the hydraulic mechanism. In these
configurations, the gland may be formed in the piston or the
cylinder of the hydraulic element.
Prior seal elements have included plastic sealing surfaces
which cover the entire sealing surface of the seal. These
plastic seal elements were in some cases made from
polytetrafluoroethylene (PTFE), urethanes, or elastomers.
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Many known sealing arrangements utilize a three piece configuration with an
energizer/seal element/ backup ring being first placed in the gland and a
second separate
sealing element then being placed adjacent the energizer/seal element and a
third separate
backup ring placed against the seal element.
Configurations of this type are problematic in that they are difficult to
install. Three
piece configurations are additionally problematic as the additional seal parts
create
additional gap tolerance concerns. Additionally, standard backup rings are
rectangular in
cross section and only protect the seal ring from the gap created by the
groove body and the
moving element (which can also be referred to as a moving body, the moving
element/body including a moving surface). During operation under pressure, the
entire
backup ring is forced down on the rod significantly contributing to friction.
Further,
proper film control may be lost by such uncontrolled movement.
What is needed in the art is a seal arrangement having improved leakage
control,
reduced friction, and increased lifetime for sealing environments adapted for
reciprocation,
rotary, oscillating, and static uses.
What is also needed in the art is a seal arrangement which allows a portion of
the
seal to contact the surface to be sealed and which is able to create
controlled and non-linear
load patterns at the point of seal element and backup ring contact.
CA 02371537 2002-03-22
SUMMARY OF THE INVENTION
The present invention is directed to overcome the above-
mentioned shortcomings in the art, and provide a sealing
apparatus with the unique construction that tends to prohibit
seal rotation during operation with superior fluid film control.
The present invention is in three parts. First is that of an
elastomer energizer, which may be in the shape of a square ring,
o-ring, or an other custom design for energizing the seal system.
Second is that of a seal element or ring having a particular
geometry and composition. Third is an backup ring (reinforcing
ring) having a particular shape, structural material, and
engineered flex. The flex of the backup ring is particularly
designed to occur under various conditions, thereby increasing
sealing and protecting the seal ring, and at other times
releasing from the sealing surface to reduce and/or eliminate
friction.
The geometric layout of the backup ring element ensures firm
contact between the seal and groove bottom, independently of the
seal pressure and radial position of the moving part, and
concentrates contact forces against the moving part by means of
an engineered flex of the backup ring. In the installed state,
the backup ring has a radial height exceeding that of the housing
groove. Further, the influence of the compression ring or
energizer is balanced out by positioning the seal apex near or
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particularly in front of the axial position of the center of the
energizer. The seal apex itself is defined, in one form of the
invention, by an inlet angle upstream of the apex of preferably
more than 300 to the moving part, and a downstream slip angle of
greater than 50 preferably greater than 7 .
The invention of the backup ring utilizes a flexible area
under the rear portion of the annular seal to support the seal,
preventing damage from the gap between the groove body and the
moving element. This area will also support the seal element and
minimize the deflection of the seal element down stream, and
against the moving body to provide better fluid film control.
This function also minimizes radial loading on the moving element
as pressure increases. The axial length of the support area may
be dependent on the position of the energizer ring. The backup
ring for enhanced performance should pass under five percent to
ninety-five percent (5% to 95%) of the energizer ring and in
an alternate embodiment twenty percent to forty percent (20% to
40%) of the energizer ring. For optimum performance in an
alternate embodiment, the backup ring should pass under twenty-
seven percent to thirty-three percent (27% to 33%) of the
energizer ring.
Depending upon the geometry of the seal, the sealed pressure
produces a net torque on the angular seal, which works to force
the assembly down upon the moving part, or alternatively to
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improve contact with the groove bottom. The direction and
relative magnitude of this improvement can be approximated by the
ratio of radial groove height divided by the axial distance from
the seal apex to where the seal meets the groove bottom. When
the ratio exceeds one, seal contact with the groove bottom is
improved with pressure, and in the present invention this ratio
exceed 1.25.
