Electric motor and hand wheel actuator assembly including motor

Abstract

The present application relates to an electric motor comprising a stator with a plurality of phase windings and a rotor with a plurality of magnetic poles and connected to a shaft; and wherein the stator comprises an outer annular yoke, a plurality of discrete teeth separate from the annular yoke, each tooth comprising a rod and a tooth tip located at an end of the rod closest to the rotor, and an inner annular sleeve located in an air gap between an inwardly facing end of the stator tooth and the rotor, and wherein the inner sleeve comprises a positioning feature located in the outer annular yoke and the inner annular sleeve. The positioning feature positions and supports the tooth in a form-fitting manner via the tooth tip.

Description

Technical Field

[0001] The present invention relates to electric motors and, in particular but not exclusively, to electric motors suitable for use in hand wheel actuator assemblies of steer-by-wire systems for vehicles. 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. Summary of the invention

[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 actuation system, which includes one or more electric motors coupled to the steering wheel. The secondary motor or motors respond 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. The laminations typically comprise electrical steel sheets. This is both a cost-effective method of manufacturing the motor and prevents current from flowing axially through the stator steel 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 steel. Due to the elimination or severe limitation of current flowing axially, this prior art motor construction exhibits lower drag torque. Other components may be fixed to the stator steel, such as phase windings, end caps and guide wires.

[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 stator winding phases open circuited will have almost zero drag torque and will only need a small amount of external torque to spin, while 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 ability to turn the steering wheel shaft in most use cases. 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 conditions at the interface between the wheel and the road surface, 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 braking torque principle. For example, see Hendershot & Miller ISBN 978-0-9840687-0-8, page 507, which discusses the braking torque generated in a line-start permanent magnet motor due to current flowing through an external short circuit. Braking torque is generated when at least one closed circuit passes through the motor phase and the current generated by the motor rotating will flow through the closed circuit. 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.

[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 same that can provide a desired level of rotational resistance when the motor is not energized.

[0011] In most applications, due to packaging constraints, the motor in the handwheel actuator assembly is advantageously as small as possible, especially the overall length and diameter of the motor. The reduced size does present challenges to assembly, especially applying the wire coils on the stator teeth. In many systems, it is not desirable for the motor to resist rotation when unpowered, but it is generally desirable for the motor to be as compact as possible. It is another object of the present invention, in at least one aspect, to provide a motor that is simpler to assemble, especially when the motor must be small to fit into a limited space, as is often the case in applications such as automotive systems.

[0012] According to a first aspect, the present invention provides an electric 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

[0013] The stator comprises an outer annular yoke, a plurality of discrete teeth separated from the annular yoke, each tooth comprising a rod and a tooth tip, the tooth tip being located at an end of the rod closest to the rotor,

[0014] and an inner annular sleeve located in an air gap between what would otherwise be inwardly facing ends of the stator teeth and the rotor, and wherein the inner sleeve includes locating features that positively locate and support the teeth by the tooth ends.

[0015] The inner sleeve may comprise a conductive material, where conductive material refers to a material having a low electrical resistance, such as a metal, a metal alloy, or a metal matrix composite material. When the inner annular yoke comprises a conductive material, this will provide a magnetic flux path extending axially along the motor bore, so that the rotation of the rotor generates eddy currents in the sleeve that resist the rotation of the rotor. The sleeve may also optionally be magnetically permeable so that it generates hysteresis losses, which can supplement the eddy current losses. Eddy currents generate a drag torque that is proportional to speed, while hysteresis will generate a constant drag torque. Thus, the complementary hysteresis losses will help increase the drag at low speeds.

[0016] In the alternative, if the objective is to minimize rather than increase the spin losses of the motor, the inner sleeve may comprise insulating material.

[0017] The material or a portion of the material may also be magnetically permeable where this provides advantages for the desired application of the motor. Careful selection of shape, permeability, and saturation flux density helps achieve an optimal flux density to reduce the torque ripple or cogging torque of the motor without significantly affecting the torque capability. In addition, if the material is magnetically permeable, the air gap permeability variation between the main tooth ends and the material located in the slot opening between the main tooth ends can be reduced, which can reduce rotor losses in high-speed motors. The permeability of the material and the saturation flux density can be selected to achieve the best application results. The relative permeability of some soft magnetic composites can be as low as 18, while the relative permeability of electrical steel can be as high as 4000. The saturation flux density can vary from 0.9T to over 1.5T.

