Patent Publication Number: US-2021170856-A1

Title: Drive device for a vehicle axle of a two-track vehicle

Description:
The invention relates to a drive device for a vehicle axle, in particular a rear axle, of a two-track vehicle, according to the generic term of claim  1 . 
     DE 10 2014 015 793 A1 discloses a generic drive device for a vehicle rear axle having an axle differential, which can be connected to a primary drive unit (for example, a combustion engine) on its input side, and can on its output side be connected to the vehicle wheels of the vehicle axle by means of flanged shafts arranged on both sides. The vehicle axle is associated with an additional drive unit (in particular, an electric motor), as well as a switchable superposition gearbox. The superposition gearbox can be switched to a torque-distribution gear stage, in which a drive torque generated by the additional drive unit is generated, wherein a torque distribution to the two vehicle wheels can be changed depending on the torque and its rotational direction. Alternatively, the superposition gearbox can be switched to a hybrid mode, in which the drive torque generated by the additional drive unit can be coupled to both flanged shafts of the vehicle wheels in an evenly distributed manner in a switchable hybrid gear stage via the axle differential. In certain driving situations, e.g., during cornering, the vehicle handling can be supported via a torque redistribution (torque vectoring or differential-lock function) by engaging the torque distribution gear stage. Thus, a drive torque can be shifted toward the outside vehicle wheel (torque vectoring) when entering a curve during cornering. Alternatively/additionally, the drive torque can be shifted toward the inside vehicle wheel (differential-lock function) when exiting the curve during cornering. By contrast, a boost function can be performed when hybrid mode is activated, for example. 
     In the aforementioned DE 10 2014 015 793 A1, the superposition gearbox has a total of three planetary gear units that can be switched via two brakes to provide the hybrid mode or the torque-distribution mode, resulting in an overall arrangement requiring a large installation space. 
     The problem underlying the invention is to provide a drive device for a vehicle axle of a two-track vehicle, which is designed in an installation space-saving manner in comparison to the prior art, and in which it is possible to expand/reduce functionality with simple means, specifically while requiring less space and providing increased driving dynamics. 
     The problem is solved by the characteristics of claim  1 . Preferred further developments of the invention are disclosed in the dependent claims. 
     According to the characterizing portion of claim  1 , the three planetary gear units in the superposition gearbox are coupled with each other in such a way that a load path in which all three planetary gear units are engaged is formed in the superposition gearbox when the first hybrid gear stage is activated. By contrast, when the second hybrid gear stage is activated, as well as when the torque-distribution gear stage is activated, a load path is formed in the superposition gearbox, in which exactly two planetary gear units are engaged. In this way, different gear ratios can be easily realized in the first hybrid gear stage and in the second hybrid gear stage, as well as in the torque-distribution gear stage. When the second hybrid gear stage is activated, the load path is formed without a power split. 
     Different gear ratios can be easily realized in the first hybrid gear stage and in the second hybrid gear stage with the invention. 
     In a technical implementation, the three planetary gear units can be arranged consecutively in a row and coaxially to the flanged shaft. The first planetary gear unit, located on the input side of the gearbox, can be connected in a rotationally fixed manner via its input element—i.e., sun gear—to a gearbox input shaft driven by the additional drive unit. A second planetary gear unit, located on the output side of the gearbox, can have a hybrid output flange at its output element—i.e. a planetary gear carrier supporting planetary gears—which output flange is seated on a gearbox output shaft in a rotationally fixed manner, which gearbox output shaft is operationally connected to an input side of the axle differential. 
     With regard to a torque conversion, it is preferred if the additional drive unit is coupled with the gearbox input shaft via a countershaft stage. The additional drive unit may preferably be arranged parallel to the flanged shaft for installation space reasons, wherein the countershaft stage can be a single-stage spur gear stage, for example. 
