Abstract:
A planetary gear and a drive unit having the planetary gear, the planetary gear being characterized by very good integratability. For this purpose, a planetary gear ( 5 ) for transmitting a drive torque in a vehicle is proposed, having a first sun wheel attachment ( 12   a ) and a second sun wheel attachment ( 12   b ), each of the sun wheel attachments ( 12   a, b ) being coupled to a shaft ( 2   a, b ) in a rotationally fixed manner, and the sun wheel attachments ( 12   a, b ) being rotatable relative to one another, and the sun wheel attachments ( 12   a, b ) being situated in an overlapping area ( 11 ), overlapping in the radial direction.

Description:
[0001]    The present invention relates to a planetary gear for transmitting a drive torque in a vehicle, having a first sun wheel attachment and a second sun wheel attachment, each of the sun wheel attachments being coupled to a shaft in a rotationally fixed manner, and the sun wheel attachments being rotatable relative to one another. Moreover, the present invention relates to a drive unit having the planetary gear. 
       BACKGROUND 
       [0002]    Planetary gears are often used in differentials for transmitting drive torques in vehicles. The planetary gear may be used in various specific embodiments, for example in distribution differentials or in axle differentials. 
         [0003]    These types of planetary gears usually have at least one sun wheel, and multiple planet wheels which mesh with the sun wheel and which are rotatably supported in a planet carrier via pins. The planet carrier may likewise in turn be coupled to a gearwheel in a rotationally fixed manner. In known designs, differentials have two coupled planetary gear sets, whereby, for example, a drive torque is introduced via a sum shaft and distributed over two differential shafts, each differential shaft being coupled to a sun wheel of one of the planetary gear sets. These types of differentials based on planetary gears are characterized in particular by a compact design. 
         [0004]    The publication DE 10 2007 040 475 A1, which likely constitutes the most proximate prior art, relates to a spur gear differential, in particular for motor vehicles, having a drive element which is connected to a planet carrier in a rotationally fixed manner, at least one pair of intermeshing planet wheels being rotatably mounted in the planet carrier, and each of the planet wheels meshing with one toothed driven gear. In the figures, the driven gears are practically mirror-symmetrical with respect to one another relative to a radial plane. 
       SUMMARY OF THE INVENTION 
       [0005]    It is an object of the present invention to provide a planetary gear and a drive unit having the planetary gear, the planetary gear being characterized by very good integratability. 
         [0006]    The present invention provides a planetary gear which is suitable and/or designed for transmitting a drive torque in a drive train of a vehicle. The drive torque is conducted, in particular by an engine, to wheels of the vehicle, with the planetary gear connected in between. In particular, the planetary gear is designed as a differential, for example as an axle differential or a distribution differential, in particular as a spur gear differential. As an axle differential, the planetary gear distributes the drive torque to two axles of the vehicle, and as a distribution differential, the planetary gear distributes the drive torque to two wheels of one axle of the vehicle. 
         [0007]    The planetary gear includes a first and a second sun wheel attachment, each sun wheel attachment being coupled to a shaft in a rotationally fixed manner. The sun wheel attachments and/or the shafts are mounted so that they are rotatable relative to one another. In particular, the shafts are designed as differential shafts in the planetary gear, which conduct the drive torque of a sum shaft, for example, from the planetary gear. The sun wheel attachments preferably include a gearwheel area which in particular has a spur gearing. 
         [0008]    Within the scope of the present invention, it is proposed that the sun wheel attachments are situated in an overlap area, overlapping in the radial direction, in particular with respect to at least one, preferably both, shafts. Thus, if a vector which radially projects from the rotational axis formed by the shaft(s) is viewed, this vector initially passes through one sun wheel attachment and then through the other sun wheel attachment. 
         [0009]    The present invention is based on the consideration that additional degrees of freedom with regard to the positioning of the gearwheel areas of the sun wheel attachments are obtained due to the overlapping design of the sun wheel attachments. Thus, it is possible in particular to shift the position of the gearwheel areas of the sun wheel attachments in the axial direction during construction, and thus adapt to the needs of an installation situation. Integration of the planetary gear into an assembly is thus simplified. 
         [0010]    In one preferred refinement of the present invention, the overlap area is designed as a supporting area in which the sun wheel attachments are supported in the radial direction via a radial bearing or via a friction area. Thus, one of the sun wheel attachments is supported on the other in the radial direction. This support in the radial direction has a guiding function for the planetary gear, in particular in the design as a differential. Thus, for example, it is conceivable that shifting or tilting of the shafts which occurs due to stresses may be compensated for by the coupling of the sun wheel attachments. A more stable operating performance of the planetary gear may be achieved in this way. 
