Patent Description:
Designing electromagnetic induction machines, such as electric motors, often requires standardizing some dimensions while allowing the motor to vary in other respects to cover an entire range of operating requirements. In one example and for a family of motors each providing different operating characteristics, an outer diameter of the motor may be consistent, while the motor axial length (i.e., packaging length) is changed to accommodate different windings. Improvements in motor design techniques that may lead to improvements in motor efficiency, motor cooling, reduction in costs, and standardization of parts and packaging are desirable.

<CIT> discloses an ironless stator, brushless, single coil motor, with co-axial cylinders rotating together by common attachment to a shaft running in bearings in a motor frame.

<CIT> discloses an electrical machine comprising a dual rotor that is rotatably mounted to a stator.

<CIT> discloses a wheel motor comprising a stator portion defining air circulation openings and a rotor portion comprising an annular case enclosing permanent magnets.

According to a first aspect of the present invention there is provided an electric motor comprising: a rotor adapted to rotate about a rotation axis; a stator axially aligned to the rotor and centered to the rotation axis, wherein the rotor is a dual rotor including an inner rotor segment and an outer rotor segment disposed radially outward from the inner rotor segment, and the inner rotor segment radially defines an inner cavity axially aligned to the rotor and the stator; a stationary shaft disposed in the inner cavity, extending along the rotation axis, and spaced radially inward from the inner rotor segment; a mounting plate axially defining the inner cavity, attached to the stationary shaft, and adapted to support the stator; and a motor drive including electronic elements disposed at least in-part in the inner cavity; wherein the motor drive is directly supported by the stationary shaft.

The stator may be radially disposed between the inner and outer rotor segments.

The stator is optionally a coreless stator.

The motor drive may be completely disposed in the inner cavity.

The motor drive optionally includes a circuit board.

The motor drive may be directly supported by the mounting plate.

The inner rotor segment, the outer rotor segment, and the stator optionally each define a respective plurality of openings for the radially outward flow of cooling air from the inner cavity.

The stationary shaft is optionally hollow for the axial flow of cooling air.

The stationary shaft optionally defines at least one opening for the radially outward flow of cooling air into the inner cavity.

The stationary shaft and the mounting plate may be metallic.

However, it should be understood that the following description and drawings are intended to be exemplary in nature and non-limiting.

Various features will become apparent to those skilled in the art from the following detailed description of the disclosed exemplary embodiments.

Referring to <FIG>, an electromagnetic machine <NUM> adapted to convert electrical energy to mechanical energy, or vice-versa, is illustrated. Examples of the electromagnetic machine <NUM> may include an electric motor and a generator. The electromagnetic machine <NUM> may include a housing <NUM>, a motor drive <NUM>, a stator <NUM>, and a rotor <NUM>. The housing <NUM> is adapted to house the circuit board <NUM>, the stator <NUM>, and the rotor <NUM>. The circuit board <NUM> may be attached to the stator <NUM>. As is generally known in the art of electric motors, the stator <NUM> and the rotor <NUM> are axially aligned to one-another and are generally centered about a rotation axis A. The stator <NUM> may be stationary, and the rotor <NUM> is adapted to rotate about the rotation axis A. Together, the circuit board <NUM> and the stator <NUM> may be identified as a stator assembly <NUM>. In one example, the electromagnetic machine <NUM> may be coreless. In another, non-limiting, example, the motor drive <NUM> may be, or may include, a circuit board that may be printed.

The stator <NUM> may include a support structure assembly <NUM>, and a plurality of coils <NUM>. The support structure assembly <NUM> may include a mounting plate <NUM>, bearings <NUM>, a support structure <NUM>, and a plurality of bobbins <NUM> (see <FIG>). Each one of the plurality of coils <NUM> may be one about a respective one of the plurality of bobbins <NUM>. The support structure <NUM> is adapted to support, and attach to, the plurality of bobbins <NUM>. The mounting plate <NUM> may be adapted to support, and attach to, the support structure <NUM> and the bearings <NUM> for substantially frictionless rotation of the rotor <NUM> about the axis A. The motor drive <NUM> may attach to an axial side <NUM> of the mounting plate <NUM>, and the support structure <NUM> may attach to an opposite axial side <NUM> of the mounting plate. In another embodiment, the mounting plate <NUM> may be an integral and unitary part of the support structure <NUM>. In another embodiment, the mounting plate <NUM> may be an integral and unitary part of the motor drive <NUM> which may be a circuit board. In yet another embodiment, the stator <NUM> may not include the mounting plate <NUM>, and instead, the motor drive <NUM> as a circuit board also functions as a structural member from the stator <NUM>.