     The first planetary gear unit located on the input side can be lockable or detachable from a gearbox housing via its planetary gear carrier, which supports planetary gears, by means of a hybrid switching element SH 2 . The first planetary gear unit can have a radially outer ring gear which meshes with the planetary gears of the first planetary gear unit. In the same manner, the second planetary gear unit can have a radially outer ring gear which meshes with the planetary gears of the second planetary gear unit. The two ring gears of the first and second planetary gear units preferably can be arranged on a common ring gear shaft in a rotationally fixed manner. In addition, the sun gear of the second planetary gear unit can be attached to the gearbox housing in such a manner that it is fixed relative to the housing. 
     In the above gearbox structure, the following constellation results when the second hybrid stage H 2  is activated: The planetary gear carrier of the first planetary gear unit can be locked to the gearbox housing by means of the hybrid switching element SH 2 . In this case, a load path or a drive torque flow is formed from the additional drive unit via the first planetary gear unit and the second planetary gear unit to the input side of the axle differential. 
     In one concrete embodiment, the above axle differential may have a Ravigneaux gear set, in which planetary gears of a first planetary gear set mesh both with a radial outer ring gear, which forms the input side of the axle differential, and with planetary gears of a second planetary gear set. In addition, the planetary gears of the first planetary set mesh with a first, large sun gear. The planetary gears of the second planetary gear set, on the other hand, do not engage with the gears of the outer ring gear and mesh with a second, small sun gear, which is positioned axially adjacent to the first, large sun gear. The two planetary gear sets are supported rotatably on a shared planetary gear carrier in such a Ravigneaux set in a manner known from the state of the art. Such an axle differential can be connected to the superposition gearbox as follows: The first, large sun gear can be arranged on a torque-distribution output shaft in a rotationally fixed manner, while the second, small sun gear is seated on one flanged shaft (on the side of the gearbox) in a rotationally fixed manner, and the shared planetary gear carrier is seated on the other flanged shaft (away from the gearbox) in a rotationally fixed manner. 
     The aforementioned torque-distribution output shaft can support a torque-distribution flange in a rotationally fixed manner. This flange can be operationally coupled with or decoupled from the planetary gear carrier of the first planetary gear unit via a first torque-distribution switching element STV. 
     When the torque-distribution gear stage TV is activated, the following results: The torque-distribution flange can be coupled with the planetary gear carrier of the first planetary gear unit when the torque-distribution switching element STV is actuated. This results in a load path from the additional drive unit into the first planetary gear unit. A power split is conducted on the planetary gear carrier of the first planetary gear unit PG 1 , in which a first partial path leads via the shared ring gear shaft to the second planetary gear unit PG 2  and from its hybrid output flange to the axle differential input side. A second partial path is directed via the closed torque-distribution switching element STV, as well as via the torque-distribution output shaft to the first, large sun gear of the axle differential. 
     In the aforementioned torque-distribution gear stage TV, the drive torque generated by the additional drive unit is not only directed to the axle differential input side, but also to the first, large sun gear of the axle differential. The torque distribution between the vehicle wheels is changed depending on the amount and the rotational direction of the drive torque introduced into the first, large sun gear. 
     In a further, installation space-saving version, the planetary gear carrier of the first planetary gear unit can be supported in a rotationally fixed manner on an intermediate shaft. This can preferably be realized as an outer hollow shaft. In this case, the intermediate shaft, the gearbox input shaft (as an inner hollow shaft), and the flanged shaft on the gearbox side can be arranged coaxially and nested into each other. 
     In the same manner, the gearbox output shaft may also be formed as an outer hollow shaft, inside which the torque-distribution output shaft (as an inner hollow shaft) is arranged, within which the flanged shaft on the gearbox side is routed. 
