Electric motor and hand wheel actuator assembly including motor

Abstract

The present application relates to a motor comprising a stator with a plurality of phase windings and a rotor with a plurality of magnetic poles and connected to a shaft. The stator includes a ferromagnetic material defining a yoke and a plurality of teeth, and further includes at least one strip of conductive material covering at least a portion of one tooth or covering at least a portion of the yoke in a region between adjacent teeth and in direct contact with the teeth, where the strip provides an electrical path between the strip and the tooth or the portion of the yoke, wherein the belt is wound around the upper and lower end regions of the portion of the tooth or yoke and extends axially along opposite side surfaces of the tooth or yoke, and wherein the belt is isolated from any external motor drive current source. The invention also relates to a mechanical assembly comprising the motor.

Description

Technical Field

[0001] The present invention relates to an electric motor, and in particular to an electric motor suitable for use in a hand wheel actuator assembly of a steer-by-wire system of a vehicle. Background Art

[0002] Electric motors are widely used and increasingly common in automotive applications. For example, an electric power steering system is known in which an electric motor device applies an assist torque to a portion of the steering system to make it easier for the driver to turn the wheels of the vehicle. The amount of the assist torque is determined based on a control algorithm that receives as input one or more parameters, such as the torque applied by the driver to the steering column to turn the wheels, the vehicle speed, etc.

[0003] Another example of an electric motor in an automotive application is a steer-by-wire system. During normal use, these systems have no direct mechanical connection between the handwheel moved by the driver and the steering wheel. These systems rely on sensors to transmit user input data on the steering wheel to a control unit, which integrates the user input data with other information (such as vehicle speed and yaw rate) to transmit control signals to the primary motor, which physically actuates the vehicle's steering rack. The control unit also filters out unwanted feedback from the front wheels and provides a response signal to a secondary electric motor that is coupled to the steering wheel. The secondary motor responds to specific user inputs on the steering wheel to provide the driver with appropriate resistance and feedback to simulate the feel of a conventional steering system. The secondary motor is connected to the shaft supporting the handwheel through a gear train, and these three parts together form the handwheel actuator assembly.

[0004] The motor in a steer-by-wire system is typically provided with a stator comprising laminations stacked together in an axial direction. This is both a cost-effective method of manufacturing the motor and prevents current from flowing axially through the stator by applying an electrically insulating coating between the individual laminations in the stack. This reduces energy losses within the motor caused by current flowing axially in the stator. By eliminating or severely limiting current flowing axially, this prior art motor structure exhibits lower drag torque.

[0005] The term "drag torque" as used in this description refers to the torque produced when a motor is spinning that opposes any torque applied to the motor. A motor with all phases of the rotor open circuit will have almost zero drag torque and will only need a small amount of external torque to spin, whereas a motor with very high drag torque will require an equally large or greater amount of external torque to spin the rotor.

[0006] In a steer-by-wire system, if a part of the assembly fails or malfunctions, the steering ability of the vehicle may be affected. Therefore, it is desirable to provide a structure for at least temporary fail-safe operation of the assembly. US2006 / 0042858A1 discloses a steering device, including a steering assembly, which includes a handwheel actuator. The handwheel actuator includes a steering column for supporting a steering wheel, a gear mechanism and two motors, each motor for providing torque to the steering column. Single motor handwheel actuator assemblies are also known.

[0007] When the steer-by-wire system is powered on and operating normally, the HWA applies torque to the shaft carrying the handwheel, resisting the driver's attempt to turn the steering wheel shaft. During most of the system's operation, one or more motors within the handwheel actuator operate to provide controlled resistance to the driver. This allows the driver to feel the interface between the wheel and the road, which would be lost if the mechanical connection between the handwheel and the wheel was removed.

[0008] It is not desirable for the hand wheel to be able to turn freely, and it is always desirable that there is a small amount of resistance to movement which the driver can readily overcome. Preferably, this resistance to movement is constant or proportional to the hand wheel speed to obtain a good steering feel. It is well known in the prior art to provide resistance to movement by absorbing energy within the motor drive electronics using the principle of braking torque. For example, see the material published by Hendershot & Miller ISBN 978-0-9840687-0-8, page 507, where they talk about the braking torque generated by a line-start permanent magnet motor due to current flowing through an external short circuit. When at least one closed loop passes through the motor phase, the current generated by the motor when it rotates will flow in this loop, thereby generating a braking torque. This requires active control of the motor drive circuit to operate (usually close) the appropriate phase switch and force the motor to close the circuit. Summary of the invention

[0009] Applicants recognize that it is desirable that such resistance should exist even if power is removed from the system. Where resistance is achieved by applying an appropriate current to the motor, the resistance is eliminated in the event of a fault if the motor is unable to provide or generate current internally. Applicants also recognize that it is desirable to minimize electrical connections to the motor and avoid the use of auxiliary windings and connected controls to create resistance to motion in the event of a system fault.