[0018] In the motor of the present invention, the sleeve is conductive and the motor generates a desired level of eddy current and hysteresis losses when the rotor rotates without power being supplied to the motor, so the conductive material sleeve in the air gap between the stator and the rotor provides a relatively high resistance to rotation.

[0019] The present invention provides for the installation of a conductive part in the motor which fits inside the stator bore within the magnetic air gap of the machine for supporting the individual teeth. This provides an assembly benefit in that the teeth can be more easily accessed from the outside of the motor, for example to install the windings, and then the outer yoke can be assembled. This is an advantage that can be realized in applications requiring high motor braking torque, in addition to the optional provision of a conductive sleeve.

[0020] The inner annular sleeve may comprise a solid wall tubular sleeve which fits in the air gap between the rotor and the stator.

[0021] The rotor may be mounted concentrically within the stator, both sharing a common axis.

[0022] The outer yoke may include a set of locating features on an inner surface that engage with the ends of the teeth furthest from the rotor.

[0023] The outer surface of the inner sleeve may include a plurality of ribs, each rib extending radially outward into the space between the ends of adjacent stator teeth to locate each tooth. The sidewall of each rib may include an undercut that receives a portion of the tooth head so that the tooth cannot move away from the inner sleeve in a radial, tangential or circumferential direction. Installation may be performed by sliding the tooth axially into the space between adjacent ribs, either linearly or using a torsional motion, depending on the shape of the tooth and the locating feature structure.

[0024] In an alternative embodiment, the inner sleeve may include a set of grooves on the outer circumferential surface, each groove locating a tooth end. Similarly, the side walls of the grooves may be formed with undercuts to constrain the teeth in a form-fitting manner. The side walls of each groove may include an undercut that receives a portion of the tooth head so that the tooth cannot move away from the inner sleeve in a radial, tangential or circumferential direction. Installation may be performed by sliding the tooth axially into the groove, either linearly or using a torsional motion, depending on the shape of the tooth and the locating feature structure.

[0025] The inner sleeve may comprise an overmolded structure, with at least a portion of the distal end of each tooth embedded in the overmolded inner sleeve, the void occupied by the tooth defining a locating feature for the tooth.

[0026] To form a motor with an overmolded inner sleeve, the tooth segments can be positioned in their intended positions in a mold suitable for injection molding with the aid of a tool. This is particularly useful if the sleeve component is made of plastic or any injection moldable material. Ultimately, the sleeve is combined with all stator teeth to form a solid component, which are firmly embedded in the sleeve material without the need for further assembly.

[0027] The motor may include a set of coil windings that are wrapped around the teeth and connected together to form individual phases. For example, there may be three phases, with the coils of each phase being wound around two or more teeth. The windings may be arranged in a variety of different ways, depending on the performance characteristics of the motor, the number of slots and poles required, and the motor drive and control strategies that may be used with the motor.

[0028] Since the teeth are separate from the outer yoke prior to assembly, the coils can be individually wound around the teeth before the teeth are inserted into the recesses of the sleeve, and the entire star assembly can then be inserted into the circular yoke that serves as the machine back iron. The coils can also be individually wound around a suitable fixture or tool, which is then placed into position around the desired tooth or teeth.

[0029] Each tooth may comprise a generally rectangular block having an enlarged tip extending along one edge engaging the inner sleeve.The block may comprise a stack of conductive plate laminations.

[0030] In a concentrated winding machine, preferably each tooth is provided with a loop of conductive wire which is wound on the rod of the tooth between the tooth head and the end in contact with the outer annular yoke. In a distributed winding machine, the loop can be wound on different teeth and their different sides after the teeth have been inserted or embedded in the sleeve grooves. The coils can also be slot-shaped. The slots can contain one or more coil sides, usually called "winding layers".

[0031] The inner diameter / bore of the stator sleeve does not have to be perfectly circular, but can have protrusions, recesses, flat portions, radii, chamfers or any other unique geometry that can help keep the magnetic flux density as sinusoidal as possible, thereby reducing the ripple component of the damping torque or the torque ripple during normal operation of the machine.

