Patent Publication Number: US-2018034343-A1

Title: Electric machine unit with groove for receiving a protective cap

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an electric machine unit having an electric machine and having power electronics mounted thereon. 
     Electric machine units having an electric machine and having power electronics mounted thereon are used for example in motor vehicles as starters or generators or in combined form as starter-generators or so-called boost recuperation machines (BRM). They may have, for example, a separately excited electric machine with rotor winding (exciter winding) and stator winding and, as power electronics, a power converter with regulator (e.g. generator regulator or field regulator) which is connected downstream of the stator winding and which regulates the voltage generated by the electric machine and/or the torque generated by the electric machine. 
     To protect the electrical phases against being touched, the power electronics should be covered by means of a protective cap. In the case of relatively high voltages, such as are used for example in the case of BRMs (48 V), the protective cap should be electrically conductive in order to maintain the electromagnetic compatibility (EMC). This is expedient because, with 48 V rated voltage and PWM actuation of the electrical phases, the emission of electromagnetic waves is several times greater than in the case of conventional 12/14 V machines. 
     During the operation of the electric machine, vibrations arise which lead to oscillation of the electric machine with power electronics. As a result, the protective cap is also caused to oscillate. These inherent oscillations of the protective cap can lead to damage to the protective cap or to adjacent components. Furthermore, disturbing noises can arise as a result of the oscillations. To prevent or at least minimize the oscillations of the protective cap, the protective cap may be fixed by means of multiple bolts through the top side thereof. 
     SUMMARY OF THE INVENTION 
     According to the invention, an electric machine unit having an electric machine and having power electronics mounted thereon is proposed. 
     The invention proposes that the protective cap for the power electronics be fixed not only at the top side but also at the side wall by virtue of the side wall being, at its free edge, arranged at least in sections in a groove. 
     Specifically, it has been found that the fixing at the top side is on its own not sufficient to suppress vibrations, because the side walls of the protective cap are also caused to oscillate. The groove fixes the side wall of the protective cap in a radial direction. As a result, an oscillation of the side wall is prevented or at least reduced. 
     The groove is preferably formed at least in sections as a U-shaped depression. This shape is particularly easy to produce and is insensitive during the assembly process. 
     A connection plate which is arranged between electric machine and power electronics preferably has the groove. Such connection plates between electric machine and power electronics may be used in the conventional manner for providing electrical contact elements for the phases that are led out of the electric machine, to which contact elements the power electronics are then connected. At the same time, the connection plate may provide fastening means for the fastening of the power electronics. 
     The connection plate is preferably formed from plastic. Therefore, it is firstly the case that the plate itself and also the groove situated thereon are easy to produce, in particular by injection molding (plastics injection-molded part), and secondly, the connection plate simultaneously has an electrically insulating action. It is preferably possible for molds for conventional connection plates to be further developed to include a groove. The fixing is thus virtually cost-neutral, because only a slightly greater amount of plastics material is required for the connection plate. 
     The groove expediently runs on the outer edge of the connection plate, wherein it is expediently the case that more than 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% of the circumference is covered. 
     The groove preferably has alignment means which align the protective cap relative to the electric machine with respect to a rotation about an axis perpendicular to the top side of the protective cap. This facilitates the alignment of the protective cap on the electric machine, which permits reliable insertion of the fastening bolts. 
     The alignment means preferably have at least one groove delimitation, in particular a groove discontinuation or groove interruption. The groove is thus not a continuous groove but is a groove which is delimited, in particular interrupted, at points or in sections, wherein the protective cap expediently has corresponding interruptions in the free edge of the side wall in order to permit an engagement of interrupted edge and interrupted groove into one another. The invention is inexpensive to implement because it is merely necessary for the mold for the connection plate to be slightly modified. 
     For simplified assembly, the groove delimitation and/or the side wall may have an insertion bevel. 
     The protective cap is preferably electrically conductive in order to improve the electromagnetic compatibility. It may for example be metallic, composed of electrically conductive plastic, or composed of plastic with an electrically conductive coating. 
     It is furthermore preferable if the protective cap has a burr at its free edge. This embodiment enables the side wall to be wedged in the groove, which results in a particularly secure hold. The holding force is increased and the side wall lies in the groove without play. In particular if the protective cap is produced as a deep-drawn part composed of a metal sheet, a burr is formed at the free edge of the side wall as a result of the punching process. The burr protrudes outwardly or inwardly depending on the punching direction and has a sharp edge. It is particularly advantageous for precisely this punching burr to be utilized for the optimized fixing of the side wall in the groove. 
     Further advantages and refinements of the invention will emerge from the description and from the appended drawing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is illustrated schematically on the basis of an exemplary embodiment in the drawing and will be described below with reference to the drawing. 
         FIG. 1  shows an electric machine unit according to a preferred embodiment in a perspective view. 
         FIG. 2  shows a longitudinal section through the electric machine unit from  FIG. 1 . 
         FIG. 3  shows the detail outlined in  FIG. 2 , regarding the arrangement of a side wall of the protective cap in a groove of a connection plate, in an enlarged view. 
         FIG. 4  shows the protective cap and the connection plate separately in a perspective view. 
         FIG. 5  shows an enlarged detail of the free edge of the protective cap with punching burr. 
         FIG. 6  shows the electric machine unit from  FIG. 1  in a perspective view from above. 
         FIG. 7  shows the detail outlined in  FIG. 6 , regarding the alignment of the side wall of the protective cap in the groove of the connection plate, in an enlarged view. 
     