         [0011]    The sun wheel attachments are particularly preferably supported with respect to one another via a radial bearing which may be designed, for example, as a sliding bearing or also as any desired roller bearing, in particular as a needle bearing. In other specific embodiments it is possible for the sun wheel attachments to be mutually supported via a friction area which in a targeted manner causes increased friction between the sun wheel attachments, and thus between the shafts, in order to brake a relative rotation of the two shafts with respect to one another. 
         [0012]    The sun wheel attachments particularly preferably have running surfaces in the overlap area which are situated coaxially and concentrically with respect to one another. In particular, the running surfaces are designed in the form of straight hollow cylinders. In a first specific embodiment, the running surfaces themselves form the sliding bearing, and are designed to roll over one another in direct contact. In another specific embodiment, a component, for example a sliding device, in particular a slide bush, or a rolling element device, in particular a cage or a sleeve having rolling elements, in particular needles, is situated in between. While the specific embodiment in which the sun wheel attachments roll directly over one another via the running surfaces is characterized by a reduced number of components, the specific embodiments in which a component is introduced in between have advantages with regard to installation or service life. 
         [0013]    In one possible design of a specific embodiment of the present invention, each of the sun wheel attachments has an attachment area for the rotationally fixed mounting or bearing on the associated shaft, and has the gearwheel area. In particular, the attachment area and the gearwheel area are designed in one piece. The rotationally fixed mounting may be achieved, for example, by a form fit in the direction of rotation, the attachment area having grooves which, for example, are oriented in the axial direction and open radially inwardly, so that the attachment area for the rotationally fixed mounting is pushed onto the associated shaft which is complementary to the attachment area, and is secured in the direction of rotation in a form-locked manner. 
         [0014]    In the design implementation, it is preferred that at least one of the gearwheel areas protrudes in the axial direction relative to its attachment area. For example, the sun wheel attachment has an offset design in a longitudinal section of the rotational axis of the shafts. Together with the gearwheel area which is shifted in the axial direction, the sun wheel attachment protrudes beyond the attachment area of the other sun wheel attachment. It is particularly preferred that the protruding gearwheel area overlaps the attachment area of the other gearwheel attachment, forming the overlap area and/or the supporting area. In this specific embodiment, it is possible for the gearwheel areas of the two sun wheel attachments to be very close to one another in the axial direction, but, viewed from the axial position, not to be symmetrically or centrally situated, but, rather, to be asymmetrically shifted in the direction of the one sun wheel attachment. It is thus possible to avoid interfering contours in the integration of the planetary gears for one or both of the gearwheel areas. The optional mutual radial support is particularly advantageous, since this ensures that the structure is not mechanically unstable. 
         [0015]    With the aim of further increasing the mechanical stability and/or rigidity, it is preferred that at least one axial bearing is provided via which the sun wheel attachments are mutually supported. For example, an axial ring which rolls off on both sun wheel attachments is situated between the sun wheel attachments. Alternatively or additionally, the sun wheel attachments are supported with respect to a stop which is fixed to the housing, in particular with respect to the housing itself, or a differential cage. Here as well, it is conceivable to provide an axial ring. Instead of an axial ring, it is possible to position sliding disks between the bearing partners. 
         [0016]    Thus, in a combined specific embodiment of the present invention, each sun wheel attachment is triply supported, namely, a first time in the axial direction with respect to a stop which is fixed to the housing, in particular with respect to the housing itself, or the differential cage, a second time, likewise in the axial direction, with respect to the other sun wheel attachment, and a third time in the radial direction relative to the other sun wheel attachment. As a result of this triple bearing of the sun wheel attachment, which is designed in particular as a driven sun wheel, very high mechanical rigidity is achieved. 
         [0017]    The planetary gear according to the present invention may particularly preferably be used when the planetary gear additionally includes two planet wheel sets, the first planet wheel set meshing with one sun wheel attachment, and the second planet wheel set meshing with the other sun wheel attachment, and the planets of the first planet wheel set meshing with the planets of the second planet wheel set. In this configuration, for design reasons it is advantageous to position the gearwheel sections of the sun wheel attachments as close as possible to one another in the axial direction, this close arrangement being achievable in a particularly simple manner due to the implementation according to the present invention. 
