U.S. patent application number 12/401331 was filed with the patent office on 2011-05-05 for motor grounding seal.
Invention is credited to Thomas D. Coe, David C. Orlowski.
Application Number | 20110101618 12/401331 |
Document ID | / |
Family ID | 37595629 |
Filed Date | 2011-05-05 |
United States Patent
Application |
20110101618 |
Kind Code |
A1 |
Orlowski; David C. ; et
al. |
May 5, 2011 |
Motor Grounding Seal
Abstract
A shaft seal assembly is disclosed having a stator including a
main body and axial and radial projections therefrom. The rotor is
radially extended and encompasses the axial and radial projections
from said stator. A passageway formed between the radial projection
of stator and rotor results in an axial passageway having its
opening facing rearwardly from the rotor and away from the source
of impinging coolant and/or contaminant. A concentric
circumferential receptor groove in the stator facing the housing
allows insertion of conductive means for transmission of
electrostatic charge away from the shaft through the shaft seal
assembly to the housing and ground. The receptor groove is opposite
the axial passageway and provides for both a substantially lower
contaminant environment and improved engagement with conductive
means.
Inventors: |
Orlowski; David C.; (Punta
Gorda, FL) ; Coe; Thomas D.; (Milan, IL) |
Family ID: |
37595629 |
Appl. No.: |
12/401331 |
Filed: |
March 10, 2009 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11378208 |
Mar 17, 2006 |
7521827 |
|
|
12401331 |
|
|
|
|
60693548 |
Jun 25, 2005 |
|
|
|
Current U.S.
Class: |
277/412 ;
29/428 |
Current CPC
Class: |
F16J 15/4478 20130101;
Y10T 29/49826 20150115; F16C 33/80 20130101; H02K 5/10 20130101;
H02K 11/40 20160101 |
Class at
Publication: |
277/412 ;
29/428 |
International
Class: |
F16J 15/447 20060101
F16J015/447; B23P 11/00 20060101 B23P011/00 |
Claims
1. A labyrinth type seal for sealing a rotatable shaft entering a
grounded housing comprising: a) a housing; b) a stator surrounding
a shaft and affixed to the housing, said stator having a main body
and projections extending both axially and radially beyond said
main body, said radial projections being greater than said axial
projection; c) a rotor surrounding said shaft and rotatively
connected to said shaft; said rotor having a main body and
projections extending both radially and axially; d) a circular
circumferential receptor groove placed within the rotor and facing
said shaft; e) a circumferential conductive means, said conductive
means placed within said receptor groove and engaged with said
shaft to conduct electrical currents away from said shaft to said
grounded housing; and f) said rotor and said stator abutted and
intermeshed with each other on said shaft, said rotor radial
projections extending radially outwardly farther than any radial
projections of said stator.
2. A seal accordance to claim 1 wherein the radial space between
said radial rotor projections and said radial stator projections
forms a first axial passage.
3. A seal in accordance with claim 2, wherein said first passageway
includes a first axial passage opening to a space in said stator
and facing the body of the stator between said housing and the
radial extensions of the rotor and stator.
4. A seal in accordance with claim 3, wherein said dimension of
said axial passage is constant.
5. A seal in accordance with claim 4, wherein the dimension of said
axial passage is predetermined.
6. A seal in accordance with claim 3, wherein said opening of said
axial passage faces away from injected coolant, said rotor
projection and towards said housing.
7. A seal accordance with claim 2, wherein said main body of said
stator surrounds a portion of said rotor.
8. A seal in accordance with claim 2, wherein the radius of the
radial internal surface of the rotor radial projection encompassing
said stator is greater than the radius of the exterior surface of
said radial projection of said stator.
9. A seal in accordance with claim 1, wherein there is at least one
labyrinth formed between the main body of said stator and the main
body of said rotor.
10. A seal in accordance with claim 1, wherein said rotor and said
stator are restrained from relative axial movement between each
other.
11. A seal in accordance with claim 1, wherein a groove is formed
in said main body of said stator, said groove augmenting the radial
extension of said radial projection from said stator.
