U.S. patent application number 10/014711 was filed with the patent office on 2003-06-12 for brushless motor having double insulation.
Invention is credited to Agnes, Michael Jeffrey, McCormick, Garrett Patrick, Walter, Richard Thomas, Yahnker, Christopher Ryan.
Application Number | 20030107278 10/014711 |
Document ID | / |
Family ID | 21767206 |
Filed Date | 2003-06-12 |
United States Patent
Application |
20030107278 |
Kind Code |
A1 |
Agnes, Michael Jeffrey ; et
al. |
June 12, 2003 |
BRUSHLESS MOTOR HAVING DOUBLE INSULATION
Abstract
A double insulated electronically commutated brushless motor for
coupling to a gearbox of a motor driven product. The motor includes
a first layer of electrical insulation that includes a plurality of
insulating strips formed in the shape of stator slots and inserted
into the stator slots before windings are wound in the stator
slots. Additionally, the first layer of electrical insulation
includes a plurality of insulating strips wedged between the
winding and a mouth of the winding slots after the windings are
inserted. The motor further includes a second layer of electrical
insulation made up of an insulating tube pressed onto a shaft
between the shaft and a rotor stack.
Inventors: |
Agnes, Michael Jeffrey; (Bel
Air, MD) ; McCormick, Garrett Patrick; (Baltimore,
MD) ; Walter, Richard Thomas; (Baldwin, MD) ;
Yahnker, Christopher Ryan; (Eldersburg, MD) |
Correspondence
Address: |
Christopher M. Brock and Scott T. Gray
Harness, Dickey & Pierce, P.L.C.
Suite 400
5445 Corporate Drive
Troy
MI
48098-2683
US
|
Family ID: |
21767206 |
Appl. No.: |
10/014711 |
Filed: |
December 11, 2001 |
Current U.S.
Class: |
310/89 |
Current CPC
Class: |
H02K 2211/03 20130101;
H02K 3/345 20130101; H02K 11/33 20160101; H02K 29/10 20130101; H02K
1/185 20130101; H02K 1/30 20130101; H02K 11/40 20160101 |
Class at
Publication: |
310/89 |
International
Class: |
H02K 005/00 |
Claims
What is claimed is:
1. An electronically commutated brushless motor comprising: a motor
housing; a bearing end cap coupled to said motor housing adapted to
couple said motor to an implement of a motor driven product; and a
double insulated rotor and stator assembly annularly fitted in said
housing.
2. The motor of claim 1, wherein said double insulated rotor and
stator assembly comprises a stator assembly configured to provide a
first layer of electrical insulation.
3. The motor of claim 2, wherein said stator assembly comprises: a
stator stack comprising a stack of steel laminations comprising a
plurality of stator slots; a plurality of windings wound in said
stator slots, said windings configured to generate a revolving
magnetic field; and non-conductive electrically insulating material
disposed into said stator slots around said windings in said stator
slots, said insulating material configured to provide electrical
insulation between said stator stack and said windings.
4. The motor of claim 3, wherein said insulating material
comprises: a plurality of first strips of insulating material
inserted into said stator slots before said windings are inserted
in said stator slots; and a plurality of second strips of
insulating material inserted into a mouth of said stator slots
after said windings are inserted in said stator slots.
5. The motor of claim 1, wherein said double insulated rotor and
stator assembly comprises a rotor assembly configured to provide a
second layer of electrical insulation.
6. The motor of claim 5, wherein said rotor assembly comprises: a
shaft configured to deliver torque to said implement; a rotor stack
coupled to said shaft comprising a stack of steel laminations
configured to rotate in a revolving magnetic field and thereby
deliver torque to said shaft; and an insulating tube comprising a
non-conductive electrically insulating material covering said shaft
between said shaft and said rotor stack, said insulating material
adapted to provide electrical insulation between said rotor stack
and said shaft secured thereto.
7. The motor of claim 6, wherein said insulating material comprises
a fiberglass tube.
8. The motor of claim 1, wherein said motor housing is constructed
of a non-conductive material.
9. The motor of claim 1, wherein said stator assembly is installed
into said motor housing using a non-conductive intermediate
device.
