This invention relates to the field of motors and generators, and more particularly, to brushless motors and generators which generate at least one common magnetic field, typically with a stationary coil, coaxial about the motor shaft, in addition to one or more other magnetic fields which share the magnetic circuit of the common field.

BAΓΪKΠROLTND OF THE INVENTION Ever since the development of a practical motor, there has been a continuous series of developments, usually evolutionary but sometimes revolutionary, intended to improve aspects of the motor including but not limited to its performance, reliability, life, economy, and ease of manufacture.

Recently, the most dramatic developments in motor design have been in the field of special purpose motors either designed or optimized for specific tasks. These special purpose motors include servos, stepper motors, fast acceleration motors, i.e., high torque to inertia (such as printed circuit motors) , positioners, linear motors, to name a few.

Each of these specialized motors have found specific,

"targeted" applications.

The dramatic decrease in semiconductor cost and the ability to produce application specific integrated circuits (ASIC's) quickly and economically has made the development of "smart" motors, i.e. motor systems with integral controllers, a competitive option. Brushless D.C. motors, as discussed in U.S. Patent No. 4,743,813, and polyphase steppers and motors, as discussed in U.S. Patent No.

5,111,095, are two familiar examples.

Still there is a continuing need for a motor structure which could be dynamically reconfigured, for example, as a torque motor, a stepper motor, a synchronous motor, or a generator. Such a motor would preferably be extremely simple and economic to manufacture while still being able to achieve superior performance.

OB-TECTS AND SUMMARY OF THE INVENTION It is an object of the present invention to provide a motor and method of operating the motor which is capable of generating a magnetic field with an axial coil disposed coaxial with the motor shaft that obviate the problems and limitations of the prior art devices.

It is yet another object of the present invention to provide a motor and method of operating the motor wherein a first magnetic field generated by

a stationary axial coil disposed about the motor shaft interacts with one or more other magnetic fields disposed radially from the shaft to produce shaft rotation. Yet another object is to provide an improved motor characteristics when operating as a motor or an electrical generator or an electric brake, can be easily and quickly changed by reconfiguring the external connections and powering pattern. In accordance with the invention, a motor has a rotatable shaft which may be nonferromagnetic with a ferromagnetic rotor secured to it. The rotor has at least two and typically more rotor poles or a subset of the rotor poles. One or more stationary axial coils are wrapped coaxially about the rotor or rotor magnetic extension for generating a magnetic field in all of the rotor poles. At least two and typically more stationary field poles having a field coil wrapped about each are disposed adjacent to the rotation surface swept by the rotor poles. Each of the field poles generates a magnetic field to magnetically interact with the magnetic field in the rotor poles . A control system is provided for selectively energizing the stationary coils coaxial with the rotor and the field coils wrapped about the field poles.

Other mechanical configurations will be obvious to one ordinarily skilled in the art, which will not

significantly alter the resultant magnetic field geometry and are therefore considered within the scope of the invention.

According to the invention, a method of operating said motor comprises the steps of energizing the axial coil to generate a magnetic field in the rotor poles and also energizing the field coils to generate magnetic fields in the field poles. The interaction of the rotor poles' magnetic fields with the field coils' magnetic fields causes the rotor to rotate. The method also includes the step of selectively energizing the stationary coil and the two or more field coils.

Also according to the invention, an electric generator includes a shaft with a rotor secured thereto. The rotor has a plurality of rotor poles. An external power source rotates the shaft. A stationary coil mounted axially about the shaft generates a magnetic field in the rotor poles. Multiple field coils are provided about the rotor for generating electric power output. A control system is provided for selectively energizing the stationary coil to cause the field coils to generate current. Also according to the invention, a number of different embodiments are provided which incorporate the principles of using multiple stationary axial coils about multiple rotors, securing all the rotors to a common shaft, and providing each rotor with its

own rotor poles and field poles for generating interacting magnetic fields that turn the common rotor motor shaft.

