Transverse flux machine with asymmetric stator

Abstract

The invention relates to a transverse flux machine with an asymmetric stator. A transverse flux machine, TFM, includes: a rotor assembly configured to rotate about an axis; and a stator assembly. The stator assembly includes a plurality of stator windings and a plurality of stator cores each configured to direct magnetic flux toward the rotor assembly in each of an axial direction and a radial direction. Each of the stator cores defines an annular shape and holds a corresponding one of the plurality of stator windings. The plurality of stator cores includes an outer stator core positioned adjacent an axial end of the stator assembly, and an inner stator core spaced apart from the axial end of the stator assembly. The inner stator core defines at least one dimension that is different from a corresponding dimension of the outer stator core.

Description

Technical Field

[0001] The present disclosure relates to transverse flux electric machines and to the use of such transverse flux electric machines in handwheel (steering wheel) actuators of a steering system of a vehicle. Background Art

[0002] Vehicles (such as cars, trucks, sport utility vehicles, crossovers, minivans, ships, aircraft, all-terrain vehicles, recreational vehicles, or other suitable forms of transportation) typically include a steering system, such as an electric power steering (EPS) system, a steer-by-wire (SbW) steering system, a hydraulic steering system, or other suitable steering systems. Such a steering system of a vehicle typically controls various aspects of steering the vehicle (including providing steering assistance to an operator of the vehicle, controlling steerable wheels of the vehicle, etc.).

[0003] Steer-by-wire (SbW) is a direct evolution of an electric power steering (EPS) system, where there is no mechanical connection between the handwheel and the steering rack. An EPS system may include a single actuator, the sole purpose of which is to provide assistance to the driver during a steering action. However, in an SbW system, there may be two electric actuators / motors with different functions. The electric actuator attached to the rack in an SbW system is referred to as a road wheel actuator (RWA), while the actuator on the driver side is referred to as a handwheel actuator (HWA). The RWA has the same assistance-providing function as the EPS system actuator. On the other hand, the HWA is more used as a feedback motor rather than providing assistance to the driver. In the absence of the HWA, the handwheel on the SbW system would only freewheel since there is no mechanical connection / friction. The HWA has opened up a large number of design-related opportunities due to its functionality.

[0004] Based on its functionality, the torque-speed curves of different actuators used in a steering system can also be different. The very different operating domains of EPS / RWA and HWA have prompted design explorations of HWA technology. Summary of the Invention

[0005] The present disclosure generally relates to transverse flux electric machines.

[0006] One aspect of the disclosed embodiments includes a transverse flux machine (TFM). The TFM includes: a rotor assembly configured to rotate about an axis; and a stator assembly. The stator assembly includes a plurality of stator windings and a plurality of stator cores, each of the plurality of stator cores being configured to direct magnetic flux toward the rotor assembly in each of an axial direction and a radial direction. Each of these stator cores defines an annular shape and holds a corresponding one of the plurality of stator windings. The plurality of stator cores includes outer stator cores positioned adjacent an axial end of the stator assembly, and inner stator cores spaced apart from the axial end of the stator assembly. The inner stator cores define at least one dimension that is different from a corresponding dimension of the outer stator cores.

[0007] One aspect of the disclosed embodiments includes a steer-by-wire system for a vehicle. The steer-by-wire system includes a handwheel actuator coupled to apply torque to a steering wheel. The handwheel actuator includes a transverse flux machine (TFM). The TFM includes: a rotor assembly configured to rotate about an axis; and a stator assembly. The stator assembly includes a plurality of stator windings and a plurality of stator cores, each of the plurality of stator cores being configured to direct magnetic flux toward the rotor assembly in each of an axial direction and a radial direction. Each of these stator cores defines an annular shape and holds a corresponding one of the plurality of stator windings. The plurality of stator cores includes outer stator cores positioned adjacent an axial end of the stator assembly, and inner stator cores spaced apart from the axial end of the stator assembly. The inner stator cores define at least one dimension that is different from a corresponding dimension of the outer stator cores.

[0008] These and other aspects of the disclosure are disclosed in the following detailed description of the embodiments, the appended claims, and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present disclosure is best understood from the following detailed description when read in conjunction with the accompanying drawings. It should be emphasized that, in accordance with common practice, the various features of the drawings are not drawn to scale. Instead, the dimensions of the various features are arbitrarily enlarged or reduced for clarity.

[0010] Figure 1 is a schematic diagram of an electric power steering (EPS) system in accordance with the principles of the present disclosure.

[0011] Figure 2 Generally illustrates an electric power steering (EPS) system in accordance with the principles of the present disclosure.

[0012] Figure 3Generally illustrates a steer-by-wire (SbW) steering system in accordance with the principles of the present disclosure.

[0013] Figure 4 Is a schematic diagram of a motor drive system in accordance with the principles of the present disclosure.

[0014] Figure 5 Shows a graph illustrating the torque-speed curve of a steering system actuator in accordance with the principles of the present disclosure.

[0015] Figure 6 Shows a graph illustrating the torque-speed curve of a direct drive handwheel actuator in an SbW steering system.

[0016] Figure 7 Shows a cross-sectional view of a radial flux machine (RFM) in accordance with the principles of the present disclosure.

[0017] Figure 8 Shows a cross-sectional view of an axial flux machine (AFM) in accordance with the principles of the present disclosure.

[0018] Figure 9 Shows a cross-sectional view of a transverse flux machine (TFM) in accordance with the principles of the present disclosure.

[0019] Figure 10 Shows a partial perspective view of a TFM having a flux concentrating outer rotor and a single-piece stator in accordance with the principles of the present disclosure.

[0020] Figure 11 Shows a perspective view of a stator in an outer rotor TFM in accordance with the principles of the present disclosure.

[0021] Figure 12 Shows a graph illustrating the flux linkage imbalance between the phases of a three-phase TFM.

[0022] Figure 13 Shows a graph illustrating the phase currents in a three-phase TFM.

[0023] Figures 14A to 14C Shows the flux density during the peak current of each of the three phases of a three-phase TFM having a flux linkage imbalance;

[0024] Figure 15 Shows an end view of a portion of an outer rotor TFM.

[0025] Figure 16 Shows a perspective view of a portion of a stator assembly of an outer rotor TFM in accordance with the principles of the present disclosure.

[0026] Figure 17A graph showing the average torque in Newton meters (Nm) generated by an outer rotor TFM with B-phase stator teeth having different angular widths is shown.

[0027] Figure 18 A graph showing the torque ripple (%) of an outer rotor TFM with B-phase stator teeth having different angular widths is shown.

[0028] Figure 19 A perspective view of a section of a stator assembly of an outer rotor TFM according to the principles of the present disclosure is shown, and various different parameters are indicated.

[0029] Figure 20 A graph showing the average torque in Newton meters (Nm) generated by an outer rotor TFM with a B-phase stator core having different back iron depth values is shown.

[0030] Figure 21 A graph showing the torque ripple (%) of an outer rotor TFM with a B-phase stator core having different back iron depth values is shown.