Referring to <FIG> and <FIG>, the plurality of bobbins <NUM> may generally be the same, with each including a core <NUM> extending along a centerline C and two opposite flanges <NUM>, <NUM>. The core <NUM> extends between and may form into the flanges <NUM>, <NUM>. The flanges <NUM>, <NUM> may be substantially normal to the centerline C. When the electromagnetic machine <NUM> is fully assembled, each centerline C may be generally normal to, and intersects, the axis A, and the coils <NUM> are generally wound about the respective cores <NUM> and centerlines C. More specifically, each core <NUM> may extend in a radial direction with respect to axis A, such that the flange <NUM> is an outer flange, and the flange <NUM> is an inner flange located radially inward from the outer flange.

The support structure <NUM> may include at least one ring (i.e., two illustrated as <NUM>, <NUM>). Both rings <NUM>, <NUM> may be centered about axis A, and may be axially spaced apart from one another. Each bobbin <NUM> may be axially elongated with respect to axis A, and may include opposite end portions <NUM>, <NUM>. When the support structure assembly <NUM> is assembled, the ring <NUM> may be an outer ring located radially outward from the plurality of bobbins <NUM>, and the ring <NUM> may be an inner ring located radially inward from the bobbins <NUM>. In one example and during manufacture, each coil <NUM> may be wound about a respective bobbin <NUM> prior to attaching the bobbins <NUM> to the rings <NUM>, <NUM>. Moreover, each bobbin <NUM> may be releasably attached to one, or both, of the rings <NUM>, <NUM> (e.g., snap fitted) for easy removal to perform maintenance on any particular bobbin <NUM> and/or coil <NUM>.

Referring to <FIG>, the motor drive <NUM> is generally illustrated as a circuit board that is substantially planar, circular and/or annular in shape, and substantially normal to axis A. The circuit board may be a printed circuit board, and is generally configured to wire the plurality of coils <NUM> in a predefined configuration to achieve, for example, the desired output torque, and/or speed, of the electromagnetic machine <NUM>. That is, the motor drive <NUM>, as a circuit board, may enable the use of universal components for multiple motor applications, by generally providing options on how the coils <NUM> are wired together (i.e., series, parallel, and combinations thereof). In one embodiment, the plurality of bobbins <NUM> may each be the same, and may be universal bobbins capable of being applied to a variety of motor applications with different output parameters. Similarly, the stator support structure assembly <NUM>, and/or the support structure <NUM>, may be universal, capable of being applied to a variety of motor applications utilizing the universal bobbins <NUM> and/or universal coils <NUM>.

Referring to <FIG>, the plurality of coils <NUM> (i.e., four illustrated), may have a coil configuration <NUM> where the coils <NUM> are electrically wired in series to one another (see <FIG>), may have a coil configuration <NUM> where the coils <NUM> are electrically wired in parallel to one another (see <FIG>), or may have a coil configuration <NUM> where the coils <NUM> are electrically wired in a combination of both parallel and series arrangements. The output of the motor torque and speed may be different depending upon the coil configuration <NUM>, <NUM>, <NUM> applied.

The motor drive <NUM> as a circuit board provides an easy and efficient means of choosing the desired coil configuration <NUM>, <NUM>, <NUM>. For example, the circuit board may include a plurality of connection points <NUM> (e.g., through-hole pads) and zero resistance jumpers, or printed tracers, <NUM> arranged to provide, for example, three individual coil configuration imprints (i.e., one illustrated in <FIG>), with each footprint associated with a respective coil configuration <NUM>, <NUM>, <NUM>.

As best shown in <FIG>, the universal coils <NUM> may each include positive and negative leads <NUM>, <NUM>, each projecting in a common axial direction with respect to axis A. In general, lead <NUM> may be spaced radially outward from lead <NUM>, and by a common radial distance for each coil <NUM>. The leads <NUM>, <NUM> may also be circumferentially spaced, by a common circumferential distance, from the leads <NUM>, <NUM> of the circumferentially adjacent coil <NUM>. In one embodiment, the leads <NUM>, <NUM> of the coils <NUM>, may project axially through the mounting plate <NUM>, and through the aligned connection points <NUM> for electrical connection to the associated jumpers <NUM>.