    
    
     DETAILED DESCRIPTION 
     Firstly, on the basis of  FIGS. 1 to 5 , an overall description will be given of a preferred embodiment of an electric machine unit  1  according to the invention, with an advantageous refinement illustrated in  FIGS. 6 and 7  then being described. 
     The electric machine unit  1  is for example in the form of a boost recuperation machine (BRM) for a boost recuperation system (BRS) and has a claw-pole machine  10  as an electric machine and power electronics  20  mounted thereon. Said electric machine unit has for example a rated voltage of 48 V. 
     The housing of the claw-pole machine  10  is composed substantially of two bearing plates  101  and  102  with mounting arms for the fastening of the electric machine unit for example to the internal combustion engine. The bearing plates fix the stator  110 . 
     Between the claw-pole machine  10  and the power electronics  20  there is situated a connection plate  120 . The connection plate  120  is in this case in the form of a plastics injection-molded part and serves inter alia for the contacting of the electrical phases of stator  110  and power electronics  20 . 
     A protective cap  130  largely covers the power electronics  20 . The protective cap is, at its top side, held on the claw-pole machine  10 , specifically on the bearing plate  102 , by means of bolts  140 . A side wall of the protective cap is denoted by  131 . Furthermore, in the preferred embodiment illustrated here, an in this case outwardly projecting punching burr is situated at the free edge  132  of the side wall  131 . The punching burr is formed for example during the process of production of the protective cap. It protrudes outwardly or inwardly depending on the punching direction and has a sharp edge. 
     The connection plate has multiple grooves distributed over the circumference and formed in this case as U-shaped receptacles  121  (or one groove with multiple interruptions) for the lateral fixing of the protective cap, wherein the side wall  131  engages at its free edge  132  into the groove  121 . 
     The punching burr at the free edge  132  of the protective cap can additionally, during the assembly process, become wedged in the plastics material of the U-shaped receptacle  121  of the connection plate. The lateral fixing of the protective cap is thereby improved. 
     The lateral fixing of the protective cap by means of U-shaped receptacles on the connection plate is inexpensive to implement, because only a slightly greater amount of plastics material is required. 
       FIG. 6  shows a preferred refinement of the electric machine unit  1  obliquely from above, in order to illustrate the region of the alignment means, which in this case is in the form of a groove delimitation. 
       FIG. 7  shows an enlarged detail from  FIG. 5  with an illustration of two U-shaped receptacles  121   l  (left) and  121   r  (right) of the connection plate  120 , with alignment means formed in this case as a groove delimitation or groove discontinuity  122   l ,  122   r.    
     The left-hand groove delimitation  122   l  delimits the travel of the left-hand side wall  131   l  and thus a rotation of the protective cap about an axis perpendicular to the top side toward the right. The right-hand delimitation  122   r  delimits the travel of the right-hand side wall  131   r  and thus a rotation of the protective cap about an axis perpendicular to the top side toward the left. Thus, altogether, the angle range of the alignment of the protective cap about an axis perpendicular to the top side is restricted, such that insertion of the fastening bolts  140  is made easily possible. 
     To simplify the mounting of the protective cap  130 , the groove delimitations  122  have insertion bevels  123   l  and  123   r.  Alternatively, the insertion bevel may also be provided on the side wall of the protective cap. 
     The lateral fixing by means of U-shaped receptacles with groove delimitation can be implemented inexpensively, because only a slightly greater amount of plastics material is required on the connection plate.