[0010] An object of the present invention is to provide a motor and a handwheel actuator assembly incorporating the motor that can provide a desired level of rotational resistance when the motor is not energized.

[0011] According to a first aspect, the present invention provides a motor comprising a stator and a rotor, wherein the stator has a plurality of phase windings, the rotor has a plurality of magnetic poles and is connected to a shaft; and

[0012] wherein the stator comprises ferromagnetic material defining a yoke and a plurality of teeth, and further comprises at least one strip of electrically conductive material covering at least a portion of a tooth or covering at least a portion of the yoke in the region between adjacent teeth and in direct contact with the teeth, wherein the strip provides an electrical path between the strip and the portion of the teeth or yoke, wherein the strip is wound around upper and lower end regions of the portion of the teeth or yoke and extends axially along opposite side surfaces of the teeth or yoke, and wherein the strip is isolated from a motor drive circuit and has no electrical connection to any portion of the drive circuit or other power source.

[0013] The belt may be in direct contact with the teeth or that portion of the yoke over part or all of its length.

[0014] The belt may be uninsulated at least on the side facing the teeth, so as to provide a direct conductive path between the belt and the teeth.The belt may be completely free of insulation.

[0015] The motor of the present invention generates a desired level of eddy current and hysteresis losses when the rotor is rotated without power being supplied, and thus has a relatively high rotational resistance, which is achieved by the lamination stack having one or more conductive strips wound in the axial direction. The use of conductive strips provides a design that is very suitable for mass production of electric motors, and the conductive strips occupy very little space in the motor, so that in most cases the size of the motor does not need to be increased.

[0016] The belt may be passed only once around the entire tooth or a portion of the yoke so as to pass only once across the upper and lower surfaces of the tooth and both sides or the upper and lower surfaces of the yoke and the inwardly facing side and the outwardly facing side. Alternatively, the belt may comprise an elongated strip which may be passed multiple times around a portion of the tooth or yoke.

[0017] In the alternative case where the stator comprises a stack of laminations, the band may enclose a portion comprising a subset of the laminations.A plurality of bands may be provided, each band enclosing a respective subset of the laminations.

[0018] For example, the stator can be divided into three sections in the axial direction, each of which is wound with a tape. Then, in each section, the tape will surround a portion of the upper surface and the lower surface.

[0019] The side of the belt facing the tooth or yoke can be in direct contact with the surface of the tooth or yoke in all areas or substantially all positions. Alternatively, at least one area of ​​the belt can be separated from the surface of the tooth or yoke.

[0020] The band may comprise a strip of material shaped to provide a flat top portion, opposing flat side portions and a flat bottom portion. The width of the strip forming the band, measured in the circumferential direction of the stator, is at least 5 times the thickness of the band measured in the radial direction of the motor.

[0021] The stator may include a stack of laminations and the strips may include strips of steel or other material coated with a conductive material that prevents corrosion from contact with dissimilar materials.

[0022] The belt may be welded in place relative to the teeth or yoke.

[0023] The strip can be welded to one or more stator laminations at one or more locations to ensure good electrical contact, or it can be close to the teeth or yoke. Since current can now also flow from one conductive lamination to another conductive lamination, this advantageously amplifies the conductive effect of the strip.

[0024] The bands on the stator can be held in place by indentations in the teeth, which if made of steel will not significantly reduce the flux carrying capacity.

[0025] Optionally, the band can be tightened after initial assembly to ensure that the band is in contact with the stator laminations and does not "fall off".

[0026] The laminations may or may not be coated with insulating material.

[0027] The stator can be made using standard lamination stamping processes, with the bands being an additional component to enable tooling to be reused, with the bands only added in applications where damping is required.

[0028] The motor may include a stator including lossy steel laminations that do not meet the loss (W / kg) requirements of the M470-50A standard.

[0029] The steel may comprise a low silicon content steel, the silicon content may be less than 1% by weight.

[0030] An example of a steel used to form the stator plate of the handwheel actuator assembly of the present invention in which the drag torque is mainly due to eddy current losses is a free machining low carbon steel such as EN1A or ASTM 1215.

