ROTOR FOR A PERMANENT MAGNETIC ELECTRIC MACHINE

Abstract

A rotor assembly for an electric machine comprises first laminates, second laminates, and a rotor shaft, wherein the first laminates and the second laminates are stacked on the rotor shaft. Each of the first laminates comprises a first inner section and a plurality of first outer sections, wherein the first inner section and the first outer sections define a plurality of first cavities, the plurality of first outer sections being attached to the first inner sections by a plurality of bridges. Each of the second laminates comprises a second inner section and a plurality of second outer sections. The second inner section and the plurality of second outer sections delimit multiple second cavities, the second outer sections being attached to the second inner sections by multiple second webs and having no bridges.

Description

INTRODUCTION

[0001] Electric motor / generators, including internal permanent magnet (IPM) electric machines, can be used as torque-generating devices in vehicles. However, high-speed IPM rotors with retaining sleeves generally suffer from lower torque density compared to non-sleeved rotors because the air gap between a rotor assembly and a stator is effectively increased by the presence of the retaining sleeve.

[0002] A rotor assembly for an IPM electric machine includes a laminate stack having a plurality of magnetic pole sections created by permanent magnets inserted into and secured within a plurality of cavities formed in the laminate stack. The laminates of the laminate stack include web portions and bridges to provide structural and mechanical integrity near the plurality of cavities. In some embodiments, the webs may be removed to reduce flux leakage and compensate for lower torque. However, the webs are retained to maintain the integrity of the laminations, which leads to flux leakage. The thickness of the bridges and / or webs may be determined by manufacturing capabilities rather than centrifugal loading at high speeds.

[0003] It can be advantageous to have electric machines with increased torque density, increased power density, increased high-speed performance, and other performance characteristics that minimize flux leakage, improve thermal management, fit within available packaging, and / or reuse part or component designs to minimize engineering effort and design validation. DESCRIPTION

[0004] The concepts described herein provide a permanent magnet electric machine with a rotor assembly that advantageously reduces flux leakage by removing bridges in at least a portion of the laminations forming the rotor assembly. This can serve to increase torque density and power density compared to similarly designed electric machines that have bridges in all laminations forming the rotor assembly.

[0005] One aspect of the disclosure may include a rotor assembly for an electric machine including a plurality of first disc-shaped laminates, a plurality of second disc-shaped laminates, a rotor shaft, a shroud, and a plurality of permanent magnets, wherein the plurality of first disc-shaped laminates and the plurality of second disc-shaped laminates are arranged in a stack on the rotor shaft. Each of the plurality of first disc-shaped laminates includes a first inner portion and a plurality of first outer portions, the first inner portion and the plurality of first outer portions defining a plurality of first cavities, the plurality of first outer portions being attached to the first inner portions via a plurality of bridges.Each of the plurality of second disc-shaped laminates comprises a second inner portion and a plurality of second outer portions, the second inner portion and the plurality of second outer portions forming a plurality of second cavities, the plurality of second outer portions being attached to the second inner portions via a plurality of second webs and without a bridge.

[0006] Another aspect of the disclosure may include aligning the plurality of first disc-shaped laminates with the plurality of second disc-shaped laminates such that the plurality of first cavities are aligned with the plurality of second cavities to form a plurality of axially disposed cavities, the plurality of axially disposed cavities defining a plurality of magnetic pole portions that are radially disposed.

[0007] Another aspect of the disclosure may include the plurality of permanent magnets being arranged in the plurality of axially arranged cavities.

[0008] Another aspect of the disclosure may be that the plurality of axially disposed cavities define a plurality of prisms arranged in a single V arrangement for each of the plurality of magnetic pole sections.

[0009] Another aspect of the disclosure may be that the plurality of axially disposed cavities define a plurality of prisms arranged in a double-V arrangement for each of the plurality of magnetic pole sections.

[0010] Another aspect of the disclosure may be that the plurality of axially arranged cavities define a plurality of prisms arranged in a U-arrangement for each of the plurality of magnetic pole sections.

