Electric motor, in particular a small motor

Electrical generator or motor structure – Dynamoelectric – Rotary

Patent

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Details

310 40MM, H02K 2126

Patent

active

044450591

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a an electric motor, in particular a small motor, having at least two two-component field magnets opposite one another are facing an armature.


BACKGROUND

Two-component magnets have come into use in motors in response to requirements for the maximum possible magnetic flux on the one hand, and coercive field intensity in order to prevent demagnetization phenomena, on the other. It is not possible to satisfy both these requirements with a single magnetic material, because magnetic materials having high remanence have low coercive field intensity, and magnetic materials with a high coercive field intensity have low remanence. The danger of demagnetization of a magnet used in a motor is particularly great at the ends of the magnet, and is especially apparent when starting the motor at low temperatures and at the trailing edge. It has been proposed to use two-component magnets with highly coercive magnetic material at the trailing edge, and otherwise fabricating the magnet of a magnetic material having the greatest possible remanence. The material of maximum remanence has, however, lesser coercive field intensity in comparison with the highly coercive material.
The sections of the different materials are adjacent to one another in the circumferential direction of the motor; these sections of different magnetic material extend in the axial direction of the armature and protrude beyond the armature at either end by some distance. This axial magnetic overhang results in a further substantial increase in flux, i.e. 26%, given a magnet length 1.4 times the armature length, for example, and with a ratio of the armature diameter to the armature length of 1.83.


THE INVENTION

It is an object to provide an electric motor, and more particularly a permanent magnet field structure thefor, which, given the same dimensions as a motor, provides higher motor output or, with changed dimensions, and retaining a given power output, permits a saving in material.
Briefly, magnetic material of high coercive magnetic field strength is located at one or both circumferential end portions of the magnets, the remainder of the magnets being formed of highly remanent magnetic material. To increase the effective flux on the armature windings, the highly remanent magnetic material overlaps and extends axially beyond the projected outline of the core of the armature, even at the end portions where, in approximate alignment with the armature core, the highly coercive magnetic material is located.
The electric motor according to the invention, in particular a small motor, has the advantage that the permanent magnets arranged according to the invention deliver increased flux as compared to conventional two-component magnets, yet the resistance to demagnetization remains unchanged. Demagnetization at the trailing edge of the magnet--with respect to the rotational direction of the rotor--occurs only in the vicinity of the armature core. Demagnetization-resistant material is present, only where required, i.e. over the armature core. Thus, there is no sacrifice of demagnetization resistance. Because of the remaining parts of the magnet protruding beyond the ends of the armature, which are made of highly remanent magnetic material, the effective flux obtainable from the material of high remanence is increased while the overall geometry of the permanent magnets remains unchanged.
A motor whose permanent magnets are each 25.times.42 mm in size and whose armature core length is 30 mm, provides an increase of 2.8% in the magnetic flux, given a ratio between the two sections of different magnetic materials of 14/11, viewed in the circumferential direction. The increased flux yield with the geometry remaining unchanged also means higher power on the part of the motor; or, if the motor power remains constant, a saving in the weight of copper can be achieved. In the example mentioned above, the saving in copper, in a 12 V motor of 1.1 kW, is 5.2%.


DRAWING

The invention is shown in terms of an exemplary embodiment illustrated i

REFERENCES:
patent: 2048161 (1936-07-01), Klaiber
patent: 3567979 (1971-03-01), Jaffe
patent: 3594599 (1971-07-01), West
patent: 3906268 (1975-09-01), de Graffenried
patent: 3939371 (1976-02-01), Murakami
patent: 4110718 (1978-08-01), Odor
patent: 4112320 (1978-09-01), Mohr
patent: 4237397 (1980-12-01), Mohr
patent: 4383193 (1983-05-01), Tomite

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