Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-11-28
2002-04-09
Mullins, Burton S. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S063000, C310S071000, C310S091000, C310S263000, C310S058000
Reexamination Certificate
active
06369471
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention is directed toward rotating electric machines having a slip ring.
2. Description of the Related Art
A conventional alternator
10
is illustrated in
FIG. 1
sometimes referred to herein as a generator. Alternator
10
has a rotor assembly generally designated by the reference numeral
20
and stator assembly generally designated by the reference numeral
15
. The rotor assembly
20
includes a shaft
21
supporting all rotating magnetic circuit structures thereof including conventional pole-members
16
A and
16
B, rotor core
17
and field coil
18
wound upon bobbin
12
. Additionally, all other non-magnetic circuit rotating structures are carried thereby, including air circulation fans
19
and
27
located at axially opposite sides of the pole-members, and a slip ring assembly
30
located at one extreme end of the shaft. Fan
27
is formed from sheet metal stock and spot welded to pole-member
16
B while fan
19
is formed from an appropriate thermoplastic material and heat staked to tower extensions (not shown) from the field coil bobbin
12
. The shaft
21
in turn is rotatably supported within a housing
26
by a pair of bearings
23
and
22
. Bearing
23
is located between the slip ring assembly
30
and the fan
19
.
Coil leads
18
A of field coil
18
are wrapped about respective posts
12
A of bobbin
12
and pass through holes
13
in fan
19
. Slip ring assembly
30
is made of a pair of copper rings
31
, each having a slip ring lead
32
joined such as by welding thereto. The copper rings and wires are molded into a thermoset material to complete the slip ring assembly. Slip ring assembly
30
is pressed onto the end of rotor shaft
21
and the slip ring leads
32
are routed into channels along the shaft
21
where they are joined, such as by twisting and welding, to the coil leads
18
A of field coil
18
via a joint
24
. The joint
24
is then bent to the surface of the fan
19
and received in a pyramid-shaped tab structure
25
. The joint
24
is then secured to fan
19
by ultrasonic welding of the plastic material of the tab
25
. Bearing
23
is assembled to pass over the slip ring assembly
30
to retain the lead wires
32
securely within the shaft channels. The configuration in
FIG. 1
, however, presents several manufacturing challenges which may affect long-term durability.
First, the weld connection at joint
24
may be made imperfectly, for example, where the weld bead contains a partial crack or fissure. Such a joint will normally pass electrical tests conducted during manufacture. However, during the service life of generator
10
, the rotational forces (i.e., centrifugal forces) that come to bear on joint
24
, either directly or indirectly (e.g., via flexure of the fan body when it rotates) may cause the crack to propagate until the electrical connection is broken entirely, resulting in an open condition in the field winding circuit. This will cause the generator to fail.
Second, the above-mentioned ultrasonic welding operation may incompletely melt the plastic in the vicinity of the joint
24
, resulting in gaps or voids. These gaps or voids may allow the wires or joint
24
itself to move during operation of the generator (i.e., rotation of the rotor). This movement may fatigue the metal, causing it to break, resulting in an open circuit and failure of the generator. Additionally, a weld horn that is used in the ultrasonic welding operation may contact the wires or joint
24
directly (not just the tab
25
). The high vibration imparted by the weld horn may fatigue the wires or joint
24
, perhaps not severe enough to cause a break that could be detected during manufacture via electrical testing. Moreover, the weld horn may crush, flatten or otherwise deform the wires or joint, thereby weakening it. The wires/joint, thus weakened, may fail during operation of the generator.
Third, slip ring conductor
32
may be pulled too tight when joint
24
is made, causing it to rise slightly out of the channel in the shaft and fan hub where it is designed to reside. Bearing
23
, when assembled onto shaft
21
, may contact conductor
32
, deforming or possibly cutting the wire's outer insulation. Such a condition will ground the rotor winding, causing the generator to fail.
Fourth, the connection of conductors
32
to respective slip rings
31
is conventionally made via brazing. As shown in
FIG. 1
, such connections are disposed proximate a radially outermost portion of the slip ring assembly
30
. Rotational forces increase with increases in distance from the main axis, and may therefore weaken such connections, causing some to fail.
U.S. Pat. No. 5,625,244 to Bradfield discloses a slip ring and fan assembly having channels on an inside (i.e., rotor segment facing) surface of the fan for routing coil leads to the slip ring assembly. However, the channels do not provide any mechanism for retaining the leads.
There is therefore a need for an improved alternator and/or portions thereof that minimize or eliminate one or more of the problems as set forth above.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a solution to one or more of the problems set forth in the Background. An advantage of a fan in accordance with the present invention is that it provides a mechanism, in cooperation with a rotor segment, to secure or retain a rotor coil lead without any additional manufacturing steps. Another advantage is that it eliminates the routing of leads on the outer, front surface of the fan (as described in the Background), eliminating the need for the front welding connection employed on conventional configurations. The present invention further minimizes or eliminates axial movement of the fan which has previously fatigued broken leads. Further, routing of the leads under the fan protects the leads from environmental conditions. Still another advantage of a fan according to the invention relates to its improved rigidity, which minimizes flexure and oscillation of the fan during operation (i.e., during the operation of an alternator that includes the inventive fan).
A fan is provided for use in a dynamoelectric machine of the type having a rotor with a rotatable shaft disposed along a longitudinal axis and a field coil having a pair of coil leads. The fan includes a hub portion having a central aperture configured to accommodate the shaft, and a carrier portion. The carrier portion extends radially outwardly from the hub and has a plurality of vanes on a first side thereof. The carrier also includes a second side opposite the first side configured to contact an engagement surface of the rotor. The carrier further includes a pair of channels on the second side for routing of the coil leads. According to the invention, when the fan is assembled into the dynamoelectric machine against the rotor, each channel has a substantially uniform depth taken relative to the rotor's engagement surface over a predetermined radial length. In a preferred embodiment, the uniform depth is selected so as to allow the use of a compressible insulating sleeve for surrounding each coil lead. The lead/sleeve combination is compressed when the fan is assembled against the rotor. The compression provides a retention function, holding the leads in place during the remainder of the manufacture of the machine as well as during operation.
REFERENCES:
patent: 4565936 (1986-01-01), Ikegami et al.
patent: 4588911 (1986-05-01), Gold
patent: 4961016 (1990-10-01), Peng et al.
patent: 4992691 (1991-02-01), Mlynarz
patent: 5235229 (1993-08-01), Tanaka et al.
patent: 5241230 (1993-08-01), Tanaka et al.
patent: 5254896 (1993-10-01), Bradfield et al.
patent: 5625244 (1997-04-01), Bradfield
Shields Steve J.
Whitted Mitchell L.
Delphi Technologies Inc.
Dobrowitsky Margaret A.
Mullins Burton S.
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