     As mentioned above, the third planetary gear unit is only engaged into the load path when the first hybrid stage is activated. Otherwise, the third planetary gear unit remains load-free when the second hybrid stage is activated or when the torque-distribution gear stage is activated. The third planetary gear unit has a sun gear that is seated in a rotationally fixed manner on the intermediate shaft, specifically together with the already mentioned planetary gear carrier of the first planetary gear unit. The sun gear of the third planetary gear unit can mesh with planetary gears supported by a planetary gear carrier. The planetary gears can also engage with the gears of a radial outer ring gear. Preferably, the planetary gear carrier of the third planetary gear unit can be connected in a rotationally fixed manner to the shared ring gear shaft. By contrast, the ring gear of the third planetary gear unit can be locked or detached from the gearbox housing by means of a hybrid switching element SH 1 . 
     In the gearbox structure defined above, the following constellation results when the first hybrid stage is activated: In the first hybrid stage H 1 , the ring gear of the third planetary gear unit is locked to the gearbox housing by means of the hybrid switching element SH 1 . In this case, a load path is formed from the additional drive unit to the first planetary gear unit and from there to the sun gear of the third planetary gear unit via the planetary gear carrier of the first planetary gear unit as well as via the intermediate shaft. The load path continues from the planetary gear carrier of the third planetary gear unit to the common ring gear shaft, as well as via the planetary gear carrier of the second planetary gear unit and the hybrid output flange to the input side of the axle differential. A power split occurs at the ring gear of the first planetary gear unit, in which a main power path leads toward the second planetary gear unit and a loss path with low reactive power branches off to the planetary gears of the first planetary gear unit. The resulting power loss is due to the inertia of the planetary gears of the first planetary gear unit, which somewhat decelerates the ring gear shaft. The discharged reactive power is fed back to the main power path on the planetary gear carrier of the first planetary gear unit. 
     The torque-distribution switching element STV can be realized as a shift clutch, by means of which the planetary gear carrier of the first planetary gear unit can be coupled with the torque-distribution output flange. 
     Alternatively, the torque-distribution switching element STV can be realized as a shift sleeve, which is arranged in a rotationally fixed manner with its internal gears and axially displaceable between a neutral position and a switching position on an external gear of the torque-distribution output flange. In the neutral position, the torque-distribution output flange is decoupled from the planetary gear carrier of the first planetary gear unit. In the switching position, the gears of the shift sleeve additionally engage with an external gear of the planetary gear carrier in order to transfer torque. 
     The first hybrid switching element HSE 1  and the second hybrid switching element HSE 2  can be two independent switching elements or alternatively can be combined into a shared hybrid switching element HSE. In this case, the shared hybrid switching element HSE can be realized as a shift sleeve axially adjustable on both sides, and can be adjustable from its neutral position either into the first hybrid gear stage H 1  or into the second hybrid gear stage H 2 . 
    
    
     
       In the following, two exemplary embodiments of the invention are described on the basis of the attached drawings. 
       The drawings show: 
         FIG. 1  A drive device for a vehicle rear axle of a two-track vehicle in a schematic representation 
         FIGS. 2 to 4  Respectively, views according to  FIG. 1 , with highlighted drive torque flow when the second hybrid gear stage is activated ( FIG. 2 ), when the torque-distribution gear stage is activated ( FIG. 3 ), and when the first hybrid gear stage ( FIG. 4 ) is activated 
         FIG. 5  A drive arrangement according to a second exemplary embodiment 
     
    
    
       FIG. 1  shows a drive device for a vehicle rear axle HA of a two-track vehicle in an approximate, schematic representation. The drive device indicated in  FIG. 1  may be part of an all-wheel drive in which a front-mounted combustion engine (not shown) drives the front wheels of the vehicle as a primary drive unit via a gearbox as well as a center differential and a front axle differential. The center differential can be operationally connected to the input side  13  of a rear axle differential  3  via a drive shaft as well as via a bevel-gear drive  4 . A clutch K is connected between the bevel-gear drive  4  and the input side  13  of the rear axle differential  3 , by means of which clutch K the rear axle HA can be operationally decoupled from the drive shaft. 
