Patent Publication Number: US-2022224187-A1

Title: Electric Drive Unit for a Motor Vehicle

Description:
The invention relates to an electric drive unit according to the preamble of claim  1 . 
     The invention relates additionally to an electric drive unit according to the preamble of independent claim  24 . 
     From WO 98/40958 there is known an electric drive unit having two electric drives arranged on axes of rotation which are in alignment with one another. Although the two electric drives are located within a housing casing of a common drive housing, they are otherwise independent of one another and accordingly are each provided with their own rotor shaft, the shaft ends of which rotor shafts are guided out of the drive housing facing away from one another. The other, mutually adjacent shaft ends of the rotor shafts are both rotatably mounted in a bearing housing. The bearing housing is the central region of a bearing plate, which is in the form of a round plate and divides the drive housing into a first housing portion having the first electric drive and a second housing portion having the second electric drive. 
     Since one of the two rotary bearings of the rotor shaft is located at the bearing plate having the bearing housing arranged centrally therein, the bearing plate is correspondingly largely dimensioned, especially since the bearing plate, as well as supporting the shaft forces, also contributes towards the strength of the drive housing. The overall length of the drive housing is therefore determined not only by the dimensions of the electric drive units themselves, but also by the additional installation space occupied by the bearing plate. 
     The object underlying the invention is to provide an electric drive unit having two electric drives arranged one behind the other in a common drive housing, which drive unit is compact in the longitudinal direction without disadvantages in terms of the strength of the drive housing being associated therewith. 
     In order to achieve this object, there is proposed an electric drive unit having the features of claim  1 . In this electric drive unit, a closed plate does not serve as the bearing plate, but rather components of the bearing plate are struts which extend outwards from the bearing housing arranged centrally in the bearing plate. These struts together form a connecting region which connects the centrally arranged bearing housing to the housing casing of the drive housing. Since the bearing plate is not a component with an unbroken surface, but rather the connecting region of the bearing plate is formed only of the individual struts, openings and thus voids remain between the struts. The openings provide space, for example, for electrical connections of the electric drives or for cooling measures, and thus space for measures that would otherwise occupy additional installation space in the drive housing. The bearing plate and the bearing housing can be arranged in the drive housing in a form- and force-fitting manner, wherein a one-piece form of a drive housing with a bearing plate and a bearing housing by casting is also possible. 
     At the same time, it has been found that, for adequate stability of the bearing plate and thus for the required overall strength of the drive housing, it is not necessary for the bearing plate to be in the form of a plate with an unbroken surface. Adequate stiffening and thus a contribution to the overall strength of the drive housing can also be achieved with a bearing plate comprising discrete struts which extend radially outwards from the bearing housing and thus establish the only connection with the surrounding housing casing. 
     In order to achieve the mentioned object, there is further proposed an electric drive unit having the features of claim  24 . This drive unit is characterized by at least one coolant channel which leads from a coolant opening in the housing casing through the connecting region into the bearing housing. 
     In this electric drive unit too, the mutually adjacent shaft ends of the rotor shafts are both rotatably mounted in a bearing housing which is the central region of a bearing plate rigidly arranged in the drive housing. A portion of the bearing plate forms a connecting region which extends outwards from the bearing housing and connects the bearing housing to the housing casing. In addition to its static, strength-determining function, the connecting region has an additional function inasmuch as a coolant channel leads through it, via which, for example, motor components or also transmission components can be supplied with cooling liquid. 
     For this purpose, the coolant channel leads, preferably radially, from a coolant opening in the housing casing through the connecting region into the bearing housing. By means of these structural steps, cooling measures which are necessary for the drive unit are relocated into the bearing plate. Space is therefore created in the bearing plate for measures that would otherwise occupy additional installation space in the drive housing. 
     It is further possible, adapted to the available space, for cooling fins to be formed on the outer surface of the housing casing and/or of the coolant tank, in order to increase the removal of heat from the inside to the outside. 
     Preferred embodiments of the electric drive units are described in the respective dependent claims. 