[0011] Another aspect of the disclosure may be that the enclosure is arranged to encapsulate an outer peripheral surface of the rotor assembly defined by the plurality of first disc-shaped laminates and the plurality of second disc-shaped laminates.

[0012] Another aspect of the disclosure may be that the wrap is a carbon fiber fabric that encloses the outer peripheral surface of the rotor assembly.

[0013] Another aspect of the disclosure may include the plurality of first disc-shaped laminates and the plurality of second disc-shaped laminates being arranged in the stack on the rotor shaft, wherein a first of the plurality of first disc-shaped laminates is arranged at a first end of the stack and a second of the plurality of first disc-shaped laminates is arranged at a second end of the stack.

[0014] Another aspect of the disclosure may include one-third of the first disc-shaped laminates being arranged in a central part of the stack.

[0015] Another aspect of the disclosure may include a permanent magnet rotor assembly for an electric machine including a plurality of first disc-shaped laminations, a plurality of second disc-shaped laminations, and a rotor shaft. The plurality of first disc-shaped laminations and the plurality of second disc-shaped laminations are arranged in a nested stack on the rotor shaft, each of the plurality of first disc-shaped laminations having a first inner portion and a plurality of first outer portions, and the first inner portion and the plurality of first outer portions defining a plurality of first cavities. The plurality of first outer portions are attached to the first inner portions via a first web member and a plurality of bridges.Each of the plurality of second disc-shaped laminates comprises a second inner portion and a plurality of second outer portions, the second inner portion and the plurality of second outer portions forming a plurality of second cavities, the plurality of second outer portions being attached to the second inner portions via a plurality of second webs and not having a bridge.

[0016] Another aspect of the disclosure may include aligning the plurality of first disc-shaped laminates with the plurality of second disc-shaped laminates such that the plurality of first cavities are aligned with the plurality of second cavities to form a plurality of axially disposed cavities, the plurality of axially disposed cavities defining a plurality of magnetic pole portions that are radially disposed.

[0017] Another aspect of the disclosure may include an electrified powertrain for a vehicle including a DC power source, a multiphase inverter, a multiphase rotating electric machine, and a torque actuator, wherein the multiphase rotating electric machine includes a rotor assembly and a stator. The rotor assembly includes a plurality of first disc-shaped laminates, a plurality of second disc-shaped laminates, and a rotor shaft.The plurality of first disc-shaped laminates and the plurality of second disc-shaped laminates are arranged in a stack on the rotor shaft, each of the plurality of first disc-shaped laminates having a first inner portion and a plurality of first outer portions, the first inner portion and the plurality of first outer portions defining a plurality of first cavities, and the plurality of first outer portions being attached to the first inner portions via a first web and a plurality of bridges. Each of the plurality of second disc-shaped laminates comprises a second inner portion and a plurality of second outer portions, the second inner portion and the plurality of second outer portions forming a plurality of second cavities, the plurality of second outer portions being attached to the second inner portions via a plurality of second webs and without a bridge.

[0018] The above features and advantages, as well as other features and advantages of the present teachings, will be readily apparent from the following detailed description of some of the best modes and other embodiments for carrying out the present teachings, as defined in the appended claims, taken in conjunction with the accompanying figures. BRIEF DESCRIPTION OF THE CHARACTERS

[0019] One or more embodiments will now be described by way of example with reference to the accompanying figures, in which: Fig. 1 is a schematic diagram of a system including a multi-phase, multi-pole permanent magnet motor / generator, a DC power source, an inverter, and a controller according to the present disclosure. Fig. 2 is a schematic illustration of a cutaway end view of an embodiment of an internal permanent magnet (IPM) electric machine according to the disclosure. Fig. 3 is a schematic illustration of a cutaway end view of a portion of a first laminate of a rotor assembly and a stator of an IPM electric machine according to the disclosure. Fig. 4 is a schematic illustration of a cutaway end view of a portion of a second laminate of a rotor assembly and a stator of an IPM electric machine according to the disclosure. Fig. 5 is a schematic representation of an isometric view of a rotor assembly according to the disclosure. Fig. 6 is a schematic illustration of an isometric view of another embodiment of a rotor assembly according to the disclosure.