10. A method for providing protection against electrical shock when
a user comes into contact with accessible metal of a motor driven
product coupled to an electronically commutated brushless motor,
the motor including a motor housing, a rotor assembly and a stator
assembly annularly fitted in the housing, said method comprising:
providing a first layer of insulation in the stator assembly; and
providing a second layer of insulation in the rotor assembly.
11. The method of claim 10, wherein providing a first layer of
insulation comprises: providing a stator stack including a
plurality of stator slots; providing a plurality of stator windings
for generating a revolving magnetic field, the stator windings
being wound in the stator slots; and using electrical insulation
between the stator stack and the stator windings.
12. The method of claim 11, wherein using electrical insulation
comprises: providing a plurality of first insulating strips formed
in the shape of the stator slots and inserted into the stator slots
before the stator windings are wound in the stator slots, the
insulating strips being constructed of a non-conductive
electrically insulating material; and providing a plurality of
second insulating strips inserted into a mouth of the stator slots
after the windings are inserted in the stator slots, the insulating
strips being constructed of a non-conductive electrically
insulating material.
13. The method of claim 12, wherein providing a plurality of first
insulating strips comprises providing first insulating strips that
extend at either end of the stator stack, and wherein providing a
plurality of second insulating strips comprises providing second
insulating strips that extend at either end of the stator
stack.
14. The method of claim 10, wherein providing a second layer of
insulation comprises: providing a shaft for transferring torque to
a gearbox of the motor driven product; providing a rotor stack
connected to the shaft for rotating in a magnetic field, thereby
delivering torque to the shaft; and using electrical insulation
between the rotor stack and the shaft.
15. The method of claim 14, wherein providing electrical insulation
comprises providing an insulating tube pressed onto the shaft, the
insulating tube being constructed of a non-conductive, electrically
insulating material.
16. The method of claim 15, wherein providing an insulating tube
comprises providing a fiberglass insulating tube.
17. The method of claim 10 further comprises providing a
supplemental layer of insulation, the supplemental layer of
insulation including said motor housing being constructed of a
non-conductive material.
18. The method of claim 10 further comprises providing a
supplemental layer of insulation, the supplemental layer of
insulation including said stator assembly being installed into said
motor housing using a non-conductive intermediate device.
19. An electronically commutated brushless motor configured to be
coupled to an implement of a motor driven product, said motor
comprising: a stator stack comprising a stack of steel laminations
including a plurality of stator slots; a plurality of windings
wound in said stator slots, said windings configured to generate a
revolving magnetic field; a first layer of electrical insulation
between current carrying components of said motor and accessible
metal of said motor, said first layer comprising a non-conductive
electrically insulating material disposed into said stator slots
around said windings in said stator slots; a shaft configured to
deliver torque to said implement; a rotor stack comprising a stack
of steel laminations configured to rotate in said revolving
magnetic field and thereby deliver torque to said shaft; and a
second layer of electrical insulation between current carrying
components of said motor and accessible metal of said motor, said
second layer comprising a non-conductive electrically insulating
tube pressed onto said shaft between said shaft and said rotor
stack.
20. The motor of claim 19, wherein said non-conductive electrically
insulating material of said first layer comprises: a plurality of
first strips of insulating material inserted into said stator slots
before said windings are inserted in said stator slots; and a
plurality of second strips of insulating material inserted into a
mouth of said stator slots after said windings are inserted in said
stator slots.
Description
FIELD OF INVENTION
[0001] The invention relates generally to electronically commutated
brushless motors, such as switched reluctance motors, high
frequency induction motors, brushless AC motors, and brushless DC
motors. More particularly, the invention relates to an
electronically commutated brushless motor design and assembly
process that provides a robust brushless motor capable of meeting
the unique functional requirements in various applications, such as
portable table saws, miter saws, site saws, and TGS-type
combination saws.
BACKGROUND OF THE INVENTION
[0002] Prior art electronically commutated brushless motors suffer
from various limitations. One limitation is a restriction of
airflow through the motor. In a typical universal motor housing,
air is drawn in through vents in an end cap, passes over a brush
gear assembly and windings, through a fan and exhausts out the
other end of the motor.
