Electric motor with continuously variable magnetic properties and vehicle with such an electric motor

Abstract

Electric motor (16) capable of generating a total motor torque with continuously variable magnetic and reluctance torque components, the electric motor (16) comprising: a stator arrangement (26) with stator windings (26W) and a stator core (26C) with an axial length (L S ); a rotor arrangement (33) comprising a rotor shaft (17) and a cylindrical rotor hub (33R) each with respective axial lengths (L R ) includes, wherein the cylindrical rotor hub (33R) has a first end (E1) with a first mean magnetic field strength and a second end (E2) with a second mean magnetic field strength, the second mean magnetic field strength being weaker than the first mean magnetic field strength; and a return spring (64) located near the first or second end (E1, E2) of the rotor hub (33R); wherein the rotor hub (33R) is displaceable relative to the rotor shaft (17), wherein the axial length (L R ) the rotor hub (33R) the axial length (L S ) of the stator core (26C) and the rotor hub (33R) is configured to move along the axial length of the rotor shaft (17) to vary the contributions of the magnetic and reluctance torque components to the total motor torque in response to different speed and torque operating points of the electric motor (16) relative to each other; characterized by a controller (50) configured to receive a set of input signals, including a rotational speed of the electric motor (16) and a torque generated by the electric motor (16), and to displace the rotor hub (33R) along the axial length (L R) the rotor shaft (17) in response depending on the received rotational speed and torque, in order to continuously vary the relative contributions of the magnetic and reluctance torque components to the total motor torque; wherein the controller (50) is further configured to apply a magnetic flux attenuation stator current to the stator windings (26W) in order to limit the rotor hub (33R) along the axial length (L R ) of the rotor shaft (17) to be passively displaced.

Description

The present invention relates to an electric motor according to the preamble of claim 1 and to a vehicle according to the preamble of claim 5, of the type substantially known from JP 2010-206972 A.Further prior art is evident from the publications JP 2010-166742 A and US 2007 / 0241628 A1.INITIATIONElectric motors are used to generate torque and drive a large number of electromechanical systems. Such electric motors, such as traction electric motors and motor / generator units, include a rotor hub and a shaft concentrically disposed with respect to the stator assembly. The interaction of electromagnetic fields of the rotor hub and stator assemblies is closely controlled in a manner that causes the fields to alternately attract and repel, resulting in rotation of the rotor shaft. The rotation of the rotor shaft may be utilized for use in power generation, drive systems, and other useful applications.In a permanent magnet type electric motor, rare earth magnets are surface mounted or embedded in the laminations of the rotor hub. The stator assembly includes a stator core defining a plurality of stator slots. The stator slots are individually wound with the wires forming the stator windings, each of the stator windings corresponding to different electrical phases in a polyphase configuration. When the stator windings are sequentially energized, the end effect is the generation of a rotating electromagnetic field. The rotating electromagnetic field then acts in a push-pull manner to the permanent magnet field of the rotor hub, wherein the resulting forces rotate the rotor shaft.SUMMARYA permanent magnet type electric motor is presented herein. Due to its construction, the electric motor has continuously variable magnetic reluctance characteristics selected depending on the instantaneous rotational speed and the instantaneous torque of the electric motor. As compared to internal combustion engines, operation of an electric motor is energy efficient at low speed, high torque operating conditions, such as when motor torque is used to rapidly accelerate a vehicle from a standstill. However, as engine speed increases and engine torque decreases, the efficiency benefits provided by the electric motor tend to decrease. A solution to this phenomenon can be found in the disclosed electric motor, which specifically addresses the aforementioned problems in high speed / low torque power without compromising the structural integrity and packaging requirements of the electric motor.The electric motor is characterized according to the invention by the features of claim 1.The rotor hub described herein may be positioned at a calibrated distance from the stator assembly and configured with calibrated constant magnetic reluctance characteristics. The rotor hub includes first and second ends having different magnetic field