[0031] An example of a steel used to form the stator of a handwheel actuator assembly of the present invention in which the drag torque is primarily due to hysteresis losses is C75 carbon spring steel, which may be in the form of a 0.5 mm thick plate.

[0032] The coercivity of the steel stator material is at least 20 times, or at least 30 times, that of electrical steel such as M470-50A.

[0033] When tested in accordance with ASTM Standard A927 / A927M-11 (Standard Test Method for Alternating Current Magnetic Properties of Toroidal Iron Core Specimens Using the Voltmeter-Ammeter-Wattmeter Method), the material used to manufacture the stator can have a specific total loss greater than 30 W / kg when excited by a sinusoidal magnetic flux density with an amplitude of 1 Tesla and a frequency of 50 Hz.

[0034] The motor stator can be configured so that the effective loss per unit mass of the motor stator assembly excluding the copper windings is at least 30 watts per kilogram. This figure exceeds any standard electrical steel used in electric motors, especially in existing vehicle electric power steering assemblies.

[0035] The motor may be configured to provide at least 60%, or at least 70%, or 80%, or substantially all resistance to rotation of the output shaft as drag torque over a non-zero speed range for at least one speed within the range. The motor may provide all or substantially all resistance to rotation of the output shaft, meaning at least an order of magnitude greater than any resistance provided by mechanical friction present in the motor.

[0036] Taking into account the gear connection provided between the motor and the output shaft, the motor may be configured to provide a drag torque of at least 2 Nm over an approximate range of non-zero rotational speeds of the output shaft.

[0037] The drag torque of the motor may provide at least 60% or at least 70% or more resistance to shaft rotation when the shaft rotates at 180 degrees per second. It may provide all or substantially all resistance to shaft rotation, meaning at least an order of magnitude greater than any resistance provided by existing mechanical friction.

[0038] According to a second aspect of the present invention, there is provided a mechanical assembly comprising:

[0039] case;

[0040] a shaft rotatably mounted relative to the housing;

[0041] One or more motors, each having a stator with a plurality of phase windings and a rotor with a plurality of magnetic poles connected to a shaft;

[0042] control circuitry adapted to control the flow of current to or from the or each motor so as to apply a net torque to the shaft during normal operation, and

[0043] The stator of at least one of the motors includes ferromagnetic material defining a yoke and a plurality of teeth, and further includes at least one strip of conductive material covering at least one tooth or covering the yoke in the region between adjacent teeth, and wherein the strip is wound around upper and lower end regions of that portion of the tooth or yoke and extends axially along opposite side surfaces of the tooth or yoke.

[0044] The belt may be uninsulated on at least one side facing the tooth to provide an electrical path between the belt and the tooth, wherein the belt wraps around upper and lower end regions of the tooth or yoke and extends axially along opposite side surfaces of the tooth or yoke.

[0045] The belt may be electrically isolated from any motor drive circuitry so that it cannot receive any motor drive current.

[0046] The mechanical assembly may include a gearbox including a first gear fixed relative to the shaft and a second gear fixed relative to the output of the motor, rotation of the first gear causing rotation of the second gear.

[0047] The two gears may be directly meshed or may be connected to each other by a belt. Where the mechanism is part of a hand wheel actuator assembly, the hand wheel actuator may include: a second gear connected to the shaft and configured to rotate with the shaft; and a second motor having an output portion driving a corresponding second output gear, the second output gear being engaged with the first gear and thereby engaged with the shaft.

[0048] The second motor can also generate a large drag torque, so that when the motor has no power, the sum of the drag torques of the two motors produces a large resistance to the rotation of the hand wheel.

[0049] Alternatively, the second motor may be of more conventional construction, using electrical steel as the rotor so that the rotor does not contribute significantly to the overall rotational resistance when unpowered. Thus, the first motor may provide much greater drag torque than the second motor, such as at least twice the drag torque.

[0050] The motor may comprise a brushless permanent magnet type motor comprising a rotor and a stator having a number of windings regularly arranged around circumferentially spaced teeth.

[0051] The shaft can be connected directly to the handwheel by means of a spline connector on the end of the shaft to fit into the internal spline connector of the handwheel. Therefore, the shaft will rotate at the same speed as the handwheel. If a motor is connected directly to the shaft, the motor will also rotate at the same speed. If the motor is connected to the shaft through a gearbox, their rotation speed will be different from the rotation speed of the handwheel.

