Patent Description:
Electric machines such as interior permanent magnet (IPM) motors and/or generators have been widely used in a variety of applications including aircraft, automobiles and industrial usage. Therefore, a requirement for lightweight and high-power density IPM motors/generators has resulted in the design of higher speed motors and generators to maximize the power to weight ratio. Hence, a trend is increasing acceptance of IPM machines offering high machine speed, high power density, reduced mass and cost.

In a conventional IPM machine, multiple permanent magnets are embedded inside multiple laminations of a rotor. The mechanical stresses in the rotor are concentrated in multiple bridges and center posts. For higher speed applications, the thickness of the multiple bridges and center posts have to be increased for enhanced structural strength of the rotor and various other parts. The increased thickness leads to more magnet flux leakage into the multiple bridges and center posts, which leakage significantly reduces the machine power density, resulting in decreased efficiency of the machine because additional stator current is required. Further, in an application such as aircraft engines, such electric machines are disposed in a very harsh environment effected by hot gasses exiting the aircraft engine. Also, a space available to dispose such electric machines is limited in the aircraft engines.

<CIT> discloses a rotor assembly that has a rotor support hub which includes a plurality of first fir tree connection parts arranged about a periphery the rotor support hub. The rotor assembly further has a plurality of rotor segments each having a second connection part. Each of the second connection parts are cooperable with at least one of the plurality of first connection parts to connect each of the rotor segments about the periphery the rotor support hub. A plurality of fixing parts in the form of roll pins are each configured to be received between cooperating first and second connection parts and to form an inference fit there between so as to secure the rotor segments to the rotor support hub. Indentations may facilitate location of the pin. The rotor segments and support hub may comprise a plurality of laminations with the rotor hub being non-magnetic material. The pin may also be a rod, bar, cylinder, or prism and may be magnetic or non-magnetic.

<CIT> discloses a commutator-less direct current motor with a high-pole, permanent magnet.

<CIT> discloses a spoke rotor for an electrical machine, with a rotor shaft rotatable about a rotor axis, with a base body which is arranged concentrically about the rotor axis, and with a permanent magnet which is arranged in a recess of the base body like a spoke, the rotor shaft and / or a connecting sleeve arranged between the rotor shaft and the base body, with which the base body is fixed to the rotor shaft, are made from a diamagnetic material and / or from a paramagnetic material with a permeability number less than <NUM>.

<CIT> discloses an electric machine, such as an Internal Permanent magnet or Synchronous Reluctance machine, having X phases, that includes a stator assembly, having M slots, with a stator core and stator teeth, that is further configured with stator windings to generate a stator magnetic field when excited with alternating currents and extends along a longitudinal axis with an inner surface that defines a cavity; and a rotor assembly, having N poles, disposed within the cavity which is configured to rotate about the longitudinal axis, wherein the rotor assembly includes a shaft, a rotor core located circumferentially around the shaft. The machine is configured such that a value k = M / (X * N) wherein k is a non-integer greater than about <NUM>. The electric machine may alternatively, or additionally, include a non-uniformed gap between the exterior surface of the rotor spokes and the interior stator surface of the stator.

In accordance with the embodiment of the present specification, a turbo machine is presented comprising a turbine, a tail cone disposed downstream of the turbine, and the electric machine disposed inside the tail cone and mechanically coupled to the turbine. Wherein the electric machine includes a stator and a rotor disposed concentric to the stator. The rotor includes at least one rotor module. A rotor module of the at least one rotor module includes a rotor hub having a hub body, and a plurality of first protrusions and a plurality of second protrusions located alternatingly on a periphery of the hub body and protruding radially from the hub body, where one or more first protrusions of the plurality of first protrusions include an elongated portion and a head portion, and one or more second protrusions of the plurality of second protrusions include a wedge-shaped profile having a base portion and a top portion, wherein a width of the top portion is more than a width of the base portion. The rotor module further includes a magnetic core having a plurality of core members disposed on the rotor hub, where a core member of the plurality of core members is disposed between adjacent second protrusions of the plurality of second protrusions such that the head portion of the first protrusion located between the adjacent second protrusions engages with the core member, and each of the one or more second protrusions extends at least partially in a space between adjacent core members of the plurality of core members. Moreover, the rotor module includes a plurality of permanent magnets, where a permanent magnet of the plurality of permanent magnets is disposed in a space between the adjacent core members.

