Patent Abstract:
A support device and method for fixing a bearing on a bearing shield of a housing of an electric machine. Rotatably mounted in the support device is a rotor with a shaft. The support device is substantially flat and comprises a plurality of fastening openings that are grouped about a central opening. The support device comprises at least one design break point that acts to provide a local limit to the excess stress in the material of the support device.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/121,705, filed May 10, 2011, which is a U.S. national phase filing of PCT/EP2009/062516, filed Sep. 28, 2009, which claims priority to German Patent Application 10 2008 042 552.4, filed Oct. 2, 2008. 
    
    
     BACKGROUND OF THE INVENTION 
     As a rule, air-cooled generators for applications in the automotive sector are mounted by means of a locating bearing in a first bearing plate (A bearing plate) and a floating bearing in a second bearing plate (B bearing plate). A ball bearing which is used as a bearing is fixed axially here between a bearing plate and a support plate. As a result of the generally present bearing play, oscillations of the rotor occur as overall body in the axial direction. This phenomenon which is also called rotor bouncing occurs as a rule between 100 Hz and 500 Hz and is generally associated with very high mechanical loadings in the generator on various components. 
     DE 44 03 957 A1 relates to a flange bearing. Said flange bearing serves to receive a prong shaft of the winch or the pick-up drum of a harvester or of another correspondingly equipped agricultural machine. The flange bearing comprises a bearing body which is divided on one side and the outer casing of which has a cylindrical center section. The latter is adjoined by sections which are beveled conically on both sides. The bearing body is provided with a web which permits positionally accurate insertion of the bearings into the receptacle of a winch star and at the same time serves as antirotation safeguard. The bearing halves are connected elastically to one another by an integral hinge, a cutout being provided in an adjacent manner to the integral hinge, which cutout facilitates the widening of the bearing body, which is produced from a robust plastic, during mounting and dismantling. This solution concerns a hinge which can be bent more easily on account of the lower rigidity at a notched point. 
     U.S. Pat. No. 3,431,032 discloses a cylindrical bearing housing which has a milled slot as viewed in the axial direction. As a result, internal stresses which are produced are dissipated, such as residual stresses which are produced during casting. Deformation of the bearing housing is possible as a result of the slot. 
     DE 10 2004 053 078 A1 relates to a bearing arrangement. The latter comprises a bearing carrier which is connected to a bearing which is preferably configured as an antifriction bearing. In one of its bearing rings, the bearing has a groove which extends in the circumferential direction. At least one projection which is arranged on the bearing carrier and extends in the radial direction engages into said groove. At a circumferential point, the bearing carrier has a slot which extends substantially in the radial direction. 
     Finally, WO 03/081750 A1 discloses a generator for a vehicle, the generator comprising a support plate which has a slot which extends in the radial direction. Said slot which extends in the radial direction serves as tolerance compensation means. According to this solution, any stresses which possibly occur during the screwing connection of the support plate are dissipated, since a deformation of the material of the support plate is possible as a result of the slot and accordingly a dissipation of the stresses can take place. 
     SUMMARY OF THE INVENTION 
     The present invention is based on the object of protecting the components of the generator from excessive mechanical loadings, in particular excessively high oscillating accelerations, acting on the components of the generator for too long. 
     Following the solution which is proposed according to the invention, in an electric machine, for instance a generator which is used in the automotive sector, the support plate is configured in the region of the mounting in such a way that its macroscopic geometry changes during the operation of the generator. In particular, the change in the macroscopic geometry of the support plate is manifested by visible plastic deformations up to and including fractures of the support plate. The change in the geometry of the support plate achieves a situation where mechanical component loadings in the frequency range, for example, between 100 Hz and 500 Hz act for only a short time period on the components of the electric machine, for instance of a generator and for the most part are absorbed by the material of the support plate. To this extent, the material of the support plate acts as an absorber or damper, in particular for high mechanical oscillating accelerations. 
     The change in the macroscopic geometry of the support plate is achieved by the induced enforcement of fractures in the case of excessive loads as a result of defined predetermined break points. To this end, notches can be made at defined points of the support plate, which notches lead to high but locally delimited excessive loadings of the material of the support plate. If said delimited excessive loadings exceed a limiting value, this necessarily leads to the occurrence of a plastic deformation and, as a final consequence, to the formation of fractures. As a result of the support plates being partially or completely fractured at one or more points, the transmission of high mechanical component loadings to the components of the generator is avoided and damped or absorbed by the partially/completely fractured support plate. 
