Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1994-09-28
1998-05-12
LaBalle, Clayton E.
Electrical generator or motor structure
Dynamoelectric
Rotary
H02K 122
Patent
active
057510890
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention is concerned with two-phase or section wise twophase permanent magnetized, brushless DC motors and generators, rotating or linear.
BACKGROUND OF THE INVENTION
Most electric motors can equally well be used as a motor or as a generator. In the following the word motor is generally used even if all described embodiments equally well can be used as generators.
Many electric motors or generators can be built either as rotating or linear machines with little changes. In the following it should be understood that even if some embodiments are described only for rotational or linear machines, the same principles can be applied for the other kind of electric machine. Thus for instance the words "slide" or "slider" and "rotor" may signify basically the same part.
The market for brushless DC motors in the range of several Watts and higher is totally dominated by designs having stators where the windings of three phases are overlapping. This means that the area circumvented by a coil belonging to one phase do not only contain a flux carrying iron pole; it will also circumvent slots containing windings belonging to other phases. This gives a not very efficient use of pole iron mass and/or requires long copper windings.
The market for brushless DC motors in the range of several Watts and higher is also totally dominated by designs having rotors where the permanent magnets are assembled on a magnetic flux permeable support structure (normally made of iron) that closes the flux path. This structure gives a high inertia or mass of the rotor.
A typical prior art motor is disclosed in the international application PCT/DE86/00437. This motor has two stator parts and both stator parts carry windings of more than one phase. This means that the area circumvented by a coil belonging to one phase do not only contain a flux carrying iron pole; it will also circumvent slots containing windings belonging to other phases. This gives an inefficient use of the pole iron mass and requires long copper windings, that is this prior motor is heavy and has high copper losses. Furthermore, to use the multi-phase windings efficiently, the magnets must cover a large part of the circumference, thus giving rotors with a high moment of inertia.
Motors where each stator is divided into two parts offer increased possibilities for simplified windings and thus for low cost motors. There are several prior art designs using a single coil winding concentric with the motor axis for each pase. However, they have severe limitations when used for highly efficient low inertia motors.
One such prior art motor is disclosed in U.S. Pat. No. 4,714,853. Here an annular permanent magnet rotor, which has a basically cylindrical shape, is inserted between two stator parts, each carrying one phase. Each stator is made of two mating, cuplike pole pieces of a single steel plate defining an annular closed space where the windings are located. The pole pieces have a plurality of salient poles facing the rotor. The radial thickness of the teeth is constant, and there is a considerable gap between the salient poles from each pole piece. If used with small motors using weak magnets (the preferred embodiment in FIG. 2 of U.S. Pat. No. 4,714,853 evidently uses ferrite magnets), the total flux generated will easily pass through a steel sheet of acceptable thickness. If run with low speeds, the flux change frequency will be low, thus giving acceptable eddy current losses in the pole pieces. The eddy currents will however increase rapidly for larger motors and higher energy permanent magnet material. Both of these cases will require an increased pole piece thickness, which will rapidly increase the eddy currents at a given speed. Higher speeds will also increase the eddy currents due to higher flux change rates. If the tangential gap between the salient poles is kept small, the self-inductance of the phase winding and the portion of the rotor flux lost due to stray flux between the salient teeth will be considerable and will increase rapidly
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LaBalle Clayton E.
Stridsberg Innovation AB
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