[0031] Figure 22 A graph showing the average torque in Newton meters (Nm) generated by an outer rotor TFM with a B-phase stator core having different combinations of back iron depth and tooth angular width is shown.

[0032] Figure 23 A graph showing the torque ripple (%) for an outer rotor TFM with a B-phase stator core having different combinations of back iron depth and tooth angular width is shown. Detailed Description

[0033] The following discussion pertains to various embodiments of the present disclosure. Although one or more of these embodiments may be preferred, the disclosed embodiments should not be construed or otherwise used to limit the scope of the present disclosure (including the claims). Additionally, those skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only as an illustration of that embodiment and is not intended to imply that the scope of the present disclosure (including the claims) is limited to that embodiment.

[0034] As described, a vehicle (such as a car, truck, sport utility vehicle, crossover vehicle, minivan, ship, aircraft, all-terrain vehicle, recreational vehicle, or other suitable form of transportation) typically includes a steering system, such as an EPS system, an SbW steering system, a hydraulic steering system, or other suitable steering system. The steering system of such a vehicle typically controls various aspects of steering the vehicle (including providing steering assistance to an operator of the vehicle, controlling steerable wheels of the vehicle, etc.).

[0035] Figure 1 FIG. is a schematic view of an electric power steering system (EPS) 40 suitable for implementing the disclosed technology. The EPS includes a steering mechanism 36, which includes a rack and pinion type mechanism having a rack (not shown) located within a housing 50 and a pinion (also not shown) located below a gear housing 52. When an operator input, hereinafter represented as a steering wheel 26 (e.g., a hand wheel, etc.), is rotated, an upper steering shaft 29 rotates, and a lower steering shaft 51 connected to the upper steering shaft 29 by a universal joint 34 causes the pinion to rotate. The rotation of the pinion moves the rack, which moves a tie rod 38 (only one is shown), which in turn moves a steering knuckle 39 (only one is shown), which rotates a steerable wheel 44 (only one is shown).

[0036] Electric power steering assistance is provided by a steering motion control system generally represented by reference numeral 24 and includes a controller 16 and a motor, which may be a permanent magnet synchronous motor and is hereinafter represented as motor 19. The controller 16 is powered by a vehicle power source 10 through a supply conductor 12. The controller 16 receives a vehicle speed signal 14 representing the vehicle speed from a vehicle speed sensor 17. The steering angle is measured by a position sensor 32, which may be an optical encoder type sensor, a variable resistor type sensor, or any other suitable type of position sensor, and provides a position signal 20 to the controller 16. The motor speed may be measured by a tachometer or any other device and is sent to the controller 16 as a speed signal 21. The motor speed represented as ω m can be measured, calculated, or a combination of both. For example, the motor speed ω m can be calculated as the change in motor position measured by the position sensor 32 over a specified time interval. For example, the motor speed ω m can be determined as the derivative of the motor position θ m with respect to time. It should be understood that there are many well-known methods for performing the derivative function.

[0037] When the steering wheel 26 is turned, the torque sensor 28 senses the torque applied to the steering wheel 26 by the vehicle operator. The torque sensor 28 may include a torsion bar (not shown) and a variable resistor type sensor (also not shown) that outputs a torque signal 18 related to the amount of twist on the torsion bar to the controller 16. Although this is one type of torque sensor, any other suitable torque sensing device used in conjunction with known signal processing techniques will be sufficient. In response to various inputs, the controller sends a command 22 to the motor 19, which provides torque assist to the steering system via a worm 47 and a worm gear 48, thereby providing torque assist to vehicle steering.

[0038] It should be noted that although the disclosed embodiments are described by reference to motor control for electric steering applications, it should be understood that such reference is merely illustrative and that the disclosed embodiments may be applied to any motor control application employing an electric motor, such as steering, valve control, etc. Additionally, the references and descriptions herein may be applied to many forms of parameter sensors, including but not limited to torque, position, speed, etc. It should also be noted that the electric machines referred to herein include but are not limited to motors, and hereinafter, for brevity and simplicity, will be referred to non - restrictively only as motors.

[0039] In the steering motion control system 24 as depicted, the controller 16 calculates commands for delivering the desired output power using torque, position, speed, etc. The controller 16 is arranged to communicate with various systems and sensors of the motor control system. The controller 16 receives signals from each system sensor, quantifies the received information, and in response thereto provides an output command signal, in this case, for example, to the motor 19. The controller 16 is configured to generate a corresponding voltage from an inverter (not shown), which may optionally be combined with the controller 16 and will be referred to herein as the controller 16, such that when applied to the motor 19, a desired torque or position is produced. In one or more examples, the controller 16 operates in a feedback control mode (as a current regulator) to generate the command 22. Alternatively, in one or more examples, the controller 16 operates in a feed - forward control mode to generate the command 22. Since these voltages are related to the position and speed of the motor 19 and the desired torque, the position and / or speed of the rotor and the torque applied by the operator are determined. A position encoder is connected to the steering shaft 51 to detect the angular position θ. The encoder may sense the rotational position based on optical detection, magnetic field changes, or other methods. Typical position sensors include potentiometers, resolvers, synchros, encoders, etc., and combinations including at least one of the foregoing. The position encoder outputs a position signal 20 that indicates the angular position of the steering shaft 51 and thereby the angular position of the motor 19.

[0040] The desired torque can be determined by one or more torque sensors 28, which send a torque signal 18 indicative of the applied torque. Such torque sensors 28 and the torque signal 18 therefrom can respond to a flexible torsion bar, spring, or similar device (not shown) configured to provide a response indicative of the applied torque.

[0041] In one or more examples, a temperature sensor 23 is located at the motor 19. Preferably, the temperature sensor 23 is configured to directly measure the temperature of the sensing portion of the motor 19. The temperature sensor 23 sends a temperature signal 25 to the controller 16 to facilitate the processing and compensation as specified herein. Typical temperature sensors include thermocouples, thermistors, thermostats, etc., and combinations including at least one of the foregoing sensors, which provide a calibrated signal proportional to a specific temperature when appropriately placed.

[0042] Position signals 20, speed signals 21, torque signals 18, etc. are applied to the controller 16. The controller 16 processes all input signals to generate values corresponding to each signal, thereby producing rotor position values, motor speed values, and torque values that can be used in processing in algorithms as specified herein. Measurement signals (such as the aforementioned measurement signals) are also typically linearized, compensated, and filtered as needed to enhance the characteristics of the acquired signals or eliminate their undesirable characteristics. For example, the signals can be linearized to increase processing speed or address the large dynamic range of the signals. Additionally, frequency - or time - based compensation and filtering can be employed to eliminate noise or avoid undesirable spectral characteristics.

[0043] To perform the specified functions and desired processing, and thus the calculations (e.g., identification of motor parameters, control algorithms, etc.), the controller 16 can include, but is not limited to, a processor, computer, DSP, memory, storage device, register, timing, interrupt, communication interface, and input / output signal interface, etc., and combinations including at least one of the foregoing. For example, the controller 16 can include input signal processing and filtering to enable accurate sampling and conversion or acquisition of such signals from the communication interface.

