Printed circuit board axial flux machine for steer-by-wire hand-held actuator
Patent Information
- Application Number
- DE102024128633
- Authority / Receiving Office
- DE · DE
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-10-06
- Filing Date
- 2024-10-02
- Publication Date
- 2025-04-10
Smart Images
Figure 00000000_0000_ABST
Abstract
Description
TECHNICAL FIELDThis disclosure relates to axial flux electric machines having windings on printed circuit boards (PCBs) and applications of such axial flux electric machines in a hand wheel actuator of a steering system for a vehicle.BACKGROUNDA vehicle, such as a car, truck, sport utility vehicle, crossover, mini-van, watercraft, aircraft, sport utility vehicle, recreational vehicle, or other suitable means of transport, typically includes a steering system, such as an electronic power steering (EPS), steer-by-wire steering (SbW), hydraulic steering system, or other suitable steering system. The steering system of such a vehicle typically controls various aspects of vehicle steering, including providing a steering assist to the driver of the vehicle, controlling steerable wheels of the vehicle, and the like.Steer-by-wire (SbW) is a direct development of electric power steering (EPS) in which there is no mechanical connection between the hand wheel and the rack. An EPS system may include a single actuator, the sole purpose of which is to assist the driver in steering. However, in the SbW system, there may be two electric actuators / motors having different functions. The electric actuator mounted to the rack in an SbW system is referred to as a roadwheel actuator (RWA), while the driver side actuator is referred to as a handwheel actuator (HWA). The RWA has the same support function as an actuator of an EPS system. The HWA, on the other hand, functions more as a feedback motor and less as assistance to the driver. Without HWA, the hand wheel would simply run idle in an SbW system due to the lack of any mechanical coupling / friction. The HWA opens up a variety of design possibilities on account of its functionality.As a function of function, the torque-speed curves of the various actuators used in steering systems may be different. The very different operating ranges of EPS / RWA and HWA motivate to develop designs for HWA technology.SUMMARYThis disclosure relates generally to axial flow electric machines.One aspect of the disclosed embodiments includes an axial flow machine (AFM). The AFM includes a rotor assembly configured to rotate about an axis. The rotor assembly includes a first rotor core and a second rotor core, wherein a plurality of permanent magnets are attached to each of the first rotor core and the second rotor core, and wherein the first rotor core and the second rotor core are spaced apart from each other and parallel to each other and perpendicular to the axis. The AFM also includes a stator assembly. The stator assembly includes at least one PCB located between and parallel to the first rotor core and the second rotor core. The at least one PCB defines a stator winding configured to generate a magnetic flux in an axial direction through each of the first rotor core and the second rotor core to cause the AFM to generate a torque.One aspect of the disclosed embodiments includes a steer-by-wire system for a vehicle. The steer-by-wire system includes a hand wheel actuator coupled to transmit torque to a steering wheel. The hand wheel actuator includes an axial flow machine (AFM). The AFM includes a rotor assembly configured to rotate about an axis. The rotor assembly includes a first rotor core and a second rotor core, wherein a plurality of permanent magnets are attached to each of the first rotor core and the second rotor core, and wherein the first rotor core and the second rotor core are spaced apart from each other and parallel to each other and perpendicular to the axis. The AFM also includes a stator assembly. The stator assembly includes at least one PCB located between and parallel to the first rotor core and the second rotor core. The at least one PCB defines a stator winding configured to generate a magnetic flux in an axial direction through each of the first rotor core and the second rotor core to cause the AFM to generate a torque.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 DRAWINGSThe disclosure will be best understood from the following detailed description when read in conjunction with the accompanying drawings. It is emphasized that the various features of the drawings are not to scale according to common practice. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. FIG. 1 is a schematic illustration of an electric power steering (EPS) system according to the principles of the present disclosure. FIG. 2 basically illustrates an electric power steering (EPS) system according to the principles of the present disclosure. FIG. 3 illustrates a steer-by-wire (SbW) steering system according to the principles of the present disclosure. FIG. 4 is a schematic illustration of a motor drive system according to the principles of the present disclosure. FIG. 5 is a diagram illustrating torque-speed curves of steering system actuators according to the principles of the present disclosure. FIG. 6 is a cross-sectional view of a radial flow machine (RFM) in accordance with the principles of the present disclosure. FIG. 7 is a cross-sectional view of an axial flow machine (AFM) in accordance with the principles of the present disclosure. FIG. 8 shows a cross-sectional view of a first AFM assembly with a slotted stator core. FIG. 9 is a cross-sectional view of a second AFM assembly having a slotless stator core in accordance with the principles of the present disclosure. FIG. 10 shows a cross-sectional view of a third AFM assembly according to the principles of the present disclosure, with two rotor cores extending parallel and spaced apart from each other, and with a stator assembly including two parallel-array PCBs located between the two rotor cores. FIG. 11 shows a cross-sectional view of an AFM device according to the principles of the present disclosure, with sets of two rotor cores, respectively, that are parallel and spaced apart from each other, and with a stator assembly that includes two sets of PCBs, respectively, that are arranged parallel and are located between a corresponding pair of rotor cores. FIG. 12 shows a cross-sectional view of a fourth AFM assembly, including a passively attenuating PCB, in accordance with the principles of the present disclosure. FIG. 13 shows a cross-sectional view of a fifth AFM package with shorted windings within a PCB or between the two PCBs. FIG. 14 shows a schematic illustration of stator windings within an AFM in accordance with the principles of the present disclosure. FIG. 15 is a graph indicating brake torque as a function of speed for an AFM according to the principles of the present disclosure with shorted windings having different numbers of turns. FIG. 16 is a graph indicating short circuit current as a function of speed for an AFM according to the principles of the present disclosure with short-circuited windings having different numbers of turns. FIG. 17 shows a schematic illustration of stator windings within an AFM during switched braking, in accordance with the principles of the present disclosure. FIG. 18 is a graph indicating braking torque as a function of speed for an AFM according to the principles of the present disclosure with shorted windings of various resistances. FIG. 19 is a graph indicating short circuit current as a function of speed for an AFM according to the principles of the present disclosure with short-circuited windings of various resistors. FIG. 20 shows a plot of torque over time including curves representing the braking torque, active winding generated torque, and total torque of a passive braking AFM according to the principles of the present disclosure. FIG. 21 shows a PCB package with a partial cut-out to show various winding configurations according to the principles of the present disclosure.DETAILED DESCRIPTIONThe following discussion relates to various embodiments of the