BRIEF DESCRIPTION OF THE DRAWINGS The structure, operation, and advantages of the presently preferred embodiment of the invention will become further apparent upon consideration of the following description taken in conjunction with the accompanying drawings, wherein: Figure 1 is a cut-away, cross sectioned view of a single-sided motor in accordance with a first embodiment of the invention;

Figure 2 is a cut-away view along the line 2-2 of Figure 1; Figure 3 is a cut-away, cross sectioned view of a double sided motor in accordance with a second embodiment of the invention;

Figure 4 is a cut-away view along line 4-4 of Figure 3 ; Figure 5 is a cut-away, cross sectioned view of a motor having two rotor and three field poles in accordance with a third embodiment of the invention;

Figure 6 is a cut-away view along line 6-6 of Figure 5; Figure 7A is a cut-away, cross sectioned view of a motor having six rotor poles in accordance with a third embodiment of the invention; and

Figure 7B is a cut-away view along line 7B-7B of Figure 7A.

DETAILED DESCRIPTION OF THE INVENTION

On -Sided Axial Field Motor Referring to Figures 1 and 2 of the drawings, like elements are assigned like reference numbers, with suffixes A,B,C and D indicating 4 horizontal quadrants, and suffix E indicating upper half and suffix F indicating lower half. Figures 1 and 2 are cut-away drawings of a single-sided motor system 10 incorporating the concept of the present invention. Motor 10 has a stationary axial coil 12 about shaft 22 of rotor 14. Rotor 14 has four rotor poles 16A, 16B,16C,16D (16A- 16D) extending out radially. Four field coils

18A,18B, 18C, 18D (18A-18D) are positioned about four field poles 20A, 20B, 20C,20D (20A-20D) which extend inward radially from yoke 24.

Motor 10 does not use brushes and is free of magnets, although magnets can be incorporated if they confer an advantage in a particular application. The central concept shared by motor 10 with the other embodiments of the present invention relates to the use of a magnetic field generated by a stationary axial coil 12 disposed coaxially with shaft 22. Coil

12 is generally constructed of wire wound around a bobbin 23 and can be connected to control system 38. The magnetic field generated by coil 12 interacts

with several other magnetic fields imposed on field poles 20A-20D, which do not necessarily interact strongly with each other, but which share a magnetic circuit (or closed loop of magnetic flux) with the magnetic field generated by coil 12. The magnetic fields imposed on field poles 20A-20D can be generated by various means, such as by field coils 18A-18D and/or by permanent magnets (not shown) which generate a magnetic field through field poles 20A- 20D.

Shaft 22 is preferably made of non-ferromagnetic material in applications utilizing more than one axial field coil to enhance separation. The two opposite ends, 30E,30F of shaft 22 are supported by bearings 58E,58F comprising inner bearing races

26E,26F, ball bearings 28E,28F and outer races 32E,32F. The components of bearings 58E,58F are preferably made of ferromagnetic material to help carry flux and minimize total loop reluctance into the total yoke/rotor circuit. Shaft 22 is located at the center line of field poles 20A-20D and aligned perpendicular to the plane containing field poles 20A-20D.

Motor 10 has a cup-shaped ferromagnetic yoke 24 from which four stationary field poles 20A-20D extend inward towards shaft 22. Around each field pole 20A- 20D is wound a field coil 18A-18D, respectively. Each field coil 18A-18D is powered by control system