Flexibility to allow radial displacement of the moving part
is determined by the radial height of the sealing element,
defined as that portion of the seal element which lies downstream
of the radial line going through the downstream end position of
the energizer. In the present invention, a line can be drawn
downstream from the point where this line intersects the moving
surface forming an angle with the moving surface of at least 7
without contacting the solid part of the seal.
The backup ring includes a clearance on the inner diameter
with the moving element. This allows the flexible area of the
support ring to deform and make contact therewith at a desired
pressure level. The stress taken up in the deflection of the
support ring is eliminated from the additive friction resulting
from increased contact area and stresses of the annular ring.
The radial clearance of the most up-stream edge should be from 0
to 0.050 inches (0.25 mm). Further, in another form of the
invention, the angle of the inner diameter surface of the backup
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ring should be minimized to be between 0 to 10 degrees, so that when
unpressurized, hoop
stress within the backup ring and/ or backup ring flex area will lift the area
from the
moving surface, thereby reducing friction and supporting transmission of a
fluid film.
In a broad aspect, the present invention provides an annular seal arrangement
for
sealing between a static machine part and a dynamic machine part, such as
between a
cylinder head and a piston rod of a hydraulic cylinder, said annular seal
arrangement
comprising: a compression ring; and a seal element made of a resilient
material and
energized and surrounded by said compression ring, the seal element being
installed with
the compression ring in a common, rectangular housing groove defined by the
static
machine part, the seal element separating the compression ring from a moving
surface of
the dynamic machine part and a downstream wall of the housing groove, the
outer diameter
of the seal element having a radial extent which is one of greater than and
equal to a radial
extent of a groove bottom of the housing groove before the annular seal
arrangement is
installed in the housing groove.
In the seal arrangement of the present invention the radial extent of the
outer
diameter of the seal element preferably exceeds the radial extent of the
groove bottom by
between 0 and 1.50 mm before the annular seal arrangement is installed in the
housing
groove. A radial height of the seal element is preferably one of greater than
and equal to a
radial height of the housing groove before the annular seal arrangement is
installed in the
housing groove.
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Preferably, the radial height of the seal element exceeds the radial height of
the
housing groove by between 0 and 25% before the annular seal arrangement is
installed in
the housing groove.
Preferably, the seal element is laid out with a seal apex defined by an
upstream seal
angle of more than 15 and a downstream slip angle of more than 2 , the seal
apex being
formed by one of the intersection of the upstream seal angle and the
downstream slip
angle, a flat shape with a width of no more than 1 mm, and a convex shape with
a width of
no more than 1 mm. Preferably, a position of the seal apex is axially located
near a center
of the compression ring when the annular seal arrangement is installed in the
housing
groove.
The seal element may be laid out with a seal apex defined by an upstream seal
angle of more than 40 and a downstream slip angle of more than 10 , the seal
apex being
formed by one of the intersection of the upstream seal angle and the
downstream slip
angle, a flat shape with a width of no more than 1 mm, and a convex shape with
a width of
no more than 0.75 mm.
The seal element may be laid out with a seal apex defined by an upstream seal
angle between 45 and 50 , and a downstream slip angle between 12 and 17 .
In the seal arrangement of the present invention the seal element is laid out
such
that the ratio: Radial groove height / axial distance from a seal apex to
where the seal
element meets the groove bottom, exceeds 1.25.
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The seal element may be laid out such that the ratio: Radial groove height /
axial
distance from a seal apex to where the seal element meets the groove bottom,
exceeds
1.75.
Moreover, the seal element may be laid out such that a straight line can be
drawn
from a seal apex through a body of the seal element to a radial line defining
a downstream
wall of the seal element, and that a first said radial line forms an angle
with the moving
surface of at least 40 .
The seal element may be laid out such that a straight line can be drawn from a
seal
apex through a body of the seal element to a radial line defining a downstream
wall of the
seal element, and that a first said radial line forms an angle with the moving
surface of at
least 50 .
In the seal arrangement of the present invention, from a radial line going
through a
downstream end position of the compression ring a line can preferably be drawn
downstream from a point where the radial line intersects the moving surface,
forming an
angle with the moving surface of at least 7 without contacting the seal
element.
