MOTOR ENDSHIELD ASSEMBLY FOR AN ELECTRONICALLY COMMUTATED MOTOR

ENSEMBLE ECRAN D'EXTREMITE POUR MOTEUR A COMMUTATION ELECTRONIQUE

English Abstract

An endshield assembly (100) for an electronically commutated motor includes an
endshield (100), a control assembly (104) and a power assembly (106). The
endshield (100) includes a plurality of recessed fins (132) on an outer
surface, and a substantially flat raised portion on an internal surface. The
raised portion is in contact with a thermal pad (112). The control assembly
(104) includes the thermal pad (112) and a control board (108) on which is
located a plurality of power transistors (110). The thermal pad (112) provides
thermal contact between the transistors (110) and the endshield (100) to
enable the endshield (100) to dissipate heat from the transistors (110). The
transistors (110) include a plurality of leads (128) that extend substantially
parallel to the control board (108) which enable the leads (128) to be coated
for protection against harsh environments. The power assembly (106) includes a
power board (138) having an insulator (146) positioned between the power board
(138) and the control board (108).

French Abstract

L'invention concerne un ensemble écran d'extrémité (100) pour moteur à commutation électronique, comprenant un écran d'extrémité (100), un ensemble de commande (104) et un ensemble de puissance (106). L'écran d'extrémité (100) comprend plusieurs ailettes en cavité (132) sur une surface extérieure, et une partie plate sensiblement surélevée sur une surface interne. La partie surélevée est en contact avec un tampon thermique (112). L'ensemble de commande (104) englobe le tampon thermique (112) et un panneau de commande (108) sur lequel se trouvent plusieurs transistors de puissance (110). Le tampon thermique (112) assure le contact thermique entre les transistors (110) et l'écran d'extrémité (100), permettant ainsi à cet écran (100) de dissiper la chaleur provenant des transistors (110), Lesdits transistors (110) comportent plusieurs conducteurs (128) qui s'étendent sensiblement parallèlement au panneau de commande (108), ce qui permet de revêtir les conducteurs (128) pour les protéger contre des conditions ambiantes rigoureuses. L'ensemble de puissance (106) comprend un panneau de puissance (138) doté d'un isolant (146) qui est placé entre le panneau de puissance (138) et le panneau de commande (108).