strengths, i.e., a weak field end and a strong field end. Such field strength disparity may be constructed in various ways, for example, by varying the size, strength, type, quality, number, and / or arrangement of a set of rare earth permanent magnets along an axial length of the rotor hub. Alternatively, the rotor hub may be constructed as a mechanically uniform structure with variable levels of magnetization, e.g., by magnetizing the first and second ends at different levels of magnetic field strength, without necessarily attaching or embedding different permanent magnets. The rotor hub may have constant magnetic reluctance characteristics along an axial length of the rotor hub. The rotor hub may have different magnetic reluctance characteristics along an axial length of the rotor hub, for example an increased reluctance ratio at the weak field end of the rotor hub.The position of the rotor hub along the axial length of the rotor shaft may be automatically and continuously varied during operation of the electric motor anywhere between and including the determined first and second axial positions on the rotor shaft. This allows for the continuous change of magnetic torque contribution to the total output torque of the electric motor and, by default, a continuous change of magnetic torque. For example, when the rotor hub translates or slides along the rotor shaft to a first axial position, the motor output torque may consist of a reluctance torque of about 25%, with the remaining 75% being a magnetic torque. The magnetic torque contribution to the total motor torque of the electric motor may decrease to a lower level, such as 50% magnetic torque, where the reluctance torque contribution increases to 50% in this particular example mixture, and where this change in relative torque contribution occurs when the rotor hub is displaced to a second axial position along the rotor shaft.Certain embodiments of the present invention may include an actuator configured to apply an actuation force to the rotor hub at a magnitude sufficient to translate the rotor hub along the rotor shaft. In other embodiments, the self-actuation of the rotor hub can be realized by the controlled application of a magnetic flux-weakening electric current into the phase windings of the stator arrangement, wherein the field changes caused by the introduction of the stator current optionally serve for attracting or repelling the rotor hub. A return spring may be used to facilitate passive actuation and axial return movement of the rotor hub.Furthermore, according to the invention, a vehicle is presented which is distinguished by the features of claim 5.The vehicle includes the above-mentioned electric motor, and a transmission, a controller, and a load. The transmission is connected to the load, e.g., to a set of road wheels, a propeller, or a drive axle, and is configured to provide an output torque to the load in response to an input torque. The electric motor is operable to generate the input torque to the transmission and may be constructed as set forth above. The controller is programmed or otherwise configured to receive input signals including a measured, calculated, or estimated speed and an output torque of the electric motor and control a displacement of the rotor hub along the axial length of the rotor shaft in response to such input signals. The distance of displacement is sufficient to vary the magnetic torque component and thus the relative magnetic and reluctance torque contributions in a manner appropriate for the current speed and torque of the electric motor.In addition, a method for controlling the electric motor will be described. The method may include determining, via a controller and one or more sensors, a speed and an output torque of the electric motor and also determining a desired axial position of a cylindrical rotor hub of the rotor assembly using a look-up table. The desired axial position corresponds to the received engine speed and the engine torque. The method also includes translating the rotor hub along the axial length of a rotor shaft of the rotor assembly to the determined desired axial position such that the relative magnetic and reluctance torque contributions are continuously varied in real time in response to the determined speed and torque.The above and other functions and advantages of the present invention will be readily apparent from the following detailed description of the embodiments and best modes for carrying out the invention when taken in connection with the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a schematic top view of an exemplary vehicle with a permanent magnet type electric motor having a displaceable rotor hub providing continuously variable magnetic properties. FIG. 2 is a schematic illustration of the side view of the electric machine of FIG. 1 according to a non-inventive embodiment. FIG. 3 is a schematic side view of the electric