     In addition to the formation of notches at defined points of the support plate, plastic deformations can be forced in the support plate in the case of overloads, for instance also as a result of local rigidities, such as tapering regions of the support plate. This results in a reduction in the loading of the functionally important components of the support plate. 
     The support plate which is proposed according to the invention is designed, in particular, in such a way that at least one crack, that is to say a partial fracture or a complete fracture of the support plate, is produced in the case of more than 150,000 load changes with accelerations over 400 m/s 2 . Accelerations of this type do not occur during the normal vehicle operation. In contrast, no fractures or cracks may be produced in the case of accelerations below 300 m/s 2 . After the occurrence of at least one fracture in the support plate which is proposed according to the invention, the response characteristic of the generator changes, as a result of which the maximum load is reduced on account of damping effects which are produced. 
     Should the fracture faces not rub against one another after the fracture of the support plate, this is associated with a loss of friction energy. However, a completely fractured or partially fractured support plate will have a lower rigidity in comparison with an intact, that is to say unfractured, support plate. A reduced rigidity of the support plate leads to greater deformations of the latter and, as a result, additionally to damping potential which results in addition to the damping potential which exists at the fracture face. It is a further positive effect that the transmission characteristic of the generator can be influenced positively by the lower rigidity of the support plate. This effect is substantially independent of whether the fracture faces of the support plate rub against one another or whether this is not the case. 
     With regard to the pitch circle of the support plate screws, it is to be aimed for that it corresponds to the pitch circle of the holes which are formed in the support plate, that is to say the two pitch circles have identical dimensions. 
     In that design variant of the support plate proposed according to the invention which is provided with notches at defined points, it is to be aimed for that the geometry of the notch is designed in such a way that said notch has a stress concentration factor of K t &gt;2.0. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following text, the invention will be described in more detail using the drawing, in which: 
         FIG. 1  shows a longitudinal section through a generator, 
         FIG. 2  shows the plan view of a conventionally configured support plate, 
         FIG. 3  shows a first design variant of the support plate which is proposed according to the invention, 
         FIG. 3   a  shows the changing macroscopic geometry of the support plate in accordance with the first embodiment according to  FIG. 3 , 
         FIG. 4  shows a further, second possible embodiment of the support plate which is proposed according to the invention, 
         FIG. 4   a  shows the change which is produced in the macroscopic geometry of the support plate in accordance with the second embodiment according to  FIG. 4 , 
         FIG. 5  shows a further, third possible embodiment of the support plate which is proposed according to the invention, 
         FIG. 5   a  shows the changing macroscopic geometry of the third embodiment (shown in  FIG. 5 ) of the support plate which is proposed according to the invention, 
         FIG. 6  shows a horizontal sectional profile through the support plate, 
         FIG. 7  shows a sectional profile in accordance with the sectional profile A-A which is shown in  FIG. 6 , 
         FIG. 7   a  shows the plastic deformation which is produced in the sectional plane in accordance with the illustration in  FIG. 7 , 
         FIG. 8  shows a vertical section through the support plate, 
         FIGS. 9 and 9   a  show the illustration of fracture faces which are produced during the complete or partial fracture of the support plate which is proposed according to the invention, and 
         FIGS. 10 and 10   a  show macroscopic geometry changes which are produced in the support plate which is proposed according to the invention, in the sectional plane of the section B-B in accordance with  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION 
     The illustration according to  FIG. 1  shows a section through an electric machine  10 , configured here as a generator or three-phase generator for motor vehicles. Said electric machine  10  has, inter alia, a two-part housing  13  which consists of a first bearing plate  13 . 1  and a second bearing plate  13 . 2 . The first bearing plate  13 . 1  and the second bearing plate  13 . 2  receive a stator  16  between them, which stator  16  firstly consists of a substantially circularly annular stator iron  17  and in the radially inwardly directed, axially extending grooves of which a stator winding  18  is inserted. Said annular stator  16  surrounds a rotor  20  with its radially inwardly directed grooved surface, which rotor  20  can be configured as a claw pole rotor. The rotor  20  consists, inter alia, of two claw pole plates  22  and  23 , on the external circumference of which claw pole fingers  24  and  25  which extend in the axial direction are arranged. The claw pole plates  22  and  23  are arranged within the rotor  20  in such a way that their claw pole fingers  24  and  25  which extend in the axial direction alternate one another on the circumference of the rotor  20 . This results in magnetically required intermediate spaces between the oppositely magnetized claw pole fingers  24  and  25  which are called claw pole intermediate spaces. The rotor  20  is mounted rotatably in the first and second bearing plates  13 . 1  and  13 . 2  by means of a shaft  27  and in each case one antifriction bearing  28  which is situated on in each case one rotor side. 
