A motor and a steer-by-wire steering wheel actuator

Abstract

The present invention relates to an electromagnetic motor, comprising: an inner stator including a plurality of stator teeth, each stator tooth being surrounded by one or more turns of wire; a controller that generates a set of currents that are applied to phase windings of the inner stator to produce a pattern of magnetic poles spaced around the inner stator, the spacing between the magnetic poles being greater than the spacing between adjacent stator teeth of the inner stator; an outer stator that is concentric with the inner stator and includes a set of alternating magnetic poles, the spacing between adjacent magnetic poles being less than the spacing of the magnetic poles of the first array generated by the controller; and an intermediate rotor member located between the two stators and including an array of pole pieces, wherein the pole pieces of the rotor shape the magnetic flux acting between the two stators and, thereby, in use, the controller is arranged to control the torque applied to the rotor by moving the pattern of magnetic poles of the inner stator around the axis of the torque generator. The present invention also relates to a steering wheel actuator assembly for a steer-by-wire steering system for a vehicle.

Description

Technical Field

[0001] In one aspect, the present invention relates to an electric motor particularly, but not exclusively, suitable for use as a feedback torque generator.In another aspect, the present invention relates to a steer-by-wire steering wheel actuator including a feedback torque generator for a motor vehicle. Background Art

[0002] Feedback torque generators are known to be used in a range of applications. One such application is in steer-by-wire steering systems. In conventional systems, e.g. Figure 1 In the system shown, a steering wheel 1 is connected to one or more steerable wheels (not shown) of the vehicle via a mechanical linkage. In this example, the linkage comprises a steering column shaft 2, one end of which is connected to a boss 3 of the steering wheel and the other end to a rack and pinion gearbox 4 that drives a steering rack 5. This mechanical linkage provides the driver with some important feedback about what is happening at the interface between the tires and the road, helping them control the vehicle.

[0003] In a steer-by-wire steering system, such as Figure 2 As shown, there is no direct mechanical connection between the wheels (not shown) and the steering wheel 11. Therefore, some form of artificial steering feel must be applied to the steering wheel to give the driver some indication of what is happening at the tire / road interface and to simulate the forces generated when the vehicle goes over a bump or hole in the road.

[0004] Thus, in steer-by-wire systems, it is known to provide a feedback torque generator 12 that applies torque to the steering wheel. The movement of the wheels is achieved by actuators such as motors 13, which drive a steering rack 14 via a rack and pinion gearbox 15. The magnitude and direction of the torque applied to the steering wheel are controlled by an electronic control unit (ECU 16), which receives signals from a series of sensors (not shown) mounted on the vehicle that measure parameters such as vehicle speed, the relative rotational speeds of the various wheels of the vehicle, the vehicle's roll angle, and the position of the steering wheel. The ECU 16 also controls the function of the motors that cause the wheels to steer.

[0005] Feedback torque can be applied to the steering wheel in various ways, such as through an electric motor or through an arrangement of springs, dampers, and brakes. This can be used to allow the driver to feel the wheel hit a rock or hole, or to reduce the feel in the steering wheel when the tire is driving on a low-friction surface (for example, a wet or icy road).

[0006] The term steering wheel in this specification should be interpreted broadly to include both: a conventional steering wheel having a generally circular continuous or discontinuous rim supported by a hub that a driver can grasp; and a device having a pair of opposed handgrips supported by a hub that can rotate about a circular path, similar to a yoke commonly used in an aircraft. For example, the handgrips and the hub can form a W, M, or U-shaped configuration. In each case, by connecting the hub to a generator of feedback torque, the feedback torque is typically applied through the hub to the portion grasped by the driver.

