Conductive stator sleeve with overhung sleeve for passive damping

Abstract

An electric motor 200, particularly for a steering wheel for a steer-by-wire vehicle, has a stator 201 with a plurality of windings and a rotor 202 with a plurality of magnet poles. Stator 201 has a y

Claims

1. An electric motor comprising a stator and a rotor, the stator carrying a plurality of phase windings and the rotor carrying a plurality of magnet poles and being connected to a shaft; andin which the stator comprises a yoke having a plurality of teeth, each tooth comprising a stem and a tooth tip that is located at the end of the stem closest to the rotor, whereby the region of the motor in which the tooth tips and the magnets directly face one another defines a cylindrical active magnetic region that bounds the magnetic flux that passes radially between the magnets of the rotor and the tips of the teeth of the stator,and further comprising a sleeve of electrically conductive material that is located between the inwardly facing tips of the stator teeth and the rotor the sleeve providing a flux path that extends axially along the motor bore so that rotation of the rotor generates eddy currents within the sleeve that resist rotor rotation,further in which the conductive sleeve has an axial length that is longer than the axial length of the active magnetic region and is positioned such that at least one end of the sleeve protrudes axially beyond the adjacent axial end of the active magnetic region.

2. A motor according to claim 1 in which the sleeve extends beyond the active magnetic region at both ends of the motor.

3. A motor according to claim 2 in which the sleeve extends beyond each end by the same amount at each end.

4. A motor according to any preceding claim in which the sleeve has a greater axial length than both the rotor magnets and the stator teeth tips so that it protrudes beyond the end of the stator tooth tips and rotor magnets at least at one end of the motor.

5. A motor according to claim 4 in which the sleeve extends beyond both the stator teeth and the rotor magnets at bot ends of the motor.

6. A motor according to any one of claims 1 to 3 in which the rotor magnets have a greater axial length than the stator pole tips and the sleeve extends beyond the adjacent end or at both ends of the stator teeth tips but need not beyond one or both ends of the rotor magnets.

7. A motor according to any one of claims 1 to 3 in which the stator teeth tips extend beyond the adjacent ends of the rotor magnets at one end or at both ends of the motor and the sleeve extends beyond the ends of the rotor magnets but does not extend beyond one or both ends of the stator teeth tips8. A motor according to any preceding claim in which the sleeve has a length at least 5 percent longer, or 10 percent longer, or at least 15 percent longer, or at least 30 percent longer than the active magnetic region of the motor.

9. A motor according to any preceding claim in which the conductive sleeve comprises a solid walled tubular sleeve that is fitted in the airgap between the rotor and the stator.

10. A motor according to any preceding claim in which the sleeve has an inner circumferential wall having a uniform radius at all points and the outer circumferential wall also have a constant radius such that the sleeve has a uniform thickness as all points.

11. A motor according to any preceding claim in which the outer surface of the sleeve includes a plurality of ribs, each rib extending radially outward into a space between adjacent tips of the stator teeth.

12. A motor according to any preceding claim in which the radially outer facing surfaces of the sleeve are an interference fit within the airgap with the radially inward facing surfaces of the tips of the teeth.

13. A motor according to any preceding claim in which the inner sleeve comprises a magnetically permeable material.

14. A motor according to any preceding claim in which the stator is coated in a lacquer where it contacts the sleeve.

15. A motor according to any preceding claim in which the sleeve is tin plated or otherwise passivated to prevent galvanic corrosion if the sleeve material is too far apart in the metal nobility order compared to the stator material.5 16. A motor according to any preceding claim in which the sleeve comprises a metalor metal alloy.

17. A motor according to claim 16 in which the sleeve is a copper sleeve.10 18. A motor according to any preceding claim which comprises a part of a handwheelactuator assembly of a steer by wire vehicle that comprises:a housing;a shaft rotatably mounted with respect to the housing;a second motor; and15 a control circuit adapted to control the current flowing into or out of the two motors to cause a net torque to be applied to the shaft during normal operation.A

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