Note: Descriptions are shown in the official language in which they were submitted.
CA 02887776 2015-04-09
ROTARY SEAL WITH IMPROVED FILM DISTRIBUTION
[0002] This application is a divisional application of Canadian Patent File
No. 2,697,678 filed
September 2nd, 2008 from PCT Application No. PCT/US2008/010320.
BACKGROUND OF THE INVENTION
1. Field of the Invention.
[0003] This invention relates to hydrodynamic rotary seals for bi-directional
rotation that are
used to retain a lubricant and exclude an environment. More specifically, this
invention relates
to cooperative features that improve seal lubrication in conditions such as
high operating
temperature, skew-resisting confinement, high differential pressure, high
initial compression,
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adverse tolerance accumulation, circumferential compression, high modulus seal
materials, thin
viscosity lubricants, third body seal surface wear, and/or material swell
(collectively referred to
as "severe operating conditions").
2. Description of the Related Art.
[0004] Hydrodynamic seals used in down-hole oilfield tools are being
challenged to operate at
ever-greater temperatures and differential pressures. Such seals are installed
with interference
(i.e., compression) and establish sealing by blocking the leak path. For
general examples of
such seals, see FIG. 3 of U.S. Pat. 5,230,520, FIG. 4 of U.S. Pat. 6,315,302,
and FIG. 6 of U.S.
Pat. 6,382,634.
[0005] Upon installation in a compressed condition, hydrodynamic seals define
a "footprint"
representing the shape of the "dynamic sealing interface," and the two terms
are generally
interchangeable. Examples of footprints are shown in FIG. 2 of assignee's U.S.
Pat. 4,610,319
and FIG. 13 of assignee's U.S. Pat. 5,230,520.
[0006] Smaller seal cross-sections are desirable because shaft and housing
wall thickness can be
maximized. Miniaturization impacts seal lubrication, as described in U.S. Pat.
Appl. Pub.
US2007/0205563, paras. [0036]-[0039]. For a given dimensional compression,
interfacial
contact pressure increases as a seal cross-section is miniaturized. With
radial seals,
circumferential compression increases as diameter is miniaturized, increasing
footprint spread
and contact pressure.
[0007] The skew-induced wear mechanism described and illustrated in FIG. 3-27
of the Kalsi
Seals Handbook, Rev. 1 is addressed with skew-resisting confinement of the
seal, which
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increases interfacial contact pressure and footprint spread. The term "skew-
resisting
confinement," as used herein, encompasses (1) constraint imposed by seal
contact with fixed
location gland walls as disclosed in U.S. Pat. 6,315,302, and (2) spring-
loading through a
moveable gland wall, as disclosed in FIG. 3-28 of the Kalsi Seals Handbook,
Rev. 1.
[0008] Generally, the conventional wisdom regarding how such hydrodynamic
seals lubricate
has been described in U.S. Pat. 4,610,319 at col. 9, lines 6-22 and U.S. Pat.
5,230,520, col. 3,
lines 30-53. In the '520 patent, FIG. 13 uses a curved arrow to illustrate the
conventional
wisdom that a normal velocity component VN urges the lubricant toward the
environment. The
emphasis on VN has caused undue focus on inlet efficiency over the years, and
diverted
attention from finding other potential lubrication factors. Such conventional
wisdom of how
these seals operate has been repeated in numerous other patents and commercial
literature. See,
for example, U.S. Patents 5,678,829 (col. 4, lines 14-33), 5,738,358 (col. 2,
lines 17-57),
5,873,576 (col. 2, lines 26-65), 6,036,192 (col. 2, lines 26-65), 6,120,036
(col. 2, lines 18-45),
6,227,547 (col. 11, lines 16-40), 6,315,302 (col. 10, lines 31-46), 6,334,619
(col. 1, line 57- col.
2, line 5), 6,382,634 (col. 11, lines 4-9), 6,685,194 (col. 4, lines 51-55),
and 6,767,016 (col. 1,
line 27 - col. 2, line 16). Additionally, the conventional wisdom has been
that the footprint
wave height, per se, is important to lubrication. "Footprint wave height" as
used herein refers to
the difference in width between the widest and narrowest parts of the
footprint.
[0009] The use of the aforementioned conventional wisdom (relating to VN and
footprint wave
height) is inadequate in designing highly effective hydrodynamic rotary seals
for use in severe
operating conditions. The use of the conventional wisdom in the design of
seals for severe
operating conditions has resulted in limited seal effectiveness.
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(0010] Another bit of the conventional wisdom pertaining to hydrodynamic
rotary seals is
related to physical hydrodynamic inlet convergence. A general (and correct)
tenant is that more
gradual convergence produces more efficient in-pumping. U.S. Patents
6,315,302, 6,382,634
and 6,685,194 teach the use of gradual convergences. Experience has shown that
despite their
inlet efficiency, such seals lubricate sub-optimally because their designs are
based on the
conventional wisdom pertaining to footprint wave height and VN.
[0011] U.S. Patent 6,109,618 teaches the use of abrupt trailing edge
geometries, that are
unsuitable as hydrodynamic inlets, on seals suitable only for uni-directional
rotation. This
abrupt geometry is on the trailing edges of the waves, and is coupled with a
very gently
converging inlet geometry on the leading edges. Due to the high hydrodynamic
leakage of such
geometry, and the small reservoir size of downhole tools, downhole seals
cannot employ such
geometries.
[0012] The prior art seals are constructed from elastomers which suffer
accelerated degradation
at elevated temperature. For example, media resistance problems, gas
permeation, swelling,
compression set, and pressure related extrusion damage all become worse at
elevated
temperature. A bi-directional rotation seal that operates with less torque and
produces less seal-
generated heat would be desirable, in order to moderate such degradation.
[0013] Circumferential slippage of a seal with respect to its groove occurs
more often with large
diameter seals because the moment arms between the static and dynamic sealing
interfaces are
more nearly equal, and the static sealing interface has less mechanical
advantage. Rotational
slippage is particularly undesirable in large diameter seals because the
slippage can vary around
the circumference of the seal, causing undesirable localized stretching. It is
also undesirable in
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seals exposed to high differential pressure because slippage can accelerate
seal extrusion
damage. Slippage is exacerbated by seal or shaft wear because such wear
increases running
torque. A bi-directional seal that has lower running torque and more
resistance to wear is
therefore desirable.
[0014] It is desirable to overcome the aforementioned limitations of prior art
seals.
SUMMARY OF THE INVENTION
[00151 The present invention relates to generally circular rotary seals that
are suitable for bi-
directional rotation, and overcome the aforementioned prior art problems. The
seals are used to
establish sealing between a machine component (such as a housing) and a
relatively rotatable
surface (such as a shaft), in order to separate a lubricating media from an
environment. Seal
geometry on a dynamic lip interacts with the lubricating media during relative
rotation to wedge
a lubricating film into the dynamic sealing interface between the seal and the
relatively rotatable
surface. A portion of the lubricating film migrates toward, and into the
environment and thus
provides a contaminant flushing action.
[00161 The rotary seal includes a dynamic lip that deforms when compressed
into sealing
engagement with the relatively rotatable surface, defining a hydrodynamic
wedging angle with
respect to the relatively rotatable surface, and defining an interfacial
contact footprint of
generally circular configuration but varying in width. A non-circular (i.e.,
wavy) footprint edge
hydrodynamically wedges the lubricating film into the interfacial contact
footprint.
[0017] One aspect of a preferred embodiment of the present invention involves
a newly
established variable referred to as EwH. EwH is used herein for a dimension
that represents the
difference in size between Dimension B2 and Width WI in which Dimension B2 is
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dimension from a second footprint edge to a location P2 defining the maximum
interfacial
contact pressure at the widest footprint location and Width W1 is the
footprint width at the
narrowest footprint location. In other words, the value of EwH is calculated
as Dimension B2
minus the Width W1, and the result may be a positive or negative number,
depending on the
circumstances.
[0018] It has now been discovered that in the aforementioned cases described
in the
Background, the lubrication problem occurs because the value of Ewig
approaches zero or
becomes negative¨a circumstance not contemplated under the conventional wisdom
because
EwH and its import were unknown. As seal temperature increases, lubrication
decreases as the
value of Eval decreases. As lubrication decreases, the seal generates more and
more heat due to
increasing asperity friction, causing a loss of lubricant film viscosity.
These factors further
increase seal temperature, compounding the problem and leading to an
unsustainable runaway
operating condition. Thus, in one embodiment of the rotary seal of the present
invention the
value of EwH is maintained positive.
[0019] Another embodiment of the present invention is a generally circular,
hydrodynamically
lubricating rotary seal that accomplishes improved lubrication through the
cooperative benefits
of a modified zig-zag wave pattern, a variably sized inlet curvature that is a
tighter curvature
near the widest parts of the dynamic lip, and a less tight curvature near the
narrower portions of
the dynamic lip, and a dynamic lip flank that is more steeply sloped near the
widest parts of the
dynamic lip, and less steep near the narrower parts of the dynamic lip.
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[0020] The modified zig-zag wave pattern improves interfacial contact pressure
gradients and
the orientation and/or location of the pressure gradients in critical
locations. The variable
radius controls the magnitude of the pressure at a critical location, and
provides improved
inlet convergence, while enhancing factors that contribute to lubrication in
severe operating
conditions. The variable slope of the dynamic lip flank provides a number of
benefits related
to a variety of seal performance issues, the most important of which is to
minimize seal
volume for improved compatibility with skew-resisting confinement.
[0021] The seal preferably provides a dynamic exclusionary intersection of
abrupt
substantially circular form that provides the interfacial contact footprint
with an environment
edge that resists environmental intrusion. The seal can be configured for
dynamic sealing
against a shaft, a bore, or a face. Simplified embodiments are possible
wherein one or more
features of the preferred embodiment are omitted.
[0022] One aspect of this invention seeks to provide a hydrodynamic rotary
seal having low
torque for reduced wear and heat generation. Another aspect of an embodiment
seeks to
improve distribution of lubricant across the dynamic sealing interface,
particularly at high
operating temperatures. Another aspect of yet another embodiment seeks to
conserve void
volume within the seal gland, to provide adequate room for seal thermal
expansion,
considering seal tolerances and as-manufactured variations in the coefficient
of thermal
expansion of the sealing material, with a view toward improved accommodation
of skew-
resisting confinement.
[0022a] A preferred aspect of the invention contemplates a rotary seal
assembly including a
first machine component having a seal groove defined by generally opposing
first and second
groove walls and a peripheral groove wall, a second machine component located
at least
partially within the first machine component having a relatively rotatable
surface in generally
opposed relation to the peripheral groove wall and rotatable relative to the
first machine
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component, and a generally ring-shaped interference-type rotary seal located
at least partially
within the seal groove that has a volume and includes a seal body of resilient
thermally
expandable sealing material. The seal body has axially-facing first and second
seal ends. In
an uncompressed condition, the seal body includes a dynamic lip of generally
circular form.
The dynamic lip has an abrupt dynamic exclusionary intersection, a dynamic
surface facing
radially inward, a lubricant side flank that is non-circular having a slope in
an axial direction
and located in spaced relation with respect to the dynamic exclusionary
intersection, and an
inlet curvature located between and separating the dynamic surface and the
lubricant side
flank and located in spaced relation with respect to the dynamic exclusionary
intersection and
being at least a portion of a wavy, rotationally bi-directional hydrodynamic
geometry. The
seal body includes an inwardly facing surface between the first seal end and
at least part of
the lubricant side flank. The inwardly facing surface and the lubricant side
flank are located
entirely radially outward of and spaced from the dynamic surface. The dynamic
surface
extends from the inlet curvature to the dynamic exclusionary intersection, and
the dynamic
surface has at least two wider surface locations, at least one of the wider
surface locations is
the widest surface location between two narrower surface locations, at least
one of the two
narrower surface locations is the narrowest surface location between the at
least two wider
surface locations. The inlet curvature adjoins the lubricant side flank and
the dynamic
surface and extends from one of the narrower surface locations, past the
widest surface
location and past the narrowest surface location to one of the wider surface
locations. The
dynamic lip is held in compression against the relatively rotatable surface
and defines a
circumferential interfacial contact footprint against the relatively rotatable
surface. The
interfacial contact footprint includes peripheral first and second footprint
edges with the first
footprint edge being generally wavy, where a footprint width is defined
between the first and
second footprint edges, the interfacial contact footprint has at least two
wider footprint
locations, at least one of the wider footprint locations is the widest
footprint location between
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two narrower footprint locations, and at least one of the two narrower
footprint locations is
the narrowest footprint location between the at least two wider footprint
locations. The slope
of the lubricant side flank in the uncompressed condition is steepest at the
widest surface
location minimizing the volume, and the compression establishing interfacial
contact pressure
within the interfacial contact footprint includes a lubricant-side pressure
ridge along the first
footprint edge. The lubricant-side pressure ridge has a ridgeline established
by the maximum
interfacial contact pressure of the lubricant-side pressure ridge at each
circumferential
location of the interfacial contact footprint, and at the widest footprint
location the interfacial
contact pressure increases from zero at the first footprint edge to a greater
value at a Position
P2 on the ridgeline. The rotary seal maintains a positive value of EwH,
wherein
EwH = Dimension B2 - Width W1
where Dimension B2 is an axial length from the second footprint edge to the
Position P2 on
the ridgeline at the widest footprint location, and Width W1 is the axial
footprint width at the
narrowest footprint location, and the Dimension B2 is governed at least in
part by the inlet
curvature at the widest dynamic surface location.