12. A shaft seal assembly as described in claim 1 wherein the
conductive means promotes conduction of shaft voltage and is
selected from the group consisting of fibrous conductive brushes, a
metallic insert with solid conductor ring, an electrically
conductive insert ring having a metallic base and a solid
conductive ring and combinations thereof.
13. A labyrinth type seal for sealing a rotatable shaft entering a
grounded housing comprising: a. a grounded housing; b. a stator
surrounding a shaft and affixed to the housing, said stator having
a main body and projections extending both axially and radially
beyond said main body, said radial projections being greater than
said axial projection; c. a rotor surrounding said shaft and
rotatively connected to said shaft; said rotor having a main body
and projections extending both radially and axially; d. a circular
circumferential receptor groove placed within the rotor and facing
said shaft; e. a circumferential brush ring having an annular
frame, said frame including: i. first and second frame members
defining an annular channel; ii. a plurality of electrically
conductive filament brushes electrically connected to said annular
frame, said filament brushes being sufficiently small to induce
ionization in the presence of an electrical field, said filament
brushes being retained between said first and second frame members
and having distal end portions disposed in said channel; f. wherein
said electrical charges produced through ionization are collected
for conduction through said filament brushes to and through said
annular frame, to and through said stator and to said grounded
housing, away from said shaft; and g. said rotor and said stator
are abutted and intermeshed with each other on said shaft, said
rotor radial projections extending radially outwardly farther than
any radial projections of said stator.
14. A seal in accordance with claim 13 wherein the radial space
between said radial rotor projections and said radial stator
projections forms a first axial passage.
15. A seal in accordance with claim 14, wherein said first
passageway includes a first axial passage opening to a space in
said stator and facing the body of the stator between said housing
and the radial extensions of said rotor and said stator.
16. A seal in accordance with claim 15, wherein said dimension of
said axial passage is constant.
17. A seal in accordance with claim 16, wherein the dimension of
said axial passage is predetermined.
18. A seal in accordance with claim 15, wherein said opening of
said axial passage faces away from injected coolant, said rotor
projection and towards said housing.
19. A seal accordance with claim 14, wherein said main body of said
stator surrounds a portion of said rotor.
20. A seal in accordance with claim 14, wherein the radius of the
radial internal surface of the rotor radial projection encompassing
said stator is greater than the radius of the exterior surface of
said radial projection of said stator.
21. A seal in accordance with claim 13, wherein there is at least
one labyrinth formed between the main body of said stator and the
main body of said rotor.
22. A method of sealing a shaft exiting a grounded housing and
conducting electrostatic charge away from said shaft to the
grounded housing, the method comprising: a. fixing a stator having
a main body and a projection extending both radially and axially
beyond the main body of said stator concentrically about the shaft
wherein the radial projections are greater than the axial
projection; b. mounting a rotor sealed on the shaft in close
relation to the housing for rotation with the shaft and providing
the rotor with radial projections extending radially outwardly
farther than any radial projections of said stator and said rotor
encompassing the radial extremity of the radial projection of the
stator and having overlapping radially spaced surfaces forming an
axial passage between the surfaces of the rotor and the stator
projections, wherein said opening of said axial passage faces away
from said rotor and toward the body of said stator; c. mounting a
conductive means within said rotor to engage said shaft and promote
transmission of shaft voltage bearing currents; and d. transmitting
said shaft voltage from said shaft through said conductive means,
said rotor and said grounded housing.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of and claims
priority from U.S. patent application Ser. No. 11/378,208 filed on
Mar. 17, 2006, which claimed the benefit of U.S. provisional App.
No. 60/693,548, filed Jun. 25, 2005, both of which are incorporated
herein in their entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to an improved bearing
isolator sealing device, and more particularly, to a bearing
isolator for directing electrostatic charge to ground while
retaining lubrication solution and repelling contamination such as
water, dust, dirt, sand and paper stock from the bearing
environment and away from the shaft grounding ring, within the
bearing cavity of a hub assembly such as an electrical motor
bearing for engagement with a rotatable shaft.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0003] No federal funds were used to develop or create the
invention disclosed and described in the patent application.
REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM
LISTING COMPACT DISK APPENDIX
[0004] (Not Applicable)
BACKGROUND OF THE INVENTION
[0005] This invention relates generally to shaft sealing devices
for use with rotating equipment. Adequate maintenance of rotating
equipment is difficult to obtain because of extreme equipment duty
cycles, the lessening of service factors, design and the lack of
spare rotating equipment in most processing plants. This is
especially true of machine tool spindles, wet end paper machine
rolls, aluminum rolling mills and steam quench pumps and other
equipment utilizing extreme contamination affecting lubrication.
Various forms of shaft sealing devices have been utilized to try to
protect the integrity of the bearing environment, including rubber
lip seals, clearance labyrinth seals, and attraction magnetic
seals. Lip seals or other contacting shaft seals can quickly wear
out and fail and are also known to permit excessive amounts of
moisture and other contaminants to immigrate into the oil reservoir
of the operating equipment even before failure had exposed the
interface between the rotor and the stator to the contaminants or
lubricants at the radial extremity of the seal. The problem of seal
wear and damage as applied to electrical motors using variable
frequency drives is compounded because of the very nature of the
control of electricity connected to variable frequency drive
(hereinafter referred to as VFD) controlled motors.
[0006] VFDs regulate the speed of a motor by converting sinusoidal
line alternating current (AC) voltage to direct current (DC)
voltage, then back to a pulse width modulated (PWM) AC voltage of
variable frequency. The switching frequency of these pulses ranges
from 1 kHz up to 20 kHz and is referred to as the "carrier
frequency." The ratio of change in voltage to the change in time
(.DELTA.V/.DELTA.T) creates what has been described as a parasitic
capacitance between the motor stator and the rotor, which induces a
voltage on the rotor shaft. If the voltage induced on the shaft,
which is referred to as "common mode voltage" or "shaft voltage,"
builds up to a sufficient level, it can discharge to ground through
the bearings. Current that finds its way to ground through the
motor bearings in this manner is called "bearing current.".sup.1
.sup.1
http:www.greenheck.com/technical/tech_detail.php?display=files/Product_gu-
ide/fal17.sub.--03
[0007] There are many causes of bearing current including voltage
pulse overshoot in the VFD, non-symmetry of the motor's magnetic
circuit, supply unbalances, transient conditions, and others.
[0008] Any of these conditions can occur independently or
simultaneously to create bearing currents in the motor shaft..sup.2
.sup.2
http:www.greenheck.com/technical/tech_detail.php?display=files/Product_gu-
ide/fal17.sub.--03
[0009] Shaft voltage accumulates on the rotor until it exceeds the
dielectric capacity of the motor bearing lubricant, then the
voltage discharges in a short pulse to ground through the bearing.
After discharge, the voltage again accumulates on the shaft and the
cycle repeats itself. This random and frequent discharging has an
electric discharge machining (EDM) effect, causing pitting of the
bearing's rolling elements and raceways. Initially, these
discharges create a "frosted" or "sandblasted" effect. Over time,
this deterioration causes a groove pattern in the bearing race
called "fluting" which is an indication that the bearing has
sustained severe damage. Eventually, the deterioration will lead to
complete bearing and failure..sup.3 .sup.3See www.Greenheck.com
[0010] The prior art teaches numerous methods of handling shaft
voltages including using a shielded cable, grounding the shaft,
insulated bearings and installation of a Faraday shield. For
example, see published U.S. Patent Applications 2004/0233592 and
2004/0185215 filed by Oh et al., which are incorporated herein by
reference. Most external applications add to costs, complexity and
exposure to external environmental factors. Insulated bearings
provide an internal solution by eliminating the path to ground
through the bearing for current to flow. But, installing insulated
bearings does not eliminate the shaft voltage, which will still
find the lowest impedance path to ground. Thus, insulated bearings
are not effective if the impedance path is through the driven load.
