Rotor lamination stress relief

A multilayer laminated rotor is mountable on a shaft for rotation relative to a stator of a rotary electric machine arrangement. The rotor has a plurality of laminas, joined together, and voids for receiving magnets. An annular rotor section, which surrounds a shaft opening within which the shaft is receivable, extends between the shaft opening and a radially outer circumferential rotor surface. The annular section mentioned includes an undulating series of the voids in void groups extending from the radially outer circumferential rotor surface inwardly toward the shaft opening and then back toward the radially outer circumferential rotor surface, as well as a solid radially interior portion without any of the voids. Distal voids in the void groups include curved, arcuate, or recurved stress relieving features extending inwardly from radially innermost corner locations of the distal voids.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention concerns stress relief in a multilayer rotor configuration usable in a rotary electric machine arrangement.

2. Description of Related Art

U.S. Pat. No. 6,794,784 to Takahashi et al. discloses a rotor core having permanent magnets received in embedding holes provided, in one arrangement, with radiussed portions serving to minimize stress.

U.S. Pat. No. 7,436,096 to Guven et al. illustrates the orientation of magnetic flux created by adjacent magnet clusters.

U.S. Pat. No. 7,498,708 to Brown et al. concerns a rotor core including web material disposed between adjacent magnet receiving slots and providing improved stress reduction and magnet restraint.

The disclosures of U.S. Pat. No. 6,794,784 to Takahashi et al., U.S. Pat. No. 7,436,096 to Guven et al., and U.S. Pat. No. 7,498,708 to Brown et al. are all incorporated herein by reference in their entireties as non-essential subject matter.

SUMMARY OF THE INVENTION

A multilayer laminated rotor according to this invention is mountable on a shaft for rotation relative to a stator of a rotary electric machine arrangement. The rotor has a plurality of laminas, joined together, and voids for receiving magnets. The rotor has an annular section, surrounding a shaft opening within which the shaft is receivable, that extends between the shaft opening and a radially outer circumferential rotor surface. The annular section mentioned includes an undulating series of the voids in void groups extending from the radially outer circumferential rotor surface inwardly toward the shaft opening and then back toward the radially outer circumferential rotor surface, as well as a solid radially interior portion without any of the voids. Distal voids in the void groups include curved, arcuate, or recurved void sections extending inwardly from radially innermost corner locations of the distal voids. These inwardly extending void sections delimit the solid radially interior portion of the annular section. The undulating series of voids extends circumferentially completely around the rotor.

The void sections are shaped so as to extend primarily parallel to a magnetic flux direction when the rotor is in use, and provide stress relief to webs of material located between the pair of distal voids and an intermediate void interposed between the distal voids. This stress relief results from displacement of rotor hoop stress away from the webs of material mentioned.

The invention additionally concerns an individual lamina to be included in a multilayer laminated rotor such as that referred to.

DETAILED DESCRIPTION OF THE INVENTION

An interior permanent magnet rotor lamina10used in production of a multilayer laminated rotor according to the present invention is shown, in plan view, inFIG. 1. It will be understood by those of ordinary skill in the art that the lamina10shown inFIG. 1is an endmost lamina of multiple (e.g., fifty) laminas joined together in a lamination stack to produce the rotor12constituting part of a rotary electric machine arrangement, such as a motor, generator, or motor/generator. The laminas may be stamped from sheets of steel or other suitable material. A rotor shaft (not shown) is receivable within a shaft opening14of the rotor12to impart rotational motion to the rotor. A radially inwardly projecting tooth or key16may be used in conjunction with a corresponding recess in the rotor shaft to help secure the rotor12against rotation relative to the rotor shaft.

Each lamina10has an annular section surrounding the shaft opening14and extending between that shaft opening14and a radially outer circumferential surface20of the overall rotor12. The annular section is provided with a series18of magnet receiving holes, voids, or orifices (hereafter referred to as voids for simplicity) located adjacent a radially outer lamina surface. When the laminas10are joined together in a stack to collectively define the rotor12, the voids of adjacent laminas align and are located near the radially outer circumferential rotor surface20. Permanent magnets22are receivable within the voids, as shown inFIG. 2. The permanent magnets22may be inserted into the voids after the laminas10are joined together, or, if desired, the voids may be aligned with the magnets22as the laminas10are slid over the magnets22so that the magnets22serve as guides to position the laminas10properly during rotor construction. Once a selected number of laminas10have been joined together, the magnets22have been potted, glued, or otherwise secured in place, and the laminated rotor12is completed, the permanent magnets22extend axially relative to the rotor12through the aligned voids of the stack of laminas10to a desired extent. The magnets22thereafter remain fixed within the voids to cooperate with windings disposed around poles of a stator, within which the overall rotor12is rotatable.