[0052] Alternatively, the shaft can be connected to the handwheel via a gearbox. In this case, the shaft can rotate at a different speed than the handwheel.

[0053] The motor may form part of a handwheel actuator assembly for a steer-by-wire vehicle, wherein the motor rotor is connected to a shaft which in turn is connected to a handwheel of the vehicle, the handwheel actuator assembly being configured such that when the control circuit is de-energized or disconnected and the handwheel rotates at a speed of 180 degrees per second, the motor combination as a whole provides a drag torque of at least 50% of the resistance to rotation of the shaft and a torque of at least 2 Nm on the handwheel.

[0054] The handwheel actuator assembly may comprise two motors according to the first aspect of the invention, the rotor of each motor being connected to a shaft which in turn is connected to the handwheel.

[0055] By providing one or more motors, at least one of which provides a significant effective level of drag torque, the driver must apply a torque of at least 2 Nm at a handwheel speed of 180 degrees per second to maintain the handwheel at a constant speed of 180 degrees per second because the drag must be overcome before any additional torque can be used to accelerate the handwheel. This level of drag is generally considered acceptable in vehicle handwheel actuator applications. If it is too low, the steering feel is too light and it may be too easy to steer at high speeds, thereby affecting stability; but if it is too high, the steering may be too heavy and the driver may have difficulty turning the steering wheel and maneuvering the vehicle. When in electrical contact with the stator laminations, the conductive metal coating acts to increase the conductivity between adjacent laminations to approach the conductivity of solid magnetic elements (such as a stator stack), thereby generating larger eddy currents than would normally be the case with insulating laminations in the stack.

[0056] The present invention damps otherwise uncontrolled rotation without the need for electronics, additional mechanical parts or complexity, thereby preventing the steering wheel from spinning freely when the power is disconnected, the motor is disconnected or under certain fault conditions that render the control unit inoperable. As is known in the prior art, the circuit is protected from damage due to heat buildup without dissipating energy in the drive circuit, and the heat loss is transferred to the motor for better control of the heat loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] One embodiment of the present invention will now be described, by way of example only, with reference to and as shown in the accompanying drawings, in which:

[0058] Figure 1 The key mechanical components of one embodiment of a hand wheel actuator assembly according to one aspect of the present invention are shown, which includes a pair of motors, each of which may fall within another aspect of the present invention;

[0059] Figure 2 Another embodiment of a hand wheel actuator assembly designed according to one aspect of the present invention is shown;

[0060] Figure 3shows the general arrangement of an electronic control unit which controls the two motors of a dual motor drive assembly according to the first aspect of the invention;

[0061] Figure 4 shows the layout of a steer-by-wire system including a dual motor drive assembly according to the first aspect of the invention;

[0062] Figure 5 (a) and (b) are BH curves of magnetic flux density B and magnetizing force H for soft steel (such as electrical steel) and less soft steel (such as carbon steel);

[0063] Figure 6 It shows Figure 1 and Figure 2 A comparison diagram of the BH curve of the non-electrical steel and the BH curve of the electrical steel selected for use in the motor of the embodiment;

[0064] Figure 7 shows the increase in total flux of a motor when constructed using non-electrical steel and electrical steel; and

[0065] Figure 8 Shows that it can be used Figure 1 A cross-sectional view of the structure of the motor stator and rotor in the mechanism;

[0066] Fig. 9 Shows that it can be used Figure 1 Cross-sectional views of alternative configurations of motor stators and rotors in a mechanism of;

[0067] Fig.10 yes Figure 8 A partial view of the teeth and surrounding yoke of the stator, with the conductive tape first fixed and then wound into place;

[0068] Fig.11 yes Fig. 9 A partial view of the teeth of a stator and surrounding yoke, with the conductive tape first fixed and then wrapped in place around the yoke, and an optional tape wrapped around the teeth. DETAILED DESCRIPTION

[0069] Figure 1 A hand wheel actuator (HWA) assembly for a vehicle according to a first aspect of the invention is shown. The example is a dual motor assembly having two motors, each connected to a common shaft via a respective gearbox. The invention may be implemented as a single motor or by direct connection of the motor rotor to the shaft without a gearbox. The motor has special characteristics, embodying the first aspect of the invention, and examples of motor construction are shown in Figures 8 to 11 By describing the potential use of these motors in handwheel drive assemblies, the advantages of these motors over conventional motors in such applications can be easily understood.

