Transverse flux machine with segmented rotor

Abstract

The invention relates to a transverse flux machine with a segmented rotor. A transverse flux machine, TFM, includes a rotor assembly configured to rotate about an axis and including a plurality of axially stacked segments. Each of the plurality of segments includes a plurality of rotor cores and a plurality of permanent magnets. The TFM also includes a stator assembly including a transverse flux core configured to direct magnetic flux toward the rotor assembly in each of an axial direction and a radial direction. A steer-by-wire steering system for a vehicle includes a hand wheel actuator coupled to apply torque to a steering wheel. The hand wheel actuator includes a transverse flux machine (TFM) including a stator assembly and a rotor assembly configured to rotate about an axis. The rotor assembly includes a plurality of axially stacked segments. Each of the plurality of segments includes a plurality of rotor cores and a plurality of permanent magnets.

Description

Technical Field

[0001] The present disclosure relates to transverse flux electric machines and the use of such transverse flux electric machines in hand wheel actuators of steering systems of vehicles. Background Art

[0002] Vehicles (such as cars, trucks, sport utility vehicles, crossovers, minivans, boats, aircraft, all-terrain vehicles, RVs, 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 system. The steering system of such a vehicle typically controls various aspects of the vehicle's steering, including providing steering assistance to the operator of the vehicle, controlling the vehicle's steerable wheels, etc.

[0003] Steer-by-wire (SbW) is a direct evolution of the Electric Power Steering (EPS) system, where there is no mechanical connection between the handwheel and the steering rack. EPS systems may include a single actuator whose sole purpose is to provide assistance to the driver during steering maneuvers. However, on an SbW system, there may be two electric actuators / motors with different functionalities. The electric actuator attached to the rack in an SbW system is called a wheel actuator (RWA), while the actuator on the driver's side is called a handwheel actuator (HWA). The RWA has the same assistance-providing function as the EPS system actuator. On the other hand, the HWA is used more as a feedback motor rather than providing assistance to the driver. In the absence of the HWA, the handwheel on the SbW system would just idle due to the absence of any mechanical connection / friction. The HWA opens up a multitude of design-related opportunities due to its functionality.

[0004] The torque-speed curves of different actuators used in the steering system may also be different based on their functionality.The very different operating domains of EPS / RWA and HWA motivate the design exploration of HWA technology. Summary of the invention

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

[0006] One aspect of the disclosed embodiment includes a transverse flux machine (TFM). The transverse flux machine includes a rotor assembly configured to rotate about an axis and including a plurality of axially stacked segments, each of the plurality of segments including a plurality of rotor cores and a plurality of permanent magnets; and a stator assembly including a transverse flux core configured to direct magnetic flux toward the rotor assembly in each of an axial direction and a radial direction.

[0007] One aspect of the disclosed embodiment includes a steer-by-wire steering system for a vehicle. The steer-by-wire steering system includes a handwheel actuator coupled to apply torque to a steering wheel. The handwheel actuator includes a transverse flux machine (TFM). The transverse flux machine includes: a rotor assembly configured to rotate about an axis and including a plurality of axially stacked segments, each of the plurality of segments including a plurality of rotor cores and a plurality of permanent magnets; and a stator assembly including a transverse flux core configured to direct magnetic flux toward the rotor assembly in each of an axial direction and a radial direction.

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

[0009] The present disclosure is best understood from the following embodiments when read in conjunction with the accompanying drawings. It should be emphasized that, according to common practice, the various features of the drawings are not drawn to scale. Instead, the sizes 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 An electric power steering (EPS) system according to the principles of the present disclosure is generally illustrated.

[0012] Figure 3 A steer-by-wire (SbW) steering system according to the principles of the present disclosure is generally illustrated.

[0013] Figure 4 is a schematic diagram of a motor drive system according to the principles of the present disclosure.

[0014] Figure 5 A graph illustrating a torque-speed curve for a steering system actuator according to the principles of the present disclosure is shown.

[0015] Figure 6 A graph illustrating a torque-speed curve for a direct-drive handwheel actuator in an SbW steering system is shown.

[0016] Figure 7 A cross-sectional view of a radial flux machine (RFM) according to the principles of the present disclosure is shown.

[0017] Figure 8 Shown is a cross-sectional view of an axial flux machine (AFM) according to the principles of the present disclosure.

[0018] Fig. 9A cross-sectional view of a transverse flux machine (TFM) according to the principles of the present disclosure is shown.

[0019] Fig.10 A partial perspective view of a TFM having a flux concentrating outer rotor and a one-piece stator in accordance with the principles of the present disclosure is shown.

[0020] Fig.11 A perspective view of a stator in an outer rotor TFM according to the principles of the present disclosure is shown.

[0021] Fig.12 A graph illustrating the flux imbalance between the phases of a three-phase TFM is shown.

[0022] Fig.13 A graph illustrating phase currents in a three-phase TFM is shown.

[0023] FIG. 14A to FIG. 14C The magnetic flux density during peak current of each of the three phases of a three-phase TFM with flux linkage imbalance is shown.

[0024] Fig.15A A perspective view of a rotor assembly of a TFM according to the principles of the present disclosure is shown.

[0025] Fig. 15B Shows Fig.15A An enlarged cross-sectional partial view of a rotor assembly.

[0026] Fig.16 Shows Fig.15A A perspective view of a portion of a rotor assembly.

[0027] Fig.17 A perspective view of a portion of a rotor assembly is shown, the rotor assembly including a plurality of segments stacked axially.

[0028] Fig.18 A graph illustrating magnet losses in Watts (W) for a three-phase TFM having a rotor assembly with a solid rotor portion and a segmented portion during operation at 60 RPM and 125 A and 120 RPM and 9.3 A is shown.

[0029] FIG. 19A to FIG. 19C Each shows a perspective view of a portion of a rotor assembly having various different arrangements of a plurality of permanent magnets.

[0030] Fig. 20 A graph illustrating average torque in Newton meters (Nm) for a three-phase TFM for a rotor assembly where the outer segments each have permanent magnets of the same strength and the inner segments have permanent magnets of various different strengths is shown.