[0003] In an electronically commutated brushless motor, air is also
drawn in through an end cap but first must pass around the
periphery of an electronics control module, installed at one axial
end of the housing, before the air can pass through the rest of the
motor. Thus, the electronics control module, which includes a
potting boat holding an encapsulated printed circuit board (PCB),
impedes the airflow by causing the air to first pass around the
electronics control module. After passing around the electronics
control module the air passes down through channels created by
extruded fins of aluminum heat sinks, thereby cooling electronic
components attached to the heat sinks. The air then continues over
stator windings, passes through and around the stator, through a
fan and exhausts out through the end of the motor. Thus, in
electronically commutated brushless motors the electronics control
module restricts the airflow through the motor.
[0004] The obstruction to airflow in electronically commutated
brushless motors is further compounded by the housing molding
process. To effectively mold and produce the housing, it must have
draft added on both its internal (core) and external (cavity)
sides. Since the geometry at the mouth of the housing is fixed by
mounting interface requirements with existing products, the draft
closes (i.e., narrows) the housing down about the electronics
control module, thereby further restricting the airflow around the
electronics control module and through the motor.
[0005] A second limitation of known electronically commutated
brushless motors is that the motor is typically longer than a
typical universal motor. Due to the longer motor, electronically
commutated brushless motors are difficult to utilize in many power
tools where it is desirable to keep the overall axial length of the
motor, or housing, as short as possible. This is especially true
with saws, such as miter saws and other saws, because when the saw
(and the motor coupled to the saw) is tilted at an angle, an extra
long motor housing can cause interference with a fence or the table
of the saw. For example, in a TGS-type combination saw, the axial
length of the motor housing must be short enough so that it does
not protrude beyond the frame of the saw. If it does it will
prevent the table from being flipped over. As another example, the
axial length of the motor in a small portable table saw should be
such that when attached to the saw gear case, the motor housing
should fit inside the skirt that forms the base of the table. As
yet another example, in a miter saw, where the bevel and miter
functions will tip the end of the motor towards the table, the
axial length of the motor should be such that the motor does not
contact the table fence.
[0006] A third limitation of known electronically commutated
brushless motors is the inability to insure proper alignment of the
registering means on the rotor shaft with the rotor pole, and the
position sensor with the stator during the assembly process. The
registering means could be any suitable registering means such as
an interrupter or a magnet, and the position sensor could any
suitable sensor such as an optical sensor or a Hall Effect sensor.
In typical electronically commutated brushless motors, the position
of the registering means, relative to the position sensor,
determines the position of the rotor, relative to the stator. In
electronically commutated brushless motors it is critically
important to know the exact position of the rotor when the
electronic switching signals, which switch the direction of the
flux in the motor winding(s), are provided by an electronic
controller. If the alignment of the registering means with the
rotor pole is off, or the alignment of the position sensor with the
stator is not precisely set, then the position of the registering
means, as detected by the position sensor, will provide an
inaccurate indication of the position of the rotor, relative to the
stator. If the position of the rotor is not accurately determined,
the electronic switching motor will very quickly lose power and
torque.
[0007] A fourth limitation of known electronically commutated
brushless motors is meeting the requirements for double insulated
construction as described by Underwriters Laboratories (UL) and
other compliance agencies. Double insulated motor designs, which
eliminate the need for a ground wire in the power cord, have been
implemented on universal motors. This is a preferred construction
for hand held and table mounted power tools since the alternative,
grounded tools, rely on there being a solid ground connection
available on a job site, which often is not the case. The basic
requirement is that the design must provide at least two levels of
insulation between live components, such as the windings, and any
metallic components, such as the shaft or screws, that are
accessible to the user. Known electronically commutated brushless
motors do not implement a double insulated construction design.
[0008] Therefore, it would be desirable to provide an
electronically commutated brushless motor design that provides
increased airflow through the motor. It would further be desirable
provide an electronically commutated brushless motor having an
overall axial length suitable for applications requiring a shorter
motor. Even further, it would be desirable to provide an
electronically commutated brushless motor design that insures
accurate alignment of the optical encoder with the rotor poles, and
accurate alignment of the optical sensor with the stator during
assembly of the motor. Further yet, it would be desirable to
provide an electronically commutated brushless motor that
implements a double insulated design without significantly
increasing the cost or complicating the manufacturability and/or
assembly of the overall motor.
BRIEF SUMMARY OF THE INVENTION
[0009] The present invention relates to an electronically
commutated brushless motor design, which overcomes the various
drawbacks described above. In a preferred form, the invention
relates to brushless AC motor, although it will be appreciated that
the invention is also applicable to brushless DC motors.
