Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1999-06-02
2000-10-03
LaBalle, Clayton
Electrical generator or motor structure
Dynamoelectric
Rotary
310156, H02K 124, H02K 2112, H02K 2114
Patent
active
061277649
DESCRIPTION:
BRIEF SUMMARY
This invention relates to electrical machines, motors or generators, in which a travelling magnetic field causes the relative movement of the parts of the machines. More particularly, the invention relates to machines of the kind defined in the precharacterising parts of the independent claims.
For convenience, the description of the invention which follows is limited to rotational machines, namely motors, in which the part which carries the winding is stationary and designated as the stator, while the other part is designated as the rotor and mounted for rotation within the stator. The teeth of the stator and the poles of the rotor are arranged in annular concentric rows and separated by a cylindrical air gap. As will be readily understood, however, the relative movement of the parts need not be a rotational movement, but may be a linear or curvilinear relative movement. A combined rotational and linear relative movement is also within the scope of the invention. Moreover, the stator may be positioned inside the rotor, and the air gap need not be cylindrical but may be arcuate in cross-section or conical, for example.
In a common type of motor of the kind with which the invention is concerned the poles of the rotor are comprised of generally radially polarized permanent magnets the polarities of which alternate circumferentially. The permanent magnets may be mounted on the circumferential surface of the rotor or they may be mounted in rotor recesses (buried or nested magnets). Motors with surface mounted magnets are normally preferred, because they utilize the expensive permanent-magnetic material more economically than do motors with other magnet mounting designs.
An object of the present invention is to achieve a significant reduction of the amount of permanent-magnetic material with only a relatively small reduction of the torque produced by the motor.
A further object of the invention is to provide a machine of the kind indicated which lends itself to operation in the so-called field weakening mode; known machines with surface mounted permanent magnets on the rotor are severely limited in respect of such operation.
The invention is based on a combination of two observations.
Firstly, a high-performance permanent-magnetic body and a soft-iron body whose saturation flux density is roughly the same as the remanence of the permanent magnet are very similar in respect of their magnetic properties whenever the external magnetising field acts in the direction of the intrinsic polarization of the permanent magnet.
Secondly, in a permanent-magnet motor of the kind mentioned above which is provided with surface mounted permanent magnets and is supplied from a properly adjusted electronic drive, such as a servo amplifier, only one-half of the volume of each permanent magnet is exposed to a demagnetising field while the other half is exposed to a magnetic field in the direction of the intrinsic polarization of the permanent magnet.
From these observations it can be concluded that a considerable portion of the last-mentioned volume can be replaced with a body of soft-magnetic material having a suitable level of saturation flux density.
In accordance with one aspect of the invention there is provided an electric machine of the kind indicated in which comprises a permanent-magnetic pole section and an adjacent soft-magnetic pole section, along the air gap, and the air gap has at the surface thereof facing the air gap a saturation flux density which is no higher than the flux density in the air gap which causes magnetic saturation of the teeth of the row of teeth of the first part.
In a motor according to this aspect of the invention a saving of roughly 50 percent of the expensive permanent-magnetic material can be replaced with inexpensive soft-magnetic material without losing more than a small fraction of the torque.
In accordance with another aspect of the invention there is provided an electric machine of the kind indicated in which at least a section of at least some poles of the pole row of the second part cons
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