[0020] The accompanying figures are not necessarily to scale and represent a somewhat simplified representation of various features of the present disclosure as disclosed herein, including, for example, specific dimensions, orientations, positions, and shapes. Details associated with such features will be determined in part by the particular intended application and environment of use. DETAILED DESCRIPTION

[0021] The components of the embodiments described and illustrated herein can be arranged and configured in a variety of different configurations. Therefore, the following detailed description is not intended to limit the scope of the claimed disclosure, but is merely representative of possible embodiments thereof. Moreover, while numerous specific details are set forth in the following description in order to provide a thorough understanding of the embodiments disclosed herein, some embodiments may be practiced without some of these details. Also, in the interest of clarity, detailed descriptions of certain technical details known in the art have been omitted so as not to unnecessarily obscure the disclosure.Furthermore, the disclosure as shown and described herein may be practiced without any element not expressly disclosed herein.

[0022] The present disclosure may be embodied in many different forms. Representative examples of the disclosure are illustrated in the drawings and described in detail herein as non-limiting examples of the disclosed principles. To this end, elements and limitations described herein but not expressly recited in the claims are not to be incorporated into the claims, either individually or collectively, by implication, inference, or otherwise.

[0023] For the purposes of this description, the use of the singular includes the plural and vice versa, unless expressly excluded; the terms "and" and "or" apply both subjunctive and disjunctive; and the words "including," "containing," "comprising," "having," and the like mean "including without limitation." Furthermore, words of approximation such as "approximately," "almost," "substantially," "generally," "about," etc., may be used herein to mean "at, near, or almost at," or "within 0-5% of," or "within acceptable manufacturing tolerances," or logical combinations thereof.

[0024] As used herein, the term "system" refers to mechanical and electrical hardware, software, firmware, electronic control components, processing logic and / or processors, individually or in combination, including without limitation: application specific integrated circuit (ASIC), an electronic circuit, a processor (common, dedicated or group) that executes one or more software or firmware programs, memory device(s) that electrically store software or firmware instructions, a combinational logic circuit and / or other components that provide the described functionality.

[0025] Terms such as "vertical," "horizontal," "left," "right," "top," "bottom," and similar expressions are non-limiting terms that merely describe the various elements as illustrated in the figures and are not intended to limit the scope of the disclosure.

[0026] The term “electric machine” as used herein refers to an electric motor / generator with a rotor and a stator that is capable of converting electrical energy into mechanical energy and / or converting mechanical energy into electrical energy by electromagnetic force.

[0027] With reference to the drawings, in which like reference numbers refer to like or similar components in the different figures, the Fig. 1 and Fig. 2 schematically illustrates elements of an electrified powertrain 100, which includes a direct current source 102, a multi-phase inverter 104, a multi-phase electric rotary motor / generator (electric machine) 10, and a torque actuator 120, the operation of which is monitored and controlled by a controller 130. In one embodiment, the electrified powertrain 100 is arranged to generate and transmit torque to the torque actuator 120, which may be in the form of one or more drive wheels, to effect work, e.g., propulsion, when deployed in a vehicle. The controller 130 executes control routines to control and manage the operation of the multi-phase inverter 104. In one embodiment, the electrified powertrain 100 is mounted on a vehicle and is capable of generating traction torque for vehicle propulsion.When mounted on a vehicle, the vehicle may include, but not be limited to, a mobile platform in the form of a commercial vehicle, an industrial vehicle, an agricultural vehicle, a passenger car, an aircraft, a watercraft, a train, an off-road vehicle, a personal transporter, a robot, and the like to fulfill the purposes of this disclosure. Non-limiting examples of vehicles employing electrified powertrains 100 include electric vehicles (EVs) and various hybrid electric vehicles (HEVs). Alternatively, the electrified powertrain 100 may also be an element of a stationary system.

