32 for supply of hydraulic fluid. A shared transmission pump 34 provides sufficient hydraulic pressure for the fluid to selectively actuate hydraulically activated elements of the transmission 16, the TC assembly 18 and, for some implementations, the engine disconnect device 28.

The ICE assembly 12 operates to propel the vehicle 10 independently of the electric traction motor 14, e.g., in an “engine-only” operating mode, or in cooperation with the motor 14, e.g., in “vehicle-launch” or “motor-boost” operating modes. In the example depicted in FIG. 1, the ICE assembly 12 may be any available or hereafter developed engine, such as a compression-ignited diesel engine or a spark-ignited gasoline or flex-fuel engine, which is readily adapted to provide its available power output typically at a number of revolutions per minute (RPM). Although not explicitly portrayed in FIG. 1, it should be appreciated that the final drive system 11 may take on any available configuration, including front wheel drive (FWD) layouts, rear wheel drive (RWD) layouts, four-wheel drive (4WD) layouts, all-wheel drive (AWD) layouts, six-by-four (6×4) layouts, etc.

FIG. 1 also depicts an electric motor/generator unit (“motor”) 14 that operatively connects via a rotor shaft, motor support hub, or belt (collectively motor output member 29) to the hydrodynamic torque converter 18. The torque converter 18, in turn, drivingly connects the motor 14 to an input shaft 17 of the transmission 16. The electric motor/generator unit 14 is composed of an annular stator assembly 21 that circumscribes and is concentric with a cylindrical rotor assembly 23. Electric power is provided to the stator 21 through a high-voltage (HV) electrical system, including electrical rails/cables 27 that pass through the motor housing via suitable sealing and insulating feedthroughs (not illustrated). Conversely, electric power may be provided from the MGU 14 to an onboard traction battery pack 30, e.g., during a regenerative braking mode. Operation of any of the illustrated powertrain components may be governed by an onboard or remote vehicle controller or module or network of controllers/modules/devices, all variations of which are represented in FIG. 1 by a programmable electronic control unit (ECU) 25.

Power transmission 16 may use differential gearing 24 to achieve selectively variable torque and speed ratios between transmission input and output shafts 17 and 19, respectively. One form of differential gearing is the epicyclic planetary gear arrangement, which offers the advantage of compactness and different torque and speed ratios among members of the planetary gearing. Traditionally, hydraulically actuated torque establishing devices, such as clutches and brakes, are selectively engageable to activate the aforementioned gear elements for establishing desired forward and reverse speed ratios between the transmission's input and output shafts 17, 19. While envisioned as a 6-speed or 8-speed automatic transmission, the power transmission 16 may optionally take on other functionally appropriate configurations, including Continuously Variable Transmission (CVT) architectures, manual or automated-manual transmissions, etc.

Hydrodynamic torque converter assembly 18 operates as a fluid coupling for operatively connecting the engine 12 and motor 14 with the internal epicyclic gearing 24 of the power transmission 16. Disposed within an internal fluid chamber of the torque converter assembly 18 is a bladed impeller 36 facing a bladed turbine 38. The impeller 36 is juxtaposed in serial power-flow fluid communication with the turbine 38, with a TC stator (not shown) interposed between the impeller 36 and turbine 38 to selectively alter fluid flow therebetween. The transfer of torque from the engine and motor output members 13, 29 to the transmission 16 via the TC assembly 18 may be through stirring excitation of hydraulic fluid, such as transmission oil, inside the TC's internal fluid chamber caused by rotation of the impeller and turbine 36, 38 blades. To protect these components, the torque converter assembly 18 is constructed with a TC pump housing, defined principally by a transmission-side pump shell 40 that is fixedly attached to an engine-side pump cover 42 such that a working hydraulic fluid chamber is formed therebetween.