The rotor of the electric machine further comprises a non-magnetic insert disposed between the adjacent core members to retain the permanent magnet disposed in the space between the adjacent core members and the rotor hub is made of one or more non-magnetic materials.

These and other features, aspects, and advantages of the present specification will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:.

It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions may be made to achieve the developer's specific goals such as compliance with system-related and business-related constraints.

Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this specification belongs. The terms "first", "second", and the like, as used herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. Also, the terms "a" and "an" do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. The use of "including," "comprising" or "having" and variations thereof herein are meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The terms "connected" and "coupled" are not restricted to physical or mechanical connections or couplings, and can include electrical connections or couplings, whether direct or indirect.

As used herein, the terms "may" and "may be" indicate a possibility of an occurrence within a set of circumstances; a possession of a specified property, characteristic or function; and/or qualify another verb by expressing one or more of an ability, capability, or possibility associated with the qualified verb. Accordingly, usage of "may" and "may be" indicates that a modified term is apparently appropriate, capable, or suitable for an indicated capacity, function, or usage, while taking into account that in some circumstances, the modified term may sometimes not be appropriate, capable, or suitable.

As will be described in detail hereinafter, various embodiments of an electric machine are presented. The electric machine includes a stator and a rotor disposed concentric to the stator. The rotor includes at least one rotor module. A rotor module of the at least one rotor module includes a rotor hub having a hub body, and a plurality of first protrusions and a plurality of second protrusions located alternatingly on a periphery of the hub body and protruding radially from the hub body, wherein one or more first protrusions of the plurality of first protrusions include an elongated portion and a head portion, and one or more second protrusions of the plurality of second protrusions include a wedge-shaped profile. The rotor module further includes a magnetic core having a plurality of core members disposed on the rotor hub, wherein a core member of the plurality of core members is disposed between adjacent second protrusions of the plurality of second protrusions such that the head portion of the first protrusion located between the adjacent second protrusions engages with the core member, and each of the one or more second protrusions extends at least partially in a space between adjacent core members of the plurality of core members, and wherein the one or more second protrusions include a base portion and a top portion, wherein a width of the top portion is more than a width of the base portion. Moreover, the rotor module includes a plurality of permanent magnets, wherein a permanent magnet of the plurality of permanent magnets is disposed in a space between the adjacent core members.

Referring now to <FIG>, a cross-sectional perspective view of an electric machine <NUM> is presented, in accordance with one embodiment of the present specification. In <FIG>, reference numerals <NUM>, <NUM>, and <NUM> respectively represent a radial direction, an axial direction, and a tangential direction of the electric machine <NUM>. In some embodiments, the electric machine <NUM> may be configured to be operated as a generator, while in certain embodiments, the electric machine <NUM> may be configured to be operated as a motor, without limiting the scope of the present specification. For consistency of illustration, the electric machine <NUM> will be described as the generator in the description hereinafter.

As depicted in <FIG>, the electric machine <NUM> includes a stator <NUM> and a rotor <NUM>. Typically, the stator <NUM> includes a single-phase or multi-phase (e.g., three phase) stator winding (not shown). By way of example, in order to minimize coupling among phase windings in the stator winding, the stator winding may be arranged as a fractional slot concentrated tooth winding, in some embodiments. It will be appreciated that other types of stator winding arrangements, including but not limited to, integral slot distributed windings and/or fractional slot distributed windings, may also be employed without limiting the scope of the present specification.

The rotor <NUM> may be disposed concentric to the stator <NUM>. In the embodiment of <FIG>, the rotor <NUM> is shown as disposed concentrically inside the stator <NUM>. In certain other embodiments, a rotor may be disposed concentrically outside a stator with appropriate structural changes (see <FIG>, for example), as will be apparent to those skilled in the art.

