ELECTRICAL MACHINE

TECHNICAL FIELD

[0001] This invention relates to electric machines and, more particularly, to electromagnetic devices such as rotary motors and generators, and linear actuators and solenoids. BACKGROUND

[0002] In generators, input energy is mechanical work and output energy is electrical work. In motors, input energy is electrical work and output energy is mechanical work. Most electrical machines are reversible and can function as either motors or generators.

[0003] In motors, electrical energy input imparts motion to one or more components of the machine, such as rotors, solenoids, or actuators. Solenoids and actuators typically move linearly whereas rotors rotate.

[0004] Many modern applications of electric motors require high power density. For example, modern automobiles increasingly use electrical energy in either hybrid vehicles or battery vehicles. Automobile performance is significantly enhanced with lightweight electric motors mounted directly on the automobile body or its wheels. At a given motor speed, shigh power density requires high torque density.

SUMMARY OF THE DISCLOSURE

[0005] The present disclosure relates to electrical machines and more specifically to electrical machines that do work on moving objects. The present invention has numerous unique features that maximize the magnetic flux density in a magnetic circuit for electromagnetic motors, generators, solenoids, and actuators.

[0006] The rotor moves through the stator magnetic circuit at an angle; thus, the surface area between the rotor and stator is increased, which reduces the reluctance and increases the magnetic flux in the circuit. The result is greater magnetic force between the stator and rotor pole, and hence greater torque.

[0007] If the air gaps that the rotor passes through are angled with respect to the major magnetic flux path through the stator and rotor pole loop, then the surface area of the air gap will be maximized, as a function of the sine of the angle between the major magnetic flux path and the direction of rotation of the rotor pole, and result in a greater magnetic force between the stator and rotor pole.

[0008] Before undertaking the DETAILED DESCRIPTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms "include" and "comprise," as well as derivatives thereof, mean inclusion without limitation; the term "or," is inclusive, meaning and/or; the phrases "associated with" and "associated therewith," as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] For a more complete understanding of this disclosure and its features, reference is now made to the following description, taken in conjunction with the accompanying drawings and tables, in which:

[0010] Figure 1 shows a magnetic circuit consisting laminated ferromagnetic material separated by thin insulating layers that prevent energy-robbing eddy currents;

[0011] Figure 2 show an magnetic circuit identical to Figure 1, except the linear actuator is also comprised of laminated ferromagnetic material;

[0012] Figure 3 is identical to Figure 2, except that the linear actuator is drawn into the magnetic circuit at an increased angle (φ > 90°);

[0013] Figure 4 is identical to Figure 2, except the side of the actuator is at an increased angle (ω > 90°);

[0014] Figure 5 is identical to Figure 2, except the side of the actuator is "rippled";

[0015] Figure 6 is a cross-sectional illustration of a single transverse-flux stator and rotor pole magnetic flux loop showing the air gaps that the rotor pole passes through around an axis that is horizontally located in the plane of the page;

[0016] Figure 7 is a cross-sectional illustration of a single transverse-flux stator and rotor pole magnetic flux loop showing the air gaps that are angled in one direction with respect to the magnetic flux path through the stator and rotor poles;

[0017] Figure 8 is a cross-sectional illustration of an alternative embodiment of Figure 7, wherein the stator and rotor pole are at an angle compared to Figures 6 and 7 while the air gaps are also angled with respect to the magnetic flux path;

[0018] Figure 9 is an illustration of an alternative embodiment of Figure 8, wherein the air gaps are angled in two different directions with respect to the magnetic flux loop of the stator and rotor pole;

[0019] Figure 10 is an illustration of another view of the embodiment shown in Figure 9;

[0020] Figure 11 is a cross-sectional illustration of a radial-flux electrical machine;

[0021] Figure 12 is an illustration of an axial-flux electrical machine;

[0022] Figure 13 is an illustration of a transverse-flux electrical machine; and [0023] Figure 14 is an illustration of an electrical machine that improves upon the designs described in U.S. Patent No. 7,663,283.

DETAILED DESCRIPTION

[0024] The FIGURES described below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure invention may be implemented in any type of suitably arranged device or system. Additionally, the drawings are not necessarily drawn to scale.