disclosure. Although one or more of these embodiments may be preferred, the disclosed embodiments should not be interpreted or otherwise used as limiting the scope of the disclosure, including the claims. Moreover, those skilled in the art will understand that the following description has a broad scope of application and the discussion of an embodiment is intended to be exemplary of this embodiment only and does not mean that the scope of the disclosure, including the claims, is limited to this embodiment.As described, a vehicle such as a car, truck, sport utility vehicle, crossover, mini-van, watercraft, aircraft, sport utility vehicle, recreational vehicle, or other suitable means of transport usually includes a steering system such as an EPS system, SbW steering system, hydraulic steering system, or other suitable steering system. The steering system of such a vehicle typically controls various aspects of vehicle steering, including providing a steering assist to the driver of the vehicle, controlling steerable wheels of the vehicle, and the like.The present disclosure provides an axial flow machine (AFM) that is particularly well suited for transmission design and high speed operation. The AFM may include a modular stator having a spatially offset three-phase or polyphase structure. The AFM may include a printed circuit board (PCB) structure and a slotless stator topology. The AFM may be a structure having a single rotor pack or multiple rotor packs with high volumetric and gravimetric torque density. The AFM is relatively simple and efficient to manufacture and can provide suitable performance for a variety of applications in an EPS and / or SbW system.The present disclosure provides an AFM structure that provides damping in an off or faulty state of the motor. To achieve motor damping, the layers of the PCB may be shortened or a separate PCB may be incorporated. Moreover, the number of turns and the coil's track width in the shorted PCB may be completely different than in the active PCB of the machine. An additional ohmic resistance allows the short-circuit current and the braking torque of the machine to be controlled in the short-circuited PCB. This additional ohmic resistance may be implemented directly into the PCB to reduce manufacturing difficulties and the overall cost of the machine. Moreover, additional circuitry along with the gate drivers and switches may be implemented in the PCB to control the connections of the coil depending on the speed of operation. These additional circuitry may also be implemented in the same PCB to reduce the cost and difficulty in manufacturing the machine.FIG. 1 is a schematic illustration of an electric power steering (EPS) system 40 suitable for implementing the disclosed techniques. The EPS includes a steering mechanism 36 including a rack and pinion type mechanism having a rack (not shown) inside a housing 50 and a pinion (also not shown) below a gear housing 52. When the operation input, hereinafter referred to as a steering wheel 26 (e.g., a hand wheel or the like) is turned, the upper steering shaft 29 rotates, and the lower steering shaft 51 connected to the upper steering shaft 29 through the universal joint 34 turns the pinion. The rotation of the pinion moves the rack which in turn moves tie rods 38 (only one shown) which in turn move the steering knuckles 39 (only one shown) each rotating a steerable wheel 44 (only one shown).The electric power steering assist is provided by the steering motion control system, generally designated by the reference numeral 24, which includes the controller 16 and an electric machine, which could be a permanent magnet synchronous motor and will be referred to herein as the motor 19. The controller 16 is supplied with current from the on-board power supply system 10 via the supply lines 12. The controller 16 receives a vehicle speed signal 14 representative of the vehicle speed from a vehicle speed sensor 17. The steering angle is measured by position sensor 32, which may be an optical coding-based sensor, a variable resistance sensor, or any other suitable type of position sensor, and provides a position signal 20 to controller 16. Engine speed may be measured with a tachometer or other device and transmitted as speed signal 21 to controller 16. A motor speed, denoted ω m may be measured, calculated, or a combination thereof. For example, the motor speed ω m may be calculated as a change in a motor position θ as measured by a position sensor 32 over a prescribed time interval. Thus, the motor speed ω m may be determined as a derivative of the motor position θ m with time. It should be appreciated that there are numerous known methods for determining a derivative.When the steering wheel 26 is turned, the torque sensor 28 detects the torque that the operator applies to the steering wheel 26. The torque sensor 28 may include a torsion bar (not shown) and a variable resistance sensor (also not shown) that outputs a torque signal 18 related to the amount of torsion of the torsion bar to the controller 16. This is only one type of torque sensor, but any other suitable device for torque detection is sufficient in connection with known signal processing techniques. In response to the various inputs, the controller sends a command 22 to the motor 19 which provides torque assist to the steering system via worm 47 and worm gear 48 to provide torque assist to the vehicle steering system.It should be appreciated that while the disclosed embodiments are described with reference to motor control for electric steering applications, it is understood that such references are exemplary only and the disclosed embodiments may be applied to any motor control application employing an electric motor, e.g., steering, valve control, and the like. Moreover, the references and descriptions herein may apply to many forms of parameter sensors, including, but not limited to, torque, position, speed, and the like. It should also be noted that references herein to electric machines include motors, and only motors are referred to below for brevity and simplicity, but are not intended to be limiting thereto.In the steering motion control system 24, as shown, the controller 16 uses torque, position, speed, and the like to determine one or more commands to provide the required output power. The controller 16 is in communication with the various systems and sensors of the engine control system. The controller 16 receives signals from each of the sensors of the system, quantify the information received, and in response, provide one or more output control signals, in this case, for example, to the motor 19. the controller 16 is configured to generate the corresponding voltage(s) with an inverter (not shown), which may optionally be integrated with the controller 16, referred to herein as controller 16, such that upon application to the motor 19, the desired torque or position is produced. In one or more examples, the controller 16 operates in a closed-loop control mode, namely as a current regulator, to generate the command 22. Alternatively, in one or more examples, the controller 16 operates in a feedforward 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 exerted by an operator are determined. A position sensor is connected to the steering shaft 51 to detect the angular position θ. The position sensor can detect the rotational position based on optical detection, magnetic field changes or other methods. Typical position sensors include potentiometers, resolvers, rotary coil pickups, position encoders, and the like, as well as combinations comprising at least one of the aforementioned sensors. The position sensor outputs a position signal 20 which indicates the angular position of the steering shaft 51 and thus that of the motor 19.The desired torque may be determined by one or more torque sensors 28 that transmit the torque signals 18 indicative of an acting torque. Because such a torque sensor 28 and the torque signals 18 thereof may respond to a compliant torsion bar, spring, or similar device (not shown), they may be configured to provide a response indicative of the applied torque.In