Abstract:
The engine ( 2 ) has a rotor ( 5 ) rotationally mounted about a rotational axis (A) and is provided with a superconductive winding ( 10 ) arranged in a winding support ( 9 ). In order to fix the winding support inside an external rotor housing ( 7 ), a rigid connecting device ( 8   a ) having a hollow cylindrical connecting element ( 12   c ) made of fiber reinforced plastic is provided on the torque transmitting side (AS). The connecting element ( 12   c ) is configured as a single piece and consists of end parts located on the front face and a central part located between the latter, wherein the end parts are corrugated in peripheral direction and are non-corrugated in the central part. The end parts of the connecting element ( 12   c ) are connected to and engage with one another in a non-positive fit manner in groovelike recesses of flangelike end pieces ( 12   a   , 12   b ) made of metal.

Description:
DESCRIPTION  
         [0001]    Machine having a superconducting winding, which is arranged in a winding former, and having means for torque transmission from the winding former to a shaft part  
           [0002]    The invention relates to a machine having a rotor which is mounted such that it can rotate about a rotation axis and has a rotor outer housing which is attached to axial rotor shaft parts and encloses a winding former with a superconducting winding. The rotor also has means for holding the winding former within the rotor outer housing, which means comprise a rigid connecting device, on a torque-transmitting side, between the winding former and the associated rotor shaft part with at least one torque-transmitting, hollow-cylindrical connecting element composed of plastic reinforced with fiber material. Furthermore, means are provided for cooling and thermal insulation of the superconducting winding. A corresponding machine is disclosed in U.S. Pat. No. 5,880,547 A.  
           [0003]    Electrical machines, in particular generators or motors, generally have a rotating field winding and a stationary stator winding. In this case, the current density and hence the specific power of the machine, that is to say the power per kilogram of its own weight, can be increased, and the efficiency of the machine can also be increased by the use of cryogenic conductors, in particular superconducting conductors.  
           [0004]    Cryogenic windings for electrical machines generally have to be thermally insulated from the environment and have to be kept at the necessary low temperature by means of a coolant. Effective thermal insulation can in this case be achieved only if the cryogenic parts of the machine are as far as possible separated from the warm outer area by a hard vacuum with a residual gas pressure of generally less than 10 −3  mbar, and if connecting parts between these cryogenic parts and the warm outer area transmit as little heat as possible.  
           [0005]    Two variants in particular are known for vacuum insulation of rotors with cryogenic rotor windings and warm stator windings: in a first embodiment, the rotor has a warm outer housing and a closed vacuum area which rotates with it. The vacuum area should in this case surround the cryogenic area on all sides (see, for example, “Siemens Research and Development Reports”, Volume 5, 1976, No. 1, pages 10 to 16). However, heat is transmitted in an undesirable manner to the cryogenic parts via supports which extend through the vacuum area. In a second embodiment, the essentially cold rotor rotates in a hard vacuum. In this case, the outer boundary of the hard vacuum area is defined by the inner bore in the stator. However, an arrangement such as this requires shaft seals which are proof against a hard vacuum between the rotor and the stator (see, for example, DE 27 53 461 A).  
           [0006]    The machine which is disclosed in the initially cited US-A document uses the first-mentioned embodiment. The superconducting winding of its rotor is located in the interior of a rotor cystostat which, together with flanged shafts that are fitted, forms an outer housing of the rotor. Helium cooling is provided for the superconductors of the winding. In contrast, the outer contour of the rotor outer housing is at approximately room temperature, and even possibly above room temperature during operation. The useful torque from the machine is produced in the rotor winding. The rotor winding is arranged in a cold winding former which is itself suspended or held in an insulated manner in the rotor outer housing, which acts as the cryostat. In this case, this suspension or retention on the drive side of the rotor, which is frequently referred to as the A side of the machine, must be sufficiently robust to transmit the torque from the cold winding former to a shaft part on the drive side. A corresponding rigid connecting device must therefore be designed to be relatively solid in order to transmit torque,  
           [0007]    and must be connected to the winding former and to the drive-side shaft part such that power can be transmitted. This leads to heat unavoidably being introduced into the cold area of the rotor. The connecting device is therefore frequently itself cooled (see, for example, “Handbook of Applied Superconductivity”, Vol. 2: Ed.: B. Seeber, Institute of Physics Publishing, Bristol (GB),  1998 , pages 1497 to 1499 and 1522 to 1530).  
