Abstract:
A method and a magnetic levitation vehicle operating with this method are described. For the control of support gaps ( 10   a   , 10   b ) that are formed during operation of the magnetic levitation vehicle ( 1 ) between a track ( 2, 3, 4 ) and a number of carrying magnets ( 6   a   , 6   b ) fastened to said magnetic levitation vehicle ( 1 ) and provided with windings ( 16   a   , 16   b ), wherein at least two carrying magnets ( 6   a   , 6   b ) in adjacent positions act upon a suspension frame ( 8 ) of said magnetic levitation vehicle ( 1 ), the electrical currents flowing through the windings ( 16   a   , 16   b ) are so controlled that the support gaps ( 10   a   , 10   b ) between these two carrying magnets ( 6   a   , 6   b ) and the track ( 2, 3, 4 ) adopt pre-determined nominal values (na, nb). In accordance with the invention and in case that the currents through the windings ( 16   a   , 16   b ) of the adjacent carrying magnets ( 6   a ) are different under normal conditions, the nominal values (na, nb) for the support gaps ( 10   a   , 10   b ) are altered such that the current through the windings ( 16   a  or  16   b ) of a carrying magnet ( 6   a   , 6   b ) with the lower electric current is increased and/or the electric current through the winding ( 16   b  and/or  16   a ) of a carrying magnet ( 6   b   , 6   a ) with the larger electric current is reduced.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   The invention described and claimed hereinbelow is also described in German Patent Application DE 10 2004 013 692.0 filed on Mar. 18, 2004. This German Patent Application, whose subject matter is incorporated here by reference, provides the basis for a claim of priority of invention under 35 U.S.C. 119(a)-(d). 
   BACKGROUND OF THE INVENTION 
   The present invention relates to a method for control of support gaps for a magnetic levitation vehicle, and also to a magnetic levitation vehicle with a control circuit operating with said method. 
   The invention relates to a method pursuant to the preamble of claim  1  and to a magnetic levitation vehicle pursuant to the preamble of claim  4 . 
   Magnetic levitation vehicles, particularly those equipped with long stator linear motors, have a number of carrying (supporting) magnets mounted in the direction of travel and facing a guideway for the magnetic levitation vehicle, particularly a long stator mounted to it. For operation of the magnetic levitation vehicle, the carrying magnets are activated at first in order to form support gaps of a given height between the guideway and the magnetic levitation vehicle (e.g. 10 mm). Next the magnetic levitation vehicle is set in motion, for which purpose the carrying magnets in case of long stator linear motors simultaneously supply the excitation field for the linear motor (e.g. DE 39 17 058 C1). Compliance with the nominal values defined for the support gaps is assured by gap sensors (e.g. DE 35 16 036 C2) and control circuits connected to them which control the electrical currents in the windings of the carrying magnets in such a manner that the support gaps during operation substantially retain the same size (e.g. “Magnetschnellbahn Transrapid-Technik und System”, Thyssen Transrapid GmbH, MSB Tr10/96). 
   The carrying magnets of such magnetic levitation vehicles are generally mounted to support brackets which in turn are fastened to suspension frames or the like for a car body. The mechanical setup is preferably so chosen that two support brackets each are provided at the longitudinal ends of the suspension frames and fastened to different carrying magnets in a way that at least two neighbouring carrying magnets act there upon the suspension frame. 
   On account of unavoidable tolerances, e.g. in the sensor signals indicating the actual values of the support gaps, in the control circuits connected with the sensors as well as in the mechanical structure, it may happen that the windings of neighbouring carrying magnets are flown through by differently high electrical currents, although they establish the same support gap. This is undesirable, because different electrical currents lead to different loads of the windings, e.g. due to heat development. 
   SUMMARY OF THE INVENTION 
   The technical problem underlying the present invention therefore is to modify the method and the magnetic levitation vehicle of the above mentioned species in such a manner that differences, if any, between the electrical currents flowing through the windings of neighbouring carrying magnets are reduced or even brought to zero despite the above mentioned tolerances. 
