Linear induction motor

Claim 2

A polyphase linear induction motor comprising a primary member and a secondary member spaced magnetically apart transversely of the motor, said primary member comprising magnetic material and polyphase winding means formed on said magnetic material and arranged, when energized from a polyphase alternating current supply, for creating a field of magnetomotive force which travels longitudinally of the primary member, said secondary member comprising electrically conductive material and further magnetic material for forming in combination with the primary member magnetic material low reluctance paths for the passage of the working flux created by said travelling field, said low reluctance paths passing through the electrically conductive material whereby the working flux induces in the electrically conductive material currents which react with the working flux to produce a longitudinally directed force between the primary and secondary members, the arrangement being such that each said low reluctance path lies substantially in a plane which is transverse to the motor whereby for a given flux density in the airgap between the primary and secondary members the depth of magnetic material required is substantially independent of the pole pitch.

Claim 3

A polyphase linear induction motor comprising a primary member and a secondary member spaced magnetically apart transversely of the motor, said primary member comprising magnetic material and polyphase winding means formed on said magnetic material and arranged, when energized from a polyphase alternating current supply, for creating a field of magnetomotive force which travels longitudinally of the primary member, said secondary member comprising electrically conductive material and further magnetic material for forming in combination with the primary member magnetic material low reluctance paths for the passage of the working flux created by said travelling field, said low reluctance paths passing through the electrically conductive material whereby the working flux induces in the electrically conductive material currents which react with the working flux to produce a longitudinally directed force between the primary and secondary members, the arrangement being such that each said low reluctance path lies substantially in a plane which is transverse to the motor whereby for a given flux density in the airgap between the primary and secondary members the depth of magnetic material required is substantially independent of the pole pitch, each said low reluctance path passing only once through the electrically conductive material.

Claim 4

A polyphase linear induction motor comprising a primary member and a secondary member spaced magnetically apart transversely of the motor, said primary member comprising magnetic material and polyphase winding means formed on said magnetic material and arranged, when energized from a polyphase alternating current supply, for creating a field of magnetomotive force which travels longitudinally of the primary member, said secondary member comprising electrically conductive material and further magnetic material for forming in combination with the primary member magnetic material low reluctance paths for the passage of the working flux created by said travelling field, said low reluctance paths passing through the electrically conductive material whereby the working flux induces in the electrically conductive material currents which react with the working flux to produce a longitudinally directed force between the primary and secondary members, the arrangement being such that each said low reluctance path lies substantially in a plane which is transverse to the motor whereby for a given flux density in the airgap between the primary and secondary members the depth of magnetic material required is substantially independent of the pole pitch, each said low reluctance path passing only once through the electrically conductive material.

Claim 5

A linear induction motor according to claim 1, wherein the primary and secondary member magnetic material is so arranged that the low reluctance paths are provided in longitudinally spaced pairs, the low reluctance paths of each pair being side-by-side transversely of the motor and being in part provided in common by a common portion of the primary member magnetic material, working flux passing in the low reluctance paths of each pair passing in the respective said common portion in an additive manner.

Claim 6

A linear induction motor according to claim 2, wherein the primary and secondary member magnetic material is so arranged that the low reluctance paths are provided in longitudinally spaced pairs, the low reluctance paths of each pair being side-by-side transversely of the motor and being in art provided in common by a common portion of the primary member magnetic material, working flux passing in the low reluctance paths of each pair passing in the respective said common portion in an additive manner, the electrically conductive material being so disposed that in each low reluctance path the conductive material lies between the secondary member magnetic material and only the respective said common portion of the primary member magnEtic material.

Claim 7

A linear induction motor according to claim 3, wherein the polyphase winding means is disposed wholly on the said common portions of the primary member magnetic material.

Claim 8

A linear induction motor according to claim 3, wherein the polyphase winding means is disposed on the said common portions of the primary member magnetic material and also on further parts of the primary member magnetic material separately providing further parts of the low reluctance paths.