Definitions

[0025] The following provide definitions for general guidance concerning items disclosed herein. It should be expressly understood that such definitions should in no way be used to limit the scope of the invention.

[0026] Magnetic circuit - The magnetic circuit is a closed loop of ferromagnetic material. The magnetic circuit is analogous to a closed loop of pipe.

[0027] Copper coil - A copper coil coil wraps around the magnetic circuit. (Note: In principal, any electrical conductor could be used; however, copper is the most common material. A generic term for copper coil is "electric phase coil.") When electricity flow through the copper coil, it creates magnetism inside the magnetic circuit. The copper coil is analogous to a pump in the closed-loop pipe. Although a copper coil may be used to refer to certain embodiments, other material may also be used while still availing from the teachings of this disclosure.

[0028] Magnetic field intensity (H) - The magnetic field strength increases with the number of windings and the current in the copper coil. The magnetic field intensity is analogous to pressure produced by a pump.

[0029] Magnetic flux - The magnetic flux is an extensive quantity that describes the total strength of magnetism and is measured in webers (Wb). The magnetic flux is analogous to the total mass flow in the closed pipe measured in kg/s.

[0030] Magnetic flux density (B) - The magnetic flux density is an intensive quantity that describes the strength of the magnetism per cross-sectional area of the magnetic circuit and is measured in webers per square meter (Wb/m2) or tesla (T). The magnetic flux density is analogous to the mass flux (i.e., flow per cross-sectional area of pipe) measured in kg/(m2 s). [0031] Magnetic saturation - As the magnetic field intensity H increases, the magnetic flux density B increases to a limiting value that depends upon the properties of the ferromagnetic material. The phenomenon of magnetic saturation is analogous to a closed loop of pipe filled with a porous material, such as sand or gravel. Even at high pump pressure differences, friction limits the amount of fluid flow through the porous material. The flow characteristics will depend on the properties of the porous material. Small-diameter porous material (e.g., sand) will have a small mass flux because of the high friction whereas large-diameter porous material (e.g., gravel) will have a large mass flux because of the reduced friction.

Contextual Overview

[0032] In generators, input energy is mechanical work and output energy is electrical work. In motors, input energy is electrical work and output energy is mechanical work. Most electrical machines are reversible and can function as either motors or generators. The following discussion focuses on electric motors; however, it is understood that the machines may be reversed and function as electric generators.

[0033] In motors, electrical energy input imparts motion to one or more components of the machine, such as rotors, solenoids, or actuators. Solenoids and actuators typically move linearly whereas rotors rotate. The following discussion focuses on rotary motors.

[0034] In rotary motors, the magnetic flux density generated by the stator(s) produces a resultant force that converts electrical work into mechanical work. The most common classes of rotary motors follow: (1) induction, (2) permanent magnet, and (3) reluctance. Common subclasses of motors include the following: (la) AC induction, (2a) brushed DC permanent magnet, (2b) brushless DC permanent magnet, (3a) switched reluctance, and (3b) synchronous reluctance. Further delineation of rotary motors is achieved by referencing the direction of the magnetic flux path: (1) radial, (2) axial, and (3) transverse. Radial flux is the most common.

[0035] AC induction motors contain coils in both the stator and rotor. The coils in the stator produce magnetic fields that oscillate at the same frequency as the AC current. The rotor rotational frequency is slightly less than the frequency of the AC current, so-called "slip." As a rotor coil slips past the stator magnetic fields, the dynamic magnetic field in the rotor coil induces a current. The resulting induced current generates its own magnetic field that opposes the applied field from the stator, and hence generates torque. The greater the slippage, the greater the torque, so such motors are self-regulating and hence very simple. Induction motors are not a topic of this patent and hence are not discussed further. The remainder of the discussion focuses on permanent magnet and reluctance motors.

[0036] Commonly, the ferromagnetic stator core of the permanent magnet or reluctance electric motors is a single component comprised of stacked-together individual insulated laminations that contain all of the active magnetic poles. The stator core is wrapped with copper coil(s) that are energized by an electrical current and voltage to generate a magnetic flux density within the stator core. The stator core plus the copper coil(s) is collectively described as the "stator."