[0070] The assembly 1 comprises a first motor 10 having a rotor 101 and a stator 102, and a second motor 11 having a rotor 111 and a stator 112, the first motor 10 being connected to a first worm gear 6, and the second motor 11 being connected to a second worm gear 7. Each worm gear 6, 7 comprises a threaded shaft which engages with a gear 4 connected to a steering column shaft 3, so that torque can be transmitted from the worm gear 6, 7 to the gear 4 connected to the steering column shaft 3. The gear 4 is operatively connected to a driver's hand wheel (not shown) via the steering column shaft 3. In this example, each of the two motors 10, 11 is a brushless permanent magnet type motor, and each comprises a rotor 101, 111 and a stator 102, 112, with a number of windings regularly surrounding teeth spaced apart in the circumferential direction. The arrangement of the two motors 10, 11, the shaft 3, the worm gears 6, 7 and the gear 4 together form a dual motor electrical assembly.

[0071] Each of the two motors 10, 11 is controlled by an electronic control unit (ECU) 20. The ECU 20 controls the level of current applied to the windings and thereby controls the level of torque produced by each motor 10, 11.

[0072] In this example, the two motors 10, 11 are of similar design, producing similar maximum torque levels. However, within the scope of the present disclosure, an asymmetric design may be employed, wherein one motor 10, 11 produces a higher torque level than the other motor 10, 11.

[0073] One of the functions of the hand wheel actuator (HWA) assembly is to provide feedback force to the driver to provide proper steering feel. This can be achieved by controlling the torque of the motors 10, 11 based on signals from the hand wheel actuator (such as column angle) and signals from other vehicle systems (such as vehicle speed, rack angle, lateral acceleration and yaw rate).

[0074] The use of two motors 10, 11 helps to eliminate squeaks. If a single electric motor is used in the torque feedback unit, the motor can be held in locking contact with the gear with the aid of a spring. However, under certain driving conditions, the spring action is not strong enough, which may cause the gear to "squeak" during sinusoidal motion or abrupt changes in steering column position.

[0075] The use of two motors 10, 11 that can be actively controlled (such as the motors in this embodiment) can improve the problems associated with using a single motor. In this arrangement, both motors 10, 11 are controlled by the ECU 20 to provide torque feedback to the steering column and ensure that the worms 6, 7 of both motors 10, 11 are in constant contact with the gear 4 to minimize abnormal noise. By using two motors 10, 11 in this way, friction can also be actively managed to provide feedback force to the driver.

[0076] like Figure 1 As shown, the motors 10, 11 are received and fixed on two-part extensions extending in the transverse direction of the housing 2. The worm gears 6, 7 of each motor are supported relative to the housing by two sets of bearings. The first set of bearings 41 supports the first end of each worm gear 6, 7 away from its corresponding motor 10, 11, and the second set of bearings 42 supports the second end of each worm gear 6, 7 close to its corresponding motor 10, 11.

[0077] Figure 2 The axis of rotation of the shaft 3 is shown, marked with a dotted line 5, extending vertically through the gear 4. The periphery of the gear 4 is formed as a worm gear, which engages with two identical worms 6, 7, respectively, located on opposite sides of the longitudinal axis 5 of the shaft 3. Each worm 6, 7 is connected to an output shaft 8, 9 of a respective electric motor 10, 11.

[0078] The axes of the output shafts 8, 9 of the two motors 10, 11 are arranged perpendicular to the rotation axis of the shaft 3, and the axes of the two motors may also be inclined relative to each other to reduce the overall size of the assembly.

[0079] The motors 10, 11 are controlled by an electronic control unit (ECU) 20 so that when the level of input torque applied by the handwheel to the shaft 3 is low, the motors 10, 11 act on the gear 4 in opposite directions to eliminate backlash. When the level of input torque applied by the handwheel to the shaft 3 is high, the motors 10, 11 act on the gear 4 in the same direction to help the shaft 3 rotate. Here, the motors 10, 11 acting in a certain "direction" refers to the direction of the torque applied by the motors 10, 11 to the gear 4.

[0080] By using two independent motors 10, 11, they can be controlled to apply torque to the gear 4 in opposite directions in the first operating mode, thereby eliminating the need to use precision components to control backlash. In addition, by using two independent motors 10, 11, they can be controlled to apply torque to the gear 4 in the same direction in the second operating mode, so that the motors 10, 11 and the gear components 4, 6, 7 can be specified to be half the rated value of the required total system torque, thereby reducing the size and cost of the drive assembly 1.