Therefore, the prior art does not teach an internal, low wearing
method or apparatus to efficaciously ground shaft voltage and avoid
electric discharge machining of bearings leading to premature
bearing failure.
SUMMARY OF THE INVENTION
[0011] An objective of the present invention is to provide an
improvement to seals or bearing isolators to prevent leakage of
lubricant and entry of contaminants by encompassing the stator
within the rotor to create an axially directed interface at the
radial extremity of the rotor. It is also an objective of the
present invention to disclose and claim a seal or bearing isolator
for rotating equipment that retains lubricants, prevents
contamination and conducts and transmits and directs accumulated
bearing current to ground.
[0012] Prior art seals traditionally had the interface between the
rotor and the stator exposed radially to the contaminants or
lubricants at the radial extremity of the seal. The projection of
an axial portion of the stator into the rotor has been expanded
radially. This projection or protruding member of the stator into
the rotor has been expanded radially beyond the diameter of the
major portion or body of the stator.
[0013] The rotor and the recess rotor, which previously surrounded
the stator projection or insertion, is also extended radially
beyond the major portion of the stator. The rotor now encompasses
the stator, or a substantial portion of the stator's radial
projection, in such a manner that the interface presented to the
ingress of the lubricant or contaminates is facing axially and
rearwardly. The axial facing interface presents limited access to
the internal of the seal and a constant dimensional interface
between the rotor and the stator regardless of any axial movement
of the rotor with respect to the stator.
[0014] A groove may be machined into the stator to accentuate the
novel radial extension of the rotor and the stator. This groove
improves the ability of the seal to prevent contaminants from
entering the axial interface gap between the rotor and the stator.
This novel improvement, i.e., the encapsulation of the radial
extension stator by the rotor, enables the interface gap between
the accessible portions of the stator and the rotor to be of a
predetermined dimension. The improvement also means that there is
no fluctuation or variation in the interface gap resulting from any
relative axial movement between the rotor and the stator.
[0015] This novel seal or bearing isolator will operate to vastly
improve the rejection or ingress of contaminants into the interface
gap between the rotor and stator. The entrance to the interface gap
is facing or directed away from the normal flow of contaminants,
i.e., along the axis of the shaft toward the housing. The interface
gap can be machined to extremely close tolerances because there is
no movement radially between the rotor and the stator and any axial
movement does not affect the radial interface.
[0016] The increased rejection of contaminants also provides an
opportunity to reduce shaft voltage and attendant bearing wear
caused by electrostatic discharge machining Placement of a receptor
groove in the stator of the above described shaft seal assembly
allows insertion of a conductive insert. This insert can be a
metallic or non-metallic solid, machined or molded. The insert can
also be a metallic ring having conductive filament brushes affixed
therein. Although any type of metal compatible with operating
conditions and metallurgy may be selected, bronze, gold or aluminum
are believed to be preferred metals because of increased
conductivity, strength, corrosion and wear resistance. Combining
the receptor groove and conduction means with the benefits of the
improved bearing isolator reduces the environmental exposure of the
conduction means.
[0017] It has been found that a bearing isolator assembly having a
rotor and stator manufactured from bronze has improved charge
dissipation qualities. The preferred bronze metallurgy is that
meeting specification 932 (also referred to as 932000 or "bearing
bronze"). This bronze is preferred for bearings and bearing
isolators because it has excellent load capacity and antifriction
qualities. This bearing bronze alloy also has good machining
characteristics and resists many chemicals. It is believed that the
specified bronze offers increased shaft voltage collection
properties comparable to the ubiquitous lighting rod due to the
relatively low electrical resistivity (85.9 ohms-cmil/ft@68 F or
14.29 microhm-cm@20 C) and high electrical conductivity (12%
IACS@68 F or 0.07 MegaSiemens/cm@20 C) of the material
selected.