     On its output side, the rear axle differential  3  is operationally coupled with the vehicle rear wheels  9  of the vehicle rear axle HA via flanged shafts  5 ,  7  arranged on both sides. In  FIG. 1 , the rear axle differential  3  is a planetary gear differential with a Ravigneaux gear set, in which planetary gears  11  of a first planetary gear set mesh both with a radial outer ring gear  13 , which forms the input side of the axle differential  3 , and with planetary gears  15  of a second planetary gear set. In addition, the planetary gears  11  of the first planetary gear set engage with a first, large sun gear  17 . The planetary gears  15  of the second planetary gear set, on the other hand, engage with a second, small sun gear  19 . Both planetary gear sets are rotatably supported on a shared planetary gear carrier  21 , which is seated in a rotationally fixed manner on a flanged shaft  5  located away from the gearbox. By contrast, the second, small sun gear  19  is seated in a rotationally fixed manner on the flanged shaft  7  on the gearbox side, while the first, large sun gear  17  is seated in a rotationally fixed manner on a torque-distribution output shaft  23 , which is connected to the superposition gearbox  25 . 
     The rear axle HA has an already mentioned superposition gearbox  25  and an electric motor  26 . The superposition gearbox  25  can be operated in a hybrid mode or in a torque-distribution mode (i.e., electronic torque vectoring or differential-lock function), as described below. In hybrid mode, a drive torque generated by the electric motor  26  is coupled in an evenly distributed manner to the two flanged shafts  5 ,  7  via the superposition gearbox  25  and via the rear axle differential  3 . The hybrid mode can be implemented purely by means of the electric motor  26  or in a combination of the electric motor  26  with the combustion engine (for example, for a boost function). 
     In the torque-distribution mode, the drive torque generated by the electric motor  26  is not only directed to the input side (i.e., the ring gear  13 ) of the axle differential  3 , but also, via the superposition gearbox  25 , to the first, large sun gear  17  of the axle differential  3 , in order to change a torque distribution to the two rear wheels  9 . The application of the torque to the first, large sun gear  17  takes place via a torque-distribution flange  67  seated on the torque-distribution-output shaft  23 . The torque distribution between the vehicle wheels  9  is performed depending on the amount and the rotational direction of the drive torque generated by the electric motor  26 . 
     The gearbox structure of the superposition gearbox  25  is explained below on the basis of  FIG. 1 : Accordingly, the superposition gearbox  25  has a first planetary gear unit PG 1  on its input-side, a second planetary gear unit PG 2  and a third planetary gear unit PG 3 , which, seen in the transverse direction y of the vehicle, are arranged directly adjacent to each other and coaxially aligned on the flanged shaft  7  on the gearbox side. The middle, first planetary gear unit PG 1  is connected in a rotationally fixed manner via its sun gear  35  (which acts as an input element) with a gearbox input shaft  36  driven by the electric motor  26 . The first planetary gear unit PG 1  located on the input side can be locked or detached from a gearbox housing  41  via its planetary gear carrier  39 , which supports planetary gears  37 , by means of a hybrid switching element SH 2 . In addition, the first planetary gear unit PG 1  has a radial outer ring gear  43 , which meshes with the planetary gears  37  and which is a one-piece component of a ring gear shaft  45 . The planetary gear carrier  39  of the first planetary gear unit PG 1  is connected in a rotationally fixed manner with an intermediate shaft  47 , specifically together with a locking flange  49 , which interacts with the hybrid switching element HS 2 . 
     The second planetary gear unit PG 2  located on the gearbox output side has a radial outer ring gear  51 , which is seated in a rotationally fixed manner together with the ring gear  43  of the first planetary gear unit PG 1  on the shared ring gear shaft  45 . The ring gear  51  meshes with radial inner planetary gears  53 , which are supported rotatably on a planetary gear carrier  55  and engage with a sun gear  57 . In  FIG. 1 , the sun gear  57  of the second planetary gear unit PG 2  is attached non-rotatably to a housing wall of the gearbox housing  41 . The planetary gear carrier  55  has a hybrid output flange  59 , which is seated in a rotationally fixed manner on a gearbox output shaft  61 , which is connected in a rotationally fixed manner with the input-side ring gear  13  of the axle differential  3  via a connection flange  63 . 