Further, the rotor <NUM> may include at least one rotor module. In the embodiment of <FIG>, the rotor <NUM> is shown to include a single rotor module <NUM>. In such a configuration of the rotor <NUM> with the single rotor module <NUM>, an axial length of the rotor module <NUM> may be equal to or substantially equal to an axial length of the stator <NUM>. In some embodiments, the rotor <NUM> may include two or more rotor modules (see <FIG> and <FIG>, described later). In such a configuration of the rotor <NUM> with two or more rotor modules, an axial length of a stack of the rotor modules may be equal to or substantially equal to an axial length of the stator <NUM>.

In some embodiments, the rotor module <NUM> may include a rotor hub <NUM>, a magnetic core <NUM>, and a plurality of permanent magnets <NUM>. The rotor hub <NUM> may also be referred to as a rotor shaft. The rotor hub <NUM> may be formed using multiple laminations. In some other embodiments, the rotor hub <NUM> may be non-laminated.

In some embodiments, the rotor hub <NUM> is made of one or more magnetic materials. In some embodiments, the rotor hub <NUM> is made of one or more non-magnetic materials. Examples of the non-magnetic materials used to form the non-magnetic inserts <NUM> may include, but are not limited to, rubber, plastic, mica, stainless steel, or combinations thereof. Advantageously, use of the non-magnetic rotor-hub <NUM> enhances magnetic performance as non-magnetic material(s) of the rotor-hub <NUM> does not interfere with the operation of a magnetic circuit of the electric machine <NUM>. Therefore, in the description hereinafter the rotor hub <NUM> is described as non-magnetic rotor hub <NUM>.

The non-magnetic rotor hub <NUM> includes a hub body <NUM>, a plurality of first protrusions <NUM>, and a plurality of second protrusions <NUM>. The hub body <NUM> is an annular structure and the first protrusions <NUM> and the second protrusions <NUM> are formed on a periphery of the hub body <NUM>. Further, the first and second protrusions <NUM>, <NUM> protrude radially from the hub body <NUM>. In particular, as depicted in the embodiment of <FIG> where the rotor <NUM> is disposed concentrically inside the stator <NUM>, the first protrusions <NUM> and the second protrusions <NUM> are located on an outer periphery of the hub body <NUM>. Moreover, in the embodiment of <FIG>, the first protrusions <NUM> and the second protrusions <NUM> protrude radially outwardly from the hub body <NUM>. However, in some embodiments where the rotor <NUM> is disposed concentrically outside the stator <NUM>, the first protrusions <NUM> and the second protrusions <NUM> may be located on an inner periphery of the hub body <NUM> and protrude radially inwardly from the hub body <NUM>.

Further, in order to describe additional detailed information about a structure of the rotor <NUM>, <FIG> is described in conjunction with various enlarged views of portions of the rotor <NUM>, for example, using enlarged views shown in <FIG>. By way of example, <FIG> depicts an enlarged view <NUM> of a portion <NUM> of the rotor <NUM> of the electric machine <NUM> of <FIG>, in accordance with one embodiment of the present specification. Further, <FIG> is an enlarged view <NUM> of the portion <NUM> of the rotor <NUM> of the electric machine <NUM> of <FIG>, in accordance with another embodiment of the present specification. Furthermore, <FIG> is an enlarged view <NUM> of the portion <NUM> of the rotor <NUM> of the electric machine <NUM> of <FIG>, in accordance with another embodiment of the present specification. Moreover, <FIG> is an enlarged view <NUM> of a portion <NUM> of the rotor <NUM> of the electric machine <NUM> of <FIG>, in accordance with one embodiment of the present specification.

In some embodiments, as depicted in more details in the enlarged view <NUM> of <FIG>, one or more first protrusions of the plurality of first protrusions <NUM> includes an elongated portion <NUM> and a head portion <NUM>. The head portion <NUM> may include a bulged shape (as depicted in <FIG>), a plurality of teeth (not shown), or a combination thereof. In some embodiments, the plurality of teeth may also be formed on the elongated portion <NUM>. By way of example, the first protrusion <NUM> may have a shape similar to a Christmas tree.