[0044] Figure 2 An electric power steering (EPS) system is generally illustrated, and Figure 3 A steer - by - wire (SbW) steering system is generally illustrated. Figure 2 The EPS system of Figure 1 can be similar to or equivalent to Figure 3 The SbW system of Figure 1The steer-by-wire (SbW) system 40, which is different in that there is no physical linkage between the steering wheel 26 and the steerable wheels 44 and has two separate and independent motors 19a, 19b. As shown in the figure, the SbW system includes a first motor 19a (also referred to as a hand wheel actuator (HWA)), which is configured to provide torque to the steering wheel 26 for providing haptic feedback to the driver.

[0045] Steer-by-wire (SbW) is a direct evolution of the electric power steering (EPS) system, in which there is no mechanical coupling between the steering wheel 26 and the steering rack. As Figure 2 can be seen, the EPS system may include a single actuator 19, whose sole purpose is to provide assistance to the driver during a steering maneuver. However, in the SbW system, there are two electric actuators / motors with different functions. The electric actuator attached to the steering mechanism 36 in the SbW system is called a road wheel actuator (RWA) 19b, while the actuator on the driver side is called a hand wheel actuator (HWA) 19a. The RWA 19b can provide the same assistance function as the actuator 19 in the EPS system. On the other hand, the HWA 19a is more used as a feedback motor rather than providing assistance to the driver. In the absence of the HWA 19a, the hand wheel on the SbW system will only spin freely since there is no mechanical coupling / friction.

[0046] In some embodiments, the steering system may include a controller, such as Figure 4 the controller 100 generally illustrated. The controller 100 can include any suitable controller. The controller 100 can be configured to control various functions of, for example, the vehicle system described herein. The controller 100 can include a processor 102 and a memory 104. The processor 102 can include any suitable processor, such as the processors described herein. Additionally or alternatively, in addition to or different from the processor 102, the controller 100 can include any suitable number of processors. The memory 104 can include a single disk or multiple disks (e.g., a hard disk drive) and includes a storage management module that manages one or more partitions within the memory 104. In some embodiments, the memory 104 can include flash memory, semiconductor (solid-state) memory, etc. The memory 104 can include random access memory (RAM), read-only memory (ROM), or a combination thereof. The memory 104 can include instructions that, when executed by the processor 102, cause the processor 102 to at least control various functions of the steering system and / or any other suitable functions, including those of the systems and methods described herein.

[0047] The controller 100 may receive one or more signals from various measurement devices or sensors 106 indicating sensed or measured characteristics of the vehicle. The sensors 106 may include any suitable sensors, measurement devices, and / or other suitable mechanisms. For example, the sensors 106 may include one or more torque sensors or devices, one or more handwheel position sensors or devices, one or more motor position sensors or devices, one or more motor angle sensors or devices, other suitable sensors or devices, or combinations thereof. The one or more signals may indicate handwheel torque, handwheel angle, motor angle or position, vehicle speed, other suitable information, or combinations thereof.

[0048] Figure 5 A graph showing the torque-speed curves of the exemplary steering system actuators 19, 19a, and 19b is shown. Based on their functionality, the different steering system actuators 19, 19a, 19b have different speed curves. As Figure 5 indicated by the dashed line in, the RWA 19b and the EPS actuator 19 in SbW each operate in the first quadrant (Q1) of the torque-speed curve. The positive direction of the speed in Q1 indicates that the actuator acts in the same direction as the driver's handwheel movement and provides assistance. However, as indicated by the solid line, the HWA 19a of the SbW system mainly operates in the second quadrant (Q2) of the torque-speed curve. The HWA 19a moves in the opposite direction to the driver's handwheel movement (speed -ve) and provides feedback to the driver. This feedback may be necessary for providing the driver with a general steering feel and road condition feedback. Additionally, some low-speed assistance (Q1 operation) from the HWA 19a may also be required, as Figure 5 visible in.

[0049] The HWA 19a may include an electric motor coupled to apply torque to the steering wheel 26 configuration, such as a worm gear drive, a belt drive, and / or a direct drive. For the case of worm gear and belt drives, a low torque (~3 Nm) and high speed (3000 rpm) PMSM can be used as the actuator. Both surface-mounted PMSM (SPMSM) and interior PMSM (IPMSM) topologies can be used for such HWA architectures. Additionally, due to their similarity (in terms of torque-speed range), a large number of components can be directly transferred from the column EPS (CEPS) system to the worm gear or belt-driven SbW handwheel system. For the direct drive case, a high torque (about 30 Nm for exit / entry) and low speed (about 200 rpm to 300 rpm) actuator is required. For the direct drive architecture, the number of mechanical components is reduced, which in turn has the potential to reduce cost and weight. Additionally, the reduction in weight is directly related to an increase in range efficiency or mileage (miles per gallon). However, traditional PMSMs need to be redesigned for the high torque and low speed output requirements of the direct drive architecture.

[0050] Based on its functionality, the torque-speed curves of different actuators used in the steering system also change. As Figure 5 shown, the RWA and EPS actuators in the SbW system each operate in the first quadrant (Q1) of the torque-speed curve. The positive direction of the speed in Q1 indicates that the actuator acts in the same direction as the driver's handwheel movement and provides assistance. However, the SbW HWA mainly operates in the second quadrant (Q2) of the torque-speed curve. The HWA moves in the opposite direction to the driver's handwheel movement (speed -ve) and provides feedback to the driver. This feedback is necessary for providing the driver with a general steering feel and road condition feedback. Additionally, some low-speed assistance (Q1 operation) from the HWA may also be required, as Figure 5 visible. The very different operating domains of the EPS / RWA and HWA have prompted the design exploration of HWA technology.

[0051] The HWA can include an electric motor coupled to apply torque to the steering wheel 26 configuration, such as a worm gear drive, a belt drive, and / or a direct drive. For the case of worm gear and belt drives, a low torque (about 3 Nm) and high speed (3000 rpm) PMSM can be used as the actuator. Both surface-mounted PMSM (SPMSM) and interior PMSM (IPMSM) topologies can be used for such HWA architectures. Additionally, due to their similarity (in terms of torque-speed range), a large number of components can be directly transferred from the column EPS (CEPS) system to the worm gear or belt-driven SbW handwheel system. For the direct drive case, a high torque (about 30 Nm for exit / entry) and low speed (about 200 rpm to 300 rpm) actuator is required. For the direct drive architecture, the number of mechanical components is reduced, which in turn has the potential to reduce cost and weight. Additionally, the reduction in weight is directly related to an increase in range efficiency or mileage (miles / gallon). However, traditional PMSMs need to be redesigned for the high torque and low speed output requirements of the direct drive architecture.