           [0008]    At the same time, this connecting device also provides the drive-side centring for the cold winding former. On the opposite rotor side, which is also referred to as the non-drive side or in general also as the B side, because important connections for operation of the machine, such as a coolant supply, are provided in it, virtually no torque is emitted. Only the functions of centring and thermal insulation therefore need essentially be provided here. Furthermore, measures must be provided there to compensate for the shrinkage of the cooled-down winding former.  
           [0009]    In order to reduce the amount of heat which is introduced into the cooled superconducting area of the rotor, one specific embodiment of the known machine provides for the torque-transmitting connecting device to have, at least on the drive side, a hollow-cylindrical connecting element composed of a glass-fiber-reinforced plastic. This hollow cylinder is provided in each of its two axial ends with a coupling element made of steel, which is connected to the winding former and to the drive shaft such that power can be transmitted. The mechanical connection between the hollow cylinder composed of plastic and the coupling elements composed of steel must ensure a high degree of resistance to overloading and fatigue strength in response to alternating loads since considerably greater torques than during normal operation occur on motors such as these, for example during starting and in the event of various defects, and these must not cause any damage to the connecting device. However, the US-A document contains no details relating to the connection between the hollow cylinder and the coupling elements.  
           [0010]    In addition to metallic superconductor materials such as NbTi or Nb 3 Sn which have been known for a long time and are used in the machines mentioned above, metal-oxide superconductor materials with critical temperatures above 77 K have been known since 1987 as well. Attempts have been made using conductors made of such high-T c  superconductor materials, which are also referred to HTS materials, to produce superconducting windings for machines (see, for example, WO98/02953). Owing to the temperature differences between the operating temperature of the superconductor material and the outside temperature in the warmer rotor outer housing, even machines with this type of conductor require measures to reduce the temperature which is introduced into the superconducting area.  
           [0011]    The object of the present invention is to specify a suitable connecting device for torque transmission for a machine having the features mentioned initially, which device allows a connection which transmits power and ensures high fatigue strength and a high overload capacity in a relatively simple manner between the cold winding former and the associated warm rotor shaft part, and which in the process limits conductive heat losses to the cold winding former.  
           [0012]    According to the invention, this object is achieved by the features of claim  1 . According to this, in the case of the machine with the features mentioned initially, the connecting element should be composed integrally of end-face end parts with a center part located in between them, the end parts should have a corrugated shape seen in the circumferential direction, while the center part should not be corrugated, the connecting element should be connected on the end parts to flange-like end pieces composed of metal such that power can be transmitted when they engage in one another, with  
           [0013]    α) the end parts projecting completely and the center part in each case projecting to a certain extent into groove-like recesses in the respective flange-like end piece,  
           [0014]    β) at least one side wall of each recess having a corrugated shape which is matched to the corrugated shape of the respective end part,  
           [0015]    γ) the corrugated shape of each end part resting at least partially on the corrugated shape of the side wall of the corresponding recess, and  
           [0016]    δ) those parts of the connecting element which are arranged in the recesses being fixed by means of at least partial filling of the remaining areas of the recesses.  
           [0017]    Furthermore, the flange-like end pieces in the machine should be connected in a power-transmitting manner to an associated part of the winding former and/or to a side part, which is connected to the rotor shaft part, of the rotor outer housing.  
           [0018]    The advantages which are associated with this refinement of the machine are that the particular refinement of the hollow-cylindrical connecting element results in a good power-transmitting connection between the poorly thermally conducting part of the hollow-cylindrical connecting element and the metal parts of the winding former, at least in the area of its end-face end parts and owing to the corresponding configuration of the flange-like end pieces in the connecting area with these end parts. In this case, problems with the shear strength, in particular with respect to overloading and during continuous operation, are advantageously avoided in the connecting area between the plastic and the metal, which otherwise represents a weak point for torque transmission, in that the torque is now primarily transmitted by compression and less by shear in the groove-like cutouts. In order to improve the power transmission, the connecting element may be adhesively bonded to the flange-like end pieces. In this case, the end parts are effectively wedged into the groove-like recesses in the respective flange-like end piece by means of the filling. This is because the corresponding wedges composed of the filling material,  
           [0019]    such as a plastic which can be cured, then at least largely fill the intermediate spaces between the corrugated end parts and the side walls of the groove-like recesses. A wedging process such as this not only prevents the connecting element from sliding out of the recesses; in fact, this also improves the power transmission by means of compression forces instead of shear forces in the “metal-plastic” connecting area.  
