U.S. patent application number 14/366856 was filed with the patent office on 2014-12-18 for earth and/or sealing assembly for electric motors.
The applicant listed for this patent is Pope Electric Motors Pty Ltd. Invention is credited to Peter Finck.
Application Number | 20140369821 14/366856 |
Document ID | / |
Family ID | 48667502 |
Filed Date | 2014-12-18 |
United States Patent
Application |
20140369821 |
Kind Code |
A1 |
Finck; Peter |
December 18, 2014 |
EARTH AND/OR SEALING ASSEMBLY FOR ELECTRIC MOTORS
Abstract
The present invention relates to a shaft earth and/or sealing
assembly for use with housed rotating equipment such as electric
motors to earth the shaft and also provide an IP69K-rated seal that
is flame and spark resistant.
Inventors: |
Finck; Peter; (North
Plympton, AU) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Pope Electric Motors Pty Ltd |
North Plympton |
|
AU |
|
|
Family ID: |
48667502 |
Appl. No.: |
14/366856 |
Filed: |
December 19, 2012 |
PCT Filed: |
December 19, 2012 |
PCT NO: |
PCT/AU2012/001561 |
371 Date: |
June 19, 2014 |
Current U.S.
Class: |
415/174.5 |
Current CPC
Class: |
H02K 5/124 20130101;
H02K 5/10 20130101; F01D 11/02 20130101; H02K 11/40 20160101 |
Class at
Publication: |
415/174.5 |
International
Class: |
F01D 11/02 20060101
F01D011/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 21, 2011 |
AU |
2011905348 |
Claims
1-9. (canceled)
10. A sealing assembly for an electric motor having a rotatable
drive shaft, a housing and at least one bearing, said sealing
assembly including: a bearing cap associated with said at least one
bearing and mounted to an end of said motor housing, said bearing
cap accommodating a slinger in contact with said shaft, the slinger
being rotatable together with said shaft; a slinger cover disposed
on an outer end of said bearing cap, the slinger cover defining a
chamber between the slinger cover and the slinger, said slinger
cover and slinger including axially extending, close tolerance
surfaces forming a labyrinth between an exterior of the slinger
cover and inside said chamber.
11. The sealing assembly as defined in claim 10 wherein said close
tolerance labyrinth surfaces includes an inner surface of the
slinger cover adjacent the shaft including an axially extending,
annular male portion and two annular female portions on either side
thereof.
12. The sealing assembly as defined in claim 11 wherein said close
tolerance labyrinth surfaces includes an outer surface of the
slinger adjacent the shaft including two axially extending male
portions and one female portion there between.
13. The sealing assembly as defined in claim 12 wherein the male
portion of the slinger cover is adapted to extend inside the female
portion of the slinger, and the male portions of the slinger extend
inside the two female portions of the cover.
14. The sealing assembly as defined in claim 10 wherein said
chamber includes a portion in which an electrically conductive
material is accommodated to enable contact between said
electrically conductive material and a surface of the slinger.
15. The sealing assembly as defined in claim 14 wherein said
electrically conductive material is a sacrificial portion of an
earth brush that is spring biased against said slinger surface.
16. (canceled)
17. (canceled)
18. (canceled)
19. The sealing assembly as defined in claim 15 wherein the slinger
cover includes a socket extending from an exterior of said slinger
cover to inside said chamber, said earth brush being shaped for
insertion into said socket and said socket being positioned such
that when the earth brush is inserted, the sacrificial portion
contacts the slinger.
20. The sealing assembly as defined in claim 15 wherein said
electrically conductive material further includes electrically
conductive lubricant which fills said chamber.
21. The sealing assembly as defined in claim 14 wherein said
electrically conductive material is conductive lubricant which
fills said chamber.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a shaft earth and/or
sealing assembly for use with rotating equipment such as electric
motors.
BACKGROUND OF THE INVENTION
[0002] Various shaft sealing devices have been utilized to try to
protect the integrity of a bearing environment. However, seals that
are often used are known to quickly wear to failure and are also
known to permit excessive amounts of moisture and other
contaminants to immigrate into the oil reservoir of the operating
equipment. The problem of seal wear and damage, with respect to
electrical motors using variable frequency drives (VFDs) for
example, is exacerbated because of the very nature of the control
of electricity connected to variable frequency drive (VFD)
controlled motors.
[0003] 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,
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".
[0004] There are many causes of bearing current including voltage
pulse overshoot in the VFD, non-symmetry of the motor's magnetic
circuit, supply imbalances, and transient conditions, among other
causes. Any of these conditions can occur independently or
simultaneously to create bearing currents in the motor shaft.