[0032] The height of the sleeve measured in the axial direction of the motor may be substantially the same as the height of the stator. Thus, it may extend from one end of the stator to the other. It may be shorter or longer relative to the stator.

[0033] The sleeve may include a plurality of cutouts extending from the inner circumferential wall to the outer circumferential wall of the sleeve, defining strips of material providing an axial conductive path between the cutouts. The cutouts may allow air to flow from one side of the sleeve to the other, which may aid in cooling the motor.

[0034] The stator sleeve may be located within an air gap whose length, measured radially from the center of rotation, is adapted to achieve the desired electromagnetic characteristics of the electric motor. In high-speed machines such as fuel cell compressors, it may be smaller to increase the torque produced per unit volume, or larger to reduce eddy current losses in the rotor.

[0035] The sleeve has a length (also measured radially) that will best achieve desired performance aspects, such as mechanical strength, maximization of electrical losses (if the goal is to increase torque resistance to motion) or minimization of aerodynamic losses and rotor electromagnetic losses (if the goal is to reduce torque resistance to motion).

[0036] The sleeve may comprise a metal or metal alloy and may be homogeneous, for example, it may be cast, or it may be pressed or rolled from a homogeneous blank material.

[0037] The sleeve can be made of plastic and injection-molded onto the rectangular teeth, or it can be made separately and the teeth can be inserted into their grooves in a next step.

[0038] The sleeve may comprise a copper sleeve or an aluminum sleeve, or any other material that provides the desired properties for the application or that facilitates manufacturing or reduces cost.

[0039] When the goal is to maximize braking torque, the highest possible conductivity is beneficial, making copper the most useful choice per unit mass and per unit cost, but aluminum alloys can also be used to reduce cost or prevent galvanic corrosion.

[0040] When the goal is to minimize losses and braking torque, such as in the case of high-speed compressors, the material can be any plastic that provides the necessary mechanical strength, is easy to manufacture, and is cost-effective. Such a material may have low magnetic losses and moderate to low magnetic permeability, which may help improve some aspects of the magnetic performance.

[0041] The lower the resistance of the stator sleeve, the greater the losses, and therefore the greater the drag torque felt when the shaft rotates. In embodiments targeting high braking torque, the sleeve may have a resistivity generally less than 5e-8Ωm. When the sleeve is made of an aluminum alloy, its resistivity may be approximately 3.8e-8Ωm; when made of copper, its resistivity is 1.724e-8Ωm. The resistivity of any alloy material that provides the necessary electrochemical or mechanical properties to prevent corrosion and improve manufacturability may deviate from these values. Thus, the radial length or thickness of the sleeve may be increased or decreased accordingly to achieve the desired amount of braking torque.

[0042] The motor stator may be configured such that at a rotational speed of 1000 rpm, the effective losses per unit mass of the motor stator assembly excluding the copper windings are at least 50 watts per kilogram of EM-active motor material.

[0043] The sleeve can be the primary source of motor drag, but may also be combined with other features to provide a controllable amount of drag.

[0044] The motor may be configured to provide at least 60% or at least 70% or 80% or substantially all resistance to rotation of the rotor 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. Rotational resistance is typically amplified by the gear set.

[0045] 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.

[0046] 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.

[0047] In other arrangements where low drag torque is desired, the inner sleeve may be an electrically insulating material such as epoxy etc. This allows the advantage of ease of assembly to be achieved on motors which may have low drag.

[0048] According to a second aspect, the present invention provides a method for assembling a motor having the features of the first aspect, comprising:

[0049] Provides an inner sleeve and a separate set of stator teeth,

[0050] forming the subassembly by securing individual teeth to the inner sleeve using the locating features of the inner sleeve to form a star-shaped subassembly and winding wire around the teeth to form a coil; and

[0051] The subassembly is inserted axially into the outer annular yoke.

[0052] This aspect of the method has the potential to achieve a higher slot fill factor and better tooth position control, which in turn can reduce the pole-step toothing and thus achieve better steering feel, compared to the prior art arrangement in which the teeth are fixed only at the outer ends by an integral outer yoke, resulting in less asymmetry.

[0053] Additionally, allowing for a higher fill factor means that there is more space in the slot for a highly conductive ring to compensate for the sleeve eddy current losses.