           [0020]    Particularly uniform distribution of the forces when torque is being transmitted can be ensured by the corrugation on the at least one side wall of each cutout and the interlock with the respective correspondingly corrugated end part, seen in the circumferential direction. Since, in addition, the uncorrugated center part (which is in the form of a smooth hollow cylinder) of the connecting element likewise projects to a certain extent into each of the cutouts, where it is fixed and is thus connected to the respective metal end piece such that power can be transmitted, this avoids particular loads in the transitional area between the corrugated end part and the uncorrugated center part. The uncorrugated configuration of the center part also advantageously helps to reduce the risk of this part bulging.  
           [0021]    Advantageous refinements of the machine according to the invention can be found in the dependent claims.  
           [0022]    It can thus advantageously be regarded as advantageous to provide the end parts with a corrugated shape that is distributed uniformly over the circumference. In this case, the corrugated shape may preferably be sinusoidal. Such a refinement of the end parts and hence of the at least one side wall of the respectively associated groove-like recess makes it possible to ensure that power is transmitted particularly uniformly between these parts.  
           [0023]    It is also particularly advantageous for at least the majority (that is to say more than half) of the fibers of the fiber material to extend without any interruption over each transitional area between  
           [0024]    the respective end part and the center part of the connecting element. This is because fibers which pass through these areas contribute to these intrinsically critical areas being able to transmit a high power load. Known fiber materials, in particular glass fibers or carbon fibers, may be used as the fibers.  
           [0025]    In order to improve the power transmission and to ensure good torque transmission between the flange-like end pieces and the winding former, or the drive-side rotor shaft part, the end pieces are each advantageously provided with an end-face tooth system which engages in a corresponding tooth system of the respective mating piece. The tooth system may in this case intrinsically be designed to be self-locking. Appropriate tooth systems are known per se.  
           [0026]    Either metallic low-T c  superconductor material or, in particular, metal-oxide high-T c  superconductor material may be used for the conductors of the superconducting winding. The use of metal-oxide high-T c  superconductor material makes the cooling process easier.  
           [0027]    Further advantageous refinements of the machine according to the invention are the subject matter of the remaining dependent claims. 
       
    
    
       [0028]    One preferred exemplary embodiment of a machine according to the invention will be explained in more detail in the following text with reference to the drawing in which, in each case shown schematically:  
         [0029]    [0029]FIG. 1 shows one possible embodiment of the machine, in the form of a longitudinal section,  
         [0030]    [0030]FIG. 2 shows a specific refinement of a connecting device for this machine, in the form of a longitudinal section,  
         [0031]    [0031]FIG. 3 shows a front view of a flange-like end piece of the connecting device shown in FIG. 2, and  
         [0032]    FIGS.  4  to  6  respectively show a front view, an oblique view and a longitudinal section view of a connecting element for the connecting device shown in FIG. 2. 
     
    
       [0033]    Corresponding parts in the figures are provided with the same reference symbols.  
         [0034]    The embodiment of the machine as described in the following text may in particular be a synchronous motor or a generator. Other fields of application or use for corresponding machines are, of course, also possible, for example for high rotation speeds, compact drives, for example for ships or for so-called offshore facilities such as drilling platforms. The machine according to the invention has a rotating superconducting winding which in principle allows the use of metallic LTS material (low-T c  superconductor material) or, in particular, oxide HTS material (high-T c  superconductor material). The latter material is assumed to have been chosen for the following exemplary embodiment. The winding may comprise a coil or a system of coils in an arrangement with 2, 4 or some other number of poles. The basic design of a synchronous machine such as this is shown in FIG. 1, based on the assumption of known embodiments of such machines (see, for example, the prior art as cited above).  
