Patent Publication Number: US-2022234438-A1

Title: Electric Drive Unit for a Motor Vehicle

Description:
The invention relates to an electric drive unit for a motor vehicle, having an electric drive, a transmission which is connected downstream of the electric drive in the power flow direction and is arranged in a transmission housing, means for circulating cooling liquid in the interior of the transmission housing, and a rotatably arranged input or output shaft of the transmission, wherein the transmission housing is comprised of a housing shell, which annularly surrounds a central axis, and of an end wall, and wherein the end wall extends radially outward from an opening for the input or the output shaft as far as a connecting region in which the end wall and the housing shell are connected to each other. 
     An electric drive unit of this type is used as a traction drive of a vehicle. It is preferably used as part of an electric drive axle for a utility vehicle. In this type of vehicle axle, a multi-stage transmission is connected downstream of the electric drive, which is arranged close to the center of the vehicle for weight advantages. The transmission is arranged by itself or else together with the electric drive in a housing which is comprised of a housing shell enclosing the interior of the transmission, including the transmission elements arranged therein, and an end wall closing the interior on the end side. The housing shell is predominantly annular. The end wall extends substantially radially and is provided centrally with an opening through which the transmission input shaft or the transmission output shaft leads. 
     In order to cool the transmission elements, cooling liquid is circulated in the interior of the transmission housing, this taking place in a circuit in which the cooling liquid flows as far as possible through all the mechanically loaded regions of the transmission, including the rolling bearings present for the rotating transmission elements. The cooling liquid used is preferably a transmission oil, and this liquid therefore lubricates the transmission elements and also transports away heat. 
     In particular if the transmission is designed as a planetary gearing, the transmission oil is intensely rotated on the inner side of the housing shell. The rotation of the oil causes the formation of an oil sump running annularly around the inner side of the transmission housing. In the case of an injection-type lubrication system, this makes the ideal drainage of the lubricant difficult. In particular, in the course of the circulation of the oil, extraction of the oil by suction is made difficult since, due to this rotation, the oil flows at a high speed past the oil drain which is provided, instead of fully entering the latter. 
     The invention is based on the object of using structural measures to improve the flow conditions, in particular in those regions of the transmission housing in which, over the course of the circulation of the cooling liquid, the latter is removed, or extracted by suction, from the transmission housing. 
     In order to achieve this object, an electric drive unit comprising the features of claim  1  is proposed. 
     An additional annular chamber, which is connected to the interior of the transmission housing only via individual openings, is used here for calming the cooling liquid flowing or rotating at high speed in other regions of the transmission housing. For the cooling liquid, the annular chamber has the function of a calming zone. For this purpose, the annular calming zone is preferably arranged on a large diameter. The annular calming zone is open toward the interior on certain circumferential portions, namely in the region of the individual openings, such that cooling liquid and in particular transmission oil can flow via these openings into the annular chamber and is calmed therein. On other circumferential portions, by contrast, the annular chamber is substantially closed in relation to the transmission interior, and therefore, in these circumferential regions, no substantial exchange of cooling liquid takes place, and the fluid and especially the flow thereof in these regions of the annular chamber can be calmed. As a result of calming the flow, the extraction of the oil by suction or the drainage of oil is substantially improved, in particular if the space conditions in the region of the extraction of the oil by suction are in any case dimensioned tightly. 
     According to a preferred refinement of the annular calming zone, it is advantageous if the openings alternate with opening-free circumferential portions in the circumferential direction. For example, there can be in each case six to ten openings and opening-free circumferential portions of the annular chamber. 
     With regard to the annular chamber used as calming zone, it is proposed that the wall of the annular chamber is formed partially by the housing shell and partially by the end wall, the end wall being a partition between the transmission and the electric motor of the drive unit. 
     In order for the annular chamber to be arranged on a large diameter, it is proposed that the diameter of the annular chamber is larger than the largest diameter which the inner side of the housing shell has outside the region of the annular chamber. 
     Furthermore, it is proposed that the annular chamber is delimited toward the interior by an inner chamber wall, and toward the outer side of the housing shell by an outer chamber wall, wherein the openings and the opening-free circumferential portions are located in or on the inner chamber wall. 
     According to a refinement which is advantageous especially in terms of production, the inner chamber wall is crenellated, wherein the crenellations form the opening-free circumferential portions, and the circumferential regions between the crenellations form the openings. The axial extent of the openings, i.e., the extent thereof in the direction of the axis, is preferably smaller than the axial length of the annular chamber. 