     On the side facing the second planetary gear unit PG 2 , the planetary gear carrier  39  of the first planetary gear unit PG 1  is extended with an axial bar  65 , which supports a torque-distribution switching element STV. This interacts with a torque-distribution output flange  67 , which is seated in a rotationally fixed manner on the already mentioned torque-distribution output shaft  23 , which is connected to the first, large sun gear  17  of the axle differential  3 . 
     In  FIG. 1 , the third planetary gear unit PG 3  has a sun gear  68  which is arranged on the intermediate shaft  47  in a rotationally fixed manner together with the planetary gear carrier  39  of the first planetary gear unit PG 1  and the locking flange  49 . The sun gear  68  meshes with planetary gears  69 , which are supported by a planetary gear carrier  71  and also engage with a radial outer ring gear  73 . The planetary gear carrier  71  is attached in a rotationally fixed manner to the shared ring gear shaft  45 , while the ring gear  73  can be locked to or detached from the gearbox housing  41  by means of a hybrid switching element SH 1 . 
     The gearbox input shaft  36  is connected to the electric motor  26 , which is positioned parallel to the flanged shafts  5 ,  7 , via a single-stage spur gear stage  40 , which acts as a countershaft. In addition, the intermediate shaft  47  is realized as an outer hollow shaft, within which the gearbox input shaft  36  (as an inner hollow shaft) is arranged coaxially. The gearbox-side flanged shaft  7  extends within the gearbox input shaft  36 . In the same way, the gearbox output shaft  61  also is formed as an outer hollow shaft, inside which extends the torque-distribution output shaft  23  (as an inner hollow shaft). The gearbox-side flanged shaft  7  extends within the latter. 
     In order to explain the operating principle of the drive device, a driving situation is described on the basis of  FIG. 2 , in which the second hybrid gear stage H 2  is activated. In the present case, the second hybrid gear stage H 2  is designed as a CO 2 -optimized driving gear as an example, which gear can be actuated at higher driving speeds. When the second hybrid gear stage H 2  is activated, the locking flange  49  is attached in a fixed manner to the gearbox housing  41  by means of the switching element SH 2 . This results in a load path without power splits, in which the drive torque generated by the electric motor  26  is first directed to the sun gear  35  of the first planetary gear unit PG 1  via the countershaft  40  and the gearbox input shaft  36 . The planetary gear carrier  39  of the first planetary gear unit PG 1 , which is locked in position by means of the hybrid switching element SH 2 , acts as a reactive element, via which the drive torque is directed to the shared ring gear shaft  45 . From there, the load path is routed via the planetary gear carrier  55  of the second planetary gear unit PG 2  and its hybrid output flange  59  to the input-side ring gear  13  of the axle differential  3 . From there, the drive torque is evenly distributed between the two flanged shafts  5 ,  7  via the Ravigneaux set. In  FIG. 2  (as well as in  FIGS. 3, 4 and 5 ), the load paths are marked with a solid line, while power-dissipation load paths, through which reactive power passes, are indicated by a dotted line. 
       FIG. 3  shows another driving situation, in which, in contrast to  FIG. 2 , the superposition gearbox  25  is not operated in hybrid mode, but in torque-distribution mode. This mode is activated during cornering, for example, to achieve a torque difference between the flanged shafts  5 ,  7 . In the torque-distribution mode, the two hybrid switching elements HS 1 , HS 2  are released, while the torque-distribution switching element STV is activated. This results in a load path, in which the drive torque generated by the electric motor  26  is first directed to the first planetary gear unit PG 1 . A power split is conducted on its planetary gear carrier  39 , in which a first partial path leads via the shared ring gear shaft  45  to the second planetary gear unit PG 2  and from the latter&#39;s hybrid output flange  59  on to the axle differential input side (ring gear  13 ). A second partial path results via the closed torque-distribution switching element STV, the torque-distribution output flange  67 , as well as via the torque-distribution output shaft  23  to the first, large sun gear  17  of the axle differential  3 . Therein, the rotational direction and the amount of the drive torque generated by the electric motor  26  is designed in such a way that a torque is applied to or received from the first planetary gear set of the axle differential, whereby a torque distribution changes between the two flanged shafts  5 ,  7 . 