Further, one or more second protrusions of the plurality of second protrusions <NUM> include a wedge-shaped profile. In particular, as shown in an expanded view <NUM> of a region <NUM> of the rotor module <NUM>, the wedge-shaped profile of the second protrusions <NUM> includes a base portion <NUM> and a top portion <NUM>. In accordance with aspects of the present specification, a width (Wtop) of the top portion <NUM> is more than a width (Wbase) of the base portion <NUM>. Advantageously, the alternating first and second protrusions <NUM>, <NUM> transfer the mass loading of the magnetic elements (e.g., the magnetic core <NUM> and/or the permanent magnets <NUM>) to the hub body <NUM>.

Moreover, the magnetic core <NUM> includes a plurality of core members <NUM>. The core members <NUM> are disposed on the non-magnetic rotor hub <NUM>, where a core member <NUM> of the plurality of core members <NUM> is disposed between adjacent second protrusions <NUM> of the plurality of second protrusions <NUM> such that the head portion <NUM> of the first protrusion <NUM> that is located between the adjacent second protrusions <NUM> engages with the core member <NUM>. Moreover, each of the one or more second protrusions <NUM> extends at least partially in a space between adjacent core members <NUM> of the plurality of core members <NUM>. Such an arrangement of the core members <NUM> and the first and second protrusions <NUM>, <NUM> creates a dynamic lock between the core members <NUM> and the second protrusions <NUM>. For example, during operation of the electric machine <NUM>, when radial forces are exerted on the core members <NUM>, the core members <NUM> tend to drift radially away from their positions. However, the head portion <NUM> of the first protrusions <NUM> may cause flaring/widening of legs <NUM> of the core members <NUM>. Such widening of the legs <NUM> further pushes the legs <NUM> toward side edges of the second protrusions <NUM>. Due to the wedge shape of the second protrusions <NUM>, a radial movement of the core members <NUM> may be restricted, thereby improving structural integrity of the rotor <NUM>. Advantageously, an additional rotor wrapping, which is traditionally being utilized to hold the magnetic members of a conventional rotor in place, is not required for the rotor <NUM>, in accordance with the aspects of the present specification. Also, lack of such additional rotor wrapping or layers of material not only reduces overall cost of materials but also result in a compact structure of the electric machine <NUM>.

In some embodiments, one or more core members <NUM> of the plurality of core members <NUM> of the magnetic core <NUM> have laminated structure. By way of example, as depicted in <FIG>, each core member <NUM> is shown to include four laminations 130a, 130b, 130c, and 130d. In some other embodiments, the core members <NUM> may include any number of laminations, without limiting the scope of the present specification. The laminations 130a-130d in each of the one or more core members <NUM> are stacked in the axial direction <NUM> of the electric machine <NUM>. It will be appreciated that the laminations 130a-130d are made from an appropriate magnetic steel to support the objective of high magnetic field in the air gap with an acceptable amount of loss within the rotor <NUM>. Non-limiting examples of the magnetic steel used to form the laminations 130a-130d may include silicon steel, nickel steel, or combinations thereof. Alternatively, the laminations 130a-130d may be formed using sintered magnetic composites, also known as soft magnetic composites (SMC). In some embodiments, the laminations 130a-130d may be heat-treated to provide continuous laminations of a bi-state magnetic material. Non-limiting examples of the bi-state magnetic material include dual phase ferromagnetic material with a composition of Iron (Fe), <NUM>% Chromium (Cr), <NUM>% Nickel (Ni), <NUM>% Aluminum (Al), <NUM>% Carbon (C). In other non-limiting example of the dual phase ferromagnetic material, Cobalt is added to increase the magnetization. In yet another non-limiting example of dual phase ferromagnetic material, chromium may be replaced by weaker carbide forms, such as Mn. This increases the magnetization and further reduces the thermal gradient required to create the dual-phase structure. In another embodiment, the laminations 130a-130d may be subjected to a localized surface treatment to form the non-ferromagnetic regions.

