Abstract:
Two-stage or three-stage spur gear transmission having a single-piece housing which has a drive-input-side cover opening and a closing cover which closes off said cover opening, having a drive output shaft which supports a drive output gearwheel between two bearings, and having an intermediate shaft which supports an intermediate gearwheel, which is driven directly or indirectly by an input drive pinion, and an intermediate pinion, which meshes with the drive output gearwheel, and is mounted by means of two intermediate shaft bearings which are adjacent to the intermediate pinion. The two intermediate shaft bearings which are adjacent to the intermediate pinion are arranged in a drive-output-side chamber, which is preferably not undercut in the direction of the assembly opening, of the housing. A third intermediate shaft bearing is arranged in a bearing bore of the cover. Said cover is centered on said third intermediate shaft bearing along a parting joint which runs perpendicular to the axis direction.

Description:
BACKGROUND OF THE TECHNOLOGY 
       [0001]    A known spur gear transmission of EP-A-686788 has a single-piece housing. The latter forms, between a drive-output-side housing wall and a partition, a drive-output-side chamber which contains the drive output shaft with the drive output gearwheel. In order that the drive output gearwheel can be mounted in the drive-output-side chamber, its side wall has to have an assembly opening. This is achieved in that the drive-input-side housing cover is connected to the transmission housing by means of a parting joint which runs at an incline and extends above the drive-output-side chamber. The cover is connected to the transmission housing by fastening screws which run in an axially parallel manner, that is to say not perpendicularly to the parting joint. The housing also forms a drive-input-side chamber into which the motor pinion projects through the cover. Said motor pinion meshes with an intermediate gearwheel which is arranged on an intermediate shaft in the drive-input-side chamber. The intermediate shaft supports an intermediate pinion which drives the drive output gearwheel. Said intermediate shaft is mounted at both sides of the intermediate pinion, specifically in the drive-output-side wall and in the partition. The drive-input-side, exposed end of the intermediate shaft projects into a corresponding bore of the cover in order to centre the latter. This bore is not designed as a bearing. 
         [0002]    Said known arrangement has not been proven. Firstly, the assembly is very difficult because the fastening screws exert forces on the cover, which forces have a force component running parallel to the parting joint, which force component seeks to move the cover relative to the housing. However, a movement of said type absolutely must be avoided because it leads to friction contact of the shaft with the centering bore in the cover. This can not only result in damage to the shaft, but can also lead to overloading of the intermediate shaft bearing. It is not obvious how this problem could be solved. In particular, the inclined parting joint cannot easily be replaced with the otherwise customary parting joint which runs perpendicularly to the axial direction because then the assembly of the drive output gearwheel would not be possible. A further disadvantage of the known construction consists in that the inclination of the parting joint requires precise adjustment of the cover about an axis perpendicular to the inclined parting joint, since an imprecise positioning of the cover with respect to this axis would lead to an angular error in the toothing of the input drive pinion with the intermediate gearwheel of the first stage. It is barely practically possible to obtain said precise adjustment. Finally, the known transmission has the disadvantage that the stiffness of the housing is impaired by the inclined profile of the parting joint which extends into the drive-output-side chamber. 
         [0003]    Given that the drive output shaft can be mounted with the drive output gearwheel and the associated bearings in the housing which is designed without an undercut, the creation of a lateral assembly opening by an inclined cover joint is unnecessary. The disadvantages explained above can thus be avoided. The assembly is very simple because after inserting the shafts and wheels it is necessary merely to put on the cover. As a result of the third bearing, which is provided in the cover, of the intermediate shaft, the cover is automatically centered. In contrast, the triple bearing arrangement leads to favourable force conditions at the intermediate shaft and its bearings, thereby permitting smaller dimensioning of said bearings and therefore a reduction of the spatial requirement. There are also no additional assembly steps required for axially fixing the shaft, because said axial fixing can be effected by means of the two bearings at the ends of the shaft. 
         [0004]    Although a triple bearing arrangement of a transmission shaft is known (“SEW Eurodrive” brochure, FIG. 5.3), this relates to a transmission having a multi-part housing which has an assembly opening not only at the drive input side but also at the drive output side of a housing central part and contains a partition. The triple bearing arrangement of the intermediate shaft of said transmission is situated in bearing bores which are formed by the housing central part. This entails cumbersome assembly, because the intermediate shaft and its bearings must be mounted from both sides of the housing central part. In addition, the multi-part design of the housing has the disadvantages, in relation to single-part housings having only one assembly opening, of reduced stiffness or, for the same stiffness, increased weight and increased costs. It is not possible to gather any indications from said prior art of how to facilitate assembly and avoid centering errors in the transmission specified at the beginning. 
