Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-08-11
2002-04-23
Mullins, Burton S. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S091000, C417S423140
Reexamination Certificate
active
06376950
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates, in general, to an air compressor that is powered by an electrical motor.
More particularly, the present invention relates to an air compressor, driven by an electrical motor, which is used to supply compressed air to the air brake system of a railed vehicle (e.g., a train or light rail vehicle).
Even more particularly, the present invention relates to the relationship between the bearing plate of the air compressor and the stator frame of the electric motor. As is discussed more fully below, the bearing plate of the air compressor and the stator frame of the bearing plate should have a particular spatial alignment to one another, in order to ensure a relatively long and trouble free service operation of the combined air compressor and electric motor.
BACKGROUND OF THE INVENTION
The following background information is provided to assist the reader to understand the invention described and claimed herein. Accordingly, any terms used herein are not intended to be limited to any particular narrow interpretation unless specifically so indicated.
The use of an air compressor to supply compressed air for the operation of an air brake system is well known. In a railed vehicle, the air compressor is typically located in the locomotive of the train, etc. Earlier air compressors for trains were often powered via a power takeoff linkage from the engine of the locomotive. More modern diesel locomotives typically employ electric motors to supply tractive power, with the electrical power being generated onboard. The air compressors of diesel locomotives are, therefore, typically driven by electrical power, which is readily available onboard.
A main compressed air reservoir is normally employed. The main reservoir supplies compressed air to the “brake pipe,” which runs the length of the train. The electric motor that drives the air compressor is typically started and stopped on an “as needed” basis, so as to maintain the compressed air pressure in the main reservoir within determined limits. Thus, the electric motor may be started and stopped repeatedly over the service life of the unit.
FIG. 1
is a simplified isometric view of an air compressor unit that is widely employed within the railroad industry for supplying compressed air for use in air braking systems, namely, a “3-CD” Air Compressor manufactured by the Westinghouse Air Brake Company® division of Wabtec Corporation® (1001 Air Brake Avenue, Wilmerding, Pa.). Particulars of the “3-CD” Air Compressor are set forth in the pamphlet entitled “Instructions for Disassembly, Repair and Assembly of ‘3-CD’ Air Compressors,” published by the above-identified Westinghouse Air Brake Company® (copyright 1994), this document being hereby expressly incorporated by reference into the present application, with the same effect as if fully set forth herein.
In
FIG. 1
, a “3-CD” air compressor is generally indicated by reference numeral
10
. The air compressor
10
includes a crankshaft
12
, which is driven by an external power source and which, in turn, drives the internal compression parts of the air compressor
10
(e.g., pistons, valves, etc.). The crankshaft
12
is rotationally supported and positioned by typically two inboard rotational bearings, one such inboard bearing
14
being shown in phantom in FIG.
1
. The inboard bearing
14
is supported and positioned by a generally key-shaped bearing plate
16
, which also serves to close a portion of the crankcase of the air compressor
10
. It will be seen that the crankshaft
12
projects outward from and beyond the bearing plate
16
.
FIG. 2
illustrates the manner in which an electric motor, generally indicated by reference numeral
18
, has heretofore been mated with the air compressor
10
, in order to provide power to the air compressor
10
. The electric motor generally includes a stator frame
20
, a stator
22
, and a rotor
24
. The stator frame
20
has, in the past, been connected to the exposed face of the bearing plate
16
by bolts
25
which pass through holes
26
provided in an inwardly projecting lip
28
provided on the rearward face of the stator frame
20
. The bolts then engage a series of threaded blind holes
30
provided in the outwardly exposed face of the bearing plate
16
. The stator frame is therefore “cantilevered” from the exposed face of the bearing plate
16
and secured in this position by the bolts.
The stator frame
20
may be viewed as the “housing” of the electric motor
18
, serving to enclose the stationary stator
22
and the rotating rotor
24
. The electric motor
18
is typically an induction type motor, and often a three-phase AC induction type motor. The stator
22
typically includes a plurality of coil windings and is fixedly mounted to the interior surface of the stator frame
20
. The rotor
24
non-rotationally engages the protruding portion of the crankshaft
12
(i.e., is fixedly mounted with respect to the crankshaft
12
) and is therefore encircled by the fixed stator
22
. Typically, the rotor
24
is press fitted onto the crankshaft
12
, and a protruding axial spline provided on the interior cylindrical surface of the rotor
24
engages a groove provided on the crankshaft
12
.
An endnut
32
may engage a threaded portion
34
provided on the outboard distal end of the crankshaft
12
to axially retain the rotor
24
on the crankshaft
12
.
The dimensional difference between the interior diameter of the stator
22
and the exterior diameter of the rotor
24
is relatively small, typically on the order of between about {fraction (40/1000)} and about {fraction (50/1000)} of an inch. If the rotor
24
is not maintained in a substantially central alignment with respect to the encircling stator
22
, the rotor
24
may come into contact with the stator
22
. Such rubbing degrades performance. In severe cases, contact of the rotor
24
with the stator
22
can short out the windings of the stator
22
, thereby “burning out” the electric motor
18
.
During startup of the electric motor
18
, it has been discovered that a non-symmetric radial force is exerted on the rotor
24
, and thus the crankshaft
12
. Thus, during startup, forces are exerted on the rotor
24
which tend to “cant” the rotor
24
with respect to the stator
22
. Over time in service, these forces can lead to the rubbing described above and, ultimately, can result in the above-described shorting and burning out of the electric motor
18
.
There is disclosed in U.S. patent application Ser. No. 09/593,558, entitled “Locomotive Air Compressor with an Electric Motor Supported by an External Bearing” and in U.S. Ser. No. 09/593,559, entitled “Locomotive Air Compressor with Motor Supported by Outside Bearing” (both of these pending U.S. applications being assigned to the same assignee as the present application), various arrangements for providing what is herein referred to as a “third” or (alternatively) an “outboard” bearing. Such a third or outboard bearing provides additional support for the outboard distal end of the crankshaft
12
, and considerably prevents (or at least substantially reduces) any canting of the crankshaft
12
and the rotor
24
attached thereto with respect to the stator
22
.
There are an extremely high number of air compressors of the “3-CD” type in service. It is desirable, therefore, to provide an apparatus and method for “retrofitting” such in-service air compressors with such a third or outboard bearing. Such an apparatus and method are disclosed herein.
Since relatively tight tolerances are required in the alignment between the stator frame
20
(which ultimately determines the positioning of the stator
22
) and the crankshaft
12
(which ultimately determines the positioning of the rotor
24
), it has heretofore been the practice in the industry to carefully machine both the outwardly exposed face of the bearing plate
16
and the rearward face of the stator frame
20
(i.e., including the inwardly projecting lip
28
provided on the rearward face of the stator frame
20
) to relatively exact
Cunkelman Brian L.
Goettel Walter E.
Shaffer Ronald
Varney James
James Ray & Associates
Mullins Burton S.
Westinghouse Air Brake Technologies Corporation
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