   In keeping with these objects, one feature of the present invention resides, briefly stated, in a method applied in a magnetic levitation vehicle to control support gaps that are formed during operation of the magnetic levitation vehicle between a track and a number of carrying magnets fastened to said magnetic levitation vehicle and provided with windings wherein at least two carrying magnets in adjacent positions act upon a suspension frame of said magnetic levitation vehicle and wherein the electrical currents flowing through the windings are so controlled that the support gaps between these two carrying magnets in said adjacent positions and the track adopt pre-determined nominal values of equal size, characterized in that in case that for obtaining said predetermined values the currents through the windings of the adjacent carrying magnets must be different under normal conditions, the nominal values for the support gaps are altered such that the current through the windings of a carrying magnet with the lower electric current is increased and/or the electric current through the winding of a carrying magnet with the larger electric current is reduced. 
   Another feature of the present invention resides, in a magnetic levitation vehicle having control circuits for controlling support gaps formed during its operation between a track and a number of carrying magnets fastened to said vehicle and provided with windings wherein the control circuits have means for controlling electrical currents flowing through said windings in such a way that the support gaps adopt pre-determined nominal values, characterized in that means for correcting respective nominal values is dependence on the electrical currents flowing through said windings are assigned to the control circuits of at least two adjacent carrying magnets. 
   The invention bears the advantage that when undesirable differences occur between the winding currents of neighbouring carrying magnets a levelling of the magnetic currents is performed, and that slight differences in the support gaps generated by the respective carrying magnets are tolerated instead thereof. Such deviations from the nominal values for the support gaps are taken-up and absorbed by the mechanical structures of the suspension frames, without impairing the travelling comfort or entailing other disadvantages, and therefore these deviations can be tolerated without any problem. 
   The invention is explained in greater detail hereinbelow by means of an embodiment and based on the drawings enclosed hereto wherein: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  schematically shows a partial section through a usual magnetic levitation vehicle in the area of a track provided with a long stator; 
       FIG. 2  schematically shows two control circuits for neighbouring carrying magnets of a magnetic levitation vehicle; and 
       FIG. 3  in various graphical representations shows the control strategy pursued by the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  and  FIG. 2  schematically show a magnetic levitation vehicle  1  which is conventionally movably mounted on a guideway extending in longitudinal direction of a route, said guideway being comprised of supports  2  made of steel and/or concrete as well as guideway plates  3  mounted on it. The propulsion of the magnetic levitation vehicle  1  is effected, for example, by a long stator motor which comprises stator packets  4  affixed underneath said guideway plate  3  and arranged consecutively in the longitudinal direction thereof. As shown on  FIG. 2 , the stator packets  4  have alternatingly succeeding teeth  5   a  and grooves  5   b  into which three-phase alternating current windings are inserted (not shown) that are fed with three-phase current of a variable amplitude and frequency. The actual excitation field of the long stator motor is generated by magnet arrangements acting as carrying magnets  6   a ,  6   b  which are affixed by at least one lateral support bracket  7  to a suspension frame  8  of said magnetic levitation vehicle  1  and which have magnet poles  9   a ,  9   b  facing the grooves  5   b  of stator packets  4 . The carrying magnets  6   a ,  6   b  not only provide the excitation field, but also fulfil the function of carrying and levitating by maintaining given gaps  10   a  and/or  10   b  with heights of sa and/or sb between said carrying magnets  6   a ,  6   b  and said guideway or the stator packets  4  thereof during operation of the magnetic levitation vehicle  1 . 
   For a proper guidance of the magnetic levitation vehicle  1  on the track, the guideway plate  3  is provided with laterally affixed lateral guide rails  11 , which are faced by guiding magnets  12  also mounted to the support brackets  7  and serving for maintaining a gap  14  corresponding to gap  10   a ,  10   b  between itself and the guiding rail  10  during operation of the vehicle. 