     With regard to the cross-sectional geometry of the annular chamber, it is furthermore proposed that the length of the annular chamber in the axial direction is greater than the maximum width of the annular chamber, as measured between the inner and the outer chamber wall. 
     Preferably, bores or channels are provided in the housing shell, which lead from the annular chamber as far as the outer side of the housing shell. In conjunction with the guiding of the coolant, these bores or channels can be used for different functions and purposes. For example, the outer ends of the bores or channels can be provided with a thread in order thus to arrange a vent valve, a vent filter, a measuring plug for detecting the cooling liquid level, a magnetically operating catch device for metal chips, or a temperature sensor in the respective bore or in the respective channel. One of the bores or channels, preferably located at the lowest point of the annular chamber, serves for letting out or discharging the transmission oil into a collector arranged below. 
     Since the functions linked to the bores or channels sometimes need a relatively large amount of space, it is proposed by a further refinement that the housing shell is formed around the annular chamber as a flange which is widened radially in relation to the remaining housing shell, and that the bores or channels lead through the flange as far as the outer side thereof. The additional volume which is connected to the radially widened flange can therefore be usable for obtaining space for sufficiently large bores or channels, and space for the technical intended purposes associated with these bores or channels. 
     In addition, the flange can be used for the screw connection of the transmission housing, for example to the directly adjacent motor housing of the electric drive. For this purpose, it is advantageous if the flange is provided with axial openings, which are arranged distributed over its circumference, for receiving screws or threaded bolts, for example threaded bolts as rigid connecting elements between transmission housing and motor housing. 
     In order to obtain particularly favorable flow conditions in the region of the calming zone, it is proposed that the end wall is provided with a collar extending into the annular chamber, and that the transition between the radially extending part of the end wall and the collar is designed as a rounded portion. The radius of this rounded portion is preferably between 25% and 75% of the maximum width of the annular chamber, as measured between the inner chamber wall and the outer chamber wall. 
     The wall of the annular chamber, to the extent that the wall is formed by the housing shell, is a U-shaped wall of a groove which is open toward the end wall. 
     The groove which is open toward the end wall creates the possibility, on the end wall, of integrally forming a collar which extends into the annular chamber, wherein the collar lies against one of the walls of the groove, preferably against the radially outer wall of the groove. 
     In this refinement, the groove not only has the task of calming the coolant flow, but the groove is at the same time a centering element in order to fix the end wall in the connecting region in a precise alignment on the housing shell. For this mutual alignment, it is additionally advantageous if the collar or centering collar integrally formed on the end wall lies against the corresponding wall of the groove with the interposition of at least one annular seal, and thus a liquid-tight connection between end wall and housing shell is achieved in the connecting region. 
     The seal is preferably inserted into a sealing groove which is formed in the collar or centering collar. 
     With a refinement of the electric drive unit, it is proposed that the transmission is a planetary gearing, the ring transmission of which is the inner side of the housing shell that is provided with a toothing. The toothing is designed as a helical toothing in such a manner that the cooling liquid which has accumulated in the toothing is transported in the direction of the longitudinal portion of the housing shell that has the openings. 
    
    
     
       Further advantages and details of the electric drive axle for a utility vehicle emerge from the description below of an exemplary embodiment which is reproduced in the drawing. In detail, 
         FIG. 1 : shows an electric drive axle for a utility vehicle with a multi-stage transmission in the form of a double planetary gearing, a transmission housing receiving the transmission, a motor housing placed on this transmission housing, and an axle housing likewise placed on the transmission housing; 
         FIG. 2 : shows a perspective partial section of the transmission housing, together with a planet carrier of the transmission; 
         FIG. 3 : shows a perspective partial section of the transmission housing, together with an end wall arranged between the transmission housing and the motor housing; 
         FIG. 3 a   : shows an enlarged detail of the connecting region from  FIG. 3 ; 
         FIG. 4 : shows a longitudinal section through parts of the transmission and through the end wall, but without the transmission housing; 
         FIG. 5 : shows a further perspective view of the transmission housing from a different viewing angle; 
         FIG. 6 : shows a side view of the transmission housing; and 
         FIG. 7 : shows a section through the transmission housing according to the section plane VII-VII denoted in  FIG. 6 . 
