External-rotor reluctance motor

Claim 2

An external-rotor reluctance motor having a rotor provided with a plurality of pole portions each having respective pole ends, a pole span between said ends and a pole middle, said rotor having a given effective yoke cross-section over part of the respective span and a lesser effective yoke cross-section in the vicinity of a respective pole middle and over a substantial portion of the associated pole span, and wherein said rotor has an outer periphery, and wherein said rotor is provided over a substantial portion of a respective pole span with a plurality of circumferentially spaced yoke-reducing non-magnetic portions of different dimensions spaced from said outer periphery and serving to reduce said given effective yoke cross-section to said lower effective yoke cross-section, and wherein said rotor comprises circumferentially spaced magnetically conductive flux-path portions separating adjacent ones of said non-magnetic portions and wherein said non-magnetic portions are largest in the region of the respective pole middle and smaller in the other regions of the respective pole span.

Claim 3

A motor as defined in claim 1, wherein said non-magnetic portions are largest in the region of the respective pole middle and successively smaller in direction towards the respective pole ends.

Claim 4

A motor as defined in claim 1, said rotor being provided with slots filled with electrically conductive non-magnetic material forming a squirrel-cage winding, and said rotor having an inner periphery, and further having radially inwardly projecting teeth provided in the region of said inner periphery; and Wherein at least some of said magnetically conductive flux-path portions are substantially aligned with and merge into respective neighboring teeth.

Claim 5

A motor as defined in claim 2, said rotor being provided with slots filled with electrically conductive non-magnetic material forming a squirrel-cage winding, and said rotor having an inner periphery, and further having radially inwardly projecting teeth provided in the region of said inner periphery; and wherein at least some of said magnetically conductive flux-path portions are substantially aligned with respective neighboring teeth and merge into the same.

Claim 6

A motor as defined in claim 4, wherein at least some of said non-magnetic portions merge with neighboring slots of said squirrel-cage winding.

Claim 7

A motor as defined in claim 3, each of said teeth having an effective respective cross-sectional dimension and each of said magnetically conductive flux-path portions having a respective effective cross-sectional dimension, and wherein the effective cross-sectional dimension of at least some of said flux-path portions is substantially equal to the effective cross-sectional dimension of respective neighboring teeth.

Claim 8

A motor as defined in claim 4, wherein said flux-path portions of respective pole portions of said rotor to either side of the respective pole middle are so dimensioned that during idling of said motor the majority of said flux-path portions are in magnetic saturation.

Claim 9

A motor as defined in claim 1, wherein said flux-path portions of respective pole portions of said rotor to either side of the respective pole middle are so dimensioned that during idling of said motor the majority of said flux-path portions are in magnetic saturation.

Claim 10

A motor as defined in claim 8, said inwardly projecting teethbeing provided in the region of said rotor inner periphery on a substantial part of the pole span of at least one pole portion, and each of said teeth having a respective cross-sectional dimension, and wherein the respective cross-sectional dimension of teeth located in the vicinity of the pole middle is greater than the respective cross-sectional dimension of teeth located in the vicinity of the respective pole ends.

Claim 11

A motor as defined in claim 1, wherein said rotor comprises a plurality of stacked substantially identical rotor plates each having a plurality of yoke-reducing cut-outs, said plates being stacked with said cut-outs in registry, and said cut-outs forming yoke-reducing cavities extending lengthwise of said rotor; and wherein said yoke-reducing non-magnetic portions are accommodated in respective ones of said yoke-reducing cavities, wherein said non-magnetic portions accommodated in said cavities consist at least substantially of electrically conductive material, and wherein said conductive material is aluminum.

Claim 12

A motor as defined in claim 1, wherein said rotor comprises a plurality of stacked substantially identical rotor plates each having a yoke-reducing cut-out per pole, each yoke-reducing cut-out being located in the vicinity of the respective pole middle and extending over a substantial portion of the respective pole span, said plates being stacked with said yoke-reducing cut-outs in registry so as to form yoke-reducing cavities extending lengthwise of the rotor; and further including portions of non-magnetic material accommodated in said yoke-reducing cavities.