Moreover, in one embodiment from a radial line going through a downstream end
position of the compression ring, a line can be drawn downstream from a point
where the
radial line intersects the moving surface, forming an angle with the moving
surface of at
least 14 without contacting the seal element.
In another embodiment, from a radial line going through a downstream end
position of the compression ring, a line can be drawn downstream from a point
where the
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radial line intersects the moving surface, forming an angle with the moving
surface of at
least 18 and not more than 24 without contacting the seal element.
Preferably, the present invention further includes a support ring positioned
adjacent
the seal element, in which the outer diameter of the support ring meets or
radially exceeds
the groove bottom.
The present invention may include a support ring positioned adjacent the seal
element, in which the outer diameter of the support ring radially exceeds the
groove
bottom by between 0 and 0.75 mm.
A support ring positioned adjacent the seal element of the present invention
may
hvae a radial height of the support ring being equal to or less than a depth
of the housing
groove.
In one embodiment of the present invention a support ring positioned adjacent
the
seal element, may have an internal diameter of the support ring exceeds the
moving surface
by 0 to 0.5 mm.
In another embodiment a support ring positioned adjacent the seal element may
have an inner surface of the support ring with an angle away from the moving
surface
greater than I' but less than 5 .
In the seal arrangement of the present invention the compression ring may be
an
O-ring.
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6d
BRIEF DESCRIPTION OF THE DRAWINGS
The above-mentioned and other features and advantages of this invention, and
the
manner of attaining them, will become more apparent and the invention will be
better
understood by reference to the following description of an embodiment of the
invention taken in conjunction with the accompanying drawings, wherein:
Fig. I is a sectional view of one embodiment of an annular seal formed in
accordance with the teachings of the present invention;
Fig. 2 is a sectional view of another embodiment of an annular seal formed in
accordance with the teachings of the present invention; and
Fig. 3 is a sectional view of yet another embodiment of an annular seal formed
in
accordance with the teachings of the present invention.
Corresponding reference characters indicate corresponding parts throughout the
several views. The exemplification set out herein illustrates one preferred
embodiment of
the invention, in
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one form, and such exemplification is not to be construed as limiting the
scope of the
invention in any manner.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the drawings and particularly to Fig. 1, there is shown a
seal 8 in
accordance with the teachings of the current invention. The annular
configuration of seal 8
illustrated in Fig. I is not meant to be limiting in any way as the seal
structure taught by the
current invention may be utilized in seals of differing configuration, such as
linear or
elliptical seals, for example and can be utilized in reciprocation, rotary,
oscillating, and
static configurations. Annular seal 8, as shown, generally seals between two
concentric
members with annular seal 8 being held in place by a gland 13 (which can be
variously
referred to as a groove channel or a housing groove) contained within either
of the
concentric members.
As explained above, the sealing geometry utilizes an energizer/seal element 12
having a semicircular or rectangular surface which is designed to be first
inserted into the
gland.
Elastomeric energizer 12 may be made of known materials, methods, shapes, and
sizes including but not limited to, square, 0, and custom shapes.
Seal element 18 includes a top surface 10 that is sized in length sufficient
to
interfere with the groove channel and prevent seal element rotation toward the
dynamic
surface. The further contact of energizer 12 in the embodiment of Fig. 1
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occurs at line Z, a theoretical line, dropped through seal
element 18 tangent to the furthest edge, the furthest nearest
edge of the energizer 12.
A seal element backup ring or support ring 52 is shown
disposed between seal element 18 and gland wall 16. In the
present invention, backup ring 52 includes an upstanding, in
radial direction portion 53 and a horizontal, in axial direction
portion 54, forming in cross section a substantial L-shape.
Horizontal portion 54 at its most distal surface, forms an edge
or point 59, through which an imaginary line X is dropped, as
shown on Figs. 1-3.
A main feature of the new backup ring 52 includes the use of
a flexible area or portion 60, which is oriented under the rear
portion of seal element 18 to support seal element 18 and prevent
seal damage (e.g. extrusion) into the gap between the groove body
and moving element. Area 60 also supports the seal element and
minimizes deflection of the seal element downstream and against
the moving body providing better fluid control. This function of
area 60 minimized radial loading on the moving element as
pressure increases.
