Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-11-28
2002-08-20
Mullins, Burton S. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S071000
Reexamination Certificate
active
06437475
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 is ultrasonically welded 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. A one-piece slip ring assembly is disclosed in U.S. Pat. No. 4,961,016 issued to Gold. 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) 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 or welding. As shown in
FIG. 1
, the slip ring connections are located near a radially outermost portion of the slip ring assembly
30
itself. 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 assembly having channels for capturing coil leads and routing them through the slip ring assembly to an axially outermost end. The channels, however, are disclosed as being of uniform size, allowing an insulating sleeve associated with the coil leads to emerge from the slip ring assembly and possibly interfere with an electrical connection. In addition, the channels route the coil leads near a radially outermost portion of the slip ring assembly, subjecting the leads/connections to an increased centrifugal force, increasing the chance of a failed electrical connection.
There is therefore a need for an improved generator that minimizes or eliminates 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 slip ring assembly in accordance with the present invention is that it reduces the number of electrical connections compared to conventional designs. This reduced number of connections reduces manufacturing complexity and improves durability. Another advantage is that it provides a more robust mechanical and electrical slip ring connection, inasmuch as it is subjected to reduced centrifugal forces by being located nearer the main axis of the slip ring assembly. Yet another advantage is that interference of an insulating sleeve associated with the rotor coil leads is reduced, via routing through-bores that have a reduced diameter exit aperture, preventing the sleeve from exiting.
These and other features and advantages are achieved by a slip ring assembly in accordance with the present invention. A slip ring assembly is provided for supplying current to a rotor winding of a rotor of an alternating current generator and includes a body portion having a main axis formed of electrical insulating material, the insulator body having a central bore configured to be secured to a rotatable rotor shaft, the body portion having first and second opposing ends, the first end configured to face the rotor, a pair of spaced electrically conductive slip rings engaging the body portion, each slip ring having a respective coupling terminal extending from the second end of the insulator body portion, characterized in that the body portion has a pair of longitudinally extending through-bores configured to allow rotor winding leads to pass from the first end to the second end.
REFERENCES:
patent: 1431295 (1922-10-01), Evans
patent: 1870236 (1932-09-01), Chervenka
patent: 2718604 (1955-09-01), Herrick
patent: 4406961 (1983-09-01), Pflueger et al.
patent: 4588911 (1986-05-01), Gold
patent: 4645962 (1987-02-01), Freeman
patent: 4961016 (1990-10-01), Peng et al.
patent: 4992691 (1991-02-01), Mlynarz
patent: 5625244 (1997-04-01), Bradfield
patent: 3248219 (1984-07-01), None
patent: 2029122 (1980-03-01), None
Brutchen George William
Buck Derrick S.
Delphi Technologies Inc.
Dobrowitsky Margaret A.
Mullins Burton S.
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