38 with individual coil outputs numbered to match the associated motor coils. Control system 38 is typically controlled by means such as a microprocessor (not shown) . Rotor 14 is substantially a cylindrical structure of ferromagnetic material securely mounted on shaft 22 between bearings 58E, 58F. Multiple lobes 15A, 15B, 15C, 15D (15A-15D) are contiguous with and extend radially outward from rotor 14 to form rotor poles 16A-16D, which typically have curved outer faces 17A, 17B, 17C, 17D (17A-17D) each with a convex shape that face corresponding curved outer faces 21A, 21B, 21C, 21D (21A-21D) with a concave shape of each the field poles 20A-20D. The concave and convex curvatures 21A-21D and 17A-17D, respectively, are shaped to form an equal air gap 46A, 46B, 46C, 46D (46A-46D) therebetween. While four field and rotor poles are illustrated, it is within the terms of the invention to use any number desired. Rotor 14 includes a rotor support 29, which is material that fills the space between rotor poles 20A-20D. It is preferably made of non-conductive, nonferromagnetic material such as plastic to eliminate eddy current losses. The separation between poles 20A-20D to each other is relatively large. Air gap 46A-46D between outer faces 17A-17D of rotor poles 16A-16D and outer faces 21A-21D of field poles 18A-18D is relative

small, typically about .003 inches to about .005 inches. Air gap 46A-46D provides the dominant reluctance in the magnetic circuit formed through axial coil 12, rotor 14, rotor poles 16A-16D, field poles 20A-20D, yoke 24, and bearing 58A. A preferred direction of rotation and motor start-up can be provided by varying the arc length of rotor poles 16A-16D relative to the arc length of field poles 20A-20C or by varying the horizontal width of air gaps 46A-46D along their lengths.

Simple Timing Sequence: Four Poles at a Time

There are many possible timing sequences to power motor 10. One simple timing sequence is as follows: A constant DC current through axial coil 12 generates a constant magnetic field through rotor 14 and rotor poles 16A-16D. Control system 38 activates all field coils 18A-18D in unison with constant DC current to generate a magnetic field in field poles 20A-20D opposing that in rotor poles 16A-16D. The opposing magnetic fields cause rotor poles 16A-16D to be repelled from field poles 20A-20D so that rotor 14 rotates 1/8 turn. Then, control system 38 reverses the current flow through field coils 18A-18D, which in turn reverses the magnetic field in field poles 20A-20D. This causes rotor poles 16A to be attracted to the successive field pole of field poles 20A-20D, so that rotor 14 rotates another 1/8 turn. If the timing sequence is paced correctly, all "1/8 turns"

are in the same direction. Continuously repeating this sequence amounts to powering field coils 18A-18D with a square wave to produce continuous rotor rotation. Before field coils 18A-18D are activated, the magnetic field generated by axial coil 12 causes rotor poles 16A-16D to be attracted to field poles 20A-20D, causing a "locked rotor" condition. Therefore, field coils 18A-18D should be designed to produce a stronger magnetic field than that in rotor poles 16A-16D for the repelling force to overcome the "locked rotor" condition.

Alternative timing sequences of coil excitation are possible. To achieve desired effects, 1) the current through rotor coil 12 can be time-varied, 2) field coils 18A-18D need not be activated in unison, 3) the repelling step or attracting step can be eliminated altogether, 4) the excitation signal need not be square wave (it can be a sinewave for example) , and 5) the excitation sequence may be or may not be timed to match the rotor position. Examples of some of these possibilities are illustrated below. Another Timing Sequence: Two Poles at a Time For example, in another possible timing sequence, control system 38 maintains constant current through axial coil 12 and excites field coils 18A-18D as described above except that only two field

coils are excited at a time, such that one pair only does the attracting (at the appropriate times) and the other pair only does the repelling. Another Timing Sequence: One Pole at a Timp Another possible timing sequence is as follows.

Control system 38 maintains constant current through axial coil 12. It sequentially excites each field coil 18A-18D with a brief square pulse (duration of less than 1/8 turn) , always with the same current direction such that each excitation causes only repulsion between the excited field pole (either of 18A-18D) and the nearest rotor pole (either of 16A- 16D) . Hence, there is no attraction step in this example, and rotor 14 rotates 1/4 turn with each excitation.