   Magnetic levitation vehicles  1  and their magnet arrangements are generally known to an expert, e.g. through printed publications U.S. Pat. No. 4,698,895, DE 39 28 278 A1, and PCT WO 97/30504 A1, which for the sake of simplicity are made a part of the present disclosure by reference thereto. 
   The embodiment according to  FIG. 2  shows two neighbored carrying magnets  6   a  and  6   b  which are mounted one behind the other in the direction of travel, from which magnets  6   a ,  6   b  only two end sections facing each other and having a magnet pole  9   a  and  9   b  each are shown. In fact, each carrying magnet  6   a ,  6   b  is preferably comprised of a magnet arrangement having a number of e.g. twelve magnet poles  9   a  and/or  9   b  mounted at a certain distance to each other in the direction of travel. Each magnet pole  9   a ,  9   b  comprises a core  15   a ,  15   b  and a winding  16   a ,  16   b  surrounding it. 
   For example, the carrying magnets  6   a ,  6   b  face the stator packets  4  in such a way that the quantities sa and sb of the support gaps  10   a ,  10   b  for instance amount to 17 mm, when the magnetic levitation vehicle  1  is out of operation, i.e. when it is in a status set down on a gliding rail, while a value of 10 mm is maintained, for example, to establish the suspended status which is typical of the magnetic levitation vehicle  1 . 
   The control circuits  17   a  and  17   b  schematically indicated on  FIG. 2  serve for maintaining the given nominal values of e.g. 10 mm for the support gaps  10   a ,  10   b . The control circuit  17   a  has a gap sensor  19   a , which measures the actual size or the actual value, respectively, of gap  10   a  between the carrying magnet  6   a  or its magnet pole  9   a  and the stator packets  4  and which supplies an electrical signal that corresponds to the actual value of the quantity sa. The gap sensor  18   a  is connected via a comparative circuit  19   a  to which a nominal value for gap  10   a  is fed to via a line  20   a  to a controller  21   a . The comparative circuit  19   a  compares the actual values sa of the gap sensor  18   a  with the nominal value na and supplies at its output a differential signal by means of which a control signal is generated in the controller  21  and fed to an actuator element  22   a . The actuator element  22   a  generates an electrical current for the winding  16   a  of the carrying magnet  6   a  and particularly supplies such an electric current to this winding  16   a  that the size sa of gap  10   a  permanently substantially corresponds to the nominal value na that is pre-determined via the line  20   a.    
   The control circuit  17   b  is set-up accordingly, which is the reason why its component parts are designated with the corresponding reference symbols  18   b  to  22   b  and nb. The control circuit  17   b  serves for controlling a gap  10   b  of the size sb between the carrying magnets  6   b  and the stator packets  4 . 
   Finally, in  FIG. 2 , one of the suspension frames  8  of the magnetic levitation vehicle  1  is indicated which is supported at one end by the carrying magnet  6   a  and at the other end by the neighbouring carrying magnet  6   b . In a normal case, therefore, both carrying magnets  6   a  and  6   b  should adjust and set the respective support gap  10   a ,  10   b  substantially to identical values na and nb as schematically shown on  FIG. 3   b . Because of the tolerances outlined hereinabove (e.g. faults in measuring signals of gap sensors  18   a ,  18   b ), it may happen that the electric currents through the windings  16   a ,  16   b  of the two carrying magnets  6   a  and  6   b  acting upon the suspension frame  8  differ from each other. This is indicated for example on  FIG. 3   a , where the reference number  23   a  indicates the electric current through the winding  16   a , and where the reference numbers  23   b  indicates the electric current through the winding  16   b . For avoidance of such different electric currents, the procedure according to this invention is as follows. 