[0028] The controller 130 may be embodied as one or more digital computing devices and may include one or more processors 134 and a memory 132. A control routine 136 may be stored as an executable instruction set in the memory 132 and executed by one of the processors 134 of the controller 130. The controller 130 communicates with the multiphase inverter 104 to control its operation in response to the execution of the control routine 136 to operate the electric machine 10.

[0029] The term "control unit" and related terms such as microcontroller, control module, module, controller, control unit, processor and similar terms refer to one or more combinations of application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), electronic circuits, central processing units, e.g., microprocessors and associated memory components in the form of transient and / or non-transitory memory components and storage devices (read-only, programmable read-only, random access, hard disk devices, etc.).The non-transitory memory component is capable of storing machine-readable instructions in the form of one or more software or firmware programs or routines, combinational logic circuits, input / output circuits and devices, signal conditioning and buffering circuits, and other components accessible by one or more processors to provide described functionality. Input / output circuits and devices include analog-to-digital converters and related devices that monitor inputs from sensors, where such inputs are monitored at a preset sampling frequency or in response to a triggering event. Software, firmware, programs, instructions, control routines, code, algorithms, and similar terms refer to controller-executable instruction sets, including calibrations and lookup tables.

[0030] The electric machine 10 includes a cylindrically shaped rotor assembly 20 mounted on a rotor shaft 16 and located within an annular stator 50, the rotor assembly 20 being coaxial with a rotor opening formed in the stator 50. Other elements of the electric machine 10, such as end caps, shaft bearings, electrical terminals, etc., are included but not shown. The electrical windings of the stator 50 are arranged with a number of electrical phases and a number of electrical turns per phase. Depending on the specific arrangement, the number of electrical phases can range from 3 to 6, and the number of conductor layers can range from 4 to 12.

[0031] The multiphase inverter 104 includes a plurality of solid-state switches arranged and controllable to convert DC electrical power to AC electrical power and to convert AC electrical power to DC electrical power using a pulse-width modulation signal 108 or other control technique. The multiphase inverter 104 is arranged and controllable to convert DC power from the DC power source 102 to AC power to actuate the electric machine 10 by electromagnetic force. The electric machine 10 is controllable to rotate and generate mechanical torque, which is transmitted to the torque actuator 120 via a rotatable member 112 and a gear train 114 when operated in a torque-generating mode.The electric machine 10 is controllable to generate an alternating electric current from the mechanical torque provided by the torque actuator 120 by electromagnetic force, which is converted by the multi-phase inverter 104 into direct electric current for storage in the direct current source 102 when operated in a power generation mode. The torque actuator 120, in one embodiment, includes a vehicle wheel that transmits torque to a ground surface to effect forward motion as part of a traction drive system.

[0032] The DC power source 102 may be a rechargeable electrochemical battery device, a fuel cell, an ultracapacitor, and / or other electrical energy storage / generation technology. The DC power source 102 is connected to the multiphase inverter 104 via a high-voltage DC bus 103, and the multiphase inverter 104 is connected to the electric machine 10 via a plurality of electrical power lines 106.

[0033] Fig. 2 schematically shows an embodiment of the electric machine 10, which in one embodiment is an indoor permanent magnet (IPM) device. The IPM electric machine 10 includes a cylindrically shaped rotor assembly 20 disposed on a rotor shaft 16 and located within an annular stator 50, the rotor assembly 20 being coaxial with a rotor opening 60 formed in the stator 50. Other elements of the IPM electric machine 10, e.g., end caps, shaft bearings, electrical connectors, etc., are included but not shown. The IPM electric machine 10 is illustrated in association with a radial axis 13 and a longitudinal axis 12, the longitudinal axis 12 being defined by the rotor shaft 16.

