Abstract:
A power-branched transmission for an agricultural vehicle is configured as a power-branched transmission having a secondary coupling. The transmission comprises a summation planetary gear set ( 5 ), the planetary gear of which are configured as a double planetary gear ( 8 ).

Description:
[0001]    This application is a National Stage completion of PCT/EP2008/060756 filed Aug. 15, 2008, which claims priority from German patent application serial no. 10 2007 047 194.9 filed Oct. 2, 2007 and German patent application serial no. 10 2008 040 444.6 filed Jul. 16, 2008. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a power-branched transmission. 
       BACKGROUND OF THE INVENTION 
       [0003]    Generic power-branched transmissions are used in work machines or agricultural machines, such as tractors, in which the external shape of the transmission has to be long and slender. 
         [0004]    A power-branched transmission that has a variator configured as a hydrostatic device is known from DE 10 2006 025 348 A1. The power-branched transmission is equipped with a power splitting planetary gear set, wherein a shaft of the planetary gear set is operatively connected to a first shaft of the variator and drives a variable displacement pump by means of it. Another shaft of the planetary gear set is connected via a gear stage to another shaft of the variator, which in turn is operatively connected to the hydraulic motor of the variator. The third shaft of the planetary gear set is connected to a transmission input of the power-branched transmission, which is connected to a drive mechanism. In addition, the second shaft of the variator is configured with a plurality of fixed gears, which mesh with a plurality of idler gears that are arranged on a countershaft, wherein the idler gears can be connected, via shift elements, to the countershaft in a rotationally fixed manner for implementing different drive modes and/or transmission ranges for forward driving and at least one drive mode for reverse driving. 
         [0005]    Disadvantageously, the changes between drive modes cannot be carried out synchronously, so that power shifting with simultaneous correction of the transmission ratio in the region of the hydrostatic device has to be carried out in order to avoid interruption of the torque flow at any rate when changing a drive mode. During such shifts, disturbing reaction torques occur in the drive train that can be perceived as a jerk by the operator during operation. 
       SUMMARY OF THE INVENTION 
       [0006]    The underlying object of the present invention is to create a power-branched transmission which can be used in a work machine or agricultural vehicle, such as a tractor, which has a simple design and by means of which synchronous drive mode changes can be carried out. 
         [0007]    This object is attained by a generic power-branched transmission that also has the characteristic features described in the main claim. 
         [0008]    The power-branched transmission has an input shaft, which can be driven by a drive motor, for example an internal combustion engine. A summation planetary gear set is connected to the input shaft on one hand and to a variator on the other hand. The summation planetary gear set has a planet carrier, at least one sun gear and a ring gear. The planet carrier is operatively connected to the input shaft via a spur gear. The variator has a first and a second shaft, wherein the first shaft is connected to the sun gear of the summation planetary gear set in a rotationally fixed manner, and the second shaft is operatively connected to the ring gear of the summation planetary gear set via a spur gear. The variator preferably comprises a hydrostatic pump and a hydrostatic motor, wherein the hydrostatic motor and the hydrostatic pump can be configured as bent-axis drive units and the displacement volume can be adjusted by means of a common double yoke. This hydrostatic variator may, for example, be implemented like the variator of DE 10 2006 025 347 B3. 
         [0009]    The axis of rotation of the sun gear of the summation planetary gear set is arranged parallel to the input shaft, the axes of rotation of the first and second shafts of the variator are likewise parallel, and an output shaft of the transmission, which is connected to a drive axle that drives the drive wheels, is likewise parallel to the input shaft. The input shaft, the sun gear and the output shaft are spaced apart from one another. The summation planetary gear set has a double planetary gear, by means of which the stationary transmission ratio of the planetary gear set can be expanded such that the radial installation space available for the transmission is maintained. Thus, it is possible to create a slender transmission in the radial direction. The ring gear of the double planetary gear set can be connected, via a shift device, to a first spur gear, by means of which the output shaft can be driven, and via a shift device to a second spur gear, by means of which the output shaft can be driven. A sun gear of the summation planetary gear set can be connected, via a shift device, to a third spur gear that drives the input shaft, and, via a shift device, to a fourth spur gear that drives the output shaft. The shift devices are thus arranged downstream of the summation planetary gear set. The power-branched transmission is thus configured as an infinitely variable power-branched transmission comprising a secondary coupling. 
         [0010]    In another embodiment of the present invention, the summation planetary gear set has two sun gears, one sun gear meshing with a first planetary gear of the double planetary gear and the second sun gear with the second planetary gear of the double planetary gear. The first sun gear is connected to the variator, and the second sun gear is connected to the output shaft by means of the shift device either via the third or fourth spur gear. The ring gear can either mesh with one planetary gear of the double planetary gear or with the other planetary gear of the double planetary gear. This way, additional degrees of freedom are available for the design, which allow for adaptation to the special use of the vehicles. Different transmission ratios are shifted by way of the shift devices within which the transmission ratio can be infinitely varied using the variator. The power-branched transmission can be started from a standstill, as a result of which the strain on the variator is reduced in a very simple way compared to the transmission devices known from practice, where a starting torque is completely conducted over the variator when starting a work machine. 
         [0011]    In another advantageous embodiment of the transmission device according to the invention, a reversal of the direction of rotation between the transmission input and the transmission output can be implemented by means of a valve device of the hydrostatic circuit of the variator, via which a delivery unit can be switched in the hydraulic circuit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Further characteristics will be apparent form the description of the drawings. The drawings show: 
           [0013]      FIG. 1  a transmission diagram of the power-branched transmission, wherein the summation planetary gear set has a sun gear; 
           [0014]      FIG. 2  a transmission diagram of the power-branched transmission, wherein the summation planetary gear set has two sun gears, and the ring gear is operatively connected to the first planetary wheel; and 
           [0015]      FIG. 3  a transmission diagram of the power-branched transmission, wherein the summation planetary gear set has two sun gears, and the ring gear is operatively connected to the second planetary gear. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]    
       FIG. 1 
     