[0037] Typically, the rotor is comprised of separate ferromagnetic or permanent magnet components. In the absence of the rotor, the stator magnetic circuit is open and cannot sustain magnetic flux density. At particular angular positions, the rotor interacts with the stator magnetic circuit and completes it. When the rotor is fully misaligned with the stator, the magnetic flux density through the magnetic circuit is zero (i.e., zero energy in the magnetic circuit). When the rotor is fully aligned with the stator, the magnetic flux density through the magnetic circuit is maximum (i.e., maximum energy in the magnetic circuit). As the rotor rotates from fully misaligned to fully aligned, the magnetic flux density through the magnetic circuit increases allowing the energy of the magnetic circuit to increase from zero to maximum. By definition, energy is a force exerted over a distance. As the energy of the electric circuit increases, a force is generated on the rotor. The force is generated at a radius from the center of rotation, thus producing torque that acts on the rotor. In summary, as the rotor rotates and completes the magnetic circuit of the stator, torque acts on the rotor thus producing shaft power.

[0038] Many modern applications of electric motors require high power density. For example, modern automobiles increasingly use electrical energy in either hybrid vehicles or battery vehicles. Automobile performance is significantly enhanced with lightweight electric motors mounted directly on the automobile body or its wheels. At a given motor speed, high power density requires high torque density.

[0039] In an electric motor, high torque is achieved via the following methods: • Increase the number of poles - The torque produced in a single magnetic circuit is multiplied by the number of circuits along the periphery of the motor. Increasing the number of poles directly increases the torque.

• Increase the magnetic flux - In the magnetic circuit, stronger magnetic flux results in greater maximum energy and hence greater torque.

[0040] In the magnetic circuit, the maximum magnetic flux is determined by the following factors:

• Increase magnetic field intensity - Magnetic field intensity is the product of current and number of windings. The designer of electric motors selects the smallest wire gauge that can handle the current without overheating, and thus pack as many coils into a given volume as possible. To increase the amount of copper wire in the volume, some designers will select wire with a square cross section that packs more tightly than wire with a round cross section.

• Select high permeability materials - As the magnetic field intensity increases, the ferromagnetic core saturates and can no longer accommodate a greater magnetic flux density. Selecting materials that saturate with a high magnetic flux density increases the maximum energy in the magnetic circuit, and hence the torque.

• Minimize air gaps - For a given magnetic field intensity, in ferromagnetic materials the magnetic flux density is large. In contrast, for the same magnetic field intensity, in air the magnetic flux density is small. Thus, in a magnetic circuit, the presence of an air gap between the rotor and stator creates "reluctance," i.e., the magnetic analogy to resistance in electrical circuits. Designers of electric motors minimize air gaps based on manufacturability limits and thermal expansion considerations.

• Increase rotor/stator contact area - The reluctance of an air gap can be reduced by enlarging the cross-sectional contact area between the rotor and stator. This is analogous to adding parallel resistors to reduce the overall resistance of an electric circuit, which effectively increases the cross-sectional area through which electrons can flow.

[0041] This latter point is a key feature for certain embodiments described herein. [0042] Motor design considerations related to the rotor/stator air gap parameters:

1. Iron losses largely depend upon air gap flux density. Low iron losses enable lower operating temperatures and higher efficiency for electric motors.

2. Higher flux density in the air gap reduces machine size.

3. Higher flux density in the air gap reduces motor cost.

4. Maximizing the surface area between the stator and rotor poles maximizes magnetic flux transmission, which minimizes the volume of materials required.

5. Higher flux density in the air gap increases the overload capacity of the motor.

6. The greater the air gap surface area, the higher the torque capable from the electric motor.

7. The torque-per-unit-rotor volume (TRV) is a measure on the effectiveness of an electric motor and can help determine how "good" an electric motor is. The TRV is related to the tangential stress by the equation TRV =2o ^mean where o ^mean is the shear stress in the air gap between the rotor and stator (in N/m ² ).

8. The greater the air gap pole surface area the higher the electric loading allowable in the motor windings.

9. Rotor size is determined by the air gap surface area and a larger air gap surface area enables a smaller rotor size and hence a smaller motor size.

10. The increased surface area at the rotor/stator interface concentrates the magnetic flux density. This allows the use of low-cost ferrite magnets to achieve motor efficiency and performance that equals or exceeds much more expensive motors that use rare-earth magnets.

