Patent Description:
The present invention is directed to providing a rotor assembly for an electric machine according to independent claim <NUM>.

Embodiments of the invention may be implemented in any environment using a synchronous electric machine or main machine, a specific example of which is a generator. The generator is currently contemplated to be implemented in a jet engine environment. Embodiments of the invention may alternatively include a starter/generator and may provide turbine engine starting capabilities, wherein the starter/generator provides the mechanical power to drive the turbine engine through a starting method. A brief summary of the contemplated generator environment should aid in a more complete understanding.

<FIG> illustrates an electric machine assembly <NUM> mounted on or within a gas turbine aircraft engine. The gas turbine engine may be a turbofan engine, such as a General Electric GEnx or CF6 series engine, commonly used in modern commercial and military aviation or it could be a variety of other known gas turbine engines such as a turboprop or turboshaft.

The electrical machine assembly <NUM> comprises a first machine <NUM> having an exciter rotor <NUM> and an exciter stator <NUM>, and a synchronous second machine <NUM> having a main machine rotor <NUM> and a main machine stator <NUM>. At least one power connection is provided on the exterior of the electrical machine assembly <NUM> to provide for the transfer of electrical power to and from the electrical machine assembly <NUM>. Power is transmitted by this power connection, shown as an electrical power cable <NUM>, directly or indirectly, to the electrical load and may provide for a three phase with a ground reference output from the electrical machine assembly <NUM>.

The electrical machine assembly <NUM> further comprises a rotatable shaft <NUM> mechanically coupled to a source of axial rotation, which may be a gas turbine engine, about an axis of rotation <NUM>. The rotatable shaft <NUM> is supported by spaced bearings <NUM>. The exciter rotor <NUM> and main machine rotor <NUM> are mounted to the rotatable shaft <NUM> for rotation relative to the stators <NUM>, <NUM>, which are rotationally fixed within the electrical machine assembly <NUM>. The stators <NUM>, <NUM> may be mounted to any suitable part of a housing portion of the electrical machine assembly <NUM>. The rotatable shaft <NUM> is configured such that mechanical force from a running turbine engine provides rotation to the shaft <NUM>. Alternatively, in the example of a starter/generator, rotation of the rotatable shaft <NUM> of the electrical machine assembly <NUM> during a starting mode produces a mechanical force that is transferred through the shaft <NUM> to provide rotation to the turbine engine.

The rotatable shaft <NUM> may further include a central coolant passage <NUM> extending axially along the interior of the shaft <NUM>. The central coolant passage <NUM> allows coolant, for example, oil or air, to flow through the interior of the rotatable shaft <NUM>. In the illustrated embodiment, the second machine <NUM> is located in the rear of the electric machine assembly <NUM> and the first machine <NUM> is positioned in the front of the electric machine assembly <NUM>. Other positions of the first machine <NUM> and the second machine <NUM> are envisioned.

<FIG> illustrates a perspective view of the main machine rotor assembly <NUM> according to the invention with at least a portion of the axial front end of the assembly <NUM> cut away. The rotor assembly <NUM> is shown comprising a core <NUM> having at least two posts <NUM> extending radially from the core <NUM>, about each of which a rotor winding <NUM>, which may be electrically isolated from each other, is wound to define a pole <NUM> for the assembly <NUM>. As shown, each of four poles <NUM> of the rotor assembly <NUM> includes one rotor winding <NUM>, wound axially about a post <NUM> to define a rotor winding set <NUM>. The core <NUM> is molded, formed, or bored from a non-laminated or non-lamination, solid or unitary body material. One such example of a core body material may be steel. Alternate body materials and formations of the core <NUM> are envisioned, for instance, using additive manufacturing.

According to the invention, each pole <NUM> of the rotor assembly <NUM> further comprises a cap <NUM>. The rotor assembly <NUM> further comprises additional radial elements <NUM> spaced radially about the assembly <NUM>, adjacent to, and in an alternating arrangement with, the multitude of caps <NUM>. Each cap <NUM> at least partially overlies each post <NUM>, pole <NUM>, and rotor winding set <NUM>, and is spaced from each adjacent cap <NUM> by the radial element <NUM>, such that the collective cap <NUM>, radial element <NUM>, and posts <NUM> of the core <NUM> define an axially extending winding slot <NUM> for receiving the rotor windings <NUM>.