one or more examples, a temperature sensor 23 is located on 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 provides a temperature signal 25 to the controller 16 to enable processing and compensation described herein. Typical temperature sensors include thermocouples, thermistors, temperature monitors and the like, and at least one of the combinations comprising the aforementioned sensors, which, when placed accordingly, provide a calibrateable signal proportional to the respective temperature.The controller 16 is supplied with, among other things, the position signal 20, the speed signal 21 and the torque signals 18. The controller 16 processes all input signals to generate values corresponding to the individual signals resulting in a rotor position value, an engine speed value, and a torque value available for processing in the algorithms as specified herein. Measurement signals such as those mentioned above are usually also linearized, compensated and filtered as desired in order to improve the properties of the detected signal or to eliminate undesirable properties. For example, the signals may be linearized to improve processing speed or to accommodate a wide dynamic range of the signal. In addition, frequency or time based compensation and filtering may be used to remove noise or to avert undesirable spectral characteristics.To perform the prescribed functions and desired processing, as well as calculations therefor (e.g., determination of engine parameters, control algorithms, and the like), controller 16 may include, among other things, one or more processor(s), computers, DSP(s), mass storage, memory, registers, clocks, interrupt(s), communication interface(s), and input / output signal interfaces, and the like, as well as at least one of the combinations comprising the aforementioned components. For example, controller 16 may include input signal processing and filtering to enable accurate sampling and conversion or detection of such signals from communication interfaces.As used herein, variables having a tilt (~) above the variable symbol represent an approximation that can be determined by mathematical calculation, a look-up table, etc. Variables with a bar above the variable symbol represent a vector size. Variables with an elevated star (*) represent commands or desired setpoint values.FIG. 2 basically illustrates an electric power steering (EPS) system, and FIG. 3 fundamentally illustrates a steer-by-wire (SbW) steering system. The EPS system of FIG. 2 may be similar or completely similar to the EPS system 40 of FIG. 1, except that the motor 19 is directly mounted to the steering mechanism 36. The SbW system of FIG. 2 may be similar or completely similar to the EPS system 40 of FIG. 1, except that it does not have a physical connection between the steering wheel 26 and the steerable wheels 44 and has two separate and independent motors 19 a, 19 b. As shown, the SbW system includes a first motor 19 a, also called a hand wheel actuator (HWA), configured to transmit torque to the steering wheel 26 to provide haptic feedback to a driver.Steer-by-wire (SbW) is a direct development of the electric power steering system (EPS) in which there is no mechanical connection between the steering wheel 26 and the rack. As seen in Figure 2, an EPS system may include a single actuator 19, the sole purpose of which is to assist the driver in steering. In the SbW system, however, there are two electric actuators / motors having different functions. The electric actuator on the driver side is known as a hand wheel actuator (HWA) 19a, while the electric actuator mounted to the steering mechanism 36 in an SbW system is referred to as a road wheel actuator (RWA) 19b. The RWA 19 bmay provide the same assist function as the actuator 19 in an EPS system. The HWA 19a, on the other hand, functions more as a feedback motor and less as a driver assistance. Without HWA 19a, the hand wheel would simply be free running in an SbW system due to the lack of any mechanical coupling / friction.FIG. 4 shows a motor control system 100 including a permanent magnet double winding synchronous motor (DW-PMSM), also called a double winding synchronous motor (DWSM) or a double winding motor 60, converters 66 aand 66 b(each of which includes a gate driver and a corresponding inverter), and a motor controller 70 (also referred to as a controller). The dual winding motor 60 can be used in various applications, such as for the motor 19 in the steering motion control system 24 shown in FIG. 1, or for either the HWA 19a or the RWA 19b. The power converters 66 aand 66 bmay include multiple switching devices, such as field effect transistors (FETs) for switching high current loads and gate driver circuits for operating the switching devices.The dual winding motor 60 includes a first winding set 62 aand a second winding set 62 bwhich is electrically independent of the first winding set 62 a. The dual winding motor 60 is capable of generating electromagnetic torque upon energizing one or both of the winding sets 62a, 62b. The two winding sets 62 aand 62 bmay each include three phases, and thus each of the two winding sets 62 a, 62 bmay include three-phase windings. Alternatively, each of the winding sets 62 a, 62 bmay include any number of winding phases, for example five or seven phases. In some embodiments, the dual winding motor 60 is a permanent magnet polyphase synchronous machine (PMSM). Each of the winding sets 62a, 62b may function by itself, and the dual winding motor 60 may be operated by energizing either or both of the winding sets 62a, 62b.The engine control system 100 includes a controller 150. Controller 150 may be any suitable controller. The controller 150 may be configured to control, for example, the various functions of the vehicle systems described herein. The controller 150 may include a processor 152 and a memory 154. Processor 152 may include any suitable processor, such as those described herein. Additionally or alternatively, controller 150 may include a suitable number of processors, in addition to or different from processor 152. The memory 154 may comprise a single disk or a plurality of disks (e.g., hard disks) and includes a memory management module that manages one or more partitions within the memory 154. In some embodiments, the memory 154 may include flash memory, solid state memory (semiconductor memory), or the like. The memory 154 may include random access memory (RAM), read only memory (ROM), or a combination thereof. The memory 154 may include instructions that, when executed by the processor 152, cause the processor 152 to control at least some functions of the steering system and / or other suitable functions, including those of the systems and methods described herein.The controller 150 may receive one or more signals from various measurement devices or sensors that indicate sensed or measured characteristics of the vehicle. The sensors may include any suitable sensors, measurement devices, and / or other suitable mechanisms. The sensors may include, for example, one or more torque sensors or devices, one or more hand 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 a combination thereof. The one or more signals may indicate a hand wheel torque, a hand wheel angle, a motor angle or position, a vehicle speed, other suitable information, or a combination thereof.The power converters 66 aand 66 bare configured to supply alternating voltages (AC) to the winding sets 62 aand 62 b, respectively. The winding sets 62 a, 62 bare connected to their respective converters 66 a, 66 bvia the phase lines 68 aand 68 b. This configuration may provide redundancy so that the dual winding motor 60 may continue to function even in the event of a complete loss or failure of one of the winding sets 62 a, 62 b, one of the motor lines 68 a, 68 band / or one of the power converters 66 a, 66 b. The power converters 66 a, 66 bmay be implemented with galvanic isolation for additional redundancy.The controller 150 may generate a voltage command V* based on a motor torque command T e* or otherwise, and provide the voltage command V* to each of the converters 