[0081] exist Figure 1 and Figure 2In the embodiment shown, the worms 6, 7 engage with diametrically opposite portions of the gear 4. The threads of the worms 6, 7 have the same helical direction, i.e. both are left-hand threads. The motors 10, 11 are arranged so that they are located on the same side of the gear 4 (both motors 10, 11 are located on one side of an imaginary plane perpendicular to the axes of the worms 6, 7 and passing through the center point of the gear 4). Figure 2 Taking the perspective shown as an example, driving the two motors 10 and 11 clockwise will apply torques in opposite directions to the gear 4 , with the motor 10 applying a clockwise torque to the gear 4 and the motor 11 applying an opposite counterclockwise torque to the gear 4 .

[0082] Figure 2 Another embodiment of the hand wheel actuator assembly 1 according to the first aspect of the present invention is shown. Figure 1 and Figure 2 The illustrated embodiment is substantially similar, the only difference being the positioning of the motors 10, 11. Components and functional units which are identical or equivalent in function and / or structure to the previous embodiment are provided with the same reference numerals and are not described separately. Figure 1 The relevant instructions apply in a similar manner to Figure 3 , with the exception of the positioning of the two motors 10 , 11 .

[0083] exist Figure 2 In the embodiment, worms 6, 7 are engaged with diametrically opposite portions of gear 4, and the threads of worms 6, 7 have the same helical direction, i.e., in this example, they are both right-hand threads. Motors 10, 11 are configured so that they are located on opposite sides of gear 4 (motor 10 is located on one side of an imaginary plane perpendicular to the axes of worms 6, 7 and passing through the center point of gear 4, and motor 11 is located on the other side of the imaginary plane).

[0084] The driver applies torque in the clockwise direction, causing the hand wheel 26 and the steering column shaft 3 to rotate about the dotted line 5. The rotation is detected by a rotation sensor (not shown). Then, the ECU 20 controls the first motor 10 to apply torque in the opposite direction. In the first operating mode, the second motor 11 is actuated by the ECU 20 to apply a counteracting torque 32 in the opposite direction to the torque 30 of the first motor 10 to reduce gear noise. In addition, in the second operating mode, the second motor 11 is actuated by the ECU 20 to apply a torque 34 in the same direction as the torque 30 of the first motor 10 to increase the feedback torque of the steering column shaft 3.

[0085] The net result of the torques generated by the first and second motors 10, 11 is to apply feedback torque to the steering column shaft 3 and the hand wheel 26, thereby providing the driver with a road feel. In this example, the feedback torque is applied in the opposite direction to the torque applied by the driver to the hand wheel 26. In this way, the "squeak" generated between the worm 6, 7 and the gear 4 can be eliminated or significantly reduced.

[0086] Figure 3 A portion of the HWA assembly 80 is shown, showing the general arrangement of an electronic control unit (ECU) 20 that controls each of the two motors 10, 11. The ECU 20 may include a hand wheel actuator (HWA) control system 21 and first and second motor controllers 22, 23 that control the first and second motors 10, 11, respectively. A reference demand signal is input into the HWA control system 21, which distributes torque demands to each of the first and second motors 10, 11. These motor torque demands are converted into motor current demands and transmitted to the first and second motor controllers 22, 23. Each motor 10, 11 provides operational feedback to its corresponding motor controller 22, 23. The HWA control system 21 is configured to calculate the magnitude of mechanical friction using the motor torque demands. In another embodiment, the HWA control system 21 may be implemented as an ECU separate from the first and second motor controllers 22, 23.

[0087] Figure 4 The overall layout of a steer-by-wire system 100 for a vehicle is shown, which includes a handwheel actuator (HWA) assembly 80 according to the first aspect of the present invention. The HWA assembly 80 supports the driver's handwheel 26 and measures the driver's demand, which is usually a steering angle. The steering controller 81 converts the driver's demand into a position demand, which is sent to the front axle actuator (FAA) 82. The FAA 82 controls the steering angle of the vehicle to achieve the position demand. The FAA 82 can feed back the operating status and measurement results to the steering controller 81.

[0088] The steering controller 81 combines the feedback from the FAA 82 with other information measured in the vehicle (e.g., lateral acceleration) to determine the target feedback torque that the vehicle driver should feel. This feedback requirement is then sent to the HWA control system 21 and implemented by the first and second motor controllers 22, 23 controlling the first and second motors 10, 11, respectively.