Each cap <NUM> is formed or comprised by a plurality of laminations, for instance, cobalt laminations. In this instance, cobalt laminations may comprise the cap <NUM> due to its high magnetic and electrical resistance properties, and thus, its ability to minimize eddy currents at the surface of each pole <NUM>. Cobalt laminations are merely one example of a material used to construct the cap <NUM>, and alternate material composition or compositions are envisioned. Comparing the cap <NUM> to the core <NUM>, the cap <NUM> is less electrically conductive than the core <NUM> and may be less thermally conductive than the core <NUM>.

Each cap <NUM> is removably coupled with the posts <NUM> of the core <NUM> via an interlocking of the cap <NUM> with the posts <NUM>. As shown, the interlock comprises a projection <NUM> on the cap <NUM> and a recess <NUM> on the post <NUM>, wherein both the cap projection <NUM> and post recess <NUM> have partially circular, complementary cross sections, such that the projection <NUM> is received within the post recess <NUM> to removably couple the cap <NUM> to the post <NUM>. Alternatively, comparative examples not according to the invention are envisioned wherein the interlocking elements are reversed, for example, a projection <NUM> on the post <NUM>, and a recess <NUM> on the cap <NUM>.

According to the invention, the core <NUM> further defines internal coolant passages <NUM> on the posts <NUM>, located adjacent to, and extending axially in parallel with, the winding slots <NUM>, and radial coolant passages <NUM> extending radially from the center of the core <NUM> to each internal coolant passage <NUM>. The internal coolant passages <NUM> may be, for example, molded, formed, or bored into the core <NUM>, and are at least partially separated from the rotor windings <NUM> by, for instance, a thin portion of the post <NUM>, allowing for thermal transfer between the windings <NUM> and the coolant. The rotatable shaft <NUM> may additionally include a plurality of coolant passage holes <NUM> that are radially spaced about the shaft <NUM> such that they may align with radial coolant passages <NUM>, and may allow for coolant to flow from the central coolant passage <NUM> to and from the radial coolant passages <NUM>.

The assembled rotatable shaft <NUM> with coolant passage holes <NUM> and central coolant passage <NUM>, and core <NUM> with internal coolant passages <NUM> and radial coolant passages <NUM> defines a coolant path wherein coolant may fluidly traverse, flow, or be forcibly pumped from the coolant passage holes <NUM>, through the radial coolant passage <NUM>, to the internal coolant passage <NUM>, and returned to the central coolant passage <NUM>. The rear axial end of the rotor assembly <NUM> may comprise a duplicate set of coolant passage holes <NUM> and radial coolant passages <NUM> such that the coolant may traverse, flow, or be forcibly pumped axially along the central coolant passage <NUM> and internal coolant passages <NUM> to form a coolant loop. In this example, the entire coolant loop may be internal to the core <NUM>. Alternative flows, paths, and loops of the coolant through the coolant passage holes <NUM>, radial coolant passages <NUM>, and internal coolant passages <NUM>, and central coolant passage <NUM> are envisioned.

Turning now to <FIG>, the rotor assembly <NUM> is shown further comprising a second projection <NUM> on at least a portion of the post <NUM> that is keyed to be received in a second recess <NUM> of the radial element <NUM>. The second projection <NUM> and second recess <NUM> have similar cross sections such that the projection <NUM> is received within the recess <NUM> to removably couple the radial element <NUM> to the core <NUM>. Additionally, the radial element <NUM> is shown further abutting a biasing element, such as a wedge <NUM>, configured such that the coupling of the radial element <NUM> to the core <NUM> biases or secures the rotor windings <NUM> into the winding slot <NUM>. The biasing of the rotor windings <NUM> into the winding slot <NUM> ensures a physical contact between the windings <NUM> and slot <NUM>, which serves to enhance the thermal transfer via conduction. Alternative couplings are envisioned wherein removably coupling the compressive radial element <NUM> to the core <NUM> biases the rotor windings <NUM> into the winding slot <NUM>.

According to the invention, the core <NUM> further comprises a winding seat <NUM> at the interface of the rotor windings <NUM> and the posts <NUM>, for receiving the rotor windings <NUM>. The winding seat <NUM> may further comprise a thermally conductive, electrically isolating layer <NUM> separating the rotor windings <NUM> from the posts <NUM>. This thermally conductive layer <NUM> may be, for example, formed by a coating applied to the winding seat <NUM>. Alternative thermally conductive layer <NUM> formations and assemblies are envisioned, such as adhesion by glue, mechanical fastening, etc. Also as shown, the radial coolant passage <NUM> may further extend along a channel <NUM> of the winding seat <NUM>, wherein the channel <NUM> is not adjacent to the internal coolant passage <NUM>. Alternatively, the channel <NUM> may further comprise additional internal coolant passages <NUM> that run axially along the axis of rotation <NUM>, parallel to, or intersecting with the existing passages <NUM>.