66 aand 66 b. For example, controller 150 may include a voltage command generator (not shown) to generate voltage command V* at one or more optimizations and / or to cause the electric motor drive system to satisfy one or more operating limits, such as limits on the voltage and / or current generated by or supplied to the electric motor drive system. Feedforward voltage regulation may include a technique provided in the present disclosure, although other feedforward techniques may also be used.The power converters 66 aand 66 bare configured to supply alternating voltages (AC) to the winding sets 62 aand 62 b, respectively. The winding sets 62 a, 62 bare connected to their respective converters 66 a, 66 bvia the phase lines 68 aand 68 b. This configuration may provide redundancy so that the dual winding motor 60 may continue to function even in the event of a complete loss or failure of one of the winding sets 62 a, 62 b, one of the motor lines 68 a, 68 band / or one of the power converters 66 a, 66 b. The power converters 66 a, 66 bmay be implemented with galvanic isolation for additional redundancy.FIG. 5 is a graph illustrating torque-speed curves of the steering system actuators 19, 19a, and 19b. The various steering system actuators 19, 19 a, 19 bhave different torque-speed curves as a function of function. As indicated by the dashed line in FIG. 5, the EPS actuator 19 and the RWA 19 bin an SbW system each operate in the first quadrant (Q 1) of the torque-speed curve. The positive direction of speed in Q 1 suggests that the actuator is acting in the same direction as the driver's hand wheel movement and provides assistance. However, as indicated by the solid line, the HWA 19 aof the SbW system predominantly operates in the second quadrant (Q 2) of the torque-speed curve. The HWA 19a moves in the opposite direction (speed -ve) to the hand wheel movement of the driver and provides feedback to the driver. This feedback may be required to provide the driver with a typical steering feel and road condition feedback. In addition, some low speed assist (Q1 operation) of the HWA 19a may also be required, as seen in FIG. 5.The HWA 19 amay include an electric motor coupled to transmit torque to the steering wheel 26, in configurations such as a worm gear drive, a belt drive, and / or a direct drive. In a worm gear drive and a belt drive, the low torque is about 3 Newton-meters (Nm) and the high speed is about 3000 revolutions per minute (U / min). PMSMs can be used as the actuator. For such HWA architectures, both surface mount PMSM topologies (SPMSM) and internal PMSM topologies (IPMSM) may be used. Moreover, due to their similarity (in terms of torque-speed ranges), numerous components can be transferred directly from column EPS systems (CEPS) to worm or belt drive SbW hand wheel systems.The torque-speed curves of the various actuators used in steering systems also change as a function of function. As shown in FIG. 5, in an SbW system, the EPS actuator and the RWA each operate in the first quadrant (Q 1) of the torque-speed curve. The positive direction of speed in Q 1 suggests that the actuator is acting in the same direction as the driver's hand wheel movement and provides assistance. However, the SbW-HWA mostly operates in the second quadrant (Q 2) of the torque-speed curve. The HWA moves opposite (speed -ve) to the hand wheel movement of the driver and provides feedback to the driver. This feedback is necessary to give the driver a typical steering feel and a road condition feedback. Moreover, some low speed support (Q1 operation) of the HWA may also be required, as seen in FIG. 5. The very different operating ranges of EPS / RWA and HWA motivate to develop designs for HWA technology.The HWA may include an electric motor coupled to transmit torque to the steering wheel 26, in configurations such as a worm gear drive, a belt drive, and / or a direct drive. In a worm wheel drive and a belt drive, low torque (~3 Nm) and high speed (~3000 U / min) PMSMs may be used as the actuator. For such HWA architectures, both surface mount PMSM topologies (SPMSM) and internal PMSM topologies (IPMSM) may be used. Moreover, due to their similarity (in terms of torque-speed ranges), numerous components can be transferred directly from column EPS systems (CEPS) to worm or belt drive SbW hand wheel systems.FIG. 6 shows a cross-sectional view of a radial flow machine (RFM). FIG. 7 is a cross-sectional view of an axial flow machine (AFM). The RFM as well as the AFM device includes a shaft configured to rotate about an axis A. The distinction between RFM and AFM configurations may be made based on the direction of magnetic flux.The RFM of FIG. 6 includes a first rotor assembly 110 awith a first rotor core 112 amounted to rotate about an axis A with a first shaft 114 a. The rotor assembly 110a is located in a first housing 115a, and the first shaft 114a extends through and out of the first housing 115a 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 radially outward. The RFM of FIG. 6 also includes a first stator assembly 120 ahaving a first stator core 122 awith a set of first windings 124 aextending therethrough that conduct electrical current in an axial direction, parallel to axis A, and perpendicular to magnetic flux.The AFM of FIG. 7 includes a second rotor assembly 110 bwith a second rotor core 112 bmounted to rotate about an axis A with a second shaft 114 b. The second rotor assembly 110 bis located in a second housing 115 b, and the second shaft 114 bextends through and out of the second housing 115 band is supported by a pair of second bearings 116 b. A set of second permanent magnets 118 bis mounted on the second rotor core 112 band generates magnetic flux in the axial direction, parallel to axis A. The AFM of FIG. 7 also includes a second stator assembly 120 bthat includes a second stator core 122 bwith a set of second windings 124 bextending therethrough that conduct electrical current in the radial direction, perpendicular to axis A, and perpendicular to the magnetic flux.As shown in FIG. 6, the magnetic flux in the RFM is primarily in a radial direction, perpendicular to axis A. As shown in FIG. 7, the magnetic flux in the AFM is primarily in an axial direction, parallel to axis A. RFM configuration and AFM configuration may provide different volumetric and gravimetric power densities, respectively.The present disclosure provides an axial flow machine (AFM) topology for a SbW gear drive HWA architecture. Axial flow machines have the potential of offering considerable advantages with regard to power density in the high-speed and low-torque range of a toothed SbW-HWA compared to conventional radial flow machines.FIG. 8 shows a cross-sectional view of a first AFM assembly 200 having a slotted stator core. The first AFM assembly 200 includes a rotor assembly 210 and a first stator assembly 220 having a first stator core 222. The rotor assembly 210 is mounted on a motor shaft and is configured to rotate about an axis (not shown in the figures) while the first stator assembly 220 remains stationary. The rotor assembly 210 includes a rotor core 212 that extends in a planar plane perpendicular to the axis of rotation. The rotor assembly 210 includes two permanent magnets 214 a, 214 bdisposed on a surface of the first rotor core 212 and facing the first stator assembly 220. The first stator core 222 defines two teeth 224 each having an I-shaped cross section and extending toward a corresponding one of the two permanent magnets 214 a, 214 b. In addition, the first stator assembly 220 includes a first winding 226 disposed around each of the two teeth 224 of the first stator core 222.FIG. 9 shows a cross-sectional view of a second AFM assembly 250 in accordance with the principles of the present disclosure. The second AFM assembly 250 includes a rotor assembly 210 similar or completely similar to the rotor assembly 210 of the first AFM assembly 200. Additionally, the second AFM assembly 250 includes a second stator assembly 260, which may be referred to as a slotless stator because it does not include the teeth 224 nor corresponding slots therebetween. Instead, the