[0018] This embodiment improves upon shaft brushes typically
mounted external of the motor housing. Previous tests of a
combination shaft seal assembly with a concentric inserted
conductive brush engaged with the shaft have shown substantial
reduction in shaft voltage and attendant electrostatic discharge
machining Direct seating between the conduction ring means and the
bearing isolator portion of the motor ground seal improves the
conduction to ground over a simple housing in combination with a
conduction means as taught by the prior art. Those practiced in the
arts will understand that this improvement requires the electric
motor base to be grounded, as is the norm.
[0019] It is therefore an objective of the present invention to
disclose and claim an electric motor for rotating equipment having
bearing isolator means that retains lubricants, prevents
contamination and conducts and transmits and directs bearing
current to ground.
[0020] It is another objective of the present invention to disclose
and claim a bearing isolator for rotating equipment that retains
lubricants, prevents contamination and conducts electrostatic
discharge (shaft voltage) to improve bearing operating life.
[0021] It is another objective of the present invention to disclose
and claim a bearing isolator for rotating equipment that retains
lubricants, prevents contamination and provides adequate
grounding.
[0022] It is another objective of the present invention to disclose
and claim a bearing isolator for rotating equipment that retains
lubricants, prevents contamination and provides a low impedance
ground path for the voltage to flow to earth ground without passing
through the motor bearings or other components while protecting and
isolating the typically delicate shaft grounding ring from the
elements.
[0023] Other objects, advantages and embodiments of the invention
will become apparent upon the reading the following detailed
description and upon reference to drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a perspective exterior view of motor ground seal
assembly mounted to a motor housing.
[0025] FIG. 2 is a sectional view of the present invention as shown
in FIG. 1.
[0026] FIG. 3 is a sectional view of another embodiment of the
present invention as shown in FIG. 2 wherein a conduction ring is
shown with a plurality of conductive brushes.
[0027] FIG. 4 is a sectional view of another embodiment of the
present invention wherein a metallic conduction ring is shown with
an insert having conductive properties.
[0028] FIG. 5 is a sectional view of another embodiment as shown in
FIG. 2 wherein the conductive ring is solid.
[0029] FIG. 6 is another embodiment of the present invention as
shown in FIG. 2.
[0030] FIG. 7 is a side view of the present invention illustrating
the concentric nature of the invention.
[0031] FIG. 8 is a perspective view of the motor ground seal
assembly.
DETAILED DESCRIPTION
Element Listing
TABLE-US-00001 [0032] Description Element No. Drive bearing 2
Conductive brushes 3 Receptor groove 4 Brush ring 5 Metallic insert
with solid conductor ring 6 Conductive insert ring 7 O-ring 8 Solid
conductive ring 9 Rotatable shaft 10 Housing 11 Rotatable shaft
center 12 Rotor 13 Rotor surface 13a Stator 14 Stator surface 14a
O-ring 15 Brush ring frame 16 O-ring 17 Motor ground seal assembly
18 Radial projection 19 first radial Interface gap 20 second radial
interface gap 21 Stator groove 22
DETAILED DESCRIPTION
[0033] FIG. 1 illustrates a perspective view of the present
invention applied to a rotatable shaft 10 of an electrical motor
controller having a variable frequency drive (VFD). (Motor not
shown) The motor grounding Seal.TM. assembly 18 shown in FIG. 1 may
be mounted to rotatable shaft 10 on either one or both sides of the
motor housing assembly 11. The motor grounding Seal.TM. assembly 18
may be flange-mounted or press-fit or attached by other means to a
housing 11. The present invention will also function with a
rotating housing and stationary shaft. (Not shown)
[0034] As shown in FIGS. 2-6, the rotor 13 faces outboard and is
engaged with an inboard facing stator 14. The receptor groove 4
allows placement of one of the following conduction means with the
motor grounding seal assembly 18: a solid conductive ring having
conductive filament brushes 3 attached therein, a solid conductive
ring having conductive filament brushes 3 attached therein and a
metallic annular frame surrounding the conductive ring, a metallic
insert with solid conductor ring 6, or a conductive insert ring 7.
The receptor groove 4 as shown can also be utilized on other shaft
seal assemblies and bearing isolators or combinations therein which
use only labyrinths.