[0010] In one aspect of the present invention a housing of the
motor is provided with a draft angle that increases the airflow
through the housing to allow more efficiently cooling of the
motor.
[0011] In a second aspect of the present invention the
electronically commutated brushless motor design provides a
capacitor mounting arrangement that allows the overall axial length
of the motor to be made shorter. The capacitors are mounted on a
circuit board, which is adapted to slide into a housing protrusion,
or bulge, formed on the sidewall of the housing rather than at one
axial end of the housing. Thus, the overall axial length of the
housing is made shorter, thereby allowing a wider range of
applications for the motor in which the motor must be situated into
different positions without interfering with other components of
its associated tool.
[0012] In a third aspect of the present invention the
electronically commutated brushless motor provides a housing that
allows accurate alignment of a stator and a position sensor, such
as an optical sensor, relative to each other. This is accomplished
by using a housing molding core that produces a housing that
includes both a bridge on which the position sensor is mounted, and
stator locating ribs. Typically, the molding core for the housing
forms locating ribs on an interior surface of the housing, which
are used to precisely align the stator when it is inserted into the
housing, but does not include a mounting bridge for the position
sensor. By molding the housing to include both a position sensor
mounting bridge and the stator locating ribs, variances in the
positioning of the position sensor, relative to the stator, are
avoided. Therefore, the position sensor and the stator will be
accurately aligned when installed, without the need for time
consuming alignment procedures, or tests, during the assembly of
the motor.
[0013] In a fourth aspect of the present invention the
electronically commutated brushless motor incorporates a double
insulation (DI) feature, thereby eliminating the need for a direct
ground cable in the power cord. The DI design includes insulating
strips between the stator and stator windings, and an insulating
sleeve disposed between the rotor shaft and the rotor laminations.
Therefore, there are two layers of insulation between metal parts
accessible to a user and parts of the motor in which electrical
current flows. Alternatively, the motor housing, which supports the
stator, is also constructed of a non-conductive material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The present invention will become more fully understood from
the detailed description and accompanying drawings, wherein;
[0015] FIG. 1 is a perspective view of a electronically commutated
brushless motor in accordance with a preferred embodiment of the
present invention;
[0016] FIG. 2 is an exploded view of the motor shown in FIG. 1,
showing how the components of the motor are assembled;
[0017] FIG. 3 is an exploded view of the interior of the distal end
of the motor housing shown in FIG. 2;
[0018] FIG. 4 is an exploded view of the distal end of the motor
shown in FIG. 2, showing how the components at the distal end of
the motor are assembled;
[0019] FIG. 5 is an exploded view of the housing shown in FIG. 4,
showing how film capacitors are slideably inserted into a motor
housing bulge;
[0020] FIG. 6 is an exploded view of a stator stack shown in FIG.
2;
[0021] FIG. 7 is an exploded view of the stator and rotor assembly
shown in FIG. 2;
[0022] FIG. 8 is cross-sectional view of the motor shown in FIG. 1;
and
[0023] FIG. 9 is a schematic of the housing of the motor shown in
Figure, showing the location of the parting line of the core and
cavity used to mold the housing.
DETAILED DESCRIPTION OF THE INVENTION
[0024] FIG. 1 is a perspective view of an electronically commutated
brushless motor 10 in accordance with a preferred embodiment of the
present invention. Motor 10 is a self-contained motor, which can be
bolted directly onto a gearbox or other support means of a product,
such as a power tool. Motor 10 includes a plastic motor housing 14
having an integrally formed bulge 18 protruding from an outer
surface of a sidewall of the motor housing, wherein a plurality of
capacitors (not shown) are inserted. Housing 14 is closed at a
distal end by a vented end cap 22, and closed at the opposing
proximal end by a bearing end cap 26.
[0025] FIG. 2 is an exploded view of motor 10 (shown in FIG. 1)
showing how the components of motor 10 are assembled. A stator
stack 30, a rotor 34 and a baffle 38 are fitted annularly inside
housing 14. Stator stack 30 is a stack of steel laminations fitted
with stator windings (described in reference to FIG. 6 below). The
stator windings are sequentially energized with electrical current,
thereby generating a revolving magnetic field. Stator stack 30 is
precisely positioned within housing 14 using a plurality of
locating ribs 40 formed on an inside surface 14a of a sidewall of
housing 14. The locating ribs 40 fit into stator channels 42
integrally formed in stator stack 30. Stator stack 30 is then
pressed into housing 14, having an interference fit, and secured in
place with two screws (not shown).
