US 20090072676 A1
An electric machine, such as a switched reluctance motor (SRM), having one or more transverse flux axes is described. The rotor and stator of the electric machine have more than one phase, not necessarily of even number. Flux guidance regions within the stator are angularly and spatially located such that they may be transverse, or not coinciding with, the plane perpendicular to the axis of shaft rotation. The flux guidance regions are composed so as to contain a magnetic field whose flux is guided in either a loop or coupled configuration. In the loop configuration, multiple flux guidance paths that are able to operate simultaneously exist within each chuck arrangement. In the coupled configuration, a single primary flux guidance path exists within the chuck arrangement. Transverse flux guidance allows for the removal and replacement of stator windings without significant disassembly or removal of the motor.
1. An electric machine having a rotational axis, the machine comprising:
a rotor assembly comprising:
a rotor hub disposed in a rotational plane that is substantially perpendicular to the rotational axis; and
a plurality of rotor teeth affixed to the rotor hub, the rotor teeth disposed in a substantially circular path about the rotational axis, the rotor teeth including at least a first rotor tooth, a second rotor tooth and a third rotor tooth; and
one or more stator chuck arrangements disposed around and adjacent the rotor assembly, each stator chuck arrangement comprising a plurality of stator chuck sets including at least a first stator chuck set and a second stator chuck set, each stator chuck set comprising at least a first stator chuck and a second stator chuck, the first and second stator chucks each having a first chuck pole, a second chuck pole and a chuck winding, the first and second chuck poles being disposed adjacent the rotor teeth as the rotor assembly rotates about the rotational axis,
where during operation of the electric machine, a flux path passes from the first chuck pole of the first chuck of the first stator chuck set into the first rotor tooth, through the first rotor tooth and into the first chuck pole of the second stator chuck of the first stator chuck set, from the first chuck pole of the second stator chuck of the first stator chuck set to the second chuck pole of the second stator chuck of the first stator chuck set, and from the second chuck pole of the second stator chuck of the first stator chuck set into the second rotor tooth.
This continuation application claims priority to co-pending U.S. patent application Ser. No. 11/128,823 entitled R
This invention relates to the field of electric machines, including electric motors and generators. More particularly, this invention relates to switched and variable reluctance machines, such as a switched reluctance motor (SRM) or generator, or a variable reluctance motor (VRM) or generator, having one or more transverse flux axes.
The conventional switched reluctance motor has been around for well over a century. However, commercial viability and widespread utilization of the SRM has been hindered in recent decades for various reasons including poor control techniques, excessive audible noise, and large torque ripple. Despite these disadvantages, the SRM is of interest due its relatively simple construction and resulting lower cost when compared to other traditional electric motors. Because the traditional reluctance motor only has stator windings, the points of failure can only be the windings and shaft bearings. This provides for higher reliability. Additionally, with sufficient phase count the traditional SRM is able to function in the event of a phase failure as there is no flux linkage between phases to produce back-emf on the failed phase.
The traditional SRM topology, such as shown in
For example, as shown in
A common variation to the reluctance motor design is the stacking of multiple reluctance motors, end to end, along a common shaft, at angular offsets so as to increase the magnitude of the generated torque and reduce torque ripple.
Numerous schemes for increasing the controllability of the traditional reluctance motor have been implemented. These schemes vary from innovative control algorithms to novel tooth designs. In one scheme described in U.S. Pat. No. 6,700,272, the motor runs at high speeds yet produces low shaft revolutions per minute (RPM). This allows for reduced torque ripple and results in a shaft RPM usable by most applications, thereby eliminating the need for a gearbox. This particular method has been accomplished through the introduction of differing flux guidance paths that result in a planetary gear effect between the rotor and stator. Despite this, the overall motor topology and planar torque production method is not different from that of the traditional SRM.
No known prior SRM design schemes have altered the fundamental design of the reluctance motor such that the path of the flux linkage through a rotor tooth is variable with position.
The switched or variable reluctance motor of the present invention has a primary flux path passing through the center of a stator chuck, through a pole of the stator chuck, through a rotor tooth, through a complimentary stator chuck, through another rotor tooth, and finally through either the originating chuck pole or a different chuck pole. This flux path lies in planes that may be transverse to (not coinciding with) the plane that is perpendicular to the axis of shaft rotation. While this flux path may include the plane perpendicular to the axis of shaft rotation, this perpendicular plane is not the sole flux path plane. With such a flux path, the motor generates or consumes useful torque with increased use of the volume of the motor, providing for smaller motors and increased energy density.