FIG. 2 illustrates an example of an electric machine 114 that employs persistent-state magnetic materials that exchange electromagnetic forces with electrically conductive windings to convert electrical energy into mechanical energy, and vice versa. The electric machine 114 has a multiphase, conductor-wound stator assembly 116 that nests therein and circumscribes a magnet-bearing synchronous reluctance rotor assembly 118. While available for use in automotive and non-automotive applications alike, the electric machine 114 of FIG. 2 may be particularly suited for use in a hybrid-electric powertrain as a traction motor (e.g., motor 14 FIG. 1) with an engine (e.g., ICE assembly 12), and to operate in at least an engine-cranking mode, a regenerative-charging mode, and a torque-assist mode. Electric machine 114 may be designed to achieve: a relatively high efficiency (e.g., at least 85% efficiency over a calibrated output power and speed range); a relatively high power density (e.g., greater than 1500 watts per liter) and torque density (e.g., greater than 5 Newton-meters per liter); a relatively wide peak power range (e.g., four to six kilowatts or greater); a high maximum speed (e.g., at least 18,000 rpm); a reduced mass and inertia (e.g., for fast dynamic response to user output demands); and to fit into a relatively small packaging space. Innumerable alternative architectures may be employed by the electric machine 114 to meet similar and alternative operating parameters.

With continuing reference to FIG. 2, the stator assembly 116 is coaxial with and surrounds the rotor assembly 118 while maintaining a small airgap 115 therebetween. In accord with the illustrated example, this airgap 115 may be about 0.2 millimeters (mm) to about 1.2 mm, for example, in order to maximize power output and minimize the number of permanent magnets 120 borne by the rotor assembly 118 to provide a desired power output. The representative stator and rotor assemblies 116, 118 of FIG. 2 are concentrically aligned about a shared longitudinal center axis A of the electric machine 114. The stator assembly 116 has an annular stator core 126 with a central bore 122 that nests therein the rotor assembly 118. The rotor assembly 118 has a cylindrical rotor core 128, e.g., that keys, splines, welds, etc., to an output shaft (e.g., motor output member 29 of FIG. 1). It should be appreciated that a protective and insulating outer housing (e.g., motor housing 31 in FIG. 1) may surround an outer periphery of the stator assembly 116 and can rotatably support the rotor and rotor output shaft of the electric machine 114.

Rotor assembly 118 of FIG. 2 is fabricated with a rotor core 128, which may have a right-circular cylinder geometry with a toroidal shape, for supporting multiple permanent magnets 120 (twenty-four (24) PMs in the illustrated example) that are circumferentially spaced around a central bore 124. Specifically, the rotor core 128 may be stamped, precision machined, and assembled with multiple rotor slots 130 arranged in radially spaced barrier layers (e.g., four distinct barrier layers). A first barrier layer 130A of slots 130 may be positioned closest to an inner periphery of the rotor core 128, while a fourth barrier layer 130D of slots 130 may be positioned furthest from the rotor body's inner periphery than the other barrier layers. A second barrier layer 130B may be radially interposed between the first and third barrier layers 130A, 130C, while a third barrier layer 130C may be radially interposed between the second and fourth barrier layers 130B, 130D. For at least some embodiments, only select barrier layers (e.g., the first and third barrier layers 130A, 130C) may house magnets 120, while other select barrier layers (e.g., the second and fourth barrier layers 130B, 130D) do not house magnets 120 and, thus, act as flux barriers. In other embodiments, only one or all of the barrier layers may comprise slots storing therein permanent magnets. The rotor core 128 may be fabricated from metallic disc-shaped laminates, including high-grade steel blanks, that are stacked and adhered together to maintain high-speed rotational stress within predetermined limits.

Stator assembly 116 of FIG. 2 is fabricated with a stator core 126, which may also have a right-circular cylinder geometry with a generally annular shape and may have multiple circumferentially spaced, radially elongated stator slots 132 (e.g., 60 total slots in the illustrated example). Each stator slot 132 extends axially through the stator core 126, parallel to the rotational axis A of the electric machine 114. These stator slots 132 house electrically conductive, multiphase electromagnetic stator windings 134. Stator windings 134—also referred to herein as “wire windings” or “bar windings”—may be grouped into different sets, each of which may carry an identical number of phases of electrical current, such as three, five, six, or seven phases. In addition, the stator windings 134 may extend axially beyond open longitudinal ends of the stator core 126. A ratio of an outer diameter of the stator core 126 to an axial length of the stator core 126 may be not less than 1.5 and not greater than 3.5, for example, to satisfy packing space constraints for a desired application of the electric machine 114, such as the vehicle powertrain of FIG. 1.

