Patent Application
20180205302
The subject matter disclosed herein relates to permanent magnet (PM) brushless machines and, more particularly, to PM brushless machines with an outer rotor having certain dimensional features.
An electric motor is an electrical machine that converts electrical energy into mechanical energy. Generally, an electric motor that is configured as a PM brushless machine can include a rotor that rotates about its longitudinal axis, a stator that includes teeth about which conductive windings are wound and an air gap defined between the rotor and the stator. In normal motoring modes, most electric motors operate through the interaction between an electric motor's magnetic field and winding currents to generate force within the motor. That is, current applied to the conductive windings generates a magnetic flux that interacts with permanent magnets installed in the rotor to cause the rotor to rotate.
PM brushless machines are one type of electric motor and tend to have the highest power density, the highest efficiency and the best dynamic performance of all standard electric motors or machines. On the other hand, PM brushless machines are often expensive machines and produce cogging torque if the stator has slots for a winding. The cogging torque results from interactions of the rotor on the stator slot openings at a zero current state.
According to one aspect of the disclosure, an electric machine is provided and includes a stator that includes teeth, conductive windings configured to be wound about the teeth and a rotor rotatable about the stator. The rotor includes an annular core defining first slots along a circumferential dimension and one or more second slots along the circumferential dimension between neighboring first slots, permanent magnets disposable in the first slots and cage windings disposable in the second slots.
In accordance with additional or alternative embodiments, the rotor includes laminations of steel or soft magnetic composites and the cage windings include one or more of copper, aluminum and brass.
In accordance with additional or alternative embodiments, pairs of second slots are defined along the circumferential dimension between pairs of neighboring first slots.
In accordance with additional or alternative embodiments, a first distance between the permanent magnets and an outer diameter of the annular core is greater than a second distance between the permanent magnets and an inner diameter of the annular core and a third distance between the permanent magnets and a nearest one of the second slots is less than or equal to the second distance.
In accordance with additional or alternative embodiments, the second distance is about 0.5 to 2 mm, inclusively, and the third distance is less than or equal to 1.5 mm.
In accordance with additional or alternative embodiments, the electric machine further includes cage winding end rings.
In accordance with additional or alternative embodiments, the electric machine further includes cage winding end ring segments.
In accordance with additional or alternative embodiments, the first slots and the permanent magnets have at least one of inner and outer curvatures.
According to another aspect of the disclosure, an electric machine is provided and includes a stator that includes teeth, conductive windings configured to be wound about the teeth and a rotor rotatable about the stator. The rotor includes an annular core defining first slots along a circumferential dimension and one or more second slots along the circumferential dimension between neighboring first slots, permanent magnets disposable in the first slots and cage windings disposable in the second slots. A first distance between the permanent magnets and an outer diameter of the annular core being greater than a second distance between the permanent magnets and an inner diameter of the annular core and a third distance between the permanent magnets and a nearest one of the second slots being less than or equal to the second distance.
In accordance with additional or alternative embodiments, the rotor includes laminations of steel or soft magnetic composites and the cage windings include one or more of copper, aluminum and brass.
In accordance with additional or alternative embodiments, pairs of second slots are defined along the circumferential dimension between pairs of neighboring first slots.
In accordance with additional or alternative embodiments, the second distance is about 0.5 to 2 mm, inclusively, and the third distance is less than or equal to 1.5 mm.
In accordance with additional or alternative embodiments, the electric machine further includes cage winding end rings.
In accordance with additional or alternative embodiments, the electic machine further includes cage winding end ring segments.
According to yet another aspect of the disclosure, an electric machine is provided and includes a stator that includes a hub and teeth extending radially outwardly from the hub, conductive windings wound about the teeth and a rotor. The rotor is disposed to rotate about an air gap defined about the stator. The rotor includes an annular core formed to define first slots along a circumferential dimension and one or more second slots along the circumferential dimension between neighboring first slots, permanent magnets disposed in the first slots and cage windings disposed in the second slots. A first distance between respective outer edges of the permanent magnets and an outer diameter of the annular core is greater than a second distance between respective inner edges of the permanent magnets and an inner diameter of the annular core and a third distance between respective lateral edges of the permanent magnets and a nearest one of the second slots is less than or equal to the second distance.
In accordance with additional or alternative embodiments, the rotor includes laminations of steel or soft magnetic composites and the cage windings include one or more of copper, aluminum and brass.
In accordance with additional or alternative embodiments, pairs of second slots are defined along the circumferential dimension between pairs of neighboring first slots.