Claims

Claims:
1. A motor endshield assembly comprising:
an endshield comprising an outer surface and an inner surface, said outer
surface including a plurality of fins;
a control assembly in contact with said inner surface; and
a power assembly connected to said control assembly.
2. A motor endshield assembly in accordance with Claim 1 wherein said
inner surface further comprises a substantially flat raised area for
contacting said
control assembly.
3. A motor endshield assembly in accordance with Claim 1 wherein said
control assembly comprises a control board and a plurality of power
transistors
connected to said control board.
4. A motor endshield assembly in accordance with Claim 1 wherein said
control assembly further comprises a thermal pad placed between said power
transistors and said endshield, said thermal pad for transferring heat from
said
transistors to said endshield and for electrically isolating said transistors.
5. A motor endshield assembly in accordance with Claim 1 wherein said
endshield is configured as a heatsink.
6. A motor endshield assembly in accordance with Claim 3 wherein
each said power transistor comprises a plurality of leads, each said lead
extending
substantially parallel to said control board.
7. A motor endshield assembly in accordance with Claim 6 wherein said
transistors comprise a top surface, a bottom surface, a front, a back, and a
tab, said
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bottom surface contacting said control board, said tab extending from said
back
along said top surface.
8. A motor endshield assembly in accordance with Claim 7 wherein said
power transistor leads extend from said front of said power transistors at a
position
that is closer to said bottom surface than to said top surface.
9. A motor endshield in accordance with Claim 8 wherein said tabs
comprise metal, said tabs contact said thermal pad which provides a thermal
interface to said endshield.
10. A motor endshield assembly in accordance with Claim 2 wherein said
recessed fins extend from said substantially flat raised portion.
11. A motor endshield assembly in accordance with Claim 1 further
comprising a cap plug opening extending through said endshield and a cap plug
covering said cap plug opening.
12. A motor endshield assembly in accordance with Claim 1 wherein said
endshield further comprises aluminum.
13. A motor endshield assembly in accordance with Claim 3 wherein said
power assembly comprises a power board and an insulator positioned between
said
power board and said control board.
14. A motor endshield assembly in accordance with Claim 13 further
comprising:
a first spacer extending between said control board and said power assembly;
a plurality of clamp bars positioned between said power assembly and said
power transistors, said first spacer and said clamp bars extending through
said
insulator; and
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a second spacer extending between said control board and said endshield.
15. A motor endshield assembly in accordance with Claim 1 wherein said
endshield further comprises a plurality of bolt openings that extend through
said
endshield for receiving a through bolt.
16. A motor endshield for an electronically commutated motor, said
endshield comprising:
an internal surface comprising a substantially flat raised area;
an external surface comprising a plurality of recessed fins and a raised
cylindrical portion surrounding said opening; and
a shaft opening configured to receive a motor shaft.
17. A motor endshield in accordance with Claim 16 wherein said
recessed fins extend from said substantially flat raised portion.
18. A motor endshield in accordance with Claim 16 further comprising a
cap plug opening extending through said endshield.
19. A motor endshield in accordance with Claim 16 further comprising a
plurality of recessed openings extending through said endshield, each said
recessed
opening for receiving a through bolt.
20. A motor endshield in accordance with Claim 16 wherein said
endshield further comprises aluminum, said endshield configured as a heatsink.
21. A method of assembling a motor endshield assembly for an
electronically commutated motor, the motor endshield assembly including a
control
assembly, a power assembly, and an endshield with an inner surface and an
outer
surface, said method comprising the steps of:
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positioning the control assembly in contact with the inner surface of the
endshield; and
connecting the power assembly to the control assembly.
22. A method in accordance with Claim 21 wherein the control assembly
includes a thermal pad and a control board with power transistors connected
thereto,
said step of positioning further comprising the steps of:
positioning the power transistors in thermal contact with the thermal pad;
and
placing the thermal pad in contact with the endshield.
23. A method in accordance with Claim 22 wherein the endshield inner
surface includes a substantially flat raised portion, and the endshield outer
surface
includes a plurality of recessed fins, the recessed fins extending from the
raised
portion, said method of placing the thermal pad comprising the step of placing
the
thermal pad in contact with the substantially flat raised portion of the
endshield such
that the power transistors are in thermal contact with the recessed fins,
wherein a
thermal pathway is provided to dissipate heat from the transistors to the
recessed
fins and then to the ambient environment.
24. A method in accordance with Claim 23 wherein the power assembly
includes an insulator, a plurality of clamp bars, a spacer, and a power board,
and
wherein said step of connecting the power assembly to the control assembly
comprises the step of placing the power assembly in contact with the control
board.
25. A method in accordance with Claim 24 wherein said method further
includes the step of positioning the clamp bars to apply pressure to the
transistors to
enhance the thermal contact between the transistors and the recessed fins of
the
endshield.
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Description