[0005] 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 failure.
[0006] In addition to the need for grounding an electric motor
shaft, there is a general need particularly in the mining sector
for electric motors to be IP69K-rated and also flame and spark
proof. To achieve this rating, the motor must be dust tight and
capable of withstanding high-pressure and steam cleaning.
SUMMARY OF THE INVENTION
[0007] Therefore in one aspect, the present invention provides an
earth assembly for an electric motor having a rotatable drive
shaft, a housing and a bearing journalled about said shaft at at
least one end thereof, said earth assembly characterised by: [0008]
a bearing cover associated with said bearing and mounted to an end
of said motor housing, said bearing cover accommodating a slinger
in contact with said shaft, the slinger being rotatable together
with said shaft; [0009] a slinger cover disposed on an outer end of
said bearing cover, the slinger cover defining a chamber between
the slinger cover and the slinger, said chamber including a portion
in which an electrically conductive material is accommodated to
enable contact between said electrically conductive material and a
surface of the slinger.
[0010] In an embodiment, said electrically conductive material is a
sacrificial portion of an earth brush that is spring biased against
said slinger surface.
[0011] In an embodiment, said slinger cover includes a socket
extending from an exterior of said slinger cover to inside said
chamber, said earth brush being shaped for insertion into said
socket and said socket being positioned such that when the earth
brush is inserted, the sacrificial portion contacts said slinger
surface.
[0012] In an embodiment, said socket includes an internal thread
and said earth brush includes a screw head having an external
thread configured to engage the internal thread, the sacrificial
portion being spaced from the screw head by a compression spring
that biases said sacrificial portion towards said surface.
[0013] In an embodiment, the assembly further includes a wear
indicator configured to indicate to an operator when the earth
brush sacrificial portion is worn to a predetermined level.
[0014] In an embodiment, said electrically conductive material
further includes electrically conductive lubricant which fills said
chamber.
[0015] In an alternative embodiment, said electrically conductive
material is conductive lubricant which fills said chamber.
[0016] In an embodiment, the slinger and slinger cover include
axially extending, close tolerance surfaces forming a labyrinth
between an exterior of said slinger and bearing covers and inside
said chamber.
[0017] In another aspect, the present invention provides an
electric motor including an earth assembly as characterised in
paras. [007] to [014].
[0018] In another aspect, the present invention provides a sealing
assembly for an electric motor having a rotatable drive shaft, a
housing and at least one bearing, said sealing assembly including:
[0019] a bearing cover associated with said at least one bearing
and mounted to an end of said motor housing, said bearing cover
accommodating a slinger in contact with said shaft, the slinger
being rotatable together with said shaft; [0020] a slinger cover
disposed on an outer end of said bearing cover, the slinger cover
defining a chamber between the slinger cover and the slinger, said
slinger cover and slinger including axially extending, close
tolerance surfaces forming a labyrinth between an exterior of the
slinger and bearing covers and inside said chamber.
[0021] In an embodiment, said close tolerance labyrinth surfaces
includes an inner surface of the slinger cover adjacent the shaft
including an axially extending, annular male portion and two
annular female portions on either side thereof.
[0022] In an embodiment, said close tolerance labyrinth surfaces
includes an outer surface of the slinger adjacent the shaft
including two axially extending male portions and one female
portion there between.
[0023] In an embodiment, the male portion of the slinger cover is
adapted to extend inside the female portion of the slinger, and the
male portions of the slinger extend inside the two female portions
of the cover.
[0024] In an embodiment, said chamber includes a portion in which
an electrically conductive material is accommodated to enable
contact between said electrically conductive material and a surface
of the slinger.
[0025] In an embodiment, said electrically conductive material is a
sacrificial portion of an earth brush that is spring biased against
said slinger surface, the slinger cover including a socket
extending from an exterior of said slinger cover to inside said
chamber, said earth brush being shaped for insertion into said
socket and said socket being positioned such that when the earth
brush is inserted, the sacrificial portion contacts one of said
slinger male portions.
[0026] In another aspect, the invention provides an electric motor
including a sealing assembly as characterised in any one of paras.
[016] to [021].