     If the connecting region of the bearing plate consists of individual struts, it is advantageous, in order to achieve openings that are as large as possible between the struts, if the struts only form the outer circumference of the bearing plate and connect the bearing plate to the housing casing of the drive housing with their outer ends. The struts are thus connected to one another only at their inner ends, namely via the bearing housing, and not at their outer ends. The outer ends of the struts are instead connected only to the housing casing of the drive housing. 
     The connecting region of the bearing plate is preferably formed by three or more struts, which divide an equal number of three or more openings at the bearing plate. The openings preferably have the form of opening segments arranged around the bearing housing. 
     According to one embodiment, a first opening is located at the bottom in the drive housing. A coolant opening formed at the bottom in the housing casing of the drive housing opens radially into this first opening. In this manner, the coolant opening connects the first opening to a coolant tank arranged in a liquid-tight manner on the outside of the housing casing. 
     Since the first opening serves only as the mouth of the coolant opening, the first opening can be relatively small. It is therefore proposed that the first opening is smaller than any of the further openings. The further openings are preferably each of the same size. 
     Through at least one of the struts there runs a coolant channel which leads from a coolant opening, with which the housing casing is provided in a prolongation of the strut, into the bearing housing. It is thus possible to guide coolant via the coolant channel formed in the strut into the region of the bearing housing arranged centrally in the bearing plate, for example in order to supply coolant to the rolling bearings arranged there for the shaft ends of the rotor shafts. 
     The coolant opening is preferably a threaded bore, the cross section of which is larger than the cross section of the coolant channel running in the strut, wherein a coolant connection piece is screwed into the threaded bore. 
     With a further embodiment it is proposed that the struts, when seen in the circumferential direction of the bearing plate, are of different widths, and that the width of the strut through which the coolant channel runs is larger than the width of a strut without a coolant channel running therein. 
     It is further proposed that separate rolling bearings for the shaft ends of the two rotor shafts are arranged in the bearing housing. Each rolling bearing encloses the respective shaft end with its inner ring and is supported in the bearing housing with its outer ring. The bearing housing is provided with a through-opening arranged centrally therein, into which the respective shaft ends extend from both sides and into which the coolant channel opens. 
     According to a further embodiment, a window is formed in the housing casing in the region of each of two openings of the bearing plate, through which window and through the respective opening electric lines are guided in a space-saving manner to the electric drives. 
     The windows are preferably arranged on circumferential portions of the housing casing that are remote from one another. The windows are covered on the outside by protective boxes, wherein the protective boxes can be fixed in a modular manner to the drive housing or are cast in one piece with the drive housing. Located in the protective boxes are electrical connectors, to which the electric lines leading to the electric motors are connected. In order to keep the external dimensions of the electric drive unit small, the protective boxes preferably have a main extent parallel to the longitudinal direction of the drive housing. 
     It is further advantageous for the compact construction of the drive unit if first electric lines lead to a first terminal block which is mounted on the first electric drive and extends into one opening, and if second electric lines lead to a second terminal block which is mounted on the second electric drive and extends into the other opening. The voids provided by the openings in the bearing plate are therefore used to accommodate the terminal blocks of the electric drives in a space-saving manner. 
     This embodiment is particularly advantageous if the two terminal blocks are arranged on different circumferential portions in the housing casing, and if the terminal blocks extend so far into the respective opening that the terminal blocks overlap partly in the longitudinal direction of the drive housing. 
     With regard to the connection of the struts to the housing casing of the drive housing, it is proposed that each strut is supported axially against a fin which projects inwards from the housing casing, wherein the fin is welded in that position to the housing casing. The fin is preferably a one-piece component of the housing casing. In another possible embodiment, the housing casing and the bearing plate are manufactured in one piece, for example by casting. 
     The fin is preferably composed in the circumferential direction of individual, separate fin segments, wherein the fin segments are arranged only on circumferential portions of the housing casing at which the struts are located. This embodiment also contributes to making the opening segments between the fins as large as possible. 
