Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1998-07-14
2001-01-23
Mullins, Burton (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C211S201000
Reexamination Certificate
active
06177750
ABSTRACT:
TECHNICAL FIELD
The invention generally relates to dynamoelectric machines with rotors having attached shafts. In particular, the invention involves attachment of a shaft to a rotor core while maintaining intact a solid central portion of laminations in the rotor core.
BACKGROUND OF THE INVENTION
Typical induction motor designs have a rotor including a plurality of laminated sheets (laminations) and a shaft attached to the rotor. Interaction between magnetic fields created by the rotor and a stator surrounding the rotor causes torque to be created in the rotor. This torque rotates the rotor, thereby also rotating the attached shaft. Therefore it is desirable that the connection between the shaft and the rotor be sufficiently strong to allow transmission of the torque from the rotor to the shaft. An additional requirement in attaching the shaft to the rotor core is that the rotor should be strong enough, both torsionally and laterally, to withstand any load, such as a belt load, to which it will be subjected. Further, the rotor should be strong enough so that parts of it do not crack, break, or otherwise fail while it is spinning, particularly at higher speeds.
Conventionally, shafts have been attached to rotor cores through a central hole in the laminations making up the rotor core. The shaft is attached to the rotor core by means such as heat shrinking, welding, and/or a key on the shaft that fits into a slot in the laminations, thereby allowing the core to transmit torque to the shaft.
The conventional method of attaching the shaft to the core through a central hole has the drawback of inducing a stress concentration in the laminations. It is well known that the presence of even a very small hole at the axis of a rotating disc will cause the stress of the material bounding the hole to double when compared with the stress at the center of a solid disk. See, e.g., Adel S. Saada,
Elasticity: Theory and Applications
, p. 337 (1983). Thus the central hole in the laminations leads to high tangential stresses in the lamination material in the vicinity of the hole. These high stresses can lead to failure of the rotor, due to radial cracks in the laminations.
In view of the above, it would be desirable to attach a shaft to a rotor core of a dynamoelectric machine without disturbing the lamination material in the vicinity of the axis of the rotor.
SUMMARY OF THE INVENTION
According to one aspect of the invention, a shaft or shafts are connected to a rotor core without the need for a central hole in the laminations of the core. The shaft is connected to the core by attaching the shaft to a rotor end plate (or forming the shaft and the end plate as a single unit) and connecting the end plate to the core at a distance away from the axis of the core. The rotor may have similar end plates at both ends, the end plates attached to each other and to the core by through studs or bolts that pass through holes in the laminations. The holes and the studs or bolts are evenly circumferentially spaced at a distance from the axis. The through studs or bolts are secured at either end, clamping the end plates with the rotor core between them.
According to another aspect of the invention, the rotor end plate provides support to the rotor end ring that forms part of the squirrel cage of the rotor core. The end plate includes a lip or other portion which restrains movement of the end ring in lateral and/or axial direction(s) as the rotor rotates. For example, the rotor may have a lip which is machined to be at or nearly in contact with the end ring when the rotor is at rest.
According to yet another aspect of the invention, a dynamoelectric machine includes a rotor having a core and an axis of rotation, the core including a plurality of laminations; a rotor end plate coupled to a first end of the rotor core; and a rotor shaft coupled to the rotor end plate. The rotor shaft rotates about the axis of rotation of the rotor, and at least a portion of the plurality of laminations intersect the axis of rotation.
According to a further aspect of the invention, a dynamoelectric machine includes a rotor having a rotor core including a plurality of laminations, wherein at least one of the plurality of laminations has a solid central portion that is coincident with an axis of rotation of the rotor.
According to a still further aspect of the invention, an induction motor includes a rotor having a core and an axis of rotation, the core including a plurality of laminations; a rotor end plate coupled to a first end of the rotor; and a rotor shaft coupled to the rotor end plate and projecting in one direction from the end plate away from the rotor, the rotor shaft rotating about the axis of rotation of the rotor.
Yet according to another aspect of the present invention a method of fabricating a dynamoelectric machine includes the steps of: using lamination sheets as at least part of a core of a rotor, at least one of the lamination sheets having a solid central portion; and using an end plate to couple a shaft to the rotor.
To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principals of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
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Amin Himanshu S.
Horn John J.
Mullins Burton
Reliance Electric Technologies LLC
Walbrun William R.
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