<FIG> illustrates one embodiment of the core <NUM> of the rotor assembly <NUM> according to the invention with the cap <NUM>, radial elements <NUM>, rotor windings <NUM>, and other removable components detached.

During generating operation, the rotor assembly <NUM> is rotated about the axis of rotation <NUM> by a mechanical force, such as a turbine engine, coupled with the rotatable shaft <NUM>. During rotation, the rotor windings <NUM> are energized to create a pole <NUM>, for example, DC power from a rectified AC power output of the exciter rotor <NUM>. The rotation of the pole <NUM> relative to the main machine stator <NUM> generates a power output, such as an AC power output, which is then transmitted by the electrical power cable <NUM> to an electrical system, for instance, a power distribution node.

The DC current transmitted through the energized rotor windings <NUM> generates heat in the windings <NUM>. Since the core <NUM> is more thermally conductive than the cap <NUM>, a portion of the generated heat is transferred away from the rotor winding <NUM> via the thermally conductive layer <NUM> of the winding seat <NUM>, to the core <NUM>. Additionally, the wedges <NUM> bias the rotor windings <NUM> toward the winding seat <NUM> to ensure a firm thermal conduction interface between the windings <NUM> and the seat <NUM>.

The rotor assembly <NUM> is also configured to remove heat generated in the rotor windings <NUM>, as well as heat transferred to the core <NUM>, via the above described coolant paths and loops <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. For instance, the coolant traversing through the rotor assembly <NUM> may directly remove the heat generated by the rotor windings <NUM> via the thermally conductive layer <NUM> directly adjacent to the internal coolant passages <NUM>. In another instance, the heat generated may be first transferred to the core <NUM> as described above, and then transferred to the coolant via the coolant paths and loops <NUM>, <NUM>, <NUM>, <NUM>, <NUM>.

As the rotor assembly <NUM> rotates at the anticipated high rotations per minute (RPMs), the centrifugal forces tend to push the rotor windings <NUM> radially outward, which may create a gap between the thermally conductive layer <NUM> and the windings <NUM>. This thermal transfer by convection across the gap between the rotor windings <NUM> and the thermally conductive layer <NUM> is less effective, and thus, undesirable. The collective coupling of the cap <NUM>, the radial element <NUM>, and the wedges <NUM> to the rotor assembly <NUM> tend to oppose the centrifugal forces on the rotor windings <NUM>, and help improve the thermal transfer from the windings <NUM> to the coolant via conduction, by ensuring the winding <NUM> stays in place and in contact with the thermally conductive layer <NUM> of the winding seat <NUM>.

Additionally, during generating operation, the rotation of the rotor assembly <NUM> relative to the main machine stator <NUM> typically causes eddy current losses due to the changing magnetic field and/or magnetic flux harmonics in the air gap between the energized poles <NUM> and stator <NUM>. Since these eddy current losses occur mainly at or near the pole <NUM> surface, the losses may be minimized due to the lamination structure of the cap <NUM>, which is less electrically conductive, and thus less magnetically affected, by the losses. Fewer eddy current losses also results in less heat generated by the losses at or near the pole <NUM> surface.

During generating operation, the projection <NUM> and recess <NUM> also provides a secured interlocking of the cap <NUM> to the posts <NUM> and the core <NUM>. For instance, during rotation, centrifugal forces may attempt to separate the cap <NUM> from the posts <NUM> and core <NUM>. The interlocking of the cap <NUM> to the posts <NUM> and the core <NUM> by the interlocked projection <NUM> and the recess <NUM> prevents or retards this separation. Also, the interlocking of the cap <NUM> to the posts <NUM> and the core <NUM> provides an anti-rotation lock configured to retard the relative rotation of the cap <NUM> and the post <NUM>. The assembly of the radial elements <NUM> further support the anti-rotation lock configuration.

<FIG> illustrates an alternative rotor assembly <NUM> according to a second embodiment of the invention. The second embodiment is similar to the first embodiment; therefore, like parts will be identified with like numerals increased by <NUM>, with it being understood that the description of the like parts of the first embodiment applies to the second embodiment, unless otherwise noted. A difference between the first embodiment and the second embodiment is that each cap <NUM> alternatively comprises at least a partial trapezoidal projection <NUM> cross section. Correspondingly, the core <NUM> will have a complementary trapezoidal cross section in the recess <NUM> of the post <NUM> for removably coupling the cap <NUM> to the core <NUM>. Alternate trapezoidal, or otherwise interlocking cross sections, are envisioned.