In one embodiment, the motor drive <NUM>, as a circuit board, may generally include three mountable positions <NUM>, <NUM>, <NUM>, with each mountable position associated with a respective coil configuration imprint. During manufacture, or assembly, simply rotating the circuit board between the mountable positions <NUM>, <NUM>, <NUM> is the means of selecting the desired coil configuration <NUM>, <NUM>, <NUM>. More specifically, if the plurality of coils is twelve coils, the number of connection points <NUM> for leads <NUM> may be three times the number of coils, which may be thirty-six connection points where only twelve are actually used. When used, the leads <NUM> may project axially through the respective through-hole pads <NUM> for soldering to the respective tracer <NUM>. The same principle may apply for the leads <NUM>. In another embodiment, the circuit board may include only one coil configuration imprint; however, to establish a desired motor type, the correct circuit board with the desired coil configuration imprint is chosen.

Referring to <FIG> and <FIG>, the rotor <NUM> may be a dual rotor having an outer rotor segment <NUM> spaced radially outward from, and concentric too, an inner rotor segment <NUM>. Each segment <NUM>, <NUM> may include a plurality of permanent magnets <NUM> for interaction with the coils <NUM> as is generally known in the art of motors and generators. The outer and inner rotor segments <NUM>, <NUM> may include boundaries that radially define an annular chamber <NUM>. When the electromagnetic machine <NUM> is assembled, the outer rotor segment <NUM>, the stator <NUM> is substantially in the annular chamber <NUM>, the inner rotor segment <NUM> and the stator <NUM> (i.e., bobbins <NUM> and coils <NUM>) are generally axially aligned to one another, and the stator <NUM> is generally spaced radially from and between the outer and inner rotor segments <NUM>, <NUM>.

To provide air cooling for the stator <NUM>, cooling air (see arrows <NUM> in <FIG>) may flow through various channels, spaces, and/or gaps provided in and between the stator <NUM> and the rotor <NUM>. In one embodiment, the inner rotor segment <NUM> and the stator <NUM> may include boundaries that define a cooling flow gap <NUM> that may be substantially annular in shape, and is part of the annular chamber <NUM>. The core <NUM> of each bobbin <NUM> may include at least one cooling flow opening <NUM> (e.g., hole, six illustrated in <FIG>) that extend, or communicate, radially through the bobbin <NUM> with respect to axis A. The outer rotor segment <NUM> and the stator <NUM> may include boundaries that define a cooling flow gap <NUM> that may be substantially annular in shape, is part of the annular chamber <NUM>, and is located radially outward from gap <NUM>. In addition, the outer rotor segment <NUM> includes boundaries that define a plurality of openings <NUM> (e.g., holes) that extend, or communicate, radially through the outer rotor segment <NUM> with respect to axis A.

When the electromagnetic machine <NUM> (e.g., motor) is assembled, the gap <NUM> is in direct communication with the bobbin openings <NUM>. The openings <NUM> communicate directly with, and between, the gaps <NUM>, <NUM>, and the gap <NUM> communicates directly with the outer rotor segment openings <NUM>. In operation, cooling air <NUM> may flow axially through the gap <NUM>, then radially outward through the bobbin openings <NUM>. From the bobbin openings <NUM>, the cooling air <NUM> flows through the gap <NUM>, then radially through the outer rotor segment openings <NUM>.

Referring to <FIG> and <FIG>, another embodiment of the motor drive <NUM> of the stator assembly <NUM> may include a controller <NUM> configured to select one of the coil configurations <NUM>, <NUM>, <NUM> based on sensory input. That is, the motor drive <NUM> may not include the multitude of configuration imprints previously described, and instead, may rely on the controller <NUM> to select the appropriate coil configuration to optimize operation of the electromagnetic machine <NUM>. In this embodiment, each coil lead <NUM>, <NUM> may still electrically connect to through-hole pads <NUM> as previously described in the example of the motor drive <NUM> being a circuit board; however, at least some of the zero-resistance jumpers, or tracers, may be routed directly to a switch <NUM> of the motor drive <NUM>.

The controller <NUM> may include a processor <NUM> (e.g., microprocessor) and an electronic storage medium <NUM> that may be computer readable and writeable. A self-adapt logic module <NUM>, which may be software-based, is stored in the electronic storage medium <NUM> and executed by the processor <NUM> for control of the switch <NUM>. Depending upon the selected, or commanded, orientation of the switch <NUM>, the plurality of electric coils <NUM> may be orientated in one of the configurations <NUM>, <NUM>, <NUM>. Non-limiting examples of the switch <NUM> may include a simple, mechanical, switch, at least one transistor switch, and/or a multitude of micro-switches. The motor drive <NUM> may further include other electronic elements <NUM> (see <FIG>) as is known by those skilled in the art of motor drives.