Another Timing Sequence: Time-Varying Axial F eld In another possible timing sequence, control system 38 excites each of the field coils 18A-18D with the same constant current. First, rotor coil 12 is excited with a current direction that causes each rotor pole 16A-16D to be repelled by its corresponding field pole 20A-20D. Then, the current direction is reversed by control system 38 to cause each rotor pole 16A-16D to be attracted to the next field pole 20A-20D. Rotor 14 rotates 1/4 turn with each repetition of this 2-step sequence similar to the four poles at a time example. More ΠT T.esπ Field Poles than Rotor Poles

Motor 10, described so far, has the same number of field poles as rotor poles. However, it is also within the terms of the invention to provide more or less field poles than rotor poles. In the case of more field poles than rotor poles, the extra field pole(s) can serve as a tachometer pick-off for speed regulation or stepper control. It is also within the scope of the invention to use any momentarily unused field pole as a tachometer pick-off for speed regulation or stepper control.

Electric Generator

Also, in accordance with the invention, motor 10 can serve as an electrical generator. This is accomplished by driving shaft 22 with an external device, such as a motor 39, while axial coil 12 is excited. The field coil(s) (not activated) will generate electricity, serving as a generator output. Further in accordance with the invention, motor 10 can be used as a brake. This is accomplished by running the system as an electrical generator as just described and directing the generator output from the field coils to a resistive load which dissipates the rotational energy of shaft 22 as heat.

Smooth rotation is obviously best achieved when the excitation sequence is timed to match the rotor position. However, the excitation sequence does not have to be timed to match the rotor position and

control system 38 can be an arbitrary switched source. This is especially the case when motor 10 serves as a stepper motor, where the number of rotations is critical but smooth rotation is not. This can be enhanced by a differing number of rotor and field poles where stepping the field can drag the rotor.

Reconfiguring the function

The aforementioned examples illustrate how motor 10 can be reconfigured by simply modifying the excitation pattern to achieve different speeds and functions (motor, brake, etc.). Moreover, the speed and function can be reconfigured during operation. For example, if the motor 10 were used to power an automobile, it could function as a motor while traveling uphill and function as a brake or generator while traveling downhill.

Double-Sided Motor with Multiple Axial Co ls

While Motor 10 operates effectively with a single axial coil 12, it is also within the scope of the invention to construct a second embodiment of a motor using multiple stationary axial coils and possibly multiple rotors. In this embodiment, all of the rotors are secured to a common shaft and each rotor has its own rotor poles and field poles for generating magnetic fields which interact to turn the common shaft.

Motor 50, the second embodiment of the invention, is illustrated in Figures 3 and 4. The construction and operation of motor 50 are similar to those of the first embodiment, i.e., motor 10. The component reference numbers in Figures 3 and 4 correspond with those of Figures 1 and 2. Like elements are assigned like reference numbers, with suffixes A,B,C and D indicating four horizontal quadrants, and suffix E indicating upper half and suffix F indicating lower half .

Motor 50 has two rotor poles 16B and 16D which are now connected to a second isolated rotor magnetic circuit axial section 14E positioned above the first rotor magnetic circuit axial section 14F. The second rotor magnetic circuit with axial section 14E has its own field coil 12E so that the magnetic field applied to the upper rotor magnetic circuit axial section 14E and its rotor poles 16B and 16D (see Figure 4) can be different than that applied to the lower rotor magnetic circuit axial section 14F and its rotor poles 16A and 16C.

In Figures 3 and 4, motor 50 has two stationary axial coils 12E,12F positioned around rotor axial sections 14E,14F, respectively. Rotor axial sections 14E,14F are both securely mounted to shaft 22 with shielding sleeve 15 of a nonmagnetic material in between. Rotor axial section 14E has two rotor poles 16B and 16D, and rotor section 14F has two rotor

poles 16A and 16C. Motor 50 also has four field coils 18A, 18B, 18C, 18D (18A-18D) mounted about four field poles 20A, 20B, 20C, 20D (20A-20D) .