[0052] Figure 6 A graph showing the torque-speed curve of the HWA 19a in the SbW steering system with a direct drive configuration (1:1 gear ratio) is shown. As shown, the HWA 19a typically operates at speeds between -200 revolutions per minute (RPM) and +80 RPM, and generates torques between 0 Newton meters (Nm) and about 30 Newton meters (Nm). The transverse flux machine has the potential to perform in such low-speed high-torque direct drive applications.

[0053] Figure 7 A cross-sectional view of a radial flux machine (RFM) is shown. Figure 8 A cross-sectional view of an axial flux machine (AFM) is shown. Figure 9A cross-sectional view of a transverse flux machine (TFM) is shown. Each of the RFM, AFM, and TFM devices includes a shaft configured to rotate about an axis A. Classification among the RFM, AFM, and TFM configurations can be based on the direction of the magnetic flux.

[0054] Figure 7 The RFM of includes a first rotor assembly 110a having a first rotor core 112a attached to rotate about the axis A together with a first shaft 114a. The first rotor assembly 110a is located within a first housing 115a, and the first shaft 114a extends through the first housing 115a and extends outside the first housing and is supported by a pair of first bearings 116a. A set of first permanent magnets 118a is attached to the first rotor core 112a and generates a magnetic flux extending radially outward. Figure 7 The RFM of further includes a first stator assembly 120a having a first stator core 122a, where a set of first windings 124a extends through the first stator core and carries current in an axial direction parallel to the axis A and perpendicular to the magnetic flux.

[0055] Figure 8 The AFM of includes a second rotor assembly 110b having a second rotor core 112b attached to rotate about the axis A together with a second shaft 114b. The second rotor assembly 110b is located within a second housing 115b, and the second shaft 114b extends through the second housing 115b and extends outside the second housing and is supported by a pair of second bearings 116b. A set of second permanent magnets 118b is attached to the second rotor core 112b and generates a magnetic flux extending in an axial direction parallel to the axis A. Figure 8 The AFM of further includes a second stator assembly 120b having a second stator core 122b, where a set of second windings 124b extends through the second stator core and carries current in a radial direction perpendicular to the axis A and perpendicular to the magnetic flux.

[0056] Figure 9 The TFM of includes a third rotor assembly 110c having a third rotor core 112c attached to rotate about the axis A together with a third shaft 114c. The third rotor assembly 110c is located within a third housing 115c, and the third shaft 114c extends through the third housing 115c and extends outside the third housing and is supported by a pair of third bearings 116c. A set of third permanent magnets 118c is attached to the third rotor core 112c and generates a magnetic flux that extends radially inward at a first position, axially through the third rotor core 112c, and extends radially outward at a second position axially spaced from the first position. Figure 9The TFM also includes a third stator assembly 120c having a third stator core 122c, with a set of third windings 124c extending through the third stator core and carrying current in a circumferential direction perpendicular to axis A and perpendicular to the magnetic flux. As shown, the third stator core 122c defines a U-shaped configuration, with open ends aligned with the third permanent magnets 118c at a first position and a second position for providing a closed rectangular path of magnetic flux together with the third rotor core 112c.

[0057] Figures 7 to 9 The magnetic flux directions in three motor topologies are shown. For the RFM, the magnetic flux moves radially in the air gap, while for the AFM, the magnetic flux moves axially from the stator to the rotor and vice versa. However, as Figure 9 can be seen, for the TFM, the magnetic flux moves in both the radial plane and the axial plane. Although several topologies of the TFM can be identified from the literature, the 3D (radial and axial) magnetic flux path is a common feature across different topologies. Compared with the radial flux machine, the TFM is known for having a higher volume power density and weight power density. The AFM and the TFM are known to have comparable power densities. However, the simplicity of the toroidal windings in the TFM has the potential to make the manufacturing process easier and cost-saving.

[0058] As Figure 7 shown, the magnetic flux in the RFM mainly extends in the radial direction perpendicular to axis A. As Figure 8 shown, the magnetic flux in the AFM mainly extends in the axial direction parallel to axis A. As Figure 9 shown, the magnetic flux in the TFM defines a closed-loop path, with some parts extending in the radial direction perpendicular to axis A and other parts extending in the axial direction parallel to axis A. The RFM, AFM, and TFM configurations can each provide different volume power densities and weight power densities. The TFM configuration can be particularly well-suited for low-speed and high-torque operations.

[0059] The present disclosure provides a transverse flux machine (TFM) topology for a direct drive SbW HWA architecture. The transverse flux machine has the potential to provide significant power density advantages over conventional radial flux machines in the low-speed high-torque operating region of a direct drive SbW HWA. Conventional RFMs can be laminated in the radial X-Y plane to accommodate their 2D magnetic flux paths and reduce eddy current losses at high operating frequencies. The AFM can also be laminated in the axial X-Z plane to assist the axial travel of the magnetic flux from the stator to the rotor and vice versa. However, as Figure 9 can be seen, for the TFM, the magnetic flux moves in both the axial direction and the radial direction between the third stator assembly 120c and the third rotor assembly 110c.

[0060] If the TFM includes a laminated core, depending on the core position and the expected direction of magnetic flux travel, laminations in the X-Y and X-Z directions will be required. This can severely complicate the manufacturing process of the TFM. To avoid complication and ensure 3D magnetic flux travel in the TFM core, soft magnetic core (SMC) materials can be used for either or both of the rotor core and / or the stator core. The SMC material includes insulated iron particles pressed into a core shape. The electrical insulation between the iron particles of the pressed SMC core significantly reduces eddy current losses at higher operating frequencies.

[0061] Several TFM topologies have been considered, which are good at different performance regions. TFM designs generally indicate a trend towards increasing volumetric torque density. However, for steering applications, the actuator is subject to more stringent constraints such as torque ripple, cogging torque, friction losses, etc. In addition, manufacturability is an important criterion.

[0062] Reducing the number of parts in the TFM can simplify the manufacturing process. In addition, compared with other rotor topologies, the flux-concentrating rotor structure exhibits higher power density and reduced magnet weight. In addition, compared with the needle-wound radial flux machine, the toroidal winding structure of the TFM simplifies the winding process. Due to the manufacturing considerations provided by the topology, Figure 10 the TFM design shown can be particularly advantageous. The stator core can be axially stacked and circumferentially space-shifted to form a multiphase machine.

[0063] Figure 10 A TFM 200 with an outer rotor configuration is presented, which has a rotor assembly 210 configured to rotate about an axis, where the rotor extends annularly around a stator assembly 220. Figure 10 A 45-degree segment of the TFM 200 is shown, with markings indicating the magnetic flux. However, the complete TFM 200 will include eight such segments. The rotor assembly 210 includes a plurality of pairs of permanent magnets 212a, 212b, which are arranged at regular angular intervals and are configured to generate magnetic flux in the circumferential direction between them.