[0034] The rotor assembly 20 comprises a plurality of first disc-shaped laminates 21 interleaved with a plurality of second disc-shaped laminates 22 and arranged in a stack. As described with reference to Fig. 3 et seq., each of the first and second disc-shaped laminates 21, 22 comprises an inner portion 23 and an outer portion 24 that define and circumscribe a plurality of cavities 32 that receive and house a plurality of permanent magnets 33. The first disc-shaped laminations 21 are nested with the second disc-shaped laminations 22 and are mounted on the rotor shaft 16 and enclosed by an annular sleeve or enclosure 40. Each of the first disc-shaped laminates 21 and the second disc-shaped laminates 22 is a stamped sheet formed from a ferrous material and manufactured using a stamping process.Each of the first disc-shaped laminates 21 and the second disc-shaped laminates 22 is a disc-shaped device formed with a uniform thickness and a constant outer diameter and having a centrally located shaft opening 26 and a plurality of magnetic pole portions 30 formed thereon. A single one of the magnetic pole portions 30 is illustrated. Further details regarding one embodiment of the first disc-shaped laminates 21 will be described with reference to FIG. Fig. 3, and further details relating to an embodiment of the second disc-shaped laminates 22 will be described with reference to Fig. 4 described.

[0035] As in Fig. 2, the magnetic pole sections 30 repeat around an outer peripheral region of the first and second disc-shaped laminates 21, 22 and define the number of magnetic poles of the rotor assembly 20. As illustrated, and by way of non-limiting example, there are eight magnetic pole sections 30, defining a total of four magnetic pole pairs for the rotor assembly 20. It is understood that the number of magnetic pole sections 30 may be different in other embodiments without limitation.

[0036] Each of the magnetic pole sections 30 includes a plurality of cavities 32, which may be arranged in a double-V arrangement (as shown) or another arrangement. Other examples of arrangements of the magnetic pole sections 30 and the plurality of cavities 32 may include, as non-limiting examples, the plurality of cavities 32 arranged in a single-V arrangement, a U arrangement, or another arrangement.

[0037] The plurality of first and second disc-shaped laminates 21, 22 are assembled with the rotor shaft 16, which is inserted into the shaft openings 26 such that the magnetic pole portions 30 are concentrically aligned to define and form a plurality of cavities 32 that run parallel to the longitudinal axis 12 defined by the rotor shaft 16. The plurality of cavities 32 each accommodate a plurality of permanent magnets 33, which are prism-shaped elements with a rectangular, trapezoidal, dovetail-shaped, or other cross-section. Further details regarding the plurality of cavities 32 and the permanent magnets 33 will be described with reference to Fig. described in more detail.

[0038] The permanent magnets 33 can be made of rare earth materials and can be described by a longitudinal axis and a rectangular cross-sectional area with a major axis and a minor axis. A rare earth magnet is made of alloys of rare earth materials, such as reduced-dysprosium material or another suitable material. Other rare earth materials can include neodymium and samarium. Alternatively, the permanent magnets 33 can also be made of non-rare earth materials such as ferrite, alnico (aluminum-nickel-cobalt), FeCo (iron-cobalt), MnBi (manganese-bismuth), etc., or combinations thereof.

[0039] The annular shroud 40 is made of carbon fiber or another material and encloses an outer peripheral surface 27 of the rotor assembly 20. As non-limiting examples, the annular shroud 40 may instead be made of stainless steel, fiberglass, titanium alloy, etc. The annular shroud 40 is arranged to provide a holding force that counteracts the centrifugal force associated with the rotation of the rotor assembly 20.

[0040] The outer dimensions of the rotor assembly 20 include an outer diameter 29. The outer diameter 29 is connected to the outer circumferential surface 27 of the rotor assembly 20 and the annular casing 40 and is measured with respect to the radial axis 13.