         [0018]    The further subject matter of the present invention relates to a drive unit for a vehicle, characterized by a planetary gear. The drive unit has at least one electric motor for providing the drive torque. The planetary gear is preferably designed as a distribution gear, the drive torque of the electric motor being coupled via a sum shaft, and supplied via the sun wheel attachments and the shafts as differential shafts. To achieve a particularly compact design, the electric motor is preferably situated coaxially with respect to the shafts. In particular, the main shaft of the electric motor is situated coaxially with respect to at least one of the shafts. In particular, the main shaft is implemented as a hollow shaft which coaxially and/or concentrically encloses the at least one shaft. 
         [0019]    In one possible refinement of the present invention, the drive unit includes a superposition gear and an additional electric motor, the superposition gear and/or the additional electric motor being situated coaxially with respect to at least one of the shafts. For this purpose, the superposition gear is designed to, in addition to the drive torque, selectively apply an additional torque to either one shaft or the other shaft, or to both shafts. In particular, the main shaft of the additional electric motor is situated coaxially with respect to at least one of the shafts. In particular, the main shaft is implemented as a hollow shaft which coaxially and/or concentrically encloses the at least one shaft. 
         [0020]    This results in a possible design which in the axial direction has the first electric motor initially, then the distribution gear designed as the planetary gear, followed by the superposition gear, and lastly, the additional electric motor, all mentioned components being situated coaxially with respect to the shafts, resulting in a very compact design overall. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    Further features, advantages, and effects of the present invention result from the following description of one preferred exemplary embodiment of the present invention. 
           [0022]      FIG. 1  shows a schematic longitudinal section of a drive unit as a first exemplary embodiment of the present invention; 
           [0023]      FIG. 2  shows, in the same illustration as  FIG. 1 , a detail enlargement in the area of the sun wheel attachments; 
           [0024]      FIG. 3  shows a detail illustration of the two sun wheel attachments in the preceding figures; and 
           [0025]      FIG. 4  shows a schematic three-dimensional illustration of the sun wheels together with the meshing planets. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]      FIG. 1  shows a schematic cross-sectional illustration of a drive unit  1  which may be used, for example, for driving a vehicle. As outputs, drive unit  1  has two differential shafts  2   a, b  which at their ends are provided with domes  3   a, b  in order to be articulatedly coupled to shafts of drive wheels of a vehicle. However, in a similar specific embodiment a drive unit  1  may be achieved which provides a drive torque for a front axle area and a rear axle area via the two differential shafts  2   a, b.    
         [0027]    In the axial direction, drive unit  1  is divided into a first electric motor  4  which provides the main drive torque for differential shafts  2   a, b, a  distribution gear  5  which distributes the main drive torque of electric motor  4  to the two differential shafts  2   a, b, a  superposition gear  6 , and a second electric motor  7 , the superposition gear being designed to superimpose the drive torque of electric motor  7  onto the main torque and selectively transmit same to both differential shafts  2   a, b , or, when the vehicle negotiates curves, for example, to one of differential shafts  2   a  or  2   b . Electric motor  4 , distribution gear  5 , superposition gear  6 , and electric motor  7  are each situated coaxially and concentrically with respect to differential shafts  2   a, b , resulting in an extremely compact design overall which has an axial length of less than 65 cm, for example, and a diameter of less than 35 cm. 
         [0028]    Distribution gear  5  is designed as a planetary gear having two coupled planetary gear sets, a sun wheel  8   a  and  8   b  being associated with differential shaft  2   a  and  2   b , respectively. 
         [0029]      FIG. 2  illustrates a detail enlargement of drive unit  1  in the area of sun wheels  8   a  and  b . It is apparent from this illustration that sun wheels  8   a, b  have different diameters, and in each case mesh with a planetary gear set  9   a, b  associated with the sun wheels. With regard to the configuration of planetary gear sets  9   a, b , reference is made to the schematic three-dimensional illustration in  FIG. 4 . 
         [0030]      FIG. 4  shows a schematic three-dimensional illustration of only the association of sun wheels  8   a, b  relative to the two planetary gear sets  9   a, b , as a function diagram. It is apparent that sun wheel  8   a  and  8   b  in each case mesh with an associated planetary gear set  9   a  and  9   b . In addition, the planets of planetary gear sets  9   a, b  mesh with one another. This very specific configuration is easily achievable when sun wheels  8   a, b  are very close to one another in the axial direction. 
