Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-09-13
2001-02-13
Nguyen, Tran (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S254100
Reexamination Certificate
active
06188158
ABSTRACT:
BACKGROUND OF THE INVENTION
(1). Field of the Invention
This invention pertains to the field of dynamoelectric devices such as electric motors and generators that are used to convert energy in either electrical or mechanical form into the other. More particularly, this invention pertains to the use of a self-locking retaining member, frequently referred to as a top stick, positioned between stator poles to prevent windings from entering the air gap between the stator and rotor. The use of self locking retaining members increases the safety and reliability of dynamoelectric devices by preventing undesirable axial translation of retaining members that may occur during severe operating conditions of dynamoelectric devices.
(2). Description of the Related Art
There are numerous types of dynamoelectric devices in the prior art. A typical dynamoelectric device of the prior art in represented generally by the numeral
20
as shown in cross-section in FIG.
1
. In general, the dynamoelectric device is comprised of a rotor
22
that is revolvable about an axis
24
, a plurality of stator poles
26
positioned circumferentially about the rotor
22
, and windings
28
. A slot
30
extending in the direction of the axis
24
is formed between every two immediately adjacent stator poles
26
, as is more clearly shown in detail in FIG.
2
. The windings
28
consist of at least one electrically conductive coated wire wound within the slots
30
about one or more of the stator poles
26
.
Typically, a slot liner
32
is positioned between the windings
28
and the stator poles
26
within the slots
30
to prevent the windings
28
from directly contacting the stator poles
26
. The slot liners
32
are generally rectangular insulating sheets made of polymeric or fibrous material and have two opposite ends
33
, the first end
33
positioned adjacent one of the two stator poles
26
that defines the slot
30
and the second end
33
positioned adjacent the other stator pole
26
. Additionally, a liner cap
34
made of material similar to the slot liner
32
, commonly referred to as a wedge, may extend from the first end
33
of the slot liner
32
to the second end
33
, thereby covering the inner most surface of the windings
28
. By “inner” and “inwardly”, what is meant is, radially inward toward the axis
24
of the rotor
22
.
A failure mode of such prior art devices arises when the windings
28
migrate from between stator poles
26
radially inward into the air gap
36
between the rotor
22
and stator poles
26
, interfering with the moving rotor assembly. This failure occurs frequently in devices with large slot fills or large slot openings between stator poles wherein typical wire retention methods are insufficient. This is often a concern in switched reluctance motors that are subject to high winding temperatures or vibration loads. Recently, this failure mode has become an increasing concern when utilizing switched reluctance motors in safety critical applications such as in the automotive steering industry.
In those prior art devices having liner caps
34
, they are generally radially non-rigid and therefore unable to prevent radial migration of the windings
28
. One method utilized in prior art devices to prevent winding migration has been to varnish the windings, thereby preventing the wire passes that comprise the winding from moving independently of one another. This method has been shown to be beneficial in preventing winding migration but not at elevated winding temperatures. At elevated winding temperatures, the varnish strength is reduced and the varnish may therefore be unable to prevent winding migration. Additionally, the varnishing process typically has a considerably lengthy cycle time and high burden cost during production of dynamoelectric devices.
To reduce the cycle time and burden cost associated with the varnishing method, a similar method of preventing the wire passes that comprise the winding from moving independently of one another has been to utilize bondable wire coatings. This method, as is the case with the varnish method, is beneficial in preventing winding migration but not at elevated winding temperatures.
To prevent winding migration inherent to both the varnish and bondable wire coating methods at elevated temperatures, retaining members, commonly referred to as top sticks, have been developed in the prior art to provide a barrier between the windings
28
and the air gap
36
between the stator and rotor. This method is typically used as a secondary restraint in conjunction with other retention methods such as utilizing a bondable coating on the windings
28
. Prior art retaining members are generally rectangular members that are slid axially into the slots between stator poles during assembly of the dynamoelectric devices. A typical prior art retaining member
38
is shown in
FIGS. 3-5
. The top stick retaining member
38
is shown in a plan view in
FIG. 3
with its radially inner side shown. The retaining member is shown in cross section in FIG.
4
.
FIG. 5
is a partial view of the retaining member in one operative environment assembled in a dynamoelectric device between a pair of adjacent stator poles
26
and retaining a winding
28
between the poles.
The prior art retaining member
38
is formed of a generally rigid material that provides a barrier in the slot
30
between the windings
28
and the air gap
36
. As can be seen in
FIGS. 4 and 5
, the prior art retaining member
38
has a radially inner surface
40
that faces inwardly toward the rotor and has a width slightly less than that of the slot
30
inwhich it is positioned. The inner surface
40
is often slightly curved, matching the radius of the inward most surfaces of the stator poles
26
so as to maintain a uniform air gap
36
between the rotor
22
and stator poles
26
. The T-shaped cross section of the main body of the retaining member
38
as seen in
FIG. 4
provides the main body with side rails
42
that are slightly farther apart than the narrowest portion of the width of the slot
30
. The rails
42
engage with inner edges
43
of the pair of adjacent stator poles to hold the retaining member
38
radially in the slot. Thus, when an inward force is applied to the prior art retaining member, the side rails
42
prevent the prior art retaining member
38
from translating inward by engaging both the stator poles
26
that define the slot
30
.
In addition to the main body, prior art retaining members
38
have also been provided with end stops
44
positioned at one axial end of the retaining member
38
. The end stops
44
project outwardly beyond the width of the retaining member's inner surface
40
as seen in FIG.
4
and therefore are unable to fit within the slot
30
between adjacent stator poles
26
. During installation into a dynamoelectric device, the end of the retaining member
38
axially opposite the end stops
44
is inserted axially into the slot
30
. The configuration of the retaining member
38
allows it to slide axially between the inner edges
43
of the adjacent stator poles
26
until the end stops
44
engage the stator poles
26
or another axially rigid portion of the device. Thereafter, the end stops
44
prevent axial over insertion of the retaining member
38
, thereby increasing the ease of their installation.
Retaining members are advantageous over other prior art solutions in that, when properly axially aligned, they effectively prevent excessive winding migration toward the gap
36
between the stator and rotor while maintaining a low burden cost during production. However, a disadvantage associated with such prior art retaining members has been an undesired axial movement of the retaining members as a result of severe three dimensional vibration and thermal expansion and contraction of the stator poles relative to the retaining member during the life of the dynamoelectric device. In prior art devices which utilize the varnish method in combination with retaining members
38
, axial movement of the retaining members is lim
DeLuca Kenneth M.
Horst Gary E.
Ketterer Charles P.
Poag Andrew F.
Emerson Electric Co.
Howell & Haferkamp LC
Nguyen Tran
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