         [0017]    A drive engine  1  drives an input shaft  2  which drives the planet carrier  4  of a summation planetary gear set  5  via a spur gear  3 . At least one double planetary gear  6  is mounted on the planet carrier  4  and is operatively connected to a sun gear  7  and a ring gear  8 . The sun gear  7  is connected to a first shaft  9  of a variator  10  in a rotationally fixed manner. The variator  10  is preferably configured as a hydraulic module having two integrated swash plate or bent-axis drive units comprising a double yoke, as disclosed in DE 10 2006 025 347 B3. It is also possible to use two separate adjusting units in a bent-axis or swash plate design. It is, however, also possible to configure the variator as an electric variator, comprising an electric generator and an electric motor. The second shaft  11  of the variator is operatively connected to the ring gear  8  via a spur gear  12 . The ring gear  8  is connected in a rotationally fixed manner to a shift device  12 , by which the ring gear  8  can be connected to the output shaft  16  either via a first spur gear  14  or a second spur gear  15 . The output shaft  16  drives a drive axle  17 . The sun gear  7  is connected in a rotationally fixed manner to a shift device  18 , by which the sun gear  7  can be connected to the output shaft  16  either via a third spur gear  19 , or via a fourth spur gear  20 . The spur gears  14 ,  15 ,  19  and  20  as well as the shift devices  13  and  18  are arranged downstream of the summation planetary gear set  5 . The output shaft  16 , the input shaft  2  as well as the sun gear shaft and/or first shaft  9  are arranged spaced apart and parallel to one another. By using a double planetary gear  8  in the summation planetary gear set  5 , the distance among the shafts  2 ,  9  and  16  can be reduced such that the transmission can be used in a tractor. 
         [0018]    
       FIG. 2 
     
         [0019]    This differs from  FIG. 1  in that the summation planetary gear set  5  has a first sun gear  21  and a second sun gear  22 , the first sun gear  21  being connected in a rotationally fixed manner to the first shaft  9  and operatively connected to the double planetary gear  6 , and the second sun gear  22  being connected in a rotationally fixed manner to the shift device  13 , and operatively connected to the double planetary gear  6 . The ring gear  8  is operatively connected to the planetary gear of the double planetary gear  6  which has the smaller diameter. 
         [0020]    
       FIG. 3 
     
         [0021]    The difference here in comparison to  FIG. 2  is that the ring gear  8  is operatively connected to the double planetary gear  6  which has the larger diameter. 
       REFERENCE NUMERALS 
       [0000]    
       
           1  drive engine 
           2  input shaft 
           3  spur gear 
           4  planet carrier 
           5  summation planetary gear set 
           6  double planetary gear 
           7  sun gear 
           8  ring gear 
           9  first shaft 
           10  variator 
           11  second shaft 
           12  spur gear 
           13  shift device 
           14  first spur gear 
           15  second spur gear 
           16  output shaft 
           17  drive axle 
           18  shift device 
           19  third spur gear 
           20  fourth spur gear 
           21  first sun gear 
           22  second sun gear