The present invention relates to rotary electric motors, more particularly to motors having a plurality of cascaded pairs of permanent magnet rotor annular rings and stator annular rings, each pair having a plurality of axial air gap flux paths between the rotor and stator elements.
The above-identified copending related U.S. applications describe formation of electromagnet core segments as isolated magnetically permeable structures configured in an annular ring. Isolation of the electromagnet core segments permits individual concentration of flux in the magnetic cores, with a minimum of flux loss or deleterious transformer interference effects with other electromagnet members. Operational advantages can be gained by configuring a single pole pair as an isolated electromagnet group. Magnetic path isolation of the individual pole pair from other pole groups eliminates a flux transformer effect on an adjacent group when the energization of the pole pair windings is switched. The lack of additional poles within the group avoids any such effects within a group. Further benefits are described from utilization of three dimensional aspects of motor structure, such as a structural configuration wherein axially aligned stator poles and axially aligned rotor magnets provide highly concentrated flux distribution. Such configuration provides a greater number of poles with the same individual active air gap surface areas and/or greater total active air gap surface area than conventional motors having the same air gap diameter.
In summary, concentration of flux, maximization of flux, minimization of flux loss and transformer interference effects, are all contributing factors in the attainment of efficient motor operation with high torque capability. Motor structural configurations in which multiple poles are in axial alignment to provide efficient operation at high torque output have been described in the above-identified copending applications. Such arrangements, due to the relatively great volume occupied by the large number of stator core elements and rotor poles, are advantageous for use in environments in which space and weight considerations are not at a premium. There is a continuing need for motor structural configurations that provide these improved attributes as well as economy of size and geometry.
The above-identified copending Maslov et al. application Ser. No. 10/134,365, addresses these needs by development of motor structural configurations to increase the surface areas of opposing stator poles and rotor poles across a plurality of air gaps. The relatively larger surfaces in which flux can be concentrated promote high torque capacity. These concepts are further structurally developed in the present invention.
Advantages of the present invention are achieved, at least in part, by increasing those surface areas of stator and rotor elements that interact to produce electromotive force. The structural features of one such configuration of the invention are embodied in a motor that comprises a rotor and a stator in which a plurality of separated electromagnet core segments are disposed coaxially about an axis of rotation. The stator core segments form an annular stator ring bounded by an inner and outer diameter. The core segments are affixed, without ferromagnetic contact with each other, to a non-ferromagnetic support structure.
The rotor is configured in an annular ring that at least partially surrounds the annular stator to define a radial air gap and a pair of axial air gaps through which flux paths are produced to generate electromotive force. The rotor ring is formed of magnetically permeable material with a U-shaped cross-sectional configuration having sides joined by a cross wall. A plurality of permanent magnets is distributed along inner surfaces of the rotor sides and cross wall, thereby facing the two axial air gaps and the radial air gap. The permanent magnets successively alternate in polarity along the circumference of the rotor ring surfaces. The permanent magnets on the two side walls are respectively in axial alignment with each other and have opposite magnetic polarities. Each relatively flat permanent magnet is a magnetic dipole having one magnetic polarity at its surface facing an air gap and the opposite magnetic polarity at its surface mounted to the side wall or cross wall. The permanent magnets mounted on the side walls thus have magnetic polar orientation in the axial direction while the permanent magnets mounted on the cross wall have magnetic polar orientation in the radial direction.
Each stator electromagnet core segment comprises a pair of poles aligned in a direction generally parallel to the axis of rotation and joined by a ferromagnetic connecting portion having a winding formed thereon. Each stator electromagnet pole may be of a generally rectangular configuration, viewed in a cross-section taken in a plane parallel to the axis of rotation. The pole thus has a first pole surface, generally perpendicular to the axis of rotation and facing one of the axial air gaps, and a second surface facing the radial air gap. The winding, when energized, produces magnetic poles of opposite polarity at the two poles of the pole pair. A change in the direction of current effects a reversal of these magnetic polarities.
In one embodiment of the invention, the plurality of permanent magnets on the cross wall comprises two sets of magnets that are in axial alignment with each other and the magnets on the side walls. Each pair of adjacent side wall magnets and cross wall magnets are of the same magnetic polarity and opposite to the pair of side wall magnets and cross wall magnets located at the axially opposite side. When the winding of a stator electromagnet is energized in the vicinity of a set of aligned side wall and cross wall magnets, opposite magnetic polarities are formed in the electromagnet poles. The adjacent side wall and cross wall magnets aid each other in the production of either attractive or repulsive forces with respect to the stator poles that face the magnets across the axial and radial air gaps. Flux distribution is improved by the concentration of flux through the increased surfaces of the stator poles and rotor magnets, while minimizing stray flux.
In a beneficial variation of the above described motor structure, each stator pole face has an L-shaped cross sectional pole configuration, one portion of the xe2x80x9cLxe2x80x9d facing a rotor side wall across an axial air gap and the other portion of the xe2x80x9cLxe2x80x9d facing, at the outer stator diameter, the rotor cross wall across the radial air gap. In this arrangement, the stator pole surface area for flux distribution can be increased by the L extension of the radial surface, while maintaining the dimension of the connecting portion between poles that accommodates the winding.
As a further variation of the present invention, each adjacent pair of side wall and cross wall permanent magnets may be replaced with a single permanent magnet that has an L-shaped cross-sectional configuration. The magnet is mounted at inner surfaces of the corner junction of a side wall and the cross wall to provide maximum flux distribution. The magnet is a dipole having the same magnetic polarity on both inner surfaces. The magnet thus has two inner surfaces, each interactively facing a surface of a respective stator pole.
Advantages of the present invention can be realized with cascaded motors that incorporate the various structural features described above. One such cascaded motor configuration may contain a plurality of rotor annular rings centered about an axis of rotation and axially adjacent each other, each ring having disposed therein a plurality of permanent magnets. A plurality of stator annular rings are respectively in concentric alignment with, and at least partially surrounded by, the rotor rings. Each stator ring contains separated electromagnet core segments disposed coaxially about the axis of rotation. Two axial air gaps are formed between each stator ring and its respective rotor ring. Each rotor annular ring has a U-shaped cross section with two side walls connected by a cross wall, an inner surface of each of the side walls having permanent magnet surfaces facing one of the axial air gaps. Each stator core segment comprises a pair of poles integrally aligned by a linking portion, upon which a winding is formed, and having pole surfaces facing the axial air gaps.
Axially adjacent rotor annular rings of the cascaded motor may be in contact with each other and share a common side wall of magnetically permeable material. Permanent magnets on opposite surfaces of the common side wall are of opposite magnetic polarity and aligned with each other in a direction substantially parallel to the axis of rotation. Additional permanent magnets may be circumferentially distributed on an inner surface of at least one rotor cross wall to face stator pole surfaces across an annular radial air gap that separates the rotor cross wall from a stator annular ring. The permanent magnets on the cross wall form two sets of magnets, the magnets of each set being adjacent to, and in axial alignment with, permanent magnets on a respective side wall, adjacent side magnets and cross wall magnets being of the same magnetic polarity. The permanent magnets on the cross wall may be separated from or integral with the adjacent permanent magnets on the respective side walls to form L-shaped in cross-sections. The stator poles may have rectangular or L-shaped cross-sections.
Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the invention is shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.