     The limitation to individual fin segments additionally has the advantage that the housing casing can be provided on the circumferential portions without fin segments, for example, with windows, openings or similar apertures. 
     The bearing plate is preferably arranged in the drive housing in such a manner that the bearing plate is at the same axial distance from each of the two electric drives. 
    
    
     
       Further advantages and details will become apparent from the following description of an exemplary embodiment, wherein reference is made to the drawings. In the drawings: 
         FIG. 1 : shows, in a perspective overall view, an electric drive unit fora motor vehicle integrated into a vehicle axle; 
         FIG. 2 : is a longitudinal view of the drive unit, wherein the central region is depicted as a longitudinal section in a perpendicular sectional plane in  FIG. 1 ; 
         FIG. 3 : is a further longitudinal view of the drive unit, wherein the central region is depicted as a longitudinal section in a horizontal sectional plane in  FIG. 1 ; 
         FIG. 4 : shows, in an enlarged view compared to  FIG. 2 , the central region of the electric drive unit including a bearing plate arranged there; 
         FIG. 5 : shows the electric drive unit from viewing direction V indicated in  FIG. 1 ; 
         FIG. 6 : shows a cross section through the electric drive unit in the region of the bearing plate; 
         FIG. 7 : shows a detail of the bearing plate; 
         FIG. 8 : shows a further detail of the bearing plate, here in a perspective view; 
         FIG. 9 : is a longitudinal view of a second embodiment of the drive unit, wherein the central region is depicted as a longitudinal section in a perpendicular sectional plane. 
     
    
    
       FIG. 1  shows, in an overall view, the middle longitudinal portion of an electrically driven vehicle axle. The portions arranged further to the outside of the vehicle on both sides and individual parts of the vehicle axle are not shown. These include, for example, the steering knuckles of the vehicle axle which follow at the outside of the vehicle and on which the wheel hubs with the vehicle wheels are rotatably mounted. Tube portions  2  depicted in  FIG. 1  belong in each case to a drive shaft via which the drive torque reaches the respective vehicle wheel. 
       FIG. 1  shows the middle region of the electric axle, which in terms of housing is composed especially of a drive housing  3 , in which two electric drives are located, a first transmission housing  3 A at one end of the drive housing  3 , and a second transmission housing  3 B at the other end of the drive housing  3 . In the drive housings  3 A,  3 B there are located the transmission and preferably planetary gears, via which the power passes from the electric drives  5 A,  5 B to the drive shafts which are visible at the tube portions  2 . 
     The drive housing  3  consists predominantly of a housing casing  4 , which is substantially cylindrical in form. The drive housing  3  is closed at both end faces by flanges screwed thereto. In the exemplary embodiment described here, the flanges are components of the respective transmission housing  3 A,  3 B. 
     According to  FIG. 2 , the interior of the drive housing  3  is substantially in two parts, with a first electric drive  5 A occupying one half of the drive housing  3  and a second electric drive  5 B occupying the other half of the drive housing  3 . The axes of rotation A of the two electric drives  5 A,  5 B are in alignment, without being coupled with one another. The two electric drives  5 A,  5 B are therefore located in the housing casing  4  and thus inside the common drive housing  3 , but they are otherwise independent of one another and accordingly are each provided with their own drive shaft  8 A,  8 B. The first shaft ends of the drive shafts lead away from one another to the respective transmission. The two other shaft ends  10 A,  10 B of the rotor shafts  8 A,  8 B, that is to say the shaft ends that face one another or are adjacent to one another, are both rotatably mounted, without being mechanically coupled, in a common bearing housing  25 . 
       FIG. 2  further shows the stator of the electric drives  5 A,  5 B and in each case the rotor  8 , which is rotationally fixed with its respective rotor shaft  8 A,  8 B. The two rotor shafts rotate on the same axis of rotation, that is to say the axes of rotation A of the rotor shafts are in alignment with one another and they both extend in the longitudinal direction of the drive housing  3 . 
     The two electric drives  5 A,  5 B thus work independently of one another, which does not rule out the possibility that they may be operated, for example, in a synchronized manner. 