[0054] The subassembly may be press fit into the outer annular yoke.

[0055] Each tooth may be press fit into the inner sleeve.

[0056] The method may include applying an adhesive to one or more surfaces during assembly such that when assembly is complete, the cured adhesive secures the teeth to the outer yoke and, optionally, to the inner sleeve.

[0057] The step of securing the teeth to the inner sleeve may include engaging the distal ends of the teeth with grooves in the inner sleeve or with grooves between adjacent ribs on the outer surface of the inner sleeve.

[0058] According to a second aspect, the present invention provides a method for assembling a motor having the features of the first aspect, comprising:

[0059] A set of individual stator teeth is placed into a mold or other holding device.

[0060] forming the subassembly by overmolding an inner sleeve encapsulating at least a portion of a distal end of each tooth to form a star-shaped subassembly and winding wires around the teeth to form a coil; and

[0061] The subassembly is inserted axially into the outer annular yoke.

[0062] According to a fourth aspect of the present invention, there is provided a hand wheel actuator assembly for a steer-by-wire vehicle, comprising:

[0063] shell;

[0064] a shaft rotatably mounted relative to the housing;

[0065] 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;

[0066] 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

[0067] At least one of the motors comprises a motor according to the first aspect of the invention and the inner sleeve comprises an electrically conductive material and optionally a magnetically conductive material.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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 3 Nm on the handwheel.

[0076] 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.

[0077] 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 3 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.

[0078] 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

[0079] 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:

[0080] 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;

[0081] Figure 2 Another embodiment of a hand wheel actuator assembly designed according to one aspect of the present invention is shown;

[0082] 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;

[0083] 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;

[0084] Figure 5 shows a first step of assembling one embodiment of a motor to form a subassembly according to one aspect of the present invention;

[0085] Figure 6 Shows Figure 5 The remaining assembly steps of the motor;

[0086] Figure 7 An alternative motor with an overmolded inner sleeve is shown, which represents one embodiment of a motor according to the present invention; and

[0087] Figure 8 shows that the rotor is rotating while the motor is isolated from the power supply Figure 5 Eddy current density of a simple sleeve. DETAILED DESCRIPTION

[0088] 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 by a respective gearbox. The invention may be implemented as a single motor or by direct connection of the motor rotor to the shaft without the need for a gearbox. The motor has special characteristics which embody 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 a hand wheel drive assembly, the advantages of these motors over conventional motors in such applications may be readily appreciated.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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).

[0093] 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.

[0094] 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.

[0095] 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.

[0096] Figure 2The 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] exist Figure 1 and Figure 2 In 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 .

[0101] 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 2The 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 .

[0102] 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).

[0103] 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.

[0104] 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.

[0105] Figure 3A 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.

[0106] 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.

[0107] 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.

[0108] Figure 4 The 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] Figure Figure 5 and Figure 6 A first configuration of a motor 200 is shown, which may be used as Figure 1 and Figure 2 One or both of the motors 1, 11. These figures also show a sequence of assembly steps that can be used to assemble the motor.

[0115] The motor 200 comprises a rotor 202 and a stator 201. The stator 201 comprises three types of mechanical parts: an outer annular yoke 203, a set of nine teeth 204 and an inner sleeve 205. In addition, a coil of conductive wire is provided which surrounds the teeth to form an electrical circuit.

[0116] The outer yoke body 203 comprises a tube having generally circular inner and outer diameters, the tube forming a support for providing support for the motor teeth at their outermost ends.

[0117] Each tooth 204 is identical and comprises rectangular electrical steel laminations stacked together. Each tooth has a stem and a portion at one end that widens to form an arcuate tip. These tips and the rotor 202 together form a cylindrical air gap 206.

[0118] The inner sleeve 205 is also a continuous tube and has a smooth inner wall which faces the motor rotor across the air gap. Figure 5 As best shown in FIG. 1 , the outer wall of the sleeve 205 is provided with a series of grooves 209 extending axially along the sleeve. In this example, the grooves 209 are defined between a pair of axial ribs 208 extending from the outer surface of the sleeve. They can also be considered as grooves formed in the outer surface, whichever interpretation is correct. The sidewalls of each groove 209 are undercut, and the cross-section of the groove 209 matches the cross-section of the enlarged end of the tooth 204. When installed, as Figure 5 As shown on the right, each slot 209 receives and positions a tooth 204 which is retained by the tip.