[0064] The rotor assembly 210 further includes a plurality of flux concentration cores 214 located between each pair of permanent magnets 212a, 212b of the pair of permanent magnets 212a, 212b and configured to conduct magnetic flux therebetween. The rotor assembly 210 further includes a plurality of flux divergence cores 216, each flux divergence core being located between adjacent pairs of permanent magnets 212a, 212b. The rotor assembly 210 has a tubular shape and extends between a first axial end 218a and a second axial end 218b. In some embodiments, either or both of the flux concentration cores 214 and / or the flux divergence cores 216 may be made of soft magnetic core (SMC) material. However, other types of materials may be used for either or both of the flux concentration cores 214 and / or the flux divergence cores 216.

[0065] Also as Figure 10 shown, the stator assembly 220 includes a stator core 222 having a U-shaped cross-section (which may also be referred to as a transverse flux core), having a tubular portion 223 that has an inner wall 226 and an outer wall 227. The stator core 222 further includes a first arm 228 and a second arm 229, each arm extending radially outward from the tubular portion 223 toward the rotor assembly 210. The arms 228, 229 are spaced apart from each other in the axial direction, and each of the arms 228, 229 is adjacent to a corresponding axial end of the tubular portion 223. The winding 224 extends annularly around the tubular portion 223, extends through the center of the U-shaped cross-section of the stator core 222, and extends in a winding slot between the first arm 228 and the second arm 229. The winding 224 conducts current in the circumferential direction. The stator core 222 is configured to direct magnetic flux toward the rotor assembly 210 in each of the axial and radial directions.

[0066] As shown, the first arm 228 includes an arcuate recess 230 to define two first teeth 232 on either side thereof. The second arm 229 also includes an arcuate recess 230 to define two second teeth 233 on either side thereof. The second teeth 233 are angularly spaced from the first teeth 232. In this way, magnetic flux is directed from each of the flux concentration cores 214 adjacent the first axial end 218, across the air gap, and into the first teeth 232 of the stator core 222 adjacent thereto. The magnetic flux is directed into the tubular portion 223 of the stator core 222, where the magnetic flux is continuous in the axial direction. The magnetic flux is also directed out of the tubular portion 223 of the stator core 222 and radially outward through the second teeth 233 of the stator core 222 adjacent the second axial end 218b, where the magnetic flux crosses the air gap and returns to the flux concentration cores 214, thus completing a closed path.

[0067] TFM can be particularly well-suited for direct drive low-speed operation. TFM can include a modular, spatially-shifted three-phase stator architecture. TFM can include a simple toroidal winding with an inner stator topology. TFM can provide a relatively low phase resistance, independent of the number of stator slots and rotor poles. TFM can include an outer rotor structure with high volumetric torque density and weight torque density. TFM can be manufactured relatively easily and efficiently and can provide suitable performance for a variety of applications in EPS and / or SbW systems.

[0068] Number of poles

[0069] The phase resistance and coil cross-section in the toroidal TFM are independent of the number of poles, which enables a higher torque density to be achieved in TFM compared to RFM. Additionally, for the expected SbW direct drive HWA application, the operating speed is low. This means that even if a higher number of pole TFM is selected, the fundamental electrical frequency of operation will be within the conventional EPS margin. For example, for a 12-slot 8-pole SbW HWA with a gear ratio of 11:1, at 2500 motor rpm, the fundamental frequency is 166.67 Hz. On the other hand, for a TFM with 100 poles and a direct drive configuration, at 227.27 motor rpm, the fundamental frequency is 189.39 Hz. The limiting number of poles (P 最大 ) can be calculated using Equation (1):

[0070]

[0071] where n 限制 is the maximum motor speed in rpm, and f e，最大 is the maximum fundamental electrical frequency that can be handled by the motor drive.

[0072] Furthermore, despite the higher number of poles in TFM, the phase resistance does not increase, which can provide reduced copper losses and thus improved efficiency and thermal performance.

[0073] Inner rotor / outer rotor topology

[0074] The general sizing equation for TFM can be written as Equation (2):

[0075]

[0076] where P R is the rated output power, K phi is the ratio of the electrical loading on the rotor and stator (K phi can be equal to zero), m is the number of phases, K eis the BEMF factor that incorporates the winding distribution factor Kw and per unit part of the total air-gap area spanned by the salient poles (if any) of the machine, K i is the current waveform factor, K p is the electric power waveform factor, K L is the stack length L e Ratio with respect to the diameter D of the air-gap surface, n is the machine efficiency, B g of, and B g is the air-gap flux density, A is the total electric loading, f is the drive frequency, p is the number of pole pairs, D o is the outer diameter of the machine, and λ o is D g and D o between.

[0077] As is evident from Equation (2), the rated power of the TFM and thus the torque output are proportional to the square of the outer diameter D o of the machine. Substituting D g / D o for λ o , it can be seen from Equation (2) that the output power is directly related to the square of D g . From the interior rotor TFM to the exterior rotor TFM, the diameter of the air-gap surface can be increased for better space utilization. This results in a higher volumetric torque density in the exterior rotor TFM. Additionally, in the exterior rotor TFM, the winding process is relatively simpler. According to the present disclosure, both the exterior rotor TFM and the interior rotor TFM are systematically optimized.

[0078] Figure 11 Shows a perspective view of the stator assembly 220 for an exterior rotor TFM, which is configured to have a rotor (not shown) disposed annularly therearound. The stator assembly 220 includes three stator cores 222a, 222b, 222c, including a stator core 222a for phase A, a stator core 222b for phase B, and a stator core 222c for phase C. Each of the three stator cores 222a, 222b, 222c has a similar or identical annular shape that is axially stacked and circumferentially shifted from each other. Each of the three stator cores 222a, 222b, 222c of the stator assembly 220 contains corresponding windings 224a, 224b, 224c for the corresponding phases, and the stator core extends circumferentially through the corresponding winding. Each stator core of the three stator cores 222a, 222b, 222c of the stator assembly 220 also defines a plurality of teeth having regular angular intervals and extending radially outward.

[0079] The stacked assembly of the TFM stator results in an inherent asymmetry problem. As Figure 11As shown, in the three-phase TFM, the B-phase stator core 222b is stacked between the A-phase stator core 222a and the C-phase stator core 222c. The A-phase stator core 222a and the C-phase stator core 222c can each be referred to as an outer core because of their positions adjacent to the axial ends of the stator assembly. The B-phase stator core 222b can be referred to as an inner stator core because its position is spaced apart from the axial ends of the stator assembly.

[0080] The TFM 200 is shown in the figure as a three-phase machine having three stator cores 222a, 222b, 222c. However, the principles of the present disclosure can be applied to other polyphase configurations, such as a five-phase device having two outer cores and three inner stator cores, with each outer core located at opposite axial ends of the stator assembly 220 and the three inner stator cores located therebetween.