     The rotor  20  has a total of two axial side faces, to which in each case one ventilator  30  is fixed. Said ventilator  30  consists substantially of a plate-shaped or disc-shaped section, from which ventilator vanes emanate in a known manner. The ventilator  30  serves to make an exchange of air possible via openings  40  in the bearing plates  13 . 1  and  13 . 2  between the outer side of the electric machine  10  and the interior of the electric machine  10 . To this end, the openings  40  are provided substantially at the axial ends of the bearing plates  13 . 1  and  13 . 2 , via which openings  40  cooling air is sucked into the interior of the electric machine  10  by means of the ventilator  30 . Said cooling air is accelerated radially to the outside by the rotation of the ventilator  30 , with the result that said cooling air can pass through the winding projection  45  which is permeable to cooling air. The winding projection  45  is cooled by this effect. After passing through the winding projection  45  or after flowing around said winding projection  45 , the cooling air follows a path radially to the outside, through an opening which is not shown in  FIG. 1 . 
     Furthermore, it is apparent from the illustration in accordance with  FIG. 1  that a protective cap  47  which protects various components against environmental influences is situated on the right hand side. Thus, for example, this protective cap  47  covers a slip ring assembly  49  which serves to supply an exciter winding  51  with exciter current. A cooling body  53  which acts here as a positive cooling body is arranged around said slip ring assembly  49 . The second bearing plate  13 . 2  acts as what is known as a negative cooling body. A connecting plate  56  is arranged between the second bearing plate  13 . 2  and the cooling body  53 , which connecting plate  56  serves to connect negative diodes  58  which are arranged in the bearing plate  13 . 2  and positive diodes (not shown here in this illustration) in the cooling body  53  to one another and therefore to realize a bridge circuit which is known per se. A support plate of the electric machine  10  is denoted by designation  60  in  FIG. 1 . 
     A support plate in accordance with the prior art which is used on an electric machine can be gathered from the illustration in accordance with  FIG. 2 . 
     The support plate  60  which can be of rectangular, round or, as shown in  FIG. 2 , square configuration comprises a through opening  64  and a number of fastening openings  62 . The fastening openings  62  can be produced as punched holes, as drilled holes with or without threads, or the like. The antifriction bearings  28  which are shown in section in accordance with  FIG. 1  are fixed in the housing of the electric machine  10  by way of the support plate  60  in accordance with the illustration in  FIG. 2 . It is apparent from the illustration in accordance with  FIG. 2  that the support plate  60  which is shown there is of planar configuration in relation to its outer and its inner borders. 
       FIG. 3  shows a support plate which is proposed according to the invention and is illustrated in a first design variant. 
     It is apparent from the illustration in accordance with  FIG. 3  that the opening  64  has an internal diameter  80  and contains a number of fastening openings  62 . A first outer notch  66  and a second outer notch  68  which lies opposite the former are situated in each case in a 6 o&#39;clock arrangement and 12 o&#39;clock arrangement on the outer edge of the support plate  60  in accordance with the illustration in  FIG. 3 . The first outer notch  66  and the second outer notch  68  could also be configured to be turned by 90°, that is to say could be configured in the 3 o&#39;clock and the 9 o&#39;clock arrangement. Two outer notches  66 ,  68  which lie opposite one another are preferably formed on the support plate  12  in its first embodiment. 