motor of FIG. 2 according to an embodiment of the invention. FIG. 4 is a flow chart describing an example method for controlling an axial position of a rotor hub of the electric motor illustrated in FIGS. 1-3 to thereby continuously vary the magnetic characteristics of the electric motor.DETAILED DESCRIPTIONReferring to the drawings, wherein like reference numerals refer to like components, an example vehicle 10 having an electric powertrain 12 is illustrated in FIG. 1. The electric powertrain 12 in turn includes a high voltage battery pack (B Hv) 14, electrically connected to a permanent magnet electric motor (M E) 16. The electric motor 16 may be used as a traction motor onboard the vehicle 10 to generate motor torque (arrow T M) at a level sufficient to propel the vehicle 10 as an electric generator and / or perform other useful work onboard the vehicle 10.Advantageous applications of the electric motor 16 are not limited to mobile or vehicle applications in general or to motor vehicle drive applications in particular. One of ordinary skill in the art will appreciate that the attendant advantages of the disclosed electric motor 16, when constructed as described below with reference to FIGS. 2 and 3, may be extended to stationary and mobile applications that rely on the use of motor torque (arrow T M) under high speed / low torque operating conditions of the electric motor 16. The electric motor 16 can be actively controlled according to the exemplary embodiment of FIG. 2, or passively controlled according to the exemplary embodiment of FIG. 3. An example control method 100 may be used with either the active or passive embodiment, with an example of the method 100 shown in FIG. 4.With respect to the example vehicle 10 shown in FIG. 1, the battery 14 may be charged via an external charging station 11, for example, via a DC fast charging station shown, where the charging voltage may be applied directly to the battery pack 14 using an applied DC voltage (VDC), via a charge coupling device 20, via a DC bus 22, via a voltage regulator 24 with internal semiconductor and / or mechanical switches S 1, or via an available AC charging system (not shown).As shown, when the electric motor 16 is embodied as a multi-phase device, the electric powertrain 12 may include a power inverter module (PIM) 18 electrically connected to the battery pack 14 via the DC bus 22. Internal semiconductor switches (not shown) of the PIM 18 are automatically controlled via pulse width modulation or other desired switching techniques to generate an AC output suitable for energizing the electric motor 16. An AC bus 40 is used to electrically connect the PIM 18 to the individual phase windings of the electric motor 16. A DC / DC voltage converter / auxiliary power module (APM) 19 may be used to reduce a voltage level of the DC bus 22 to a lower auxiliary level, e.g., 12-15 VDC, which in turn may be stored in an auxiliary battery pack (B AUX) 44 for use in powering low voltage electrical systems onboard the vehicle 10.A rotor shaft 17 of the electric motor 16 may be selectively connected to a load, for example, an input member 28 of a transmission (T) 30, via actuation of a clutch 32. Rotor shaft 17 rotates to provide input torque (arrow T I) to input member 28 of transmission 30 whenever electric motor 16 is operated as a traction electric motor and / or electric motor 16 may be operated as a generator, as desired. For example, engine torque (arrow T M) may be provided from the energized electric motor 16 to the input member 28 and / or to another load in the form of an output member 37 of the transmission 30 and a set of drive wheels 34 connected to the output member 37, depending on the configuration of the electric powertrain 12. The output torque (arrow T O) from the transmission 30 may be transmitted to the drive wheels 34 via one or more drive axles 36. The direction of energy flow may be reversed during a regenerative event, such as regenerative braking, to charge the battery pack 14, i.e., with regenerative torque from the rotating electric motor 16 that generates electricity supplied to the battery pack 14 so as to increase or maintain its state of charge.A controller (C) 50 may be used to control the running operation of the electric motor 16 in response to a set of input signals (arrow CC I) by the transmission of a set of control signals (arrow CC O) in the manner set forth below with reference to FIG. 4. the controller 50 may be embodied as one or more electronic control units having the required memory (M) and a processor (P), as well as other associated hardware and software, e.g., a clock or timer, input / output circuits, etc. The memory (M) may include sufficient capacities of read-only memory, for example magnetic or optical memory. Instructions embodying the method 100 may be programmed into the memory (M) and executed by the processor(s) (P) during operation of the vehicle 10 to