[0035] As shown in FIGS. 2-6, the location of the gap with respect
to the rotor 13 and stator 14 surfaces and the direction of the
opening interface gaps 20 and 21 are both important elements of one
embodiment of the motor grounding seal assembly 18. The rotor 13
extends radially well beyond the major diameter of the stator 14.
This permits the rotor 13 to encompass the also radially extended
projection 19 of the stator 14. It is important that this radial
extension of the rotor 13 extends beyond the basic radial dimension
of stator 14. See U.S. Pat. No. 6,419,233 issued to Orlowski and
incorporated by reference herein. This requires a departure from
the prior art wherein the rotor 13 was radially co-extensive with
the major diameter of the stator 14.
[0036] The second radial interface gap 21 between the rotor 13 and
stator 14 that is exposed to the contamination or lubricants is now
fixed in dimension and independent of any relative axial movement
between the rotor 13 and the stator 14. The first radial interface
gap 20 is still subject to variation in dimension by any relative
axial movement between the rotor 13 and the stator 14.
[0037] This relative movement is not significant to the operation
in as much as only a small amount of contaminants have been able to
enter the labyrinth because of the size and location of the first
radial interface gap 20. The removal of the interface gap 21 from
variations is more important in seals where the stator 13 and the
rotor 14 are not restrained from relative movement.
[0038] The orientation of the opening of the interface gap 21 is
important regardless of relative movement between the rotor 14 and
stator 13. The axial orientation of the second radial interface gap
21 controls entrance of contaminants. Reduction or elimination of
contaminants improves both the life and performance of the
conductive means. The opening of the second radial interface gap 21
is now facing rearwardly toward the housing 11 and away from the
contaminant stream. The contaminant or cooling stream will normally
be directed along the axis of the shaft 10 and toward the housing
11.
[0039] A first stator groove 22 may be cut in the stator 14. This
stator groove 22 enhances and accentuates the benefits of the
radial extension of the rotor 13 and the stator 14 with the
resultant orientation and independence of the second radial
interface gap 21. The motor ground seal assembly may be made from
any machinable metal such as stainless steel or having low
resistivity including bronze, aluminum, copper, gold and
combinations thereof.
[0040] A second groove may be cut into the stator 14 on the inboard
side facing away from the rotor 13 and into the housing 11. This
receptor groove 4 allows insertion of a circumferential ring-like
structure. The embodiment illustrated in FIG. 2 shows a solid
conductive ring 9 having conductive filaments or brushes 3 in
contact with said shaft 10. The concentric solid conduction ring 9
may be flange-mounted, press-fit or attached by other means to and
or within receptor groove 4.
[0041] FIG. 3 describes another embodiment of the present invention
wherein the conductive insert is a brush ring 5 having a metallic
base or frame 16, preferably made from a low resistivity material
such as bronze, copper, gold or aluminum, having a plurality of
fibrous conductive brushes 3 engaged with rotatable shaft 10 for
transmission of bearing currents to ground. In this embodiment, the
circumference of the brush ring 5 is force-fitted into the receptor
groove 4 in the motor ground seal assembly 18, by means of a
slightly tapered bore in said receptor groove 4 (not shown) to
accommodate imperfections and dimensional tolerance of the brush
ring 5 surrounding the filament brushes 3. In the preferred
embodiment, the brush ring 5 would be as described in published
U.S. Patent Applications 2004/0233592 and 2004/0185215 filed by Oh
et al. The brush ring 5 incorporates technology sold as an "AEGIS
SGR.TM. Conductive MicroFiber.TM. brush" by Electro Static
Technology--an Illinois Tool Works Company.
[0042] The motor grounding seal assembly 18 improves conduction and
reduces the effects of "bearing current" by enhancing and
increasing the rigidity of circumferential brush ring 5, thereby
increasing the resistance to deformation of the brush ring frame 16
during operation. Deformation of the brush ring 5 and frame 16
during operation is a problem because it destabilizes the spatial
relationship between the tip of the brushes, or the shaft facing
surfaces of other conductive means, and the rotating shaft 10. The
resulting change in spatial relationship, which although small and
within normal machine operating tolerances, negatively affects the
conduction of the electrostatic discharge (shaft voltage) from the
rotating shaft to ground, thus resulting in the decreased
performance of prior art grounding devices.