[0007] In a steer-by-wire application, the feedback torque generator must provide a relatively high level of torque at low speeds, and to achieve this cost-effectively using an electric motor, it has been proposed to connect the steering wheel to the electric motor through a reduction gearbox, where the rotational speed of the motor is greater than the rotational speed of the steering wheel by an amount set by the gear ratio of the gearbox. The use of the gearbox allows a relatively low-cost motor to provide the required torque at low speeds. However, due to the need to provide a separate motor and gearbox, this arrangement is complex and inherently bulky. Summary of the Invention

[0008] An object of a first aspect of the present invention is to provide a motor suitable for certain applications as a feedback torque generator, which motor improves the limitations in the prior art generators of connecting an electric motor to a gearbox.

[0009] According to the first aspect, the present invention provides an electromagnetic motor, comprising:

[0010] An inner stator including a plurality of stator teeth, each stator tooth surrounded by one or more turns of wire,

[0011] A controller that generates a set of currents that are applied to phase windings of the inner stator to produce a spaced-apart pattern of magnetic poles around the inner stator, the spacing between the poles being greater than the spacing between adjacent teeth of the inner stator,

[0012] An outer stator that is concentric with the inner stator and includes an alternating set of magnetic poles, the spacing between adjacent magnetic poles being less than the spacing of the poles of the first array generated by the controller, and

[0013] An intermediate rotor member located between the inner stator and the outer stator and including an array of pole pieces, wherein the pole pieces of the rotor form a magnetic flux that acts between the inner stator and the outer stator, and

[0014] Thus, in use, the controller is arranged to control the torque applied to the rotor by moving the pattern of magnetic poles of the inner stator around the axis of the torque generator.

[0015] In the present invention, the controller generates a moving flux pattern at the inner stator, which interacts with a stationary flux pattern from the outer stator (the stationary flux pattern from the outer stator is shaped by the pole pieces of the rotor), so that torque is applied to the rotor. The rotor will rotate in the direction following the rotation of the stationary pole pattern of the inner stator, but at a reduced speed, such that there is some inherent gearing in the actuator to allow the actuator to provide a relatively high torque at low rotor speeds and provide a relatively high force density.

[0016] The inner stator can be supplied with current that generates a movable pattern including two magnetic poles, and the outer stator can have more than two magnetic poles, and the pole pieces can shape the magnetic flux of the magnetic poles from the second magnetic pole to generate two magnetic poles in the region where the magnetic flux from the first stationary portion meets the magnetic flux from the second stationary portion.

[0017] The movable pattern can be a constant pattern that simply moves around the axis of the inner stator. For example, in the case of two magnetic poles, the two magnetic poles can always be evenly spaced apart, but the positions of the two magnetic poles will move under the control of the controller.

[0018] In a possible arrangement, the outer stator can be composed of 44 magnetic poles generated by 22 pairs of magnets, and the rotor can be composed of 26 pole pieces, and the controller can generate four pairs of magnetic pole pairs on the inner stator, each pair of magnetic pole pairs including a north pole and a south pole. Other numbers of magnetic poles and pole pieces can be provided within the scope of the present invention.

[0019] Other numbers of magnetic poles and pole pieces can be used with the aim of coupling the strong, preferably first, harmonic of the magnetic flux from the second stationary portion by the pole pieces to the matching pole pattern generated by the windings and teeth of the first stationary portion.

[0020] The inner stator can define four pairs of magnetic poles, the second stationary portion can define more than four pairs of magnetic poles, and the pole pieces can shape the magnetic flux of the magnetic poles from the second magnetic pole to generate four pairs of magnetic poles in the region where the magnetic flux from the outer stator portion meets the magnetic flux from the inner stator.

[0021] Other numbers of magnetic poles and pole pieces can be used with the aim of coupling the strong, preferably first, harmonic of the magnetic flux from the second stationary portion by the pole pieces to the matching pole pattern generated by the windings and teeth of the first stationary portion.

[0022] The pole pieces of the rotor may include ferrous metal pole pieces, most preferably steel pole pieces. The pole pieces may be supported by a non-ferrous carrier. For example, the pole pieces may be fixed to the carrier or embedded within the carrier. Unlike linear actuators of the prior art, the pole pieces do not need to be magnets, as the function of the pole pieces is merely to shape the magnetic flux from the second stationary portion within the air gap between the two stators.