second stator assembly 260 includes a second stator core 262 and a printed circuit board (PCB) 264 attached thereto that extends parallel to and spaced apart from the rotor core 212.FIG. 10 shows a cross-sectional view of a third AFM assembly 280 in accordance with the principles of the present disclosure. The third AFM assembly 280 includes a dual PCB and dual rotor structure without a stator core made of magnetic material such as steel. The third AFM assembly 280 includes two rotor assemblies 210, each of which may be similar or completely similar to the rotor assembly 210 of the first AFM assembly 200. The two rotor arrangements 210 each have a rotor core 212, wherein the two rotor cores are spaced apart from one another and arranged parallel to one another and perpendicular to the axis of rotation (not shown in the figure). Each of the two rotor assemblies 210 also includes a plurality of permanent magnets 214 a, 214 bdisposed on one surface of the corresponding rotor core 212 and facing the other of the two rotor assemblies 210.The third AFM assembly 280 also includes a first active PCB 264 aand a second active PCB 264 barranged side by side and respectively located between and parallel to the two rotor cores 212. Each of the first active PCB 264 aand the second active PCB 264 bdefines a stator winding (not shown in FIG. 12 ) configured to generate a magnetic flux in the axial direction through each of the two rotor cores 212 to cause the third AFM assembly 280 to generate torque. As shown, the magnetic flux defines a closed loop path 282.In some embodiments, the third AFM assembly 280 may be configured as a dual winding device. For example, the first active PCB 264 amay define the first winding set 62 aand the second active PCB 264 bmay define the second winding set 62 b.FIG. 11 shows a cross-sectional view of an AFM device 300 in accordance with the principles of the present disclosure. The AFM device 300 may also be referred to as an AFM. The AFM device 300 includes a two-stage structure, wherein two of the third AFM assemblies 280 are each coupled to a motor shaft 314 to rotate about an axis A. Each of the third AFM assemblies 280 in the AFM device 300 may also be referred to as an AFM stage. It should be appreciated that this is merely an example and an AFM may be constructed with a different number of AFM assemblies 280.The AFM device 300 includes a housing 315 extending about the motor shaft 314, with bearings 316 supporting the motor shaft 314 to allow the motor shaft 314 to rotate about the axis. The AFM device 300 includes four rotor assemblies 210, each of which may be similar or entirely similar to the rotor assembly 210 of the first AFM assembly 200, and each includes a rotor core 212 attached to the motor shaft 314 via a rotor mount 302. The rotor cores 212 are each spaced apart from and parallel to each other and perpendicular to the axis A. The AFM device 300 also includes two sets of two active PCBs 264 a, 264 b, each set of active PCBs 264 a, 264 bbeing disposed between and parallel to two corresponding rotor cores 212. Each of the active PCBs 264 a, 264 bmay be held stationary by PCB holders 304 attached to the housing 315.FIG. 12 shows a cross-sectional view of a fourth AFM assembly 350 in accordance with the principles of the present disclosure. The fourth AFM assembly 350 may be similar or completely similar to the third AFM assembly 280, with a passive attenuating PCB 352 added between the first active PCB 264 aand the second active PCB 264 b. The passive damping PCB 352 defines one or more passive damping windings 372, each having a shorted configuration to generate a braking torque. In some embodiments, the passive damping windings 372 of the passive damping PCB 352 may be permanently shorted, thereby causing the passive damping PCB 352 to produce a constant braking torque at all times. Alternatively or additionally, some or all of the passive attenuating windings 372 of the passive attenuating PCB 352 may be selectively connected in the shorted configuration. For example, the passive damping windings 372 can be selectively switched into the short-circuit configuration, as a result of which it is possible to generate the braking torque in a targeted manner and / or to vary the magnitude thereof.FIG. 13 shows a cross-sectional view of a fifth AFM assembly 370 in accordance with the principles of the present disclosure. The fifth AFM package 370 may be similar or completely similar to the third AFM package 280, with a passive damping winding 372 added within the first active PCB 264 aand / or the second active PCB 264 b. The passive damping winding 372 may have a short-circuited configuration to generate a braking torque. In some embodiments, the passive damping winding 372 may be permanently shorted, thereby causing the passive damping winding 372 to produce a constant braking torque at all times. Alternatively or additionally, some or all of the passive damping windings 372 may be selectively connected in the shorted configuration. For example, the passive damping windings 372 can be selectively switched into the short-circuit configuration, as a result of which it is possible to generate the braking torque in a targeted manner and / or to vary the magnitude thereof.FIG. 14 shows an electrical schematic of the stator windings within the fourth AFM package 350. As shown, the fourth AFM package 350 includes the first active PCB 264 adefining each of the A-phase stator windings 266 a, the B-phase stator windings 266 b, and the C-phase stator windings 266 c. Each of the stator windings 266 a, 266 b, 266 cincludes four coils in parallel between a respective motor line, respectively designated phase A, phase B, and phase C, and a common neutral conductor. The second active PCB 264 bhas a similar configuration, defining each of the D-phase stator windings 266 d, the E-phase stator windings 266 e, and the F-phase stator windings 266 f. Thus, the stator windings 266 a, 266 b, 266 cof the first active PCB 264 aand the stator windings 266 d, 266 e, 266 fof the second active PCB 264 bhave star connections, respectively. Alternatively, the stator windings may have a delta connection. Each of the four coils making up each stator winding may have a resistance of 550 milliohms (550 mΩ). However, the coils may also have different resistances and the stator windings 266a, 266b, 266c may have a different number of associated turns.FIG. 14 also shows an electrical schematic of the passive attenuating PCB 352 including the passive attenuating coils 268a, 268b, 268c comprising the passive attenuating windings 372. As shown, the passive damping windings 372 include four first passive damping coils 268a, each connected in series and in series with a first additional resistive resistor 270a. The passive damping windings 372 also include four second passive damping coils 268b, each connected in series and in series with a second additional resistive resistor 270b. The passive damping windings 372 also include four third passive damping coils 268c, each connected in series and connected in series with a third additional resistive resistor 270c. However, each of the series connections may include a different number of passive damping coils 268 a, 268 b, 268 c. The series connections of the passive damping coils 268a, 268b, 268c and the corresponding additional resistors 270a, 270b, 270c are connected in parallel, respectively. The additional ohmic resistors 270 a, 270 b, 270 care optional and may generate an additional braking torque and / or limit the short circuit current generated in the passive damping windings 372, and thus protect the passive damping windings 372 from over current conditions that may cause permanent damage, such as breakage of the passive damping windings 372.FIGS. 15-16 show diagrams that indicate the braking torque and the short-circuit current as a function of the rotational speed for an AFM having passive damping windings 372 with twenty-five turns (NT=25) and fifty turns (NT=50), respectively. As shown, the brake torque and the short circuit current each increase linearly with speed, and the AFM with