[0031] Fig.21A graph illustrating torque ripple (%) for a three-phase TFM for a rotor assembly where the outer segments each have permanent magnets of the same strength and the inner segments have permanent magnets of various different strengths is shown. DETAILED DESCRIPTION

[0032] The following discussion is directed to various embodiments of the present disclosure. Although one or more of these embodiments may be preferred, the disclosed embodiments should not be interpreted or otherwise used to limit the scope of the present disclosure (including the claims). In addition, it will be understood by those skilled in the art that the following description has a wide range of applications, and the discussion of any embodiment is only meant to illustrate the embodiment, and is not intended to imply that the scope of the present disclosure (including the claims) is limited to the embodiment.

[0033] As described, a vehicle (such as a car, truck, sport utility vehicle, crossover, minivan, boat, airplane, all-terrain vehicle, RV or other suitable form of transportation) typically includes a steering system, such as an EPS system, a SbW steering system, a hydraulic steering system or other suitable steering system. The steering system of such a vehicle typically controls various aspects of the vehicle's steering, including providing steering assistance to the operator of the vehicle, controlling the vehicle's steerable wheels, etc.

[0034] Figure 1 is a schematic diagram 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 turned, an upper steering shaft 29 is rotated, and a lower steering shaft 51 connected to the upper steering shaft 29 by a universal joint 34 rotates the pinion. Rotation of the pinion moves the rack, which moves tie rods 38 (only one shown), which in turn move steering knuckles 39 (only one shown), which rotate steerable wheels 44 (only one shown).

[0035] The electric power steering assistance is provided by a steering motion control system generally indicated by reference numeral 24 and includes a controller 16 and an electric machine, which may be a permanent magnet synchronous motor and is hereinafter indicated as motor 19. The controller 16 is powered by a vehicle power supply 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 optically encoded sensor, a variable resistance sensor, or any 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 sent to the controller 16 as a speed signal 21. Expressed as ω m The motor speed 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 as measured by the position sensor 32 over a specified time interval. For example, the motor speed ω m can be determined as the motor position θ m Derivative with respect to time. It will be appreciated that there are many well-known methods for performing derivative functions.

[0036] 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 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 assistance to the steering system through the worm 47 and the worm gear 48, thereby providing torque assistance to the vehicle steering.

[0037] 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 references are merely illustrative and the disclosed embodiments may be applied to any motor control application employing an electric motor, such as steering, valve control, etc. In addition, 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 referenced herein include but are not limited to motors, and hereinafter, for the sake of brevity and simplicity, reference will be made to motors only without limitation.

[0038] In the steering motion control system 24 as depicted, the controller 16 uses torque, position, speed, etc. to calculate a command for delivering the required output power. The controller 16 is configured 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 provides an output command signal in response thereto, 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 be optionally combined with the controller 16 and will be referred to as the controller 16 in this article, so that when applied to the motor 19, a desired torque or position is generated. 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 feedforward control mode to generate the command 22. Because 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. The position encoder is connected to the steering shaft 51 to detect the angular position θ. The encoder can sense the rotational position based on optical detection, magnetic field changes, or other methods. Typical position sensors include potentiometers, resolvers, synchronizers, encoders, etc., and combinations comprising 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 .

[0039] The desired torque may be determined by one or more torque sensors 28 that send a torque signal 18 indicative of the applied torque. Such torque sensors 28 and the torque signal 18 therefrom may be responsive to a flexible torsion bar, spring, or similar device (not shown) configured to provide a response indicative of the applied torque.

[0040] In one or more examples, the 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 specified herein. Typical temperature sensors include thermocouples, thermistors, thermostats, etc., and combinations including at least one of the foregoing sensors, which provide a calibratable signal proportional to a specific temperature when properly placed.

[0041] Position signal 20, speed signal 21, and torque signal 18, among others, are applied to controller 16. 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 for processing in the algorithm specified herein. Measurement signals (such as those described above) are also typically linearized, compensated, and filtered as needed to enhance the characteristics of the acquired signal or eliminate its undesirable characteristics. For example, this signal can be linearized to increase processing speed, or to address the large dynamic range of the signal. In addition, frequency or time-based compensation and filtering can be used to eliminate noise or avoid undesirable spectral characteristics.

[0042] In order to perform the specified functions and the desired processing, and calculations therefor (e.g., identification of motor parameters, control algorithms, etc.), the controller 16 may include, but is not limited to, a processor, a computer, a DSP, a memory, a storage device, a register, a timing, an interrupt, a communication interface, and an input / output signal interface, etc., and a combination including at least one of the foregoing. For example, the controller 16 may include input signal processing and filtering to enable accurate sampling and conversion or acquisition of such signals from the communication interface.

[0043] 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 can be similar to or equivalent to Figure 1 The EPS system 40 differs in that the motor 19 is mounted directly to the steering mechanism 36 . Figure 3 The SbW system can be similar to or equivalent to Figure 1 The EPS system 40 of FIG. 1 is different in that there is no physical linkage between the steering wheel 26 and the steerable wheels 44 and there are two separate and independent motors 19a, 19b. As shown, the SbW system includes a first motor 19a (also known as a hand wheel actuator (HWA)) configured to provide torque to the steering wheel 26 for providing tactile feedback to the driver.

[0044] Steer-by-wire (SbW) is a direct evolution of the Electric Power Steering (EPS) system, where there is no mechanical link between the steering wheel 26 and the steering rack. Figure 2As can be seen in the , an EPS system may include a single actuator 19 whose sole purpose is to provide assistance to the driver during steering maneuvers. However, on an SbW system, there are two electric actuators / motors with different functions. The electric actuator attached to the steering mechanism 36 in an SbW system is called a wheel actuator (RWA) 19b, while the actuator on the driver's side is called a handwheel actuator (HWA) 19b. The RWA 19b can provide the same assistance functions as the actuator 19 in the EPS system. On the other hand, the HWA 19a is used more as a feedback motor rather than providing assistance to the driver. In the absence of the HWA 19a, the handwheel on the SbW system will simply spin due to the absence of any mechanical connection / friction.