       SUMMARY 
       [0005]    In one disclosed embodiment, the known disadvantage of a triple bearing arrangement of a shaft on account of its static indeterminacy does not apply, because the cover, as a result of the centering action caused by the shaft, is fixed in precisely that position in which the third bearing, which is arranged in the cover, is aligned with the two other bearings. Angular errors in the toothing of the first stage also cannot occur, because the cover joint is perpendicular to the axis direction. A further advantage of the invention is that the central bearing of the three shaft bearings is considerably relieved of load and can therefore be of smaller dimensions. As a result, there is a gain in space in the region of said bearing arrangement, which gain in space can be utilized for the arrangement of the drive output shaft or its bearing arrangement. While, in the case of the first-mentioned known construction, the intermediate gearwheel must be arranged as close as possible to the bearing, which is provided in the partition, of the intermediate shaft in order to limit the bending loading of the shaft, the invention opens up the possibility of arranging said gearwheel remote from the central intermediate shaft bearing. This results in a greater degree of design freedom. For example, this creates the possibility of arranging the drive-input-side drive output shaft bearing and the central intermediate shaft bearing so as to be offset with respect to one another in the axis direction, wherein the central intermediate shaft bearing can be arranged further remote from the drive input than the drive output shaft bearing. Another result of said design freedom is in housings which can be used selectively for two-stage or three-stage transmissions. In the two-stage case, the intermediate gearwheel is to be arranged close to the cover, while in the three-stage case, said intermediate gearwheel is to be mounted remote from the cover, because the position close to the cover is taken up by the further gearwheel. This different positioning of the intermediate gearwheel is possible on account of the invention despite the reduced dimensioning of the intermediate shaft and its bearings, because these are arranged at both sides of the intermediate gearwheel. 
         [0006]    The transmission in one embodiment is very easy to assemble, because, for correct assembly of the cover, it is necessary merely to mount the intermediate shaft in its drive-output-side and central bearings and subsequently to place and screw the cover in the position which is predefined in this way. It is particularly easy to assemble when the remaining structure of the housing is also easy to assemble. This applies in particular to a construction in which not only the intermediate shaft but also the drive output shaft with the associated wheels and bearings can be pre-assembled and inserted as a finished unit into the housing. This is the case in a transmission whose drive-output-side chamber is delimited only by two faces, the first of which, for holding the drive output shaft, opens without an undercut in the direction of the drive output side, while the other, for the assembly of the intermediate shaft, opens without an undercut in the direction of the drive input side. 
         [0007]    In another embodiment, the drive output shaft unit, like the intermediate shaft unit, can be mounted from the drive input side by virtue of the drive-output-side chamber, for the assembly of the drive output shaft, opening without an undercut in the direction of the drive input side. 
         [0008]    The lack of undercut is restricted by the addition that said lack of undercut should be present at least in the unprocessed state of the cast or pressed part. This is intended to prevent this feature from being evaded by means of a turning process which is carried out only during the machining stage and has no effect on the ease of assembly. In the finished state, it is sufficient if the diameter of the holding bore in the case of the drive-input-side bearing of the drive output shaft is at least so large that the drive output gearwheel and the drive-output-side drive output shaft bearing can fit through. In the case of the intermediate shaft, it is correspondingly sufficient if the holding bore in the case of the assembly-side bearing has a diameter which is so large that the intermediate pinion and the drive-output-side bearing of the intermediate shaft can fit through. It is not important whether the holding bore possibly also has a turned portion between said positions. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  shows a longitudinal section of a first exemplary embodiment with a flange-mounted motor, 
           [0010]      FIG. 2  shows a perspective view of the empty housing from the drive output side, 
           [0011]      FIG. 3  shows a corresponding view of the cover from the drive output side, 
           [0012]      FIG. 4  shows a longitudinal section through a second exemplary embodiment as per line IV-IV of  FIG. 7 , 
           [0013]      FIGS. 5 and 6  show perspective views of the empty housing of the associated cover, 
           [0014]      FIG. 7  shows a view of the open housing from the drive input side, with the intermediate shaft, 
           [0015]      FIG. 8  is a simplified illustration corresponding to  FIG. 7 , without the intermediate shaft, 
           [0016]      FIG. 9  shows a section as per line IX-IX of  FIG. 4 , 
           [0017]      FIG. 10  shows a detail from  FIG. 8 , and 
           [0018]      FIGS. 11 to 14  show successive stages of the assembly of the intermediate shaft. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    The transmission housing  1 , which in  FIG. 1  is hatched from bottom left to top right, of the first exemplary embodiment has a foot  2  and a drive-input-side opening which is closed off by a cover  3  on which, in the example illustrated, a motor  26  is flange-mounted, with an input drive pinion  7  projecting into the transmission housing. 