CA 02333949 2000-11-30
WO 00!01054 PCTiUS99/14753
MOTOR ENDSHIELD ASSEMBLY FOR AN
ELECTRONICALLY COMMUTATED MOTOR
BACKGROUND OF THE INVENTION
This invention relates generally to electric motors and more particularly, to
an endshield assembly for an electric motor.
Known electronically commutated motors have a mufti-stage winding
assembly and a magnetic assembly associated for relative rotation. The winding
stages of the mufti-stage winding assembly have a prcaet energization sequence
that
includes at least one unenergized winding stage in which an induced back EMF
appears. When integrated over time to a predetermined value, the induced back
EMF indicates the instant at which the relative angular position between the
multi-
stage winding assembly and the magnetic assembly is. suitable for the
sequential
1o commutation of the next winding stage.
The electronic circuitry for an electronically c:ommutated motor generally
includes a power circuit, a regulating circuit, and a control circuit. The
power
circuit has solid state switching devices for comrnutal:ing the power supplied
to the
electronically commutated motor to effect its energiz;ation. The regulating
circuit
~5 has various solid state components for maintaining the power supplied to
the
electronically commutated motor generally constant. The control circuit has
various
solid state components for controlling the conductivity of the switching
devices.
Some of the solid state components for an electronically commutated motor,
e.g., transistors, need to be relatively large to accommodate the currents
that must
2o pass through them. Large transistors can produce a sizable amount of heat
that
should be dissipated from the transistors in order to li:eep them functioning
properly.
It is well known in the art that to promote heat dissipation, the electronic
circuitry
for an electronically commutated motor can be positioned adjacent an outer
surface
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of an endshield of the motor. However, this increases costs since another
compartment is needed to protect the electronic circuitry.
Accordingly, it would be desirable to provide a mounting arrangement for
the electronic components of an electronically commutated motor that provides
good
s heat dissipation without significantly increasing the cost of the motor.
Additionally,
it would be desirable to eliminate the additional compartment needed to
protect the
electronic circuitry.
BRIEF SUMMARY OF THE INVENTION
Electronically commutated motors are well known, such as the motor
described in U.S. Patent No. 5,006,74, which patent is assigned to the present
to assigned and hereby incorporated herein, in its entirety, by reference.
In an exemplary embodiment of the invention., a motor endshield assembly
for an electronically commutated motor includes an endshield having an inner
surface and an outer surface, with the outer surface including a plurality of
recessed
fins. The endshield assembly according to one embodiment of the present
invention
t s includes a control assembly and a power assembly mounted thereto. The
contarol
assembly includes a control board having a plurality of power transistors. The
internal surface of the endshield includes a substantially flat raised area
that is°in
contact with the control assembly and serves as a heatsink for the power
transistors.
The transistors are in contact with a thermal pad located between the
transistors and
2o the endshield. The thermal pad electrically insulates the transistors yet
still conducts
heat from the transistors to the endshield. The recessed fins are located
directly
above the substantially flat raised portion on the endslhield and assist the
dissipation
of heat from the transistors and endshield to the ambient environment.
The power assembly includes a power board having an insulator positioned
2s between the power board and the control board. A first spacer extends
between the
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control board and the power board to provide the proper spacing therebetween.
A
plurality of clamp bars are also positioned between the power board and the
transistors. The clamp bars apply pressure to the transistors and keep the
transistors
in contact with the substantially flat raised portion of the endshield. The
first spacer
and the clamp bars extend through the insulator. A second spacer extends
between
the control board and the endshield to provide the proper spacing
therebetween.
In one embodiment, each power transistor includes a plurality of leads that
extend substantially parallel to the control board. Thf: leads exit a front
side of the
transistor at a position that is closer to a bottom of the: transistor than to
a top. The
to bottom of the transistor is in contact with the control board while the top
of the
transistor includes a tab that extends from a back side of the transistor
parallel to the
control board.
With the above described endshield assembly, only one compartment us
required since the electronic controls are located within the motor housing.
In
addition, use of the endshield as a low impedance path to dissipate heat from
the
power devices of the internal electronic circuitry to the ambient environment
provides good thermal performance for the motor. Also, since the transistor
leads
are parallel to and away from the control board, the lengths of the leads are
much
closer to the surface of the board than in many known control assemblies. The
leads
2o are thus easy to encapsulate and protect from harsh e~aernal environments.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is an exploded view of an endshield assembly in accordance with
one embodiment of the present invention;
Figure 2 is a perspective view of the endshield shown in Figure l ;
Figure 3 is a cross section of the endshield shown in Figure 2 along A-A;
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Figure 4 is a schematic illustration of the thermal pad shown in Figure 1; and
Figure 5 is a schematic illustration of the insulator shown in Figure 1.
DETAILED DESCRIPTION OF THE INVENTION
Figure 1 is an exploded view of an endshield assembly 100 for an
electronically commutated motor (not shown). Endsh~ield assembly 100 includes
an
s endshield 102, a control assembly 104, and a power assembly i06. Control
assembly 102 includes a control board 108, a plurality of transistors 110, a
thermal
pad 112, and a spacer 114. In one embodiment, spacer 114 is fabricated from
nylon
and extends between control board 108 and endshield 102. Spacer I 14 helps to
maintain a predetermined separation distance between control board 108 and
to endshield 102.
Transistors 110 include a front 116, back 118, top 120, bottom 122, and a
tab 124. Tab 124 extends from back 11$ of transiston-s 110 and has a surface
126