     Precisely in the middle between the two electric motors  5 A,  5 B there is located in the drive housing  3  a bearing plate  20  arranged transversely to the axes of rotation A. Components of the bearing plate  20  are the bearing housing  25  already mentioned, in which the shaft ends  10 A,  10 B are rotatably mounted, and a plurality of struts  21 ,  22 ,  23 . The struts  21 ,  22 ,  23  extend preferably radially outwards from the bearing housing  25 . The struts  21 ,  22 ,  23  together form a connecting region, which rigidly connects the centrally arranged bearing housing  25  to the substantially cylindrical housing casing  4  of the drive housing  3 . 
     The bearing plate  20  has several functions. A first function consists in positioning the bearing housing  25  within the drive housing  3  sufficiently rigidly that the mutually adjacent shaft ends  10 A,  10 B of the rotor shafts  8 A,  8 B are rotatably mounted in a defined manner. A further function of the bearing plate  20  consists in contributing to the strength and statics of the drive housing  3 . This is in particular because the drive housing  3  is generally tubular in form with open end faces, which are covered only by the transmission housing. A further function of the bearing plate  20  consists in accommodating coolant channels via which cooling liquid can reach the drive components in particular. 
     According to  FIGS. 6-8 , the bearing plate  20  is not a closed plate, but rather the bearing plate  20  consists especially of the struts  21 ,  22 ,  23  already mentioned, which extend preferably radially outwards from the bearing housing  25  arranged centrally in the bearing plate  20 . Only the discrete struts  21 ,  22 ,  23  form the connecting region via which the bearing housing  25  is connected to the housing casing  4 . 
     Because the bearing plate  20  is not a component with an unbroken surface, an equal number of openings  31 ,  32 ,  33 , and thus voids, remain between the struts. The openings  31 ,  32 ,  33 , or voids, provide space for cooling measures and for accommodating electrical terminal blocks. They thus provide space in particular for measures that would otherwise occupy additional installation space in the drive housing  3 . 
     For the stability of the bearing plate  20  and thus the required strength of the drive housing  3 , it is also not necessary that the bearing plate  20  is a plate with an unbroken surface. The bearing plate  20  with a connecting region of discrete struts  21 ,  22 ,  23  also permits sufficient stiffening and thus contributes to the strength of the drive housing  3  overall. 
     According to  FIGS. 6-8 , the bearing plate  20  preferably has three struts  21 ,  22 ,  23  in total. These are so arranged relative to one another that, when viewed along the axis of rotation A, they together depict an upside-down “Y”. This is because the angular distance between the two struts  22 ,  23  is smaller than the angular distance of each of these two struts  22 ,  23  from the strut  21 . Hereinbelow, the strut  21 , which extends upwards when the drive axle is mounted in the vehicle, will be referred to as the first strut, and the struts  22  and  23  that point obliquely downwards in the vehicle will be referred to as the second and third strut. 
     Between the second strut  22  and the third strut  23  there is a first opening  31  in the form of an opening segment. Between the first strut  21  and the second strut  22  there is an opening  33  likewise in the form of an opening segment. Between the first strut  21  and the third strut  23  there is an opening  32  likewise in the form of an opening segment. 
     In the exemplary embodiment, the openings, or opening segments,  32 ,  33  are of the same size, whereas the opening  31  that is at the bottom when the vehicle axle is mounted has a smaller opening area because of the smaller angle between the struts  22 ,  23 . 
     The struts  21 ,  22 ,  23  are of different widths in the circumferential direction of the bearing plate. The width of the two struts  22 ,  23 , through each of which a coolant channel  40  runs, is larger than the width of the first strut  21 , through which a coolant channel does not run. Such cross sections of the struts in which a coolant channel  40  does not run can additionally be of smaller thickness. For example, the struts of cross sections that are not used for cooling purposes can be provided with weight-reducing recesses. 