[0045] In some embodiments, the steering system may include a controller such as Figure 4 Controller 100 is generally illustrated. Controller 100 may include any suitable controller. Controller 100 may be configured to control various functions of a vehicle system, such as described herein. Controller 100 may include processor 102 and memory 104. Processor 102 may include any suitable processor, such as the processor described herein. Additionally or alternatively, in addition to or different from processor 102, controller 100 may include any suitable number of processors. Memory 104 may include a single disk or multiple disks (e.g., a hard disk drive), and include a storage management module that manages one or more partitions within memory 104. In some embodiments, memory 104 may include flash memory, semiconductor (solid-state) memory, etc. Memory 104 may include random access memory (RAM), read-only memory (ROM), or a combination thereof. Memory 104 may include instructions that, when executed by processor 102, cause processor 102 to at least control various functions of a steering system and / or any other suitable functions, including those of the systems and methods described herein.

[0046] The controller 100 may receive one or more signals indicating sensed or measured characteristics of the vehicle from various measurement devices or sensors 106. 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 steering wheel 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 steering wheel torque, steering wheel angle, motor angle or motor position, vehicle speed, other suitable information, or combinations thereof.

[0047] Figure 5Graphs illustrating torque-speed curves for steering system actuators 19, 19a and 19b are shown. Different steering system actuators 19, 19a, 19b have different speed curves based on their functionality. Figure 5 As indicated by the dashed lines in , the EPS actuator 19 and RWA 19b in the SbW each operate in the first quadrant (Q1) of the torque-speed curve. The positive direction of the velocity 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 lines, the HWA 19a of the SbW system operates primarily in the second quadrant (Q2) of the torque-speed curve. The HWA 19a moves opposite to the driver's handwheel movement (velocity -ve) and provides feedback to the driver. This feedback may be necessary to provide the driver with general steering feel and road condition feedback. In addition, some low-speed assistance (Q1 operation) from the HWA 19a may also be required, such as Figure 5 Visible in.

[0048] The HWA 19a may include an electric motor connected to apply torque to the steering wheel 26 configuration, such as a worm gear drive, belt drive, and / or direct drive. For the case of worm gear and belt drive, a low torque (~3Nm) and high speed (3000rpm) PMSM can be used as an actuator. Both surface mounted PMSM (SPMSM) and internal PMSM (IPMSM) topologies can be used for such HWA architectures. In addition, 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 (~30Nm for outlet / inlet) and low speed (~200-300rpm) 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. In addition, the reduction in weight is directly related to the range efficiency or mileage (miles per gallon) increase. However, conventional PMSMs need to be redesigned for the high torque and low speed output requirements of the direct drive architecture.

[0049] The torque-speed curves of the different actuators used in the steering system also vary based on their functionality. Figure 5As shown, the EPS actuator and RWA in the SbW system each operate in the first quadrant (Q1) of the torque-speed curve. The positive direction of velocity in Q1 indicates that the actuator is acting in the same direction as the driver's handwheel movement and providing assistance. However, the SbW HWA operates primarily in the second quadrant (Q2) of the torque-speed curve. The HWA moves opposite to the driver's handwheel movement (velocity -ve) and provides feedback to the driver. This feedback is necessary to provide general steering feel and road condition feedback to the driver. In addition, some low-speed assistance (Q1 operation) from the HWA may also be required, such as Figure 5 The very different operation domains of EPS / RWA and HWA motivate the design exploration of HWA technology.

[0050] The HWA may include an electric motor connected to apply torque to the steering wheel 26 configuration, such as a worm gear drive, a belt drive, and / or a direct drive. In the case of worm gears and belt drives, a low torque (~3Nm) and high speed (3000rpm) PMSM can be used as an actuator. Both surface mounted PMSM (SPMSM) and internal PMSM (IPMSM) topologies can be used for such HWA architectures. In addition, due to their similarities (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 (~30Nm for the outlet / inlet) and low speed (~200-300rpm) 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. In addition, the reduction in weight is directly related to the range efficiency or mileage (miles / gallon) increase. However, the traditional PMSM needs to be redesigned for the high torque and low speed output requirements of the direct drive architecture.

[0051] Figure 6 A graph illustrating the torque-speed curve of an HWA 19a in an SbW steering system having a direct drive configuration (1:1 gear ratio) is shown. As shown, the HWA 19a typically operates at speeds between -200 and +80 revolutions per minute (RPM) and produces torque between 0 and about 30 Newton meters (Nm). A transverse flux machine has the potential to perform in such low speed, high torque direct drive applications.

[0052] 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. Fig. 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 between RFM, AFM, and TFM configurations can be made based on the direction of the magnetic flux.

[0053] Figure 7 The RFM includes a first rotor assembly 110a having a first rotor core 112a attached for rotation with a first shaft 114a about an axis A. The first rotor assembly 110a is located within a first housing 115a, and the first shaft 114a extends through and outside the first housing 115a and is supported by a pair of first bearings 116a. A set of first permanent magnets 118a are attached to the first rotor core 112a and generate magnetic flux extending radially outward. Figure 7 The RFM also includes a first stator assembly 120a having a first stator core 122a with a set of first windings 124a extending therethrough and carrying current in an axial direction parallel to the axis A and perpendicular to the magnetic flux.

[0054] Figure 8 The AFM includes a second rotor assembly 110b having a second rotor core 112b attached so as to rotate with a second shaft 114b about an axis A. The second rotor assembly 110b is located within a second housing 115b, and the second shaft 114b extends through and outside the second housing 115b 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 also includes a second stator assembly 120b having a second stator core 122b with a set of second windings 124b extending through the second stator core and carrying current in a radial direction perpendicular to the axis A and perpendicular to the magnetic flux.

[0055] Fig. 9 The TFM includes a third rotor assembly 110c having a third rotor core 112c attached for rotation with a third shaft 114c about an axis A. The third rotor assembly 110c is located within a third housing 115c, and the third shaft 114c extends through and outside the third housing 115c and is supported by a pair of third bearings 116c. A set of third permanent magnets 118c are attached to the third rotor core 112c and generate a magnetic flux that extends radially inward at a first location, axially through the third rotor core 112c, and radially outward at a second location axially spaced from the first location. Fig. 9The TFM also includes a third stator assembly 120c having a third stator core 122c with a set of third windings 124c extending therethrough and carrying current in a circumferential direction perpendicular to the axis A and perpendicular to the magnetic flux. As shown, the third stator core 122c defines a U-shape with an open end aligned with the third permanent magnet 118c at a first position and a second position for providing a closed path of rectangular magnetic flux with the third rotor core 112c.