[0089] Figure 4The steering controller 81 is shown to be physically separate from both the HWA controller 21 and the FAA 82. Alternatively, different configurations may be used within the scope of the present disclosure in which one or more components are physically interconnected. For example, the functionality of the steering controller 81 may be physically implemented in the HWA controller 21, the FAA 82, or other control units in the vehicle, or in some combination of the three. Alternatively, the control functionality assigned to the HWA controller 21 and the FAA 82 may be implemented in part or in whole in the steering controller 81.

[0090] In the event of a fault in the motor windings preventing any current from flowing through the motor, or a motor disconnection from the control electronics, or a fault in the motor drive stage or control system including loss of power to the handwheel assembly, the operator is unable to control handwheel rotation to provide feedback. Figure 1 The motor of the hand wheel actuator assembly in is configured to ensure that there is some damping of the rotation of the wheel in this situation. This is beneficial because it feels more natural to the driver and also helps the driver avoid steering inputs at excessive speed by damping its action.

[0091] In conventional prior art hand wheel actuator assemblies, the stator of the motor is manufactured from high performance electrical steel, as it is generally desirable to reduce the level of drag torque and the resulting energy losses. Further reductions can be obtained using a laminated stator, where the electrical steel sheets are kept separated by alternating layers of insulating material.

[0092] exist Figure 1 Examples and Figure 2 In the embodiment of the invention, the two motors are identical, each configured to provide a substantial level of drag torque when the driver turns the motor by rotating the handwheel in an unpowered state. This ensures that the handwheel does not rotate freely in the event of a fault that causes the motor to lose power, or an internal fault in the motor that causes the current in the windings to be unable to produce any drive torque in the motor. Another benefit is that more energy is dissipated internally in the motor compared to a low drag torque motor, so the electronics need to work less to provide controlled resistance, and heat is dissipated internally in the motor rather than in the electronics.

[0093] It will be appreciated by those skilled in the art that, when implementing the present invention, only one of the motors needs to provide a significant drag torque, while the other motor is a conventional motor with a lower drag torque used in the hand wheel actuator of the prior art.

[0094] The drag torque mentioned here refers to the torque generated due to the energy conversion when the motor's stator rotates. Mechanical energy from the driver causes the rotor to rotate. During the rotation, the rotor and stator interact with each other in the magnetic field, generating a constantly changing magnetic flux in the stator. This will generate eddy currents and hysteresis losses, and when the current passes through the resistive material that forms the stator, the electrical energy is converted into heat energy. Therefore, mechanical energy is converted into heat energy and generates drag torque.

[0095] Figure 8 A first configuration of a motor 200 is shown in plan view and can be used as Figure 1 and Figure 2 One or both of the motors 10, 11. The motor 200 includes a rotor 202 and a stator 201. The stator 201 includes a circular yoke 201a and has a set of teeth 203, each tooth extending radially away from the yoke. Each tooth extends axially from the upper end to the lower end along the stator. The rotor 202 fits in the gap defined by the ends of these teeth 203, and its axis is the same as the axis of the stator yoke. The rotor carries a set of permanent magnets.

[0096] In this example, the stator comprises a stack of laminations in the form of sheet metal, which may be stamped or cut from a large sheet of metal. Fig.10 The top lamination can be seen in the figure, with several edges of the remaining laminations visible. The laminations are packed tightly together. An insulating coating may be provided on the surface of each lamination to help protect the metal plates from corrosion.

[0097] In this example, a belt 204 is arranged around every other tooth 203, but the present invention is not limited to this ratio of belts to teeth. Each tooth 203 can be wrapped with a belt 204, or every three or four teeth are wrapped with a belt 204, and so on, until there are only two belts opposite along the diameter.

[0098] Each metal band 204 comprises an endless loop that surrounds a corresponding tooth of the stator. The band can be formed in a variety of ways. For example, if the teeth are straight and have no protruding "tooth ends", the band can be mechanically stamped. Alternatively, the band can be wrapped around the teeth and welded. An exemplary band comprises a strip of material having a width that is a multiple of the thickness of the strip of material. Fig.10 As shown, each belt 204 fits tightly around the teeth 203 so that there is a good degree of mechanical contact between the teeth 203 and the belt 204. Since the belt 204 is electrically conductive and optionally contacts the teeth over substantially the entire inner surface as shown, it has the beneficial effect of increasing the drag torque of the motor 200 compared to the same motor without the belt. Fig.10 Also shown are several optional weld points 205 which secure the belt in position relative to the teeth 203 .

