Permanent magnet machine stator

A permanent magnet machine includes a machine housing and a stator disposed within the machine housing. The machine housing has an inner surface that extends between a first housing end and a second housing end along a central longitudinal axis. The stator has a stator core having an exterior surface and an interior surface, each extending between a first face and a second face along the central longitudinal axis. The stator core defines a plurality of openings that extend from the first face towards the second face.

BACKGROUND

Electric machines are used in automotive systems, precision tooling, or industrial drives and may have specific requirements to operate with low noise and vibration. Some sources of noise, vibration, or harshness in the electric machine may be cogging torque, torque ripple, and electromagnetic radial forces in addition to other aerodynamic or mechanical sources. An electric machine with high torque density generally has higher potential for noise and vibration that may be viewed as unacceptable. Different methods have been employed to mitigate the noise and vibrations from the electric machine, however as demands for higher torque density increases, new strategies or configurations to mitigate noise and vibrations from the electric machine must be developed.

SUMMARY

Disclosed is a stator provided with a permanent magnet machine. The stator includes a stator core disposed about a central longitudinal axis. The stator core has an exterior surface, an interior surface disposed opposite the exterior surface, the exterior surface and the interior surface each extending between a first face and a second face along the central longitudinal axis, and a plurality of stator teeth radially extending from the interior surface towards the central longitudinal axis. The stator core defines an opening that extends from the first face towards the second face and is disposed adjacent to a first stator tooth of the plurality of stator teeth.

Also disclosed is a permanent magnet machine that includes a machine housing and a stator disposed within the machine housing. The machine housing has an inner surface that extends between a first housing end and a second housing end along a central longitudinal axis. The stator has a stator core having an exterior surface and an interior surface, each extending between a first face and a second face along the central longitudinal axis. The stator core defines a plurality of openings that extend from the first face towards the second face.

DETAILED DESCRIPTION

Referring toFIGS. 1A and 1B, an electric machine, such as a permanent magnet machine10is shown. The permanent magnet machine10includes a machine housing12and a stator14that is arranged to be disposed within the machine housing12.

The machine housing12is disposed about a central longitudinal axis20. The machine housing12includes an inner surface22that extends between a first housing end24and a second housing end26along the central longitudinal axis20. The first housing end24may be an open and the second housing end26may be a closed end. The second housing end26defines an opening28that is generally aligned along the central longitudinal axis20along which a shaft or the like may extend through.

The stator14is disposed within the machine housing12and is secured to the inner surface22of the machine housing12. The stator14includes a stator core30that is disposed about the central longitudinal axis20.

Referring to the Figures, the stator core30includes an exterior surface32, an interior surface34that is disposed opposite the exterior surface32, and a plurality of stator teeth36. The exterior surface32and the interior surface34extending between a first face40and a second face42along the central longitudinal axis20. The exterior surface32faces towards the inner surface22of the machine housing12. The exterior surface32of the stator core30may be commonly referred to as the back iron of the stator14. The plurality of stator teeth36radially extend from the interior surface34towards the central longitudinal axis. A slot44is defined between adjacent stator teeth of the plurality of stator teeth36such that the slot44is defined between a first stator tooth46and a second stator tooth48that is disposed adjacent to the first stator tooth46of the plurality of stator teeth36. In such an arrangement, the slot44is circumferentially disposed between the first stator tooth46and the second stator tooth48.

The stator14may employ various fractional slot topologies, e.g. various ratios between a number of slots and a number of poles associated with the stator14. The fractional slot topologies impact a winding factor about a stator tooth of the plurality of stator teeth36and hence impact the torque density. The higher the winding factor among them, the higher the torque density. The higher torque density may result in low order vibration modes. The low mode order results from the interaction of the n-th order radial field due to the magnet poles and n-th+2 order radial field due to armature reaction. The low mode order leads to stator deformation that leads to electric machine vibrations that is perceived as noise.

The present disclosure attempts to address the machine vibrations that are perceived as noise by providing openings60in the machine housing12and/or the stator14that are arranged to damp radial forces transmitted through a stator tooth of the plurality of stator teeth36.

Referring toFIG. 1A, a discontinuous region may be defined by a first raised region62and a second raised region64of the exterior surface32of the stator14. The first raised region62is disposed proximate the first face40. The second raised region64is circumferentially and axially spaced apart from the first raised region62. The second raised region64is disposed proximate the second face42. At least one of the first raised region62and the second raised region64is arranged to engage the inner surface22of the machine housing12. The first raised region62and the second raised region64are arranged to reduce the number of points of contact between the exterior surface32of the stator14and the inner surface22of the machine housing12.

Referring toFIG. 1B, a discontinuous region may be defined by the inner surface22of the machine housing12. The discontinuous region may be defined by recessed regions66of the inner surface22of the machine housing12. The recessed regions64may extend from the inner surface22towards an outer surface of the machine housing12along an axis that is disposed transverse to the central longitudinal axis20.