   To begin with, a corrective circuit  24  ( FIG. 1 ) is provided, which has two inputs connected with the outputs of the actuator elements  22   a ,  22   b  and two outputs that each lead to one of the two comparative circuits  19   a ,  19   b  with which also the lines  20   a ,  20   b  are connected which define the nominal values na, nb for the support gaps  10   a ,  10   b . Based upon the different output values of the actuator elements  22   a  and  22   b  being proportional to the electric currents  23   a ,  23   b  ( FIG. 2   a ) flowing through the windings  16   a ,  16   b , corrective values for the nominal values na, nb of the support gaps  10   a ,  10   b  are calculated in the corrective circuit  24 . In a special case (electric current  23   a &gt;electric current  23   b ), a signal for the comparative circuit  19   b  is calculated from this difference in electric current by means of which signal the nominal value nb for the support gap  10   b  is reduced. Thereby, the winding  16   b  receives more electric current, thus making the support gap  10   b  smaller as compared with support gap  10   a , as shown on  FIG. 3   d . This influence on the nominal value nb is exerted until the electric currents through the two windings  16   a ,  16   b  are substantially equal. 
   However, a lower limit value, i.e. a pre-selected minimal value, is pre-determined for the support gap  10   b  which lies for example at 9 mm instead of the usual 10 mm and which is designated with uG on  FIG. 3   d . If no balance in electric currents through the windings  16   a ,  16   b  is achieved when reaching this limit value uG, then a corrective value is also fed now to the comparative circuit  19   a  by way of which the nominal value na for the electric current through the winding  16   a  is reduced. As a consequence hereof, the size sa of the support gap  10   a  becomes greater than the value that corresponds to the nominal value na ( FIG. 2   d ). Also this correction is only made until an upper limit value oG, i.e. for example a pre-determined maximal value of 11 mm instead of the usual 10 mm is reached. 
   Usually, a balance in the winding currents corresponding to a value  25  in  FIG. 3   c  can constantly be obtained in this way, and the magnetic levitation vehicle  1  is then operated with slightly different support gaps  10   a ,  10   b . Even if the electric currents through the two windings  16   a ,  16   b  are not yet identical to each other after these corrections have been made, they are nevertheless so close to each other that on the one hand the resultant different thermal losses in the windings  16   a ,  16   b  can be tolerated and that on the other hand the values sa, sb obtained for the support gaps  10   a ,  10   b  are adequately close to the desired nominal values na, nb, so that the different load distribution associated therewith can also be tolerated. 
   Differences between the winding currents that have once been determined by way of the corrective circuit  24  are basically maintained permanently. If they vary however, in the course of operation of the magnetic levitation vehicle, at first the enhancement of the support gap  10   a , and then, if required, also the reduction of the support gap  10   b  is cancelled. Moreover, the corrections of the nominal values na, nb as described hereinabove are immediately cancelled in case of a failure of the carrying magnets  6   a ,  6   b  involved. 
   Thus, if unavoidable fabrication tolerances and the like occur, the control strategy as described before does not intend to keep the support gaps  10   a ,  10   b  constant at equal pre-determined values sa and/or sb, but to provide for equal winding currents  25  ( FIG. 3   c ), if possible, while tolerating minor gap discrepancies. 
   The invention is not limited to the described embodiment that can be diversified in a plurality of ways. In particular, this applies to the values for the quantities na, nb of the support gaps  10   a  and  10   b , which are only given by way example, and for their upper and/or lower limit values. Furthermore, the corrective circuit  24  only represents a possible means for correction of the nominal values na, nb, because an expert in control engineering can also perform these corrections in any other expedient way. Moreover, it would be conceivable to apply the described control approach in a suitable variation also for the adaption of the winding currents to each other of more than two neighbouring carrying magnets. Besides, it is obvious that the number of windings  16   a ,  16   b  per carrying magnet  6   a ,  6   b  can be chosen to be different and that each carrying magnet  6   a ,  6   b , in particular, may be a half-magnet, for example, whose windings are connected to a control circuit allocated to it but is independent of the respective other half-magnet. It would also be possible to divide the corrective circuit  24  into two sections which are individually allocated to the control circuits  17   a  and  17   b , respectively. Finally it is self-explanatory that the different features can also be applied in combinations other than those described and shown hereinabove.