[0119] The motor can be assembled as follows:

[0120] In a first step, a coil winding is applied to each tooth 204. The teeth 204 are then secured to the inner sleeve 205 by sliding the tooth tips into the undercut slots.

[0121] Wire windings are wound around the teeth between the outer yoke body 203 and the end of the teeth, and these windings are connected together to form a set of motor phases, for example, three independent phases. The motor drive circuit can then provide current to each phase, and the modulation of the current controls the movement of the motor. Once completed, a motor like Figure 5 The star rotor subassembly is shown.

[0122] In the next step, you can Figure 5 The entire star subassembly shown on the right is slid into place within the outer yoke 203, as shown in FIG. Figure 6 The end of the tooth 204 closest to the outer yoke 203 engages with the small positioning groove 210 on the inner surface of the outer yoke. The rotor is then placed in the stator. Figure 6 shown.

[0123] When assembled, each tooth 204 extends axially along the stator from the upper end to the lower end. The rotor 202 fits in the gap defined by the ends of these teeth 203, with its axis being the same as the axis of the stator yoke. The rotor carries a set of permanent magnets 206.

[0124] The stator teeth 204 and the rotor 202 define an air gap. In this example, the air gap is about 1.2 mm. An inner yoke sleeve 207 made of a conductive material is located in the air gap, and its length is about 0.4 mm. Its outer surface abuts against the end of the tooth, thus occupying one third of the air gap, leaving a true air gap of 0.8 mm.

[0125] In this example, the inner sleeve 205 is a copper tube with a completely cylindrical inner and outer bore. In a modified form, the sleeve may be provided with various grooves or ribs on the inner or outer bore or both, which extend axially along the sleeve. Where external ribs are provided, these external ribs may extend into the circumferential space between adjacent teeth 204.

[0126] Figure 8 It shows how eddy currents form in the sleeve due to its low electrical resistance and relatively large thickness compared to the air gap length. These eddy currents provide resistance to the rotation of the rotor, helping to dampen the motion of the motor when power is removed. The reason for this effect is that the sleeve will be stationary when the rotor is rotating, so even when the machine is not powered, the sleeve will be subject to flux reversals as the north and south magnetic poles pass radially "underneath" it. Due to this flux reversal, if the tube is made of a conductive material, eddy currents will be generated, resulting in heat losses. This will appear as a damping torque on the force that rotates the rotor shaft. By carefully choosing the (usually high) conductivity, thickness, and other geometric features, a machine can be designed to match a specific level of damping torque.

[0127] Figure 7 A second exemplary motor 300 within the scope of the present invention is shown. Figure 5 and Figure 6 The motor in the embodiment is similar except that the inner sleeve 305 is in the form of an overmolded form into which the ends of the individual teeth 304 are embedded to be fixed in place. Where similar parts are provided, the same reference numerals are used as in the first embodiment but increased by 100, and the description of each component in the first embodiment is also applicable to the second embodiment and is not repeated here.

[0128] For construction Figure 7 The motor 300 in FIG. 1 is provided with a set of teeth. The windings may be applied to the teeth while they are separated, as shown, or may be applied to the teeth at a later stage in the process. The teeth are then arranged in a mold (not shown) in the desired relative orientation. This Figure 7. Epoxy or other moldable material is then poured into the mold or otherwise poured onto the teeth. This forms the shape of the inner sleeve 305, which is allowed to cool if it is a thermosetting material or to cure if it is a chemically curing material. Once cured, the inner sleeve will securely position the teeth in a close fitting pocket defining a locating feature structure. The star-shaped stator 301 formed in this manner will be inserted into the outer annular stator yoke in the same manner as the first embodiment.

[0129] While this motor is particularly useful for hand wheel actuator applications due to the ease of assembly and high detent torque, the motor can be constructed with an inner sleeve of insulating material such as epoxy etc. This allows it to be used in applications where low detent torque is desired while also allowing it to be used in applications where the advantages of easy access to the teeth and easy winding formation are desired.