[0056] Figures 7 to 9 Figure 1 shows the direction of the flux in the three motor topologies. For the RFM, the flux moves radially in the air gap, while for the AFM, the flux moves axially from the stator to the rotor and vice versa. Fig. 9 As can be seen in Figure 1, for a TFM, the flux moves in both the radial and axial planes. Although several topologies of TFM can be identified from the literature, the 3D (radial and axial) flux path is a common feature across the different topologies. TFMs are known to have higher volumetric and gravimetric power densities than radial flux machines. AFMs and TFMs are known to have comparable power densities. However, the simplicity of the toroidal windings in a TFM has the potential to ease the manufacturing process and save costs.

[0057] like Figure 7 As shown, the magnetic flux in the RFM extends mainly in the radial direction perpendicular to the axis A. Figure 8 As shown, the magnetic flux in the AFM extends mainly in the axial direction parallel to the axis A. Fig. 9 As shown, the magnetic flux in the TFM defines a closed loop path, with portions extending in a radial direction perpendicular to the axis A and other portions extending in an axial direction parallel to the axis A. The RFM, AFM, and TFM configurations may each provide different volumetric power densities and gravimetric power densities. The TFM configuration may be particularly well suited for low speed and high torque operation.

[0058] The present disclosure provides a transverse flux machine (TFM) topology for direct drive SbW HWA architectures. Transverse flux machines have the potential to provide significant power density advantages over conventional radial flux machines in the low speed, high torque operating region of direct drive SbW HWAs. Conventional RFMs can be stacked in the radial XY plane to accommodate their 2D flux paths and reduce eddy current losses at high frequency operation. AFMs can also be stacked in the axial XZ plane to assist the axial travel of flux from stator to rotor and vice versa. However, as Fig. 9 As can be seen in FIG. 1 , for the TFM, the magnetic flux moves in the axial direction and the radial direction between the third stator assembly 120 c and the third rotor assembly 110 c.

[0059] If the TFM includes a laminated core, it will be necessary to have XY and XZ directional laminations, depending on the core position and the expected direction of flux travel. This can seriously complicate the manufacturing process of the TFM. To avoid complications and ensure 3D flux travel in the TFM core, soft magnetic core (SMC) materials can be used for either or both of the rotor core and / or stator core. SMC materials include insulating iron particles that are 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.

[0060] Several TFM topologies have been considered, which excel in different performance areas. TFM designs generally indicate a trend towards increasing volumetric torque density. However, for steering applications, the actuators are subject to tighter constraints of torque ripple, cogging torque, friction losses, etc. In addition, ease of manufacturing is an important criterion.

[0061] Reducing the number of parts in a TFM simplifies the manufacturing process. In addition, the flux concentrated rotor structure exhibits higher power density and reduced magnet weight compared to other rotor topologies. In addition, the toroidal winding structure of the TFM simplifies the winding process compared to a pin-wound radial flux machine. Due to the manufacturing considerations offered by the topology, Fig.10 The TFM design shown may be particularly advantageous.Stator cores may be axially stacked and circumferentially spatially displaced to form a multi-phase electrical machine.

[0062] Fig.10 A TFM 200 having an external rotor configuration is presented having a rotor assembly 210 configured to rotate about an axis, wherein the rotor extends annularly around a stator assembly 220 . Fig.10 A 45 degree segment of the TFM 200 is shown, with markings indicating magnetic flux. However, a complete TFM 200 would include eight such segments. The rotor assembly 210 includes a plurality of pairs of permanent magnets 212a, 212b arranged at regular angular intervals and configured to generate magnetic flux therebetween in a circumferential direction.

[0063] The rotor assembly 210 also includes a plurality of flux concentrating cores 214 located between the permanent magnets 212a, 212b in each pair of permanent magnets 212a, 212b and configured to conduct magnetic flux therebetween. The rotor assembly 210 also includes a plurality of flux diverging cores 216, each of which is 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 concentrating cores 214 and / or the flux diverging cores 216 may be made of a soft magnetic core (SMC) material. However, other types of materials may be used for either or both of the flux concentrating cores 214 and / or the flux diverging cores 216.

[0064] Also like Fig.10 As shown, the stator assembly 220 includes a stator core 222 having a U-shaped cross-section having an inner cylindrical portion 224 and a pair of arms 226 extending radially outward from each end of the inner cylindrical portion 224 and toward the rotor assembly 210. The winding 228 extends through the center of the U-shaped cross-section of the stator core 222 in the circumferential direction and conducts current in the circumferential direction.

[0065] As shown, each arm 226 of the stator core 222 includes an arcuate recess 230 to define two radially extending protrusions 232 that are angularly spaced apart so as to align with adjacent ones of the flux concentrating cores 214. In this manner, magnetic flux is directed from each of the flux concentrating cores 214 adjacent to the first axial end 218, across the air gap, and into the radially extending protrusions 232 of the stator core 222 adjacent thereto. The magnetic flux is directed into the inner cylindrical portion 224 of the stator core 222, where it is continuous in the axial direction. The magnetic flux is also directed out of the inner cylindrical portion 224 of the stator core 222 and radially outward through the arm 226 of the stator core 222 adjacent to the second axial end 218b, where the magnetic flux crosses the air gap and returns to the flux concentrating core 214, thereby completing a closed path.

[0066] TFMs may be particularly well suited for direct drive low speed operation. TFMs may include a modular, spatially displaced, three-phase stator architecture. TFMs may include a simple toroidal winding with an inner stator topology. TFMs may provide relatively low phase resistance regardless of the number of stator slots and rotor poles. TFMs may include an outer rotor structure with high volumetric torque density and weight torque density. TFMs may be relatively easily and efficiently manufactured and may provide suitable performance for a variety of applications in EPS and / or SbW systems.

[0067] Number of poles

[0068] The phase resistance and coil cross-section in the wrap-around TFM are independent of the number of poles, which enables higher torque density to be achieved in the TFM compared to the RFM. In addition, for the intended SbW direct drive HWA application, the operating speed is low. This indicates that even if a higher pole count 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 an 11:1 gear ratio, the fundamental frequency is 166.67 Hz at 2500 motor rpm. On the other hand, for a TFM with 100 poles and a direct drive configuration, the fundamental frequency is 189.39 Hz at 227.27 motor rpm. The limiting number of poles for a TFM (P 最大 ) can be calculated using equation (1):

[0069]

[0070] where n 限制 is the maximum motor speed in rpm, f e,最大 is the maximum fundamental electrical frequency that can be handled by the motor drive.