[0081] Figure 12 A graph is shown illustrating the magnetic flux imbalance between the rotor assembly 210 and the three stator cores 222a, 222b, 222c of the stator assembly 220 in an exemplary three-phase TFM, where each of the three stator cores 222a, 222b, 222c has a similar or identical construction. Figure 12 The differences in the peak magnetic fluxes ΔΨ between phase A, phase B, and phase C of the three stator cores 222a, 222b, 222c are illustrated respectively. As shown, the peak magnetic flux of phase B is higher than that of phase A and phase C, and its peak is about 0.005 Weber (Wb) higher than the peak magnetic fluxes of phase A and phase C. This asymmetry in the magnetic flux can generate second-order torque fluctuations during the operation of the TFM. This difference in the peak magnetic flux may be due to the fact that the B-phase stator core 222b is sandwiched between the A-phase stator core 222a and the C-phase stator core 222c and is not as exposed to air as the A-phase stator core 222a and the C-phase stator core 222c. The magnetic flux leakage from the A-phase stator core 222a and the C-phase stator core 222c also contributes to increasing the magnetic flux in the B-phase stator core 222b.

[0082] Figure 13 A graph is shown illustrating the phase currents in an exemplary three-phase TFM, including the time step (1) of the peak A-phase current, the time step (2) of the peak B-phase current, and the time step (3) of the peak C-phase current. Figures 14A to 14C The magnetic flux densities in a three-phase TFM are shown when the windings have equal number of turns on all phases (NA = NB = NC, where NA, NB, NC are the number of turns of phase A, phase B, and phase C respectively) and during times (1), (2), and (3) respectively. The asymmetric magnetic flux results in asymmetric saturation in the TFM stator core. As Figure 14B shown, compared with the other two stator cores 222a, 222c, the B-phase stator core 222b saturates more (higher magnetic flux density at time 2). This asymmetric saturation causes torque fluctuations.

[0083] Figure 15 Shows an end view of a portion of the TFM 200, including a portion of the stator assembly 220 and a corresponding portion of the rotor assembly 210 disposed annularly therearound. Figure 16 Shows a perspective view of a portion of the stator assembly 220. Figures 15 to 16 The illustrated TFM 200 has an external rotor configuration with 60 poles. However, the principles of the present disclosure can be applied to other configurations, including internal rotor configurations and / or motors with different numbers of poles.

[0084] As shown, the first tooth 232 defines an angular width BetaSx in the circumferential direction, where "x" in BetaSx represents phase A, phase B, or phase C. As previously described, the magnetic flux of the center phase (phase B) is higher compared to other phases, which introduces torque ripple in the TFM 200. To compensate for this difference in magnetic flux, the present disclosure provides a stator core 222 with teeth having different angular widths (which may also be referred to as unequal tooth spans). Here, phase A and phase C have the same tooth span, while phase B has a different tooth span (BetaSA = BetaSC ≠ BetaSB).

[0085] Figure 17 Shows a graph illustrating the average torque in Newton meters (Nm) generated by an external rotor TFM with B-phase stator teeth having different angular widths, and Figure 18 Shows a graph illustrating the torque ripple (%) of an external rotor TFM with B-phase stator teeth having different angular widths. Figures 17 to 18 Presents an analysis of the asymmetric tooth span, where BetaSA = BetaSC = 5.7 degrees and BetaSB varies within a specific range. Based on Figures 17 to 18 the results presented in, a 16.82% reduction in torque ripple can be achieved in the TFM 200 at a BetaSB value = 5.3 degrees, while only experiencing a 0.38% reduction in average torque. This shows that using an asymmetric tooth span in a TFM can be an effective way to reduce torque ripple. As Figure 19 shown, several other geometric parameters can vary between the stators of the TFM 200 to optimize torque performance.

[0086] Figure 19 Shows a perspective view of a section of the stator core 222 of the TFM 200 according to the principles of the present disclosure, and indicates various different parameters. As shown, the stator core 222 extends radially between an inner wall 226 and an outer peripheral wall 234. Also as shown, the second tooth 233 is circumferentially offset from the first tooth 232 by half of the angular spacing between the teeth 232, 233. In other words, each second tooth 233 is circumferentially aligned midway between two first teeth 232.

[0087] Figure 19 The second arm 229 is shown, which defines a distal length SBI1x in the radial direction between the outer wall 227 and the base of the arcuate recess 230. In some embodiments, the first arm 228 defines the same distal length SBI1x. However, the first arm 228 and the second arm 229 may define different distal lengths SBI1x. Figure 19 The tubular portion 223 is also shown, which defines a keeper depth SBI2x in the radial direction between the inner wall 226 and the outer wall 227. The stator core 222 also defines a winding slot height CHx in the axial direction between the first arm 228 and the second arm 229. The first tooth 232 defines a slot depth SLTDPTHx in the radial direction between the base of the arcuate recess 230 and the outer peripheral wall 234. In some embodiments, the second tooth 233 defines the same slot depth SLTDPTHx. However, the first tooth 232 and the second tooth 233 may have different slot depths SLTDPTHx. The first tooth 232 defines a first height LSTK1x in the axial direction, and the second tooth 233 defines a second height LSTK2x in the axial direction. In some embodiments, the first height LSTK1x is equal to the second height LSTK2x (LSTK1x = LSTK2x). However, the first height LSTK1x may be different from the second height LSTK2x (LSTK1x ≠ LSTK2x). The "x" in each of SBI1x, SBI2x, CHx, SLTDPTHx, LSTK1x, and LSTK2x represents phase A, phase B, or phase C.

[0088] The internal stator core or core may define one or more dimensions that are different from the corresponding dimensions of the outer stator core to compensate for asymmetric magnetic flux that might otherwise occur. The one or more dimensions may include, for example, the tooth span BetaSx and / or the keeper depth SBI2x. Additionally or alternatively, the one or more dimensions may include the distal length SBI1x, the first height LSTK1x, the second height LSTK2x, the winding slot height CHx, the slot depth SLTDPTHx, and / or any other dimension of the stator core 222.

[0089] Figure 20 A graph is shown that illustrates the average torque in Newton meters (Nm) produced by an external rotor TFM with a phase B stator core having different keeper depth values, and Figure 21 A graph is shown that illustrates the torque ripple (%) of an external rotor TFM with a phase B stator core having different keeper depth values.

[0090] The following presents a case study of varying the keeper depth SBI2B of the B-phase stator. For the nominal case, SBI2A = SBI2C = 12 mm, while the value of SBI2B varies within a specific range, as Figures 20 to 21 shown. As SBI2B increases from the nominal value, the average torque has a negligible increment, while there is an increase in torque ripple. However, as SBI2B decreases from the nominal value, a significant reduction in torque ripple is observed until SBI2B = 6 mm, after which the torque ripple starts to increase. According to Figures 20 to 21 the results presented in

[0091] Figure 22 For SBI2B = 6 mm (SBI2A = SBI2C = 12 mm), a 38.43% reduction in peak torque ripple can be achieved while experiencing less than 2% reduction in average torque. Figure 23 Graphs are shown that illustrate the average torque in Newton meters (Nm) generated by an outer rotor TFM with a B-phase stator core having different combinations of keeper depth and tooth angular width, and Figure 22 graphs are shown that illustrate the torque ripple (%) of an outer rotor TFM with a B-phase stator core having different combinations of keeper depth and tooth angular width.

[0092] This disclosure shows that torque ripple in a TFM can be significantly reduced by an asymmetric stator design without being affected in terms of average torque generation.