[0130] An example of a system where such a low drag motor is desired includes a fuel cell compressor, the inner sleeve of which can be made of an electrically insulating material to eliminate speed-related losses. With an insulating inner sleeve portion, the star-shaped stator assembly produces almost no additional losses compared to a conventional stator, while also allowing easier access from the outside to form the windings into an optimal layout. In addition to the typical ohmic losses (i.e., "DC winding losses"), there are also a large number of additional frequency (speed) related losses in the windings of high-speed machines, called "AC winding losses." The AC winding losses can be reduced by having several parallel conductors per motor turn ("hand in hand") and placing the parallel conductors belonging to the same turn as "horizontally" as possible or tangentially to the stator diameter in the slot.

[0131] The extra reach could potentially provide enough flexibility to form the coil in this optimal way, or even use a pre-wound coil and then place that pre-wound coil into the necessary slots rather than forming the winding in situ.

Claims

1. An electric 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 The stator comprises an outer annular yoke, a plurality of discrete teeth separated from the annular yoke, each tooth comprising a rod and a tooth tip, the tooth tip being located at an end of the rod closest to the rotor, and an inner annular sleeve located in an air gap between what would otherwise be inwardly facing ends of the stator teeth and the rotor, and wherein the inner sleeve includes locating features that positively locate and support the teeth by the tooth ends. 2 . The motor of claim 1 , wherein the inner sleeve comprises a conductive material.

3. The motor of claim 2, wherein the inner sleeve comprises a metal or a metal alloy or a metal matrix composite material. The motor of claim 1 , wherein the inner sleeve comprises an insulating material.

5. A motor according to any preceding claim, wherein the material is magnetically permeable.

6. A motor according to any one of the preceding claims, wherein the outer yoke comprises a set of locating features on an inner surface which engage with the ends of the teeth furthest from the rotor.

7. A motor according to any preceding claim, wherein the outer surface of the inner sleeve comprises a plurality of ribs, each rib extending radially outwardly into the space between the tips of adjacent stator teeth to locate a respective tooth.

8. The motor of claim 6, wherein the side wall of each rib includes an undercut that receives a portion of the tooth head such that the tooth cannot move away from the inner sleeve in a radial, tangential, or circumferential direction.

9. The motor according to any one of claims 1 to 6, wherein the inner sleeve comprises a set of grooves on the outer circumferential surface, each groove locating the tip of a tooth, and the side walls of the grooves are formed with undercuts to constrain the teeth in a form-fitting manner.

10. A motor according to any one of claims 1 to 6, wherein the inner sleeve comprises an overmolded structure, at least a portion of the tip of each tooth being embedded in the overmolded inner sleeve, the space occupied by the tooth defining a locating feature structure for the tooth.

11. A motor according to any preceding claim, wherein each tooth comprises a generally rectangular block having an enlarged tip extending along one edge which engages the inner sleeve.

12. A motor according to any one of the preceding claims, wherein the sleeve comprises a plurality of cut-outs extending from an inner circumferential wall to an outer circumferential wall of the sleeve, with strips of material defining therebetween providing an axial conductive path.

13. A method of assembling a motor having the features of any one of claims 1 to 12, comprising: providing an inner sleeve of conductive material and a set of individual stator teeth, forming the subassembly by securing individual teeth to the inner sleeve using locating features to form a star-shaped subassembly and wrapping wire around the teeth to form a coil; and The subassembly is inserted axially into the outer annular yoke.

14. The method of claim 13, wherein the subassembly is press fit into the outer annular yoke.

15. A method according to claim 13 or 14, comprising applying an adhesive to one or more surfaces during assembly so that when assembly is complete the cured adhesive secures the teeth to the outer yoke and optionally to the inner sleeve.

16. A method of assembling a motor having the features of any one of claims 1 to 12, comprising: A set of individual stator teeth is placed into a mold or other holding device. forming the subassembly by: overmolding an inner sleeve encapsulating at least a portion of a distal end of each tooth to form a star-shaped subassembly, and winding wire around the teeth to form a coil; as well as The subassembly is inserted axially into the outer annular yoke.

17. A hand wheel actuator assembly for a steer-by-wire vehicle, comprising: shell; 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 Wherein at least one of the motors comprises a motor according to the first aspect of the invention, and wherein the inner sleeve comprises an electrically conductive material.

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