[0022b] Yet a further aspect of the invention is a rotary seal assembly that
includes
a first machine component having a seal groove defined by generally opposing
first and
second groove walls and a peripheral groove wall, a second machine component
located at
least partially within the first machine component having a relatively
rotatable surface in
generally opposed relation to the peripheral groove wall and rotatable
relative to the first
machine component, and a generally ring-shaped interference-type rotary seal
located at least
partially within the seal groove with the rotary seal including a seal body of
at least one
resilient sealing material and the seal body having first and second seal
ends. In an
uncompressed condition, the seal body includes a dynamic lip having a dynamic
exclusionary
intersection of abrupt form, a dynamic surface facing radially inward, a
lubricant side flank
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having a slope in an axial direction, and an inlet curvature located between
and separating the
dynamic surface and the lubricant side flank where the inlet curvature is at
least part of a
hydrodynamic geometry. The seal body includes an inwardly facing surface
between the first
seal end and at least part of the lubricant side flank and the dynamic lip
projecting radially
inward of the inwardly facing surface. The lubricant side flank is located
entirely radially
outward of and spaced from the dynamic surface. The dynamic surface has an
axial width
between the dynamic exclusionary intersection and the inlet curvature that
increases from a
first narrower surface location to a first wider surface location, decreases
from the first wider
surface location to a second narrower surface location, increases from the
second narrower
surface location to a second wider surface location, and decreases from the
second wider
surface location to a third narrower surface location. The first wider surface
location is
situated between the first and second narrower surface locations and is the
widest surface
location between the first and second narrower surface locations. The second
narrower
surface location is situated between the first and second wider surface
locations and is the
narrowest surface location between the first and second wider surface
locations. The second
wider surface location is situated between the second and third narrower
surface locations
and is the widest surface location between the second and third narrower
surface locations.
The dynamic lip is held in compression against the relatively rotatable
surface and defines a
circumferential interfacial contact footprint against the relatively rotatable
surface. The
interfacial contact footprint comprises peripheral first and second footprint
edges. The first
footprint edge is generally wavy. The interfacial contact footprint has an
axial footprint
width between the first and second footprint edges that increases from a first
narrower
footprint location to a first wider footprint location, decreases from the
first wider footprint
location to a second narrower footprint location, increases from the second
narrower footprint
location to a second wider footprint location, and decreases from the second
wider footprint
location to a third narrower footprint location. The first wider footprint
location is situated
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between the first and second narrower footprint locations and is the widest
footprint location
between the first and second narrower footprint locations. The second narrower
footprint
location is situated between the first and second wider footprint locations
and is the narrowest
footprint location between the first and second wider footprint locations. The
second wider
footprint location is situated between the second and third narrower footprint
locations and is
the widest footprint location between the second and third narrower footprint
locations. The
compression of the dynamic lip against the relatively rotatable surface
establishes interfacial
contact pressure within the interfacial contact footprint including a
lubricant-side pressure
ridge along the first footprint edge. The lubricant-side pressure ridge has a
ridgeline
established by the maximum interfacial contact pressure of the lubricant-side
pressure ridge
at each circumferential location of the interfacial contact footprint. At the
first wider
footprint location the interfacial contact pressure increases from zero at the
first footprint
edge to a greater value at a Position P2 on the ridgeline. The rotary seal
maintains a positive
value of EwH, wherein
EwH = Dimension B2 - Width Wi
where Dimension B2 is an axial length from the second footprint edge to the
Position P2 at the
first wider footprint location, and Width WI is the axial footprint width at
the second
narrower footprint location, and the Dimension B2 is governed at least in part
by the inlet
curvature at the first wider dynamic surface location. The slope of the
lubricant side flank in
the uncompressed condition varies from the first wider surface location to the
second
narrower surface location, the slope being steeper at the first wider surface
location than at
the second narrower surface location, and is steeper at the first wider
footprint location than
at the second narrower footprint location. The first wider footprint location
corresponds
circumferentially to the first wider surface location, and the second narrower
surface location
corresponds circumferentially to the second narrower footprint location.
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[0022c] Still a further aspect of the invention is a rotary seal assembly that
includes a first
machine component having a seal groove defined by generally opposing first and
second
groove walls and a peripheral groove wall, a second machine component located
at least
partially within the first machine component having a relatively rotatable
surface in generally
opposed relation to the peripheral groove wall and rotatable relative to the
first machine
component, and a generally ring-shaped interference-type rotary seal located
at least partially
within the seal groove. The rotary seal includes a seal body of resilient
thermally expandable
sealing material having an operating temperature range having an upper bound
defined by an
upper temperature. The seal body has first and second seal ends where, in an
uncompressed
condition, the seal body includes a dynamic lip of generally circular form.
The dynamic lip
has an abrupt dynamic exclusionary intersection, a dynamic surface facing
radially inward, a
lubricant side flank that is non-circular having a slope in an axial direction
and located in
spaced relation with respect to the dynamic exclusionary intersection and
located entirely
radially outward of and spaced from the dynamic surface, and an inlet
curvature located
between and separating the dynamic surface and the lubricant side flank and
located in
spaced relation with respect to the dynamic exclusionary intersection and is
at least a portion
of a wavy hydrodynamic geometry. The dynamic surface is separated from the
lubricant side
flank and extends from the inlet curvature to the dynamic exclusionary
intersection. The
dynamic surface has at least two wider surface locations. At least one of the
wider surface
locations is the widest surface location between two narrower surface
locations. At least one
of the two narrower surface locations is the narrowest surface location
between the at least
two wider surface locations. The inlet curvature is located between and
adjoining the
lubricant side flank and the dynamic surface and extends from one of the
narrower surface
locations, past the widest surface location and past the narrowest surface
location to one of
the wider surface locations. The rotary seal is held in skew-resisting
confinement at the
upper temperature by virtue of simultaneous contact of the first seal end with
the first groove
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wall and the second seal end with the second groove wall. The dynamic lip is
held in
compression against the relatively rotatable surface and defines a
circumferential interfacial
contact footprint against the relatively rotatable surface. The interfacial
contact footprint
includes peripheral first and second footprint edges. The first footprint edge
is generally
wavy. The interfacial contact footprint has an axial footprint width between
the first and
second footprint edges. The interfacial contact footprint has at least two
wider footprint
locations, at least one of the wider footprint locations is the widest
footprint location between
two narrower footprint locations, at least one of the two narrower footprint
locations is the
narrowest footprint location between the at least two wider footprint
locations. The
compression of the dynamic lip against the relatively rotatable surface
establishes interfacial
contact pressure within the interfacial contact footprint including a
lubricant-side pressure
ridge along the first footprint edge. The lubricant-side pressure ridge has a
ridgeline
established by the maximum interfacial contact pressure of the lubricant-side
pressure ridge
at each circumferential location of the interfacial contact footprint. A the
widest footprint
location the interfacial contact pressure increasing from zero at the first
footprint edge to a
greater value at a Position P2 on the ridgeline. The rotary seal maintains a
positive value of
EwH at the upper temperature, wherein
EwH = Dimension B2 - Width W1
where Dimension B2 is an axial length from the second footprint edge to the
Position P2 on
the ridgeline at the widest footprint location, and Width W1 is the axial
footprint width at the
narrowest footprint location, and the Dimension B2 is governed at least in
part by the inlet
curvature at the widest dynamic surface location.
10022d1 Yet still a further aspect of the invention is a rotary seal assembly
that includes a first
machine component having a seal groove defined by generally opposing first and
second
groove walls and a peripheral groove wall, a second machine component located
at least
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partially within the first machine component having a relatively rotatable
surface in generally
opposed relation to the peripheral groove wall and rotatable relative to the
first machine
component, and a generally ring-shaped interference-type rotary seal located
at least partially
within the seal groove. The rotary seal includes a seal body of at least one
resilient thermally
expandable sealing material having an operating temperature range with an
upper bound
defined by an upper temperature. The seal body has first and second seal ends.
The rotary
seal is held in skew-resisting confinement at the upper temperature by virtue
of simultaneous
contact of the first seal end with the first groove wall and the second seal
end with the second
groove wall. In an uncompressed condition, the seal body includes a dynamic
lip and an
inwardly facing surface with the dynamic lip projecting radially inward from
the inwardly
facing surface and including a dynamic exclusionary intersection of abrupt
form, a dynamic
surface facing radially inward, a lubricant side flank having a slope and
located entirely
radially outward of and spaced from the dynamic surface, and an inlet
curvature located
between and separating the dynamic surface and the lubricant side flank. The
inlet curvature
is at least part of a hydrodynamic geometry. The dynamic surface has an axial
width between
the dynamic exclusionary intersection and the inlet curvature that increases
from a first
narrower surface location to a first wider surface location, decreases from
the first wider
surface location to a second narrower surface location, increases from the
second narrower
surface location to a second wider surface location, and decreases from the
second wider
surface location to a third narrower surface location. The first wider surface
location is
situated between the first and second narrower surface locations and is the
widest surface
location between the first and second narrower surface locations. The second
narrower
surface location is situated between the first and second wider surface
locations and is the
narrowest surface location between the first and second wider surface
locations. The second
wider surface location is situated between the second and third narrower
surface locations
and is the widest surface location between the second and third narrower
surface locations.
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The dynamic lip is held in compression against the relatively rotatable
surface and defines a
circumferential interfacial contact footprint against the relatively rotatable
surface. The
interfacial contact footprint includes peripheral first and second footprint
edges. The first
footprint edge is generally wavy. The footprint has an axial footprint width
between the first
and second footprint edges that increases from a first narrower footprint
location to a first
wider footprint location, decreases from the first wider footprint location to
a second
narrower footprint location, increases from the second narrower footprint
location to a second
wider footprint location, and decreases from the second wider footprint
location to a third
narrower footprint location. The first wider footprint location is situated
between the first
and second narrower footprint locations and is the widest footprint location
between the first
and second narrower footprint locations. The second narrower footprint
location is situated
between the first and second wider footprint locations and is the narrowest
footprint location
between the first and second wider footprint locations. The second wider
footprint location is
situated between the second and third narrower footprint locations and is the
widest footprint
location between the second and third narrower footprint locations. The
compression of the
dynamic lip against the relatively rotatable surface establishes interfacial
contact pressure
within the footprint including a lubricant-side pressure ridge along the first
footprint edge.
The lubricant-side pressure ridge has a ridgeline established by the maximum
interfacial
contact pressure of the lubricant-side pressure ridge at each circumferential
location of the
interfacial contact footprint, and at the first wider footprint location the
interfacial contact
pressure increases from zero at the first footprint edge to a greater value at
a Position P2 on
the ridgeline. The rotary seal maintains a positive value of EwH at the upper
temperature
wherein
Ewn -= Dimension B2 - Width Wi
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where Dimension B2 is an axial length from the second footprint edge to the
Position P2 on
the ridgeline at the widest footprint location, and Width W1 is the axial
footprint width at the
second narrower footprint location. The first
wider footprint location corresponds
circumferentially to the first wider surface location, and the second narrower
surface location
corresponds circumferentially to the second narrower footprint location.
[0022e] Still further, an aspect of the invention is a rotary seal for bi-
directional rotation; the
rotary seal in an uninstalled condition includes a generally ring-shaped seal
body having a
circumference. The seal body has first and second seal ends, a dynamic lip and
an inwardly
facing surface having an exposed length. The dynamic lip projects radially
inward of the
inwardly facing surface and includes a lubricant side flank, a dynamic
exclusionary
intersection of abrupt generally circular form, an inlet curvature, and a
dynamic surface
facing radially inward and ending at the abrupt dynamic exclusionary
intersection. The inlet
curvature is located between and separates the lubricant side flank and the
dynamic surface
and varies in position from the dynamic exclusionary intersection about the
circumference.
The dynamic surface is located between the inlet curvature and the dynamic
exclusionary
intersection. The dynamic surface has an axial width from the dynamic
exclusionary
intersection to the inlet curvature that varies around the circumference of
the seal body in a
wavy fashion and has at least two wider surface axial width locations and at
least two
narrower surface axial width locations. One of the narrower surface axial
width locations is
the narrowest surface axial width location between the at least two wider
surface axial width
locations and one of the at least two wider surface width locations is the
widest surface
location between the at least two narrower surface axial width locations. The
inlet curvature
adjoins the dynamic surface at and between the at least two narrower surface
axial width
locations and adjoins the dynamic surface at and between the at least two
wider surface axial
width locations. The lubricant side flank is located entirely radially outward
of and is spaced
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from the dynamic surface. At least a portion of the lubricant side flank is
located between at
least a portion of the inwardly facing surface and the inlet curvature. The
lubricant side flank
has an end thereof varying in position from the dynamic exclusionary
intersection in a wavy
fashion and has a slope in the axial direction that varies along at least part
of the
circumference. The slope of said lubricant side flank is steeper at at-least
some of the wider
surface axial width locations than at at-least some of the narrower surface
axial width
locations.
