Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1997-12-12
2002-02-19
Tamai, Karl (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S156350, C310S179000
Reexamination Certificate
active
06348751
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an electric motor with active hysteresis-based control of winding currents, and/or having an efficient stator winding arrangement, and/or adjustable air gap. The present invention also relates to the stator, windings and air gap adjustment mechanism included in the electric motor, as well as a method and system for controlling the torque produced by the motor using active hysteresis-based control of the motor's winding currents. The motor and its associated components are particularly well-suited for use in an electrically powered vehicle, as well as in hybrid vehicles using both electric power from a battery and electric power derived from a fuel-burning engine.
In the field of electrically-powered vehicles and hybrid vehicles, it is known that efficiency and versatility of a motor are key elements in a successful design. Another key element is the vehicle's weight and the motor's contribution to weight. These key elements have a significant impact on the range of the vehicle and its usefulness to consumers. These key elements also affect one another. A reduction in weight, for example, may have a negative impact on versatility. In this regard, removal of a gearing mechanism to reduce weight may limit the speed of the vehicle and hence its versatility, while improving the vehicle's efficiency and overall range.
Not all improvements, however, have negative implications with regard to other key elements. An improvement in one key element actually may provide a synergistic improvement in another of the key elements. Versatility, for example, can reduce the overall weight of a vehicle. Motors having a wide range of torque-producing speeds are more versatile and also result in a reduced need for heavy gearing elements and complicated or electrically inefficient controlling arrangements. Thus, an improvement in the motor's versatility translates into a reduction in the vehicle's overall weight and improved efficiency. The present invention aims to maximize the positive interplay between these key elements, while at the same time reducing the negative impact between the key elements.
There are many commercially available electric motors, some of which may provide improvements in one or more of the key elements described above.
SUMMARY OF THE INVENTION
A primary object of the present invention is to overcome the disadvantages associated with known electric motors, by maximizing the synergistic interplay between the aforementioned key elements.
Another object of the present invention is to provide an electric motor having a controller capable of performing active hysteresis-based control of winding currents in a manner dependent on the desired torque or winding current level, the speed of the motor (RPM), and/or other variables, for example, to selectively balance a switching efficiency of the motor's controller and resistive losses in the windings and/or to selectively provide a reduction in motor noise.
Yet another object of the present invention is to provide a stator having an electrically and magnetically efficient winding arrangement.
Still another object of the present invention is to provide a mechanism capable of adjusting the motor's air gap, thereby improving the versatility of the motor in a gear-less manner by allowing the motor to produce a high level of torque at low speeds, while the air gap is small, and allowing the motor to continue producing torque, when the air gap is larger, at higher speeds than would be permitted with the smaller air gap.
Yet another object of the present invention is to provide a discharge circuit for automatically discharging a voltage on a power bus between a motor's controller and the motor itself after the voltage on the power bus decays to a predetermined decay minimum.
To achieve these and other objects, the present invention provides a stator for an axial flux motor powered using at least two phases of electrical current. The stator includes a series of stator windings. The series is arranged in a circle which defines a circumference of the stator. The series of windings have arc sections, each of the arc sections containing windings associated with only one of the phases. The arc sections are arranged such that, when current flows through the windings, each arc section provides a magnetic field which, at any given instant of time during current flow, alternates in direction along a length of each arc segment.
The windings in each arc section may be arranged so that no two arc segments carry current of identical phase. Alternatively, more than one arc section may be associated with each phase. Preferably, the distribution of arc sections provides a favorable symmetry around the stator's circumference. For example, in a three phase, six arc section motor, the two arc sections associated with each phase are 180 degrees apart, which provides symmetry with respect to the spin axis. Other symmetries may be achieved using different configurations.
The stator preferably includes an annular stator core. The annular stator core includes a radially inner surface, a radially outer circumferential surface, and two sides extending therebetween. The annular stator core further includes slots which extend between the radially outer circumferential surface and the radially inner surface to define teeth on one of the two sides of the annular stator core. The stator windings are defined by conductive material extending through the slots and around the teeth.
The stator windings may be defined by serpentine-shaped conductors which fit between and around the stator's teeth, each serpentine-shaped conductor being coextensive with a respective one of the arc segments.
The serpentine-shaped conductors in each arc segment are stacked upon one another with an electrically insulative material disposed therebetween. The stack in each arc segment preferably includes a first set of substantially identical serpentine-shaped conductors stacked alternatingly through the stack, and a second set of serpentine-shaped conductors sandwiched between the serpentine-shaped conductors of the first set. The serpentine-shaped conductors of the second set are substantially identical to one another but different from those of the first set in that, when the first and second sets are alternatingly stacked, portions of the serpentine-shaped conductors in the first set which are outside of the slots extend around opposites sides of the teeth from portions of the serpentine-shaped conductors of the second set which are also outside of the slots.
The electrically insulative material between the conductors preferably includes openings through which adjacent ones of the serpentine-shaped conductors in each stack are electrically connected. The openings are arranged so that current flowing through each arc segment flows end-to-end through each serpentine-shaped conductor of that arc segment.
In order to reduce resistive losses in the portions of the serpentine-shaped conductors which are outside of the slots, such portions may have a larger cross sectional area than other portions of the serpentine-shaped conductors which are located in the slots.
The foregoing stator is preferably incorporated into an axial flux motor powered using at least two phases of electrical current. In addition to the stator, the axial flux motor includes a rotor having an outer circumference carrying magnetic field producing elements. The magnetic field producing elements are arranged so as to produce a magnetic field that alternates in direction around the circumference of the rotor. Preferably, the magnetic field producing elements are permanent magnets.
The stator is axially spaced from the rotor to define an air gap therebetween. In addition, the stator is selectively movable in an axial direction from the rotor to vary this air gap. Preferably, a mechanism is provided for axially moving the stator and thereby varying the air gap.
The motor can be arranged in a dual stator configuration. In th
Crain Stephen G.
Jermakian Joel B.
Knudtson Cory D.
Piacesi Robert F. D.
New Generation Motors Corporation
Pillsbury & Winthrop LLP
Tamai Karl
LandOfFree
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