[0027] In another aspect, the present invention provides an earth
and sealing assembly for an electric motor having a rotatable drive
shaft, a housing, and a bearing journalled about said shaft at at
least one end thereof, said earth assembly characterised by: [0028]
a bearing cover associated with said bearing and mounted to an end
of said motor housing, said bearing cover accommodating a slinger
in contact with said shaft, the slinger being rotatable together
with said shaft; [0029] a slinger cover disposed on an outer end of
said bearing cover, the slinger cover defining a chamber between
the slinger cover and the slinger, said chamber including a portion
in which an electrically conductive material is accommodated to
enable contact between said electrically conductive material and a
surface of the slinger to thereby ground the shaft; and [0030]
wherein said slinger cover and slinger include axially extending,
close tolerance surfaces forming a labyrinth between an exterior of
said slinger cover and inside said chamber to prevent ingress of
fluid or particulates into said chamber.
[0031] In another aspect, the invention provides an electric motor
including an earth and sealing assembly as characterised in para.
[023].
BRIEF DESCRIPTION OF THE DRAWING FIGURES
[0032] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate several
implementations of the invention and, together with the
description, serve to explain the advantages and principles of the
invention. In the drawings:
[0033] FIG. 1 illustrates a front, exploded perspective view of an
electric motor and a shaft earth and/or sealing assembly in
accordance with an embodiment of the present invention;
[0034] FIG. 2 illustrates a rear, exploded perspective view of the
electric motor and shaft earth and/or sealing assembly of FIG. 1;
and
[0035] FIG. 3 illustrates an enlarged cross sectional view of a
shaft earth and/or sealing assembly according to an embodiment
associated with an end of the electric motor, the cross sectional
view taken along the motor's longitudinal axis.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0036] The following detailed description of the invention refers
to the accompanying drawings. Although the description includes
exemplary embodiments, other embodiments are possible, and changes
may be made to the embodiments described without departing from the
spirit and scope of the invention. Wherever possible, the same
reference numbers will be used throughout the embodiments and the
following description to refer to the same and like parts.
[0037] The present invention relates, in one aspect, to a shaft
earth and/or sealing assembly 10 which in an embodiment can be
incorporated into an electric motor 12. The invention relates, in
another aspect, to an electric motor 12 incorporating a shaft earth
and/or sealing assembly 10.
[0038] Turning to FIGS. 1 and 2, there is shown an electric motor
12 according to an embodiment including a cylindrical outer housing
14 with cooling fins 16, a rotatable drive shaft 18, and a shaft
earth and/or sealing assembly 10 associated with at least one end
of the motor which in FIGS. 1 and 2 is shown in an exploded form.
It is to be understood at the outset that the invention is not
intended to be limited to use of only one assembly 10 at one end of
the motor 12. In an embodiment, the electric motor includes a shaft
earth and/or sealing assembly 10 associated with bearings 20 at
both ends. It is to be further understood that the internal
components of the electric motor are considered to be known to
those skilled in the art, and so these components are not described
in detail herein.
[0039] FIG. 3 illustrates one end of a motor 12 according to an
embodiment including the shaft 18, a roller bearing 20 journalled
around the shaft, an end shield 22, and a roller bearing cap 24,
slinger 26, and slinger cover 28 which all form part of a shaft
earth and/or sealing assembly 10 according to an embodiment. Each
of the roller bearing 20, end shield 22, roller bearing cap 24,
slinger 26, and slinger cover 28 include radial centres which are
coaxial with the centre of the shaft 18, but only the slinger 26
rotates therewith as will become apparent. There are various other
components which form part of the assembly 10 which are described
in more detail below.
[0040] A method of greasing the roller bearing 20 will now be
described with reference to FIG. 3. The end shield 22 includes an
internal cavity 30 which ensures that grease placed into the cavity
through capped opening 32 lubricates the roller bearing 20 at all
times. The grease path is indicated by arrows 34, and it can be
appreciated that grease also enters the internal cavity 36 of the
bearing cap 24 through which it can be discharged via outlet 38.
The bearing cap 24 includes V-ring seals 40 fitted for protection
against ingress into the bearing cavity 26 of water, dust, solids,
and also excess conductive lubricant which will be described in
more detail below.
[0041] Typically, fresh grease will flush old grease from the motor
and V-ring seals 40, preventing dust, water and other contaminants
entering the motor. The invention is not intended to be limited to
any one means of discharging grease from cavity 36, for example,
one could use an open chamber, a grease exhaust seal cover, a
"split rubber" membrane, a grease chute, a grease trap and tray, a
pneumatic cylinder discharge pump, or a spring loaded grease
valve.