[0093] This disclosure provides a transverse flux machine (TFM). The TFM includes: a rotor assembly configured to rotate about an axis; and a stator assembly. The stator assembly includes a plurality of stator windings and a plurality of stator cores, each of the plurality of stator cores being configured to direct magnetic flux towards the rotor assembly in each of an axial direction and a radial direction. Each of these stator cores defines an annular shape and holds a corresponding one of the plurality of stator windings. The plurality of stator cores includes an outer stator core positioned adjacent an axial end of the stator assembly, and an inner stator core spaced apart from the axial end of the stator assembly. The inner stator core defines at least one dimension that is different from a corresponding dimension of the outer stator core.

[0094] In some embodiments, each of these stator cores includes a tubular portion that extends between an inner wall and an outer wall and defines a back iron depth in the radial direction between the inner wall and the outer wall, and the at least one dimension includes the back iron depth.

[0095] In some embodiments, the back iron depth of the tubular portion of the inner stator core is approximately half of the back iron depth of the tubular portion of the outer stator core.

[0096] In some embodiments, each of these stator cores includes a tubular portion and an arm extending radially from the tubular portion toward the rotor assembly, the arm defining a plurality of teeth, each of the plurality of teeth defining an angular width in the circumferential direction, and the at least one dimension includes the angular width of the plurality of teeth.

[0097] In some embodiments, the angular width of the teeth of the inner stator core is approximately seven percent less than the angular width of the teeth of the outer stator core.

[0098] In some embodiments, each of these stator cores includes a tubular portion that extends between an inner wall and an outer wall and defines a back iron depth in the radial direction between the inner wall and the outer wall. In some embodiments, each of these stator cores includes an arm extending radially from the tubular portion toward the rotor assembly, the arm defining a plurality of teeth, each of the plurality of teeth defining an angular width in the circumferential direction, and the at least one dimension includes both the back iron depth and the angular width of the teeth.

[0099] In some embodiments, the TFM has an internal rotor configuration, and the stator assembly extends annularly around the rotor assembly.

[0100] In some embodiments, the TFM has an external rotor configuration, and the rotor assembly extends annularly around the stator assembly.

[0101] In some embodiments, at least one of the plurality of stator cores comprises soft magnetic core (SMC) material.

[0102] In some embodiments, each of these stator cores has a U-shaped cross-section, has a tubular portion and a first arm extending radially from the tubular portion toward the rotor assembly, and has a second arm spaced from the first arm and extending radially from the tubular portion toward the rotor assembly, and each of these stator cores has a corresponding stator winding of a plurality of stator windings and is disposed in a winding slot between the first arm and the second arm.

[0103] The present disclosure also provides a steer-by-wire system for a vehicle. The steer-by-wire system includes a handwheel actuator coupled to apply torque to a steering wheel. The handwheel actuator includes a transverse flux machine (TFM). The TFM includes: a rotor assembly configured to rotate about an axis; and a stator assembly. The stator assembly includes a plurality of stator windings and a plurality of stator cores, each of the plurality of stator cores being configured to direct magnetic flux toward the rotor assembly in each of an axial direction and a radial direction. Each of these stator cores defines an annular shape and holds a corresponding one of the plurality of stator windings. The plurality of stator cores includes outer stator cores positioned adjacent an axial end of the stator assembly and inner stator cores spaced apart from the axial ends of the stator assembly. The inner stator cores define at least one dimension that is different from a corresponding dimension of the outer stator cores.

[0104] In some embodiments, each of these stator cores includes a tubular portion that extends between an inner wall and an outer wall and defines a back iron depth in the radial direction between the inner wall and the outer wall, and the at least one dimension includes the back iron depth.

[0105] In some embodiments, the back iron depth of the tubular portion of the inner stator core is approximately half of the back iron depth of the tubular portion of the outer stator core.

[0106] In some embodiments, each of these stator cores includes a tubular portion and an arm extending in the radial direction from the tubular portion toward the rotor assembly, the arm defining a plurality of teeth, each of the plurality of teeth defining an angular width in the circumferential direction, and the at least one dimension includes the angular width of the plurality of teeth.

[0107] In some embodiments, the angular width of the teeth of the inner stator core is approximately seven percent less than the angular width of the teeth of the outer stator core.

[0108] In some embodiments, each of these stator cores includes a tubular portion that extends between an inner wall and an outer wall and defines a back iron depth in the radial direction between the inner wall and the outer wall, each of these stator cores includes an arm extending in the radial direction from the tubular portion toward the rotor assembly, the arm defining a plurality of teeth, each of the plurality of teeth defining an angular width in the circumferential direction, and the at least one dimension includes both the back iron depth and the angular width of the teeth.

[0109] In some embodiments, the TFM has an internal rotor configuration and the stator assembly extends annularly around the rotor assembly.

[0110] In some embodiments, the TFM has an external rotor configuration and the rotor assembly extends annularly around the stator assembly.

[0111] In some embodiments, at least one of the plurality of stator cores comprises a soft magnetic core (SMC) material.

[0112] In some embodiments, the handwheel actuator is coupled to the steering wheel via a direct drive mechanism.

[0113] The foregoing discussion is intended to illustrate the principles of the present disclosure and various embodiments. Once the foregoing disclosure is fully understood, many variations and modifications will become apparent to those skilled in the art. The appended claims are intended to be construed to cover all such variations and modifications.

[0114] As used herein, the word "example" is used to mean serving as an example, instance, or illustration. Any aspect or design described herein as an "example" is not necessarily to be construed as preferred or advantageous over other aspects or designs. Instead, the use of the word "example" is intended to present concepts in a concrete manner. As used in this application, the term "or" is intended to mean an inclusive "or" rather than an exclusive "or". That is, unless otherwise specified or clear from the context, "X includes A or B" is intended to mean any of the natural inclusive permutations. That is, if X includes A; X includes B; or X includes both A and B, then "X includes A or B" is satisfied under any of the foregoing instances. Additionally, as used in this application and the appended claims, the articles "a" and "an" shall generally be construed to mean "one or more" unless otherwise specified or clear from the context that they refer to the singular form. Further, the use of the term "an embodiment" or "one embodiment" throughout the text is not intended to refer to the same embodiment or implementation unless specifically so described.

[0115] The specific implementations of the systems, algorithms, methods, instructions, etc. described herein can be implemented in hardware, software, or any combination thereof. The hardware can include, for example, a computer, an intellectual property (IP) core, an application specific integrated circuit (ASIC), a programmable logic array, an optical processor, a programmable logic controller, microcode, a microcontroller, a server, a microprocessor, a digital signal processor, or any other suitable circuit. In the claims, the term "processor" should be understood to cover any of the foregoing hardware either individually or in combination. The terms "signal" and "data" may be used interchangeably.