[0022f] Another aspect of the invention is a hydrodynamic rotary seal for bi-
directional
rotation; the rotary seal in an uninstalled condition includes a
circumferential seal body
having a dynamic lip of generally circular form. The seal body forms a ring
comprised of
sealing material having a thermally expandable seal volume. The seal body
includes an
inwardly facing surface with the dynamic lip projecting radially inwardly from
the inwardly
facing surface and includes a dynamic exclusionary intersection of abrupt
form, a dynamic
surface facing radially inward having an end at the dynamic exclusionary
intersection, a
lubricant side flank that is non-circular located in spaced relation with
respect to the dynamic
exclusionary intersection and located entirely radially outward of and spaced
from the
dynamic surface, and an inlet curvature located between and separating the
dynamic surface
and the lubricant side flank. The dynamic surface has narrower surface
locations and wider
surface locations, each of the wider surface locations is the axially widest
surface location
between a pair of the narrower surface locations, and at least one of the
narrower surface
locations is the axially narrowest surface location between a pair of the
wider surface
locations. The inlet
curvature is at least a portion of a rotationally bi-directional
hydrodynamic inlet capable of providing hydrodynamic lubrication of the
dynamic surface in
response to clockwise and counter-clockwise relative rotation when installed
against a
relatively rotatable surface and exposed to a lubricant. The inlet curvature
adjoins the
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dynamic surface at the wider and the narrower surface locations. The lubricant
side flank has
a slope in an axial direction that varies in steepness. The slope of the
lubricant side flank is
steeper at the wider surface locations compared to the slope at the at least
one narrower
surface location, with the slope at the wider surface locations minimizing the
seal volume.
[0022g] Yet another aspect of the invention is a ring-shaped hydrodynamic
rotary seal for bi-
directional rotation; the hydrodynamic rotary seal in an uncompressed
condition includes a
ring-shaped seal body having a first end and an inwardly facing surface with
the seal body
including a dynamic lip of generally circular form projecting radially inward
from the
inwardly facing surface and having a dynamic exclusionary intersection of
abrupt form, a
dynamic surface facing radially inward, a lubricant side flank that is non-
circular and located
in spaced relation with respect to the dynamic exclusionary intersection and
located entirely
radially outward of and spaced from the dynamic surface, an inlet curvature
located between
and separating the dynamic surface and the lubricant side flank and located in
spaced relation
with respect to the dynamic exclusionary intersection and being at least a
portion of a wavy,
rotationally bi-directional hydrodynamic geometry, the dynamic surface
extending from the
inlet curvature to the dynamic exclusionary intersection. The dynamic surface
has at least
two wider surface locations with at least one of the wider surface locations
being the widest
surface location between two narrower surface locations, at least one of the
two narrower
surface locations being the narrowest surface location between the at least
two wider surface
locations. The inlet curvature is located between and adjoins the lubricant
side flank and the
dynamic surface and extends from one of the narrower surface locations, past
the widest
surface location and past the narrowest surface location to one of the wider
surface locations.
The rotary seal is comprised of seal material having a volume. The lubricant
side flank has a
slope that varies relative to the dynamic surface width, with the slope of the
lubricant side
flank being steepest at the widest surface location minimizing the volume of
the seal material.
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[0022h] Still another aspect of the invention is a hydrodynamic rotary seal
for bi-directional
rotation; the rotary seal in an uninstalled condition includes a generally
ring-shaped seal body
having a first seal end and an inwardly facing surface. The seal body includes
a dynamic lip
projecting radially inward from the inwardly facing surface and comprises a
dynamic surface
facing radially inward, a lubricant side flank having a slope and located
entirely radially
outward of and spaced from the dynamic surface, and an inlet curvature located
between and
separating the dynamic surface and the lubricant side flank. The inlet
curvature is at least part
of a rotationally bi-directional hydrodynamic geometry. The dynamic surface
has an axial
width that increases from a first narrower surface location to a first wider
surface location,
decreases from the first wider surface location to a second narrower surface
location,
increases from the second narrower surface location to a second wider surface
location, and
decreases from the second wider surface location to a third narrower surface
location. The
first wider surface location is situated between the first and second narrower
surface locations
and is the widest surface location between the first and second narrower
surface locations.
The second narrower surface location is situated between the first and second
wider surface
locations and is the narrowest surface location between the first and second
wider surface
locations. The second wider surface location is situated between the second
and third
narrower surface locations and is the widest surface location between the
second and third
narrower surface locations. The slope of the lubricant side flank varies from
the first wider
surface location to the second narrower surface location, with the slope being
steeper at the
first wider surface location than at the second narrower surface location.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0023] So that the manner in which the above recited features, advantages, and
aspects of the
present invention are attained and can be understood in detail, a more
particular description of
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the invention, briefly summarized above, may be had by reference to the
embodiments thereof
which are illustrated in the appended drawings. It is to be noted, however,
that the appended
drawings only illustrate preferred embodiments of this invention, and are
therefore not to be
considered limiting of its scope, for the invention may admit to other equally
effective
embodiments that vary only in detail.
[0024] In the drawings:
FIG. l is a graph schematically representing a typical interfacial contact
pressure
plot at a circumferential location of a hydrodynamic seal;
FIG. 2 is a fragmentary cross-sectional view of a ring-shaped hydrodynamic
seal
according to a preferred embodiment of the present invention, the seal shown
in an
installed, compressed condition;
FIG. 2A is a fragmentary view of the hydrodynamic seal of FIG. 2 in an
uncompressed condition;
FIG. 2B is a section view taken along line 2B-2B of FIGS. 2A and 5;
= FIG. 2C is a section view taken along line 2C-2C of FIGS. 2A, 3, 4, 5, 6,
7 and 8;
FIG. 2D is a section view taken along line 2D-2D of FIGS. 2A, 3, 4, 5, 6 and
7;
FIG. 2E is a fragmentary illustration of the interfacial contact footprint of
the
hydrodynamic seal of FIG. 2;
FIG. 3 is a fragmentary view of a hydrodynamic seal according to another
preferred embodiment of the present invention, the seal in an uncompressed
condition;
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FIG. 3A is a fragmentary illustration of the interfacial contact footprint of
the
hydrodynamic seal of FIG. 3;
=
FIG. 4 is a fragmentary view of a hydrodynamic seal according to another
preferred embodiment of the present invention, the seal in an uncompressed
condition;
FIG. 4A is a fragmentary illustration of the interfacial contact footprint of
the
hydrodynamic seal of FIG. 4;
FIG. 4B is a section view taken along line 4B-4B of FIGS. 4, 7 and 8;
FIG. 5 is a fragmentary view of a hydrodynamic seal according to another
preferred embodiment of the present invention, the seal in an uncompressed
condition;
FIG. 5A is a fragmentary illustration of the interfacial contact footprint of
the
hydrodynamic seal of FIG. 5;
FIG. 6 is a fragmentary view of a hydrodynamic seal according to another
preferred embodiment of the present invention, the seal in an uncompressed
condition;
FIG. 6A is a fragmentary illustration of the interfacial contact footprint of
the
hydrodynamic seal of FIG. 6;
FIG. 7 is a fragmentary view of a hydrodynamic seal according to another
preferred embodiment of the present invention, the seal in an uncompressed
condition;
FIG. 7A is a fragmentary illustration of the interfacial contact footprint of
the
hydrodynamic seal of FIG. 7;
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FIG. 7B is a graph representing the interfacial contact pressures at selected
circumferential slices of the hydrodynamic rotary seal of FIGS. 2A and 7;
FIG. 8 is a fragmentary view of a hydrodynamic seal according to another
preferred embodiment of the present invention, the seal in an uncompressed
condition;
FIG. 8A is a fragmentary illustration of the interfacial contact footprint of
the
hydrodynamic seal of FIG. 8;
FIG. 9 is a fragmentary cross-sectional view of a hydrodynamic seal according
to
another preferred embodiment of the present invention, the seal shown in an
installed,
compressed condition;
FIG. 9A is a fragmentary view of the hydrodynamic seal of FIG. 9 in an
uncompressed condition;
FIG. 10 is a fragmentary shaded perspective view of an alternative embodiment
of
the hydrodynamic seal showing a hydrodynamic inlet portion of a wave; and
FIG. 11 is a fragmentary cross-sectional view of a hydrodynamic seal according
to another preferred embodiment of the present invention, the seal shown in an
installed,
compressed condition.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
1. Description of FIG. 1
[00251 FIGURE 1 is a graph that schematically represents an interfacial
contact pressure plot at
any circumferential location of a typical seal, for example, manufactured
according to one of
CA 02887776 2015-04-09
assignee's U.S. Patents 4,610,319, 5,230,520, 6,315,302, 6,382,634, and so
forth. The
proportions of a contact pressure plot will vary depending on specific seal
geometry and
analysis constraints, but the general plot characteristics are captured in
FIG. 1. The plot has a
first footprint edge L and second footprint edge E, which correspond to the
lubricant-side and
environment-side edges, respectively, of the dynamic sealing
interface/footprint. The direction
of relative rotation between the seal and the mating relatively rotatable
surface is normal
(perpendicular) to the axis labeled "interfacial width", and normal
(perpendicular) to the page
on which the figure is printed.
[0026] At any given circumferential location of the footprint, the inlet
contact pressure rises
from zero at the first footprint edge L to a maximum at Location P. Location P
is remote from
the first footprint edge L by Dimension A, and is remote from the second
footprint edge E by
Dimension B. Width W represents the local width of the dynamic sealing
interface/footprint.
In the text that follows, these labels and dimensions (i.e., first footprint
edge L, second footprint
edge E, Location P, Dimension A, Dimension B and Width W) are, when necessary,
given a
= subscript "1" or "2" to refer to the narrowest or the widest footprint
location, respectively.
100271 The aforementioned labels and dimensions are used not only in
describing FIG. 1, but
are also used elsewhere in this "Description of the Preferred Embodiments," in
order to
facilitate communication via the use of consistent terminology. In certain
figures, the
aforementioned subscript "1" is, when necessary, modified by the addition of
an "a" or "b" to
designate specific locations on multiple wave footprint illustrations.
[0028] The footprint edge represented by second footprint edge E is
substantially circular.
Width W varies about the circumference of the seal from a narrowest location
defined by Width
11
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WI to a widest location defined by Width W2. In assignee's commercial variants
suitable for
bi-directional rotation, the variation of Width W has been sinusoidal. EwH is
a newly
established variable that is used herein for a dimension that represents the
difference in size
between Dimension B2 and Width W1. In other words, the value of EwH is
calculated as
Dimension B2 minus the Width W1, and the result may be a positive or negative
number,
depending on the circumstances.
[0029] With seals constructed in accordance with U.S. Patents 4,610,319,
5,230,520, 5,738,358,
6,120,036, 6,315,302, 6,382,634, and so forth, the interfacial contact
pressure increases from
Location P2 to Location P1, creating a zone of elevated interfacial contact
pressure near
Location P1. With the conventional sinusoidal variation of Width W, this zone
has a generally
circumferential orientation for a significant distance.
[0030] The lubricant film thickness is uneven across the Width W of the
dynamic interface, and
surface asperity contact sometimes occurs. For example, a portion of the
footprint that is
circumferentially aligned with Width W1 suffers film disruption due to the
aforementioned
circumferential contact pressure zone orientation, the sheer magnitude of
contact pressure near
Location Pi, and due to unfavorable contact pressure gradients.
100311 FIGURE 5 of U.S. Pat. 4,610,319 shows a wave pattern that addresses the
aforementioned generally circumferential contact= pressure zone orientation,
but it does not
address the zone of elevated contact pressure near Location P1. If the
teachings of FIG. 5 of the
'319 patent are followed, the waves will have undesirable facets at the widest
and narrowest
parts of the dynamic lip.
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[0032] FIGURES 2A, 2B, 2C, 2F and 9 of U.S. Pat. 6,109,618 teach the use of a
similar wave
for uni-directional rotation. These figures fail to address lubricating
problems in the vicinity of
Location P1. The narrowest part of the dynamic lip is dominated by an abrupt
restrictive
diverter 250. In FIGS. 2A and 2E of the '618 patent, the abrupt restrictive
diverter 250 is in the
form of a corner/facet between dynamic sealing surface 226 and wavy lubricant-
side 230 of
circular dynamic sealing lip 224, and in FIG. 9 the abrupt restrictive
diverter 250 is in the form
of a sharp projection. The abrupt restrictive diverter 250 causes contact
pressure to skyrocket at
the narrowest parts of the dynamic lip, making problems worse. The salient
issues were clearly
missed because the contact pressure zone 262 in FIG. 2F does not extend to
Location 131, and
the illustrated edge of the zone is circumferentially oriented at the
narrowest points of the
footprint. The footprint edge radii at the narrowest parts of the footprint
are large--indicating
that any corresponding seal fillets are much larger than needed to eliminate
the surface facets
inherent to FIG. 5 of U.S. Pat. 4,610,319.
[0033] It is desirable for a seal to be suitable for bi-directional rotation,
and to address the prior
art problems associated with the zone of elevated contact pressure near
Location P1, particularly
if the circumferential orientation of the zone could be minimized and its film
thickness could be
increased.
[0034] U.S. Patents 6,109,618 and 6,685,194 teach different ways of
implementing a variable
inlet curvature on the leading edge of a uni-directional hydrodynamic wave.
Both patents teach
the use of a curvature that is most abrupt at the narrowest parts of the
dynamic lip (for example,
see FIGS. 2 to 2E of the '618 patent, and FIGS. 4 to 4C, 5A, 7, 8, 8A, 9 and
9A of the '194
13
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patent). Because the inlet is more abrupt at the narrowest parts of the
dynamic lip, it
exacerbates contact pressure issues near Location Pi.
100351 Highly saturated nitrile ("HSN") seals made and employed in accordance
with U.S. Pat.