[0042] An advantage afforded by the present invention is that the
motor 12 meets the IP-69K rating mentioned in the preamble, as well
as being flame and spark proof. Aside from the various O-ring seals
that are used, most of which are listed and described below, a
mechanism for achieving this rating is the labyrinth created by
close tolerance annular surfaces between the slinger 26 and slinger
cover 28. In particular, the inner surface of the slinger cover 28
adjacent the central shaft 18 is shaped such that it includes an
axially extending, annular male portion 42 and female portions 44
and 46 on either side thereof. In contrast, the outer surface of
the slinger 26 adjacent the central shaft 18 is shaped such that it
includes two axially extending, annular male portions 48 and 50 and
one female annular portion 52 therebetween. Thus, when the two
components are fitted and the respective portions brought together
in close tolerance, the male portion 42 of the slinger cover is
adapted to extend inside the female portion 52 of the slinger,
while the male portions 48 and 50 of the slinger 26 extend inside
the two female portions 44 and 46 of the cover. What is thus
created is a labyrinth through which water, dust, etc, must travel
before it can reach inside a lubricant chamber 54 inside the
slinger cover 28. Of course, the intention is that no water and/or
dust particles will be able to travel through this labyrinth into
chamber 54.
[0043] Various seals in addition to those described above are used
throughout the system, including:
[0044] Oil seal 56 between the shaft 18 and slinger cover 28;
[0045] Shaft seal 58 to provide a first barrier against water and
dust ingress;
[0046] O-ring 60 between the slinger 26 and shaft 18;
[0047] O-ring 62 between bearing cap 24 and slinger cover 28;
[0048] O-rings 64 for bearing cap bolts 66 which fasten the bearing
cap 24 to the end shield 22;
[0049] O-ring 68 between the end shield 22 and motor housing 14;
and
[0050] O-ring 70 between bearing cap 24 and end shield 22.
[0051] Through testing, it has been found that the motor is sealed
to an extent that even if an internal explosion occurred (not an
uncommon occurrence in mining environments), the motor would still
remain substantially intact and so damage to the surroundings would
be minimal.
[0052] The assembly 10 is also used to earth or ground the motor
shaft 18. The reader is directed to the enlarged cross sectional
view on the upper left of FIG. 3. There is shown an earth brush 72
according to an embodiment which is adapted to make contact at all
times with a surface of male portion 48 of the slinger 26. The
skilled addressee would realise that the earth brush serves to
ground the shaft 18. In the embodiment shown, the earth brush 72 is
biased against the slinger male portion 48 through use of a grub
screw 74 and compression spring 76 adapted to provide bias to a
brush holder screw 78 at the top of the earth brush 72. The bias
provided by the spring will ensure contact is maintained. The
skilled addressee would also realise that the earth brush screw is
accessible from outside the motor. Because the slinger 26 is
rotating relative to the brush, the brush 72 will become worn and
will require replacement at appropriate intervals throughout the
life of the motor.
[0053] The slinger cover chamber 54 is adapted to be filled with
conductive lubricant via a nipple (not shown). The conductive
lubricant provides an electrically conductive path for low voltage
currents, to prevent harmful currents from discharging through the
bearing to earth. The slinger cover 28 may include a screw or
spring loaded lubricant exhaust valve 80 to seal the conductive
lubricant exhaust port 82.
[0054] It is to be understood that the present invention is not
intended to be limited to the use of an earth brush to ground the
shaft. For example, the earth brush and conductive lubricant used
in combination in the embodiment shown could equally well be used
independent of each other. For example, a conductive lubricant
could be used with the brush. In an alternate embodiment, the
spring and grub screw configuration described above could form part
of a one-piece elongate insert (not shown) including a housing
adapted to hide and protect components such as springs and/or
associated components. There are a number of earth brushes
available in the market, including conventional friction type
brushes to more evolved microfiber brushes, all of which could be
implemented within the scope of the present invention.
[0055] In an embodiment, the apparatus 10 includes a wear indicator
(not shown) used to warn an operator when the earth brush is almost
completely worn. Such an indicator could be in the form of a
microswitch (not shown) triggered when the brush is worn to a
predetermined level. It is to be understood that the apparatus 10
may include other known components and mechanisms to improve its
operation and/or performance. For example, in the embodiment shown,
the bearing housing is insulated 84 to isolate the bearing 20 from
shaft currents.
[0056] Further advantages and improvements may very well be made to
the present invention without deviating from its scope. Although
the invention has been shown and described in what is conceived to
be the most practical and preferred embodiment, it is recognized
that departures may be made therefrom within the scope and spirit
of the invention, which is not to be limited to the details
disclosed herein but is to be accorded the full scope of the claims
so as to embrace any and all equivalent devices and apparatus.
[0057] In the summary of the invention and the claims, except where
the context requires otherwise due to express language or necessary
implication, the word "comprising" is used in the sense of
"including", i.e. the features specified may be associated with
further features in various embodiments of the invention.
* * * * *