Motor 50 does not use brushes and is free of magnets, although magnets can be incorporated if they confer an advantage in a particular application. Coils 12E,12F can be constructed of wire wound around a bobbin, and can be connected to control system 38. The central concept of motor 50 is the use of two magnetic fields generated by axial coils 12E and 12F disposed coaxially about shaft 22. Each of these two magnetic fields interacts with the magnetic fields in field poles 20A-20C, 20B-20D, respectively, which do not necessarily interact strongly with each other. The magnetic fields in field poles 20A-20D can be generated by various means, such as by field coils 18A-18D and/or permanent magnets (not shown) .

Shaft 22 is preferably made of non-f rromagnetic material. Its opposite ends 30E,30F are supported by bearings 58E,58F comprising inner bearings races

26E,26F, ball bearings 28E,28F and outer races 32E,32F. The components of bearings 58E and 58F are preferably made of ferromagnetic material. Shaft 22 is at the center of field poles 20A-20D and aligned perpendicular to the plane containing field poles

20A-20D. Sleeve 15 decouples the magnetic fields of the two rotor axial sections 14E, 14F by providing additional magnetic circuit gap length and increasing

the reluctance between the two rotor axial sections.

Motor 50 has a cup-shaped ferromagnetic yokes 27E, 27F from which four stationary field poles 20A- 20D extend inward towards shaft 22. Around each field pole 20A-20D is wound a field coil 18A-18D, respectively. Each field coil 18A-18D is powered by a control system 38 with individual coil outputs numbered to match the associated motor coils. Control system 38 may be controlled by means such as a microprocessor.

Each of the magnetically separated rotor magnetic circuit axial sections 14E,14F comprises two substantially cup-shaped or "L"-shaped ferromagnetic structures securely mounted on shaft 22 between bearings 58E and 58F. One leg of the "L" shape extends vertically along the length of shaft 22. The other leg extends radially outward and is connected to rotor poles 16A-16D, which typically have curved faces and face the field poles 20A-20D, respectively (see Figure 4) . While four rotor poles 16A-16D are illustrated, it is within the terms of the invention to use any number desired. The magnetic circuits with axial sections 14E and 14F have a rotor support 29, which is material that fills the space around and between the vertical legs of the "L" shaped structures. It is preferably made of non-conductive, nonferromagnetic material such as plastic to eliminate eddy current losses and minimize inertia.

In operation, a dual-closed-loop magnetic circuit passes through axial coil 12E, rotor axial section 14E, rotor poles 16B and 16D, field poles 20B,20D, yoke 24E, and bearing 58E. Another dual- closed-loop magnetic circuit passes through axial coil 12F, rotor axial section 14F, rotor poles 16A and 16C, field poles 20A and 20C, yoke 24F, and bearing 58F.

The separation between field poles 20A-20D to each other is relatively large. Air gaps 46A-46D between rotor poles 16A-16D and field poles 20A-20D, respectively, is relatively small, typically about .003 inches to about .005 inches, and is the controlling reluctance in the two aforementioned magnetic circuits. A preferred direction of rotation and motor start-up is achieved by varying the arc length of rotor poles 16A-16D relative to the arc length of field poles 20A-20C or by varying the horizontal width of air gaps 46A-46D along their lengths.

Two-sided motor 50 can be powered with a variety of possible timing sequence.

In one configuration, axial coils 12E and 12F can be connected together in parallel, rendering motor 50 functionally identical to the one-sided motor 10 of the first embodiment. Then, all the timing sequences and explanations mentioned above for

the one-sided motor 10 apply equally well for motor 50.

However, two-sided motor 50 having the extra versatility of being able to apply different magnetic fields to different axial poles offers other timing sequence not possible with one-sided motor 10.