[0099] Fig. 9 An alternative configuration of a motor 300 having a rotor 302 and a stator 301 is shown. The stator has a yoke 301a and teeth 303, wherein a belt 304 is wound around a portion of the yoke 301a rather than around the teeth 303. In this arrangement, the belt 304 is located in the area of ​​the yoke between adjacent teeth 303. This can be Fig.11 Seen from Fig.11 It can also be noted that an optional belt around the teeth is also shown in the figure.

[0100] There are several reasons for the generation of drag torque, two of the main causes are hysteresis and the formation of eddy currents in the stator section of the motor. Figure 5 Can be used to form Figure 1 or Figure 2 This is shown for a typical soft material (such as electrical steel) and a typical not-so-soft material (such as carbon steel) in the stator of a motor. In each figure, the enclosed area represents the losses caused by the magnetic domain reversal. The more times the steel is magnetized north and south, the greater the losses, and therefore the greater the drag torque. Steel with low hysteresis losses behaves like Figure 5 (a) shows a narrow hysteresis loop; steel with large hysteresis loss behaves as Figure 5 As shown in (b), which has a wider hysteresis loop, a motor made using the latter will have a larger drag torque due to larger hysteresis losses.

[0101] Figure 6 Shown for Figure 1 and Figure 2 And other Fig. 9 and Fig.10 Different BH curves for a high hysteresis steel and an electrical steel conforming to the M470-50 specification for an example motor are shown. The reference steel is a steel that falls within the defined electrical steel specification range. The other is a steel that is more lossy and less soft, such as spring steel. The hysteresis of the less soft steel is much greater. The coercivity of the carbon steel measured in the figure is about 30 times that of the electrical steel, so the drag torque is much greater than that of the electrical steel.

[0102] like Figure 7 As shown, in practical motors, the same spring steel achieves at least as high a flux density as electrical steel at the flux density of interest, and thus provides similar motor performance.

Claims

1. A motor comprising a stator and a rotor, wherein the stator has a plurality of phase windings, and the rotor has a plurality of magnetic poles and is connected to a shaft; and wherein the stator comprises a ferromagnetic material defining a yoke and a plurality of teeth, and further comprises at least one strip of electrically conductive material covering at least a portion of a tooth or covering at least a portion of the yoke in a region between adjacent teeth and in direct contact with the teeth, wherein the strip provides an electrical path between the strip and the portion of the teeth or yoke, wherein the strip is wound around upper and lower end regions of the portion of the teeth or yoke and extends axially along opposite side surfaces of the teeth or yoke, and wherein the strip is isolated from any external source of motor drive current.

2. A motor according to claim 1, wherein each belt passes only once around the portion of the tooth or the portion of the yoke so as to pass through the upper and lower surfaces of the portion of the tooth and both sides of the portion of the tooth, or each belt passes only once around the upper and lower surfaces of the portion of the yoke and the side facing inward and the side facing outward.

3. The motor according to claim 1 or 2, wherein the inner surface of the belt facing the teeth or yoke is non-insulated and is in direct contact with the surface of the teeth or yoke.

4. A motor according to any one of the preceding claims, wherein the band comprises a strip of material shaped to provide a flat top portion, opposing flat side portions and a flat bottom portion.

5. A motor as claimed in any preceding claim in which the stator comprises a stack of steel laminations and the strip comprises a strip of steel or other material coated with a conductive material which prevents corrosion due to contact with dissimilar materials.

6. A motor as claimed in any preceding claim, wherein the belt is welded in place relative to the teeth or yoke.

7. A mechanical assembly comprising: case; a shaft rotatably mounted relative to the housing; One or more motors, each having a stator with a plurality of phase windings and a rotor with a plurality of magnetic poles connected to a shaft; control circuitry adapted to control the flow of current to or from the or each motor so as to apply a net torque to the shaft during normal operation, and The stator of at least one of the motors includes ferromagnetic material defining a yoke and a plurality of teeth, and further includes at least one strip of electrically conductive material covering at least a portion of a tooth or covering at least a portion of the yoke in the region between adjacent teeth and in direct contact with the tooth, wherein the strip provides an electrical path between the strip and the portion of the tooth or yoke, wherein the strip is wrapped around upper and lower end regions of the portion of the tooth or yoke and extends axially along opposite side surfaces of the tooth or yoke, and wherein the strip is isolated from the control circuitry so that it cannot receive current from, or cause current to flow to, any external current source.

8. Mechanical assembly according to claim 7, wherein at least one motor comprises the features of any one of claims 2 to 6.

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