[0043] The performance of the motor ground seal assembly 18
disclosed and claimed herein is further improved by aggressive
interference between the conduction means and receptor groove 4 of
the motor ground seal assembly 18. The outside diameter of the
brush ring 5 means may be up to 0.004 inches (0.102 mm) greater
than the inside diameter of the receptor groove 4. The performance
of the motor ground seal assembly 18 is further improved by
aggressive interference between the motor grounding seal assembly
18 and the housing 11 of the motor. The outside diameter of the
stator may be up to 0.004 inches (0.102 mm) greater than the inside
diameter of the motor housing 11.
[0044] FIG. 4 describes another embodiment of the present invention
wherein the metallic insert with solid conductor ring 6 has a
metallic base, preferably a low resistivity material such as
bronze, copper, gold or aluminum, and forms a circumferential
conductive ring around the rotating shaft when inserted into the
receptor groove 4 of the stator 14 for engagement with rotatable
shaft 10 for transmission of bearing currents to ground. (Not
shown)
[0045] FIG. 5 describes another embodiment of the present invention
wherein the conductive insert ring 7 is a concentric
circumferential ring affixed within the receptor groove 4 of said
stator 14 therein for engagement with shaft 10 for transmission of
bearing currents to ground. (Not shown). Reduction of deformity
aggressive interference between conduction means/receptor groove 4
and motor ground seal 18/housing 11 rotating is contemplated for
the embodiments shown and described at FIGS. 4 and 5.
[0046] The motor ground seal assembly 18 may be used with o-ring 17
between stator 14 and motor housing 11 as shown in preceding FIGS.
1-5. Performance of the motor ground seal assembly 18, however, may
be further improved by eliminating o-ring 17 and its companion
groove as shown in FIG. 6. The non-conductive nature of o-ring 17
can impede conductivity between the motor grounding seal assembly
18 and motor housing 11 thereby decreasing the overall charge
dissipation performance of the motor ground seal assembly 18.
[0047] As shown in FIG. 7, the motor ground seal assembly 18 in
combination with the motor housing 11 creates a stable concentric
system with the rotating shaft as its center point 12. Inserting
the combination of conductive brushes 3, brush rings 5 or
conductive inserts (6, 7 or 9) into the motor ground seal assembly
18 within the motor housing 10, and press or force fitting the
various conducting elements (conduction means, stator 13 and
housing 11) together, forms a relatively fixed and stable spatial
relationship between the conducting elements, thereby improving the
collection and conduction of electrostatic discharge (shaft
voltage) from the rotating shaft 10 to ground, through the
conducting elements of the motor ground seal assembly 18. This
improved motor ground sealing system directly seats major elements
together which compensates for motor shafts, which are not
necessarily perfectly round, and ensures the variation or change in
distance from the brush tips 3 to the shaft 10 surface caused by
external forces acting on the motor ground sealing system are
minimal, thus promoting effective ionization of the air surrounding
the brushes 3 and conduction of shaft voltage.
[0048] FIG. 8 is a perspective view of a circumferential filament
brush ring having an annular frame. The frame includes frame
members defining an annular channel with a plurality of
electrically conductive filament brushes connected to said annular
frame. The filament brushes are sufficiently small to induce
ionization in the presence of an electrical field. The filament
brushes are retained by the frame members and have distal end
portions disposed in the channel formed by frame members. As shown,
the circumference of the brush ring 5 was force-fitted into the
tapered receptor groove 4 in the motor ground seal assembly 18.
[0049] Having described the preferred embodiment, other features of
the present invention will undoubtedly occur to those versed in the
art, as will numerous modifications and alterations in the
embodiments of the invention illustrated, all of which may be
achieved without departing from the spirit and scope of the
invention.
* * * * *
References