Abstract:
A bearing arrangement for the rotatable mounting of a shaft ( 7 ) in relation to a housing ( 8 ), including a back-up bearing ( 9 ) which is designed as a rolling bearing, wherein the rolling bearing can absorb forces in the axial and radial direction and is designed in particular as an angular rolling bearing, especially as a two-row angular ball bearing, wherein the rolling bearing ( 9 ) is substantially free in the radial direction. The problem addressed by the invention is that of providing a bearing arrangement with a back-up bearing for a shaft, which bearing arrangement can better absorb in particular the forces occurring in the mounting of rapidly rotating, solid shafts.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a bearing arrangement having a back-up bearing, in particular as a component of the bearing of a rapidly rotating shaft. 
         [0002]    Bearings are known in practice, wherein a shaft is supported rotatably in, for example, magnetic bearings. The bearing comprises a bearing arrangement having a back-up bearing, with the at least one back-up bearing receiving the shaft if the magnetic bearing fails. During normal operation of the at least one magnetic bearing, a back-up bearing gap is formed between the outer face of the shaft and an outer face of the inner bearing ring of the back-up bearing, which outer face is directed towards the shaft. 
         [0003]    It is problematic to take up very rapidly rotating shafts having a great weight. In this instance, very high forces and moments which may damage the back-up bearing occur. Furthermore, during normal operation of the magnetic bearings, the shaft falls eccentrically relative to the axis of rotation into the back-up bearing which is consequently subjected to an impact load occurring at the periphery in a non-uniform manner. 
       SUMMARY 
       [0004]    An object of the invention is to provide a bearing arrangement which has a back-up bearing for a shaft and which can better take up particularly the forces occurring when rapidly rotating shafts are received. 
         [0005]    This object is achieved according to the invention by a bearing arrangement for rotatably supporting a shaft relative to a housing, comprising a back-up bearing which is in the form of a rolling bearing, with the rolling bearing being able to take up forces in an axial and radial direction and in particular being in the form of an angular rolling bearing, especially a two-row angular ball bearing, with the rolling bearing being substantially free in a radial direction. 
         [0006]    As a result of the freedom of the rolling bearing in a radial direction in force terms, the rolling bearing preferably takes up in an axial direction forces whose centering effect on the effect falling into the back-up bearing can be used. The rolling bearing acts in a radial direction substantially as a movable bearing. However, the rolling bearing is securely fixed in the surrounding construction and is not supported, for instance, in a floating manner so as to be generally displaceable in an axial direction. 
         [0007]    There is preferably provision for there to be provided a bearing receiving member on which the outer ring of the rolling bearing is arranged, with the bearing receiving member having a peripheral material weakening, in particular peripheral grooves. The peripheral material weakening reduces the absorption of forces in an axial direction only to a small extent but brings about a selectively produced resilience in a radial direction. 
         [0008]    There is preferably provision for a corrugated strip gap which is delimited by the outer ring to be constructed so as to be radially enlarged. The corrugated strip gap is constructed at one side by the outer face of the outer ring and at another side by a face of either a housing or a bearing receiving member which is arranged between the rolling bearing and the housing. The radial development, especially the radial extent, of the corrugated strip gap can be, for example, doubled or multiplied in a selective manner. As a result of the substantially increased construction of the corrugated strip gap, the rolling bearing provided as a back-up bearing is deflected more powerfully in a radial direction if the shaft falls into the back-up bearing and transmits forces to a lesser extent in a radial direction than in an axial direction in a preferred manner. This applies both to the case that a corrugated strip is arranged in the corrugated strip gap and to the case that no corrugated strip is provided in the corrugated strip gap and the corrugated strip gap is therefore left free. 
         [0009]    There is preferably provision for a corrugated strip ( 12 ) having reduced rigidity to be arranged in the corrugated strip gap. As a result of the reduced rigidity, the corrugated strip is very resilient with respect to radially occurring forces so that the back-up bearing takes up axial forces to a greater extent than radial forces. 