optimize the efficiency of the electric motor 16.The structure of the electric motor 16 will now be described with reference to FIGS. 2 and 3. Both figures are described in connection with loading and changing an axial position of a cylindrical rotor hub 33R with respect to a stator assembly 26, as shown by the double arrow AA in FIG. 2. However, the relative axial position of the rotor hub 33R and the stator assembly 26 determines the type of electromagnetic field interaction. Thus, although shown missing in FIGS. 2 and 3 for simplicity of illustration, alternative embodiments may be realized in accordance with the present invention in which the axial position of the rotor hub 33R remains fixed and that of the stator assembly 26 changes during operation. For example, one embodiment may include the stator assembly 26 being connected to a stationary member 75 as shown in FIG. 3 via a similar splined connection and acting with an actuator 60 as shown in FIG. 2 on a stator core 26C instead of the rotor hub 33R.Referring to FIG. 2, the electric motor 16 includes the stator assembly 26 and a rotor assembly 33 having respective axial lengths L S and L R. The stator assembly 26 includes a stator core 26C and stator windings 26W, the stator windings 26W being wound in stator slots (not shown) of the stator core 26C to form an electromagnet. Thus, the stator assembly 26 has a total axial length L ST, including the stator windings 26W. The rotor assembly 33 includes the rotor hub 33R connected to the rotor shaft 17, the rotor shaft 17 having a rotational axis A 26.The total amount of motor torque (arrow T M), i.e., the "total motor torque" noted elsewhere herein, includes separate electromagnetic and reluctance torque components whose relative contribution to total motor torque is continuously variable. The term "electromagnetic torque" describes a magnitude of torque generated by the resulting compressive / tensile forces due to interacting time-varying electromagnetic fields of the stator assembly 26 and the rotor assembly 33 in the exemplary electric motor 16 of FIG. 2. The term "reluctance" is analogous to an electrical resistance, with the magnetic flux following a path of least magnetic reluctance in a manner conceptually similar to an electrical current following a path of least electrical resistance. Thus, the term "reluctance torque" describes the time-varying torque contribution of the rotor hub 33R as the rotor hub 33R displaces to align a minimum reluctance flux path with a rotating stator field, in this case the stator field generated by the stator core 26C.Generally, the electric motor 16 generates torque at a given axial position from both the magnetic field of the rotor assembly 33 and the reluctance ratio of the rotor assembly 33. As the electric motor 16 rotates relative to the stator field by way of the stator core 26C, the reluctance changes through the rotor assembly 33. As the rotor magnetic field rotates, a resistance and back-EMF ("back EMF") are generated that oppose current passage through the stator windings 26W. The reluctance ratio produces no tension or no back tension. Thus, the ideal situation at high speeds when low torque is required is to reduce the magnetic field while maintaining or increasing the reluctance ratio. The present configuration enables this desirable result to occur.In FIG. 2, the cylindrical rotor hub 33R has respective first and second ends E 1 and E 2 that are magnetized with different average magnetic fields B 1 and B 2 having corresponding field strengths, respectively. The first end E 1 may have an average magnetic field strength that is weaker than the average magnetic field at the second end E 2 or vice versa. Thus, the magnetic field strength of the cylindrical rotor hub 33R varies along its axial length L R with strong constant reluctance characteristics. This feature allows the electromagnetic and reluctance torque contributions to motor torque (arrow T M) to be automatically varied between predetermined relative contribution levels or percentages, the variation being active or passive in response to different rotational speed and torque operating points of the electric motor 16.For example, operation of the electric motor 16 may include a low speed / high torque operating point where the magnetic torque component of the motor torque (arrow T M) is high, e.g., about 75%, and the reluctance torque component is low or about 25% consistent as in this example. Another high speed / low torque operating point may be used where the desired magnetic and reluctance torque components are approximately equal, such as 50% each. Other levels of contribution of the magnetic and reluctance torque components may be used in other embodiments depending on the application of the electric motor. Between the desired levels of contribution, i.e., at a first position as shown and a second position bounded by boundary 62, rotor hub 33R may be