For ease of manufacture and simplicity of design, it may be desirable that all of the permanent magnets 120 share an identical, rectangular polyhedron shape. Nevertheless, any one or more or all of the PM bodies may take on innumerable shapes and sizes, including other polyhedral block-type magnets, ring-shaped (annular) magnets, bread-loaf block-type magnets, curved tile magnets, etc. In a non-limiting example, each permanent magnet 120 may have a thickness of about 1.5 mm to 2.5 mm to fit within a slot 130 having complementary dimensions. A total mass of magnet material used by the electric machine 114 (i.e., the mass of all magnets 120) may be about 150 grams to about 250 grams. The permanent magnets 120 of the electric machine 114 may all be fabricated from the same material, such as Neodymium Iron Boron (NdFeB); alternatively, the magnets 120 may employ different materials, such as Samarium Cobalt (SmCo), Aluminum Nickel Cobalt (AlNiCo), or any combination of rare earth magnet materials.

Unlike the permanent magnets 120, it may be desirable that the multiphase stator windings 134 of FIG. 2 be composed of a mixture of differently shaped and sized electromagnetic conductors. As described in extensive below in the discussion of FIG. 3, the stator windings 134 may include both bar-type conductors, such as U-shaped hairpin windings, and wire-type conductors, such as copper wire windings. The legs of the hairpin windings may be inserted into the slots 132 of the stator core 126, with each leg extending through a different stator slot 132 such that the hairpin crown (or “end-turn”) extends over several of the stator slots 132 (e.g., each crown may extend across three or more slots). These hairpin windings 134 may be inserted in a “staggered” or “interleaved” pattern with respect to adjacent hairpins. Any given stator slot 132 may contain a number of hairpin legs (e.g., four to eight) and a number of segments of individual wire windings (e.g., 8 to 24). Once all of the electromagnetic windings 134 are inserted into the slots 132 of the stator core 126, the ends of the windings projecting from a longitudinal end of the stator core 126 may be bent. Electrical connections are then made to each winding 134.

During operation of the electric machine 114, e.g., in a regenerative-charging mode, the rotor assembly 118 is rotated via the rotor output shaft while the stator assembly 116 is held relatively stationary. In so doing, the permanent magnets 120 are moved past the multiphase stator windings 134; the magnetic field emitted by the permanent magnets 120 generates an electrical current in the windings 134 through electromagnetic induction. This induced electric current may be used to power a load (e.g., recharge traction battery pack 30 of FIG. 1). Conversely, during operation of the electric machine 114, e.g., in an engine-cranking mode, an EV motoring mode, or a torque-assist mode, an electric current is supplied to the stator windings 134 by a suitable power source (e.g., traction battery pack 30). Passing the supplied current through the multiphase stator windings 134 will generate a magnetic field at radially inward ends of stator teeth 136. The magnetic field output from these stator teeth 136 interacts with the permanent magnets 120 in the rotor assembly 118 such that the rotor core 128 and attached shaft rotate in unison to generate a rotational driving force.

PM traction motors may suffer from high copper loss and high AC winding (proximity/skin) effect while operating at high speeds, which may result in high motor operating temperatures and reduced torque output. Electromagnetic conductors closest to the rotor-stator airgap are more affected by winding loss and effect during high motor speeds. To mitigate such AC winding loss and effect, solid-wire or multistrand-wire conductors with reduced cross-sections are placed in the slot layers closest to the airgap. Hairpin, I-pin, or other bar conductors with larger cross-sections are placed at the slot layers furthest from the airgap to increase the slot fill-factor and lower DC winding loss. For at least some operating points of high motor speed and torque (e.g., 9000+ RPM, 400+Nm), there is a significant improvement in motor efficiency with this engineered combination of wire and bar conductors (e.g., about 30%); higher speeds (e.g., 18,000+ RPM) may achieve even higher efficiency improvements (e.g., about 50%).