6,315,302 suffer from under-lubrication at higher temperatures that are within
the generally
understood operating temperature limits of the elastomer (the 250 F
temperature stated in the
'302 patent at col. 11, line 65 through col. 12, line 2 is well within the
generally understood
operating limits of the elastomer). With tetrafluoroethylene and propylene
copolymer-
flurocarbon rubber ("TFE/P-FKM") composite seals made in accordance with U.S.
Pat. Appl.
Pub. 2006/0214379, lubrication also suffers at high temperatures that are
within the generally
understood operating temperature limits of the elastomer compounds. This
problem is
exacerbated when such seals are used with the recommended aforementioned
spring-loading.
100361 It has now been discovered that in both of the aforementioned cases,
the lubrication
problem occurs because the value of EwH approaches zero or becomes negative¨a
circumstance not contemplated under the conventional wisdom because EwH and
its import
were unknown. As seal temperature increases, lubrication decreases as the
value of EwH
decreases. As lubrication decreases, the seal generates more and more heat due
to increasing
asperity friction, causing a loss of lubricant film viscosity. These factors
further increase seal
temperature, compounding the problem and leading to an unsustainable runaway
operating
condition.
14
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[0037] These issues are a result of design decisions made on the basis of the
conventional
wisdom pertaining to footprint wave height and VN. Lubrication breaks down
even though,
under the conventional wisdom, the remaining footprint wave height is quite
satisfactory.
10038] Elastomers have a high coefficient of thermal expansion. Because there
is more material
at the widest parts of the dynamic lip, part of the differential thermal
expansion between the seal
and the housing is relieved circumferentially, causing material displacement
from the widest to
the narrowest parts of the dynamic lip, thereby increasing Width W1 relative
to Dimension B2.
[0039] Even if the circumferential transfer of thermally expanded material had
been understood,
it would not have raised alarm unless the footprint wave height (Width W2 -
Width W1) was
significantly compromised, because moderate footprint wave height loss would
not violate the
conventional wisdom concerning the theory of operation. As part of the present
invention
resulting from considerable study, applicant now understands that lubrication
can be seriously
impaired even though significant footprint wave height remains, due to the
differential growth
of Width W1 relative to Dimension B2.
[0040] As used herein, the term "un-swept zone" refers to that portion of the
footprint that is
circumferentially aligned with Width W1, and the term "swept zone" refers to
all the other area
of the footprint. In other words the swept zone is that portion of the
footprint that is
circumferentially aligned with the footprint wave height. The swept zone is
directly lubricated
by the sweep of the First Footprint Edge L across the lubricant-wetted shaft.
[0041] When the pressure of the environment is greater than that of the
lubricant, such as during
down-hole swab events, the first footprint edge Li is displaced toward the
lubricant more than
CA 02887776 2015-04-09
Location P2, owing to significant variations in the stiffness of the prior art
dynamic lip. This
impairs lubrication due to an effect that parallels the situation when the
value of EwH
approaches or equals zero, or becomes negative.
[0042] Although the "gentle" seal to shaft convergence taught by U.S. Patents
6,315,302,
6,382,634 and 6,685,194 is very effective in terms of hydrodynamic in-pumping,
and in terms
of reducing interfacial contact pressure near Location P1, such designs
significantly increase
Dimension A2 at the expense of Dimension B2. According to the conventional
wisdom, this
approach is unequivocally beneficial. With such seals, the value of EwH
approaches or equals
zero, or becomes negative, especially in severe operating conditions.
[0043] FIGURE 13 of U.S. Pat. 6,109,618 shows how pervasive the conventional
wisdom
concerning a gentle inlet convergence has been. A seal intended for bi-
directional rotation is
shown where the inlet geometry produces extremely effective in-pumping by
virtue of gentle
convergence with the shaft, but unfortunately another gentle convergence
allows the lubricant
film to escape at the trailing edge of the wave. FIGURE 13 also demonstrates a
lack of
understanding of the problems that circumferentially-oriented contact zones
cause. As shown
by the dashed line representation of the tangency location, the seal of FIG.
13 has
circumferentially-oriented zones of contact pressure that extend over most of
the circumference
of the seal. Furthermore, the contact pressure within these zones is
relatively high because of
the abrupt nature of the lip flank curvature, as shown in the section views of
FIGS. 13A and
13B.
16
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[0044] FIGURES 2 and 3 of U.S. Pat. 6,315,302 and the related discussion in
lines 50-59 of col.
18 thereof, and FIGS. 3 and 4 of U.S. Pat. 6,382,634 and the related
discussion in lines 27-33 of
col. 14 and col. 14, line 43 through col. 15, line 18 thereof, and col. 2,
lines 49-56, col. 4, lines
51-61, col. 6, lines 31-35 and col. 11, lines 33-39 of U.S. Pat. 6,685,194
also demonstrate how
pervasive the conventional wisdom has been, in relation to achieving a gentle
inlet convergence
that was believed, in conjunction with VN, to create an ideal situation for
lubricating the
interfacial contact footprint. Such geometries were eventually found to suffer
from under-
lubrication in severe service conditions. After years of research, the cause
has recently been
determined to be the result of the value of Ewn approaching or equaling zero,
or becoming
negative.
[0045] U.S. Pat. 6,685,194 exemplifies the blind adherence to conventional
wisdom, to the
exclusion of the then-unknown importance of the numeric value of EwH. For
example, in the
variable radius examples of FIGS. 4, 4A and 4B, Location P2 would coincide
with the circular
exclusion edge, so the size of Dimension B2 is zero. Even though the
footprints of these seals
have generous footprint wave height, as signified by the dashed lines, the
value of EwH is
always less than zero, even at room temperature. Such seals only lubricate in
low differential
pressure conditions. The lubrication is due to secondary factors such as side
leakage from the
swept zone (related to the fact that film thickness tends to decay gradually,
rather than abruptly,
due to the relative stiffness of the seal material; see Abstract, U.S. Pat.
6,109,618), and such as
macro-lubrication from surface finish affects.
[0046] It is a significant undesirable characteristic of the prior art bi-
directional rotation seals
that lubrication of the un-swept zone is impaired in severe operating
conditions. In some of the
17
CA 02887776 2015-04-09
prior art, the value of EwH is always less than zero, even at room
temperature. Even in the best
of the prior art, EwH is undesirably small at room temperature, and becomes
compromised in
severe operating conditions that include skew-resisting confinement.
100471 In the prior art, each molded wave is substantially identical, which
means that all
instances of Dimension B1 are substantially identical. This means that each of
the film
disturbances at and/or near any Location Pi lies in the poorly lubricated wake
of a similar
disturbance from the preceding wave. This compounds the problem by extending
the
disturbance circumferentially. The various aforementioned factors cooperate to
thin the film in
the un-swept zone. The resulting seal-generated heat exacerbates the
aforementioned increase
in the size of Width WI.
100481 U.S. Pat. 6,315,302 entitled "Skew Resisting Hydrodynamic Seal,"
teaches conservation
of void volume to accommodate skew-resisting confinement. From a void volume
conservation
standpoint, it is desirable to avoid the condition shown in FIGS. 2A and 6 of
U.S. Pat. 6,382,634
and FIG. 11 of U.S. Pat. 5,230,520, where the lubricant side flank is
truncated by the lubricant
end of the seal at the widest part of the dynamic lip, leaving very little
void volume near that
location. Likewise, it is desirable to avoid the condition shown in FIGS. 4-4C
of U.S. Pat.
6,315,302, where the lubricant side flank of the dynamic lip extends to the
lubricant end of the
seal. These examples are not only undesirable from an interfacial contact
standpoint when the
seal is installed in skew-resisting confinement, but it also negatively
impacts mold design.
[0049] In the prior art radial seals, the initial compression also causes
circumferential
compression, which is increased by thermal expansion. Since the seal
circumference is
18
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relatively long compared to the seal cross-section, circumferential
compression can cause
buckling in a manner similar to the classic textbook example of a long,
slender structural
column under compressive loading. This buckling tendency is augmented by the
variable
stiffness of the prior art seal about its circumference that is caused by the
varying dynamic lip
width.
10050] This buckling tendency is significantly worse in high temperature
seals, such as those
manufactured in accordance with FIG. 2 of U.S. Pat. Appl. Pub. US2006/0214379,
because of
the great amount of circumferential compression caused by seal thermal
expansion at high
temperature. Consequently, more spring loading is needed to prevent such
buckling, and this
spring loading further decreases the value of Ewm by increasing Width W1, to
the detriment of
lubrication.
2. Description of the seal of FIGS. 2-2E.
[0051] FIGURES 2-2E represent a preferred embodiment of the present invention.
These
figures should be studied together to best understand the preferred
embodiment. Features
throughout this specification that are represented by like numbers have the
same function.
[0052] FIGURE 2 is a fragmentary cross-sectional view that provides a general
overview of
how a preferred embodiment of the present invention may be employed when
assembled into a
machine that is shown generally at 2. The machine 2 includes a first machine
component 4 and
a second machine component 6 that defines a relatively rotatable surface 8.
The first machine
component 4 and the second machine component 6 together typically define at
least a portion of
a chamber for locating a first fluid 12.
19
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100531 A rotary seal, shown generally at 10, establishes sealing engagement
with the relatively
rotatable surface 8, to retain the first fluid 12, to partition the first
fluid 12 from a second fluid
14, and typically to exclude the second fluid 14. For the purposes of this
specification, the term
"fluid" has its broadest meaning, encompassing both liquids and gases. The
first fluid 12 is
preferably a liquid-type lubricant such as a synthetic or natural oil,
although other fluids are also
suitable in some applications. The second fluid 14 may be any type of
environment that the
rotary seal 10 may be exposed to in service, such as any type of liquid or
gaseous environment
including, but not limited to, a lubricating media, a process media, a
drilling fluid, an
atmosphere, seawater, a partial vacuum, etc.
10054] The rotary seal 10 is of generally circular, ring-like configuration
and includes at least
one dynamic lip 16 that is also generally circular in form, and is disposed in
facing relation to
the relatively rotatable surface 8. In the cross-sectional views herein, the
cutting plane of the
cross-section is aligned with and passes through the theoretical
axis/centerline of the rotary seal
10; i.e., the theoretical axis lies on the cutting plane.
[0055] When exclusion of the second fluid 14 is desired, the dynamic lip 16
preferably
incorporates a dynamic exclusionary intersection 44 (sometimes called the
"exclusion edge") of
abrupt substantially circular form that is substantially aligned with the
direction of relative
rotation, and is adapted to exclude the second fluid 14, as taught by U.S.
Pat. 4,610,319.
Although truly perfect circularity is desirable, it is seldom, if ever,
obtainable in any feature of
any manufactured product in actual practice, hence the terminology
"substantially circular
form." The dynamic exclusionary intersection 44 develops substantially no
hydrodynamic
wedging activity during relative rotation, and presents a scraping edge to
exclude the second
fluid 14 in the event of relative motion that is perpendicular to the
direction of relative rotation.
CA 02887776 2015-04-09
[0056] It is intended that the rotary seals of the present invention may
incorporate one or more
seal materials or components without departing from the spirit or scope of the
invention, and
may be composed of any suitable sealing material or materials, including
plastics and
elastomeric or rubber-like materials including, but not limited to, carbon,
fiber or fabric
reinforced elastomers. If desired, the rotary seals may be of monolithic
integral, one piece
construction as shown in FIGS. 9, 9A and 10, or may also incorporate different
materials
bonded, inter-fitted, co-vulcanized or otherwise joined together to form a
composite structure,
such as shown in U.S. Patents 5,738,358, 6,315,302, 6,685,194, 6,767,016 and
U.S. Pat. Appl.
Publications 2006/0214379 and 2006/0214380. Preferably, at least part of the
seal is
constructed of a resilient material, such as an elastomer.
[0057] Elastomers used in seal construction are compounds that include base
elastomers such
as, but not limited to, HNBR (hydrogenated nitrile, also known as HSN), FKM
(fluorocarbon
rubber), TFE/P (also known as FEPM) and EPDM. The elastomers may include other
compounding ingredients such as, but not limited to, fillers, lubricants,
processing aids, anti-
degradants, vulcanizing agents, accelerators and activators. The effects of
the ingredients are
generally understood by individuals having ordinary skill in the art of
compounding elastomers.
[0058] It is further understood that the invention can, if desired,
incorporate an energizer to load
the dynamic lip 16 against the relatively rotatable surface 8. The energizer
can take any of a
number of suitable forms known in the art including, but not limited to,
elastomeric rings and
various forms of springs such as garter springs, canted coil springs, and
cantilever springs,
without departing from the scope of the invention. If desired, the energizer
can be
located by or within an annular recess of any suitable form. For examples of
such energizers
21
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and recesses, see U.S. Patents 6,685,194 and 7,052,020, and U.S. Pat. App!.
Publications
2006/0214380 and 2007/0013143.
[0059] FIGURES 2, 2B, 2C, 2D, 4B and 11 portray seal cross-sections having the
high
temperature, composite construction taught in U.S. Pat. App!. Pub.
2006/0214379, where
preferably a first material layer 48 of TFE/P is co-vulcanized to a second
material layer 49 of
FKM.
[0060] In FIG. 2, the rotary seal 10 is oriented (i.e., positioned) at least
in part by the first
machine component 4. For the purpose of illustrating a typical application,
the machine 2 has a
generally circular seal groove that includes a first groove wall 18 and a
second groove wall 20
that are in generally opposed relation to one another, and a peripheral groove
wall 22. The first
groove wall 18 and the second groove wall 20 are often referred to as the
"lubricant-side gland
wall," and the "environment-side gland wall," respectively. The peripheral
groove wall 22 can
be substantially parallel to the relatively rotatable surface 8 as shown, or
all or part of it could
be skewed with respect to the relatively rotatable surface 8 as shown, for
example, by the prior
art of FIGS. 4, 6, 7, 8 or 9 of U.S. Pat. 5,230,520.