displaced along rotor shaft 17 as indicated by double arrow AA to provide continuously variable magnetic / reluctance contributions.The rotor hub 33R may be splined or otherwise slidably connected to the rotor shaft 17 by way of spline 72 as shown in FIG. 2, and is thus slidable along the rotor shaft 17. The axial length L R of the rotor hub 33R may exceed the axial length L S of the stator core 26C, for example, by 150 percent in an exemplary embodiment. In some embodiments, the axial length L R of the rotor hub 33R may be equal to the total axial length L ST of the stator assembly 26. The stator core 26C is separated from the rotor hub by the radial air gap G, which in some embodiments may be uniform along the axial length L S of the stator core 26C as shown. In other embodiments, the radial air gap G may gradually taper such that the air gap G is smaller at the second end E 2 than at the first end E 1.Various approaches may be used to provide the different magnetic field strengths along the axial length of the rotor hub 33R. For example, the rotor assembly 33 may include a plurality of permanent magnets 39 connected to or embedded within the rotor hub 33R, e.g., in slots (not shown) thereof. The arrangement of such slots creates a preferred path for the magnetic flux generated at different rotational positions of the rotor hub 33R. A number of the permanent magnets 39 positioned at the first end E 1 may exceed a number of the permanent magnets 39 positioned at the second end E 2.Alternatively, the number of permanent magnets 39 at the first and second ends E 1 and E 2 may be the same, where the magnetic field strength generated by the permanent magnets 39 at the first end E 1 exceeds the magnetic strength of the permanent magnets 39 used at the second end E 2. Similarly, the arrangement of such permanent magnets 39 may be varied to produce the desired magnetic field variation between the first and second ends E1 and E2, or the magnets 39 may be omitted altogether in favor of a mechanically uniform rotor hub 33R along the axial length L R of the rotor hub 33R, i.e., with varying degrees of magnetization of the laminations used to construct the rotor hub 33R in place of the arrangement of permanent magnets 39.The embodiment of FIG. 2 achieves displacement of the rotor hub 33R via actuation of the actuator 60 positioned proximate the first or second end E 1 or E 2 of the rotor hub 33R. In the illustrated embodiment, the rotor hub 33R is actively moved via the rotor shaft 17 via an actuation force (arrow F A) of the actuator 60. As noted above, axial displacement of the rotor hub 33R occurs in response to various actual rotational speed and torque operating points of the electric motor 16. Thus, the controller 50 of FIG. 1 may be used to accurately determine in real time when to displace the rotor hub 33R and thereby vary the relative magnetic / reluctance torque contributions to the total motor torque (arrow T M).In an exemplary embodiment, the controller 50 may receive a set of the input signals (arrow CC I) of FIG. 1, information indicative of the current operating point of the electric motor 16. For example, a position sensor S P may measure and report the current axial position (arrow P A, 26) of the rotor hub 33R. Similarly, a speed sensor S N and a torque sensor S T may measure / estimate and report the respective speed (arrow N 16) and the output torque (T 16) of the electric motor 16, wherein in particular the torque sensor (S T) may be configured as estimated or modeled torque logic of the controller 50 instead of a physical sensor. The controller 50 may be programmed with a look-up table 65, wherein the processor (P) reads a corresponding desired position for the current speed and torque operating point. Subsequently, the controller 50 may transmit an actuator control signal (arrow CC 60) as a possible control signal (arrow CC O) of FIG. 1 to the actuator 60 to command the actuator 60 to apply the force (arrow F A) and thus place the rotor hub 33R 65 in the corresponding desired axial position according to the look-up table.FIG. 3 shows an alternative, passively regulated embodiment of the electric motor 16 of FIG. 2 Instead of the actuator 60 of FIG. 2, implementation may be by self-actuation via stator field control and a return spring 64 disposed between a radial surface 67 of the rotor hub 33R and a stationary member 65, e.g., a motor housing. The passive embodiment operates due to the tendency of the magnetic force to repel the magnetic end of the rotor hub 33R, in this case the first end E 1. The stator controller includes sequentially changing the phase currents to the stator windings 26W so as to generate a rotating set of vectors in the stator assembly 26. The rotating vectors cooperate with the magnetic field of the rotor hub 33R and the reluctance of the rotor hub 33R to thereby rotate the rotor hub 33R. The control of the stator current is based on