AsFIG. 1shows, the series18of voids undulates, and is composed of a multiplicity of void groups24. Each void group24extends from the radially outer circumferential rotor surface inwardly toward the shaft opening14and then back toward the rotor surface20. The series18extends circumferentially completely around the lamination and, therefore, the rotor including that lamination. In the arrangement illustrated inFIGS. 1 and 2, each void group24includes a pair of opposite distal end voids26and28, and an intermediate central void30. Each of the end voids26,28is separated from the adjacent central void30by a respective web32,34of lamina material. The voids26,28, and30may include recessed fillets36at some of their corners for optimal stress concentration properties.

In the particular arrangement shown, as with the arrangement forming the subject matter of co-pending U.S. patent application Ser. No. 13/424,579 mentioned above, rotor lamina material is removed from or left out of the outer diameter region of the end voids in each void group. Avoiding the presence of this rotor lamina material has a structural benefit, as it eliminates rotational hoop stresses from the typically thin outer sections of the lamination webs, and instead forces the structural support to be cantilevered. It is to be understood that, although the particular arrangement used by way of example to describe the present invention in detail includes cantilevered magnet supports, the stress relief features according to the present invention are not limited in application to support webs with cantilevered magnet supports.

The series18of voids is arranged in such a way that, throughout the rotor12, the distal voids26,28of adjacent void groups24are located next to each other. In the cantilevered arrangement shown by way of example, the distal voids26,28in each of the void groups24, together with distal voids of adjacent void groups, define gaps38separating adjacent arc sections of the radially outer circumferential rotor surface20. These gaps38may be produced by machining away or leaving out rotor material between the adjacent arc sections. Although such a construction leaves the distal voids26,28open and exposed, flanges, nubs, bumps, or other protrusions40of material at adjacent ends of the rotor surface arc sections and common interior flanges, nubs, bumps, or other protrusions42of material located between the distal voids26,28help in positioning and retaining magnets22within the voids26,28. Different types of void series patterns, of course, can be utilized; such patterns, for example, could be roughly u-shaped, similar to that of the series18, roughly v-shaped, or flattened.

As noted, the voids26,28, and30may include recessed fillets36at some of their corners for optimal stress concentration properties. According to the present invention, in addition to these fillets36, further features44are included as extensions of the end voids26and28in each void group24to provide stress relief to the narrow webs32,34of lamina material in each group. The stress relieving “web tail” features44referred to extend inwardly from radially innermost corner locations of the end or distal voids26and28, and are additional curved, arcuate, or recurved void sections producing a modified rotor lamination geometry with reduced web stress at high rotational speeds. At the same time, the particular way in which the stress relieving features44are configured minimizes the electromagnetic impact of those features44.

Although the rotor12of the present invention does not include separate outer and inner radial permanent magnet layers such as those present in the rotor forming the subject matter of U.S. Pat. No. 7,436,096 to Guven et al. mentioned above, the present invention will have a magnetic flux orientation that is generally the same as that produced by the Guven et al. ('096) inner radial permanent magnet layer, and it will be understood fromFIGS. 2 and 3that the added stress relieving features44of the present invention extend primarily parallel to the direction of magnetic flux. The geometries of the stress relieving features44displace the rotor hoop stress towards the solid radially interior portion46of the rotor12and away from the support webs32and34. The solid radially interior rotor portion46mentioned is delimited by the stress relieving features44.

To reduce stress concentration, a large radius48is utilized to define a path followed by each feature44so that the feature curves radially inwardly and then back radially outwardly with respect to the overall rotor12. The thickness50of the void defining each feature44can remain small, minimizing flux impact, by having the feature44turn “upwards” and terminate at an end52(FIG. 3) disposed away from the structural hoop defined by the solid radially interior rotor portion46. Since one alternative would be to increase the cross-section of the structural hoop by reducing the rotor inner diameter defined by the shaft opening14, the stress relief provided by the features44allows use of rotors having reduced mass. Again, it is to be understood that the stress relief arrangement according to the present invention is not limited to support webs that have cantilevered magnet supports.

FIG. 4provides a schematic view of an enlarged rotor area surrounding one end void128of a void group included in a conventionally structured rotor, without stress relieving features according to the present invention. The shaded areas160inFIG. 4identify locations of maximum static structural equivalent stress imposed during operation of a conventionally structured rotor. By contrast, in a rotor according to the present invention, including the stress relieving features44, the locations of maximum static structural equivalent stress imposed during operation occur adjacent the ends52of the stress relieving features44and away from the narrow webs32,34of lamina material. One such location is identified by the shaded area60inFIG. 3.

A rotor incorporating rotor lamination geometry according to the present invention allows for reduced mechanical stress and reduced electromagnetic degradation from stress relief features. The geometry utilized according to the invention permits production of higher speed, higher performance electric motors and generators in a relatively simple manner, and allows rotors having reduced mass as well.

The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, and the invention should be construed to include everything within the scope of the invention ultimately claimed.