Abstract:
A power split transmission for a working machine, such as a wheel loader, having a continuously variable power branch and a mechanical power branch that are summed with one another via a summing gear ( 13 ). The summing gear ( 13 ) can be connected, via a clutch for forward drive ( 4 ) and a clutch for reverse drive ( 8 ), to an input drive. The power split transmission has shafts ( 2, 7; 32, 33 ) and only a single clutch is located on each shaft.

Description:
[0001]    This application is a National Stage completion of PCT/EP2008/060760 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 040 443.8 filed Jul. 16, 2008. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to a power split transmission. 
       BACKGROUND OF THE INVENTION 
       [0003]    Such power split transmissions have a continuously variable power branch and a mechanical power branch that are summed by a summing gear set. 
         [0004]    The document DE 10 2006 004 223 A1 discloses a power split transmission with a continuously variable power branch and a mechanical power branch that are summed in a summing gear set, wherein the summing gear set consists of a planetary gear set with a double planetary gear, two sun wheels, and an internal geared wheel. 
         [0005]    In working machinery, for example such as wheel loaders, the drive motor is positioned above the drive axle so that a transmission is needed that has a large axial distance between the input drive for the transmission and the transmission output drive. In addition, the structural space for the width and depth of the transmission is extremely limited in working machines, so that narrow, short transmissions with large axial separations are often used. 
         [0006]    The underlying problem of this invention is to provide a power split transmission that makes possible a compact structure and a large axial separation. 
       SUMMARY OF THE INVENTION 
       [0007]    The power split transmission should also be easy to shift from a first operating range to a second operating range. The problem is solved with a power split transmission of the type described that also has the characterizing features of the main claim. 
         [0008]    In accordance with the invention, the power split transmission has a continuously variable power branch and a mechanical power branch. 
         [0009]    The continuously variable power branch can be designed as a hydrostatic power branch that can have continuously variable hydrostatic units of swash plate design or inclined axle design. These hydrostatic units can be interconnected so that they can be varied by way of a common yoke. However, this can be set that so in a first position, the first hydrostatic unit is at zero displacement and the second hydrostatic unit exhibits its maximum displacement. In the second end position of the yoke, the first hydrostatic unit is adjusted to maximum displacement and the second hydrostatic unit is at zero displacement. 
         [0010]    However, it is also possible to design the continuous units as electrical units. The continuously variable power branch and the mechanical power branch are summed in a summing gear set, with the summing gear set being designed as a planetary gear set that has at least one double planetary gear that meshes with a ring geared gear and two sun gears. 
         [0011]    The power split transmission has shafts on which there are clutches, by means of which on the one hand a forward drive and a reverse drive can be switched, and on the other hand at least two operating ranges can be switched, and within which the output drive rotational speed can be continuously varied. The shafts are positioned apart from one another and there is only one single clutch on each shaft, so that a large axial separation and an otherwise compact transmission is provided. A clutch for forward drive and a clutch for reverse drive precede the summing gear set through gear wheels, whereby the clutches for the operating ranges can follow the summing gear set. 
         [0012]    The clutch for forward drive is preferably positioned coaxially with the drive of the power split transmission, and the clutch for reverse drive is on a shaft separated from the clutch for forward drive. The gear ratios of the gear wheels are preferably designed so that the shaft that is connected to the clutch for reverse drive has a higher rotational speed than the drive shaft that is connected to the clutch for forward drive. This makes it possible to place one or more consumers on the shaft with the clutch for reverse drive, for example a hydraulic pump, which has sufficient rotational speed even with lower rotational speeds on the input drive to the transmission. This hydraulic pump, for example, can be used for the hydraulic supply of the transmission system, as well as for cooling and lubricating. Another hydraulic pump can be used to supply the working hydraulic mechanism. 
         [0013]    The planet carrier of the summing gear set, which carries at least one double planetary gear, can be connected through gear wheels and the clutch for forward drive and the clutch for reverse drive, to the input shaft of the power split transmission. A first sun gear of the summing gear set is connected to the first continuously variable unit, and the ring gear of the summing gear set is in active connection with the second continuously variable unit. To switch to a first operating range, the second continuously variable unit is connected, via a clutch for the first operating range and other gears, to the output drive of the power split transmission. Except for the summing planetary gear set, the gear wheels of the power split transmission are designed as spur gears. 
         [0014]    To switch to a second operating range, the clutch for the first operating range is actuated in the disengaging direction and the clutch for the second operating range is actuated in the engaging direction, so that the second sun gear of the summing planetary set can be brought into active connection with the output drive of the power split transmission. 
         [0015]    The gear ratios of the range gears are chosen preferably so that at the end of the first operating range, at which the clutch for the first operating range is still engaged, the clutch for the second operating range has no differential rotational speed and can thus be engaged synchronously. During the change of ranges, the clutch for the first operating range is actuated in the disengaging direction and the clutch for the second operating range is actuated in the engaging direction, with only little need during this switch to correct the rotational speeds of the continuously variable units, for example the hydrostatic units, since the correction has to compensate only for leakage that occurs from the changing pressure conditions. When switching back from the second to the first operating range, the engaging and disengaging of the clutches take place in correspondingly different directions. In the second operating range, the second continuously variable unit is then adjusted from zero displacement toward maximum displacement, and the first continuously variable unit is adjusted from maximum displacement toward minimal displacement. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    Other features can be found in the Figures and Specification. 
           [0017]    The Figures show: 
           [0018]      FIG. 1  a power split transmission with two operating ranges for forward drive and two operating ranges for reverse drive; and 
           [0019]      FIG. 2  a power split transmission with three operating ranges for forward drive and three operating ranges for reverse drive. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    
       FIG. 1 
     