<FIG> illustrates an alternative rotor assembly <NUM> according to a third embodiment of the invention. The third embodiment is similar to the first and second embodiments; therefore, like parts will be identified with like numerals increased by <NUM>, with it being understood that the descriptions of the like parts of the first and second embodiments apply to the third embodiment, unless otherwise noted. A difference between the third embodiment and the first and second embodiments is that each cap <NUM> further comprises at least a second projection, shown as a corner finger <NUM> spaced from and on each side of the projection <NUM>, extending from the cap <NUM>, and abutting the opposing corners of the post <NUM> of the core <NUM>. As illustrated, the corner fingers <NUM> have at least a partial trapezoidal cross section, but may have alternative cross sections for removably coupling to and/or interlocking with the core <NUM>. Correspondingly, the core <NUM> will have a complementary cross section in at least a second recess, such as a corner finger channel <NUM> of the post <NUM>.

Alternatively, embodiments are envisioned wherein the interlocking elements are reversed, for example, corner fingers <NUM> on the post <NUM>, and corner finger channels <NUM> on the cap <NUM>. Additionally, while two corner fingers <NUM> and corresponding corner finger channels <NUM> are shown, alternative numbers of corner fingers <NUM> and corresponding corner finger channels <NUM> are envisioned.

The corner fingers <NUM> may further provide secured interlocking of the cap <NUM> to the core <NUM> during generating operation. During rotation, centrifugal forces may attempt to separate the cap <NUM> ends, farthest from the pole <NUM>, from the posts <NUM> and core <NUM>. The additional interlocking of the cap <NUM> to the core <NUM> by the corner fingers <NUM> and corresponding corner finger channels <NUM> further secures the cap <NUM> ends, preventing separation. Also, the additional interlocking of the cap <NUM> to the core <NUM> by the corner fingers <NUM> and corresponding corner finger channels <NUM> provides an additional anti-rotation lock configured to retard the relative rotation of the cap <NUM> and post <NUM>.

<FIG> illustrates an alternative rotor assembly <NUM> according to a fourth embodiment of the invention. The fourth embodiment is similar to the first, second, and third embodiments; therefore, like parts will be identified with like numerals increased by <NUM>, with it being understood that the descriptions of the like parts of the first, second, and third embodiments apply to the fourth embodiment, unless otherwise noted. A difference between the fourth embodiment and the first, second, and third embodiments is that the corner fingers <NUM> of each cap <NUM> are spaced from and on each side of the projection <NUM>, extending from cap <NUM>, but not abutting the opposing corners of the post <NUM> of the core <NUM>. As illustrated, the corner fingers <NUM> have at least a partial trapezoidal cross section, but may have alternative cross sections for removably coupling to and/or interlocking with the core <NUM>. Correspondingly, the corner finger channel <NUM> of the post <NUM> will have a complementary cross section. Alternatively, embodiments are envisioned wherein the interlocking elements are reversed, for example, corner fingers <NUM> on the post <NUM>, and corner finger channels <NUM> on the cap <NUM>. Additionally, while two corner fingers <NUM> and corresponding corner finger channels <NUM> are shown, alternative numbers of corner fingers <NUM> and corresponding corner finger channels <NUM> are envisioned.

Many other possible embodiments and configurations in addition to that shown in the above figures are contemplated by the present disclosure. For example, one embodiment of the invention contemplates more of the electrical machine assembly <NUM> components mentioned, such as poles <NUM>, caps <NUM>, rotor windings <NUM>, etc. Another embodiment of the invention contemplates using wedges <NUM> configured on different sides of the rotor windings <NUM> to bias the windings <NUM> into the winding seats <NUM>. Alternatively, additional wedges <NUM> may be included to bias more than one side of the rotor windings <NUM> into the winding seats <NUM>. Another embodiment of the invention contemplates additional coolant passage holes <NUM> and radial coolant passages <NUM> spaced axially along the rotatable shaft <NUM>, such that additional coolant paths and/or loops may be utilized to improve cooling. Additionally, the design and placement of the various components may be rearranged such that a number of different in-line configurations could be realized.

In yet another embodiment of the invention, the rotor windings set <NUM> and winding seats <NUM> may be configured with, for instance a <NUM>° clockwise and counter-clockwise rotation, compared to the illustrated example. It is envisioned that, for instance, the rotor windings <NUM> on one side of the pole <NUM> may be configured in a counter-clockwise orientation, while the corresponding windings <NUM> on the opposing side of the pole may be configured in a clockwise orientation. In this example, each rotated rotor windings <NUM> may be held in place by one or more wedges <NUM>, to ensure thermal contact between the windings <NUM> and the winding seat <NUM>. Also, additional components such as the cap <NUM> and thermally conductive layer <NUM> may also include slightly angled surfaces to match the rotated rotor windings <NUM>. A <NUM>° counter-clockwise rotation is one example of a configuration, and other angles are envisioned in both a clockwise and counter-clockwise direction.