NT=25 produces twice the brake torque and only slightly more short circuit current than the AFM with NT=50.FIG. 17 shows an electrical schematic of the stator windings within the fifth AFM package 370. As shown, the fifth AFM package 370 includes the first active PCB 264 adefining each of the A-phase stator windings 266 a, the B-phase stator windings 266 b, and the C-phase stator windings 266 c. Each of the stator windings 266 a, 266 b, 266 cincludes four coils in parallel between a respective motor line, respectively designated phase A, phase B, and phase C, and a common neutral conductor. The second active PCB 264 bhas a similar configuration, defining each of the D-phase stator windings 266 d, the E-phase stator windings 266 e, and the F-phase stator windings 266 f. Thus, the stator windings 266 a, 266 b, 266 cof the first active PCB 264 aand the stator windings 266 d, 266 e, 266 fof the second active PCB 264 bhave star connections, respectively. Alternatively, the stator windings may have a delta connection. Each of the four coils making up each stator winding may have a resistance of 550 milliohms (550 mΩ). However, the coils may also have different resistances and the stator windings 266a, 266b, 266c may have a different number of associated turns.FIG. 17 also shows that the first active PCB 264 aand the second active PCB 264 beach define one or more passive damping windings 372 that can be operated in a shorted configuration to generate a braking torque. As shown, the passive damping windings 372 of the first active PCB 264 aand the second active PCB 264 binclude two first hybrid damping windings 272 aconnected in series and connected in series with a first switch 274 aconfigured to selectively pass current through the first hybrid damping windings 272 ato cause the first hybrid damping windings 272 to generate a braking torque. The passive damping windings 372 of the first active PCB 264 aand the second active PCB 264 balso include two second hybrid damping windings 272 bconnected in series and connected in series with a second switch 274 bconfigured to selectively pass current through the second hybrid damping windings 272 bto cause the second hybrid damping windings 272 bto generate additional braking torque. The passive damping windings 372 of the first active PCB 264 aand the second active PCB 264 balso include two third hybrid damping windings 272 cconnected in series and connected in series with a third switch 274 cconfigured to selectively pass current through the third hybrid damping windings 272 cto cause the third hybrid damping windings 272 cto generate additional braking torque. In some embodiments, some or all of the hybrid damping windings 272 a, 272 b, 272 cmay be connected to the motor lines to function as additional stator windings.FIG. 17 also shows the first active PCB 264 aand the second active PCB 264 bwith switch drivers 276 configured to control the actuation of the switches 274 a, 274 b, 274 c. Thus, each of the switches 274 a, 274 b, 274 cand each of the switch drivers 276 may be disposed within or on the first active PCB 264 aand / or the second active PCB 264 b. The switch drivers 276 may control the individual actuation of the switches 274 a, 274 b, 274 cto generate variable braking torques.FIG. 18 is a graph indicating braking torque as a function of speed for an AFM having shorted windings of various resistances. FIG. 19 is a graph showing short circuit current as a function of speed for an AFM having short-circuited windings of various resistors. FIGS. 18 and 19 respectively include curves for additional ohmic resistances Radd of 0 Ω, 0.364 Ω, 0.72 Ω, and 1.1 Ω. These various values of the additional ohmic resistances Radd may be determined based on the number and / or configuration of the hybrid damping windings 272 a, 272 b, 272 c short-circuited by the switches 274 a, 274 b, 274 c. Therefore, based on the number of hybrid damping windings 272 a, 272 b, 272 cthat are short-circuited, the slopes of the braking torque and the short-circuit current can be changed.FIG. 20 shows a plot of torque over time including curves representing the braking torque, active winding generated torque, and total torque of a passive braking AFM at 750 U / min. The graph of FIG. 20 shows operation in the second quadrant (Q 2) where the total torque may be a sum of a braking torque generated by the passive damping coils 268 a, 268 b, 268 cand / or the hybrid damping windings 272 a, 272 b, 272 cand an active torque generated by the stator windings 266 a, 266 b, 266 cof the active PCBs 264 a, 264 b.FIG. 21 shows the passive attenuating PCB 352 with a partial cut away to show various winding configurations for the passive attenuating PCB 352. The various winding structures include: loop winding (a), concentric winding (b), radial loop winding (c), and arc winding (d). In one or both of the active PCBs 264 a, 264 b, similar or completely similar winding structures may be used. The passive damping windings may be different than the active windings and may be connected together to achieve a desired braking torque.The present disclosure provides an axial flow machine (AFM). The AFM includes: a rotor assembly configured to rotate about an axis and including a first rotor core and a second rotor core, wherein a plurality of permanent magnets are respectively attached to the first rotor core and the second rotor core, and wherein the first rotor core and the second rotor core are spaced apart from each other and arranged parallel to each other and perpendicular to the axis; and a stator assembly including at least one printed circuit board (PCB) located between and parallel to the first rotor core and the second rotor core. The at least one PCB defines a stator winding configured to generate a magnetic flux in an axial direction through each of the first rotor core and the second rotor core to cause the AFM to generate a torque.In some embodiments, the AFM further includes a motor shaft extending along the axis, and the first rotor core and the second rotor core are each attached to the motor shaft to rotate therewith, and the first rotor core and the second rotor core are each circumferentially arranged around the motor shaft.In some embodiments, the at least one PCB includes a first PCB and a second PCB extending parallel to each other and each located between and parallel to the first rotor core and the second rotor core.In some embodiments, the stator winding includes a first set of active windings and a second set of active windings independent of the first set of active windings, each of the first set of active windings and the second set of active windings operable to generate the magnetic flux and cause the rotor assembly to generate torque.In some embodiments, the at least one PCB includes a first PCB and a second PCB extending parallel to each other and each located between and parallel to the first rotor core and the second rotor core; and the first PCB defines the first set of active windings and the second PCB defines the second set of active windings.In some embodiments, the AFM further includes: a second rotor assembly configured to rotate about the axis and including a third rotor core and a fourth rotor core, wherein a plurality of permanent magnets are respectively attached to the third rotor core and the fourth rotor core, and wherein the third rotor core and the fourth rotor core are spaced apart from each other and arranged parallel to each other and perpendicular to the axis; and a second stator assembly including at least one second PCB located between and parallel to the third rotor core and the fourth rotor core. In some embodiments, the at least one second PCB defines a second stator winding configured to generate a magnetic flux in the axial direction through each of the third rotor core and the fourth rotor core to cause the AFM to generate torque.In some embodiments, the stator winding is one of a plurality of phase windings, the at least one PCB defining each of the plurality of phase windings.In some embodiments, the at least one PCB further includes a passive damping winding having one or more shorted