         [0035]    The machine, which is denoted in general by  2 , comprises a stationary machine outer housing  3  which is at room temperature and has a stator winding  4 . A rotor  5  is mounted in bearings  6   a  and  6   b  within this outer housing and surrounded by the stator winding  4 , such that it can rotate about a rotation axis A. For this purpose, the rotor has a rotor outer housing  7  which is in the form of a vacuum vessel and in which a winding former  9  with an HTS winding  10  is held. On its axially opposite (end) faces, this rotor outer housing in each case has a side part  7   a  or  7   b  in the form of a disk or annular disk. Each of these side parts is  
         [0036]    connected rigidly to a solid axial rotor shaft part  5   a  or  5   b , with each rotor shaft part having an associated bearing  6   a  or  6   b , respectively. A rigid tubular connecting device  8   a  is provided on the so-called drive side AS of the rotor outer housing  7  between the winding former  9  and the side part  7   a  of the rotor outer housing, which side part  7   a  is in the form of a disk and is firmly connected to the rotor shaft part  5   a . The torque is also transmitted via the rigid connecting device  8   a , designed according to the invention, with flange-like end pieces  12   a  and  12   b  at the ends and with a connecting element  12   c  running in between them (see FIG. 2). The connecting device advantageously essentially comprises a poorly thermally conductive hollow cylinder which is composed of a plastic material reinforced with fibers such as glass fibers (so-called “GFC” material). In this way, the fibers are laid in a manner known per se in the plastic material which is used as a matrix for them and is selected on the basis of its strength. The fibers in this case advantageously run obliquely in the plastic material with respect to the rotation axis A, that is to say not parallel or at right angles to it. If required, they may also be located in different layers, in which case their angle with respect to the axis may also differ. The composite material formed in this way then ensures sufficiently high mechanical stiffness for torque transmission and a high thrust modulus (G modulus) with low thermal conductivity at the same time. Further details of the connecting device are illustrated in FIG. 2. As can also be seen from FIG. 1, a further connecting device  8   b  is arranged on the non-drive side, which is the opposite side to the drive side AS and is referred to in the following text as BS, between the winding former  9  and the side part  7   b  of the rotor outer housing  7  which is in the form of a disk. A coolant supply, inter alia, for cooling the superconducting winding  10  is provided from outside the machine on this side BS via the hollow-cylindrical shaft part  5   b . Details of the coolant supply and of the sealing are known. The figure therefore does not provide a  
         [0037]    detailed illustration. A vacuum which surrounds the winding former  9  with the superconducting winding  10  is annotated V. The vacuum is formed in particular between the warm rotor outer housing  7  and the winding former  9 . Further known measures for thermal insulation, such as superinsulation, are not shown in the illustration.  
         [0038]    GFC parts are advantageously used to reduce the amount of heat which is introduced from the warm side parts  7   a  and  7   b  (which are at room temperature) of the rotor outer housing into the cold part of the winding form  9 , which is at low temperature, and hence into the cold winding  10 . One specific embodiment of a connecting device  8   a  on the drive side AS is shown in the form of the longitudinal section in FIG. 2. The connecting device  8   b  on the non-drive side BS may have corresponding features. It should also be designed to allow axial compensation for expansion resulting from shrinkage of cooled-down rotor parts.  
         [0039]    The essentially hollow-cylindrical connecting device  8   a  which can be inserted between the winding former  9  and the side part  7   a  has, as is shown in FIG. 2, a flange-like end piece  12   a  and  12   b  at each of its two opposite axial ends, with a connecting element  12   c  extending between these end pieces. While the end pieces  12   a  and  12   b  are composed of a metallic material, in particular such as steel or some other fatigue-resistant material which is suitable for use at low temperatures, the connecting element  12   c  is manufactured in particular from GFC. Both of the axial end faces of a connecting element project with end parts  16   a  and  16   b , which are shown in more detail in FIGS.  4  to  6 , into corresponding recesses or grooves  13   a  and  13   b , respectively, in the respectively associated end piece and, according to the invention, are connected to this end piece there.  
         [0040]    In order to transmit high torques between the flange-like end pieces  12   a  and  12   b  and the winding former  9 , or the drive-side side part  7   a , the respective flange-like end piece  12   a  or  12   b  is not just screwed to the respective winding former  9  or the side part  7   a . FIGS. 2 and 3 show corresponding holes for screwing on the flange-like end pieces, which are generally annotated  15   i . In fact, each end piece advantageously has an end-face tooth system  14 , which can be seen in the side view in FIG. 3, with projecting teeth  14   a  and groove-like intermediate spaces  14   b  between them. The tooth system is in this case designed in a manner known per se so as to produce a self-centring connection which can transmit power, in which case the torque can be passed on over a relatively large radius. The mating surface of the winding former  9  or of the side part  7   a  has a corresponding tooth system, with the teeth  14   a  in the tooth system  14  on the flange-like end piece  12   a  engaging in corresponding grooves in the mating surface of the winding former.  