[0026] Rotor 34 has no windings and is supported between a first
bearing 44, supported by bearing end cap 26, and a second bearing
46, supported by an integral bearing support (not shown),
incorporated into motor housing 14. Rotor 34 includes a shaft 50,
an insulating tube, or sleeve, 54, a stack of steel laminations 58,
and a cooling fan 62 that helps to direct air through the motor 10.
Stack 58 is assembled by interlocking, welding, cleating, or
bonding the steel laminations together. Insulating tube 54 is
pressed onto shaft 50 and rotor stack 58 is pressed onto insulating
tube 54. Shaft 50 connects to a product gearbox (not shown), which
in turn is coupled to a tool element such as a saw blade. The
revolving magnetic field created by the stator windings imparts a
force on rotor stack 58 causing rotor stack 58 to revolve about an
axis of shaft 50, thereby transferring torque to shaft 50, which in
turn delivers torque to gears in the product gearbox. Rotor stack
58 includes a plurality of four rotor poles 68, although it will be
appreciated that a greater or lesser plurality of rotor poles 68
could be incorporated.
[0027] Rotor 34 further includes a registering means 66, such as an
interrupter. As used herein registering means 66 is referred to as
interrupter 66, but it will be appreciated that registering means
66 could be any other suitable registering means, such as a magnet.
Interrupter 66 has a plurality of four vanes 66a, only three of
which are visible in FIG. 2. Interrupter 66 is a plastic part that
fits on the distal, or rear, end of shaft 50 and interfaces with a
position sensor (described below in reference to FIG. 3) to provide
data relating to a rotor position and a rotor speed to the
electronic controller. Slipping or spinning of the outer diameter
(OD) of second bearing 46 is prevented by a compliant material (not
shown) that fits between the OD of bearing 46 and the wall of the
bearing support, for example a rubber plug or rubber boot. After
stator 30, baffle 38 and rotor 34 are annularly fitted into housing
14, bearing end plate 26 is fitted over first bearing 44 and onto
locating points at the mouth of housing 14, then secured to plastic
housing 14 with four screws (not shown).
[0028] FIG. 3 is an exploded view of the interior of the distal end
of motor housing 14 (shown in FIG. 2). Behind the integral bearing
support (not shown) of housing 14 is a bridge 70, which supports a
position sensor 74. In the preferred embodiment, position sensor 74
is an optical sensor, and is herein referred to optical sensor 74.
However, it will be appreciated that position sensor 74 could be
any other suitable position sensor, for example, a Hall Effect
sensor. Bridge 70 is integrally formed with, and protrudes from,
and an end wall 72 of housing 14. Optical sensor 74 is inserted
under an upper portion 70a of the bridge 70 such that it fits
substantially within a hollow area 71 inside the bridge. Optical
sensor 74 includes tabs 74a and 74b, with tab 74a including an
aperture 75 and tab 74b including an aperture 77. Optical sensor 74
is attached at tab 74b to the bridge 70 by a fastener (not shown),
which extends through an aperture 80 formed in upper portion 70a of
bridge 70 and through aperture 77. End wall 72 includes a pair of
mounting bosses 72a and 72b projecting outwardly therefrom, with
each mounting boss having a blind hole 72c and a through hole 72d,
respectively. Tab 74a of optical sensor 74 is laid over mounting
boss 72b such that aperture 75 and through hole 72d are
aligned.
[0029] Once fitted into bridge 70, as described above, optical
sensor 74 is covered with a hollow plastic sensor cap 78. Optical
sensor 74 is bounded above by cap 78 and below by second bearing
46, which form a sealed chamber for housing optical sensor 74. The
sealed chamber protects optical sensor 74 from contamination by
dirt, dust, oil and moisture, and accidental triggering by external
light sources. Additionally, the distal end of motor housing 14
includes a boss 81 used in attaching vented end cap 22 (shown in
FIG. 1) to the distal end of motor housing 14.
