Commutator machine having a permanent magnet stator

Details Commutator machine having a permanent magnet stator Commutator machine having a permanent magnet stator

1987-03-03

1988-09-27

Salce, Patrick R.

Electrical generator or motor structure

Dynamoelectric

Rotary

310177, H02K 2130

Patent

active

047744260

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a commutator machine such as a small direct-current motor. A machine of this kind, in particular a small direct-current motor, is known from DE-OS No. 28 45 264 or from DE-PT No. 31 19 782. In these machines there was a limit as to how much the various machine dimensions could be varied, in particular because of the demagnetization stability of the ferrite material used, and there was a tendency, with increasing motor size, to provide a percentage increase in the armature diameter as well, while reducing the optimal magnet heights by a percentage. Known calculation methods for such permanent-magnet-excited commutator machines allowed optimizing production costs on the one hand, and weight per unit of power on the other, only within narrow limits.


SUMMARY OF THE INVENTION

The commutator machine according to the invention affords the advantage with respect to the foregoing in that a machine configuration was found utilizing a particular ferrite magnetic material which permits an especially advantageous match of the armature cross field and the exciter field and affords a favorable utilization of the volume of the machine. The ferrite magnetic material is variable in wide limits with reference to remanence and coercive field intensity.
The thickness of the magnets used is suitably selected to be constant over the length, that is over the circular segment, except for the tapering ends of the magnets.


BRIEF DESCRIPTION OF THE DRAWING

An embodiment of the invention is shown in the drawing and explained in further detail in the following description.
FIG. 1 shows a cross section through a commutator machine according to the invention,
FIG. 2 a Br/.sub.J H.sub.C diagram of the permanent magnetic ferrite materials used, and
FIG. 3 a diagram of the Br/.sub.J H.sub.C values in dependence upon various Al.sub.2 O.sub.3 additives.


DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows a cross section through a small direct-current motor having a short-circuit element 10, which together with permanent magnets 11 secured therein forms the stator 12 of the commutator machine. An armature 15 is rotatably mounted inside the stator 12, leaving an air gap 14, and an armature winding 17 is placed in the slots 16 of the armature. The armature 15 is held rotatably on a shaft 18.
FIG. 2, in the form of a diagram, shows the dependency between remanence (B.sub.r) and coercive field intensity .sub.J H.sub.C for various ferrite materials. A lower line 22 marks the state of development in 1982; a middle line 23 shows the state of development of single-substance ferrite magnets in 1985; and an upper line 24 shows the presently attainable limit in multi-substance ferrite magnets. A further limit line 25 shows the theoretically attainable limit at a remanence B.sub.r of 465 mT.
FIG. 3 shows the dependency of the B.sub.r and .sub.J H.sub.C values of permanent magnets on the addition of various amounts of Al.sub.2 O.sub.3. The shaded areas are due to the deviations that arise in the magnetic values; the decrease in the B.sub.r value and the increase in the .sub.J H.sub.C value when an increasing amount of Al.sub.2 O.sub.3 is added to the ferrite powder is clearly recognizable.
For various magnetic materials the following pairs of values occur:


______________________________________ B.sub.r (mT) .sub.J H.sub.C (kA/m) ______________________________________ Material "440" 440 280 Material "420" 420 320 Material "390" 390 360 Material "340" 340 480 ______________________________________
The values of the Al.sub.2 O.sub.3 additives are as a rule between 0 and 6% by weight.
In addition to the coercive field intensity .sub.J H.sub.C, the limiting field intensity H.sub.G, in particular, is critical for the design of commutator machines with permanent magnet excitation; the limiting field intensity is that up to which a permanent magnet is stable. The values for the remanence and for the limiting field intensity of a ferrite magnetic material can

REFERENCES:
patent: 3083310 (1963-03-01), Tweedy et al.
patent: 4082968 (1978-04-01), Jones
patent: 4454437 (1984-06-01), Tanaka et al.
van Heffen, "Ceramic Permanent Magnets for d.c. Motors, Electronic Components to Application, vol. 3, No. 2, Feb. 81, pp. 120-126.

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