         [0041]    In particular, it must also be possible to transmit high torques from the machine between the GFC connecting element  12   c  and the flange-like end pieces  12   a  and  12   b . The measures according to the invention are aimed at this purpose. Those end-face ends of the connecting element which project into the end pieces are accordingly specially designed for this purpose. As can be seen from the front view in FIG. 4, from the oblique view in FIG. 5 and from the longitudinal section view in FIG. 6, the hollow-cylindrical connecting element  12   c  has end parts  16   a  and  16   b  with a special design on both of its axial end faces. Rather than having the smooth (uncorrugated) annular form of a tubular center part  16   c , these end parts are structured or formed in the circumferential direction such that they are provided with a regular corrugation, with projections  17   j  and depressions  18   j , seen in the circumferential direction (see, in particular, FIG. 4). Such corrugation can preferably be applied during the production of the connecting element by appropriate forming while still in a deformable stage, with the fiber reinforcement advantageously not being damaged, so that the mechanical robustness of the composite material is maintained. The connecting element  12   c  is thus formed integrally with the center part  16   c  and its end-face end parts  16   a  and  16   b . The corrugation of the end parts on which the figures are based is preferably sinusoidal and, in particular, is distributed uniformly over the entire circumference, for reasons associated with good torque transmission. If required, however, other corrugation shapes may also be provided and, furthermore, the circumference need be provided with corrugation only in individual areas.  
         [0042]    The ends of the connecting element  12   c  together with its corrugated end parts are fitted into the annular, groove-like recesses  13   a  and  13   b  in the respective flange-like end piece. In order to ensure a good power-transmitting connection between the end pieces  12   a  and  12   b  and the connecting element  12   c , each of the recesses in the end pieces has on its outer side wall, seen in the radial direction, and/or its opposite inner side wall, a corrugation which corresponds to the corrugation on the respective end part  16   a  or  16   b . The respective end part is fitted in an interlocking manner to at least one of these walls. For this purpose, the remaining intermediate spaces between the side walls of the recesses and the corrugated end parts are filled with a filling composed of an adhesive material, preferably a plastic which can be cured. This thus results in wedge-like fillers for recesses which are corrugated on one side.  
         [0043]    According to the invention, the groove-like recesses should have a groove depth such that it is not just possible to completely accommodate the end parts of the connecting element, but such that a piece of the center part  16   c  also projects into each recess. To do this, the recess must, of course, have a width, which is possibly also stepped, such that both the respective end part and  
         [0044]    a piece of the center part can be inserted into it. The piece of the inserted center part is likewise adhesively bonded there to the respective metallic end piece. This makes it possible to prevent particularly high loads in the transitional area from the corrugated end part to the uncorrugated center part. Effective torque transmission between the metallic end pieces  12   a  and  12   b  and the non-metallic connecting element  12   c  is thus ensured, without there being any risk of damage to the connecting areas between these parts when high torsion forces occur. Furthermore, this is a precautionary measure against the possibility of cracks forming on edges.  
         [0045]    Other refinements of the end parts of the connecting element and hence of the associated opening in the respective end piece are, of course, also possible to the extent that projections and depressions, which engage in one another and are distributed regularly in this direction when seen in the circumferential direction, on the parts to be connected prevent any respective twisting in the circumferential direction, and ensure the required torque transmission. These requirements can be satisfied in particular with the corrugation as shown in FIGS.  4  to  6 . However, special tooth systems are also feasible.  
         [0046]    The chosen exemplary embodiment is based on the assumption that a glass-fiber-reinforced plastic (GFC) is used for the connecting element  12   c . It is, of course, also possible to use plastics reinforced with other fibers, such as carbon fibers, provided that these materials make it possible to ensure that the torque is transmitted, with little heat transmission at the same time.  
         [0047]    Furthermore, instead of having a single hollow-cylindrical connection element, the connecting device according to the invention may have two or more concentrically surrounding elements which, if required, also have their own flange-like concentrically surrounding end pieces.