         [0010]    There is preferably provision for the outer ring of the rolling bearing to be fixed to a first portion of a bearing receiving member, with a second portion of the bearing receiving member being arranged between the first portion of the bearing receiving member and the housing, and with the two portions of the bearing receiving member being resiliently supported on each other in a radial direction. The bearing receiving member is a component which is arranged between the back-up bearing and the fixed housing and which is constructed so as to be divided in two in a radial direction, with the two portions, that is to say, the first, radially inner portion in relation to the rotation axis of the shaft and the second, radially outer portion, being resiliently supported on each other. The resilient means between the two portions of the bearing receiving member takes up in particular displacements in a radial direction so that the back-up bearing can take up and transmit the forces in particular in an axial direction. 
         [0011]    There is preferably provision for the inner ring of the rolling bearing to form with the shaft a first friction face pair and for the outer ring of the rolling bearing to form a second friction face pair at least indirectly, with the friction properties of the two friction face pairs being adjusted for a friction-controlled self-centering action of the inner ring of the rolling bearing in relation to the shaft. 
         [0012]    With regard to the construction of the two friction face pairs, there is preferably provision for the friction of one of the friction face pairs to be increased by means of coatings, linings, surface roughness or surface structures in relation to the friction properties of the other friction face pair. 
         [0013]    With regard to the construction of the two friction face pairs, there is preferably further provision for the friction of the other friction face pair to be reduced by means of coatings or reduced surface roughness. 
         [0014]    There is preferably provision for an end face of the inner ring of the rolling bearing to cooperate with a radially offset edge face on the shaft. In the region of the end face, in particular axial forces are introduced into the rolling bearing. The edge face and the end face form a guiding face pair which can be used by the shaft which falls into the back-up shaft to center the inner ring. In particular, the end face and the edge face may form a first friction face pair, whose friction properties can be adjusted selectively in order to make it easier to center the inner ring in a friction-controlled manner relative to the falling shaft. That is particularly possible even if both the end face of the inner ring and the edge face on the shaft are orientated substantially radially, that is to say, at an angle of approximately 90°, relative to the rotation axis of the shaft. 
         [0015]    With regard to the edge face and the end face, there is preferably provision for the edge face and the end face to be formed so as to be at least partially inclined and to form a guiding face pair. As a result of the inclined construction, the centered orientation of the inner ring is supported in relation to the falling shaft. 
         [0016]    With regard to the edge face and the end face, there is preferably provision for the edge face and the end face to define an angle relative to the rotation axis of the shaft, in particular a high angle relative to the rotation axis. 
         [0017]    Alternatively, there is preferably provision for the edge face to partially define an angle relative to the rotation axis, and with the end face having a rounded portion which cooperates with the inclined portion of the edge face. The end face of the inner ring is partially constructed so as to be, for example, of convex-toroidal  form, with the convex-toroidal portion cooperating with the inclined portion of the edge face. 
         [0018]    There is preferably provision for a resilient element to be arranged between the edge face and the end face. The resilient element is tensioned when the shaft falls by means of the edge face into the rolling bearing onto a face of the inner ring and supports the orientation of the inner ring in relation to the falling shaft. In order to receive the resilient element, the inner ring may have an angle relative to the rotation axis of the shaft, for example, an angle of 45°, and the edge face may project substantially perpendicularly relative to the rotation axis of the shaft so that a peripheral receiving space for the resilient element is provided. 
         [0019]    Alternatively to an angular rolling bearing which can take up both axial and radial forces, there is preferably provision for the rolling bearing to be constructed as a substantially axially acting bearing, with the bearing races of the rolling members at one bearing ring of the rolling bearing being surrounded to a greater extent than at the other bearing ring of the rolling bearing. In this instance, there is provision for the rolling bearing to be constructed as a substantially axially acting bearing, with a radial adjustment taking place during the rolling contact. At the high rotary speeds which occur when the shaft is received in the back-up bearing, the surrounding action at the first bearing ring ensures that the rolling members are retained in the rolling bearing. In this instance, the other bearing ring can be constructed so as to be substantially planar. 
         [0020]    The invention also includes the use of an axial bearing, which can take up forces substantially only in an axial direction, in order to transmit forces axially to the back-up bearing. The axial bearing may be, for example, an axial cylinder roller bearing. The invention also relates to the use of an axial bearing which can take up forces only in an axial direction as an axial back-up bearing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    Other advantages and features will be appreciated from the dependent claims and the following description of preferred embodiments of the invention. 
           [0022]    The invention is described and explained in greater detail below with reference to the appended drawings. 