         [0020]    The housing  1  forms a drive-output-side chamber  5  which holds the drive output shaft  16  with the drive output gearwheel  6  and the associated bearings, specifically a drive-input-side bearing  8  in a bearing bore  9  and a drive-output-side bearing  10  in a bearing bore  11 . The chamber  5  having the bearing bores  9  and  11  is not undercut as viewed from the drive input side. The drive output shaft  16 , the gearwheel  6  and the rolling bearings  8 ,  10  can therefore be inserted as a pre-assembled unit from the drive input side. The drive output shaft unit is held axially in the chamber  5  at the drive input side by means of a projection  19  of the cover  3  and at the drive output side by a circlip or a housing collar (not shown). 
         [0021]    That part of the drive-output-side chamber  5  which holds the drive output shaft  16  is enclosed by a wall  28  which is aligned substantially axially parallel and which extends cylindrically over more than 180° at least in the region of the bearing bores  9  and  11 . Said wall  28  is connected to the foot  2 , partially by means of ribs and partially by means of a transverse wall  4 . 
         [0022]    Situated on the drive input side of the housing is a drive-input-side chamber  12  which is enclosed by walls  29  and the cover  3  and in which are situated one or more transmission stages. Shown is an example in which the input drive pinion  7  acts on an intermediate gearwheel  13  which is supported by an intermediate shaft  14 . Said intermediate shaft  14  supports, at its other end, an intermediate pinion  15  which meshes with the drive output gearwheel  6 . The drive-output-side chamber  5  has, for holding the intermediate shaft  14 , a lateral convexity  5   a  which is surrounded by walls  23  which run substantially axially parallel and is delimited at the drive output side by a wall  24 . The cylindrical inner face  20 , which extends over more than 180° in circumference, of said lateral convexity  5   a  forms the bearing bore for two rolling bearings of the intermediate shaft. Of said rolling bearings, the rolling bearing  22  is arranged at the drive-output-side end of the intermediate shaft  14  of the chamber convexity  5   a , and the rolling bearing  25  is arranged approximately at the centre of the shaft and at the drive-input-side end of the chamber convexity  5   a . This permits support of the intermediate shaft directly at both sides of the highly-loaded intermediate pinion  15 . This limits the bending moment which is to be absorbed by the intermediate shaft and permits favourable dimensioning. 
         [0023]    A third bearing  17  for the drive-input-side end of the intermediate shaft is situated in a bearing bore  18  of the cover  3 . In this way, the intermediate shaft  14  is additionally supported on the free side of the intermediate gearwheel  13 . The central bearing is correspondingly relieved of load and can therefore be of space-saving dimensions. In addition, this creates the possibility of arranging the intermediate gearwheel at a relatively great distance from the central bearing  25 , which has the advantage that said central bearing  25  of the intermediate shaft and the drive-input-side bearing  8  of the drive output shaft  16  can be arranged axially offset with respect to one another. This makes it possible to place the central bearing  25  of the intermediate shaft—as already discussed above—directly adjacent to the intermediate pinion  15 . 
         [0024]    The disadvantages of the statically indeterminate arrangement, because of which the triple bearing arrangement of a shaft is normally avoided, are evaded in that the bearing of the shaft in the cover is utilized to centre said cover. This ensures that said third bearing is mounted precisely aligned with the two other bearings. In order that there is no resulting undesired double fit of said bearing in relation to the engagement of the cover projection  19  into the bearing bore  9 , said engagement is provided with a correspondingly great degree of play. Like the drive output shaft  16 , the intermediate shaft  14  as an assembled unit with the intermediate gearwheel  13  and all bearings  17 ,  22 ,  25  can be mounted as a pre-assembled unit from the drive input side of the transmission. The assembly complexity is correspondingly low. At the same time, the advantage is obtained that the entire transmission housing with the exception of the drive-input-side cover  3  is of single-piece design and is correspondingly stiff. 