[0071] Furthermore, despite the higher number of poles in the TFM, the phase resistance does not increase, which may provide reduced copper losses and thus improve efficiency and thermal performance.

[0072] Inside rotor / outside rotor topology

[0073] The general setting size equation of TFM can be written as equation (2):

[0074]

[0075] Where P R is the rated output power, K phi is the ratio of the electrical load on the rotor to the stator (K phi can be equal to zero), m is the number of phases, K e is the BEMF factor per unit portion of the total air gap area spanned by the salient poles (if any) of the machine, K i is the current shape factor, K p is the power form factor, K L is the stack length L e Diameter D relative to the air gap surface g ratio, n is the machine efficiency, B g is the air gap flux density, A is the total electrical load, f is the drive frequency, p is the number of pole pairs, D o is the outer diameter of the machine, and λ o Yes D g and D o The ratio between them.

[0076] As is apparent from equation (2), the rated power, and therefore the torque output, of the TFM is proportional to the outer diameter D of the motor. o Proportional to the square of. g / D o Replace λ o , it can be seen from equation (2) that the output power is directly related to the square of Dg. From the inner rotor TFM to the outer rotor TFM, the diameter of the air gap surface can be increased with better space utilization. This results in a higher volume torque density in the outer rotor TFM. In addition, in the outer rotor TFM, the winding process is relatively simpler. According to the present disclosure, both the outer rotor TFM and the inner rotor TFM are systematically optimized.

[0077] Fig.11 A perspective view of a stator assembly 220 for an external rotor TFM is shown, the stator assembly being configured to have a rotor (not shown) disposed annularly therearound. The stator assembly 220 includes three stator cores 222a, 222b, 222c, including an A-phase stator core 222a, a B-phase stator core 222b, and a C-phase stator core 222c. The three stator cores 222a, 222b, 222c each have a similar or identical annular shape that is axially stacked and circumferentially displaced from each other. Each of the three stator cores 222a, 222b, 222c of the stator assembly 220 includes a corresponding winding 224a, 224b, 224c of a corresponding phase, and the stator core extends circumferentially through the corresponding winding. Each of the three stator cores 222a, 222b, 222c of the stator assembly 220 also defines a plurality of radially extending protrusions having regular angular intervals and extending radially outward.

[0078] The stacked assembly of TFM stators leads to inherent asymmetry issues. Fig.11 As shown, in the 3-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 their positions are 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 their positions are spaced apart from the axial ends of the stator assembly.

[0079] Fig.12 A graph illustrating flux linkage imbalance between a rotor assembly 210 and three stator cores 222a, 222b, 222c of a stator assembly 220 in a three-phase TFM is shown, wherein each of the three stator cores 222a, 222b, 222c has a similar or identical construction. Fig.12 The difference in peak flux AY between phases A, B, and C of the three stator cores 222a, 222b, and 222c is illustrated respectively. As shown in the figure, the peak flux of phase B is higher than the peak flux of phase A and phase C, and its peak value is about 0.005 Weber (Wb) higher than the peak flux of phase A and phase C. During the operation of the TFM, this asymmetry in the flux can produce second-order torque fluctuations. This difference in peak 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 exposed to the air as much as the A-phase stator core 222a and the C-phase stator core 222c. The flux leakage from the A-phase stator core 222a and the C-phase stator core 222c also contributes to increasing the flux in the B-phase stator core 222b.

[0080] Fig.13A graph illustrating phase currents in a three-phase TFM is shown, including a time step of peak A phase current (1), a time step of peak B phase current (2), and a time step of peak C phase current (3). FIG. 14A to FIG. 14C The magnetic flux density in the three-phase TFM during time (1), (2) and (3) is shown when the winding has equal number of turns on all phases (NA=NB=NC, NA, NB, NC are the number of turns of phase A, phase B, phase C respectively). The asymmetric flux linkage leads to asymmetric saturation in the TFM stator core. Fig. 14B As shown, the B-phase stator core 222b is more saturated (higher magnetic flux density at time 2) than the other two stator cores 222a, 222c. This asymmetric saturation causes torque ripple.

[0081] The present disclosure provides a solution to mitigate flux asymmetry in such a three-phase TFM by using windings with different numbers of turns. More specifically, the TFM of the present disclosure uses a winding in the inner stator core (i.e., B-phase winding 224b) with fewer turns than the windings in the outer core (i.e., A-phase winding 224a and C-phase winding 224c), which may each have an equal number of turns. A 60-pole TFM with 16 winding turns is provided to demonstrate the principles of the present disclosure.

[0082] Fig.15A A perspective view of a rotor assembly 210 of the TFM 200 is shown. The rotor assembly 210 may be referred to as a flux concentrating external rotor design. Fig. 15B An enlarged cross-sectional partial view of the rotor assembly 210 is shown. Arrows indicate magnetic field lines associated with the permanent magnets 212a, 212b and extending in the circumferential direction into the flux concentrating core 214. As shown, the rotor assembly 210 includes a plurality of solid rotor sections 240, each of which is similar or identical, wherein each of the solid rotor sections 240 has an elongated shape and each includes one flux concentrating core in the flux concentrating core 214 located between two permanent magnets 212a, 212b, and one flux diverging core in the flux diverging core 216 located outside the two permanent magnets 212a, 212b for spacing the permanent magnets 212a, 212b from the permanent magnets 212a, 212b of the next adjacent solid rotor section in the solid rotor section 240.

[0083] Fig.16 A perspective view of the solid rotor portion 240 of the rotor assembly 210 is shown, illustrating the elongated shape. The elongated shape of the permanent magnets 212a, 212b, the flux concentrating core 214, and the flux diverging core 216 makes each of these components and the combined solid rotor portion 240 fragile and susceptible to breakage prior to and during assembly.