     
    
    
       FIG. 1  shows, in an overview illustration, the one half of an electric drive axle for a motor vehicle. The illustrated half of the axle is used for driving a vehicle wheel  2  which is mounted rotatably on a steering knuckle  1  and is illustrated by dashed lines at the left edge of  FIG. 1 . The similarly configured second half of the drive axle is symmetrically located on the other side of the vehicle center plane M indicated in  FIG. 1 , and carries the respective vehicle wheel of the other side of the vehicle. The electric drive axle in its entirety is a rigid axle which is continuous from the one side of the vehicle to the other. 
     For each side of the vehicle, and therefore for driving the respective vehicle wheel  2 , an electric drive  5 , in particular an electric motor, is provided in the vicinity of the vehicle center plane M. A transmission  6 , here in the form of a two-stage planetary gearing, is connected downstream of each electric motor toward the outer side of the vehicle. 
     The two electric drives are situated in a common motor housing  3  which can be in the form of one part or multiple parts. Each transmission  6  is situated in a transmission housing  4  which is flange-mounted on the motor housing  3 . 
     The transmission housing  4  is assembled, inter alia, from a substantially cylindrical housing shell  11 , the inner side  7  of which annularly surrounds the transmission elements of the transmission  6 , and from an end wall  12  which is integral with the housing shell  11 . The end wall  12  is predominantly closed, but leaves a transmission opening  12   a  free in its center, through which the transmission output shaft  18 , rotating on the central axis of rotation A, of the transmission  6  leads. 
     Also at its other end, the transmission housing  4  is provided with an end wall  13  which is, however, a separate component. In a connecting region  14  encircling circularly, this end wall  13  and the housing shell  11  are connected fluid-tightly to each other. 
     In its center, the end wall  13  is provided with an opening  17  through which the input shaft  19  of the transmission leads. Said input shaft  19  of the transmission can be at the same time the motor output shaft, and it likewise rotates on the axis A. 
     The end wall  13  extends radially outward from the opening  17  for the transmission input shaft  19  as far as the connecting region  14  in which the end wall  13  and the housing shell  11  are connected fluid-tightly to each other. 
     The transmission output shaft  18  leading out of the other end wall  12  can be connected for conjoint rotation, preferably via splines, to a drive shaft which leads to the vehicle wheel  2  and drives the latter. The drive shaft rotates in a tubular axle housing  15  of the drive unit which likewise extends on the central axis A. The axle housing  15  is fastened to the end wall  12  by means of a flange  16 . 
     The axle housing  15  is provided at its vehicle-outer end with the steering knuckle  1 . In addition, the brake carrier of the vehicle brake, preferably the brake carrier of a disk brake, is fastened to the axle housing  15 . Axle guiding elements, for example a longitudinal link and optionally a transverse link of the vehicle axle, are likewise fastened to the axle housing  15 . 
     For fastening the axle housing  15  to the transmission housing  4 , the axle housing  15  is provided at its vehicle-inner end with a radially widened flange  16 . The flange  16  is rigidly screwed against the end wall  12  of the transmission housing  4  by means of a plurality of screws. 
     The connection of the motor housing  3  accommodating the electric drive  5  and of the transmission housing  4  also takes place by means of screw connections, for which purpose the respective ends of these housing parts are designed as radial flanges  25 ,  26  which are fixedly connected to one another via screws which lead through axial openings  27  in the flange  26  of the transmission housing  4 . 
     The transmission housing  4  not only has the function of a housing, but it is also itself part of the epicyclic or planetary gearing by a helical toothing  30   a , which is arranged around the axis of rotation A, of the first transmission stage and, offset axially, a helical toothing  30   b , which is arranged around the axis of rotation A, of the second transmission stage being formed on the inner side  7  of the housing shell  11 . Each of the two helical toothings  30   a ,  30   b  therefore in each case forms the ring transmission of the planetary gearing concerned. The alignment or oblique position of the teeth of the helical toothing  30   b  is opposed to the teeth of the first helical toothing  30   a . The planet wheels of the two transmission stages of the planetary gearing mesh with the helical toothings. 
     The remaining transmission elements of the planetary gearing are arranged in a planet carrier which rotates on the axis A and is inserted as a preassembled transmission carrier  17   c  into the transmission housing  4 . The central element of the transmission carrier  17   c  is the transmission output shaft  18  which rotates on the axis A and protrudes out of the likewise centrally arranged transmission opening  12   a  of the transmission housing  4 . 