In certain embodiments, the one or more core members <NUM> of the plurality of core members <NUM> may have non-laminated structure, as depicted in <FIG>. For example, as shown in <FIG>, each of the core members <NUM> is formed of a piece of material that is non-laminated. Further, in certain other embodiments, while some of the core members <NUM> have laminated structure, the remaining core members <NUM> may have the non-laminated structure.

Additionally, the rotor module <NUM> includes the plurality of permanent magnets <NUM>. A permanent magnet <NUM> of the plurality of permanent magnets <NUM> is disposed in a space between the adjacent core members <NUM>. The permanent magnets <NUM> generate a magnetic field that is radially directed (i.e., in the rotor of <FIG>, <FIG>, and <FIG>) in an air gap between the rotor <NUM> and the stator <NUM>. The magnetic field generated by the permanent magnets <NUM> induces voltage in the stator winding disposed on the stator <NUM>. In particular, the permanent magnets <NUM> provide an arrangement, which is a dovetail spoke configuration, particularly well-suited for high-speed applications. The dovetail spoke configuration provides for superior magnetic flux-concentration effects, thereby enhancing the power density of the electric machine <NUM>. The permanent magnets <NUM> may be made of materials, including but not limited to, neodymium-iron-boron, samarium-cobalt, or ferrite, or alnico. Further, although thirty permanent magnets <NUM> are shown in the embodiment of <FIG>, any suitable number of permanent magnets may be used in the rotor <NUM>, without limiting the scope of the present specification.

In some embodiments, the plurality of permanent magnets <NUM> may be disposed in the spaces between adjacent core members <NUM> such that the plurality of permanent magnets <NUM> is magnetized in the tangential direction <NUM> of the electric machine <NUM>, as shown in <FIG>, <FIG>, and <FIG>. As depicted in <FIG>, <FIG>, and <FIG>, the north and south poles of the permanent magnets <NUM> are oriented along the tangential direction <NUM> of the electric machine <NUM>. For example, in the embodiments of <FIG>, the permanent magnets <NUM> are arranged such that magnet poles having like polarity face each other with the corresponding core member <NUM> therebetween. Advantageously, such arrangement of the permanent magnets <NUM> forces the magnetic field from the permanent magnets <NUM> out through radial faces of the core member <NUM> into an air gap between the rotor <NUM> and the stator <NUM> where the magnetic field can interact with the magnetic field produced by the stator windings. Alternatively, in the embodiment of <FIG> and <FIG>, the permanent magnets <NUM> are arranged such that opposite poles of the permanent magnets <NUM> face each other with the corresponding core member <NUM> therebetween.

In certain embodiments, as depicted in <FIG>, the plurality of permanent magnets <NUM> may be disposed in the spaces between adjacent core members <NUM> such that the plurality of permanent magnets <NUM> is magnetized in the radial direction <NUM> of the electric machine <NUM>. In such a configuration of the rotor module <NUM>, the poles of the permanent magnets <NUM> are aligned along the radial direction <NUM> of the electric machine <NUM>.

Further, in certain embodiments, as depicted in various drawings the core members <NUM> are designed such that the spaces between adjacent core members <NUM> have a Diamond-like shape. Advantageously, such Diamond-like shaped spaces retain the permanent magnets <NUM> in place against the radial forces during operation of the electric machine <NUM>. Additionally, in some embodiments, the rotor <NUM> may include a plurality of non-magnetic inserts <NUM> to further ensure retention of the permanent magnets <NUM>. The non-magnetic inserts <NUM> may be disposed such that one non-magnetic insert <NUM> is disposed between the adjacent core members <NUM> toward one end of the corresponding permanent magnet <NUM> to retain the permanent magnet <NUM> in the space between the adjacent core members <NUM> against radial forces caused due to rotations of the rotor <NUM> during the operation of the electric machine. Examples of non-magnetic materials used to form the non-magnetic inserts <NUM> may include, but are not limited to, rubber, plastic, mica, stainless steel, or combinations thereof. In some embodiments, the non-magnetic inserts <NUM> may also be formed using one or more dual-phase materials, in which case the inserts <NUM> can bridge the core members <NUM>.