[0084] Fig.17 A perspective view of a segmented rotor portion 340 according to the present disclosure is shown. The segmented rotor portion 340 can be used to construct the rotor assembly 210 in place of the solid rotor portion 240. As shown, the segmented rotor portion 340 includes a stack of three rotor segments 342a, 342b, 342c, wherein a glue joint 344 connects adjacent rotor segments in the rotor segments 342a, 342b, 342c. However, the segmented rotor portion 340 may include a different number of rotor segments 342a, 342b, 342c. Each rotor segment in the rotor segments 342a, 342b, 342c includes two magnet segments 312a, 312b, a flux concentrating core segment 314 located between the two magnet segments, and a flux diverging core segment 316. When stacked together, the magnet segments 312a, 312b of the three rotor segments 342a, 342b, 342c each approximate in size and function to a corresponding one of the permanent magnets 212a, 212b of the solid rotor portion 240. Similarly, when stacked together, the flux concentrating core segments 314 of the three rotor segments 342a, 342b, 342c approximate in size and function to a corresponding flux concentrating core 214 of the solid rotor portion 240. Similarly, when stacked together, the flux diverging core segments 316 of the three rotor segments 342a, 342b, 342c approximate in size and function to a corresponding flux diverging core 216 of the solid rotor portion 240.

[0085] In some embodiments, either or both of the flux concentrating core segment 314 and / or the flux diverging core segment 316 may be made of a soft magnetic core (SMC) material. However, other types of materials may be used for either or both of the flux concentrating core segment 314 and / or the flux diverging core segment 316.

[0086] In some embodiments, and as shown, the segmented rotor portion 340 includes the same number of rotor segments 342a, 342b, 342c as the stator cores 222a, 222b, 222c in the stator assembly 220. In some embodiments, the three stator cores 222a, 222b, 222c of the stator assembly 220 can each be axially aligned with a corresponding one of the rotor segments 342a, 342b, 342c of the rotor assembly. The illustrated embodiment shows the TFM 200 as a three-phase machine having three stator cores 222a, 222b, 222c and three rotor segments 342a, 342b, 342c. However, the principles of the present disclosure can be applied to motors having stators with different numbers of phases and / or different numbers of stator cores 222a, 222b, 222c and / or different numbers of rotor segments 342a, 342b, 342c.

[0087] Fig.18Graphs illustrating magnet losses in Watts (W) for a three-phase TFM having a solid rotor portion 240 and a segmented rotor portion 340 for rotor assemblies during operation at 60 RPM and 125 A and 120 RPM and 9.3 A are shown.

[0088] FIG. 19A to FIG. 19C Each shows a perspective view of a portion of a rotor assembly 210 having various different arrangements of a plurality of permanent magnets. Fig.19A A first type 340a of segmented rotor portions 340 is shown, wherein each of the rotor segments 342a, 342b, 342c has a magnet segment 312a, 312b having N48SH type magnets, each having the same strength or residual flux density.

[0089] Fig.19B A second type 340b of segmented rotor portions 340 is shown. The second type 340b of segmented rotor portions 340 includes outer segments 342a, 342c located adjacent the axial ends of the rotor assembly 210 having N48SH type magnets. Fig.19B Also shown is a segmented rotor portion 340 including inner segments 342b that are spaced apart from the axial ends of the rotor assembly 210 and have N45SH type magnets for their magnet segments 312a, 312b. The N45SH type magnets of the inner segments 342b have a lower residual flux density than the N48SH type magnets of the outer segments 342a and 342c.

[0090] Fig.19C A third type 340c of segmented rotor portion 340 is shown, which is similar to Fig.19B An arrangement of the second type 340b is shown in which the same N48SH type magnets are present in the outer segments 342a, 342c, but in which the inner segment 342b includes N42SH type magnets having a lower residual flux density than the N45SH type magnets used in the inner segment 342b of the second type 340b of the segmented rotor portion 340.

[0091] The lower strength permanent magnets 312a, 312b in the inner segment 342b serve to counteract or compensate for the increased flux linkage that may otherwise exist on one or more phases associated with the inner segment. The lower strength permanent magnets of the magnet segments 312a, 312b in the inner segment 342b can thereby alleviate the inherent asymmetry issues present in the TFM.

[0092] In some embodiments not shown in the drawings, two of the rotor segments 342a, 342b, 342c may have different lengths in the axial direction. For example, the inner segment 342b spaced apart from the axial end of the rotor assembly 210 may have a shorter axial length than the outer segments 342a, 342c located adjacent to the axial end of the rotor assembly 210. This arrangement of the rotor segments 342a, 342b, 342c having different axial lengths may be used as an alternative or in addition to the arrangement of the rotor segments 342a, 342b, 342c having different residual magnetic flux densities.

[0093] Figure 20 to Figure 21 A graph illustrating the performance of a TFM incorporating three different types 340a, 340b, 340c of segmented rotor segments 340 is shown, the three different types being labeled Case 1, Case 2, and Case 3, respectively. Fig. 20 A graph illustrating average torque in Newton meters (Nm) for a three-phase TFM for a rotor assembly where the outer segments each have permanent magnets of the same strength and the inner segments 342b have permanent magnets of various strengths is shown. Fig.21 A graph illustrating torque ripple (%) for a three-phase TFM where the outer segments of the rotor assembly 210 each have permanent magnets of equal strength and the inner segments 342b have permanent magnets of various different strengths is shown.

[0094] As shown, reducing the residual flux density on the inner segment 342b of the rotor assembly 210 corresponds to a reduction in the average torque generated. However, the torque ripple is also significantly reduced. For example, for the N42SH grade magnets on the inner segment 342b (Case 3), the average torque is only reduced by 2.12% compared to Case 1. However, the torque ripple of Case 3 is reduced by 9.38% compared to Case 1.

[0095] The present disclosure provides a transverse flux machine (TFM). The TFM includes: a rotor assembly configured to rotate about an axis and including a plurality of axially stacked segments, each of the plurality of segments including a rotor core and a plurality of permanent magnets; and a stator assembly including a transverse flux core configured to direct magnetic flux toward the rotor assembly in each of an axial direction and a radial direction.

[0096] In some embodiments, the TFM has an inner rotor configuration with the stator assembly extending annularly around the rotor assembly.

[0097] In some embodiments, the TFM has an outer rotor configuration with the rotor assembly extending annularly around the stator assembly.

[0098] In some embodiments, the TFM is a multi-phase machine having multiple stator windings, and wherein the transverse flux core of the stator assembly includes multiple stator cores, wherein each of the stator cores defines an annular shape and holds a corresponding stator winding among the multiple stator windings, and wherein each of the stator cores is axially aligned with a corresponding segment among the multiple segments.