[0041] The stator 50, in one embodiment, includes a plurality of stamped, ferrous, disc-shaped laminations 52 arranged in a stack. Each of the disc-shaped laminates 52 is a disc-shaped device formed with a uniform thickness, and each defines a centrally located internal opening 51 shaped to dimensionally accommodate the outer diameter 29 of the rotor assembly 20, including the annular shroud 40. Each of the disc-shaped laminates 52 also includes a plurality of radially directed, inwardly extending teeth 56. The disc-shaped laminates 52 are arranged in a stack such that the internal openings 51 and the inwardly extending teeth 56 are aligned with each other. The disc-shaped laminates 52 are assembled together into a unitary device.The rotor opening 60 is formed by the concentrically aligned inner openings 51 of the plurality of disc-shaped laminates 52, and a plurality of longitudinal slots 58 are formed between the aligned, inwardly projecting teeth 56 of the plurality of disc-shaped laminates 52.

[0042] The slots 58 are configured to receive electrical windings 54 arranged in a distributed electrical winding assembly 70, which in one embodiment is made of conductive stranded wire. The strand may be made of any suitable material, such as copper or aluminum. The internal dimensions of the stator 50 include an inner diameter that defines an inner circumferential surface 28 of the stator 50. Alternatively, the electrical windings 54 may be arranged in a concentrated winding configuration.

[0043] An air gap 31 is formed between an outer peripheral surface 42 of the rotor assembly 20 (including the annular shroud 40) and the inner peripheral surface 28 of the stator 50.

[0044] The distributed electrical winding arrangement 70 of the electrical windings 54 in the stator 50 is preferably arranged to provide a rotating electrical field arrangement that generates a rotating magnetic field in the stator 50 by applying a multi-phase alternating current, which may be supplied by an integrated inverter, e.g., the inverter 104. In one embodiment, the multi-phase alternating current is a three-phase alternating current.

[0045] During operation, electromagnetic forces induced in the electrical windings 54 induce a magnetic flux that acts on the permanent magnets 33 embedded in the rotor assembly 20, thus exerting a torque that causes the rotor assembly 20 to rotate about the rotor shaft 16 within the stator 50. Alternating current (AC) motors can be broadly divided into AC induction motors and AC synchronous motors. In a rotating field AC synchronous motor, in which a stator is provided with armature windings and a rotor assembly is provided with magnetic windings, the rotor assembly is converted into an electromagnet by energizing the magnetic windings of the rotor assembly, and the rotor assembly rotates by applying a multi-phase alternating current to the stator. In applications where the electrical power is supplied by the DC power source 102, the multi-phase alternating current is generated by the inverter 104.

[0046] The electrical windings of the stator 50 are arranged with a specific number of electrical phases and a specific number of electrical turns per phase. Depending on the specific arrangement, the number of electrical phases can be between 3 and 6, and the number of conductor layers can be between 4 and 12.

[0047] Specific geometric design parameters associated with the rotor assembly 20 and the stator 50 of the IPM electric machine 10 are identified, including a first set of geometric design parameters associated with the rotor assembly 20 and a second set of geometric design parameters associated with the stator 50. The ranges for the first and second sets of geometric design parameters are selected to achieve motor operating parameters that include high drive cycle efficiency, e.g., peak efficiency greater than 90% over a wide operating range, high torque density, a wide peak power range, and a maximum speed of 21,000 rpm or more.

[0048] Fig. 3 schematically shows a first cutaway end view of a portion of the electric machine 10 having a cylindrically shaped rotor assembly 20 and a stator 50, the rotor assembly 20 being coaxial with the rotor opening 60 formed in the stator 50. A single magnetic pole portion 30 of one of the first disc-shaped laminates 21 of the rotor assembly 20 is shown. In this embodiment, the magnetic pole portion 30 of the first disc-shaped lamination 21 is formed by a plurality of first cavities 32A arranged in a double-V pattern and arranged in a nested V arrangement mirrored about the radial line 36. The plurality of first cavities 32A contain a corresponding number of permanent magnets 33. The permanent magnets 33 are prism-shaped elements with major axes parallel to a longitudinal axis of the rotor shaft 16.In this embodiment, the first disc-shaped laminate 21 includes an inner portion 23 and a first outer portion 24A that define and circumscribe the plurality of first cavities 32A. The inner portion 23 is connected to the first outer portion 24A via bridges 38 formed on the outer circumferential surface 27 of the rotor assembly 20. In one embodiment, a web is formed in the first laminate 21 along the radial line 36 between adjacent first cavities 32A. Alternatively, and as shown, no webs are formed between adjacent ones of the first cavities 32A.