[0061] For the purpose of establishing consistent nomenclature herein, the
seal "groove" is the
annular void that is defined by the first groove wall 18, the peripheral
groove wall 22, and the
second groove wall 20, and the seal "gland" is the generally enclosed annular
cavity having a
boundary that is defined by the groove and the relatively rotatable surface 8.
[0062) The peripheral groove wall 22 is located in spaced relation to the
relatively rotatable
surface 8, and it (or an energizer) compresses at least a portion of the
dynamic lip 16 against the
relatively rotatable surface 8. This compression establishes an interfacial
contact footprint,
22
CA 02887776 2015-04-09
shown generally at 38, between the dynamic lip 16 and the relatively rotatable
surface 8. The
footprint 38 has a first footprint edge located generally at L and facing the
first fluid 12, and has
a second footprint edge located generally at E and facing the second fluid 14.
The second
footprint edge E is established by compression of the dynamic exclusionary
intersection 44
against relatively rotatable surface 8.
[0063] The compression causes contact pressure at the interface (footprint 38)
between the
dynamic lip 16 and the relatively rotatable surface 8. Sealing is also
established at the interface
between a static sealing surface 46 of rotary seal 10 and the peripheral
groove wall 22. The
contact pressure at the footprint 38 establishes sealing in the same manner as
any conventional
resilient seal, such as an 0-ring or a seal having a lip that is loaded by an
energizer. The
interfacial contact pressure is related to the degree of compression, the
modulus of elasticity of
the seal material, and the shape of the rotary seal 10.
[0064] As taught by U.S. Pat. 4,610,319, the first footprint edge L is
preferably wavy. Each
wave of the footprint 38 has a leading edge and a trailing edge, relative to
the direction of
relative rotation. When the direction of relative rotation reverses, the
application of the leading
edge/trailing edge appellations also reverses.
[00651 The leading edges of the waves are sites of hydrodynamic wedging action
during
relative rotation between the dynamic lip 16 and the relatively rotatable
surface 8. This
hydrodynamic wedging action forces a film of lubricating fluid (i.e., a film
of the first fluid 12)
into the interfacial contact footprint 38 for lubrication purposes. In other
words, the dynamic lip
16 slips or hydroplanes on a film of the first fluid 12 during periods of
relative rotation. The
hydroplaning activity reduces wear and seal-generated heat, and causes a
minute flow of the
23
CA 02887776 2015-04-09
first fluid 12 past the second footprint edge E and into the second fluid 14.
When relative
rotation stops, the hydroplaning activity stops, and a static sealing
relationship is re-established.
[0066] As taught by U.S. Pat. 4,610,319, the second footprint edge E
(sometimes called the
"environment edge") is preferably substantially circular and substantially
aligned with the
possible directions of relative rotation between the dynamic lip 16 and the
relatively rotatable
surface 8, and does not produce a hydrodynamic wedging action in response to
relative rotation
between the dynamic lip 16 and the relatively rotatable surface 8.
[0067] Referring to FIG. 2, the rotary seal 10 is preferably held in skew-
resisting confinement
by virtue of simultaneously contacting the first groove wall 18 and the second
groove wall 20.
The first groove wall 18 is shown in FIG. 2 as a face of a spring-loaded seal
loading ring 24 of
the general type taught by FIG. 3-28 of the Kalsi Seals Handbook, Rev. 1. The
first groove wall
18 is loaded against the rotary seal 10 by a spring 28 that acts on the seal
loading ring 24. The
spring load is reacted to a retainer 30 of any suitable form. The spring-
loading arrangement can
take any of a number of suitable forms without departing from the scope of the
invention. For example, a disk or coil spring arrangement could be substituted
for the wave
spring arrangement. For examples of coil spring-loaded seal loading rings, see
U.S. Pat.
1,089,789, FIGS. 1 and 5, and U.S. Pat. 3,015,505. The typical spring loading
ranges from
about 15 pounds per square inch ("psi") "equivalent pressure" at room
temperature, to about 45
psi at 400 F. The "equivalent pressure" is calculated by dividing the spring
force by the
circular area of the gland.
[0068] Although the first groove wall 18 and the second groove wall 20 are
shown to be in
movable relation to one another in FIG. 2, such is not intended to limit the
scope of the
24
CA 02887776 2015-04-09
invention, for the invention admits to other equally suitable arrangements.
For example, as
shown in FIGS. 9 and 11, the first groove wall 18 and the second groove wall
20 could be fixed
in position relative to each other. Although the rotary seal 10 is shown as
having a contacting
relationship with the first groove wall 18 and the second groove wall 20 in
FIGS. 2 and 9, the
features of the present invention are also advantageous for applications where
the rotary seal 10
only contacts one groove wall at a time, as represented by FIG. 11.
[0069] As shown in FIG. 2, the rotary seal 10 preferably defines a first seal
end 34 that
generally faces the first groove wall 18 and first fluid 12, and preferably
also defines a second
seal end 36 that generally faces the second groove wall 20 and the second
fluid 14. The first
seal end 34 and the second seal end 36 are often referred to as the "lubricant
end" and the
"environment end," respectively, and are preferably in generally opposed
relation. The first seal
end 34 and second seal end 36 can take other forms without departing from the
scope of
the invention. For example, the first seal end 34 could be angulated as taught
in U.S. Pat.
6,315,302 at col. 14, lines 22-22, or could be wavy as taught in U.S. Pat.
Appl. Pub.
2007/0205563. For another example, the second seal end 36 could include a
recess for
incorporating an energizer, as is well-known in the art.
[0070] The preferred embodiment of the present invention has application where
the first
machine component 4, the second machine component 6, or both, are individually
rotatable. In
the cross-sectional assembly views herein, the direction of relative rotation
is normal
(perpendicular) to the plane of the cross-section, and approximately
concentric to the dynamic
exclusionary intersection 44. The theoretical axis of the rotary seal 10
generally coincides with
the axis of relative rotation.
CA 02887776 2015-04-09
[0071] In dynamic operation, the relatively rotatable surface 8 has relative
rotation with respect
to dynamic lip 16 and first machine component 4. The relatively rotatable
surface 8 slips with
respect to dynamic lip 16, causing the interfacial contact footprint 38 to
become a dynamic
sealing interface. In the absence of relative rotation, the interfacial
contact footprint 38 is a
static sealing interface. The rotary seal 10 preferably remains stationary
relative to the first
machine component 4, however, the prior art teaches that hydrodynamic seal
embodiments are
possible where relative rotation with the first machine component 4 is
allowable; for example,
see FIGS. 8 and 8A of U.S. Pat. 6,685,194.
[0072] In FIG. 2, the rotary seal 10 is shown located in a position that would
occur if the
pressure of the first fluid 12 were greater than or equal to the pressure of
the second fluid 14. In
such conditions, the force of the spring 28, and any differential pressure
that may be present,
forces the rotary seal 10 against the second groove wall 20. Owing to the
complimentary
shapes of the second seal end 36 and the second groove wall 20, the rotary
seal 10 is well
supported at all locations except the small clearance gap 52 (often called the
"extrusion gap")
that exists between the first machine component 4 and the relatively rotatable
surface 8.
[0073] The relatively rotatable surface 8 can take the form of an externally-
or internally-
oriented substantially cylindrical surface, as desired, with the rotary seal
10 compressed radially
between the peripheral groove wall 22 and the relatively rotatable surface 8,
in which case the
axis of relative rotation would be substantially parallel to relatively
rotatable surface 8. In a
radial sealing configuration, the dynamic lip 16 is oriented for compression
in a substantially
radial direction, and the peripheral groove wall 22 may be of substantially
cylindrical
configuration, and first groove wall 18, second groove wall 20, first seal end
34 and second seal
end 36 may, if desired, be of substantially planar configuration. In a radial
sealing
26
CA 02887776 2015-04-09
configuration, the dynamic lip 16 is located either on the inner or the outer
periphery of the seal,
depending on whether the relatively rotatable surface 8 is an external or
internal cylindrical
surface.
[0074] Alternatively, the relatively rotatable surface 8 can take the form of
a substantially
planar surface, with the rotary seal 10 compressed axially between the
peripheral groove wall 22
and the relatively rotatable surface 8 in a "face-sealing" arrangement, in
which case the axis or
relative rotation would be substantially perpendicular to the relatively
rotatable surface 8. In an
axial (face) sealing configuration, the dynamic lip 16 would be oriented for
compression in a
substantially axial direction, the peripheral groove wall 22 may be of
substantially planar
configuration, and the first groove wall 18, second groove wall 20, first seal
end 34 and second
seal end 36 may, if desired, be of substantially cylindrical configuration. In
such face-sealing
arrangements, the hydrodynamic features can be oriented to pump in a radially
outward
direction if the first fluid 12 is located inward of the dynamic lip 16, or
can be oriented to pump
in a radially inward direction if the first fluid 12 is located outward of the
dynamic lip 16. In a
face-sealing arrangement, the backup ring 24 is preferably segmented or split.
If split, the ring
itself can, if desired, provide the spring force.
[0075) Large diameter seals are torsionally weak or limp, and therefore, the
cross-section of
large diameter seals can be rotated so that the dynamic lip 16 can face a
relatively rotatable
surface 8 of substantially planar or substantially cylindrical form, or even a
sloped form. The
torsional stiffness of small diameter seals is much higher, and therefore,
small diameter seals
with a dynamic lip 16 should be manufactured in the desired orientation as
dictated by the
configuration of the relatively rotatable surface 8 in a given sealing
application.
27
CA 02887776 2015-04-09
[0076] FIGURE 2A is a fragmentary view of the rotary seal 10 in the
uncompressed condition.
To minimize curvature-related foreshortening in the illustrations, for ease of
understanding,
FIGS. 2A, 3, 4, 5, 6, 7 and 8 are portrayals of seals that are relatively
large or infinite in
diameter, or as a smaller seal would appear if a short portion thereof is
forced straight. The
hydrodynamic geometries that are shown herein are bi-directional; that is to
say they achieve
efficient hydrodynamic lubrication in response to either clockwise or counter-
clockwise relative
rotation. In other words, the rotary seal 10 is suitable for bi-directional
rotation.
[0077] FIGURES 2B-2D are section views representative of cutting planes 2B-2B,
2C-2C and
2D-2D, respectively, and represent the uncompressed cross-sectional shape of
the rotary seal 10
of the preferred embodiment. These cutting planes are used on FIGS. 2A, 3, 4,
5, 6, 7 and 8.
FIGURES 2B, 2D and 4B are section views that are representative of the
narrower portions of
the dynamic lip 16, and FIG. 2C is representative of the wider portions of the
dynamic lip 16.
[0078] Referring now to FIGS. 2B-2D, various previously defined portions of
rotary seal 10 are
labeled for orientation purposes, such as the dynamic lip 16, first seal end
34, second seal end
36, dynamic exclusionary intersection 44, static sealing surface 46, first
material layer 48, and
second material layer 49.
[0079] The static sealing surface 46 may, if desired, be defined by a
projecting static lip 54 to
provide a degree of twist-inhibiting compressive symmetry, as taught by U.S.
Pat. 5,230,520.
This arrangement provides a recessed surface 55 that, by being recessed, helps
to minimize the
volume of rotary seal 10, and thereby helps to maximize void volume within the
gland. The
projecting static lip 54 is preferably oriented in generally opposed relation
to the dynamic lip
16. If desired, the embodiments illustrated herein can be simplified by
eliminating the
28
CA 02887776 2015-04-09
projecting static lip 54, such that the static sealing surface 46 is defined
by the seal body, as
taught by U.S. Pat. 4,610,319.
[0080] The dynamic lip 16 defines a dynamic surface 56 and a lubricant side
flank 58 that are
blended by an inlet curvature 60. The dynamic surface 56 and the recessed
surface 55 need not
be parallel. The lubricant side flank 58 is located in spaced relation with
respect to the dynamic
exclusionary intersection 44 and the second seal end 36. The inlet curvature
60 can be any
suitable curved shape, such as, but not limited to, a radius, a portion of an
ellipse, a portion of a
sine wave curve, a portion of a parabolic curve, a portion of a cycloid curve,
a portion of
witch/versiera curves, or combinations thereof. If desired, the static sealing
surface 46 and/or
the dynamic surface 56 can be of tapered configuration as taught by U.S. Pat.
6,767,016.
[0081] If extended, the dynamic surface 56 and the lubricant side flank 58
would intersect at a
theoretical intersection 62 that is positioned from the dynamic exclusionary
intersection 44 by a
distance that varies along the circumference of the rotary seal. In other
words, the theoretical
intersection 62 is non-circular and wavy. The lubricant side flank 58 is also
non-circular and
wavy. In keeping with American drafting third angle projection conventional
representation,
the theoretical intersection 62 is represented by an object line in FIGS. 2A,
3, 4, 5, 6, 7 and 8,
even though blended by the inlet curvature 60. For a discussion of this
blended intersection
illustration convention, see paragraph 7.36 and FIG. 7.44(b) on page 213 of
the classic drafting
textbook "Technical Drawing," 10th edition (Prentice-Hall, Upper Saddle River,
N.J.: 1997).