[0099] In some embodiments, the rotor assembly further includes two adjacent segments of the plurality of segments attached to each other by a glued joint.

[0100] In some embodiments, the plurality of permanent magnets includes a first group of permanent magnets having a first residual magnetic flux density and a second group of permanent magnets having a second residual magnetic flux density lower than the first residual magnetic flux density.

[0101] In some embodiments, the first group of permanent magnets having the first residual magnetic flux density is disposed within an outer segment of the plurality of segments positioned adjacent to the axial end of the rotor assembly, and wherein the second group of permanent magnets having the second residual magnetic flux density is disposed within an inner segment of the plurality of segments spaced apart from the axial end of the rotor assembly.

[0102] In some embodiments, at least one rotor core of the plurality of rotor cores comprises a soft magnetic core (SMC) material.

[0103] In some embodiments, the TFM is a multiphase machine having at least three stator windings, and wherein the transverse flux core of the stator assembly comprises a plurality of stator cores, each of the stator cores defining an annular shape and holding a corresponding stator winding of the at least three stator windings. In some embodiments, each of the stator cores is axially aligned with a corresponding segment of the plurality of segments of the rotor assembly, the plurality of segments of the rotor assembly comprising two outer segments, each of the outer segments defining an axial end of the rotor assembly and comprising a first set of permanent magnets having a first residual flux density, and the plurality of segments of the rotor assembly comprising at least one inner segment, the at least one inner segment being spaced apart from the axial end of the rotor assembly and comprising a second set of permanent magnets having a second residual flux density lower than the first residual flux density.

[0104] The present disclosure also provides a steer-by-wire system for a vehicle. The steer-by-wire system includes: a handwheel actuator, which is coupled to apply torque to a steering wheel. The handwheel actuator includes a transverse flux machine (TFM). The TFM includes: a rotor assembly, which is configured to rotate about an axis and includes a plurality of axially stacked segments, each of the plurality of segments including a rotor core and a plurality of permanent magnets; and a stator assembly, which includes a transverse flux core, which is configured to direct magnetic flux toward the rotor assembly in each of an axial direction and a radial direction.

[0105] In some embodiments, the hand wheel actuator is coupled to the steering wheel via a direct drive mechanism.

[0106] In some embodiments, the TFM has an inner rotor configuration with the stator assembly extending annularly around the rotor assembly.

[0107] In some embodiments, the TFM has an outer rotor configuration with the rotor assembly extending annularly around the stator assembly.

[0108] In some embodiments, the TFM is a multi-phase machine having multiple stator windings, and the transverse flux core of the stator assembly includes multiple stator cores, each of which defines an annular shape and holds a corresponding stator winding among the multiple stator windings, and wherein each of the stator cores is axially aligned with a corresponding segment among the multiple segments.

[0109] In some embodiments, the rotor assembly further includes two adjacent segments of the plurality of segments attached to each other by a glued joint.

[0110] In some embodiments, the plurality of permanent magnets includes a first group of permanent magnets having a first residual magnetic flux density and a second group of permanent magnets having a second residual magnetic flux density lower than the first residual magnetic flux density.

[0111] In some embodiments, the first group of permanent magnets having the first residual magnetic flux density is disposed within an outer segment of the plurality of segments positioned adjacent to the axial end of the rotor assembly, and wherein the second group of permanent magnets having the second residual magnetic flux density is disposed within an inner segment of the plurality of segments spaced apart from the axial end of the rotor assembly.

[0112] In some embodiments, two segments of the plurality of segments have different lengths in the axial direction.

[0113] In some embodiments, at least one rotor core of the plurality of rotor cores comprises a soft magnetic core (SMC).

[0114] In some embodiments, the TFM is a multiphase machine having at least three stator windings, and wherein the transverse flux core of the stator assembly includes a plurality of stator cores, each of the stator cores defining an annular shape and holding a corresponding stator winding of the at least three stator windings, each of the stator cores being axially aligned with a corresponding segment of the plurality of segments of the rotor assembly, the plurality of segments of the rotor assembly including two outer segments, each of the outer segments defining an axial end of the rotor assembly and including a first group of permanent magnets having a first residual flux density, and the plurality of segments of the rotor assembly including at least one inner segment, the at least one inner segment being spaced apart from the axial end of the rotor assembly and including a second group of permanent magnets having a second residual flux density lower than the first residual flux density.

[0115] The above discussion is intended to illustrate the principles and various embodiments of the present disclosure. Once the above disclosure is fully understood, many changes and modifications will become apparent to those skilled in the art. The appended claims are intended to be interpreted as covering all such changes and modifications.

[0116] The word "example" is used herein to mean used as an example, instance or illustration. Any aspect or design described as an "example" herein is not necessarily to be interpreted as being preferred or advantageous over other aspects or designs. On the contrary, the use of the word "example" is intended to present the concept in a specific way. As used in this application, the term "or" is intended to represent an inclusive "or" rather than an exclusive "or". That is, unless otherwise specified or clearly known from the context, "X includes A or B" is intended to represent any one of the natural inclusive permutations and combinations. That is, if X includes A; X includes B; or X includes both A and B, "X includes A or B" is satisfied in any of the aforementioned examples. In addition, the articles "one" and "an" as used in this application and the appended claims should generally be interpreted as meaning "one or more", unless otherwise specified or clearly from the context to refer to the singular form. In addition, the use of the term "one embodiment" or "one embodiment" throughout the text is not intended to represent the same embodiment or embodiment, unless specifically described as such.

[0117] Implementations of the systems, algorithms, methods, instructions, etc. described herein may be implemented in hardware, software, or any combination thereof. Hardware may 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" shall be understood to include any of the foregoing hardware, either alone or in combination. The terms "signal" and "data" may be used interchangeably.

[0118] As used herein, the term module may include: a packaged functional hardware unit designed for use with other components; a set of instructions executable by a controller (e.g., a processor executing software or firmware); a processing circuit configured to perform a specific function; and an independent hardware or software component that interfaces with a larger system. For example, a module may include an application specific integrated circuit (ASIC); a field programmable gate array (FPGA); an electrical circuit; a digital logic circuit; an analog circuit; a combination of discrete circuits; a gate; and other types of hardware; or a combination thereof. In other embodiments, a module may include a memory that stores instructions that are executable by a controller to implement the features of the module.