         [0031]    To achieve the smallest possible distance between sun wheels  8   a, b , sun wheels  8   a, b  are mounted on an attachment area  10   a  and  10   b , respectively, as is apparent from  FIG. 2 , for example, so that a sun wheel support or attachment  12   a  and a sun wheel support or attachment  12   b , respectively, are formed. While sun wheel  8   a , viewed in the axial direction, is mounted centrally or symmetrically on attachment area  10   a , sun wheel  8   b  is shifted in the axial direction relative to its attachment area  10   b , so that, in the longitudinal section shown, sun wheel  8   b  is situated in an offset extension of attachment area  10   b . Sun wheel  8   a  and attachment area  10   a , and sun wheel  8   b  and attachment area  10   b , are in each case designed as one piece. By axially shifting sun wheel  8   b  relative to its attachment area  10   b , in the radial direction with respect to the rotational axis of differential shafts  2   a, b , sun wheel  8   b  is situated in an overlap area  11 , overlapping with attachment area  10   a  of sun wheel  8   a . It is also emphasized in particular that, with respect to the parting plane between differential shafts  2   a, b , the two sun wheels  8   a, b  are distinctly asymmetrical, namely, shifted to the left, in the axial direction. Thus, sun wheels  8   a, b  are situated almost completely in the axial area of differential shaft  2   a . As a result of the offset or cup-shaped design of sun wheel attachment  12   b  which is formed from sun wheel  8   b  and attachment area  10   b , a very tight axial position between sun wheel  8   a  and sun wheel  8   b  is achieved, so that the meshing of the two planet wheel sets  9   a, b  is easily implementable. 
         [0032]      FIG. 3  shows a schematic detail enlargement of sun wheel attachments  12   a, b  from the preceding figures. In this illustration it is apparent that sun wheel attachments  12   a, b  include attachment area  10   a  and  10   b , respectively, which form a tubular receptacle for differential shafts  2   a  and  2   b , respectively, and which have grooves, extending in the axial direction, for bearing sun wheel attachments  12   a  and  12   b  on differential shafts  2   a  and  2   b , respectively, in the direction of rotation in a form-locked manner. Sun wheels  8   a, b  are integrally formed in one piece with attachment areas  10   a, b , respectively, and each has a spur gearing. Sun wheel  8   b  is offset in the axial direction relative to its attachment area  10   b , so that in the radial direction this sun wheel is situated in overlap area  11 , overlapping with attachment area  10   a  of sun wheel attachment  12   a.    
         [0033]    It is optionally possible to provide a radial bearing  13  in overlap area  11 , which may be designed, for example, as a slide bush or also as a roller bearing, in particular as a needle bearing, so that the two sun wheel attachments  12   a, b  may be mutually supported in the radial direction. However, instead of a radial bearing, a friction area may be provided so that relative twisting of sun wheel attachments  12   a, b  is allowed, but the sun wheel attachments are braked by friction. In addition to this radial bearing of sun wheel attachments  12   a, b  with respect to one another, the sun wheel attachments are also supported with respect to one another in the axial direction via an optional axial bearing  14 , which may be designed as a sliding disk or as a roller element ring, for example. For radial bearing  13  as well as for axial bearing  14 , the running tracks of the bearings are each formed by the surfaces of sun wheel attachments  12   a, b.    
         [0034]    To further increase the rigidity and the mechanical stability of sun wheel attachments  12   a, b  during operation, it may optionally be provided that each of sun wheel attachments  12   a  and  12   b  is supported in the axial direction with respect to a stop disk or differential cage by a further axial bearing  15   a  and  15   b , respectively. Thus, each of sun wheel attachments  12   a, b  is triply supported, namely, for sun wheel attachment  12   a , via axial bearing  15   a , axial bearing  14 , and radial bearing  13 , and for sun wheel attachment  12   b , via axial bearing  15   b , axial bearing  14 , and radial bearing  13 . 
         [0035]    Particular advantages of the present invention are the freedom in the configuration of sun wheel attachments  12   a, b  for differential shafts  2   a, b  when installation space is limited. In particular due to radial bearing  13 , an improved bearing function of sun wheel attachments  12   a, b  under extreme load is achieved. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           1  drive unit 
           2   a, b  differential shafts 
           3   a, b  domes 
           4  electric motor 
           5  distribution gear 
           6  superposition gear 
           7  electric motor 
           8   a, b  sun wheel 
           9   a, b  planet wheel sets 
           10   a, b  attachment area 
           11  overlap area 
           12   a, b  sun wheel attachments 
           13  radial bearing 
           14  axial bearing 
           15   a, b  axial bearing