[0082] The extent of the inlet curvature 60 is represented by a first extent
line 64 and a second
extent line 66 in FIGS. 2A, 3, 4, 5, 6, 7 and 8. Preferably, a substantial
tangency exists between
the inlet curvature 60 and the lubricant side flank 58 at the first extent
line 64, and between the
29
CA 02887776 2015-04-09
inlet curvature 60 and the dynamic surface 56 at the second extent line 66.
Note that preferably
the first extent line 64 and the second extent line 66 are skewed with respect
to the possible
directions of relative rotation; in other words, they are non-circular and
wavy. Also note that
preferably second extent line 66 reverses direction at a First Reversing
Location R1 and at a
Second Reversing Location R2, and that these locations are preferably
staggered by Offset
Dimension T. Another way to say this is that some of the blending curves 84
are offset with
respect to other of the blending curves 84 by Offset Dimension T. The Offset
Dimension T and
the local cross-sectional geometry of the inlet curvature 60 in FIGS. 2A, 4,
5, 7 and 8 govern the
size of the Offset Dimension X that is shown in FIGS. 2E, 4A, 5A, 7A, and 8A,
respectively.
[0083] FIGURE 2E illustrates a fragmentary portion of the footprint (shown
generally at 38) of
the rotary seal 10 that is portrayed in FIGS. 2-2D. FIGURES 4A, 5A, 7A and 8A
illustrate a
fragmentary portion of the footprint 38 of the rotary seal 10 that is
portrayed in FIGS. 4, 5, 7
and 8, respectively. FIGURES 2E, 4A, 5A, 7A and 8A use the same nomenclature
as FIG. 1,
however the subscript "1" has, when necessary, been modified by the addition
of an "a" or "b"
to designate specific locations of the footprint 38.
[0084] Referring now to FIGS. 2A through 2E, the dynamic lip 16 has wider lip
locations 80 at
cutting plane 2C-2C and narrower lip locations 82 at cutting planes 2B-2B and
2D-2D. The
inlet curvature 60 preferably varies in curvature about the circumference of
the rotary seal 10.
At or near the wider lip locations 80, the inlet curvature 60 is preferably a
tighter curve,
compared to the curve at the narrower lip locations 82. For example, if the
inlet curvature 60 is
a variable radius, the radius might be smallest in size at and/or near cutting
planes 2C-2C (i.e.,
at and/or near the wider lip locations 80), medium in size at and/or near
cutting planes 2B-28,
CA 02887776 2015-04-09
and largest in size at and/or near cutting plane 2D-2D (i.e., at the narrower
lip locations 82).
For another example, the inlet curvature 60 might be a portion of an ellipse,
wherein the major
axis varies from being smallest at and/or near the wider lip locations 80
(i.e., at and/or near
cutting plane 2C-2C), to being largest at and/or near some of the narrower lip
locations 82 (such
as cutting plane 2D-2D) while varying to a medium size at and/or near other of
the narrower lip
locations 82 (such as at cutting planes 2B-2B). If desired, the minor and
major axes can be
identical to each other at and/or near the wider lip locations 80. It is
preferred that the inlet
curvature 60 variation be sinusoidal. Making the inlet curvature 60 smaller at
and/or near the
wider lip locations 80, as taught herein, does very little to increase the
lubricant shear area of the
footprint 38, but significantly impacts the size of Dimension B2.
[0085] Referring now to FIG. 2E, the local cross-sectional geometry of the
inlet curvature 60
(shown in FIGS. 2A-2D) governs Dimension A2 of the footprint 38, and therefore
directly
influences the size of Dimension B2. For example, if the inlet curvature 60 is
a radius, a larger
radius would produce a larger Dimension A2 and a smaller Dimension B2. This is
why the large
inlet radii on seals constructed in accordance with U.S. Patents 6,315,302 and
6,382,634 do not
perform as well as desired. The herein-disclosed understanding of the critical
relevance of
Dimension A2 and Dimension B2 is quite contrary to the conventional wisdom
that such prior
art seals are based on, and as such represents an inventive step.
[0086] Referring to FIG. 2A, the theoretical intersection 62 is preferably a
zig-zag shape
modified by small blending curves 68 at the narrower lip locations 82, and by
blending curves
69 at the wider lip locations 80, so that the inlet curvature 60 and the
lubricant side flank 58 are
un-faceted.
3]
CA 02887776 2015-04-09
[0087] The first extent line 64 and the second extent line 66 preferably have
zig-zag shapes that
are generally similar to that of the theoretical intersection 62. The zig-zag
shapes of the first
extent line 64 and the second extent line 66 are preferably blended by curves
at the wider lip
locations 80 and at the narrower lip locations 82. Of particular importance,
the second extent
line 66 is blended by blending curves 84 at the narrower lip locations 82, and
by blending
curves 86 at the wider lip locations 80. An example of an appropriate
curvature basic
dimension for the blending curves 68, blending curves 69, blending curves 84
and blending
curves 86 would be a radius in the range of 0.050" to 0.200", and preferably
in the range of
about 0.100" to 0.150". Another example would be that these blending curves
should have a
curvature basic dimension no looser than that of a 0.200" radius, and
preferably no looser than
that of a 0.150" radius. For example, a 0.250" radius would be considered to
be a looser
curvature than a 0.200" radius, and a 0.100" radius would be a tighter
curvature than a 0.200"
radius. Throughout this specification, the term "basic dimension" has the same
definition as is
given by Section 1.3.9 of ASME Y14.5M-1994 "Dimensioning and Tolerancing."
[0088] The lubricant side flank 58 preferably varies in slope about the
circumference of rotary
seal 10. Referring to FIGS. 2B-2D, the slope of the lubricant side flank 58 is
represented by
angle a. As can be seen in FIGS. 2B-2D, the slope of the lubricant side flank
58 is preferably
steeper at and/or near the wider lip locations 80, and less steep at and/or
near the narrower lip
locations 82. This slope is represented by angle a for illustrative purposes,
however, it must be
borne in mind that lubricant side flank 58 can be curved or straight, or a
combination of straight
and curved portions, when viewed in a cross-section aligned with the
theoretical axis of rotary
seal 10 (such as the illustrations of FIGS. 2B-2D). For example, instead of
being a straight line
having a variable angle about the circumference of the dynamic lip 16, the
lubricant side flank
32
CA 02887776 2015-04-09
58 could be a curve that varies in slope. One possibility is to utilize a
curve that varies from a
given radius at the narrower lip locations 82, to an infinite radius (e.g., a
straight line) at and/or
near the wider lip locations 80. When used for the lubricant side flank 58,
the difference
between a line and a curve is insignificant due to the relatively small size
of the lubricant side
flank 58. In other words, either shape, or a combination of the two, can be
used to achieve the
desired result. The core idea is that the slope of the lubricant side flank 58
changes, being
steeper near and preferably at the wider lip locations 80, and less steep
nearer and preferably at
the narrower lip locations 82. This is in contrast to the teaching of U.S.
Pat. 6,685,194; for
example, see column 15, lines 27-35 of the '194 patent. It is preferred that
the variation in the
slope of the lubricant side flank 58 be sinusoidal.
[0089] Referring to FIGS. 2-2E, in severe operating conditions the first
footprint edge L of the
footprint 38 may be defined by either the lubricant side flank 58 or by the
inlet curvature 60.
By having the least slope of the lubricant side flank 58 and the larger size
of the inlet curvature
60 near the narrower lip locations 82, a hydrodynamically efficient, gradual
convergence exists
between the dynamic lip 16 and the relatively rotatable surface 8 in the
region that is
circumferentially aligned with the EwH dimension, regardless of whether the
first footprint edge
L happens to be defined by the lubricant side flank 58 or by the inlet
curvature 60. Establishing
gentle convergence along that portion of the leading edge of the footprint 38
is desirable
because it (1) establishes an efficient hydrodynamic wedge at the portion of
the leading edge
that is circumferentially aligned with the dimension EwH, and (2) near that
portion within the
footprint 38, it establishes a desirably gradual increase in interface contact
pressure in the
circumferential direction from the First Footprint Edge L to the ridgeline 74.
Both of these
attributes are beneficial to efficient lubrication of both the swept zone and
the un-swept zone.
33
CA 02887776 2015-04-09
[0090] By making the slope of the lubricant side flank 58 steeper at the wider
lip locations 80,
the dynamic lip 16 can be wider (for more sacrificial material to accommodate
third body wear)
and the size difference between Dimension B2 and Width W1 can be maximized,
while still
fitting within a seal overall width that is compatible with the groove designs
and any spring
designs present in existing equipment. This enables the seal of the present
invention to easily
retrofit into existing equipment.
[0091] By making the slope of the lubricant side flank 58 steeper at and/or
near the wider lip
locations 80, void volume within the gland is conserved, making the rotary
seal 10 more
compatible with skew-resisting confinement in severe operating conditions. In
other words, the
varying slope of the lubricant side flank 58 helps minimize the volume of the
rotary seal 10 in
order to assure sufficient void volume within the gland to accommodate
tolerances, seal thermal
expansion, seal material displaced by compression, and swelling. This in turn
helps to maintain
interfacial contact pressure within a range that is compatible with efficient
hydrodynamic
lubrication, while accommodating a relatively large dynamic surface 56 width
at the widest
locations of the dynamic lip 16, which ensures that the value of EwH remains
positive and
effective in severe service conditions.
[0092] As mentioned previously, it is desirable to avoid the condition where
the lubricant side
flank is truncated by the lubricant end of the seal, or extends to the
lubricant end of the seal.
This undesirable seal design characteristic is addressed by the varying slope
of the lubricant side
flank 58 in the present invention.
[0093] The shallow slope of the lubricant side flank 58 at the narrower lip
locations 82 provides
those portions with more stiffness and support, compared to the situation that
would occur if the
34
CA 02887776 2015-04-09
steeper slope at the wider lip locations 80 were also used at the narrower lip
locations 82. This
stiffness allows the narrower lip locations 82 to better resist conditions
where the pressure of the
second fluid 14 is greater than that of the first fluid 12, such as during
down-hole swab events.
The additional stiffness has several benefits. It minimizes displacement of
the second footprint
edge El relative to Location P2, preserving lubrication. It reduces distortion
of the dynamic
exclusionary intersection 44, facilitating exclusion of the second fluid 14.
It also makes the
rotary seal 10 moderately less susceptible to circumferential compression-
induced buckling,
twisting and skewing in applications where the rotary seal 10 is not held in
skew-resisting
confinement.
[0094] Referring now to FIG. 2E, the footprint 38 has widest locations 70 and
narrower
locations 72. As with the prior art, a zone of increased contact pressure,
termed herein as a
"lubricant-side pressure ridge" exists near the first footprint edge L. The
center of the lubricant-
side pressure ridge is schematically illustrated by ridgeline 74. This
ridgeline 74 is
representative of the location of the peak contact pressure at any specific
circumferential
position along the lubricant-side pressure ridge. At any circumferential
location, the contact
pressure varies from a maximum value at ridgeline 74 to zero at first
footprint edge L.
[0095] While the contact pressure along the lubricant-side pressure ridge may
vary from
Location P2 to Location Pi (a) and from Location P2 to Location Pl(b), the
variable inlet curvature
60 of the seal causes the contact pressure at Location P (0 and Location P1(b)
to be much closer
in value to that at Location P2, and significantly less than the contact
pressure in the prior art at
Location P1 of FIG. 1. By so-lowering the contact pressure, lubrication of the
mating surfaces
of the rotary seal 10 and the relatively rotatable surface 8 in the vicinity
of Location P1(a) and
CA 02887776 2015-04-09
Location Pi(b) is greatly enhanced. Location P1(a) and Location Pi(b) can be
thought of as
"reversing locations" on ridgeline 74.
[0096] The ridgeline 74 is preferably a generally zig-zag shape as shown,
comprising more or
less straight lines blended by small joining curves 73 and small joining
curves 75. This shape
provides the lubricant-side pressure ridge with the advantage, as compared to
the prior art, of
not being generally circumferential over a significant circumferential
distance at and near the
narrower locations 72 of the footprint 38. This improved orientation allows
better lubrication of
the mating surfaces of the rotary seal 10 and the relatively rotatable surface
8 in the vicinity of
Location P1(a) and Location Pi(b). The keeping of the generally
circumferentially oriented
portions of the ridgeline 74 as short as practicable via use of the small
joining curves 73,
without creating a facet on the inlet curvature 60 or on the lubricant side
flank 58 while keeping
the interfacial contact pressure relatively low, is novel. An example of an
appropriate curvature
basic dimension for the joining curves 73 and the joining curves 75 would be a
radius in the
range of 0.050" to 0.200", and preferably in the range of about 0.100" to
0.150". Other curve
shapes are possible, but preferably they would have a curvature basic
dimension no looser than
that of a 0.200" radius, and preferably no looser than that of a 0.150"
radius.
[0097] Varying the size of the inlet curvature 60 to be larger at and/or near
the narrower lip
locations 82 is quite unconventional in view of the abrupt restrictive
diverter teachings of U.S.