         [0021]    A drive motor  1  drives the input drive shaft  2  for the power split transmission. The drive shaft  2  is connected in a rotationally fixed manner, to a spur gear  3 , designed as a fixed gear, and a clutch for forward drive  4 . An idler  5  that is connected in a rotationally fixed manner to the clutch for forward drive  4 , is located on the input drive shaft  2 . The spur gear  3  meshes with a spur gear  6  designed as a fixed gear, which is connected in a rotationally fixed manner, to the shaft  7 . The clutch for forward drive  8  is positioned on the shaft  7  and is connected in a rotationally fixed manner to the spur gear  6 . The idler  9  is placed on the shaft  7  and is connected in a rotationally fixed manner to the clutch for reverse drive  8 . A consumer  10 , for example a hydraulic pump, is driven by the shaft  7 . The gear ratios are preferably chosen so that the shaft  7 , and thus the consumer  10 , has a greater rotational speed than the shaft  2 . The idler  5  and the idler  9  mesh with the idler  11 , which is connected in a rotationally fixed manner to the planet carrier  12  of the summing planetary gear set  13 . The planet carrier  12  carries at least one double planetary gear  14 , with the double planetary gear mating on the one hand with the ring gear  15  and on the other hand with the first sun gear  16  and the second sun gear  17 . The first sun gear  16  is connected to the first continuously variable unit  18 , for example a hydrostat. The ring gear  15  is connected, rotationally fixed, to the idler  19 , which meshes with the spur gear  20  designed as a fixed gear. The spur gear  20  is connected to the second continuously variable unit  21 , for example a hydrostat. The second sun gear  17  is connected in a rotationally fixed manner to the spur gear  22 , which is designed as a fixed gear. The output drive  23  of the power split transmission is connected in a rotationally fixed manner to the spur gear  24 , designed as a fixed gear, which can be connected, via the spur gear  25  designed as a fixed gear, to the clutch for the first operating range  26 , and in the idler  27  to the spur gear  20 , or, via the spur gear  25 , the idler  28  can be connected to the clutch for the second operating range  29 , and the spur gear  30  designed as a fixed gear can be connected to the spur gear  22 . It is thus possible, by engaging the clutch for the first operating range  26  and disengaging the clutch for the second operating range  29 , to operate the output drive  23  in a first operating range, and by disengaging the clutch  26  and engaging the clutch  29 , to operate the output drive  23  in a second operating range. The gear ratios are established so that when the end of the first operating range is reached with the clutch  26  engaged, the idler  28  and the spur gear  30  rotate synchronously, so that the clutch  29  can be actuated in the engaging direction with no differential rotational speed. Because of the structural space, it may also be necessary to divide the gear train consisting of the idler  19 , the spur gear  20 , and the idler  27 , into two pairs of gears, whereby two spur gears are placed on the shaft  31  in the form of fixed gears. This makes it possible to provide a larger gear ratio. 
         [0022]    Because the shaft  2 , the shaft  7 , and the shafts  31 ,  32 , and  33  are positioned separated from one another, and only a single clutch is placed on each of these shafts, a power split transmission can be provided that has a compact design and has a large axial separation. 
         [0023]      FIG. 2 : 
         [0024]    This differs from  FIG. 1  only in that a third operating range is present in addition. A clutch for a third operating range  34  connects the idler  35  with the spur gear  36 , designed as a fixed gear, to switch to a third operating range, with the spur gear  36  meshing with the spur gear  30  or the spur gear  22 , and the idler  35  meshing with the spur gear  25 . A first operating range is engaged by actuating the clutch for the first operating range  26  in the engaging direction and actuating the clutch for the second operating range  29  and the clutch for the third operating range  34  in the disengaging direction, a second operating range is engaged by actuating the clutch  29  for the second operating range in the engaging direction and the clutch  26  and the clutch  34  in the disengaging direction, and a third operating range is engaged by actuating the clutch  34  in the engaging direction and actuating the clutch  26  and  29  to disengage. 
       REFERENCE LABELS 
       [0000]    
       
           1  Drive motor 
           2  Input drive shaft 
           3  Spur gear 
           4  Clutch for forward drive 
           5  Idler 
           6  Spur gear 
           7  Shaft 
           8  Clutch for reverse drive 
           9  Idler 
           10  Consumer 
           11  Idler 
           12  Planet carrier 
           13  Summing planetary gear set 
           14  Double planetary gear 
           15  Ring gear 
           16  First sun gear 
           17  Second sun gear 
           18  First continuously variable unit 
           19  Idler 
           20  Spur gear 
           21  Second continuously variable unit 
           22  Spur gear 
           23  Output drive 
           24  Spur gear 
           25  Spur gear 
           26  Clutch for the first operating range 
           27  Idler 
           28  Idler 
           29  Clutch for the second operating range 
           30  Spur gear 
           31  Shaft 
           32  Shaft 
           33  Shaft 
           34  Clutch for the third operating range 
           35  Idler 
           36  Spur gear 
           37  Shaft