Referring to <FIG>, the sensor inputs may include one or more of a temperature signal <NUM> generated by a temperature sensor <NUM>, a power source input voltage signal <NUM> generated by a voltage sensor <NUM>, a torque signal <NUM> generated by a torque sensor <NUM>, a speed signal <NUM> generated by a speed sensor <NUM>, and other sensory inputs.

The controller <NUM> may further include a database <NUM> that includes a plurality of pre-programmed values (e.g., set points) utilized by the self-adapt logic module <NUM>. In operation, the module <NUM> of the controller <NUM> may process the power source voltage signal <NUM> from the voltage sensor <NUM>, and based on the voltage, select an appropriate coil configuration to optimize performance based on a pre-programmed torque and/or speed requirement stored in the database <NUM>.

Alternatively, or in addition to, the module <NUM> of the controller <NUM> may process the temperature signal <NUM> from the temperature sensor <NUM>, which may be indicative of a stator temperature. The controller <NUM> may determine if, for example, the stator temperature is running high based on a high temperature set point stored in the database <NUM>. If the stator temperature is high, the controller <NUM> may choose a coil configuration appropriate to reduce the stator temperature, while maintaining torque and speed requirements as much as feasible.

Alternatively, or in addition to, the module <NUM> of the controller <NUM> may process the torque signal <NUM> from the torque sensor <NUM>. The torque signal <NUM> may, for example, be indicative of an output torque of the electromagnetic machine <NUM> (e.g., electric motor). This real-time output torque may be compared to a desired output torque pre-programmed into the database <NUM>. If the actual output torque is too high, or too low, the module <NUM> may cause the controller <NUM> to send a command signal (see arrow <NUM>) to the switch <NUM> to appropriately re-configure the coils <NUM> to achieve the desired torque. In one embodiment, the coil connections may be switched, thus the coil configuration changed, while the electromagnetic machine <NUM> (e.g., motor) is operating and the rotor <NUM> is rotating about rotation axis A.

Alternatively, or in addition to, the module <NUM> of the controller <NUM> may process the speed signal <NUM> from the speed sensor <NUM>. The speed signal <NUM> may, for example, be indicative of an output speed (e.g., revolutions per minute) of the electromagnetic machine <NUM>. This real-time output speed may be compared to a desired output speed pre-programmed into the database <NUM>. If the actual output speed is too high, or too low, the module <NUM> may cause the controller <NUM> to send a command signal (see arrow <NUM>) to the switch <NUM> to appropriately re-configure the coils <NUM> to achieve the desired speed.

Referring to <FIG> and <FIG>, another embodiment of an electromagnetic machine <NUM> is illustrated as an electric motor. The rotor <NUM> may be the dual rotor embodiment having the inner rotor segment <NUM> that carries a circumferentially continuous face <NUM> that faces radially inward and includes boundaries that radially define an inner cavity <NUM>. When the electromagnetic machine <NUM> is fully assembled, the inner rotor segment <NUM> is centered to axis A, the support structure <NUM> of the stator <NUM> is axially aligned to, and spaced radially outward from the inner rotor segment <NUM>, and the outer rotor segment <NUM> is axially aligned to, and spaced radially outward from the stator support structure <NUM>.

The support structure assembly <NUM> of the electromagnetic machine <NUM> may further include a stationary shaft <NUM> that is centered to axis A, located in the inner cavity <NUM>, generally axially aligned to the stator <NUM> and rotor <NUM>, and is spaced radially inward from the inner rotor segment <NUM>. The stationary shaft <NUM> may include opposite end portions <NUM>, <NUM> with the first end portion <NUM> engaged to the axial side <NUM> of the mount plate <NUM>, and the opposite end portion <NUM> generally engaged to, or supporting, the bearings <NUM>. The axial side <NUM> of the mount plate <NUM> may include boundaries that, at least in-part, axially defines the inner cavity <NUM>.