[0049] Fig. 4 schematically shows a second cutaway end view of a portion of the electric machine 10 having a cylindrically shaped rotor assembly 20 and a stator 50, the rotor assembly 20 being coaxial with the rotor opening 60 formed in the stator 50. A single magnetic pole portion 30 of one of the second disc-shaped laminates 22 of the rotor assembly 20 is shown. In this embodiment, the magnetic pole portion 30 of the second disc-shaped lamination 22 is formed by a plurality of second cavities 32B arranged in a double-V pattern and arranged in a nested V arrangement mirrored about the radial line 36. The plurality of second cavities 32B contain a corresponding plurality of permanent magnets 33. The permanent magnets 33 are prism-shaped elements with major axes parallel to a longitudinal axis of the rotor shaft 16.In this embodiment, the second disc-shaped laminate 22 includes an inner portion 23 and a second outer portion 24B that define and circumscribe the plurality of second cavities 32B. The inner portion 23 is connected to the second outer portion 24B only via webs 35 formed along the radial line 36. No bridges are formed between the inner portion 23 and the second outer portion 24B. Thus, the second outer portion 24B is attached to the inner portion 23 in a cantilevered position when the second disc-shaped laminate 22 is in an unassembled state.

[0050] Fig. 5 shows an embodiment of a portion of the rotor assembly 520, which consists of a plurality of first disc-shaped laminates 21 and a plurality of second disc-shaped laminates 22. The plurality of first disc-shaped laminates 21 and the plurality of second disc-shaped laminates 22 are nested and arranged in a stack 510, as described herein. In this embodiment, a first one of the plurality of first disc-shaped laminates 22 is arranged at a first end 511 of the stack 510, and a second one of the plurality of first disc-shaped laminates 21 is arranged at a second end 512 of the stack. In one embodiment, a third one of the plurality of first disc-shaped laminates 21 is arranged in a middle section 513 of the stack 510. The remaining sections of the stack 510 are populated by the plurality of second disc-shaped laminates 22.The second outer portions 24B of the second disc-shaped laminates 22 are secured to the inner portion 23 by the enclosure 40 during assembly of the rotor assembly 20. Furthermore, the second outer portions 24B of the disc-shaped laminates 22 are secured to the inner portions 23 because the plurality of first and second disc-shaped laminates 21, 22 are welded or otherwise joined together in the axial direction during assembly.

[0051] Fig.6 shows another embodiment of a portion of the rotor assembly 620, which consists of a plurality of first disc-shaped laminates 21 and a plurality of second disc-shaped laminates 22. The plurality of first disc-shaped laminates 21 and the plurality of second disc-shaped laminates 22 are nested and arranged in a stack 610, as described herein. In this embodiment, a first one of the plurality of first disc-shaped laminates 22 is arranged at a first end 611 of the stack 510, and a second one of the plurality of first disc-shaped laminates 21 is arranged at a second end 612 of the stack. In one embodiment, a third one of the plurality of first disc-shaped laminates 21 is arranged in a middle section 613 of the stack 610, a fourth one of the plurality of first disc-shaped laminates 21 is arranged in a first

[0052] Quarter section 614 of the stack 610, and a fifth of the plurality of first disc-shaped laminates 21 is arranged in a third quarter section 615 of the stack 610. The remaining sections of the stack 610 are occupied by the plurality of second disc-shaped laminates 22. The absence of bridges at the ends of the second cavities 32B containing the permanent magnets 33 means that the likelihood of flux leakage at these locations is lower. Again, the second outer sections 24B of the second disc-shaped laminations 22 are secured to the inner section 23 by the enclosure 40 when the rotor assembly 20 is assembled. Furthermore, the second outer sections 24B of the disc-shaped laminates 22 are secured to the inner sections 23 because the plurality of first and second disc-shaped laminates 21, 22 are welded or otherwise joined together in the axial direction during assembly.

