Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1994-03-02
1996-03-12
Skudy, R.
Electrical generator or motor structure
Dynamoelectric
Rotary
310 44, 310211, 310216, H02K 122
Patent
active
054989183
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a rotor for an electric machine, in particular for a motor for a hermetic refrigerating compressor, where the rotor has a core of magnetically conductive material with a central spindle hole and with a number of axially extended slots, which are filled with an electrically conductive material for the formation of electric conductors in the rotor, where the conductors are short-circuited by short-circuiting rings, and where the spindle hole has at least two different internal diameters.
Rotors for electric machines of the type mentioned are commonly known from asynchrous motors, and these and their mode of operation must be assumed to be known. If a motor shall operate with one bearing only, relatively high demands are made to the length of the bearing. Hermetic refrigerating compressors operate with a joint bearing for both motor and compressor, and in order to obtain an extremely compact construction it is sometimes necessary to place part of the neck of the bearing internally in the rotor. In these cases it is necessary to increase the internal diameter in a part of the axial direction of the spindle. Where the internal diameter has been increased, the concentration of the lines of magnetic flux is increased in relation to the part of the rotor without any increase of the internal diameter. If the rotor is highly magnetically loaded, a partial magnetic saturation may occur in the iron in the area where the internal diameter has been increased.
SUMMARY OF THE INVENTION
The object of the invention is to indicate a rotor designed in such a manner that magnetic saturation does not occur in areas with increased internal diameter.
This is achieved as initially described and by giving the axial slots a varying profile in their longitudinal direction and the sectional area of the slots can be smaller where the sectional area of the spindle hole is larger, and vice versa.
As a result of this the loss of magnetic power in the iron can be maintained at a uniform level in the entire axial direction of the rotor. The axially disposed slots containing the electric conductors can be designed so that the least possible magnetic resistance is encountered, without substantially increasing the electrical resistance in the conductors. In this manner it is avoided that the iron approaches saturation, and thereby a better total efficiency of the electromotor is achieved. It will also bee possible on the basis of knowledge of the course of the lines of magnetic flux in the rotor to design the slots with the highest possible consideration to the course of the lines of magnetic flux, so that a local saturation of the core is avoided. The increased concentration of the lines of magnetic flux which would occur due to the increased internal diameter of the central hole of the core, might bee reduced by designing the slots in areas with a larger internal diameter with consideration to the relatively smaller area of magnetically conductive core volume.
The invention is embodied by reducing the extention of the slots in the direction of the centre in the part of the rotor where the spindle hole has the largest internal diameter. As a result the sectional area of the core in the magnetic yoke is maintained approximately constant in spite of the varying internal diameter.
The invention is embodied by constructing the core of a laminated magnetically conductive material, where the length-wise varying profile of the slots is produced by giving the slots in the single layers of magnetically conductive material varying sizes and/or varying shape. The result of this is that the traditional, known rotor, which consists of a stack of punched, magnetically conductive disks, can be produced by giving the punched disks varying profiles, and the disks of magnetically material are then stacked so that a varying profile is obtained in the axial direction.
The invention can be embodied by producing the core by powder technology. As a result it is possible to use as a starting point the
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patent: 4439704 (1984-03-01), Adelski et al.
patent: 4796353 (1989-01-01), Mantovani
patent: 5130596 (1992-07-01), Umeki
Danfoss A/S
Skudy R.
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