Pat. 6,109,618. The present invention makes portions of the trailing edges of
the waves less
abrupt, allowing even more lubricant to escape at the wave trailing edges. The
effectiveness of
this approach was certainly not obvious prior to testing, and the excellent
results were contrary
36
CA 02887776 2015-04-09
to prior engineering judgment. The brilliance of the variable inlet curvature
60, as taught
herein, is that
(1) It reduces torque and seal generated heat, compared to the prior art, by
reducing contact
pressure, and facilitating lubrication, at and near the narrower lip locations
82 (i.e., near
the Location Pi (a) and Location Pi(b) of the footprint 38 (see FIG. 2E));
(2) Without causing the corresponding reduction in Dimension B2 that was
caused by the use
of large inlet radii at the narrowest part of the dynamic lip in the prior
art, it makes up for
the increased lubricant escape at the trailing portions of the waves by
assuring that an
efficient, gradual convergence exists between the dynamic lip 16 and the
relatively
rotatable surface 8 in the portion of the first footprint edge L that is
circumferentially
aligned with the EwH dimension, and by assuring a gradual rate of increase in
contact
pressure from that portion of the first footprint edge L to ridgeline 74, in
the
circumferential direction; and
(3) The tighter inlet curvature 60 at the wider lip locations 80 maximizes
Dimension B2, to
assure that the value of EwH remains positive throughout the useful
temperature range of
the elastomer used to construct the rotary seal 10, even when the rotary seal
10 is used in
skew-resisting confinement.
100981 The need to maintain a positive value for EwH in severe operating
conditions was by no
means obvious to the prominent group of seal experts who have been researching
such seals for
decades, who have themselves developed the relevant prior art oilfield seals,
and who have been
working intensely for years to improve the lubrication of the prior art bi-
directional rotation
seals.
37
CA 02887776 2015-04-09
100991 Contrary to conventional wisdom, it is not the previously defined
footprint wave height
that governs lubrication. What matters in severe operating conditions is that
the value of EwH
remains positive, and of sufficient size to assure lubricant migration in
severe service
conditions. Counter-intuitively, this improved lubrication occurs despite
the fact that
Dimension Ai (a) and Dimension Ai(b) are relatively large due to the variably
sized nature of the
inlet curvature 60, thus increasing the extent of the region within the un-
swept zone where the
film of the first fluid 12 has to cross unfavorable gradients.
[001001 When the present invention is used with skew-resisting constraint,
such as shown
in FIGS. 2, 9 and 9A, the value of EwH remains positive and effective
throughout the useful
temperature range of the material used in the construction of rotary seal 10.
In designing a seal
according to the preferred embodiment of the present invention, the EwH
dimension is sized
such that, unlike the prior art, it remains present (having a positive value
rather than a negative
value) and functional throughout the useful elevated temperature range of the
polymer used in
the construction of the rotary seal 10, even if used with skew-resisting
constraint. Based on the
conventional wisdom, the former ineffective design methodology was to evaluate
the footprint
wave height in extreme elevated temperature conditions. The current seal
design methodology,
which is an aspect of the present invention, is to evaluate the EwH dimension
in extreme
elevated temperature conditions that represent the upper limit of the useful
temperature range of
the polymer, to verify that the value of EwH remains positive throughout the
useful temperature
range of the material used in the construction of the seal, and preferably to
insure that the value
of EwH remains greater than or equal to 0.020". This methodology is best
implemented via
computer simulations utilizing three dimensional large displacement finite
element analysis
38
CA 02887776 2015-04-09
modeling that incorporates a conservative linear coefficient of thermal
expansion assumption of
13 X 10-5 inches per inch per degree F, and takes into account the effects of
skew-resisting
confinement.
[00101] Downhole drilling equipment is ordinarily cooled by the circulating
drilling fluid
to a temperature that is lower than the local environment. When circulation
and rotation
occasionally cease, the temperature of the equipment may reach the temperature
of the
surrounding geological environment, if allowed to soak long enough without
circulation.
Ideally, the useful elevated temperature range used in seal design should be
considered to be the
temperature that the polymer can withstand for brief periods of time so long
as adequate
lubrication is present. This "abuse temperature" is greater than the typically
quoted long-term
temperature capability of a material. For example, hydrogenated nitrile
typically is given an
extended-term temperature exposure rating of about 300 F, but in a seal
constructed of such
material and employed in accordance with U.S. Patent 6,315,302, it is highly
desirable that the
value of EwH remain positive if the seal is temporarily exposed to an "abuse
temperature" that
is 50 F higher than that, and preferably the value of EwH will remain greater
than or equal to
0.020".
[00102] The service rating of TFE/P is typically 450 F, and the service
rating of FKM is
typically 400 F. When two different temperature-rated materials are used in
the same seal, it is
the lower service rating that typically governs the seal design. Therefore, a
TFE/P-FKM
composite seal would preferably have a service rating of 400 F, and in a
spring-loaded seal
constructed of that material combination, it would be desirable that the value
of EwH remain
39
CA 02887776 2015-04-09
positive if the seal is temporarily exposed to an "abuse temperature" that is
50 F higher than
that, and preferably the value of EwH will remain greater than or equal to
0.020".
[00103] Another way to state this is that the validation temperature used
in the computer
model of the seal, when validating the seal design for a positive EwH value,
should be at least
equal to the operating temperature limit of the least temperature-capable
elastomer used in the
construction of the seal (as that operating temperature limit is generally
understood within the
elastomer industry), and preferably the validation temperature should be 50 F
greater than the
aforesaid operating temperature limit.
[00104] Referring to FIG. 2E, Dimension No and Dimension B1(b) are
preferably
different in size, so that Location P1(a) and Location P1(b) are
misaligned¨i.e., offset¨by
Offset Dimension X. This offset is desirable so that the film disturbances
created by the
direction reversals of the ridgeline 74 at Location No and Location Pi(b) do
not lie in one-
another's wake. This minimizes the circumferential extent of each such film
disturbance and
facilitates lubrication. The relative size of Dimension B1 (a) and Dimension
B1 (b) is preferably
controlled by the local cross-sectional geometry of the inlet curvature 60 of
the dynamic lip 16
that is shown in FIGS. 2-2D. In those figures, note that the size of the inlet
curvature 60 differs
between Section 2B-2B and Section 2D-2D; this causes Dimension Bi (a) and
Dimension B 1(b) to
differ at the corresponding locations of the footprint 38. The salient point,
however, is that
Location Pi(a) and Location P1(b) are offset with respect to each other,
regardless of how the
offset is achieved. Another way of saying this is that at least some of the
joining curves 73 are
CA 02887776 2015-04-09
misaligned with respect to others. In FIG. 2E, some of the waves of the
ridgeline 74 are
different than other of its waves.
[00105] The cooperative benefits of the various features provides more
complete
lubrication, especially in the un-swept zone, in either direction of rotation.
The invention is
suitable for a wider range of service conditions, including faster and slower
rotary speeds,
higher differential pressures, and thinner lubricants. Running torque is
reduced, resulting in less
self-generated heat. The result is better tolerance to high ambient
environment temperature, less
heat-related compression set, less footprint spread, less seal wear, longer
polymer life, a higher
retained modulus for improved extrusion resistance, lower interfacial contact
pressure when
installed in skew-resisting confinement, less slippage within the groove, and
less tendency to
cause floating compensation pistons to rotate.
3. Description of Simplifications and Alternate Embodiments.
[00106] The seal of FIGS. 2-2D includes several desirable features that are
most
advantageously used together, however simplifications are possible where one
or more of the
features are omitted or revert to the teachings of the prior art. FIGS. 3, 4,
5, 6, 7 and 8 represent
simplifications and alternate embodiments of the invention, and are
fragmentary views of a
rotary seal 10 in the uncompressed condition thereof, showing a seal that is
relatively large or
infinite in diameter, or as a smaller seal would appear if a short portion
thereof were forced
straight, so that no curvature-related foreshortening is apparent. Cutting
planes 2B-2B, 2C-2C,
2D-2D, and 4B-4B correspond to the cross-sections shown in FIGS. 2B, 2C, 213,
and 4B,
respectively.
41
CA 02887776 2015-04-09
[00107] To orient the reader, various previously defined features of the
rotary seal 10 are
labeled in FIGS. 3, 4, 5, 6, 7 and 8, such as the first seal end 34, second
seal end 36, theoretical
intersection 62, first extent line 64, second extent line 66, dynamic surface
56, lubricant side
flank 58, inlet curvature 60, wider lip locations 80, narrower lip locations
82, blending curves
84, blending curves 86, First Reversing Location RI, Second Reversing Location
R2 and Offset
Dimension T. Additionally, in FIGS. 3, 4 and 8, the previously designated
blending curves 68
are labeled to orient the reader.
[00108] The rotary seal 10 of FIG. 3 is a simplification of the preferred
embodiment of the
present invention that differs from that of FIG. 2A in one respect-each of the
narrower lip
locations 82 (at cutting planes 2D-2D) is substantially the same, which means
that Offset
Dimension T equals zero. The inlet curvature 60 varies in curvature about the
circumference of
the seal, being a tighter curve at cutting plane 2C-2C, and looser at cutting
plane 2D-2D.
[00109] The rotary seal 10 of FIGS. 4 and 4B is a simplification of the
preferred
embodiment of the present invention that differs from that of FIG. 2A in one
respect-the inlet
curvature 60 does not vary between cutting plane 2C-2C and cutting plane 4B-
4B, as taught by
the prior art. As a result, First Reversing Location R1 is offset from Second
Reversing Location
R2 by Offset Dimension T. In FIG. 4B, which is representative of the cutting
plane 4B-4B in
FIG. 4, various previously defined portions of rotary seal 10 are labeled for
orientation
purposes, such as angle a, dynamic lip 16, first seal end 34, second seal end
36, dynamic
exclusionary intersection 44, static sealing surface 46, first material layer
48, second material
layer 49, projecting static lip 54, lubricant side flank 58, inlet curvature
60 and theoretical
42
CA 02887776 2015-04-09
intersection 62. The inlet curvature 60 in FIG. 4 is the same as in the view
of FIG. 2C, while
the slope of the lubricant side flank 58 is shown as being the same as in FIG.
2D.
[00110] The rotary seal 10 of FIG. 5 is a simplification of the preferred
embodiment of the
present invention that differs slightly from that of FIG. 2A in that the
theoretical intersection 62
is sinusoidal, as taught by the prior art. The variable size of inlet
curvature 60 that is taught in
this specification can be used with various wavy shapes, however it is best
employed with the
modified zig-zag wave shape of FIG. 2A.
[00111] The rotary seal 10 of FIG. 6 is a simplification of the preferred
embodiment of the
present invention that differs slightly from that of FIG. 3 in that the
theoretical intersection 62 is
sinusoidal, as taught by the prior art.
[00112] The rotary seal 10 of FIG. 7 is an alternate embodiment of the
present invention
that differs slightly from that of FIG. 4 in that the theoretical intersection
62 is sinusoidal, as
taught by the prior art. In FIGS. 5, 6 and 7, The first extent line 64 and the
second extent line
66 have shapes that are similar to that of the theoretical intersection 62.
[00113] The rotary seal 10 of FIG. 8 is an alternate embodiment of the
present invention
that accomplishes the Offset Dimension T between First Reversing Location R1
and Second
Reversing Location R2 by having a different dynamic lip width at the First
Reversing Location
RI, compared to the lip width at the Second Reversing Location R2. In other
words, some of the
narrower lip locations 82 have a different width than other of the narrower
lip locations 82, and
in general, some of the waves of the dynamic lip 16 are different than other
of its waves. Also,
some of the waves of the second extent line 66 are different than other of its
waves. The inlet
43
CA 02887776 2015-04-09
curvature 60 may, if desired, be the same size throughout, as shown. Note that
some of the
blending curves 68 of the theoretical intersection 62 are offset with respect
to other of the
blending curves 68; this means that some of the waves of the theoretical
intersection 62 are
different than other of its waves.
[00114] FIGURES 3A, 4A, 5A, 6A, 7A and 8A represent the footprint 38 of the
simplifications and alternate embodiments that are shown in FIGS. 3, 4, 5, 6,
7 and 8,
respectively. To orient the reader, various previously defined portions of the
footprint 38 are
labeled in FIGS. 3A, 4A, 5A, 6A, 7A and 8A, such as Dimension Ai(a), Dimension
Al),
Dimension A2, Dimension No, Dimension BIN, Dimension B2, First Footprint Edge
L,
Second Footprint Edge E, Location No, Location Pi()), Location P2, Offset
Dimension X, first
fluid 12, second fluid 14, widest locations 70, narrower locations 72, joining
curves 73,
ridgeline 74 and joining curves 75. The previously defined Width W1 is labeled
in FIGS. 3A,
4A, 5A, 6A, and 7A to orient the reader; in FIG. 8A, two different sizes of
narrower width
location are shown as Width W1(a) and Width Wi(b).
[00115] In FIG. 3A, the peak pressure of ridgeline 74 at the narrowest
points of the
footprint 38 are circumferentially aligned, unlike those in FIG. 2E. In other
words, Dimension
No and Dimension BI(b) are similarly sized, so that Location No and Location
Pi(b) are
substantially aligned. With such a simplification, the initial tooling
manufacturing cost is
reduced because design effort is reduced.
[00116] The footprint 38 of FIG. 4A differs from that of FIG. 2E in one
important
respect¨in FIG. 4A the contact pressure is relatively high at and near
Location Pi(b) because
44
CA 02887776 2015-04-09
the inlet curvature 60 in FIG. 4 does not vary between cutting plane 2C-2C and
cutting plane
4B-4B. With this alternate embodiment, the peak pressures of the ridgeline 74
at the narrower
locations 72 of the footprint 38 are circumferentially misaligned¨i.e.,
offset¨by Offset
Dimension X so that the film disturbances created by the direction reversal of
the ridgeline 74 at
Location P1(a) and Location Pub) do not lie in one-another's wake. Some of the
waves of the
ridgeline 74 are different than other of its waves.