           [0023]      FIG. 1  is a schematic cross-section through a first embodiment of a bearing receiving member as part of a bearing arrangement according to the invention, 
           [0024]      FIG. 2  is a schematic cross-section through a second embodiment of a bearing arrangement according to the invention, with the detail “X” being illustrated to a larger scale at the bottom right-hand side, 
           [0025]      FIG. 3  is a cutout of a cross-section through a third embodiment of a bearing arrangement according to the invention, 
           [0026]      FIG. 4  is a cutout of a cross-section through a fourth embodiment of a bearing arrangement according to the invention, 
           [0027]      FIG. 5  is a cutout of a cross-section through a fifth embodiment of a bearing arrangement according to the invention, 
           [0028]      FIG. 6  is a cutout of a cross-section through a sixth embodiment of a bearing arrangement according to the invention, 
           [0029]      FIG. 7  is a cutout of a cross-section through a seventh embodiment of a bearing arrangement according to the invention, and 
           [0030]      FIG. 8  is a cutout of a cross-section through an eighth embodiment of a bearing arrangement according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]      FIG. 1  shows a bearing arrangement, in which a shaft is supported rotatably about a rotation axis  1  by means of magnetic bearings. The bearing arrangement comprises at least one back-up bearing which is in the form of a rolling bearing, particularly a two-row angular ball bearing, and can take up forces both in an axial and in a radial direction. An outer ring of the rolling bearing is arranged on an inner face  2  of a bearing receiving member  3 , which inner face is directed toward the rotation axis  1 . The bearing receiving member  3  is arranged with an outer face  4  on a connection construction on a connection construction, for example, on a housing fixed in position. An inner ring of the rolling bearing is spaced apart from the outer face of the shaft by a back-up bearing gap as long as the shaft is supported in the magnetic bearings. 
         [0032]    The bearing arrangement is part of the bearing of a rapidly rotating shaft. If the magnetic bearing fails, the shaft falls into the back-up bearing. 
         [0033]    The rolling bearing is substantially free in a radial direction and can therefore take up forces in particular in an axial direction but can take up forces in a radial direction only to a limited extent and transmit them to the surrounding construction, for example, the housing. The rolling bearing is therefore constructed so as to be rigid in an axial direction and so as to be resilient in a radial direction, perpendicularly to the extent of the rotation axis  1  of the shaft, and is consequently free in a radial direction in terms of forces. 
         [0034]    In order to arrange the rolling bearing so as to be substantially free in a radial direction, there is provision for the bearing receiving member  3 , on which the outer ring of the rolling bearing is arranged, to have a material weakening, for example, two peripheral grooves  5 ,  6 , which extend round the rotation axis  1 . The first groove  5  at one side and the second groove at the opposite second side  6  of the bearing receiving member  3  are constructed to be so deep that the deep portions of the two grooves  5 ,  6  overlap each other perpendicularly to the rotation axis  1  in the viewing direction. The grooves  5 ,  6  reduce the capability of the bearing receiving member  3  to transmit forces which occur axially parallel with the rotation axis  1  only to a small extent. However, the grooves  5 ,  6  substantially decrease the transmission of radially acting forces to the housing. 
         [0035]    The embodiments described below describe additional possibilities, by means of which it is possible to make provision for the rolling bearing to be substantially free in a radial direction. The same reference numerals indicate the same features or features which are comparable in terms of their technical effect. 
         [0036]      FIG. 2  shows a bearing arrangement for rotatably supporting a shaft (not illustrated) relative to a housing  8 , comprising a back-up bearing  9  which is in the form of a rolling bearing, with the rolling bearing being able to take up forces in an axial and radial direction and in particular being in the form of an angular rolling bearing, especially a two-row angular ball bearing. So that the rolling bearing  9  is substantially free in a radial direction, there is provision for a corrugated strip gap  10  to be constructed so as to be radially enlarged in the outer ring  11  of the rolling bearing  9 . The corrugated strip gap  10 , as the inset in  FIG. 2  shows to an enlarged scale, is increased in a radial direction perpendicularly relative to the rotation axis  1  and has a radial extent h, which is substantially greater than the general extent and which is a multiple of the general extent, for example, at least three times the general extent. 