     As is apparent from the illustration in accordance with  FIG. 3   a , cracks  70  which run from the notch bottom of the first and/or the second outer notch  66  and/or  68  inward toward the internal diameter  80  are produced during operation of the generator and during mechanical loading of the support plate  60 . Said cracks  70  represent a macroscopic change in the geometry of the support plate  60  and convert the mechanical loadings into precisely the cracks  70 , with the result that loading peaks can be absorbed not by the components of the electric machine  10  in accordance with the illustration in  FIG. 1 , but rather substantially by the support plate  60 . 
     The support device  60  is preferably configured to be plate-shaped, that is to say as a support plate. 
     It is to be noted in relation to the cracks  70  which extend from the notch bottom of the outer notches  66  and  68  in the radial direction toward the internal diameter  80  of the central opening  64  that the faces which delimit the crack  70  are relatively rough and brittle and accordingly do further damping work in the context of the present invention by rubbing on one another and accordingly absorbing oscillating accelerations with the acceptance of a slight temperature increase. 
     A further, second design variant of the support device which is proposed according to the invention and is configured to be, in particular, plate-shaped can be gathered from the illustration in accordance with  FIG. 4 . 
       FIG. 4  shows that, in addition to the first outer notch  66  and the second outer notch  68  on the external circumference of the plate-shaped support device  60 , notches which lie opposite one another, that is to say a first inner notch  72  and a second inner notch  74 , are also configured on the internal diameter  80  of the central opening  64 . In an analogous manner to the first outer notch  66  in the 12 o&#39;clock position, the first inner notch  72  is likewise situated in the 12 o&#39;clock position on the internal diameter  80  of the central opening  64 . The same applies to the second inner notch  74  which, analogously to the second outer notch  68 , is situated in the 6 o&#39;clock position on the internal diameter  80  of the central opening  64 . It goes without saying that both the inner notches  72 ,  74  and the outer notches  66  can be arranged in each case turned by 90° with respect to one another. 
       FIG. 4   a  shows the crack pattern which is produced of the cracks  70  in the case of mechanical loading of the support device  60  which is proposed according to the invention and is preferably configured to be plate-shaped. On account of the small remaining material web between the notch bottoms which face one another of the first outer notch  66  and the first inner notch  72  and the second outer notch  68  and the second outer notch  74 , relatively short cracks  70  extend, as indicated in  FIG. 4   a , between the notch bottoms which in each case point toward one another. 
     The faces which are produced and delimit the cracks  70  have a relatively high roughness, which is favorable with regard to additional damping work, via which oscillating accelerations can be dissipated. 
     A further, third design variant of the support device  60  which is proposed according to the invention and is configured to be, in particular, plate-shaped can be gathered from the illustration in accordance with  FIG. 5 . In contrast to the first design variant in accordance with  FIG. 3  and the second design variant in accordance with  FIG. 4 , the support device  60  which is proposed according to the invention and is configured to be plate-shaped has, in accordance with  FIG. 5 , shell-shaped openings  76 ,  78  which are oriented so as to lie opposite one another in the solid material of the support device  60 . This results in material webs which extend in each case from the ends of the openings  76  and  78  and extend in the radial direction both to the external circumference of the support device  60  which is configured to be plate-shaped and also to the internal diameter  80  which delimits the central opening  64 . Excessive loadings are produced in said remaining, relatively short material sections in the case of mechanical loading of the support device  60  which is proposed according to the invention, on account of oscillating accelerations which occur, which excessive loadings lead to the crack courses  70  which are shown in  FIG. 5   a , firstly in the direction of the external circumference and the support device  60  and secondly in the direction of the internal diameter  80  of the central opening  64 . 
     Fastening openings  62  are a common feature of all the design variants in accordance with  FIGS. 3 to 5  of the support device which is proposed according to the invention and is configured to be, in particular, plate-shaped. Said fastening openings  62  can be simply punched holes, or they can be drilled holes which are configured with or without internal threads. The pitch circle diameters both of the pitch circle of the fastening openings  62  and also that of the screws which penetrate the fastening openings  62  are preferably identical. 
     An illustration of the support device  60 , in which a horizontal sectional profile A-A is represented, can be gathered from the illustration in accordance with  FIG. 6 . 