     The coolant channel  40  running in the strut  22  and/or in the strut  23  extends from the bearing housing  25 , into the interior of which it opens, to a coolant opening  41  with which the housing casing  4  is provided in a prolongation of the strut. The coolant opening  41  is a threaded bore radially in the housing casing  4 . The cross section of the coolant opening  41  is larger than the cross section of the coolant channel  40  running in the strut  22 ,  23 , so that a coolant connection piece  42  can be screwed into the threaded bore without any loss of coolant pressure. Coolant is fed in via the coolant connection piece  42  and then passes via the coolant channel  40  into the center of the bearing housing  25  in order to cool the rolling bearings  45 A,  45 B of the rotor shafts arranged there. 
     The bearing housing  25  is wider, in the longitudinal direction of the drive housing  3 , than the width, or thickness, of the struts  21 ,  22 ,  23 . The bearing housing  25  is provided on the axis of rotation A with a through-opening  47 , which is composed of a plurality of longitudinal portions. The two outer longitudinal portions of the through-opening  47  are bearing seats, in which there are seated the outer rings of the rolling bearings  45 A  45 B in which the rotor shafts  8 A,  8 B are mounted. The coolant channel  40  opens in the middle longitudinal portion of the through-opening  47 . Between the mentioned longitudinal portions there is in each case a further, short longitudinal portion which serves as a coolant feed to the rolling bearings  45 A and  45 B. Via this coolant feed, which opens in each case between the inner ring and the outer ring of the rolling bearings  45 A,  45 B, a portion of the coolant flowing via the coolant channel  40  into the through-opening  47  enters the region of the rolling elements of the rolling bearings  45 A,  45 B. 
     According to  FIG. 4 , the two rotor shafts  8 A,  8 B are hollow shafts over at least a portion of their length, which hollow shafts are open facing one another. Another portion of the coolant flowing via the coolant channel  40  into the through-opening  47  can therefore flow into the rotor shafts  8 A,  8 B and from there, via transverse bores  51  formed in the rotor shafts  8 A,  8 B, into the rotor  8  of the respective electric drive. 
     For bracing the drive housing  3 , the struts  21 ,  22 ,  23  are supported with their outer ends radially against the housing casing  4 . In addition, each strut  21 ,  22 ,  23  is supported axially against a fin  60 , which is formed in one piece inside the housing casing  4 . By means of the axial support against the fin  60 , the longitudinal position of the bearing plate  20  inside the drive housing  3  is clearly defined. 
     However, the fin  60  is here not a continuous fin over the entire circumference of the housing casing  4  but is composed in the circumferential direction of individual, separate fin segments. The fin segments are preferably located only on those circumferential portions of the housing casing  4  at which the outer ends of the struts  21 ,  22 ,  23  are located. 
     Since the fin  60  is composed of individual fin segments, the housing casing  4  can be provided on the circumferential portions without fin segments with, for example, windows, openings or similar apertures. In the exemplary embodiment, this is used to form a window  62 ,  63  in the housing casing in the region of the second opening  32  and in the region of the third opening  33 . 
     Electric lines lead through the window  62 ,  63  and through the second opening  62  or the third opening  63  to terminal blocks  61 A,  61 B of the electric drives  5 A,  5 B. The two terminal blocks  61 A,  61 B are arranged inside the housing casing  4  on different, namely mutually opposite, circumferential portions. Accordingly, the two windows  62 ,  63  are also formed in the housing casing  4  on mutually opposite circumferential portions. 
     On the outside, the windows  62 ,  63  are each covered by a protective box  64 ,  65 . In the protective box  65  there are electrical connectors  59 , from which electric lines lead to the terminal block  61 A of the first electric drive  5 A. The earth conductor of the electric line is contacted in a threaded hole  69  of the bearing housing  25 . In the other protective box  64  too there are electrical connectors  59 , from which electric lines lead to the terminal block  61 B of the second electric drive  5 B. Again, the earth conductor of the electric line is contacted in a threaded hole in the bearing housing  25 . 