         [0025]    In the second exemplary embodiment, the housing  30  forms a drive-input-side chamber  32 , whose opening is closed off by the cover  31 , and a drive-output-side chamber  33 . The two chambers  32 ,  33  are separated from one another by a partition  34 . A drive input unit  35  is flange-mounted on the cover  31 , the input drive pinion  36  of which drive input unit  35  projects into the drive-input-side chamber  32 . The drive input unit can be formed by a drive motor or an intermediate housing which forms a special bearing for the shaft of the pinion  36  which is mounted in a floating manner. Alternatively, said shaft can also be mounted on the other side of the pinion  36  by means of a bearing (not illustrated) in the bearing bore  37  of the partition  34 . 
         [0026]    In the two-stage arrangement illustrated, the input drive pinion  36  acts on an intermediate gearwheel  40  which is seated on an intermediate shaft  41  which forms an intermediate pinion  42 . Said intermediate shaft  41  is mounted at three points, specifically by means of a bearing  43  in a bearing bore  44  of the cover  31 , by means of a bearing  45  in a bearing bore  46  of the partition  34 , and a bearing  47  in a bearing bore  48  in the drive-output-side wall  38  of the drive-output-side chamber  33 . The intermediate shaft  41  is fixed in its longitudinal direction in the housing by means of shoulders which delimit the bearing bores  44  and  48 . 
         [0027]    The intermediate pinion  42  acts on a drive output gearwheel  50  on the drive output shaft  51  which is mounted by means of a bearing  52  in a bearing bore  53  of the partition  34  and by means of a bearing  54  in a bearing bore  55  at the drive-output-side end of the housing. The drive output shaft  51  with the associated parts is secured in the housing by means of a circlip  56  before the bearing  54 . 
         [0028]    As can be seen in  FIGS. 5 and 7 , the partition  34  can be reinforced by means of ribs  68  and contain apertures  69  which have been omitted in some other illustrations for the sake of simplicity. 
         [0029]    The faces which form the drive-input-side chamber  32  adjoin, without an undercut, the opening which is closed off by the cover  31 . Said faces can therefore be shaped without a lost core in a pressure die casting process. That region of the drive-output-side chamber  33  in which the drive output shaft  51  is situated and which, in  FIG. 9 , appears to be delimited by the face  57  adjoins, without an undercut, the drive-output-side opening of said face  57 , which opening is formed by the bearing bore  55  and the bore faces, which are if appropriate situated at the drive output side of said bearing bore  55 , for holding a sealing cover  58 , and which opening can therefore likewise be formed without a core. 
         [0030]    The drive-output-side chamber  33  has, for holding the intermediate shaft  41 , a widening  60  which is delimited at the drive output side by the wall  38  and therefore cannot be formed from the same side as the region associated with the drive output shaft  51 . In order to be able to be formed without a core from the opposite side, the surface  61  of said widening  60  adjoins, without an undercut, a corresponding assembly opening  62  in the partition  34 . 
         [0031]    The widening  60  of the drive-output-side chamber  33  is larger than would be required for holding the intermediate shaft  41 . Said widening  60  is specifically large enough to allow the drive-output-side bearing  47  in addition to the already-mounted drive output gearwheel  50  to pass through during assembly. Said widening  60  is expediently partially delimited by a cylindrical face  61  whose central axis  64  is offset with respect to the provided axis  65  of the intermediate shaft in the direction away from the drive output shaft  51  ( FIGS. 8 and 11 ). 
         [0032]    The assembly opening  62  forms a widening of the bearing bore  46  which is provided in the partition  34  for the intermediate shaft bearing  45 . The widening results in a cutout in the peripheral face of the bearing bore  46 , in which cutout the bearing  45  is not supported. Since the width of said cutout is however smaller than the diameter of the bearing bore, the peripheral face of the bearing bore  46  extends over more than 180°, specifically over the angle α at both sides of the radius  63  which is aligned towards the drive output shaft. Said angle is so large that the resultant  64  of the forces arising from the toothing, which resultant is offset by approximately 110° with respect to said radius  63  in the case of conventional toothings, is situated within the region supported by the bearing bore  46 . 