[0023] The outer stator may include an array of permanent magnets, each magnet defining a magnetic pole of the second stationary portion. The magnets may be arranged in an alternating north-south pattern to create alternating north and south magnetic poles within the air gap between the second stationary portion and the output member.

[0024] In an alternative, the outer stator may include an array of electromagnets. Each electromagnet may include teeth around which a section of wire forming a coil is wound. Current may be supplied to the coil from a controller, which creates a fixed non-moving magnetic flux pattern defining the magnetic poles of the second stationary portion.

[0025] A single controller may drive the windings of both stators, although of course, different current patterns will be applied to the coils of each stator, as one stator requires a moving DC field while the other stator requires a fixed DC field.

[0026] According to a second aspect, the present invention provides a steering wheel actuator assembly for a steer-by-wire steering system for a vehicle, the assembly comprising: a steering wheel having at least one handgrip portion rotatable about a rotational axis of the steering wheel, the handgrip portion being grippable by a driver, the steering wheel having a hub supporting the handgrip portion; and

[0027] a feedback torque generator including an electromagnetic motor according to the first aspect of the present invention, wherein the rotor of the motor is directly or indirectly fixed to and rotates with the hub of the steering wheel, and the stator is fixed to a stationary portion of the vehicle body such that the stator cannot rotate relative to the vehicle body.

[0028] The reader will appreciate that the torque feedback actuator of the present invention shares a common rotational axis with the steering wheel such that the torque feedback actuator moves with the steering wheel about the common rotational axis at the same rotational speed.

[0029] The hub may be fixed to the rotor of the feedback torque generator by a short shaft having a rotational axis located on the rotational axes of the hub and the rotor. The short shaft may pass through the stator or extend only partially into a region within the stator.

[0030] The steering wheel hub may include a bushing that fits over one end of the short shaft. Splines on the short shaft may engage complementary splines on the bushing to prevent relative rotation between the short shaft and the steering wheel.

[0031] The motor may be axially offset from the steering wheel.

[0032] The short shaft can be supported by at least one, preferably two, bearing assemblies. The bearing assemblies can be located on the side of the motor closest to the driver, or can be located on the side of the motor furthest from the motor. One bearing assembly can be located on each side of the motor.

[0033] In the case where two or more bearing assemblies are located on the side of the motor closest to the driver, a shroud that supports one or more column switches can surround the short shaft.

[0034] The short shaft can be fixed to a bracket, which in turn is fixed to the rotor. The steering wheel in this arrangement is indirectly connected to the rotor through the short shaft and then through the housing. The short shaft can be fixed to the bracket using an interference fit, or by welding the housing to the short shaft, or using an adhesive. The splines on the short shaft can be connected to the splines of the bracket. Alternatively, the bracket can be formed integrally with the short shaft. Description of the Drawings

[0035] Three embodiments of the present invention will now be described by way of example only, where:

[0036] Figure 1 is an overview of the main components of a typical vehicle steering system;

[0037] Figure 2 is an overview of the main components of a typical prior art steer-by-wire steering system;

[0038] Figure 3 is a cross-sectional view of the motor according to the present invention as viewed along the axis of rotation of the rotor;

[0039] Figure 4 is a cross-sectional view of an embodiment of a steering wheel actuator assembly, the cross-section being perpendicular to the axis of rotation of the rotor, and the actuator assembly falling within the scope of a steer-by-wire steering system for a vehicle according to the second aspect of the present invention; and

[0040] Figure 5 (a) shows the magnetic flux pattern generated only by the outer stator magnets, and Figure 5 (b) shows the shaped magnetic flux pattern modified by the rotor poles, which pattern rotates as the rotor rotates about its axis. Detailed Description

[0041] As Figure 3 shown, the motor 100 includes an annular inner stator 101, which includes twelve stator teeth 102, each stator tooth being wound with one or more turns of wire (not shown). The wires are connected together in three phases 103 such that current can pass independently through each phase.