In one aspect of the invention, the axial length of the
flexible area 60 is dependent on the position of energizer ring
12. As shown in Figs. 1-3, flexible area 60 as bounded lines X
and Z, is oriented under energizer 12. The distance between
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lines X and Z should be approximately twenty to forty percent
(20% to 40) of the maximal axial length of energizer 12. The
length of flexible area 60 preferably may lie within the range of
twenty seven to thirty three percent (27% to 33%) of the maximal
axial length of energizer 12. Other percentages of overlap
between backup ring 52 and energizer 12 may alternatively be
utilized based on the particular operating conditions or
requirements necessary for seal system 8.
Other percentages of overlap may be necessary depending on
the construction materials of backup ring 52. Construction
materials for backup ring 52 range from elastomeric in nature to
structural plastics, to composites to metals and alloys such as
bronze, including but not limited to, polytetrafluoroethylene
(PTFE), polyurethane, high modulus plastics, structural thermal
sets, polyamides, PPS, and various combination of such materials.
Material selection may be dependent on the sealing application
and environment.
A feature of the seal element 18 is that of a smooth radius
corner 20, which makes a smooth transition from the rear half of
the surface 22, which initially begins at seal apex 24 to side
surface 21.
As shown in Fig. 1, the bottom surface 22 includes a smooth
radius corner 20. Such smooth radius without any steps,
chamfers, or sharp edges is called fully blended, which assists
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in fluid film control under dynamic motion. The size, distance, and geometry
of corner 20
may assist control of flexible portion 60 and, during pressurization, help to
first cause
backup ring 52 to be locked into place with sidewall 16. Additional loading of
corner 20
into backup ring 52 would then tend to cause flexible area 60 to flex and move
into contact
with the moving element. No particular requirement of a smooth or fully
blended
5 surface is necessitated in connection with seal element side surface 21 and
alternate
embodiment 52' as shown in Fig. 2 has a non-blended curve. In this embodiment,
side
surface contacts gland wall 16.
The embodiment of Fig. 3 shows a seal system 8 with a back up ring 52',
radially
longer than the average depth of the seal gland, thereby extending back past
back surface 17
10 (which can be referred to as the groove bottom).
Preferably, backup ring 52 in any of its forms will have a clearance on the
inner
diameter surface 56 with the moving element. Most preferably, tip edge 59 will
also have a
clearance. This permits flexible area 60 of backup ring 52 to deform and make
contact at a
desired pressure level with the moving element. The stress taken up in the
deflection of
backup ring 52 is eliminated from the additive friction resulting from
increased contact
area and stresses of seal ring 12. Preferably, the radial clearance of the tip
edge 59 should
be withing the range of 0 to 0.050 inches (0.25 mm).
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Another geometrical feature of seal element 18 and backup ring 52 is that of
the bottom
surface 22, and 56 having an angle, in comparison with an opposite horizontal
line of
between zero to 10 , which is referenced as angle A. Preferably, angle A is
greater than or
equal to 5 , Most preferable is that bottom surface 22 has an angle of 7 .
Such angle
prevents a shear effect from occurring and keeps fluid in laminar flow against
element 18
and backup ring 52. The angle A has been found to provide better fluid film
control.
Construction materials from seal element 18 range from elastomeric in nature
to
structural plastic, including but not limited to, polytetrafluoroethylene
(PTFE),
polyurethane, high modulus plastics, structural thermal sets, polyamides, PPS,
and various
combination of such materials may be utilized for the element 18.
Additionally, seal element 18 may be bonded with energizer 12, as known in the
art, with adhesive or alternate types of connection materials or methods.
While this invention has been described as having a preferred design, the
present
invention can be further modified within the spirit and scope of this
disclosure. This
application is therefore intended to cover any variations, uses, or
adaptations of the
invention using its general principles. Further, this application is intended
to cover such
departures
CA 02371537 2002-03-22
from the present disclosure as come within known or customary
practice in the art to which this invention pertains and which
fall within the limits of the appended claims.
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