         [0033]    The assembly opening  62  and the widening  60  of the drive-output-side chamber  33  are large enough for the intermediate shaft  41  with the pre-assembled drive-output-side bearing  47  as per  FIGS. 12 and 13  to be pushed in past the drive output gearwheel  50 . This makes it possible to insert the intermediate shaft  41  with the intermediate gearwheel  40  and all the associated bearings  43 ,  45 ,  47  as a pre-assembled unit into the housing. 
         [0034]    Said process is shown in various stages in  FIGS. 11 to 14 . In  FIG. 11 , it is possible to see, below the bearing bore  46  in the partition  34 , the assembly opening  62  which is adjoined without an undercut by the widening  60  of the drive-output-side chamber. Firstly, said pre-assembled unit, approximately in the position of the axis  64 , is pushed in the direction of the arrow in  FIG. 12  until the drive-output-side bearing  47  reaches the wall  38  which contains the bearing bore  48  of said bearing  47 . The unit is then pushed transversely in the direction of the arrow in  FIG. 13  in order to reach the provided axial position  65 . Here, the pinion  42  and the drive output gearwheel come into engagement with one another. Finally, the pre-assembled unit of the intermediate shaft  41  is pushed forwards as per  FIG. 14  in the direction of the arrow until the bearings  47  and  45  have found their intended position in the bearing bores  48  and  46  (see  FIG. 4 ). In order that the transverse movement out of the position of  FIG. 13  into that of  FIG. 14  is possible, the free axial spacing between the drive output gearwheel  50  and the wall  38  which forms the drive-output-side bearing bore  48  must correspond at least to the width of the drive-output-side bearing  47 . 
         [0035]    The assembly opening which is provided in the partition for the pre-assembled intermediate shaft could also be formed by the bearing bore  46  alone without the widening  62  if the bearing bore is large enough. If, however, the bearing  45  can be of small design on account of the widening  62  and on account of the additional bearing-mounting of the intermediate shaft by means of the drive-output-side bearing  47 , this has the important advantage that the intermediate shaft bearing  45  in the partition  34  can be accommodated in approximately the same plane as the bearing  52  of the drive output shaft. It is thus possible with little expenditure to reduce the installation length and the weight of the transmission. It is also thereby possible to further increase the housing stiffness, which is already increased according to the invention by means of the absence of additional assembly openings. The low cost expenditure is obtained by means of the compact design, the capability for cost-effective production of the housing in a pressure die casting process, the capability for pre-assembly of all shafts, gearwheels and bearings, and the possible dispensation with centering means on the housing cover, which is explained further below. 
         [0036]    The second exemplary embodiment shows a two-stage transmission. Said transmission can however also be of three-stage design. In this case, an additional shaft is arranged in the drive-input-side chamber, for which additional shaft the partition  34  and the cover  31  contain further bearing bores  70 ,  71 . Said additional shaft supports an additional gearwheel on which the input drive pinion acts and which is situated in the plane in which the intermediate gearwheel  40  is illustrated in the drawing. Said intermediate gearwheel  40  is moved to the left in the drawing on the intermediate shaft  41  in order to be able to interact with the pinion of the additional shaft. 
         [0037]    With regard to the desired reduction in expenditure, the triple bearing arrangement of the intermediate shaft, which is generally avoided on account of static overdeterminacy, is worth noting. In the present case, said triple bearing arrangement has on the one hand the advantage that it permits the above-described favourable dimensioning of the intermediate shaft bearing which is arranged in the partition, so that said intermediate shaft bearing can be arranged in a plane with a bearing of the drive output shaft. Said triple bearing arrangement has on the other hand the advantage that the described alternative positions for the intermediate gearwheel can be provided for two-stage and three-stage transmission, because said intermediate gearwheel is mounted at both sides. Finally, said triple bearing arrangement has the advantage of the cover centering at the bearing  44 , which is arranged in the cover, of the intermediate shaft  41 . Said cover centering is sufficient in the case of a two-stage design of the transmission. For the case of the three-stage design, the housing and the cover can be provided with additional pairs of interacting centering faces  72 ,  73 . Said centering faces  72 ,  73  are arranged so as to effect a complementary centring centering action with regard to the rotational position of the cover about the axis of the intermediate shaft bearing  43 . For this purpose, it is necessary for the centering face pairs to have a face component which encloses an angle of less than 90° with a radius  74 ,  75  which proceeds from the axis of the intermediate shaft.