[00117] The footprints 38 identified in FIGS. 5A, 6A and 7A differ from
those of FIGS.
2E, 3A and 4A, respectively, in that the ridgeline 74 and the First Footprint
Edge L are
sinusoidal rather than a modified zig-zag. In FIGS. 5A and 7A, some of the
waves of the
ridgeline 74 are different than other of its waves.
1001181 The graph of FIG. 7B represents interfacial contact pressure at
selected
circumferential slices of the rotary seal 10 of FIGS. 2A and 7. The slice
representative of the
rotary seal 10 of FIG. 2A was taken between cutting planes 2C-2C and 2B-2B,
and the slice
representative of the rotary seal 10 of FIG. 7 was taken between cutting
planes 2C-2C and 4B-
4B. One circumferential slice is aligned with Location 131(a) of FIG. 2E, and
the other
circumferential slice is aligned with Location P1(b) of FIG. 7A. Note that the
gradient and
magnitude of the FIG. 2E contact pressure is preferable to that of FIG. 7A.
This shows the
benefit of the wave pattern and the varying size of the inlet curvature 60 of
the rotary seal 10 of
FIG. 2A, compared to that of FIG. 7.
[00119] The disadvantage of the embodiments of FIGS. 5, 6 and 7, compared
to the zig-
zag counterparts of FIGS. 2A, 3 and 4, is that significant portions of the
ridgeline 74 at the
narrower locations 72 of the footprint 38 have a generally circumferential
orientation as shown
CA 02887776 2015-04-09
in FIGS. 5A, 6A and 7A, which is disruptive to the lubricating film. All of
the seals described
herein can be further simplified, if space permits, by having a lubricant side
flank 58 with a
slope that does not vary about the circumference of rotary seal 10.
[00120] FIGURE 8A is representative of the footprint 38 of the rotary seal
10 that is
shown in FIG. 8. The peak pressures of the ridgeline 74 at the narrower
locations 72 of the
footprint 38 are circumferentially misaligned¨i.e., offset¨by Offset Dimension
X so that the
film disturbances created by the direction reversal of the ridgeline 74 at
Location P1(a) and
Location P1 (b) do not lie in one-another's wake. Offset Dimension X is
governed by the Offset
Dimension T and the local cross-sectional geometry of the inlet curvature 60
that is illustrated
in FIG. 8. The un-swept zone is defined by Width WI (a), since it is smaller
than Width Wi(b).
Some of the waves of the ridgeline 74 are different than other of its waves,
and some of the
waves of the First Footprint Edge L are different than other of its waves.
[001211 FIGURE 9 is a fragmentary cross-sectional view that provides a
general overview
of another preferred embodiment of the present invention. FIGURE 9A shows the
rotary seal
of FIG. 9 in its uncompressed condition. Many of the previously described
features are
numbered in FIGS. 9 and 9A to orient the reader.
1001221 Machine 2 incorporates a first machine component 4 and a second
machine
component 6 that includes a relatively rotatable surface 8. The rotary seal 10
has a generally
circular, ring-like configuration and at least one dynamic lip 16 that is also
generally circular in
form. At least a portion of the dynamic lip 16 is held in compressed,
contacting relation with
the relatively rotatable surface 8, and establishes sealing engagement with
the relatively
rotatable surface 8, to retain a first fluid 12, to partition the first fluid
12 from a second fluid 14,
46
CA 02887776 2015-04-09
and to exclude the second fluid 14. In dynamic operation, the relatively
rotatable surface 8 has
relative rotation with respect to the dynamic lip 16 and with respect to first
machine component
4. The dynamic lip 16 incorporates a dynamic exclusionary intersection 44 of
abrupt
substantially circular form that is substantially aligned with the direction
of relative rotation.
[00123] The rotary seal 10 is oriented by the first machine component 4,
which has a
generally circular seal groove that includes a first groove wall 18 and a
second groove wall 20
that are preferably in generally opposed relation to one another. The first
machine component 4
also has a peripheral groove wall 22 that is located in spaced relation to the
relatively rotatable
surface 8, and compresses the rotary seal 10 against the relatively rotatable
surface 8.
[001241 Although first groove wall 18 and second groove wall 20 are shown
to be in fixed,
permanent relation to one another, such is not intended to limit the scope of
the invention, for
the invention admits to other equally suitable forms. For example, first
groove wall 18 and/or
second groove wall 20 could be configured to be detachable from the first
machine component
4 for ease of maintenance and repair, but then assembled in more or less fixed
location for
locating and constraining the rotary seal 10.
[001251 In FIG. 9, the rotary seal 10 is held in skew-resisting confinement
by virtue of
simultaneously contacting the first groove wall 18 and the second groove wall
20 under
operating conditions. In the prior art axially-constrained seals made in
accordance with U.S.
Pat. 6,315,302, even though the designers meticulously evaluated the footprint
wave height in
elevated temperature conditions, the heretofore unknown EwH dimension became
compromised
in elevated temperature conditions, causing loss of lubrication in the un-
swept zone. This and
47
CA 02887776 2015-04-09
other previously described lubrication problems are managed by incorporating
any, or all, of the
design features that were previously disclosed in conjunction with FIGS. 2-8.
[00126] Rotary seal 10 defines a first seal end 34 that generally faces the
first groove wall
18 and first fluid 12. Rotary seal 10 also defines a second seal end 36 that
generally faces the
second groove wall 20 and the second fluid 14. The compression of the dynamic
lip 16 against
the relatively rotatable surface 8 establishes and defines an interfacial
contact footprint, shown
generally at 38, between the dynamic lip 16 and the relatively rotatable
surface 8. The footprint
38 has a first footprint edge located generally at L and facing the first
fluid 12, and has a second
footprint edge located generally at E and facing the second fluid 14. The
second footprint edge
E is established by compression of the dynamic exclusionary intersection 44
against the
relatively rotatable surface 8. The footprint 38 can take the form of any of
the footprints shown
in FIGS. 2E, 3A, 4A, 5A, 6A, 7A or 8A, with the same characteristics and
benefits. The labels
in those figures are therefore appropriate to this discussion of FIGS. 9 and
9A.
[00127] If desired, in the uncompressed condition the first seal end 34 may
be wavy and
vary in position relative to the second seal end 36, as taught by U.S. Pat.
Appl. Pub.
2007/0205563. This embodiment, and other embodiments, may if desired also
incorporate an
exclusion edge chamfer in accordance with the teachings of U.S. Pat.
6,120,036.
[00128] The dynamic lip 16 and the footprint 38 can have any or all of the
attributes
previously described in conjunction with FIGS. 2 to 8A; the following
citations of such
attributes do not represent an exhaustive list of the previously described
attributes. The
theoretical intersection 62 can have the previously described modified zig-zag
shape, or other
desired wave shape. The slope of the lubricant side flank 58 can vary around
the circumference
48
CA 02887776 2015-04-09
of the rotary seal 10, being steepest at the widest portions of the dynamic
lip 16 to conserve
void volume, and to maximize the body length 76. The slope is represented by
angle a,
however as described previously, the lubricant side flank 58 can be straight
or curved in the
cross-sectional view shown (even if straight in the uncompressed condition,
the lubricant-side
flank 58 tends to become curved in the compressed condition). The varying
slope of the
lubricant side flank 58 allows the EwH dimension of the footprint 38 to be
increased without
increasing the volume of the rotary seal 10, compared to the prior art. The
varying slope also
tends to strengthen the narrowest parts of the dynamic lip 16. This helps the
dynamic
exclusionary intersection 44 to remain more circular when the pressure of the
second fluid 14 is
greater than the first fluid 12.
[00129] When installed in skew-resisting confinement as taught by U.S. Pat.
6,315,302
and shown here in FIG. 9, the unsupported length (from first groove wall 18 to
first footprint
edge L) of the rotary seal 10 acts as a skew-resisting spring. The varying
slope of the lubricant
side flank 58 serves to maximize the exposed length 76 of the body 78 near the
wider parts of
the dynamic lip 16, which lowers the effective spring rate of the seal body 78
by minimizing the
spring force contribution of the dynamic lip 16.
[00130] While FIG. 13 of U.S. Pat. 6,334,619 also discloses a seal with a
variably angled
flank, the purpose was not to conserve void volume or to preserve body length
76, since that
flank is in intimate contact with a similarly shaped backup ring, which
supports and constrains
the flank, and the flank extends to the end of the seal body. Here in FIG. 9,
the lubricant side
flank 58 is part of an "unconstrained geometry" as taught by U.S. Pat.
6,315,302, so that
additional compression or thermal expansion of the rotary seal 10 is
compensated by
49
CA 02887776 2015-04-09
displacement by the unconstrained geometry of the lubricant side flank 58; see
col. 11, lines 42-
46 and col. 12, lines 13-20 of the '302 patent. The seal in FIG. 13 of U.S.
Pat. 6,334,619 is not
constrained in a manner that requires or permits the flank to serve as an
unconstrained geometry
to avoid excessive confinement-related and thermal expansion-related contact
pressure. Even if
it were so-constrained, as shown in the non-varying flank examples of FIGS.
2C, 2E, 6 and 10
of U.S. Pat. 6,334,619, the "unconstrained geometry" function could not be
served by the
angulated, well-supported lip flank. In the present invention, the lubricant
side flank 58 is
located remote from the first groove wall 18, establishing void volume within
the gland.
[00131] The inlet curvature 60 can vary about the circumference of the
rotary seal 10,
being a tighter curvature at the wider portions of the dynamic lip 16, and a
looser curvature at
the narrowest portions of the dynamic lip 16. These features help to assure
adequate seal
lubrication at higher temperatures despite the higher interfacial contact
pressure associated with
skew-resisting confinement, as described previously in conjunction with FIGS.
2-2E.
[00132] FIGURE 10 is an enlarged fragmentary shaded perspective view of an
uncompressed seal of an embodiment of the present invention in an uncompressed
state, as such
a seal would be configured for radial compression against a relatively
rotatable shaft. This
figure is included to facilitate the reader's understanding of the variable
slope of the lubricant
side flank 58, the variable curvature of the inlet curvature 60, and the
generally circular
configuration of the dynamic exclusionary intersection 44. The inlet curvature
60 is a radius
that is smaller at the widest part of the dynamic lip, and larger at the
narrower part of the
dynamic lip. The lubricant side flank 58 is a sloped surface that is steeper
at the widest part of
the dynamic lip, and less steep at the narrower part of the dynamic lip. The
wave form is a
modified zig-zag shape of the type shown between cutting planes 2C-2C and 2D-
2D in FIGS.
CA 02887776 2015-04-09
2A, 3 and 4. Instead of the dual material construction shown in FIGS. 2B-2D
and 4B, the rotary
seal 10 in FIG. 10 is illustrated as being constructed from a single
elastomeric material.
[00133) The present invention also provides a lubrication advantage over
the prior art
when the seal is not constrained by the walls of the groove. FIGURE 11 is a
fragmentary cross-
sectional view of an installed, ring-shaped hydrodynamic rotary seal 10
embodying the
principles of the present invention, and installed in the machine that is
shown generally at 2.
The machine 2 includes a first .machine component 4 and a second machine
component 6 that
defines a relatively rotatable surface 8. FIGURE 11 differs from that of FIG.
2 in that the first
groove wall 18 and the second groove wall 20 are both defined by the first
machine component
4 and are not both in contact with the rotary seal 10. The arrangement shown
in FIG. 11 lacks
the backup ring 24, spring 28, and retainer 30 that are provided in FIG. 2.
The peripheral
groove wall 22 compresses the dynamic lip 16 of the rotary seal 10 against the
relatively
rotatable surface 8 of the second machine component 6, establishing a
footprint shown generally
at 38 that has Width W, a first footprint edge generally at L and a second
footprint edge
generally at E. The static sealing surface 46 has sealed engagement with the
peripheral groove
wall 22. The second footprint edge E is established by compression of dynamic
exclusionary
intersection 44 against the relatively rotatable surface 8.
[001341 The rotary seal 10 is shown in the position it would assume when
the pressure of
the first fluid 12 is greater than that of the second fluid 14. The second
seal end 36 is supported
by the second groove wall 20 at all locations except the clearance gap 52. The
first seal end 34
is not touching the first groove wall 18. The rotary seal 10 and the footprint
38 can incorporate
the features and advantages of the invention that have previously been
described, sans the
implications of skew-resisting confinement. The rotary seal 10 in FIG. 11 is
prevented from
51
CA 02887776 2015-04-09
skewing and twisting only when the pressure of the first fluid 12 is
sufficiently higher than the
pressure of the second fluid 14.
4. Conclusion.
[001351 In view of the foregoing it is evident that the present invention
is one that is well
adapted and believed to attain the aspects and features hereinabove set forth,
together with other aspects
and features which are inherent in the apparatus disclosed herein and defined
by the appended claims.
1001361 Even though several specific hydrodynamic rotary seal and seal
gland geometries
are disclosed in detail herein, many other geometrical variations employing
the basic principles
and teachings of this invention are possible.
[00137] The foregoing disclosure and description of the invention are
illustrative and
explanatory thereof, and various changes in the size, shape and materials, as
well as in the
details of the illustrated construction, may be made without departing from
the scope of the
invention defined in the appended claims. The present embodiment is,
therefore, to be considered
= as merely illustrative and not restrictive, the scope of the invention
being indicated by the claims
rather than the foregoing description, and all changes which come within the
meaning and range of
equivalence of the claims are therefore intended to be embraced therein.
52