Claim 9

A linear induction motor according to claim 4, wherein transversely of the motor the secondary member presents to the primary member two spaced portions of the secondary member magnetic material with the conductive material therebetween, the said two spaced portions opposing correspondingly spaced portions of the primary member magnetic material and the conductive material opposing the said common portions of the primary member magnetic material and extending transversely of the motor beyond the said common portions on either side thereof for providing parts of the conductive material current paths which extend longitudinally of the motor and are substantially free of working flux.

Claim 10

A linear induction motor according to claim 7, wherein the said parts of the conductive member which extend transversely of the motor beyond the said common portions of the primary member magnetic material are thicker than the part of the conductive material opposing the common portions.

Claim 11

A linear induction motor according to claim 3, wherein the primary member magnetic material comprises a plurality of longitudinally spaced and generally E-shaped stacks of transverse laminations, each lamination stack being formed of three generally parallel limb portions joined by a yoke portion and having the ends of the limb portions generally coplanar, the polyphase winding means being disposed on at least the center ones of the limb portions, the secondary member magnetic material comprising a plurality of longitudinally arranged transverse laminations and being generally U-shaped having two limb portions joined by a yoke portion and having the conductive material received within the concavity thereby defined so that the conductive material in combination with the ends of the limb portions of the secondary member magnetic material presents to the primary member a generally plane face, the ends of the outer ones of the limb portions of the primary member magnetic material being opposed to the ends of the limb portions of the secondary member magnetic material and the said center limb portions of the primary member magnetic material providing the said common portions and having their ends opposed to the conductive material, the conductive material extending transversely of the motor beyond the center limb portions on either side thereof for providing parts of the conductive material current paths which extend longitudinally of the motor and are substantially free of working flux.

Claim 12

A linear induction motor according to claim 9, wherein the parts of the conductive material which extend transversely of the motor beyond the central limb portions of the primary member magnetic material are thicker than the part of the conductive material opposing the central limb portions.

Claim 13

A linear induction motor according to claim 1, wherein the primary member magnetic material comprises a plurality of longitudinally spaced and generally U-shaped stacks of transverse laminations, each lamination stack being formed of two generally parallel limb portions joined by a yoke portion, the secondary member magnetic material comprising a plurality of longitudinally arranged transverse laminations and the conductive material being interposed between the secondary member magnetic material and the primary member magnetic material at the said limb portions thereof and extending transversely of the motor between and beyond the motor magnetic material at either side thereof for providing parts of the conductive material current paths which extend longitudinally of the motor and are substantially free of working flux.

Claim 14

A linear induction motor according to claim 11, wherein the polyphase winding means is formed on each said limb portion of each said lamination stack.

Claim 15

A linear induction motor according to claim 2, wherein the primary member magnetic material comprises a plurality of longitudinally spaced stacks of transverse laminations, each lamination stack having two generally parallel limb portions joined by a yoke portion, the polyphase winding means being disposed on a least one said limb portion of each stack, the conductive material being interposed between the secondary member magnetic material and a limb portion of each lamination stack formed with the polyphase winding means, the other limb portion of each stack directly opposing the secondary member magnetic material at its end, the conductive material extending transversely of the motor on either side of the associated limb portions for providing parts of the conductive material current paths which extend longitudinally of the motor and are substantially free of working flux.

Claim 16

A linear induction motor according to claim 1 in combination with a gas cushion vehicle and a track along which the vehicle is arranged to operate, the motor being provided for propelling the vehicle along the track and having its primary member carried by the vehicle and its secondary member forming part of the track.

Claim 17

A linear induction motor according to claim 2, wherein the primary and secondary member magnetic material is so arranged that the low reluctance paths are provided in longitudinally spaced pairs, the low reluctance paths of each pair being side-by-side transversely of the motor and being in part provided in common by a common portion of the primary member magnetic material, working flux passing in the low reluctance paths of each pair passing in the respective said common portion in an additive manner.

Claim 18

A linear induction motor according to claim 4, wherein the polyphase winding means is disposed wholly on the said common portions of the primary member magnetic material.

Claim 19

A linear induction motor according to claim 4, wherein the polyphase winding means is disposed on the said common portions of the primary member magnetic material and also on the parts of the primary member magnetic material separately providing further parts of the low reluctance paths.