[0030] Optical sensor 74 interfaces with interrupter 66 (shown in
FIG. 2) to provide data relating to rotor 34 position and speed. As
shaft 50 and interrupter 66 rotate, the passing of vanes 66a of
interrupter 66 is detected by optical sensor 74, which provides
data to a main control PCB (described below in reference to FIG.
4). The main control PCB utilizes the data to determine information
critical to proper operation of the motor 10, such as the relative
position of rotor stack 58 to stator stack 30 (shown in FIG. 2) and
the speed of rotor stack 58. Therefore, the alignment of
interrupter vanes 66a to rotor poles 68 (shown in FIG. 2), and the
alignment of stator stack 30 to optical sensor 74 is very important
for proper motor operation.
[0031] Proper alignment of stator stack 30 to optical sensor 74 is
accomplished by molding bridge 70 from the same core side of the
mold as are stator locating ribs 40. Bridge 70 includes the sensor
mounting structure, such as aperture 80 and mounting boss 72b,
which precisely orient optical sensor 74 within bridge 70. Stator
locating ribs 40 are keyed to stator stack channels 42 (shown in
FIG. 2), such that stator stack 30 is fitted into housing 14 in a
precise orientation. Therefore, the tooling that defines the sensor
mounting features in bridge 70 also defines locating ribs 40. The
fact that both bridge 70 and the stator locating ribs 40 are
incorporated into the core side of the mold insures that these
important structural components are integrally formed on the same
part (i.e. housing 14). This serves to ensure that alignment of the
optical sensor 74 relative to the position of stator stack 30 is
controlled with great accuracy and further reduces the chance of
misalignment of stator stack 30 during assembly of motor 10. It
will also be appreciated this significantly reduces assembly time
because particular care does not need to be taken in trying to
manually align these components.
[0032] FIG. 4 is an exploded view of the distal end of motor 10
(shown in FIG. 2), showing how the components at the distal end of
motor 10 are assembled. A main control PCB 82 fits behind optical
sensor 74 while preferably a pair of capacitors 86, for example,
large film capacitors, are mounted on a capacitor PCB 94 and housed
in the bulge 18 integrated into the side of the motor housing
14.
[0033] Main control PCB 82 is potted in epoxy resin inside a
plastic potting boat 98, which fits onto plastic boss 81 and
another plastic boss (not shown) that extend up from motor housing
14. Additionally, main control PCB 82 has two wing-shaped aluminum
heat sinks 102 and 106 fitted on opposite peripheral edges of main
control PCB 82. Four switching devices, in one preferred form
comprising insulated gated bipolar transistors (IGBTs), are secured
to one of heat sinks 102 and 106, and also soldered to main control
PCB 82. Additionally, four diodes are fitted to the other one of
heat sinks 102 and 106. After all of components 74, 78, 82, 94 and
98 are inserted into housing 14, vented end cap 22 is placed over
the components and secured to housing 14.
[0034] There are multiple connections (not shown) to main control
PCB 82, which include the incoming AC power, connections to the
motor leads, connections to optical sensor 74, and finally signal
level leads coming from the various switches on the product, such
as a trigger switch, a table position latch switch, or speed
control potentiometers. These connections may be either directly
soldered to main control PCB 82 and secured with potting compound
or connected using terminals. All the external leads, such as AC
power and signal level switch inputs, are bundled into a single,
multi-conductor cable (not shown), which exits motor housing 14 on
the side opposite bulge 18.
[0035] FIG. 5 is an exploded view of motor housing 14 (shown in
FIG. 4), showing how capacitors 86 are slideably inserted into
motor housing bulge 18. In order to implement brushless motor 10 in
applications where a typical universal motor is commonly utilized,
the overall axial length of the motor must be similar to the axial
length of typical universal motors.
[0036] In the preferred embodiment, motor housing 14 includes bulge
18, which houses capacitors 86, thereby minimizing the overall
axial length of motor 10. Capacitors 86 are soldered onto capacitor
PCB 94 and then strapped to capacitor PCB 94 using fasteners 110,
such as nylon cable ties. Stiffeners 114 are attached to the two
opposing longitudinal edges of capacitor PCB 94, thereby adding
structural rigidity to capacitor PCB 94. In one embodiment,
stiffeners 114 are temporarily attached to capacitor PCB 94, for
example, using clips or a snap fitting. In an alternate embodiment,
stiffeners 114 are permanently attached to capacitor PCB 94, for
example, using glue or a bracket riveted to both capacitor PCB 94
and stiffeners 114. Stiffeners 114 fit into corresponding channels
116 along the inside wall of motor housing bulge 18. In the
preferred embodiment, stiffeners 114 are drafted, and thus have a
tapered shape.