[0042] A controller 104 is provided which, in use, generates a set of currents that are applied to the phase windings of the inner stator to create a magnetic pole pattern along the tooth array, the spacing between the magnetic poles being greater than the spacing between adjacent teeth of the first fixed part. In this example, a current waveform is applied which creates a pattern having four pairs of magnetic poles (four north poles and four south poles) with equal spacing between the magnetic poles. Thus, the number of magnetic poles is less than the number of stator teeth. Importantly, by varying the current applied to the windings, the pattern of the magnetic poles can be moved along the first fixed part. The windings of the teeth 102 and the current waveform used together enable the desired magnetic pole pattern to be generated.

[0043] An annular outer stator 105 surrounds the inner stator with an air gap therebetween. The two stators share a common axis, making the outer stator concentric with the inner stator 101. The outer stator 105 includes a set of alternating magnetic poles 106, the spacing between adjacent magnetic poles being less than the spacing of the magnetic poles of the first array created by the controller. In this example, there are 44 magnets equally spaced around the outer stator 105.

[0044] Between the two stators is an annular rotor 107. The rotor includes an array of pole pieces that alternate between north and south poles. The pole pieces are supported by a non-ferrous carrier. In the example shown, there are 26 pole pieces.

[0045] The presence of the pole pieces in the air gap between the two stators shapes or deforms the magnetic flux pattern from the outer stator 105. This can be seen by comparing Figure 5 (a) and Figure 5 (b), where in Figure 5 (a), both the inner stator and the rotor are removed, and in Figure 5 (b), the rotor interacts with the outer stator. It can be seen that the rotor shapes the magnetic flux to form a pattern similar to that which would be produced by having only four pairs of north / south poles on the outer stator. Importantly, moving the rotor a small distance relative to the outer stator will result in a magnetic flux pattern of substantially the same shape, but the pattern will move in the direction of movement of the rotor. The reason for this shaping is well understood in the context of a pseudo direct drive motor and a detailed discussion is given in the international patent application WO2007 / 125284 of the University of Sheffield, where the concept is used in the design of a rotating electric machine.

[0046] The reader will appreciate that the modified magnetic flux pattern from the permanent magnets of the outer stator will interact with a similar magnetic flux pattern from the inner stator, and by moving the magnetic pole pattern of the inner stator, a Lorentz force will act on the rotor, causing the rotor to attempt to move to re-align the magnetic flux pattern to a position where no torque acts on the rotor. Since this causes movement of the rotor, the way the magnetic flux from the second fixed part changes, which results in the rotor moving much slower than the movement of the magnetic pole pattern of the first fixed part. The result is a magnetic transmission device that is advantageous for providing a high force density for the motor.

[0047] The motor 100 can be used in the steering wheel assembly 200 of a steer-by-wire system, and an exemplary embodiment falling within the scope of the second aspect of the present invention is shown in Figure 4 FIG.

[0048] The steering wheel assembly includes a steering wheel 201 having a relatively thin generally circular rim that defines a hand-grip portion rotatable about the axis of rotation of the steering wheel. The rim can be gripped by one or both hands of the driver in a conventional manner, and the driver can rotate the steering wheel about the central axis of rotation. Many other forms of steering wheels can be provided within the scope of the present invention, where the steering wheel does not need to have a circular rim.