[0116] As used herein, the term module may include an encapsulated functional hardware unit designed to be used with other components, an instruction set executable by a controller (e.g., a processor executing software or firmware), processing circuitry configured to perform a specific function, and a stand-alone hardware or software component interfacing with a larger system. For example, a module may include an application specific integrated circuit (ASIC); a field programmable gate array (FPGA); circuitry; digital logic circuitry; analog circuitry; a combination of discrete circuitry; gates; and other types of hardware; or combinations thereof. In other embodiments, a module may include a memory storing instructions executable by a controller to implement the features of the module.

[0117] Furthermore, in one aspect, for example, the systems described herein may be implemented using a general-purpose computer or a general-purpose processor having a computer program that, when executed, implements any of the various methods, algorithms, and / or instructions described herein. Additionally or alternatively, for example, a special-purpose computer / processor may be utilized that may include other hardware for implementing any of the methods, algorithms, or instructions described herein.

[0118] Moreover, all or part of an embodiment of the present disclosure may take the form of a computer program product accessible from, for example, a computer-usable medium or a computer-readable medium. A computer-usable medium or a computer-readable medium may be any device that can tangibly contain, store, transmit, or transfer a program for use by or in connection with any processor. The medium may be, for example, an electronic, magnetic, optical, electromagnetic, or semiconductor device. Other suitable media are also available.

[0119] The foregoing embodiments, implementations, and aspects have been described to enable an easy understanding of the present disclosure and not to limit the present disclosure. On the contrary, the present disclosure is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims, which scope should be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures permitted under the law.

Claims

1. A transverse flux machine, comprising: a rotor assembly configured to rotate about an axis; and a stator assembly including a plurality of stator windings and a plurality of stator cores, each of the plurality of stator cores being configured to direct magnetic flux towards the rotor assembly in each of an axial direction and a radial direction, each of the plurality of stator cores defining an annular shape and holding a corresponding one of the plurality of stator windings, wherein the plurality of stator cores includes outer stator cores positioned adjacent an axial end of the stator assembly, and inner stator cores spaced apart from the axial end of the stator assembly, and wherein the inner stator cores define at least one dimension that is different from a corresponding dimension of the outer stator cores.

2. The transverse flux machine according to claim 1, wherein each of the plurality of stator cores includes a tubular portion that extends between an inner wall and an outer wall and defines a back iron depth in a radial direction between the inner wall and the outer wall, and wherein the at least one dimension includes the back iron depth.

3. The transverse flux machine according to claim 2, wherein the back iron depth of the tubular portion of the inner stator core is approximately half of the back iron depth of the tubular portion of the outer stator core.

4. The transverse flux machine according to claim 1, wherein each of the plurality of stator cores includes a tubular portion and an arm extending from the tubular portion in a radial direction towards the rotor assembly, the arm defining a plurality of teeth, each of the plurality of teeth defining an angular width in a circumferential direction, and wherein the at least one dimension includes the angular width of the plurality of teeth.

5. The transverse flux machine according to claim 4, wherein the angular width of the teeth of the inner stator core is approximately seven percent less than the angular width of the teeth of the outer stator core.

6. The transverse flux machine according to claim 1, wherein each of the plurality of stator cores includes a tubular portion that extends between an inner wall and an outer wall and defines a back iron depth in a radial direction between the inner wall and the outer wall, wherein each of the plurality of stator cores includes an arm extending from the tubular portion in a radial direction towards the rotor assembly, the arm defining a plurality of teeth, each of the plurality of teeth defining an angular width in a circumferential direction, and wherein the at least one dimension includes both the back iron depth and the angular width of the teeth.

7. The transverse flux machine according to claim 1, wherein the transverse flux machine has an internal rotor configuration, and the stator assembly extends annularly around the rotor assembly.

8. The transverse flux machine according to claim 1, wherein the transverse flux machine has an external rotor configuration, and the rotor assembly extends annularly around the stator assembly.

9. The transverse flux machine according to claim 1, wherein at least one of the plurality of stator cores comprises a soft magnetic core material.

10. The transverse flux machine according to claim 1, wherein each of the plurality of stator cores has a U-shaped cross-section, has a tubular portion, and has a first arm radially extending from the tubular portion toward the rotor assembly, and has a second arm spaced from the first arm and radially extending from the tubular portion toward the rotor assembly, and wherein each of the plurality of stator cores has a corresponding stator winding of the plurality of stator windings, and is disposed in a winding slot between the first arm and the second arm.

11. A steer-by-wire system for a vehicle, comprising: a handwheel actuator coupled to apply torque to a steering wheel and including a transverse flux machine, wherein the transverse flux machine includes: a rotor assembly configured to rotate about an axis; and a stator assembly including a plurality of stator windings and a plurality of stator cores, each of the plurality of stator cores being configured to direct magnetic flux toward the rotor assembly in each of an axial direction and a radial direction, each of the plurality of stator cores defining an annular shape and holding a corresponding one of the plurality of stator windings, wherein the plurality of stator cores includes outer stator cores positioned adjacent an axial end of the stator assembly, and inner stator cores spaced from the axial end of the stator assembly, and wherein the inner stator cores define at least one dimension that is different from a corresponding dimension of the outer stator cores.

12. The steer-by-wire system according to claim 11, wherein each of the plurality of stator cores includes a tubular portion extending between an inner wall and an outer wall and defining a depth of a yoke in a radial direction between the inner wall and the outer wall, and wherein the at least one dimension includes the depth of the yoke.

13. The steer-by-wire system according to claim 12, wherein the depth of the yoke of the tubular portion of the inner stator core is approximately half of the depth of the yoke of the tubular portion of the outer stator core.

14. The steer-by-wire system according to claim 11, wherein each of the plurality of stator cores includes a tubular portion and an arm extending radially from the tubular portion toward the rotor assembly, the arm defining a plurality of teeth, each of the plurality of teeth defining an angular width in a circumferential direction, and wherein the at least one dimension includes the angular width of the plurality of teeth.

15. The steer-by-wire system according to claim 14, wherein the angular width of the teeth of the inner stator core is approximately seven percent less than the angular width of the teeth of the outer stator core.

16. The steer-by-wire system according to claim 11, wherein each of the plurality of stator cores includes a tubular portion extending between an inner wall and an outer wall and defining a depth of a yoke in a radial direction between the inner wall and the outer wall, Each of the plurality of stator cores includes an arm extending in a radial direction from the tubular portion toward the rotor assembly, the arm defining a plurality of teeth, each of the plurality of teeth defining an angular width in a circumferential direction, and wherein the at least one dimension includes both the keeper depth and the angular width of the teeth.

17. The steer-by-wire system according to claim 11, wherein the transverse flux machine has an internal rotor configuration and the stator assembly extends annularly around the rotor assembly.

18. The steer-by-wire system according to claim 11, wherein the transverse flux machine has an external rotor configuration and the rotor assembly extends annularly around the stator assembly.

19. The steer-by-wire system according to claim 11, wherein at least one of the plurality of stator cores comprises a soft magnetic core material.

20. The steer-by-wire system according to claim 11, wherein the handwheel actuator is coupled to the steering wheel via a direct drive mechanism.

Images