     In  FIG. 4 , another driving situation is indicated, in which the first hybrid gear stage H 1  is activated, which can be set up as a starting gear, for example. Thus, in  FIG. 4 , the ring gear  73  of the third planetary gear unit PG is locked to the gearbox housing  41  by means of the hybrid switching element SH 1 . This results in a load path from the electric motor  26  to the first planetary gear unit PG 1  and from there via its planetary gear carrier  39  as well as the intermediate shaft  47  to the sun gear  68  of the third planetary gear unit PG 3 . The load path continues via the planetary gear carrier  71  of the latter to the shared ring gear shaft  45  to the output-side second planetary gear unit PG 2 . From there, the drive torque is routed via the hybrid output flange  59  to the input side (ring gear  13 ) of the axle differential  3 . 
     As shown by a dotted line in  FIG. 4 , a power split occurs at the ring gear  43  of the first planetary gear unit PG 1 , in which a slight power dissipation is diverted from the main load path defined above toward the planetary gears  37  of the first planetary gear unit  1 . The dissipated power is fed back to the main power path at the planetary gear carrier  39  of the first planetary gear unit PG 1 . 
     In  FIGS. 1 to 4 , the torque-distribution switching element STV is realized as a shift clutch, by means of which the planetary gear carrier  39  of the first planetary gear unit PG 1  can be coupled with the torque-distribution output flange  67 . In contrast, the torque-distribution switching element STV is realized as a shift sleeve in  FIG. 5 . The latter is arranged in a rotationally fixed manner and axially displaceable between a neutral position and a switching position on an external gear of the torque-distribution output flange  67 . In the neutral position shown here, the torque-distribution output flange  67  is decoupled from the planetary gear carrier  39  of the first planetary gear unit PG 1 . In the shift position, the shift sleeve allows a torque transmission between the planetary gear carrier  39  of the first planetary gear unit PG 1  and the torque-distribution output flange  67 . 
     In  FIG. 5 , the shift sleeve is axially adjustable by means of a shifts fork  75 . The shift fork  75  is supported by a shift rail  77  for transmitting a shifting motion, which rail extends in the axial direction through the transmission gearbox  25 . The shifting motion is initiated at the end  79  of the shift rail  77  that is away from the shift fork. 
     In contrast to  FIGS. 1 to 4 , the first hybrid switching element HSE 1  and the second hybrid switching element HSE 2  are combined into a shared hybrid switching element HSE in  FIG. 5 . The shared hybrid switching element HSE is realized as a shift sleeve axially adjustable on both sides, which is adjustable from its neutral position either into the first hybrid gear stage H 1  or into the second hybrid gear stage H 2 . 
     When the first hybrid gear stage H 1  is activated, the shared hybrid switching element HSE couples the ring gear  73  of the third planetary gear unit PG 3  with a housing wall  81  of the gearbox housing  41 . When the second hybrid gear stage H 2  is activated, the shared hybrid switching element HSE couples the ring gear  73  of the third planetary gear unit PG 3  with an outer shaft  83 , which is connected in a rotationally fixed manner to the planetary gear carrier  55  of the second planetary gearbox PG 2 . 
     In  FIG. 5 , in contrast to  FIGS. 1 to 4 , the intermediate shaft  47  supports only the sun gear  68  of the third planetary gear unit PG 3  and the planetary gear carrier  39  of the first planetary gear unit PG 1 , but not the locking flange  49  shown in  FIGS. 1 to 4 .