[0043] Figure 1 shows a magnetic circuit consisting of a laminated ferromagnetic material separated by thin insulating layers that prevent energy-robbing eddy currents. The top of the magnetic circuit has a copper coil that provides magnetic field intensity that generates magnetic flux. At the bottom, the linear actuator completes the magnetic circuit by moving in the direction shown by the arrow. In this case, the linear actuator is a permanent magnet with poles that align with the polarity of the magnetic field in the magnetic circuit, which draws the linear actuator into the magnetic circuit. When the current flows in the opposite direction through the copper coil, the magnetic field will switch polarity and eject the linear actuator from the magnetic circuit. Although this drawing shows a single linear actuator, the same concept can be applied to rotating equipment in which the permanent magnet is affixed to a rotor and rotates through the stationary magnetic circuit.

[0044] The magnetic flux density may not be uniform everywhere in the magnetic circuit and may be concentrated in particular regions. Regions with low magnetic flux density can employ inexpensive, low-saturation materials (e.g., silicon iron, 1.8 tesla). Regions with high magnetic flux density can employ more expensive, high- saturation materials (e.g., Supermendur, 2.2 tesla). In cases where rapid switching is required, amorphous alloys (e.g., METGLAS, 1.6 tesla) may be employed. The need for laminations can be eliminated by using isotropic composite cores being developed by Persimmon Technologies Corp. (Wakefield, MA).

[0045] Figure 2 is identical to Figure 1, except the linear actuator is also comprised of laminated ferromagnetic material. In this embodiment, the magnetic circuit can only pull the linear actuator into the circuit when it is energized.

[0046] Figure 3 is identical to Figure 2, except that the linear actuator is drawn into the magnetic circuit at an increased angle (φ > 90°). This configuration increases the surface area between the magnetic circuit and the actuator, thereby reducing the reluctance, increasing the magnetic flux, and increasing the force on the actuator.

[0047] Figure 4 is identical to Figure 2, except the side of the actuator is at an increased angle (co > 90°). This configuration increases the surface area between the magnetic circuit and the actuator, thereby reducing the reluctance, increasing the magnetic flux, and increasing the force on the actuator.

[0048] Figure 5 is identical to Figure 2, except the side of the actuator is "rippled." This configuration increases the surface area between the magnetic circuit and the actuator, thereby reducing the reluctance, increasing the magnetic flux, and increasing the force on the actuator.

[0049] All three methods/configurations shown in Figure 3 to 5 may be employed simultaneously.

[0050] Figure 6 is a cross-sectional illustration of a single transverse-flux stator (1) and rotor (2) pole magnetic flux loop showing the air gaps (4) that the rotor (2) pole passes through around an axis that is horizontally located in the plane of the page. The transverse-flux coil (3) is located in the center of the magnetic flux loop with the phase current flowing into and out of the page. [0051] Figure 7 is a cross-sectional illustration of a single transverse-flux stator (1) and rotor (2) pole magnetic flux loop showing the air gaps (4) that are angled in one direction with respect to the magnetic flux path through the stator (1) and rotor (2) poles. The transverse flux coil (3) is located in the center of the magnetic flux loop with the phase current flowing into and out of the page.

[0052] Figure 8 is a cross-sectional illustration of an alternative embodiment of Figure 7, wherein the stator and rotor pole are at an angle compared to Figures 6 and 7 while the air gaps are also angled with respect to the magnetic flux path.

[0053] Figure 9 is an illustration of an alternative embodiment of Figure 8, wherein the air gaps (4) are angled in two different directions with respect to the magnetic flux loop of the stator (1) and rotor (2) pole. The transverse-flux coil (3) is not shown in this figure in order to more clearly see the air gaps (4) orientation with respect to the magnetic flux loop.

[0054] Figure 10 is an illustration of another view of the embodiment shown in Figure 9.

[0055] Figure 1 1 is a cross-sectional illustration of a radial-flux electrical machine. [Any more details?]

[0056] Figure 12 is an illustration of an axial -flux electrical machine. [Any more details?]

[0057] Figure 13 is an illustration of a transverse-flux electrical machine. [Any more details?]

[0058] Figure 14 is an illustration of an electrical machine that improves upon the designs described in U.S. Patent No. 7,663,283, which is hereby incorporated by reference.