For example, axial coils 12E and 12F can be activated with DC current in opposite directions from each other, causing rotor axial sections 14E and 14F to be magnetized with opposite polarity. Then, control system 38 would activate field coils 18B and 18D with a square wave (current flowing alternatingly in the forward direction and then the reverse direction) , as described above for motor 10, and activate field coils 18A and 18B with another square wave of inverted polarity (i.e. 180 degrees out of phase) from that of field coils 18B,18D. As with the first embodiment, the magnetic field generated by the field coils 18A-18D should be larger than the flux field generated by the axial coils 12E, 12F to overcome "locked rotor" condition.

Motor 50 can provide a very compact and robust system capable of high performance with little vibration, bearing wear or cogging. A minimum practical uniform gap width between the outer faces of the rotor poles 16A-16D and the outer faces of the field poles 20A-20D, respectively, is employed for minimum reluctance and maximum torque and efficiency.

While two stationary axial coils 12E, 12F are illustrated, it is within the terms of the invention to use any number of stationary axial coils, as needed with multiple rotors on a common shaft. Besides the ability to vary air gap widths, field pole face shapes and rotor face configurations, motor 50 offers great flexibility in possible timing sequences of powering the multiple axial coils. Also, the rotation can be made smoother by the ability of stacked rotors to be selectively angularly offset relative to each other to decrease "cogging" . Magnetically Coupl d Rotors

As described so far, rotor axial sections 14E, 14F are magnetically decoupled through use of sleeve 15 or use of nonferromagnetic material in shaft 22 and the structural material of rotor support 29. However, it is also within the terms of the invention to intentionally magnetically couple rotor axial sections 14E and 14F by forming them of a single continuous piece of ferromagnetic material (i.e. by using a ferromagnetic sleeve 15) , and/or by making shaft 22 out of ferromagnetic material and eliminating shielding sleeve 15. Motor 50 would then essentially have a single rotor (like motor 10) with two axial coils 12E-12F that could be powered in unison. Despite having two axial coils, the resulting motor would have the same limitation as

motor 10 of not being able to magnetize those rotor poles independently.

Flectric Generator and Electric Brake

As with the first embodiment, it is also within the terms of the invention to operate motor 50 as an electric generator as described for motor 10. The field coils can be interconnected in any desired pattern and dynamically reconfigure as desired to achieve the desired form of power output . Also, as with the first embodiment, it is also within the terms of the invention to operate motor 50 as an electric brake as described for motor 10. More or Less Field Poles than Rotor Poles

Motor 50 has the same number of field poles as rotor poles. However, as with motor 10, it is also within the terms of the invention to provide more or less field poles than rotor poles. In the case of more field poles than rotor poles, the extra field pole(s) can serve as a tachometer pick-off when not used in rotor driving for speed regulation or stepper control. It is also within the scope of the invention to use any momentarily unused field pole as a tachometer pick-off for speed regulation or stepper control . Stacked Rotors

The stacking of stationary axial coils and rotors around a shared shaft can continue resulting in a small diameter motor of superior performance.

The performance is enhanced by the ability of stacked rotors to be selectively angularly offset from each other.

Stacked motors Similarly, several one-sided motors 10 or two- sided motors 50 can be stacked by sharing a common shaft that runs through them. This offers greater torque, and shaft rotation is smoothed (i.e. less "cogging") by having the motors slightly angularly displaced one from the other.

While the rotor 14 of motor 10 is shaped somewhat like a cylinder with the rotor poles being petal shaped and forming the radial extending lobes 15A-15D, and the axial poles of motor 10 being block- shaped protrusions from the yoke, it is within the scope of the present invention to vary the shapes of the rotor, rotor poles and field poles, as long as they form appropriate closed loop paths for the magnetic field circuit (s) .

An example of other rotor and field pole shapes is illustrated by motor 60 in Figures 5 and 6. Besides illustrating other pole shapes, motor 60 illustrates a motor having a different number of rotor poles than field poles, in this case 2 rotor poles and 3 field poles.