     The cooling of the transmission  6  and of its sometimes heavily loaded teeth, pinions and bearings takes place by means of a cooling liquid which is circulated by a pump. The cooling liquid is preferably a transmission oil, and therefore the liquid both lubricates the transmission elements and also transports away heat. 
     The design in the form of a planetary gearing causes cooling liquid and lubricating fluid to be held as the result of centrifugal forces outward by the planet wheels against the helical toothings  30   a ,  30   b . The cooling liquid therefore accumulates on the inner side  7  of the housing shell  11 , and at the same time a strong rotation of the liquid takes place along this inner side  7 . The liquid has to be caught and made available again to the cooling and lubricating process by the liquid being transported back into more central regions of the transmission and into the region of rolling bearings, for example to the rolling bearings of the transmission input shaft  19  and of the transmission output shaft  18 . 
     During active circulation cooling, the oblique position of both gear wheels  30   a ,  30   b  causes a scoop effect, which is directed toward the end wall  13 , on the coolant, in association with a rotation of the transmission oil along the inner side  7 . Only in the event of a passive sump cooling is the orientation of the gear wheel  30   b  reversed such that then a scoop effect directed toward the end wall  12  also occurs. 
     As a result of the rotation of the transmission oil on the inner side  7  of the transmission housing, a powerfully flowing oil sump is formed there which, if no additional measures as previously described are taken, would make the ideal drainage of the lubricant and cooling difficult. This is because the flow which arises would make the extraction of the transmission oil by suction, which is necessary in the course of the circulation, difficult if the transmission oil were to flow at a high flow speed past the oil drain which is present, instead of fully entering the oil drain. 
     The solution to this problem resides in providing an annular chamber  33  which preferably surrounds the axis A circularly and extends in the circumferential direction along that connecting region  14  in which the end wall  13  is fastened to the housing shell  11 . It is important that the annular chamber  33  is connected to the interior  7  of the transmission housing only via individual openings  40 . The openings  40  have been distributed uniformly over the inner circumference of the annular chamber  33 . 
     The annular chamber  33  is used for calming the cooling liquid which flows at high speed in other regions of the transmission housing and powerfully rotates especially along the inner wall. For the cooling liquid, the annular chamber  33  therefore has the function of a calming zone which is open toward the interior  7  only on certain circumferential portions, namely in the region of the individual openings  40 , such that the cooling liquid or the transmission oil flows via these openings  40  into the annular chamber  33  and is calmed therein. 
     On other circumferential portions, by contrast, the annular chamber  33  is substantially closed in relation to the transmission interior  7  such that, on these other circumferential portions, no substantial exchange of liquid takes place and the liquid flow along these regions of the annular chamber  33  that are closed toward the transmission interior can be calmed. The calming of the flow leads to improved extraction of the oil by suction or to an improved drainage of oil, which takes place directly out of the annular chamber  33 , for example by a channel which opens into the annular chamber at the lowest point of the annular chamber  33  and through which the liquid can flow off downward to a collector. 
     In order that the annular chamber  33  forms the calming zone, the openings  40  alternate with opening-free circumferential portions  41  in the circumferential direction of the annular chamber. There is an equal number of openings  40  and of opening-free circumferential portions  41 ; in the exemplary embodiment, there are six openings  40  over the circumference and analogously six opening-free circumferential portions  41 . 
     The diameter of the annular chamber  33  is larger than the largest diameter which the inner side  7  of the housing shell  11  has outside the region of the annular chamber  33 . 
     By the annular chamber  33  extending along that connecting region  14  in which the end wall  13  is fastened to the housing shell  11 , the wall of the annular chamber  33  is formed partially by the housing shell  11  and partially by the end wall  13 . 
     The annular chamber  33  is delimited toward the interior  7  by an inner chamber wall  44  and toward the outer side of the housing shell  11  by an outer chamber wall  45 . The openings  40  and the opening-free circumferential portions  41  are located in or on the inner chamber wall  44 . 
     In a simple manner in terms of production, the inner chamber wall  44  is crenellated, wherein crenellations which extend parallel to the central axis A form the opening-free circumferential portions  41 , and the circumferential portions between the crenellations form the openings  40 . The crenellations and also the opening-free circumferential portions  41  arranged between the crenellations are configured rectangularly in a radial view of the inner chamber wall  44 . 