[0053] The concepts described herein provide an IPM electric machine including a rotor assembly arranged with a plurality of magnetic pole sections, each containing one or more permanent magnets, with a wrap section disposed on an outer periphery of the rotor assembly. The embodiments described herein can provide higher torque density, higher power density, lower leakage flux, and other advantages compared to similarly sized electric machines without such arrangements. This enables a better balance between cost, energy consumption, and performance by introducing design freedoms not otherwise available.

[0054] The electric machine designs described here are configured to optimize operating parameters in terms of torque, speed, power, efficiency, packaging, mass, and other constraints.

[0055] The detailed description and the drawings or illustrations are supportive and descriptive of the present teachings, but the scope of the present teachings is defined solely by the claims. While some of the best modes and other embodiments for carrying out the present teachings have been described in detail, various alternative designs and embodiments for carrying out the present teachings are defined in the appended claims.

Claims

[1] A rotor assembly for an electric machine, comprising: a plurality of first disc-shaped laminates, a plurality of second disc-shaped laminates; a rotor shaft; a casing; and a plurality of permanent magnets; wherein the plurality of first disc-shaped laminates and the plurality of second disc-shaped laminates are arranged in a stack on the rotor shaft; wherein each of the plurality of first disc-shaped laminates has a first inner portion and a plurality of first outer portions, the first inner portion and the plurality of first outer portions defining a plurality of first cavities; wherein the plurality of first outer parts are attached to the first inner parts via a first web and a plurality of bridges; wherein each of the plurality of second disc-shaped laminates has a second inner portion and a plurality of second outer portions, the second inner portion and the plurality of second outer portions forming a plurality of second cavities; and wherein the plurality of second outer sections are attached to the second inner sections via a plurality of second webs and without a bridge. [2] The rotor assembly of claim 1, wherein the plurality of first disc-shaped laminates are aligned with the plurality of second disc-shaped laminates such that the plurality of first cavities are aligned with the plurality of second cavities to form a plurality of axially disposed cavities; and wherein the plurality of axially disposed cavities define a plurality of radially disposed magnetic pole portions. [3] The rotor assembly of claim 2, wherein the plurality of permanent magnets are disposed in the plurality of axially disposed cavities. [4] The rotor assembly of claim 2, wherein the plurality of axially disposed cavities define a plurality of prisms arranged in a single V arrangement for each of the plurality of magnetic pole sections. [5] The rotor assembly of claim 2, wherein the plurality of axially disposed cavities define a plurality of prisms arranged in a double-V arrangement for each of the plurality of magnetic pole sections. [6] The rotor assembly of claim 2, wherein the plurality of axially disposed cavities define a plurality of prisms arranged in a U-arrangement for each of the plurality of magnetic pole portions. [7] The rotor assembly of claim 1, wherein the enclosure is arranged to encapsulate an outer surface of the rotor assembly defined by the plurality of first disc-shaped laminates and the plurality of second disc-shaped laminates. [8] The rotor assembly of claim 7, wherein the wrap comprises a carbon fiber fabric enclosing the outer peripheral surface of the rotor assembly. [9] The rotor assembly of claim 1, wherein the plurality of first disc-shaped laminates and the plurality of second disc-shaped laminates arranged in the stack on the rotor shaft comprise a first of the plurality of first disc-shaped laminates arranged at a first end of the stack and a second of the plurality of first disc-shaped laminates arranged at a second end of the stack. [10] The rotor assembly of claim 9, comprising a third of the plurality of first disc-shaped laminates disposed in a central portion of the stack.

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