The flux generated by the present invention links the angular positions of the chuck arrangements. Unlike in prior art SRM designs, the predominate flux flow in the present invention is not through the main rotor yoke or stator body. Instead, flux is predominately guided within the respective rotor teeth and stator chucks. In transferring the flux path and the resulting torque to a plane that is transverse to the axis of shaft rotation and independent of the respective yokes, the motor windings are made accessible for easy removal and replacement during motor maintenance.
A preferred embodiment of the invention provides an electric machine comprising a rotor assembly and one or more stator chuck arrangements disposed around and adjacent the rotor assembly. The rotor assembly includes a rotor hub and a plurality of rotor teeth. The rotor hub is disposed in a rotational plane that is substantially perpendicular to the rotational axis. The rotor teeth are affixed to the rotor hub and are disposed in a substantially circular path about the rotational axis. The rotor teeth include at least a first rotor tooth, a second rotor tooth and a third rotor tooth. Each stator chuck arrangement comprises multiple stator chuck sets including a first stator chuck set and a second stator chuck set. Each stator chuck set includes a first stator chuck and an opposing second stator chuck. The first and second stator chucks each have a first chuck pole, a second chuck pole and a chuck winding, where the first and second chuck poles are disposed adjacent the rotor teeth as the rotor assembly rotates about the rotational axis.
During operation of this preferred embodiment of the electric machine, a flux path passes from the first chuck pole of the first chuck of the first stator chuck set into the first rotor tooth, through the first rotor tooth and into the first chuck pole of the second stator chuck of the first stator chuck set. The flux path further passes from the first chuck pole of the second stator chuck of the first stator chuck set to the second chuck pole of the second stator chuck of the first stator chuck set, and from the second chuck pole of the second stator chuck of the first stator chuck set into the second rotor tooth.
During operation of one preferred embodiment, the flux path also passes through the second rotor tooth and into the second chuck pole of the first stator chuck of the first stator chuck set, and from the second chuck pole of the first stator chuck of the first stator chuck set to the first chuck pole of the first stator chuck of the first stator chuck set.
During operation of another preferred embodiment, the flux path also passes through the second rotor tooth and into the second chuck pole of a first stator chuck of the second stator chuck set, from the second chuck pole of the first stator chuck of the second stator chuck set to the first chuck pole of the first stator chuck of the second stator chuck set, and from the first chuck pole of the first stator chuck of the second stator chuck set into the third rotor tooth.
In some preferred embodiments, the stator chuck sets of one or more of the stator chuck arrangements are disposed in a substantially cylindrical relationship about the axis of rotation. In some embodiments, the stator chuck sets of one or more of the stator chuck arrangements are disposed in a substantially conical relationship about the axis of rotation.
In some embodiments, multiple-layer or tiered rotor tooth arrangements and flux paths are possible. Thus the rotor hub may hold more than one set and/or layers of rotor teeth, thereby giving rise to increased stator chuck arrangements and potentially complex flux paths. Additionally, stacking multiple embodiments of the invention end-to-end is possible as is typically done with existing SRM configurations.
In another aspect, the invention provides an electric machine that includes a rotor assembly comprising a plurality of rotor teeth disposed at least partially within the rotational plane and substantially in a circular path centered on the rotational axis of the machine. The electric machine also includes multiple stator chuck sets that each include a first stator chuck and a second stator chuck. The first stator chuck of each stator chuck set is disposed on an opposite side of the rotational plane from the second stator chuck. During operation of the electric machine, a portion of a flux path passes from the first stator chuck through a rotor tooth to the opposing second stator chuck.
In yet another aspect, the invention provides an electric machine comprising a rotor assembly, multiple stator chuck sets and a stator housing. The rotor assembly comprises a plurality of rotor teeth disposed at least partially within the rotational plane of the machine and substantially in a circular path centered on the rotational axis of the machine. Each stator chuck set comprises a first stator chuck and a second stator chuck disposed on opposite sides of the rotational plane from each other. The stator housing supports the stator chucks in fixed positions relative to the rotor assembly in such a manner that each stator chuck may be removed from the stator housing independently of each of the other stator chucks.
In general, the basic theory and analysis of the SRM of the present invention are similar to that of conventional SRM's. However, the revolved windings and other aspects of the invention provide better use of the three dimensional space thereby providing increased energy density. With increased energy density, the invention provides a motor that may be smaller and lighter in weight while still providing power and torque equivalent to much larger conventional motors.
Another advantage of the present invention is that it allows for enhanced maintainability of the motor. In the preferred embodiment, individual stator chucks/windings may be easily removed and replaced, thereby eliminating the necessity of completely rewinding the whole motor. Thus, repairs may be done with the motor in its operational position, thereby avoiding a long-term interruption in the motor operation. In fact, with sufficient controls and design considerations, it may be possible to repair the motor while it is operating. Motor performance may suffer somewhat during such a repair process, but the motor could continue to operate.