Claim 13

An external-rotor reluctance motor comprising in combination a stator provided with a stator winding; an external-rotor assembly comprising mounting means defining an axis of rotation and a magnetic external-rotor core having a generally annular transverse cross-section with a radially inner periphery and a radially outer periphery, said external-rotor core surrounding said stator and being carried by said mounting means for rotation about said axis, said magnetic external-rotor core including a plurality of circumferentially spaced flux path portions extending along the length of said external-rotor Core and forming therebetween a plurality of circumferentially spaced slots extending along the length of said external-rotor core, with said flux-path portions furthermore extending in direction from the inner periphery of said external-rotor core towards the outer periphery of said external-rotor core, and a yoke section extending in circumferential direction of said external-rotor core and joining said flux-path portions together at the radially outer portion of said external-rotor core, with the radially outermost portions of at least some of said slots being disposed at respective different radial distances from the outer periphery of said external-rotor core to form said yoke section with a width measured in direction radially of said core which has a predetermined smallest value at at least two circumferentially spaced locations to define two direct-axis pole middles presenting maximum reluctance to quadrature-axis flux passing through said locations in direction circumferentially of said external-rotor core, and has a predetermined largest value at at least two further circumferentially spaced locations to define at least two quadrature-axis pole ends presenting minimum reluctance to direct-axis flux passing through said further locations in direction circumferentially of said external-rotor core.

Claim 14

An external-rotor reluctance motor comprising in combination a stator provided with a stator winding; an external-rotor assembly comprising mounting means defining an axis of rotation and a magnetic external-rotor core having a generally annular transverse cross-section with a radially inner periphery and a radially outer periphery, said external-rotor core surrounding said stator and being carried by said mounting means for rotation about said axis, said magnetic external-rotor core including a plurality of circumferentially spaced flux path portions extending along the length of said external-rotor Core and forming therebetween a plurality of circumferentially spaced slots extending along the length of said external-rotor core, with said flux-path portions furthermore extending in direction from the inner periphery of said external-rotor core towards the outer periphery of said external-rotor core, and a yoke section extending in circumferential direction of said external-rotor core and joining said flux-path portions together at the radially outer portion of said external-rotor core, with the radially outermost portions of at least some of said slots being disposed at respective different radial distances from the outer periphery of said external-rotor core to form said yoke section with a width measured in direction radially of said core which has a predetermined smallest value at at least two circumferentially spaced locations to define two direct-axis pole middles presenting maximum reluctance to quadrature-axis flux passing through said locations in direction circumferentially of said external-rotor core, and has a predetermined largest value at at least two further circumferentially spaced locations to define at least two quadrature-axis pole ends presenting minimum reluctance to direct-axis flux passing through said further locations in direction circumferentially of said external-rotor core.

Claim 15

A motor as defined in claim 12, wherein those of said slots located to either side of said pole-middles are successively disposed at increasing radial distances from the outer periphery of said external-rotor core, so that said yoke section has a width measured in direction radially of said core which increases in direction circumferentially away from said pole-middles.

Claim 16

A motor as defined in claim 12, wherein said slots include a plurality of first slots located at the radially inward portion of said external-rotor core and a second plurality of slots located radially outwards of said first slots and discrete from said first slots, and wherein said second slots are located to either side of said pole-middles, and wherein the width of successive ones of said second slots measured in direction radially of said core decreases in direction circumferentially away from the respective pole middles.

Claim 17

A motor as defined in claim 12, wherein said slots include a plurality of circumferentially spaced first slots located at the radially inward portion of said external-rotor core, and wherein there is located at each of said pole middles a second slot having a width measured in direction radially of said external-rotor core which decreases in direction circumferentially away from the respective pole middle, and having an angular span measured with respect to said axis including a plurality of said first slots.

Claim 18

A motor as defined in claim 12, wherein said slots are filled with non-magnetic electrically conductive material forming a squirrel-cage winding.

Claim 19

A motor as defined in claim 14, wherein at least some of said second slots are substantially aligned in direction radially of said external-rotor core with some of said first slots.

Claim 20

A motor as defined in claim 12, wherein said flux-path portions and said slots are so dimensioned that in the region of said pole middles at least some of said flux-path portions are substantially magnetically saturated when said motor is idling.

Claim 21

A motor as defined in claim 12, wherein the effective width of said flux-path portions measured in direction circumferentially of said external-rotor core is greatest at said pole middles and smallest at said pole ends.