Referring now to <FIG>, a perspective view <NUM> of a rotor <NUM>, in accordance with one embodiment of the present specification. As previously noted, the rotor <NUM> of the electric machine <NUM> may include two or more rotor modules. The rotor <NUM> of <FIG>, represents one such embodiment of the rotor <NUM>. As depicted in <FIG>, the rotor <NUM> is shown to include eleven rotor modules 604a through <NUM>. The rotor modules 604a-<NUM> are stacked the axial direction <NUM> the electric machine (e.g., the electric machine <NUM>) in a non-skewed configuration as shown in <FIG>. For example, the rotor modules 604a-<NUM> may be stacked in the axial direction <NUM> such that the non-magnetic insert <NUM> of all the rotor modules 604a-<NUM> are aligned with each other. However, in certain embodiments, the rotor modules 604a-<NUM> may be stacked the axial direction <NUM> in a skewed configuration as shown in <FIG>, in accordance with one embodiment of the present specification. For example, as depicted a rotor configuration <NUM> of <FIG>, each rotor module is displaced by a fixed angle from an adjacent rotor module in a single direction (e.g., in a clockwise direction). In certain embodiments, the rotor modules may also be displaced by an irregular angle from adjacent rotor modules. In another example configuration <NUM> of <FIG>, the rotor modules are shown as skewed in a symmetrical fashion with respect to the middle rotor module 604F. In general, the rotor configurations <NUM> and <NUM> depicts a stepped skewing of the rotor modules 604a-<NUM>. Whereas, a rotor configuration <NUM> of <FIG>, depicts a sinusoidal skewing of the rotor modules 604a-<NUM>. It will be appreciated that other type of skewing arrangements that are different than those depicted in <FIG> may also be employed without limiting the scope of the present specification. Advantageously, skewing arrangements as depicted in <FIG>, aids in reducing cogging torque and electromagnetic torque ripples in the electric machine <NUM>.

The electric machine <NUM> of <FIG> is suitable for use in applications including, but not limited to, automobiles, various industrial machines, turbo machines used in aircraft engines, or combinations thereof. By way of non-limiting example, <FIG> represents a cross-sectional perspective view of a turbo machine <NUM> having an electric machine, for example, the electric machine <NUM> of <FIG>, in accordance with one embodiment of the present specification. In <FIG>, reference numerals <NUM> and <NUM> respectively represent an axial direction and a radial direction of the turbo machine <NUM>. Further, a reference numeral <NUM> represents a centerline of the turbo machine <NUM>.

In some embodiments, the turbo machine <NUM> may include a fan <NUM>, a low-pressure compressor (LPC) <NUM>, a high-pressure compressor (HPC) <NUM>, a combustor assembly <NUM>, a high-pressure turbine (HPT) <NUM>, a low-pressure turbine (LPT) <NUM>, and a tail cone <NUM>, arranged serially in the axial direction <NUM> of the turbo machine <NUM>, as depicted in <FIG>. The LPC <NUM> is coupled to the LPT <NUM> via a first shaft <NUM>. The HPC <NUM> is coupled to the HPT <NUM> via a second shaft <NUM> that is arranged concentric to the first shaft <NUM>. In some embodiments, the LPC <NUM>, the HPC <NUM>, the HPT <NUM>, and/or the LPT <NUM> may include a plurality of stages (not shown). Each stage may include a plurality of blades (not shown) mounted on the respective shafts <NUM>, <NUM>.

During operation of the turbo machine <NUM>, the fan <NUM> diverts a portion of fluid (e.g., air) toward the LPC <NUM>. The LPC <NUM> compresses the incoming fluid and directs the compressed fluid to the HPC <NUM>. The HPC <NUM> further compresses the fluid received from the LPC <NUM> and discharges the compressed fluid to the combustor assembly <NUM>. The compressed fluid is mixed with one or more fuels in the combustor assembly <NUM>. Subsequently, the mixture of the compressed fluid and the one or more fuels is combusted within the combustor assembly <NUM> to form a combustion gas. The combustion gas is discharged from the combustor assembly <NUM> to the turbines <NUM>, <NUM>. The combustion gas is expanded in the HPT <NUM> and the LPT <NUM> thereby rotating the HPT <NUM> and the LPT <NUM>.