         [0037]    There is provision, as an additional supplementary step so that the rolling bearing  9  is substantially free in a radial direction, for a corrugated strip  12  having reduced rigidity to be arranged in the corrugated strip gap  10  on the outer ring  11  of the rolling bearing  9 . The corrugated strip  12  is in the form of a thin metal sheet which extends around the rotation axis  1  of the shaft and has corrugations. 
         [0038]    There may further be provision for a corrugated strip to be constructed as a composite of at least two partial corrugated strips which are secured to each other, with each of the partial corrugated strips extending around the rotation axis  1  so that the composite comprising the partial corrugated strips has a level of rigidity which is reduced in relation to the two partial corrugated strips. 
         [0039]      FIG. 4  shows a bearing arrangement having a shaft and a back-up bearing in the form of a rolling bearing  9 , with the outer ring  11  of the rolling bearing  9  being secured to a first portion  14  of a bearing receiving member  3 , with a second portion  15  of the bearing receiving member  3  being arranged between the first portion  14  of the bearing receiving member  3  and the housing and both portions  14 ,  15  of the bearing receiving member  3  being supported in a resilient manner on each other in a radial direction. In particular, a resilient means  16  is provided between the two portions  14 ,  15  and takes up forces in a radial direction and suppresses transmission of the radial displacements from the first portion  14  to the second portion  15 . The second portion  15  displaceably supported in the first portion  14 , in particular the first portion  14  engages over the second portion  15  at the axially outer side so that axially acting forces can be transmitted between the two portions  14 ,  15 . 
         [0040]      FIG. 5  is a cutout of an inner ring  17  of a back-up bearing for receiving a shaft  7 , with an end face  18  of the inner ring  17  cooperating with a radially offset edge face  19  on the shaft  7  in order to orientate the inner ring  17  with respect to the shaft  7  in order to form a guiding face pair. 
         [0041]    The end face  18  of the shaft  7  and the edge face  19  on the shaft  7  also form in particular a portion of a first friction face pair which with a second friction face pair, formed, for example, by the outer ring of the rolling bearing and an inner face of a bearing receiving member, with the friction properties of the two friction face pairs being adjusted for a friction-controlled self-centering action of the inner ring of the rolling bearing in relation to the shaft. There is particularly provision for a coating or a lining or a surface structure to be provided on the shaft  7 , including in the region of the edge face  19 , and on the end face  18  of the inner ring  17  and on the outer face of the inner ring  17  which comes into contact with the outer face of the shaft  7 , or for the surface roughness to be adjusted so that the friction properties of the first friction face pair are increased in relation to the friction properties of the second friction face pair. 
         [0042]    There is further provision for the friction properties of the second friction face pair to be reduced by coatings or reduced surface roughness levels. The various friction properties of the two friction face pairs support orientation of the inner ring  17  relative to the shaft  7 . 
         [0043]      FIG. 6  shows an embodiment which is modified in relation to  FIG. 5  and in which there is provision for the edge face  19 ′ and the end face  18 ′ to be constructed in an inclined manner and to form a guide face pair. The end face  18 ′ and the edge face  19 ′ extend parallel and define with the rotation axis  1  a high angle  20 . As a result of the inclined construction, the inner ring  17  is urged into a centered position when the shaft  7  falls into the back-up bearing with the edge face  19 ′. 
         [0044]      FIG. 7  shows an embodiment which is modified again in relation to  FIG. 5  and  FIG. 6 . There is provision for the edge face  19 ′ to define partially an angle  21  relative to the rotation axis  1  and wherein the end face  18 ′ has a rounded portion  22  which cooperates with the inclined portion of the edge face  19 ′. 
         [0045]    The edge face  19 ′ has an inclined portion  23  which adjoins the outer face of the shaft  7  and which defines an angle with the rotation axis  1 . The inclined portion  23  of the edge face  19 ′ cooperates with a rounded portion  22  of the contour of the end face  18 ′ of the inner ring  17 , with the rounded portion  22  being able to have a circular arc profile. 
         [0046]      FIG. 8  shows an embodiment which is modified again in relation to the embodiments of  FIGS. 5 ,  6  and  7 , wherein there is provision for a resilient element  24  to be arranged between the edge face  19 ′ on the shaft  7  and the end face  18 ′ of the inner ring  17 . 