accurate knowledge of the rotational position of the rotor hub 33R, which may be measured via a resolver or encoder 70 and reported to the controller 50 as a measured rotational position (P R, 33).The controller 50 may in turn calculate and issue a stator current command to excite the stator windings 26W in a particular manner and to attenuate the stator magnetic flux, i.e., generate a magnetic flux attenuation current command (arrow CC S) as part of the control signals (arrow CC O) of FIG. 1, where the magnetic flux attenuation current command (arrow CC S) ultimately causes a flux of magnetic flux attenuation stator current to flow into the stator windings 26W. Therefore, FIG. 3 shows a possible embodiment in which a self-actuation and displacement of the rotor hub 33R is realized by means of a stator field control which is assisted by the restoring spring 64.As shown with reference to FIG. 4, the method 100 may be implemented in the logic of the controller 50 and automatically executed during ongoing operation of the electric motor 16. The method 100 may be used with the actively controlled embodiment of FIG. 2 or, with slight variations in the approach, the passively controlled embodiment of FIG. 3 as discussed below.Beginning with step S 102, the controller 50 measures, estimates, or determines the current speed and torque of the electric motor 16. for example, the speed of the rotor shaft 17 of FIG. 1 may be measured using a speed sensor S N, as schematically shown in FIG. 2, e.g., a shaft encoder, Hall effect sensor, or photoelectric sensor. The motor torque (arrow T M of FIGS. 1-3 ) may be estimated or calculated based on the measured motor speed and calibrated or measured characteristics of the electric motor 16, such as current and / or voltage. The method 100 then proceeds to step S 104.Step S 104 includes reading a target axial position of the rotor hub 33R from the look-up table 65 into the memory (M) of the controller 50. The method 100 proceeds to step S 106 when the target axial position of the rotor hub 33R has been determined.In step S 106, the controller 50 may command the axial displacement of the rotor hub 33R to the target axial position read out in step S 104. The implementation of step S 106 may vary depending on the embodiment. For example, when using the active control embodiment of FIG. 2, the controller 50 may command actuation of the actuator 60, such as by energizing a solenoid therethrough, to cause linear displacement of a plunger (not shown) of the actuator 60 and application of the force (arrow F A) to the rotor hub 33R. Thus, step S 106 may include shifting to the desired position according to the look-up table 65 with a corresponding voltage or current command and then applying the current or voltage to the actuator 60.For the exemplary passive embodiment of FIG. 3, the control action of step S 106 may include applying a calibrated stator current to the stator windings 26W of FIG. 3 to cause the rotor hub 33R to be magnetically repelled to the desired axial position due to the field interaction. In such an embodiment, the current speed and torque of the electric motor 16 may correspond to a calibrated stator current that is then applied by the controller 50 to cause linear movement or displacement of the rotor hub 33R to the desired axial position. The method 100 then proceeds to step S 108.S 108 may include determining whether the rotor hub 33R has reached the target position, for example, using a position sensor, a timer, or the like. Step S 106 is repeated in a loop with step S 108 until the target axial position is reached. The method 100 then proceeds to step S 110.Step S 110 includes suspending the position control actions of the controller 50 and continuing to step S 102. The method 100 is then repeated in a loop during operation of the electric motor 16 to continuously vary the desired magnetic characteristics / relative contributions of the magnetic and reluctance torques of the electric motor 16 as a function of the speed and torque of the electric motor 16.Using the electric motor 16 of FIG. 1 constructed according to FIG. 2 or FIG. 3 and controlled according to the example method of FIG. 4, a greater potential for efficiency gains over a given engine operating range may be possible. This is made possible by the combination of strong constant reluctance torque characteristics, strong permanent magnet torque at high loads, reduced permanent magnet torque at low loads, and compromiseless stator and rotor pole configurations. The increased length of the rotor hub 33R of FIGS. 2 and 3 as well as the addition of a slidable connection between the rotor hub 33R and the rotor shaft 17 may increase the complexity of the electric motor 16. However, existing packaging constraints may be maintained by limiting the axial length L R of the rotor hub 33R to fit within, i.e., be less than or equal to, the total length L ST- stator assembly 26.