In one embodiment, the motor drive <NUM> may be located completely in the inner cavity <NUM> to optimize motor packaging. As illustrated in <FIG>, the motor drive <NUM> may be the example of a circuit board that is supported by the stationary shaft <NUM> between the opposite end portions <NUM>, <NUM>. In another embodiment, the motor drive <NUM> may be supported by the mount plate <NUM> with any one or more of the controller <NUM>, switch <NUM>, and other electronic elements <NUM> projecting from the mount plate <NUM> and into the inner cavity <NUM>. For purposes of this embodiment, the term 'electronic elements' may include the controller <NUM> and the switch <NUM>.

In one embodiment, the stationary shaft <NUM> may be hollow having at least one open end for the axial flow of the cooling air <NUM>. In one example, the hollow shaft <NUM> may communicate through the mount plate <NUM> of the support structure assembly <NUM>. In another embodiment, the mount plate <NUM> may be closed off at the end proximate to the mount plate <NUM> promoting further cooling air flow into the inner cavity <NUM>.

In one embodiment, the mount plate <NUM> and/or the stationary shaft <NUM> may be metallic to promote cooling of the motor drive <NUM> in the inner cavity <NUM> via convection (i.e., heat sinks). In another embodiment, the hollow, stationary, shaft <NUM> may include boundaries that define at least one opening <NUM> (e.g., hole) for the radially outward flow of the cooling air <NUM> from the hollow shaft <NUM>, and into the inner cavity <NUM>. The inner rotor segment <NUM>, the stator support structure <NUM>, and the outer rotor segment <NUM> each include a respective plurality of openings <NUM>, <NUM>, <NUM> (e.g., holes, also see <FIG>) for the radially outward flow of cooling air <NUM>. When the electromagnetic machine <NUM> is assembled, the inner cavity <NUM> is in fluid communication radially between the openings <NUM>, <NUM>, the opening(s) <NUM> is in fluid communication radially between the inner cavity <NUM> and the opening(s).

When the electromagnetic machine <NUM> is fully assembled, a rotating output shaft of the electromagnetic machine <NUM> may drive a motor fan as is known by one having skill in the art (not shown). The fan may drive the air axially and radially outward through the inner cavity <NUM>. In this way, the cooling air <NUM> may cool the motor drive <NUM> and the stator <NUM>.

Referring to <FIG>, another embodiment of the stator <NUM> is illustrated along with a method of manufacture. The support structure assembly <NUM> of the present embodiment may not include the plurality of bobbins <NUM> previously described, and the support structure <NUM> may not include the rings <NUM>, <NUM>. As best shown in <FIG>, each electric coil <NUM> may include an inner winding layer <NUM>, a plurality of mid-winding layers <NUM>, and an outer winding layer <NUM>, each electrically interconnected to form the coil <NUM>. The inner winding layer <NUM> is wound about, and radially spaced from, the centerline C, and includes boundaries that define the cooling opening <NUM>. The mid-winding layers <NUM> are located radially outward from the inner winding layer <NUM> with respect to centerline C, with each successive mid-winding layer located radially outward from the adjacent mid-winding layer. The outer winding layer <NUM> is located radially outward from the mid-winding layers <NUM>, and generally represents an outer periphery of the coil <NUM>.

Referring to <FIG>, generally, each of the winding layers <NUM>, <NUM>, <NUM> may include diametrically opposite axial segments <NUM>, <NUM>, and diametrically opposite circumferential segments <NUM>, <NUM>. The axial segment <NUM> extends between, and is formed into, first ends of the respective circumferential segments <NUM>, <NUM>, and the axial segment <NUM> extends between, and is formed into, opposite second ends of the respective circumferential segments <NUM>, <NUM>. When the stator <NUM> is assembled, the axial segments <NUM>, <NUM> may each substantially extend axially with respect to the rotation axis A, and the circumferential segments <NUM>, <NUM> may be arcuate, each extending circumferentially with respect to the rotation axis A.

The coil <NUM> may be further described having diametrically opposite portions <NUM>, <NUM> that may be substantially arcuate, and diametrically opposite portion <NUM>, <NUM> that may be substantially linear, or straight. Arcuate portion <NUM> may extend between, and generally forms into ends of the respective straight portions <NUM>, <NUM>, and the arcuate portion <NUM> may extend between, and generally forms into opposite ends of the respective straight portion <NUM>, <NUM>. Each portion <NUM>, <NUM>, <NUM>, <NUM> may include a respective plurality of the segments <NUM>, <NUM>, <NUM>, <NUM>. In another example, the coil <NUM> may be substantially circular or oval, thus the portions <NUM>, <NUM> may not be straight. Examples of a winding material, or shape, may be electrically conductive, profiled, wire, and tapes or ribbons that increase fill factors.