that is an extension of, and is substantially parallel to, top 120. A
plurality of leads
128 extend from front 116 of transistor l I0. In one embodiment, leads 128
extend
15 substantially parallel to control board 108 and rnaintaiin a substantially
constant
separation distance between themselves and control board 108. Since leads 128
extend from front 116 in a location that is closer to cc>ntrol board 108 than
to top
120, leads 128 remain relatively close to control board 108 throughout their
length.
Only a small separation distance exists between leads 128 and control board
108.
2o The small separation distance allows conformal coating to easily
encapsulate leads
128 which helps to protect them from damage in harslh environments. The
encapsulation of leads 128 facilitates reducing failures. caused by moisture
in the
area of high potential. To insert leads 128 into control board 108, leads 128
must
be formed at right angles to transistor 110.
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Transistors 110 are capable of producing significant heat depending an the
amount of current that flows through them. The heat should be dissipated from
the
transistors and the surrounding motor in order to ensure proper operation of
the
motor. In one embodiment, top 120 of each transistor 110 is in thermal contact
with
thermal pad 112. Thermal pad 112 electrically isolates transistors 110 and
conducts
the heat generated by transistors 110 away from transistors 110. Thermal pad
112
contacts endshield 102 which includes an inner surface (not shown) and an
outer
surface 130 that has a plurality of recessed fins 132. In one embodiment,
endshield
102 is fabricated from cast aluminum and serves a h<:atsink for transistors
110. The
to inner surface of endshield 102 includes a substantially flat raised portion
(not
shown). The substantially flat raised portion is in thermal contact with
thermal pad
112 and is located directly beneath recessed fins 132. In one embodiment,
recessed
fins 132 extend from the substantially flat raised porl:ion. The neat from
transistors
110 travels through thermal pad I12 to endshield 102 and is dissipated from
recessed fins 132 to the ambient environment. Endslhield 102 serves as a heat
sink
to transistors 110 and helps to dissipate heat from transistors 110 to the
ambient
environment. This heat dissipation helps reduce stress on transistors 110.
Endshield 102 further includes a cap plug opening 134 and a cap plug 136 as
will be
discussed in more detail below.
2a Power assembly 106 includes a power board 138, electronic components
140; a spacer 242, a plurality of clamp bars 144, and an insulator 146.
Insulator
146 is positioned between control board 108 and pourer board 138 and
electrically
insulates portions of control board 108 from portions. of power board 138.
Spacer
142 and clamp bars 144 extend between control board 108 and power board 138.
Spacer 142 and clamp bars 144 facilitate maintaining a predetermined distance
between power board 142 and control board 108. Spacer 142 and clamp bars 144
extend through insulator 146 and are in contact with both control board 108
and
power board 138. In one embodiment, spacer 142 is fabricated from nylon.
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Clamp bars 144 are positioned on an opposite side of power board 138 from
electronic components 140 and are located between electronic components 140
and
transistors 110. Clamp bars 144 apply pressure on transistors 110 to ensure a
good
thermal interface between transistors 110 and endshiE;ld 102.
s Figure 2 is a perspective view of endshieId 102. Endshield 102 includes a
shaft opening 148 for a rotor bearing (not shown). ha one embodiment, outer
surface 130 of endshield I02 includes a raised cylinder 150 that projects from
endshield 102 and surrounds opening 148. Raised cylinder 150 includes a
resilient
ring (not shown) mounted therein. Endshield 102 fmrther includes a plurality
of bolt
l o openings 152. Bolt openings 152 extend through endshield 102 and through
bolts
(not shown) are inserted therethrough to mount endshield 102 to the shell of
an
electronically commutated motor (not shown). Cap plug opening 134, as
explained
above, extends through endshield 102 and allows access to internal components
(not
shown) during final testing and calibration. Cap plug; opening 134 permits
access to
1s the internal components without having to remove endshield 102. Cap plug
136
(not shown in Figure 2) covers cap plug opening 134 to protect the internal
components.
Figure 3 is a cross-section view of endshield :102 and illustrates an inner
surface 154 that includes a substantially flat raised portion 156. Raised
portion 156
2o is located directly beneath recessed fins 132 and is a component of a
thermal
pathway between transistors 110 (not shown in Figure 3) and recessed fins 132.
Recessed fins 132 extend from raised portion 1~4 to increase the surface area
of
outer surface 130 which facilitates the dissipation of lneat from endshield
102.
Raised cylinder 150 and bolt opening 152 are also ilhastrated in Figure 3.
25 Figure 4 is a schematic illustration of thermal pad 112. In one embodiment,
thermal pad 112 includes angled sides to permit increased contact with a
portion of
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endshield 102 (not shown in Figure 4). Thermal pad 112 has two openings I58 to
help secure thermal pad 112 to the endshield.
Figure 5 is a schematic illustration of insulator I46. Insulator 146 includes
two openings 160 through which clamp bars 144 (not shown in Figure 5) extend.
s Openings 160 are generally rectangular in shape and are positioned in close
proximity to each other. Insulator 146 also includes a shaft opening 162
through
which a shaft {not shown) of the electronically commutated motor extends.
Insulator 146 is fabricated from rnylar and provides lboth thermal and
electrical
insulation. Insulator i46 also includes a spacer opening 164 through which
spacer
142 {not shown in Figure 5) extends.
Endshield assembly 100 includes a thermal pathway that allows heat to be
dissipated from the interior of endshield assembly 100, to the ambient
environment.
This thermal pathway enables control assembly 104 and power assembly 106 to be
placed within the interior of the electronically commutated motor housing.
This
15 interior placement eliminates the need for a separate compartment to house
the
electronic controls of the motor, and facilitates reducing fabrication costs
of the
motor. In addition, the orientation of the transistor leads enables the leads
to be
encapsulated and protected from potentially harsh environmental conditions.
While the invention has been described in teams of various specific
2o 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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Representative Drawing