In accordance with the aspects of the present specification, the electric machine <NUM> of <FIG> may be disposed inside the tail cone <NUM>. However, in certain other embodiments, the electric machine <NUM> may alternatively or additionally be disposed at various locations in the turbo machine <NUM> of <FIG> without limiting the scope of the present specification. The electric machine <NUM>, when disposed in the tail cone <NUM>, may be operated as a generator or motor.

In some embodiments, the electric machine <NUM> may be mechanically coupled to the LPT <NUM>. In particular, a hub body <NUM> of the rotor <NUM> may be mechanically coupled to the LPT <NUM> via the first shaft <NUM>. Consequently, the rotations of the LPT <NUM> results in the rotations of the rotor <NUM> of the electric machine <NUM>. In some embodiments, the hub body <NUM> of the rotor <NUM> of the electric machine <NUM> is directly coupled to the first shaft <NUM>. Accordingly, the rotor <NUM> of the electric machine <NUM> may rotate at a rotational speed of the first shaft <NUM>.

In certain other embodiments (see <FIG>), to reduce a torque requirement of an electric machine, e.g., the electric machine <NUM>, the turbo machine <NUM> may include a gear box that may be connected to the rotor <NUM> of the electric machine <NUM> and the first shaft <NUM>. As will be appreciated the gear box may be used to control rotational speed of the rotor of the electric machine <NUM>. In particular, the gearbox increases the rotational speed of the electric machine, thereby reducing the torque required of the electric machine.

Referring now to <FIG>, a cross-sectional view <NUM> of a portion of a turbo machine, for example, the turbo machine <NUM> is presented in accordance with one embodiment of the present specification. As depicted in <FIG>, the rotor <NUM> of the electric machine <NUM> and is coupled to the first shaft <NUM> via a gear box <NUM>. In the embodiment of <FIG>, the gear box <NUM> is disposed axially between the LPT <NUM> and the electric machine <NUM>. In particular, the gear box <NUM> is connected axially between the first shaft <NUM> and the rotor <NUM> of the electric machine <NUM>. In some embodiments, during operation of the turbo machine <NUM>, the gear box <NUM> increases the rotational speed of the electric machine <NUM>, thereby reducing a torque required of the electric machine <NUM>.

Moving now to <FIG>, a portion <NUM> of a turbo machine, for example, the turbo machine <NUM> is presented in accordance with one embodiment of the present specification. In particular, <FIG> depicts an electric machine <NUM> that is one embodiment of the electric machine <NUM> of <FIG> however, with an inverted configuration. For example, the electric machine <NUM> includes a stator <NUM> and rotor <NUM>, where the rotor <NUM> is disposed concentrically outside the stator <NUM>. As will be appreciated, the rotor <NUM> may have a configuration similar to the rotor <NUM> of <FIG> with appropriate modifications to achieve such inverted configuration. In some embodiments, the electric machine <NUM> may be connected to a structure of the turbo machine <NUM> via a stator support mount <NUM>.

Further, the rotor <NUM> of the electric machine <NUM> is coupled to the first shaft <NUM> via a gear box <NUM>. The gear box <NUM> may be connected to a structure of the turbo machine via a gear shaft support mount <NUM>. In the embodiment of <FIG>, the gear box <NUM> is disposed aft of the electric machine <NUM>. In particular, the gear box <NUM> is connected to the first shaft <NUM> via a passage within the electric machine <NUM>. As shown in <FIG>, the gear box <NUM> is connected to the rotor <NUM> at the aft side. Further, the gear box <NUM> is coupled to the first shaft <NUM> via a gear shaft <NUM> that passes through the stator <NUM>. In some embodiments, during operation of the turbo machine <NUM>, the gear box <NUM> increases the rotational speed of the electric machine <NUM>, thereby reducing a torque required of the electric machine <NUM>.