During manufacturing, each coil <NUM> may be wound about the centerline C, separately, and generally within a plane. That is, the portions <NUM>, <NUM> may initially be straight or flat, and without an arcuate shape. The wound coil <NUM> may then be bent to provide the arcuate shape of the portions <NUM>, <NUM>. Referring to <FIG>, and in one example, the un-bent coil <NUM> may be placed into a press, or similar tool, <NUM> to obtain the arcuate shape.

Referring to <FIG> and <FIG>, with the coils <NUM> fully formed, or shaped, each coil <NUM> may be circumferentially placed about the rotation axis A. When properly positioned, the axial segment <NUM> of a first coil <NUM> is located proximate to the axial segment <NUM> of a circumferentially adjacent second coil <NUM>. The coils <NUM> may then be secured to one-another utilizing a bonding material <NUM> while preserving the cooling openings <NUM>.

In one embodiment, the bonding material <NUM> may be applied while the coils <NUM> are properly orientated within a mold (not shown). Such a mold may support an injection molding process. Examples of the bonding material <NUM> may be an adhesive, thermoplastic, injection molding plastic, or other materials having electrically insulating properties.

Advantages and benefits generally specific to the molded stator may include the allowance of a reduced radial thickness of the stator, smaller air gaps, an increase in space that can be used for the coil, enabling the use of less expensive magnets as ferrites, enables direct cooling of coils, and a reduction in material costs with respect to the stator.

The electromagnetic machine <NUM> may be coreless, and may include the dual rotor <NUM>. The novel architecture of the electromagnetic machine <NUM>, as previously described, provides a structural solution for a wide range of applications including, but not limited to, a fan driving motor family covering different voltage inputs, shaft power, torque, and RPM. The architecture may be designed as an external rotor solution or a shaft driven solution.

The architecture may generally be of a modular design that simplifies manufacturing and maintenance. The electromagnetic machine architecture may utilize sintered magnets, or molded rotor structures. The architecture may further include back iron, or may benefit from a permanent magnet Halbach array arrangement, and use such as a structural component of the electromagnetic machine <NUM>.

Referring to <FIG>, an example of an external rotor solution is illustrated as a fan assembly <NUM> that includes the electromagnetic machine <NUM> as an electric motor, and a plurality of air foils, or blades, <NUM> projecting radially outward from the outer rotor segment <NUM> of the dual rotor <NUM>.

Advantages and benefits regarding the electromagnetic machine architecture include scalability to achieve desired torque and/or speed, a lack of cogging torque, a lack of core losses, less load on bearings, extended life, and the modular design. Another advantage is negligible magnetic pull forces, and thus a simplified support structure, low sensitivity to rotor imbalance, and/or rotor-to-stator misalignment.

Other general advantages and benefits of the present disclosure include a reduction in design and manufacturing costs, a single coil winding type for an entire family of motors, coil connections conducted on a circuit board, utilization of a circuit board as part of a structural member, optimized motor packaging, and improved stator and motor drive cooling. Other advantages include the ability to wind the coils individually, or separately, on a rotary winding machine during manufacture to achieve higher fill factors, and the use of bobbin mounting rings or clips for quick assembly of the stator. Yet another advantage is the ability to change coil configurations dynamically to meet, for example, the currently required speed of a fan to optimize the motor performance.

Claim 1:
An electric motor (<NUM>) comprising:
a rotor (<NUM>) adapted to rotate about a rotation axis (A);
a stator (<NUM>) axially aligned to the rotor and centered to the rotation axis, wherein the rotor is a dual rotor including an inner rotor segment (<NUM>) and an outer rotor segment (<NUM>) disposed radially outward from the inner rotor segment, and the inner rotor segment radially defines an inner cavity (<NUM>) axially aligned to the rotor and the stator;
a stationary shaft (<NUM>) disposed in the inner cavity, extending along the rotation axis, and spaced radially inward from the inner rotor segment;
a plate (<NUM>) axially defining the inner cavity; and
a motor drive (<NUM>) including electronic elements (<NUM>, <NUM>, <NUM>) disposed at least in-part in the inner cavity;
characterised in that
the plate (<NUM>) is a mounting plate attached to the stationary shaft and adapted to support the stator; and
the motor drive (<NUM>) is directly supported by the stationary shaft (<NUM>).