[0049] The steering wheel 201 has a hub that includes a single dished arm or spoke having a first end connected to the rim and a second end connected to a sleeve 203. Depending on the type of hand-grip portion and the desired stiffness of the steering wheel, multiple spokes can be provided, and the present invention is not limited to one type of spoke. The sleeve 203 is located on the axis of rotation of the steering wheel 201 and supports the hand-grip portion. The recess in the sleeve has a set of radially inwardly projecting splines (not shown) and is pressed onto the end of the rotor 107 of the motor as shown in Figure 3 FIG., the rotor having a set of complementary radially outwardly projecting splines in a conventional manner for fixing the steering wheel to the steering shaft. The splines ensure that rotation of the steering wheel 201 will produce corresponding rotation of the rotor and that rotation of the rotor will produce corresponding rotation of the steering wheel. The feedback torque generator is of the type shown in Figure 3 FIG.

[0050] In use, when the rotor 107 rotates, the short shaft rotates, which ultimately causes the steering wheel 201 to rotate. Thus, applying torque to the rotor 107 can be used to turn the steering wheel or to apply a torque that partially resists the torque applied by the driver to the steering wheel to simulate road feel and give the driver a sense of the forces acting on the wheels and other components of the steering system.

[0051] An angular position sensor 202 is also shown that determines the angular position of the steering wheel based on the angular position of the rotor relative to the stator.

Claims

1. An electromagnetic motor, comprising: An inner stator, the inner stator including a plurality of stator teeth, each stator tooth being surrounded by one or more turns of wire, A controller, the controller generating a set of currents that are applied to the phase windings of the inner stator to produce a pattern of magnetic poles spaced around the inner stator, the spacing between the magnetic poles being greater than the spacing between adjacent stator teeth of the inner stator, An outer stator, the outer stator being concentric with the inner stator and including a set of alternating magnetic poles, the spacing between adjacent magnetic poles of the outer stator being less than the spacing of the first array of magnetic poles generated by the controller, and An intermediate rotor member, the intermediate rotor member being located between the inner stator and the outer stator and including an array of pole pieces, wherein the pole pieces of the rotor shape the pattern of magnetic flux acting between the inner stator and the outer stator, and Thus, in use, the controller is arranged to control the torque applied to the rotor by moving the pattern of magnetic poles of the inner stator around the axis of the torque generator.

2. The electromagnetic motor according to claim 1, wherein, The inner stator is supplied with a current that generates a movable pattern including two magnetic poles, the outer stator having more than two magnetic poles, and the pole pieces used shape the pattern of magnetic flux from the magnetic poles of the outer stator to produce two magnetic poles in the region where the magnetic flux from the inner stator meets the magnetic flux from the outer stator.

3. The electromagnetic motor according to claim 2, wherein The movable pattern is a constant pattern.

4. The electromagnetic motor according to any one of claims 1 to 3, wherein, The pole pieces of the rotor include iron-containing metal pole pieces.

5. The electromagnetic motor according to any one of claims 1 to 3, wherein, The outer stator includes an array of permanent magnets, each magnet defining one magnetic pole of the outer stator.

6. The electromagnetic motor according to any one of claims 1 to 3, wherein, The outer stator includes an array of electromagnets.

7. A steering wheel actuator assembly for a steer-by-wire steering system for a vehicle, the assembly comprising: A steering wheel having at least one handgrip portion rotatable about the axis of rotation of the steering wheel, the handgrip portion being grippable by a driver, the steering wheel having a hub supporting the handgrip portion; And A feedback torque generator including an electromagnetic motor according to any one of claims 1 to 6, wherein the rotor of the motor is directly or indirectly fixed to the hub of the steering wheel and rotates therewith, and the outer stator and the inner stator are fixed in place relative to a fixed portion of the vehicle body such that the outer stator and the inner stator cannot rotate relative to the vehicle body.

8. The steering wheel actuator according to claim 7, wherein, The hub is fixed to the rotor of the feedback torque generator by a short shaft having a rotational axis located on the axis of rotation of the hub and the rotor of the feedback torque generator.

9. The steering wheel actuator according to claim 8, wherein, The hub of the steering wheel includes a bushing that fits over one end of the short shaft.

10. The steering wheel actuator according to claim 7, 8 or 9, wherein, The motor is axially offset from the steering wheel.

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