displacement between said primary and said secondary ELECTROMAGNETIC LEVITATION in a longitudinal direction.

Preferably, the magnetic material of the secondary is This invention relates to electrical machines of the in contact with the electrically conductive material of kind which employ electromagnetic levitation. 5 the secondary over two regions, one on each side of the

U.S. Pat No. 3,836,799 relates to an electrical ma- longitudinal centre line of the electrically conductive chine having a secondary comprising electrically con- material, the central re^or of the electrically ccnduc-ductive material and a primary comprising a core of tive material not being in contact with the magnetic magnetic material having at least two rows of pole faces material. In one form of the invention, the secondary confronting said secondary and being arranged to pro- 10 magnetic material consists of two members, one on vide paths for working flu* between said rows of pole each side of this central region, faces in planes substantially perpendicular to said rows, In order that the invention may be more readily un-the secondary being arranged to provide longitudinal derstood, embodiments thereof will now be described paths for electric current on each side of eauh row of with reference to the accompanying drawing, in which: pole faces and transverse paths interconnecting said F1G. I is a lateral cross-sectional view of a first em-longitudinal paths, the primary being arranged, when bodiment of the invention, and energised from a polyphase alternating current supply, nG- 2 is a part sectional, part end elevations] view of to create a magnetic field operative to produce a force a tracked ground transport system incorporating an between said primary and said secondary having first electrical machine m Lccordance with a second em-components tending to maintain said primary and said 20 bodiment of the mvenuon.

secondary spaced apart from one anotte r, sccor.d com- Referring to FIG. 1, the pnmary of a Station device ponents tending to maintain said primary and s?id m accordance with Ue invention comprises two longj-

ondary in alignment with one another in a direction of U-shaped cores 10 and 12.

perpendicular to said rows of pole faces and third com- a oriented transversely and comprises a ponents tending to cause relative displacement be- 25 of laminatlons of magnetic material Each core tween said primary and said secondary in a direction a r«Pecuv= P** ot m<1!n? 35 ™ .wmdmg.

parallel to ¿id rows of pole face». Thus this electrical V4' I6'18 and 20- °ne on 1,mb- The reiauve direc-

machine consists of both a linear motor and a leviution U0,f of,cu™,n the.v™dlngs 31 arrangement caily m the drawing, ooth rows of cores 10 and 12 have i. • i j i # » . . , 30 overall width W and have pole faces of wicfrh A m

It is already known that the use of magnetic material illustrated in the ^ondary of a levitation arrangement can im- ^ secondary member comprises a sheet 22 of non-

prove the performance For example in the case of a ^ eJecu(can ^nduaive material such as alu-

sunple coil floating (with no hteraUtabihty) above a ^^ ^ ^ shcet ^ ¿umMm b sul> conriuctjng sheet secondary, it has been shown that the 3J ^ ^ ^ ^ ^ ovcrall ^ of ^ ^ ^

levitated height per unit current can, in some orcum- stnicture.Te. from the outer edge of the limb 24 of the stanc«be .ncreasedof the conducting sheet is backed ^ !(j ^ ^ Qutcr ^ ofxhc\mh 26 oflhccore 12.

by a iheet of steel. The dimensions of the system deter- Twq ^^ ^ 3G 32f ^ uniaminaled mag-mine whether a height increase is obtained. ncljc ^ db ^ on ^ itc sidc of ^

It ts an object of the present invention to provide a 40 ^t 22 to the primary cores 10 and 12. Both cores 30

system consisting of both a linear motor and a levita- ^ 32 ^ ^ ^ widlh v/ as the primary cores 10

bon arrangement having magnetic material m the sec- and 12 but they are displaced inwardly relative to the ondaxy without impairing the lateral stability of levita- primrjy corc5 10 and 12 by an amount not substantially bon" . greater than the width A of the pole faces. Preferably

According to the present invention, there is provided 45 this -mward displacement is by a distance VfeA.

an elecuiral machine having a primary comprising a If the winding of successive U-shaped cores in each core of magnetic material having at least two pairs of raw m energized with single phase alternating current, rows of pole faces disposed in a common plane and a purc icvitation effect is produced, the secondary 22 arranged to provide paths for working tlux between the being supported above the primary and stabilized later-pole faces of each row in planes substantially perpen- 50 ally in alignment therewith. If successive coils in each dicular to said row*, and a secondary confronting said row are energized phases of a polyphase alternating pole faces and comprising electrically conductive ma- current supply, in addition to the levitation effect pro-terial arranged to provide longitudinal paths for dec- duced by the single phase energization, a travelling trie current on each sidc of each row of pole faces and magnet <c field is produced in the longitudinal direction transverse paths interconnecting said longitudinal 55 %q the secondary new tends to move longitudinally paths, and at least one core member of magnetic mate- with respect to the primary. As before, the secondary k rial extending longitudinally of the electrically conduc- supported above the primary and stabilized laterally, tive material on the opposite side thereof to the pri- Any of the winding configurations described in the mary and having its lateral edges so disposed relative to above-mentioned U.S. patent may be in&L the primary that the magnetic field produced when the 60 Alternatively, the secondary cores 30 and 32 may be primary is energized from a polyphase alternating cur- symmetrically disposed with respect to the coraespcmd-rent supply a operative to produce a force between ing primary cores 10 and 12 but, in this case, the later»! said primary and said secondary having first compo- stability is decreased somewhat, nents tending to maintain said primary and said secon- In BO. a vehicle 40 has a primary member similar dary spaced spart from one another, second compo- 65 to the primary of FIG. 1 in that it comprises two sets eg nents tending to maintain said primary and said secon- primary co^es 42 and 44 mounted on its underside, dary in alignment with one another in a lateral direo Each set of cores comprises two longitudinally extend-lion and third components tending to cause relative tag rows of U-shaped corss, each core being oriented

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