configurations for generating a braking torque.In some embodiments, the at least one PCB further includes an ohmic resistor connected to the passive damping winding.In some embodiments, the at least one PCB includes: an active PCB defining the stator winding configured to generate the magnetic flux; and a passive attenuating PCB independent of the active PCB and defining the passive attenuating winding.In some embodiments, the stator winding includes a first set of active windings and a second set of active windings independent of the first set of active windings, each of the first set of active windings and the second set of active windings operable to generate the magnetic flux and cause the rotor assembly to generate torque. In some embodiments, the at least one PCB includes a first PCB and a second PCB extending parallel to each other and each located between and parallel to the first rotor core and the second rotor core, wherein the first PCB defines the first set of active windings and the second PCB defines the second set of active windings. In some embodiments, the AFM further includes a passive attenuating PCB defining the passive attenuating winding, the passive attenuating PCB being disposed adjacent to and parallel to the first PCB and the second PCB.In some embodiments, the AFM further includes a hybrid damping winding having a switch configured to selectively pass current through the hybrid damping winding to cause the hybrid damping winding to generate a braking torque.In some embodiments, the AFM further includes a switch driver configured to control actuation of the switch, wherein the hybrid snubber winding, the switch, and the switch driver are each disposed within or on the at least one PCB.In some embodiments, the AFM further includes a plurality of hybrid damping windings and a plurality of switches, each of the switches configured to selectively direct current through one or more corresponding windings of the plurality of hybrid damping windings. In some embodiments, varying a configuration of the plurality of switches to direct current through the one or more respective windings causes the AFM to generate a variable braking torque.In some embodiments, the plurality of hybrid damping windings and the plurality of switches are each disposed within or on the at least one PCB.The present disclosure provides a steer-by-wire system for a vehicle. The steer-by-wire system includes a hand wheel actuator coupled to transmit torque to a steering wheel. The hand wheel actuator includes an axial flow machine (AFM). The AFM includes a rotor assembly configured to rotate about an axis. The rotor assembly includes a first rotor core and a second rotor core, wherein a plurality of permanent magnets are attached to each of the first rotor core and the second rotor core, and wherein the first rotor core and the second rotor core are spaced apart from each other and parallel to each other and perpendicular to the axis. The AFM also includes a stator assembly. The stator assembly includes at least one PCB located between and parallel to the first rotor core and the second rotor core. The at least one PCB defines a stator winding configured to generate a magnetic flux in an axial direction through each of the first rotor core and the second rotor core to cause the AFM to generate a torque.In some embodiments, the at least one PCB includes a first PCB and a second PCB extending parallel to each other and each located between and parallel to the first rotor core and the second rotor core.In some embodiments, the stator winding includes a first set of active windings and a second set of active windings independent of the first set of active windings, each of the first set of active windings and the second set of active windings operable to generate the magnetic flux and cause the rotor assembly to generate torque.In some embodiments, the at least one PCB further includes a passive damping winding having one or more shorted configurations for generating a braking torque.In some embodiments, the at least one PCB further includes an ohmic resistor connected to the passive damping winding.The foregoing discussions are intended to illustrate the principles and various embodiments of the present disclosure. Numerous variations and modifications will be apparent to those skilled in the art once having fully understood the above disclosure. It is intended to interpret the following claims as including all such variations and modifications.The word "example" is used herein to serve as an example, instance, or illustration. Any aspect or design described herein as an "example" is not necessarily to be considered preferred or advantageous over other aspects or designs. Rather, the use of the word "example" is intended to represent 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 stated or clear from context, "X includes A or B" is intended to mean any of the natural inclusive permutations. That is, when X includes A; X includes B; or X includes both A and B, then "X includes A or B" is satisfied in each of the above cases. Moreover, the articles "a", "an" and "an" as used in this application and the appended claims should generally be construed to mean "one or more" unless otherwise stated or clearly understood from the context to refer to a singular form. Moreover, the use of the term "the implementation" or "an implementation" does not mean that it is the same embodiment or implementation unless described as such.Implementations of the systems, algorithms, methods, instructions, etc. described herein may be implemented in hardware, software, or any combination thereof. The hardware may include, for example, computers, intellectual property (IP) cores, application specific integrated circuits (ASICs), programmable logic arrays, optical processors, programmable logic controllers, microcode, microcontrollers, servers, microprocessors, digital signal processors, or any other suitable circuit. In the claims, the term "processor" is to be understood to include any of the foregoing hardware, either alone or in combination. The terms "signal" and "data" are used interchangeably.As used herein, the term module may include a packaged functional hardware unit designed for use with other components, a series of instructions executable by a controller (e.g., a processor executing software or firmware), processing circuitry configured to perform a particular function, and a self-contained hardware or software component that interfaces with a larger system. A module may include, for example, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a circuit, a digital logic circuit, an analog circuit, a combination of discrete circuits, gates, and other types of hardware, or a combination thereof. In other embodiments, a module may include a memory storing instructions executable by a controller to implement a feature of the module.Further, the systems described herein may be implemented, for example, using a general purpose computer or a general purpose processor including a computer program that, when executed, executes any of the methods, algorithms, and / or instructions described herein. Additionally or alternatively, for example, a dedicated computer / processor may be used that includes other hardware for executing the methods, algorithms, or instructions described herein.Further, all or part of the implementations of the present disclosure may take the form of a computer program product accessible from, for example, a computer-usable or computer-readable medium. A computer-usable or computer-readable medium may be any device that can, for example, tangibly contain, store, communicate, or transport the 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.The above-described embodiments, implementations, and aspects have been described in order to enable easy understanding of the present disclosure, and do not limit the present disclosure. Rather, the disclosure is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims, which scope is to be construed in its broadest sense to include all modifications and equivalent structures as permitted by the true law.