In accordance with additional or alternative embodiments, the second distance is about 0.5 to 2 mm, inclusively, and the third distance is less than or equal to 1.5 mm.
In accordance with additional or alternative embodiments, the electric machine further includes cage winding end rings.
In accordance with additional or alternative embodiments, the electric machine further includes cage winding end ring segments.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
The subject matter, which is regarded as the disclosure, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the disclosure are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
The detailed description explains embodiments of the disclosure, together with advantages and features, by way of example with reference to the drawings.
As will be described below, a permanent magnet (PM) brushless machine is provided. The PM brushless machine is relatively cost effective, produces very low cogging torque and is relatively easy to manufacture. When it is operated as a motor, the PM brushless machine produces starting asynchronous torque.
With reference to
As shown in
The rotor 40 is disposed to rotate about the central longitudinal axis A and is separated from the stator 20 by an air gap 50, which is defined about an outermost diameter of the stator 20. That is, an inner diameter 41 (see
The conductive material of the cores 31 of the conductive windings 30 may be formed of an electrically conductive material, such as a metal or a metallic alloy. In accordance with embodiments, the electrically conductive material may be copper. In accordance with further embodiments, the electric machine 10 has a reduced amount and volume of such copper. In some cases, the reduction may approach 50%. This is at least partially achieved by arranging the stator 20 as an inner stator and the rotor 40 as an outer rotor and by shortening the end turns of the conductive windings 30, which are provided at opposite longitudinal ends of the electric machine 10. The shortened end turns result from the stator 20 providing a relatively short coil pitch.
The rotor 40 may be formed of laminations 42 (see
As shown in
In accordance with embodiments, at least a pair of second slots 70 may be defined between each neighboring pair of first slots 60. Thus, for the case of the annular core 43 being formed to define eight first slots 60, as shown in
In accordance with further embodiments and with continued reference to
In operation, an electric current is applied to the conductive windings 30 to generate a magnetic flux in accordance with the number of turns of the conductive windings and the magnitude and voltage of the electric current. This magnetic flux interacts with the permanent magnets 44 and drives rotations of the rotor 40 about the central longitudinal axis A. During start-up procedures, since the electric machine 10 is not self-starting, current is induced in the cage windings 45 in order to generate an asynchronous torque which drives rotations of the rotor 40 until the rotor gets up to synchronous speed.
The permanent magnets 44 define poles of the electric machine 10 and are provided with alternating north and south polarities that are aligned with the radial dimension of the electric machine 10. That is, the permanent magnet 44 at the top of the image in
In accordance with embodiments, a first distance Da is defined between respective outer edges 440 of the permanent magnets 44 and the outer diameter 46 and is greater than a second distance Db, which is defined between respective inner edges 441 of the permanent magnets 44 and the inner diameter 41. In addition, a third distance Dc is defined between respective lateral edges 442 of the permanent magnets 44 and a nearest one of the second slots 70 and is less than or equal to the second distance Db. With such dimensions, the portions of the rotor 40 between first slots 60 and second neighboring slot 70 are highly saturated which minimizes the leakage flux between permanent magnets of different polarity and prevents deterioration of overall machine performance. In accordance with further embodiments, the second distance Db may be about 0.5 mm to about 2 mm, inclusively, and the third distance Dc may be less than or equal to about 1.5 mm.
With reference to
In accordance with further embodiments and, with reference to
With the various configurations described above, the electric machine 10 provides for a relative reduction of copper for armature or conductive windings 30 of up to 50%, an application of the cage windings 45 that naturally minimizes the leakage flux between neighboring permanent magnets 44, a substantial reduction of cogging torque by application of wide pole shoes (i.e., the first slots 60) for the permanent magnets 44, an option for replacement of rare-earth magnets with inexpensive or cheap ferrite magnets, a lower volume envelope as compared to standard PM brushless machines and stable operation as a generator due to the cage windings 45 being capable of damping oscillations due to variable loads. Overall, the electric machine 10 is relatively lightweight and of simple construction and thus may be usable in aerospace applications, for example, such as actuators, fans, air conditioning systems, nitrogen production systems, ram air turbine generators, etc. In addition, due to the high moment of inertia of the rotor 40, the electric machine 10 can be also used as integrated starter generator in land vehicles or electrical machines for flywheel energy storage systems.
While the disclosure is provided in detail in connection with only a limited number of embodiments, it should be readily understood that the disclosure is not limited to such disclosed embodiments. Rather, the disclosure can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the disclosure. Additionally, while various embodiments of the disclosure have been described, it is to be understood that the exemplary embodiment(s) may include only some of the described exemplary aspects. Accordingly, the disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