         [0047]    The edge face  19 ′ is substantially orientated perpendicularly to the rotation axis  1  and comprises a shoulder  25  which steps back in an axial direction so that a receiving space  26  is formed for the resilient element  24  which in the embodiment illustrated is in the form of a disk spring. 
         [0048]    The end face  18 ′ of the inner ring  17  has a first portion  27  which is substantially perpendicular to the rotation axis  1  and a rounded portion  22 ′ which may have in particular a circular arc profile. The resilient element  24 , that is to say, the disk spring, is arranged between the rounded portion  22 ′, the shoulder  25  at the edge face  19 ′ and the outer face of the shaft  7  in the receiving space  26 , and is relaxed and tensioned in the normal operating state of the magnetic bearings when the shaft  7  falls into the back-up bearing, in particular when the shaft  7  approaches the inner ring  17  of the back-up bearing. The resilient element  24  tensions the inner ring  17  so that the inner ring  17  can take up a favorable centered position in relation to the shaft  7 . 
         [0049]      FIG. 3  shows an embodiment in which there is provision for the rolling bearing  9 ′ which is provided as a back-up bearing to be in the form of a substantially axially acting rolling bearing so that the radial adjustment takes place during rolling contact. 
         [0050]    The rolling bearing  9 ′ in the form of a ball bearing takes up forces in a radial direction only to a limited extent and has a pressure angle which defines a small angle with the rotation axis. The inner ring of the ball bearing  9 ′ is in the form of a substantially planar disk and has a planar inner ring ball race  28  for the balls  29 . 
         [0051]    There is provision, for one bearing ring, in the embodiment for the outer ring  11 , for the outer ring ball race  30  of the rolling members, in this instance the balls  29 , to be surrounded to a greater extent than at the other bearing ring, in this instance the inner ring  17 , of the rolling bearing. 
         [0052]    An outer ring ball race  30  on the outer ring  11  of the ball bearing  9 ′ has a profile in which the radius of curvature increases with increasing spacing from the rotation axis so that the profile of the outer ring ball race  30  at the side facing away from the rotation axis  1  supports the rolling member  29  radially and extends substantially parallel relative to the rotation axis  1  or is directed back towards the rotation axis  1 . As a result of the of the rolling members  29  by the outer ring ball race  30 , centrifugal forces acting on the rolling members  29  are taken up so that a cage for guiding the rolling members  29  is unnecessary and the rolling bearing  9 ′ is constructed in a completely rolling manner. The inner ring  17  does not have any surrounding member of the inner ring ball race  28  by means of a formation at the side directed away from the rotation axis and is displaceable substantially in a radial direction relative to the outer ring  11  so that the rolling bearing  9 ′ in the form of a ball bearing can take up and transmit only forces in an axial direction. 
         [0053]    In the third embodiment illustrated in  FIG. 3 , there was provision for the radius of curvature, that is to say, the radius of the osculating circle in the region of the outer ring ball race  30  or directly adjoining the outer ring ball race  30 , to increase with increasing spacing from the rotation axis in order to form the formation on the outer ring  11  in the profile of the outer ring ball race  30 , which formation forms the surrounding member. 
         [0054]    In the third embodiment illustrated in  FIG. 3 , there was provision for the surrounding member of the outer ring ball race  30  to form a formation. Naturally, the formation may also be provided on the inner ring  17  and the outer ring  11  has a substantially planar ball race. It is further self-evident that the formation formed by the surrounding member may be provided on both bearing rings  11 ,  17 . 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           1  Rotation axis 
           2  Inner face 
           3  Bearing receiving member 
           4  Outer face 
           5  Groove 
           6  Groove 
           7  Shaft 
           8  Housing 
           9  Back-up bearing 
           10  Corrugated strip gap 
           11  Outer ring 
           12  Corrugated strip 
           13  Comparative corrugated strip 
           14  First portion of the bearing receiving member  3   
           15  Second portion of the bearing receiving member  3   
           16  Resilient means 
           17  Inner ring 
           18 ,  18 ′ End face 
           19 ,  19 ′ Edge face 
           20  Angle 
           21  Angle 
           22 ,  22 ′ Rounded portion 
           23  Inclined portion 
           24  Resilient element 
           25  Shoulder 
           26  Receiving space 
           27  Perpendicular portion 
           28  Inner ring ball race 
           29  Ball 
           30  Outer ring ball race