In traditional SRM's, acoustic noise can be a significant problem. One source of acoustic noise is aerodynamic turbulence introduced by the salient teeth moving through the air (windage). In the present invention, turbulence noise is significantly reduced because the aerodynamic profile of the rotor hub/housing can be made to match the profile of the tooth structure.
Another source of acoustic noise in traditional SRM's is planar loading due to high normal forces acting on the stator housing. In the traditional SRM design, during flux rise for each phase these normal forces act on opposing stator pole pairs which tends to “squeeze” the stator housing. During flux decline for each phase, the normal forces acting on the opposing pole pairs are reduced which allows the stator housing to “relax.” This periodic squeezing and relaxing causes the stator housing to vibrate which adds to the acoustic noise. Unlike traditional SRM's, the loading of the stator housing of the present invention is primarily transverse to the plane of rotation so that the induced stresses do not traverse through the entire housing. This localizes the loading on the stator housing, thereby significantly reducing acoustic noise.
Another advantage of the present invention is that non-symmetric pole pairs are possible, (a pseudo half-arrangement or half-phase is possible) which could be used to increase the controllability of the motor during transitions between phases.
Also, the novel topology of the present invention could easily be incorporated into a linear SRM or VRM design. While the arrangements shown in the present invention have been configured such that they encircle a shaft, the transverse nature of torque production could easily be arranged in a linear or three dimensional spline path design.
This novel topology also has relevance to magnetically actuated vibrating equipment. Typically, vibrating equipment utilizes electromagnets to attract magnetically conductive material, either of which may be coupled to a load. The spacing between the electromagnets and magnetically conductive material is typically set prior to operation, and is done so based upon a known load range. Should the load decrease, the electromagnet may produce to much force causing disruption in the application and/or damage from contact between the electromagnet and magnetically conductive material. As this design surrounds and encloses the magnetically conductive material, longer, smoother strokes are possible and would not have to be spaced based upon existing loads.
Although the description of the invention focuses on preferred embodiments of a switched reluctance motor, it will be appreciated that various aspects of the invention also apply to switched reluctance generators as well as variable reluctance motors and generators. Thus, the novel topology of the invention is applicable generally to switched reluctance machines, variable reluctance machines, including motors and generators.
Further advantages of the invention are made apparent by reference to the detailed description in conjunction with the figures, wherein elements are not to scale so as to more clearly show the details, wherein like reference numbers indicate like elements throughout the several views, and wherein:
As shown in
In the present invention, the flux linkages that produce the useful torque are made between a stator and the rotor teeth 6—not through a rotor yoke as is done in conventional SRM's. As shown in
During operation of the motor, flux linkages develop between one or more chucks 10, through one or more rotor teeth 6, and into one or more opposing chucks 10. Thus, the stator chucks 10 are the primary conduit for the stator flux. The chuck poles 10 b are profiled such that each pole has a face 10 c-10 d that is parallel to a corresponding rotor tooth face 8.
As shown in
In a preferred embodiment of the invention depicted in
Unlike a traditional SRM design, the preferred embodiment of the stator housing 16 is not part of the primary flux path or part of any electrical conduction path. Thus, the stator housing 16 need only provide mechanical integrity in supporting the stator chuck arrangements and maintaining their locations with respect to the rotor assembly 2. Preferably, wires or traces for connection of stator chuck windings as well as desired control elements are integrated into the stator housing 16. The housing 16 may be formed from practically any material that provides the desired structural rigidity, such as plastic, metal or composite materials.
As flux linkage of sufficient magnitude is established between any one of the stator chuck arrangements (such as 14 a) and the rotor teeth 6, the rotor teeth 6 will tend to align with the flux established between the opposing chuck poles 10 b in the stator chuck arrangement 14 a. Since the rotor teeth 6 are secured to the rotor hub 4, the alignment of the teeth 6 to the chuck poles 10 b causes the rotor hub 4 to rotate. As the hub 4 rotates, the teeth 6 begin to align with the poles 10 b of an adjacent stator chuck arrangement 14 b which is angularly and spatially offset from the chuck arrangement 14 a. (See
In an alternative embodiment of the invention, chuck arrangements 14 a, 14 b, 14 c may have several different configurations. For example,
It will be appreciated that some embodiments of the invention may comprise a combination of the loop and coupled configurations.
Many prior art schemes have a specific flux path passing within rotor teeth. However, the transverse nature of the flux paths of the present invention is such that the flux path through the rotor tooth is variable. Thus, the flux path may be in opposite directions for two different rotor positions or it may be angularly offset. For example,
The foregoing description of preferred embodiments for this invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments are chosen and described in an effort to provide the best illustrations of the principles of the invention and its practical application, and to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.