The embodiments disclosed herein provide a generator rotor with a cap and core assembly. One advantage that may be realized in the above embodiments is that the above described embodiments have significantly improved thermal conduction to remove heat from the assembly. The improved thermal conductivity of the core, compared to a core comprising laminated materials, coupled with the coolant paths and/or loops provide for heat removal in a much more effective fashion from the windings to the coolant. Another advantage of the above-mentioned examples, which are not part of the invention, is that the thermally conductive layer replaces the typical slot liner in the rotor in a way to provide improved mechanical integrity, along with improved thermal conductivity. The thermally conductive layer also replaces thermal conduction or cooling tubes and/or fins, reducing the number of parts, and thus increasing the reliability of the rotor assembly. The increased thermal dissipation of the rotor assembly allows for a higher speed rotation, which may otherwise generate too much heat. A higher speed rotation may result in improved power generation or improved generator efficiency without increasing generator size.

Yet another advantage of the above-mentioned examples, which are not part of the invention,
is that these examples
have significantly reduced manufacturing costs due to reduction in the amount of laminated materials, which are typically costly to produce, by replacing the core with a non-laminated material, which is typically less costly to produce. Additionally, by using a solid body core, costs can further be reduced by manufacturing processes such as boring, and auto-winding of the rotor windings. Furthermore, additional cooling tubes and fins may be eliminated from construction and assembly, wherein the prior process of welding the tubes to the assembly provided increases costs.

When designing aircraft components, important factors to address are size, weight, and reliability. The above described rotor assemblies have a decreased number of parts, making the complete system inherently more reliable. This results in possibly a lower weight, smaller sized, increased performance, and increased reliability system. The lower number of parts and reduced maintenance will lead to a lower product costs and lower operating costs. Reduced weight and size correlate to competitive advantages during flight.

To the extent not already described, the different features and structures of the various above-mentioned examples may be used in combination with each other as desired. That Thus, the various features of the different not claimed examples
may be mixed and matched as desired to form new embodiments, whether or not the new embodiments are expressly described. All combinations or permutations of features described herein are covered by this disclosure.

Claim 1:
A rotor assembly (<NUM>) for an electric machine, the rotor assembly (<NUM>) configured to rotate about an axis of rotation (<NUM>), the rotor assembly (<NUM>) comprising:
a core (<NUM>) being molded, formed, or bored from a non-laminated or non-lamination, solid or unitary body material, the core (<NUM>) having:
at least two posts (<NUM>) extending radially from the rotor core (<NUM>), and each post at least partially defining a winding seat (<NUM>) at an interface of a rotor winding (<NUM>) and the post (<NUM>); and
at least two recesses (<NUM>) positioned on and extending, based on the axis of rotation (<NUM>) of the rotor assembly (<NUM>), radially inward from a radially outer surface of each post (<NUM>);
the rotor assembly (<NUM>) further comprising:
at least two radial elements (<NUM>); and
at least two caps (<NUM>) formed by a plurality of laminations, and each cap (<NUM>) comprising at least one projection (<NUM>), each cap (<NUM>) being coupled to one of the at least two posts (<NUM>) when the at least one projection (<NUM>) is received within the respective recess (<NUM>), each cap (<NUM>) having a portion overlying the respective winding seat (<NUM>) to define an axially extending winding slot (<NUM>) with one of the at least two radial elements (<NUM>) and the respective post (<NUM>) of the core (<NUM>), wherein each radial element (<NUM>) is adjacent to a cap (<NUM>) and located circumferentially between two caps (<NUM>); and
the rotor winding (<NUM>) being wound about the respective post (<NUM>) and received by the respective winding seat (<NUM>) to define a pole (<NUM>) for the electric machine, wherein the rotor winding (<NUM>) overlies the respective post (<NUM>) and the projection (<NUM>) of the respective cap (<NUM>);
wherein the core (<NUM>) comprises at least one internal coolant passage (<NUM>) on each of the at least two posts (<NUM>) and at least one radial coolant passage (<NUM>), characterized by each internal coolant passage (<NUM>) having a radial coolant passage (<NUM>) radially extending to it from a center of the core (<NUM>); and
wherein the caps (<NUM>) are made from material that is less electrically conductive than the core (<NUM>).