The discontinuous region defined by the recessed regions66of the inner surface22of the machine housing12and/or by the first and second raised regions62,64of the exterior surface32of the stator may reduce points of contact between the exterior surface32of the stator14and the inner surface22of the machine housing12to reduce force transmittal through a stator tooth of the plurality of stator teeth36to the machine housing12and therefore reduces radiated noise and vibration by reducing deformation of the stator14without compromising motor torque density. The implementation of the recessed regions66on the inner surface22of the machine housing12and maintaining a uniform or substantially uniform exterior surface32of the stator14, the potential for magnetic loss of the permanent magnet machine10due to discontinuities on the exterior surface32of the stator14may be minimized.

The openings60of the stator core30and/or the machine housing12act as springs that damp the radial forces and reduce deformation of the stator core30or the machine housing12to reduce radiated noise and vibration. The openings60may each extend from a face of the machine housing12that is disposed at the first housing end24towards the second housing end26along the central longitudinal axis20. The openings60may be disposed between the exterior surface32and the interior surface34of the stator core30. The openings60may be disposed closer to the exterior surface32than the interior surface34, to have no to minimal effect on the electromagnetic performance of the electric machine.

The openings60may each have a circumferential width that is substantially equal to a circumferential width of at least one of the first stator tooth46and the second stator tooth48of the plurality of stator teeth36. The openings60may each have a circumferential width that is substantially equal to a circumferential width of the slot44that is defined between the first stator tooth46and the second stator tooth48of the plurality of stator teeth36. In other embodiments, the openings60may have a circumferential width that is substantially less than a circumferential width of a tooth of the plurality of stator teeth36or a width of the slot44.

The openings60may be arranged as indentations, depressions, grooves, or the like that extend from the first face40towards the second face42without extending completely through the stator core30. The openings60may be arranged as slots that extend from the first face40to the second face42such that the openings60extend completely through the stator core30. In at least one embodiment, the openings60may instead by nodules, protrusions, or the like having a mass that axially extend away from the first face40along the central longitudinal axis20. The openings60may have varying depths that are measured from the first face40towards the second face42such that the a first opening may have a first depth and a second opening circumferentially spaced apart from the first opening may have a second depth that is greater than or less than the first depth. The openings60may be circumferentially distributed about the stator core30having varying angles of distribution or varying circumferential distances between adjacent openings such that a first angle (e.g. relative to the central longitudinal axis) or first circumferential distance between a first opening and a second opening disposed adjacent the first opening may be different from (e.g. greater than or less than) a second angle or second circumferential distance between the second opening and a third opening disposed adjacent the second opening. The varying depth of the openings60or varying angle or distance between adjacent openings may vary a damping response of the stator core30.

Referring toFIG. 2A, the openings60may be arranged as a generally elliptical slot that is circumferentially aligned with at least one of the first stator tooth46and the second stator tooth48of the plurality of stator teeth36. Referring toFIG. 2B, the opening60may be arranged as a generally elliptical slot that is circumferentially aligned with the slot44that is disposed or defined between the first stator tooth46and the second stator tooth48of the plurality of stator teeth36.

Referring toFIG. 3A, the openings60may be arranged as a generally circular opening that is circumferentially aligned with at least one of the first stator tooth46and the second stator tooth48of the plurality of stator teeth36. Referring toFIG. 3B, the opening60may be arranged as a generally circular opening that is circumferentially aligned with the slot44that is disposed or defined between the first stator tooth46and the second stator tooth48of the plurality of stator teeth36.

Referring toFIG. 4A, the openings60may be arranged as a bean-shaped or ovate shaped opening that is circumferentially aligned with at least one of the first stator tooth46and the second stator tooth48of the plurality of stator teeth36. Referring toFIG. 4B, the opening60may be arranged as a bean-shaped or ovate shaped opening that is circumferentially aligned with the slot44that is disposed or defined between the first stator tooth46and the second stator tooth48of the plurality of stator teeth36.

Referring toFIG. 5A, the openings60may be arranged as a rectangular shaped opening, with rounded corners, that is circumferentially aligned with at least one of the first stator tooth46and the second stator tooth48of the plurality of stator teeth36. Referring toFIG. 5B, the opening60may be arranged as a rectangular shaped opening, with rounded corners, that is circumferentially aligned with the slot44that is disposed or defined between the first stator tooth46and the second stator tooth48of the plurality of stator teeth36.

The openings60disposed proximate the outer periphery of the stator14does not affect torque or any other electromagnetic performance of the permanent magnet machine10. The openings60may vary in number, size, shape, and location about the stator core30of the stator14. Regardless of the number, shape, or location of the openings60, the openings60reduce force transmittal through a stator tooth of the plurality of stator teeth36to the machine housing12to reduce radiated noise and vibration by reducing deformation of the stator14without compromising motor torque density.