       FIGS. 7 and 7   a  show the support device  60  in the sectional plane A-A, which support device  60  is shown in  FIG. 6  with the sectional profile A-A, is proposed according to the invention and is configured to be, in particular, plate-shaped. It is apparent from the sectional illustration in accordance with  FIG. 7  that, in the region of the central opening  64 , the support device  60  has a reduced thickness  84  in relation to its thickness  82 , that is to say a tapered section  84 . The tapered region  84  which adjoins the central opening  64  of the support device  60  which is configured to be, in particular, plate-shaped results in webs  86  which lie opposite one another and experience a plastic deformation  88  in the case of a mechanical loading of the support device  60  which is configured to be, in particular, plate-shaped, as is shown in  FIG. 7   a.    
     The plastic deformation  88  (shown in  FIG. 7   a ) of those ends of the webs  86  which lie opposite one another represents a macroscopic change in the geometry of the support device  60  which is configured to be plate-shaped, by way of which change the stresses can be dissipated which are produced in the support device  60  which is configured to be plate-shaped in the case of mechanical loading of the latter, and accordingly a complete fracture or a partial fracture is accepted of the support device  60  which is configured to be, in particular, plate-shaped, in order as a result to protect the components of the electric machine  10  in accordance with the sectional illustration in  FIG. 1  against excessive mechanical loadings in the frequency range mentioned. 
       FIG. 8  shows a sectional profile A-A, B-B.  FIG. 9  shows the profile through the support device  60  before the fracture, whereas  FIG. 9   a  represents the sectional profile after the occurrence of a fracture in the support device  60  which is proposed according to the invention. 
     A sectional profile B-B in accordance with the sectional illustration in  FIG. 8  can be gathered from  FIGS. 10 and 10   a . According to the sectional profile B-B as shown in  FIG. 10 , a planar-side notch  92  is made on one of the planar sides  94  and  96  of the support device  60  which is configured to be, in particular, plate-shaped. As a result, a reduced thickness is produced between the notch bottom of the planar-side notch  92  and the planar side  94  which lies opposite it. A crack  70 , as indicated in the illustration in accordance with  FIG. 10   a , extends precisely in this reduced thickness in the case of mechanical overloading of the support device  60  which is proposed according to the invention and is preferably configured to be plate-shaped. The crack  70  extends from the notch bottom of the planar-side notch  92  to the planar side  96 . As an alternative to the position (shown in  FIGS. 10 and 10   a ) of the planar-side notch  92  on the first planar side  94 , it goes without saying that the planar-side notch  92  can also be formed on the opposite second planar side  96  of the support device  60  which is proposed according to the invention and is configured to be, in particular, plate-shaped. 
     It is to be noted with respect to  FIGS. 3 ,  4 ,  5  and  10  that the notches which are shown there, whether they are outer notches  66 ,  68 , inner notches  72 ,  74  or planar-side notches  92 , are all preferably configured with a stress concentration factor of K t &gt;2.0. The stress concentration factor x Kt  is defined as the quotient from maximum loading and nominal loading. 
     In the embodiments shown in  FIGS. 3 ,  4 ,  5 ,  7  and  9  of the support device  60  which is proposed according to the invention and is configured to be, in particular, plate-shaped, it is to be noted that the geometry of said support device is configured in such a way that the support device  60  fractures when more than 150 000 load changes at accelerations over 400 m/s 2  occur. The support device  60  which is proposed according to the invention and is configured to be, in particular, plate-shaped is preferably dimensioned in such a way that it does not fracture in the case of accelerations below 300 m/s 2 . After the fracture or partial fracture of the support device  60  which is proposed according to the invention as a result of at least one crack  70  occurring, the response characteristic of the electric machine  10  changes, as a result of which the maximum load is reduced by way of damping effects. 
     If the fracture faces  90  which are shown in  FIG. 9   a  no longer rub against one another after the fracture, part of the friction energy, in which energy is dissipated, is lost. However, a fractured or partially fractured support device  60  will have a lower rigidity than an intact support device  60 . A reduced rigidity of the support device  60  in turn leads to somewhat greater plastic deformations  88 , as is shown in an exaggerated manner in  FIG. 7   a , and additionally leads, as a result, to damping which is to be considered to be additional damping in relation to the damping which can be achieved by way of the fracture faces  90 .

Technology Classification (CPC): 5