Strength cast rotor for an induction motor

This application relates to a rotor for an induction motor wherein counter-bored holes are formed within the laminated core to reduce the likelihood of tears (cracks) forming during casting.

Induction motors are known, and typically include a squirrel cage assembly as part of a rotor. A stator surrounds the rotor, and the rotor is typically associated with a shaft which is to be driven to perform some use.

The rotor is formed of a pack of central iron laminations which are assembled together. End laminations are assembled at each end of the pack of central laminations. The combined laminations are placed into a mold, and a molten metal, typically copper or aluminum is moved into the mold. The laminations are all formed with teeth and gaps circumferentially spaced between the teeth. The gaps between teeth form slots. The molten metal moves into the gaps between the teeth (i.e. slots), forming bars. The molten metal also flows into cylindrical volumes at each end of the rotor, formed by cavities within the mold. These form the end-rings of the rotor. The bars and end-rings are to be homogeneous as formed by the casting process.

As the metal cools, the stresses across the entire rotor vary due to localized cooling differences. The mechanical joints between the bars and the end-rings have sometimes been subject to tears due to these stresses.

A rotor for an induction motor has a plurality of central laminations defining a central bore extending along an axis. End laminations are at each axial end of the central laminations. Metal is within gaps between teeth (i.e. slots) of the laminations. The lamination teeth extend radially outwardly from a central ring portion. A bore is formed in a face of the end laminations facing outwardly, and adjacent to where the teeth connect into the central ring portion.

A motor including such a rotor, and a method are also claimed.

These and other features of the present invention can be best understood from the following specification and drawings, of which the following is a brief description.

FIG. 1 schematically shows a motor.

FIG. 2 is a cross-sectional view of a rotor associated with the motor.

FIG. 3 is another view of the rotor.

FIG. 4A shows an end lamination.

FIG. 4B shows a detail of the FIG. 4A end lamination.

FIG. 4C is a detail along the cross-section C-C of FIG. 4B .

A motor 20 is shown schematically in FIG. 1 . As known, a stator 22 surrounds a rotor 24 . A shaft 26 is mounted within a central bore 128 in the rotor 24 . As known, the stator 22 drives the rotor 24 to rotate, and thus powers some use associated with the shaft 26 . The motor, as shown in FIG. 1 , may be an induction motor.

FIG. 2 is a cross-sectional view along line 2 - 2 , and extends through bars 30 and laminations having a central ring 38 (i.e. yoke), and also through teeth 36 in the laminations. The rotor 24 includes a central lamination portion 28 which is formed of a plurality of thin plates, or central laminations, although the individual laminations are not illustrated. Portion 28 has end laminations 40 are positioned at each end of the combined central laminations 28 . The end laminations have teeth as shown at 44 , and gaps 49 between the teeth 44 (see FIG. 4A ). The rotor extends along an axis C, which is the center of bore 128 .

While the teeth and gaps may differ slightly through the central laminations at 28 , the central laminations 28 have similar structure.

Thus, as shown at the top of FIG. 2 , metal 30 sits in the gaps 49 . On the lower end, the teeth 36 / 44 extend generally to the radially outermost end of the rotor 24 . As also shown, end-rings 32 of the metal extend axially outwardly of the end laminations 40 . The end laminations 40 have a face 41 facing outwardly, and a face 43 facing the central portion 28 , or inwardly.

As shown in FIG. 3 , one can see the spaced teeth 36 and metal 30 which is extended into the gaps in the central laminations of the central portion 28 .

FIG. 4A shows the end laminations 40 . As shown, the outer face 41 has a central ring-like portion 42 , with teeth 44 extending radially outwardly and with central gaps 49 .

FIG. 4B shows a detail of two circumferentially adjacent teeth 44 and the gap between them 49 . As can be seen, a counterbore is drilled at 50 into the face 41 . Counterbore 50 is part circular and extends across two teeth 44 , and into a central bridging portion 41 which is at a root of the gap formed between the teeth (i.e. slot) 49 . As can be appreciated, two counterbore portions are found in each of the teeth 44 .

A face of counterbore 50 is shown in FIG. 4C to extend generally at a chamfer angle A measured from edge 100 of teeth 44 . In one embodiment, the angle A was 45°. In embodiments, the angle A may be between 40° and 50°. As shown, a circumferential edge 54 of the counterbore 50 is deeper than the other end 52 . Again, the angle A results in the change in depth.

As shown in FIG. 4C , the diameter d 2 of counterbore 50 , or the distance between two opposed points at 52 is .150″ (.381 cm). A depth d 1 of the counterbore at edge 54 was .046″ (.117 cm). As shown in FIG. 4B , there is a circumferential width d 3 to the teeth. In one embodiment, d 3 was .114″ (.290 cm). As is clear from FIG. 4B and 4C , the depth of the counterbore 50 is not entirely through the thickness of the teeth, but rather is merely into a portion of the thickness beginning at the face 41 .

In embodiments, the ratio of d 3 to d 2 was between 0.684 and 0.841. The ratio of d 1 to d 2 was between 0.213 and 0.407.

The chamfer counterbores may be drilled to the shape and depth as shown. The chamfer improves the flow of molten metal during casting and addresses the stress tears that occurred in the prior art.

Although embodiments of this invention have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.