     The wall of the annular chamber  33 , to the extent that this wall is formed by the housing shell  11  and not by the end wall  13 , is a U-shaped wall which runs circularly around the axis A and is in the form of a groove open toward the end wall  13 . The length of this groove and the length of the annular chamber  33  in the direction of the axis A is greater than the maximum width of the annular chamber  33 , as measured between the inner chamber wall  44  and the outer chamber wall  45 . 
     The axial extent of the openings  40 , i.e., the extent thereof in the direction of the axis A, is smaller than the axial length of the annular chamber  33 . 
     The opening-free circumferential sections  41  extend axially in the direction of the end wall  13  to such an extent that either they are in contact with the inner side  13   a  of the end wall  13 , or here only a small gap remains via which no or substantially no liquid exchange is possible. 
     The end wall  13  separates the transmission  6  from the electric drive  5 . On its side facing the transmission  6 , the end wall  13  is provided with a collar  50  which extends at a right angle to the main extent of the end wall  13  and serves inter alia as a centering collar. The collar  50  is an integral part of the end wall  13 . It is of such an axial length that it extends into the annular chamber  33 . For centering purposes, the collar  50  lies with its outer side radially against the outer chamber wall  45  with the interposition of a seal  51 . In the exemplary embodiment, the axial length of the encircling centering collar is approximately half of the axial extent of the annular chamber  33 . 
     Since the connection region  14  has to be liquid-tight, the collar  50  lies radially against the chamber wall  45  with the interposition of the annular seal  51 . The seal  51  is inserted into a sealing groove on the outer side of the collar  50 . 
     According to  FIG. 3 a   , the transition between the inner side  13   a  of the end wall  13  extending transversely with respect to the central axis A and the inner side  50   a  of the collar  50  is designed as a rounded portion  52 , and preferably as a 90° rounded portion with a radius R of the rounded portion  52  that is between 25% and 75% of the maximum width of the annular chamber  33  between the inner chamber wall  44  and the outer chamber wall  45 . The design of the transition in the form of a rounded portion  52  leads to improved guidance of the flow on the annular chamber  33 . 
     A plurality of radially running bores and channels  60  lead from the annular chamber  33  onto the outer side of the housing shell  11  and in particular onto the outer side of the flange  26  of the transmission housing since the flange  26  is arranged around the annular chamber  33 . 
     One of the radial bores or channels  60  is an oil drain via which the transmission oil which has accumulated in the annular chamber  33  and has been calmed therein can drain downward to a collector. For this reason, this bore or this channel is located at the lowest point of the flange  26 . 
     Further bores or channels  60  can be used in conjunction with the guiding of the coolant for different functions and purposes. For example, they can receive a vent valve, a vent filter, a measuring plug for detecting the cooling liquid level in the transmission, a magnetically operating catch device for metal chips which have accumulated in the liquid, or a temperature sensor for sensing the oil temperature. 
     Since the bores or channels  60  are not located in the rather thin-walled part of the transmission housing, but rather in the region of the radially widened flange  26  of the transmission housing, there is sufficient space here for such additional functional components. For example, the outer ends of the bores or channels  60  can be provided with a thread into which the respective functional component is screwed from the outside. 
     The bores or channels  60  are located on those circumferential portions of the flange  26  on which the flange does not have any of the axial openings  27 . 
     LIST OF REFERENCE CHARACTERS 
     
         
           1  Steering knuckle 
           2  Vehicle wheel 
           3  Motor housing 
           4  Transmission housing 
           5  Electric drive 
           6  Transmission 
           7  Inner side 
           11  Housing shell 
           12  End wall 
           12   a  Transmission opening 
           13  End wall 
           13   a  Inner side of end wall 
           14  Connecting region 
           15  Axle housing 
           16  Flange 
           17  Opening 
           17   c  Transmission carrier 
           18  Transmission output shaft 
           19  Transmission input shaft 
           25  Flange 
           26  Flange 
           27  Axial opening 
           30   a  Helical toothing 
           30   b  Helical toothing 
           33  Annular chamber 
           40  Opening 
           41  Opening-free circumferential portion 
           44  Inner chamber wall 
           45  Outer chamber wall 
           50  Collar, centering collar 
           50   a  Inner side of collar 
           51  Seal 
           52  Rounded portion 
           60  Bore, channel 
         A Axis, axis of rotation 
         M Vehicle center line 
         R Radius