[0119] Furthermore, in one aspect, for example, a general purpose computer or general purpose processor with a computer program can be used to implement the system described herein, which when executed implements any of the corresponding methods, algorithms and / or instructions described herein. Additionally or alternatively, for example, a special purpose computer / processor can be utilized, which may include other hardware for implementing any of the methods, algorithms or instructions described herein.

[0120] In addition, all or part of the embodiments 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 capable of, for example, tangibly containing, storing, transferring or transmitting a program for use by or in conjunction with any processor. The medium may be, for example, an electronic, magnetic, optical, electromagnetic or semiconductor device. Other suitable media are also available.

[0121] The above embodiments, specific implementations and aspects have been described to allow easy understanding of the present disclosure, and do not 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, and its scope should be given the broadest interpretation to cover 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 comprising a plurality of segments stacked axially, each segment of the plurality of segments comprising a plurality of rotor cores and a plurality of permanent magnets; as well as A stator assembly includes a transverse flux core configured to direct magnetic flux in each of an axial direction and a radial direction toward the rotor assembly.

2. The transverse flux machine of claim 1 wherein the transverse flux machine has an inner rotor configuration, the stator assembly extending annularly around the rotor assembly.

3. The transverse flux machine of claim 1, wherein the transverse flux machine has an external rotor configuration, the rotor assembly extending annularly around the stator assembly.

4. A transverse flux machine as described in claim 1, wherein the transverse flux machine is a multi-phase machine having a plurality of stator windings, and wherein the transverse flux core of the stator assembly includes a plurality of stator cores, each of the plurality of stator cores defining an annular shape and holding a corresponding stator winding of the plurality of stator windings, and wherein each of the plurality of stator cores is axially aligned with a corresponding segment of the plurality of segments. 5 . The transverse flux machine of claim 1 , wherein the rotor assembly further comprises two adjacent segments of the plurality of segments attached to each other by a glued joint. 6 . The transverse flux machine of claim 1 , wherein the plurality of permanent magnets comprises a first group of permanent magnets having a first residual flux density and a second group of permanent magnets having a second residual flux density lower than the first residual flux density.

7. A transverse flux machine as claimed in claim 6, wherein the first group of permanent magnets having the first residual flux density is disposed in an outer segment of the plurality of segments positioned adjacent to an axial end of the rotor assembly, and wherein the second group of permanent magnets having the second residual flux density is disposed in an inner segment of the plurality of segments spaced apart from the axial end of the rotor assembly.

8. The transverse flux machine of claim 1 wherein two segments of the plurality of segments have different lengths in the axial direction.

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

10. The transverse flux machine of claim 1, wherein the transverse flux machine is a multi-phase machine having at least three stator windings, and wherein the transverse flux core of the stator assembly comprises a plurality of stator cores, each stator core of the plurality of stator cores defining an annular shape and holding a corresponding stator winding of the at least three stator windings, wherein each of the stator cores is axially aligned with a corresponding one of the plurality of segments of the rotor assembly, wherein the plurality of segments of the rotor assembly include two outer segments, each of the two outer segments defining an axial end of the rotor assembly and including a first set of permanent magnets having a first residual magnetic flux density, and The plurality of segments of the rotor assembly include at least one inner segment spaced apart from the axial end of the rotor assembly and including a second set of permanent magnets having a second residual flux density lower than the first residual flux density.

11. A steer-by-wire steering system for a vehicle, comprising: a hand wheel actuator coupled to apply torque to the steering wheel; The hand wheel actuator comprises a transverse flux machine, the transverse flux machine comprising: a rotor assembly configured to rotate about an axis and comprising a plurality of segments stacked axially, each segment of the plurality of segments comprising a plurality of rotor cores and a plurality of permanent magnets; and A stator assembly includes a transverse flux core configured to direct magnetic flux in each of an axial direction and a radial direction toward the rotor assembly.

12. The steer-by-wire steering system of claim 11, wherein the hand-wheel actuator is coupled to the steering wheel via a direct drive mechanism.

13. The steer-by-wire steering system of claim 11 wherein the transverse flux machine has an inner rotor configuration, the stator assembly extending annularly around the rotor assembly.

14. The steer-by-wire steering system of claim 11 wherein the transverse flux machine has an outer rotor configuration, the rotor assembly extending annularly around the stator assembly.

15. The steer-by-wire steering system of claim 11, wherein the transverse flux machine is a multi-phase machine having a plurality of stator windings, and wherein the transverse flux core of the stator assembly comprises a plurality of stator cores, each of the plurality of stator cores defining an annular shape and holding a corresponding one of the plurality of stator windings, and wherein each of the plurality of stator cores is axially aligned with a corresponding one of the plurality of segments. 16 . The steer-by-wire steering system of claim 11 , wherein the rotor assembly further comprises two adjacent segments of the plurality of segments attached to each other by a glue joint. 17 . The steer-by-wire steering system of claim 11 , wherein the plurality of permanent magnets include a first group of permanent magnets having a first residual magnetic flux density and a second group of permanent magnets having a second residual magnetic flux density lower than the first residual magnetic flux density.

18. The steer-by-wire steering system of claim 17, wherein the first group of permanent magnets having the first residual magnetic flux density is disposed within an outer segment of the plurality of segments positioned adjacent an axial end of the rotor assembly, and wherein the second group of permanent magnets having the second residual magnetic flux density is disposed within an inner segment of the plurality of segments spaced apart from the axial end of the rotor assembly.

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

20. The steer-by-wire steering system of claim 11, wherein the transverse flux machine is a multi-phase machine having at least three stator windings, and wherein the transverse flux core of the stator assembly comprises a plurality of stator cores, each stator core of the plurality of stator cores defining an annular shape and holding a corresponding stator winding of the at least three stator windings, wherein each of the plurality of stator cores is axially aligned with a corresponding one of the plurality of segments of the rotor assembly, wherein the plurality of segments of the rotor assembly include two outer segments, each of the two outer segments defining an axial end of the rotor assembly and including a first set of permanent magnets having a first residual magnetic flux density, and The plurality of segments of the rotor assembly include at least one inner segment spaced apart from the axial end of the rotor assembly and including a second set of permanent magnets having a second residual flux density lower than the first residual flux density.

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