Claims

An electric motor (16) operable to generate a total motor torque having continuously variable magnetic and reluctance torque components, the electric motor (16) comprising: a stator assembly (26) having stator windings (26W) and a stator core (26C) having an axial length (L S); a rotor assembly (33) including a rotor shaft (17) and a cylindrical rotor hub (33R) having respective axial lengths (L R) the cylindrical rotor hub (33R) having a first end (E1) having a first average magnetic field strength and a second end (E2) having a second average magnetic field strength, the second average magnetic field strength being weaker than the first average magnetic field strength; and a return spring (64) disposed proximate one of the first and second ends (E1, E2) of the rotor hub (33R); the rotor hub (33R) being slidable with respect to the rotor shaft (17), the axial length (L R) of the rotor hub (33R) exceeding the axial length (L S) of the stator core (26C), the rotor hub (33R) being configured to slide along the axial length of the rotor shaft (17) to vary the contributions of the magnetic and reluctance torque components to the total motor torque in response to different rotational and torque operating points of the electric motor (16) relative to each other; characterized a controller (50) configured to receive a set of input signals including a speed of the electric motor (16) and a torque generated by the electric motor (16), and command a displacement of the rotor hub (33R) along the axial length (L R) of the rotor shaft (17) in response to the received speed and the received torque, thereby continuously varying the relative contributions of the magnetic and reluctance torque components to the total motor torque; wherein the controller (50) is further configured to apply a magnetic flux weakening stator current to the stator windings (26W) to passively displace the rotor hub (33R) along the axial length (L R) of the rotor shaft (17).The electric motor (16) of claim 1, wherein the axial length (L R) of the rotor hub (33R) is at least 150 percent of the axial length (L S) of the stator core (26C).The electric motor (16) of claim 2, wherein the stator hub is wound with stator windings (26W) such that the stator assembly (26) has an overall axial length (L ST) equal to or greater than the axial length (L R) of the rotor hub (33R).The electric motor (16) of claim 1, wherein the torque operating points comprise a low speed / high torque operating point where the magnetic torque component is 75 percent and the reluctance torque component is 25 percent and a high speed / low torque operating point where both the magnetic torque component and the reluctance torque component are 50 percent.A vehicle (10) comprising: a load; an electric motor (16) operable to generate the input torque for a transmission (30), wherein the input torque is a total motor torque having continuously variable magnetic and reluctance torque components, the electric motor (16) including: a stator assembly (26) having stator windings (26W) and a stator core (26C) having an axial length (L ST); and a rotor assembly (33) including a rotor shaft (17) and a cylindrical rotor hub (33R) each having an axial (L R), wherein the cylindrical rotor hub (33R) has a first end (E1) having a first average magnetic field strength and a second end (E2) having a second average magnetic field strength, and wherein the second average magnetic field strength is weaker than the first average magnetic field strength; wherein the axial length (L R) of the rotor hub (33R) exceeds the axial length (L S) of the stator core (26C), and the rotor hub (33R) is configured to translate along the axial length of the rotor shaft (17) at different rotational speed and torque operating points of the electric motor (16); a return spring (64) disposed proximate the first or second ends (E1, E2) of the rotor hub (33R); and a controller (50); characterized in that the transmission is connected to the load and configured to provide an output torque to the load in response to an input torque; the rotor hub (33R) is splined to the rotor shaft (17); and the controller (50) is configured to receive a set of input signals including a speed of the electric motor (16) and a torque generated by the electric motor (16), and command a displacement of the rotor hub (33R) along the axial length of the rotor shaft (17) in response to the received speed and the received torque, thereby continuously varying the relative contributions of the magnetic and reluctance torque components to the total motor torque; and wherein the controller (50) is further configured to apply a magnetic flux weakening stator current to the stator windings (26W) to passively displace the rotor hub (33R) along the axial length of the rotor shaft (17).

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