     The terminal block  61 A of the first electric drive  5 A extends into the opening  32 , and the terminal block  61  B of the second electric drive  5 A extends into the opening  33 . For a particularly compact arrangement, the two terminal blocks  61 A,  61 B extend so far into the respective openings  32 ,  33  that the terminal blocks  61 A,  61 B overlap partly in the longitudinal direction of the drive housing  3 . 
     In order to keep the electric drive unit within the surrounding vehicle compact, the protective boxes  64 ,  65  are in such a form that the main extent of the protective boxes  64 ,  65  is parallel to the axes of rotation A ( FIG. 1 ). The protective boxes  64 ,  65  preferably extend in one direction, so that electrical connecting cables can be laid on only one side of the vehicle. 
     On the longitudinal portion of the drive housing  3  on which the bearing plate  20  is located, the housing casing  4  is provided at its lowermost point with one or with a plurality of coolant openings  70 . Owing to this position of the coolant opening  70 , the coolant opening connects the first opening  31  arranged between the struts  22 ,  23  to a coolant tank  71  arranged on the outside of the housing casing  4 . Coolant can therefore flow off via the coolant opening  70  into the coolant tank  71  arranged at the lowermost point of the drive unit, where it can collect. 
     There is suitable as the coolant, since it also flows through parts of the electric motors, especially a cooling oil. This should have a specification such that it additionally has good lubricating properties in the lubrication of the rolling bearings  45 A,  45 B and of the further rolling bearings of the drive unit. 
       FIG. 9  shows a second embodiment of the drive housing  3 , wherein the rotor shafts are not shown in this drawing. According to  FIG. 9 , the bearing plate  20 , the bearing housing  25  and the drive housing  3  are produced in one piece by casting, wherein their structural design is the same as the multipart system according to  FIGS. 2 to 6  in the assembled state. 
     There is further formed on the outside of the drive housing  3 , in the region of the coolant channel  40 , a distributor block  72 , wherein the distributor block  72  is also formed in one piece on the drive housing  3 . The distributor block  72  has, in addition to the coolant channel  40 , also three further bores, wherein the first bore  43  runs through the distributor block  72  parallel to the axis of rotation A. The second and third bores  44 A,  44 B extend in parallel to the left and right of the coolant channel  40 , wherein they intersect the first bore  43  and pass through the outside wall of the drive housing  3 . For manufacturing reasons, the first, second and third bores  43 ,  44 A,  44 B are in the form of through-bores, wherein the bore openings on the outer side of the distributor block  72  are subsequently closed tightly by plugs  73 . 
     The first, second and third bores  43 ,  44 A,  44 B are adapted to remove coolant from the coolant channel  40  and divert it into an annular gap  74 A,  74 B which surrounds the stator externally. Via access openings, not shown, which surround the stator in an annular manner, the coolant is guided into the interior of the electric drive  5 A,  5 B, wherein it is again fed via a coolant opening, not shown, to the coolant tank, likewise not shown. Additional cooling of the electric drive unit is thus made possible. 
     LIST OF REFERENCE SIGNS 
       2  tube portion 
       3  drive housing 
       3 A transmission housing 
       3 B transmission housing 
       4  housing casing 
       5 A electric drive 
       5 B electric drive 
       8  rotor 
       8 A rotor shaft 
       8 B rotor shaft 
       10 A shaft end 
       10 B shaft end 
       20  bearing plate 
       21  strut 
       22  strut 
       23  strut 
       25  bearing housing 
       31  opening 
       32  opening 
       33  opening 
       40  coolant channel 
       41  coolant opening 
       42  coolant connection piece 
       43  first bore 
       44 A second bore 
       44 B third bore 
       45 A rolling bearing 
       45 B rolling bearing 
       47  through-opening 
       51  transverse bore 
       59  connector 
       60  fin 
       61 A terminal block 
       61 B terminal block 
       62  window 
       63  window 
       64  protective box 
       65  protective box 
       68  electric line 
       69  threaded hole for earth conductor 
       70  coolant opening 
       71  coolant tank 
       72  distributor block 
       73  plug 
       74 A annular gap 
       74 B annular gap 
     A axis of rotation