In accordance with aspects of the present application, the electric machine <NUM>, <NUM> provides a compact structure in comparison to traditional electric machines with the conventional rotors. Such compact structure is achieved at least partially due to features such as the first and second protrusions <NUM>, <NUM> in the rotor <NUM>. In particular, the arrangement of the core members <NUM> and the first and second protrusions <NUM>, <NUM> creates a dynamic lock between the core members <NUM> and the second protrusions <NUM> when radial forces are exerted on the core members <NUM>, the core members <NUM>. Due to the wedge shape of the second protrusions 118f, a radial movement of the core members <NUM> may be restricted, thereby improving structural integrity of the rotor <NUM>. Advantageously, an additional rotor wrapping, which is traditionally being utilized to hold the magnetic members of a conventional rotor in place, is not required for the rotor <NUM>, in accordance with the aspects of the present specification. Also, the lack of such additional rotor wrapping or layers of material not only reduces overall cost of materials but also result in a compact structure of the electric machine <NUM>. Further, such compact structure makes the electric machine <NUM>, <NUM> suitable for use in places such as tail cone <NUM> in the turbo machine, such as the turbo machine <NUM>. Moreover, the permanent magnets <NUM> provide an arrangement, which is a dovetail spoke configuration, particularly well-suited for high-speed applications. The dovetail spoke configuration provides for superior magnetic flux-concentration effects, thereby enhancing the power density, and hence, an efficiency of the electric machine <NUM>, <NUM>.

Claim 1:
A turbo machine (<NUM>), comprising:
a turbine (<NUM>, <NUM>);
a tail cone (<NUM>) disposed downstream of the turbine; and
an electric machine (<NUM>, <NUM>) disposed inside the tail cone (<NUM>) and mechanically coupled to the turbine;
wherein the electric machine (<NUM>, <NUM>) comprises:
a stator (<NUM>, <NUM>); and
a rotor (<NUM>, <NUM>, <NUM>) disposed concentric to the stator (<NUM>, <NUM>), the rotor (<NUM>, <NUM>, <NUM>) comprising at least one rotor module (<NUM>), wherein a rotor module (<NUM>) of the at least one rotor module (<NUM>) comprises:
a rotor hub (<NUM>) comprising:
a hub body (<NUM>); and
a plurality of first protrusions (<NUM>) and a plurality of second protrusions (<NUM>) formed alternatingly on a periphery of the hub body (<NUM>) and protruding radially from the hub body (<NUM>), wherein each first protrusion (<NUM>) of the plurality of first protrusions (<NUM>) comprises an elongated portion (<NUM>) and a head portion (<NUM>), and each second protrusion (<NUM>) of the plurality of second protrusions (<NUM>) comprises a wedge-shaped profile having a base portion (<NUM>) and a top portion (<NUM>), wherein a width of the top portion (<NUM>) is more than a width of the base portion (<NUM>);
the rotor module (<NUM>) of the at least one rotor module (<NUM>) further comprising;
a magnetic core (<NUM>) comprising a plurality of core members (<NUM>) disposed on the rotor hub (<NUM>), wherein a core member (<NUM>) of the plurality of core members (<NUM>) is disposed between adjacent second protrusions (<NUM>) of the plurality of second protrusions (<NUM>) such that the head portion (<NUM>) of the first protrusion (<NUM>) located between the adjacent second protrusions (<NUM>) engages with the core member (<NUM>), and each of the one or more second protrusions (<NUM>) extends at least partially in a space between adjacent core members (<NUM>) of the plurality of core members (<NUM>);
a plurality of permanent magnets (<NUM>), arranged in a dovetail spoke configuration, wherein a permanent magnet (<NUM>) of the plurality of permanent magnets (<NUM>) is disposed in a space between the adjacent core members (<NUM>);
wherein the rotor (<NUM>, <NUM>, <NUM>) further comprises a non-magnetic insert (<NUM>) disposed between the adjacent core members (<NUM>) to retain the permanent magnet (<NUM>) disposed in the space between the adjacent core members (<NUM>); and
wherein the rotor hub (<NUM>) is made of one or more non-magnetic materials.