Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1995-01-06
1996-11-05
LaBalle, Clayton E.
Electrical generator or motor structure
Dynamoelectric
Rotary
H02K 716
Patent
active
055720803
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an induction motor, and more particularly to a squirrel-cage rotor for a high-speed induction motor.
BACKGROUND ART
In a squirrel-cage rotor for an induction motor, a laminated core made by stacking magnetic materials, such as silicon steel plates, is provided with a plurality of slots for disposing secondary conductors therein. These slots axially extend along the outer circumferential surface of the laminated core, and are arranged at generally equal intervals in a circumferential direction. Particularly, in a high-speed induction motor used as, e.g., a spindle motor of a machine tool, the slots of a rotor are formed as axial through holes which do not open at the outer circumferential surface of a laminated core. The slots shaped as through holes in a conventional squirrel-cage rotor are generally provided with a circular profile, or a generally elliptical profile of which a major axis is oriented in the radial direction of the laminated core, in a section orthogonal to the axis of the rotor.
When the squirrel-cage rotor rotates at high speed, stress due to centrifugal force is caused in the laminated core. This stress is concentrated particularly on the minimum radius portions in relation to a center of rotation, i.e., the innermost radial portions, of the walls of the slots of the laminated core. If such a stress concentration exceeds the elastic limit of the material forming the laminated core, a permanent set or a crazing arises on the radial innermost portions of the slot walls of the laminated core. The degree of the stress concentration becomes larger when the crossing angle of the tangents on two given points adjacent to the radial innermost portion of each slot wall becomes smaller in a section orthogonal to the axis.
Even if the slots have sectional shapes which easily lead to stress concentration on the radial innermost portions of the slot walls, the stress concentration caused on the slot walls during the high-speed rotation of the rotor does not become very problematic, as long as the diameter of the laminated core is relatively small. However, in the case of a squirrel-cage rotor of a high-power induction motor, having a laminated core with a larger diameter, is rotated at high speed, the problem arises in the slots having a circular section or a generally elliptical section of which a major axis is oriented in the radial direction of the laminated core, that the stress concentration caused on the slot walls may damage the laminated core.
DISCLOSURE OF THE INVENTION
The object of the present invention is to provide a squirrel-cage rotor for an induction motor, which can reduce the stress concentration caused on the slot walls of a laminated core and increase the maximum rotation speed at which rotor can operate without the occurrence of permanent set in the laminated core, so as to enable a high-power induction motor having a large diameter rotor to be rotated at high speed.
To accomplish the above object, the present invention provides a squirrel-cage rotor for an induction motor, comprising a rotor shaft; a laminated core coaxially fixed to the shaft and having a plurality of slots axially penetrating near an outer circumferential surface of the core, each of the slots being defined by a wall having a predetermined profile which has a maximum circumferential distance larger than a maximum radial distance in a given section orthogonal to an axis; and a conductor portion including a plurality of secondary conductors arranged in the slots of the laminated core and a pair of end rings connected to the secondary conductors at both axial ends of the laminated core.
In the preferred embodiment of the present invention, each of the slots of the laminated core is defined by a wall having a generally elliptical profile of which a major axis is oriented in a circumferential direction in a given section orthogonal to an axis. Alternatively, each of the slots of the laminated core may be defined by a wall drawing different circular arcs in a gi
REFERENCES:
patent: 2048421 (1936-07-01), Ballentine
patent: 3113230 (1963-12-01), Linkous
patent: 3213306 (1965-10-01), Summers et al.
patent: 3758800 (1973-09-01), McLaughlin
patent: 3778652 (1973-12-01), Endress
patent: 4309635 (1982-01-01), Sei et al.
"Querstrome in Kafiglaufern," Stepina, E&M; Elektrotechnik und Mascinenbebau, vol. 92, No. 1, 1992, pp. 8-14.
Hayashi Yoshiyuki
Maeda Hisashi
Nakamura Kosei
Fanuc Ltd.
LaBalle Clayton E.
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