The construction and operation of motor 60 are similar to those of the first embodiment. The

component reference numbers in Figures 5 and 6 correspond to those of Figures 1 and 2. Like components in motor 60 are assigned like reference numbers, with suffixes A,B, and C indicating 3 horizontal sectors, and suffix E indicating upper half and suffix F indicating lower half.

Essentially, motor 60 is the same as motor 10, except that there are two (2) rotor poles 16A,16B, and three (3) field poles 20A,20B,20C (20A-20C) that are shaped like a sideways "U" , and the three (3) field coils 18A,18B,18C (18A-18C) that are positioned around the vertical leg of field poles 20A-20C instead of the horizontal leg.

Motor 60 operates essentially like motor 10. Current flowing through axial coil 12 produces a magnetic field in the two rotor poles 16A, 16B. Current flowing through any of the three field coils 18A-18C produces a magnetic field in the corresponding field pole 20A-20C. Rotor poles 16A,16B are attracted to their adjacent field pole

20A, 20B or 20C, whenever their (rotor pole's and adjacent field pole's) magnetic fields complement each other, forming a magnetic field circuit through the rotor pole and the adjacent field pole. Similarly, rotor poles 16A,16B are repelled by their adjacent field pole if their magnetic fields oppose each other.

One possible timing sequence of powering motor

60 with a control system 38 is as follows. Axial coil 12 is powered continuously with DC current. The three field coils 18A-18C are all activated by a square wave alternating between forward current and reverse current. The three square waves powering the three field coils are identical but offset from each other by 120 degrees. Each field pole attracts the nearest rotor pole when the electric current flows in one direction and repels the nearest rotor pole when the electric current flows in the opposite direction.

If timed correctly, rotor 14 continually rotates in one direction, one turn for every two complete square wave cycles.

Motor 60 can function as an electric generator or electric brake, in the same way as described above for motor 10.

Referring to Figures 7A and 7B, there is illustrated an alternative embodiment of motor 50 shown in Figures 3 and 4 which is essentially identical to motor 50 but which incorporates a preferred rotor construction. Specifically, the six rotor poles 16A-16F are arranged so that diametrically opposed poles, i.e. 16A, 16D, are associated with separate, isolated magnetic circuits. Therefore opposing field poles do not form a magnetic circuit spanning the rotor and inviting lock-up (cogging) . While this can also be avoided by appropriate timing of the field pole sequence for 8

poles, for example, opposing rotor poles belonging to the same magnetic circuit would require an unsymetric field coil pattern (non-cogging) with respect to the shaft axis and therefore impress first order transient side loads on the shaft bearings, 26E, 26F increasing both the wear rate and noise output.

The magnetic circuits of the upper and lower rotor flux paths are isolated by the large, high reluctance gaps provided by the shaft sleeve 15 and non-magnetic rotor structural material between the

'petals' of the two 'three blade' rotor ferromagnetic pathways. As discussed before, the gaps between isolated magnetic elements are large compared to rotor pole to field pole clearances required by manufacturing tolerances.

Similarly, the upper and lower return yokes 24E, 24F are formed of two 'three blade' ferromagnetic baskets joined structurally by nonmagnetic elements and isolated from each other. If desired, the rotor lobes can be isolated at the hub to prevent cross or transverse rotor flux paths for any axial coil configuration.

It is apparent that there has been provided in accordance with this invention apparatus and methods for that satisfy the objects, means and advantages set forth hereinbefore. According to the invention, a motor or electric generator incorporates one or more common stationary axial coils for generating a

magnetic field in rotating rotor poles and a separate structure for generating magnetic fields in field poles to magnetically interact with the rotor poles. While the invention has been described in combination with embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing teachings. Accordingly, the invention is intended to embrace all such alternatives, modi ications and variations as fall within the spirit and scope of the appended claims.