Claims
An axial flux machine (AFM) comprising: a rotor assembly configured to rotate about an axis and including a first rotor core and a second rotor core, wherein a plurality of permanent magnets are respectively attached to the first rotor core and the second rotor core, and wherein the first rotor core and the second rotor core are spaced apart from each other and arranged parallel to each other and perpendicular to the axis; and a stator assembly including at least one printed circuit board (PCB) located between and parallel to the first rotor core and the second rotor core, wherein the at least one PCB defines a stator winding configured to generate a magnetic flux in an axial direction through each of the first rotor core and the second rotor core to cause the AFM to generate a torque.The AFM of claim 1, further comprising a motor shaft extending along the axis, wherein the first rotor core and the second rotor core are each attached to the motor shaft to rotate therewith, and wherein the first rotor core and the second rotor core are each circumferentially arranged about the motor shaft.The AFM of claim 1, wherein the at least one PCB includes a first PCB and a second PCB that extend parallel to each other and are respectively located between and parallel to the first rotor core and the second rotor core.The AFM of claim 1, wherein the stator winding includes a first set of active windings and a second set of active windings independent of the first set of active windings, each of the first set of active windings and the second set of active windings operable to generate the magnetic flux and cause the rotor assembly to generate torque.The AFM of claim 4, wherein the at least one PCB includes a first PCB and a second PCB extending parallel to each other and each located between and parallel to the first rotor core and the second rotor core; and wherein the first PCB defines the first set of active windings and the second PCB defines the second set of active windings.The AFM of claim 1, further including: a second rotor assembly configured to rotate about the axis and including a third rotor core and a fourth rotor core, wherein a plurality of permanent magnets are respectively attached to the third rotor core and the fourth rotor core, and wherein the third rotor core and the fourth rotor core are spaced apart from each other and arranged parallel to each other and perpendicular to the axis; and a second stator assembly including at least one second PCB located between and parallel to the third rotor core and the fourth rotor core, wherein the at least one second PCB defines a second stator winding configured to generate a magnetic flux in an axial direction through each of the third rotor core and the fourth rotor core to cause the AFM to generate a torque.The AFM of claim 1, wherein the stator winding is one of a plurality of phase windings and wherein the at least one PCB defines each of the plurality of phase windings.The AFM of claim 1, wherein the at least one PCB further includes a passive damping winding having one or more shorted configurations for generating a braking torque.The AFM of claim 8, wherein the at least one PCB further includes an ohmic resistor connected to the passive damping winding.The AFM of claim 8, wherein the at least one PCB includes: an active PCB defining the stator winding configured to generate the magnetic flux; and a passive attenuating PCB independent of the active PCB and defining the passive attenuating winding.The AFM of claim 8, wherein the stator winding includes a first set of active windings and a second set of active windings independent of the first set of active windings, each of the first set of active windings and the second set of active windings operable to generate the magnetic flux and cause the rotor assembly to generate a torque, wherein the at least one PCB includes a first PCB and a second PCB extending parallel to each other and each located between and parallel to the first rotor core and the second rotor core, wherein the first PCB defines the first set of active windings and the second PCB defines the second set of active windings, and wherein the AFM further includes a passive attenuating PCB defining the passive attenuating winding, wherein the passive attenuating PCB is disposed adjacent to and parallel to the first PCB and the second PCB.The AFM of claim 1, further comprising a hybrid damping winding having a switch configured to selectively pass current through the hybrid damping winding to cause the hybrid damping winding to generate a braking torque.The AFM of claim 12, further comprising a switch driver configured to control actuation of the switch, wherein the hybrid attenuating winding, the switch, and the switch driver are each disposed within or on the at least one PCB.The AFM of claim 1, further comprising a plurality of hybrid damping windings and a plurality of switches, wherein each of the switches is configured to selectively direct current through one or more corresponding windings of the plurality of hybrid damping windings, and wherein varying a configuration of the plurality of switches to direct the current through the one or more corresponding windings causes the AFM to generate a variable braking torque.The AFM of claim 14, wherein the plurality of hybrid damping windings and the plurality of switches are each disposed within or on the at least one PCB.A steer-by-wire system for a vehicle, comprising: a hand wheel actuator coupled to transmit torque to a steering wheel; wherein the hand wheel actuator includes an axial flow machine (AFM) comprising: a rotor assembly configured to rotate about an axis and including a first rotor core and a second rotor core, wherein a plurality of permanent magnets are attached to each of the first rotor core and the second rotor core, and wherein the first rotor core and the second rotor core are spaced apart from each other and are arranged parallel to each other and perpendicular to the axis; and a stator assembly including at least one printed circuit board (PCB) located between and parallel to the first rotor core and the second rotor core, the at least one PCB defining a stator winding configured to generate a magnetic flux in an axial direction through each of the first rotor core and the second rotor core to cause the AFM to generate a torque.The steer-by-wire system of claim 16, wherein the at least one PCB includes a first PCB and a second PCB that extend parallel to each other and are each between and parallel to the first rotor core and the second rotor core.The steer-by-wire system of claim 16, wherein the stator winding includes a first set of active windings and a second set of active windings independent of the first set of active windings, each of the first set of active windings and the second set of active windings operable to generate the magnetic flux and cause the rotor assembly to generate torque.The steer-by-wire system of claim 16, wherein the at least one PCB further includes a passive damping winding having one or more short-circuited configurations for generating a braking torque.The steer-by-wire system of claim 19, wherein the at least one PCB further includes an ohmic resistor connected to the passive damping winding.