[0037] Stiffeners 114, are slideably inserted into corresponding
channels 116, which are also drafted, however the shape of
stiffeners 114 and corresponding channels 116 are not so limited.
End slots (not shown) at the base of motor housing bulge 18 and in
vented end cap 22 (shown in FIG. 1) capture the ends of capacitor
PCB 94. Capacitor PCB 94 is electrically connected to main control
PCB 82 using flexible lead wires 118 inserted through an aperture
120 in the side wall of housing 14. Preferably lead wires 118 are a
ribbon cable, but could be any other suitable electrical connecting
means.
[0038] FIG. 6 is an exploded view of stator stack 30 (shown in FIG.
2). In the preferred embodiment stator stack 30 comprises a stack
of laminations, known as a "unified stack", which are interlocked,
welded, cleated, or bonded to one another. A plurality of first
insulating strips 122 are formed into the shape of stator slots
124, inserted into stator slots 124 before windings or coils 126
are inserted into stator slots 124, and extend at either end of
stator stack 30. A plurality of second insulating strips 128 (shown
in FIG. 7), commonly known as "topsticks" or "coil stays", are
wedged between windings 126 and the mouth of stator slots 124 after
windings 126 are inserted into stator slots 124, and extend at
either end of stator stack 30. First insulating strips 122 and
second insulating strips 128 provide a layer of electrical
insulation between current carrying components of motor 10 and
metal parts of motor 10 that a user would normally come into
contact with, referred to herein as "accessible metal". For
example, if motor 10 is used in a hand held power saw, rotor shaft
50 is considered accessible metal because it connects through
conducting a metal-to-metal interface with the saw gearbox, which
connects through a conducting metal-to-metal interface to a saw
blade.
[0039] FIG. 7 is an exploded view of stator stack 30 (shown in FIG.
6), rotor stack 58, and shaft 50 (shown in FIG. 2) showing a double
insulation feature implemented in accordance with a preferred
embodiment of motor 10 of present invention. Electronically
commutated brushless motor 10 (shown in FIG. 2) includes two layers
of electrical insulation between accessible metal and parts of
motor 10 in which electrical current flows. One layer of insulation
comprises insulation tube 54 between shaft 50 and rotor lamination
stack 58. Insulation tube 54 is constructed of a non-conductive,
electrically insulating material such as fiberglass. Insulation
tube 54 is pressed onto shaft 50 and rotor lamination stack 58 is
then pressed onto insulation tube 54.
[0040] Another layer of insulation comprises the plurality of first
insulating strips 122 and the plurality of second insulating strips
128. First insulating strips 122 are constructed of an electrically
insulating material and fit into stator slots 124 prior to stator
windings 126, such that first insulating strips provide a first
portion of an electrical barrier between stator windings 126 and
stator laminations 30. Second insulating strips 128 are also
constructed of an electrically insulating material and are fitted
into stator slots 124 after windings 126, such that second
insulating strips 128 provide a second portion of an electrical
barrier between stator winding 126 and stator laminations 30. The
combination of first insulating strips 122 and second insulating
strips 128 totally encompass the part of stator winding 126
inserted into stator slots 124, thereby providing a complete
electrical barrier between winding 126 and stator stack 30. The
insulating material used to construct first insulating strips 122
and second insulating strips 128 can be any suitable insulating
material, for example, Mylar.RTM., or a laminated composite of
Mylar.RTM. with other materials such as rag paper or
Nomex.RTM..
[0041] Thus, insulating tube 54 disposed between shaft 50 and rotor
stack 58, and the combination of first insulating strips 122 and
second insulating strips 128 disposed between stator stack 30 and
windings 126, provide a double insulation barrier against possible
electrical shock should a user come into contact with accessible
metal if a malfunction has occurred in the motor that would
otherwise cause electrical current to be in contact with accessible
metal portion of the tool.
[0042] In an alternate embodiment housing 14 is constructed of a
non-conductive material, thereby providing a supplemental layer of
insulation within motor 10, in addition to the double insulation
barrier described above. In another alternate embodiment, stator
stack 30 is installed into motor housing using a non-conductive
intermediate device, such as a molded plastic cradle, housing, or
sleeve (not shown) into which stator stack 30 is inserted prior to
being installed in housing 14. In this embodiment the plastic
cradle would house stator stack 30 and would then fit into housing
14 thereby providing an alternate supplemental layer of insulation
between parts of motor 10 in which electrical current flows and
accessible metal.
[0043] FIG. 8 is cross-sectional view of motor 10 (shown in FIG.
2). In the electronically commutated brushless motor 10, air is
drawn in through vented end cap 22, passes around the periphery of
potting boat 98 and main control PCB 82, through channels created
by extruded fins of aluminum heat sinks 102 and 106, continues over
stator windings 126, passes through and around stator stack 30,
through cooling fan 62, and exhausts out bearing end cap 26.
[0044] Potting boat 98 and main PCB 82 impede this airflow by
causing an obstruction to a more direct flow of air into heat sinks
102 and 106. The obstruction to airflow is further compounded by
the molding process of housing 14. To effectively mold and produce
housing 14, it must have draft added on both its internal core and
external cavity sides of the mold. The draft closes the space
between an internal wall of housing 14 and potting boat 98, thereby
further restricting the airflow around through the motor.
[0045] FIG. 9 is a schematic of the housing 14 (shown in FIG. 2),
showing the location of the parting line of the core and cavity
used to mold housing 14. Housing 14 is designed to provide more
area at the distal end, or rear, of housing 14 than known
electronically commutated brushless motor housings. The increased
area provides greater space around potting boat 98 (shown in FIG.
4), which allows improved airflow through the motor 10 (shown in
FIG. 1).
[0046] Generally, when designing molding tools for a motor housing,
such as motor housing 14, a specified angle of draft .theta. in the
core, and a specified angle of draft .alpha. in the cavity, are
designed into the molding tools to make removal of the housing from
the mold easier. The draft incorporated into the core and cavity
create taper in the sidewall of the housing that extends away from
a parting line between the core and cavity. Specifically, draft
angle .alpha. in the cavity creates taper in an exterior surface of
the housing.
[0047] The interfacing surface at which the core and cavity meet,
and separate, during the molding process is referred to as the
parting line. Draft angles .theta. and .alpha. are measured from a
plane perpendicular to the parting line. Since draft angle .alpha.
creates taper in the exterior surface, the further the parting line
is away from the distal end of the housing, or the closer the
parting line is to the proximal end, the smaller the outside
diameter of the distal end of the housing will be. The inside
diameter of the distal end of the housing directly relates to the
outside diameter. Thus, the further away the parting line is from
the distal end of the housing, the smaller the inside diameter of
the distal end will be, thereby providing less area for air to flow
in the distal end of the housing.
[0048] Referring to FIG. 9, the parting line of housing 14 is shown
located closer to the distal end "D" of housing 14, rather than at,
or near, the proximal end "P" of housing 14, as is generally the
case in known motor housings. Having the parting line located
closer to the distal end D of housing 14 reduces the amount of
taper of exterior surface 130, and therefore provides an increased
outside diameter of the distal end, which in turn provides an
increased inside diameter of the distal end of housing 14. The
increased inside diameter increases the area at the distal end,
thereby providing more room for air to flow around potting boat 98
(shown in FIG. 4).
[0049] Therefore, electronically commutated brushless motor 10
provides a modular motor that fits the existing mounting schemes
for typical universal motors. Motor 10 includes a housing having a
bulge wherein two large capacitors are placed, thereby providing a
brushless motor having an overall axial length comparable to
typical universal motors. Additionally, proper alignment of the
position sensor to the stator is achieved by molding the mounting
features for both the position sensor and the stator using the same
molding core. Furthermore, motor 10 implements a double insulation
design in an electronically commutated brushless motor. Even
further, the design of motor 10 provides improved airflow through
the motor by moving the parting line of the molding core and
cavity, thereby permitting the housing to be molded using less
taper, which in turn allows more space for air to flow around the
electronics control module of the motor.
[0050] While the invention has been described in terms of various
specific embodiments, those skilled in the art will recognize that
the invention can be practiced with modification within the spirit
and scope of the claims.
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