Abstract:
A powershift transmission for a work vehicle is disclosed having two modes of applying power: a direct connection through a series of gears, and a connection through a torque converter integral with the transmission. The two paths branch at the input shaft, on which is mounted and which drives a torque converter that has a gear coupled to its output. Another gear on the input shaft is connected to that shaft by a hydraulic clutch. When the clutch is engaged, the transmission provides several high-range forward gear ratios through a direct gear drive. When that clutch is disconnected, the torque converter supplies power to the transmission to low forward and low reverse ranges of gear ratios. The transmission includes a first countershaft, on which are mounted a reverse master clutch engaged in all reverse gear ratios) and a forward low range clutch, which is engaged in the low range of forward gear ratios. The reverse master clutch couples the countershaft directly to the output shaft. The forward low-range clutch connects the countershaft to a second countershaft. The second countershaft and the output shaft each has two speed clutches. Only one of these speed clutches is engaged in any individual gear ratio. The output shaft is also engaged to a mechanical front wheel drive output shaft via a clutch. This output shaft is engaged via that clutch and counter-rotates with the output shaft to drive the front wheels or tracks of the vehicle.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to a dual power flow counter shaft transmission for a heavy duty work vehicle, and more particularly to a dual power flow counter shaft transmission having a plurality of forward and reverse speeds utilizing constant mesh gearing, a torque converter, and a plurality of fluid actuated rotating disc-type clutches so constructed and arranged as to provide maximum compactness and speed reduction ratio flexibility.  
         BACKGROUND OF THE INVENTION  
         [0002]    Counter shaft transmissions having a plurality of speed ratios in each direction of operation have been found to be particularly useful in the drive line of heavy duty work vehicles, such as wheel loaders, rubber tired log skidders and lift trucks. These transmissions are advantageous in that a plurality of rotating disc-type clutches and associated continually meshing gears can be so positioned on the usual parallel shafts as to allow considerable design flexibility and adaptability to the elevational drop requirement between the input and output axes.  
           [0003]    One of the problems with these prior counter shaft transmissions is that they provide only a limited number of fixed gear ratios between the input and the output shaft. When operating at low speeds, these fixed gear ratios require a significant and abrupt change as one gear ratio is disengaged and the other gear ratio is engaged. While some of this abruptness can be eliminated by careful design of the clutch valve controllers, it cannot all be eliminated. In addition, by providing several closely spaced low range gear ratios, the work vehicle will spend a large amount of time shifting between those ratios to achieve the optimum gear ratio.  
           [0004]    Accordingly, what is needed is a structurally simple, constant mesh counter shaft transmission that includes a torque converter that is engaged in a low range of gear ratios and is disengaged in a high range of gear ratios when the vehicle is operated at high speeds over the road.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention is directed to providing such a transmission. In one embodiment of the invention, there is provided a dual power flow counter shaft transmission for a work vehicle that has an input shaft rotationally coupled to and driven by the vehicles engine. The input shaft has a first gear mounted for free rotation thereon and a first hydraulic clutch disposed to connect the first gear to the input shaft for conjoint rotation. A second gear is also mounted on the input shaft for free rotation thereon. A torque converter is disposed to couple the input shaft to the second gear to transmit power from the input shaft through the torque converter to the second gear, thereby driving the second gear.  
           [0006]    A first counter shaft is also provided in the transmission and has a third gear mounted for free rotation thereon, a fourth gear mounted for free rotation thereon, and a fifth gear mounted for conjoint rotation with the first counter shaft. A second clutch is provided to connect the third gear with the first counter shaft. A third clutch is provided to connect the fourth gear to the first counter shaft. The first gear and the fourth gear are engaged to each other in continuous mesh. The fifth gear and the second gear are also engaged to each other in continuous mesh.  
           [0007]    A second counter shaft is provided having a sixth gear mounted thereon for free rotation. A seventh gear is mounted on the third counter shaft for conjoint rotation. An eighth gear is mounted on the third counter shaft for conjoint rotation. A ninth gear is mounted on the third counter shaft for free rotation.  
           [0008]    A fourth clutch is disposed on the second counter shaft to connect the sixth gear with the second counter shaft for conjoint rotation therewith. A fifth clutch is provided on the second counter shaft to connect the ninth gear with the second counter shaft for conjoint rotation therewith. The eighth gear and the fourth gear are in continuous meshing engagement.  
           [0009]    A first output shaft is provided having a tenth gear mounted thereon for conjoint rotation. An eleventh gear and twelfth gear are mounted thereon for free rotation (with respect to the first output shaft) and for conjoint rotation (with respect to each other). A thirteenth gear is mounted on the output shaft for free rotation thereon and a fourteenth gear is mounted on the first output shaft for conjoint rotation therewith. A sixth clutch is disposed on the first output shaft to connect the eleventh and twelfth gears, which always rotate conjointly, to the first output shaft for conjoint rotation therewith. A fifteenth gear is mounted on the first output shaft for conjoint rotation therewith. A seventh clutch is disposed on the first output shaft to connect the thirteenth gear with the first output shaft for conjoint rotation therewith. The third gear on the first counter shaft is engaged with the twelfth gear on the first output shaft for continuous meshing engagement. The fourth gear on the first counter shaft is engaged to the eighth gear on the second counter shaft for continuous meshing engagement. The sixth gear on the second counter shaft is engaged with the tenth gear on the first output shaft for continuous meshing engagement. The seventh gear on the second counter shaft is connected to the eleventh gear on the first output shaft for continuous meshing engagement. The eighth gear on the second counter shaft is coupled to the thirteenth gear on the first output shaft for continuous meshing engagement. The ninth gear on the second counter shaft is coupled to the fourteenth gear on the first output shaft for continuous meshing engagement.  
           [0010]    A mechanical front wheel drive output shaft is also provided having a sixteenth gear mounted for free rotation thereon. An eighth clutch is provided on the mechanical front wheel drive output shaft to connect the sixteenth gear to that shaft for conjoint rotation therewith.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The present invention will become more fully understood from the following detailed description, taken in conjunction with the accompanying drawings, wherein like reference numerals refer to like parts, in which:  
         [0012]    [0012]FIG. 1 is a diagrammatic, developed, but substantially side elevational view of an eight-speed forward, four-speed reverse dual power flow counter shaft transmission constructed in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0013]    [0013]FIG. 1 shows the layout of gears, shafts, and clutches of transmission  10 . The transmission shafts are supported in transmission case  11  on bearings  13  in a conventional manner. Transmission  10  selectively drives rear drive wheels or tracks  15 , as well as a mechanical front wheel (or track) drive  17 . While not shown, the wheels or tracks can be, and preferably are, driven through additional drive elements  100 , which may include transfer cases, rear differentials and simple reduction gear sets. Similar drive elements  102  may be disposed between MFD shaft  20  and front wheels or tracks  17 . In the preferred embodiment, there are five (5) shafts, an input or first shaft  12 , a first counter shaft  14 , a second counter shaft  16 , a first output shaft  18 , and a mechanical front wheel drive output shaft  20 . Input shaft  12  drives a power take off (PTO) or pump  22 . The pump is a hydraulic pump and is used to provide auxiliary hydraulic fluid typically for implements attached to the vehicle. The PTO is similarly connected to an implement that is driven by a rotating shaft. The vehicle&#39;s engine  23  is rotationally coupled to and drives input shaft  12 . A first gear  24  is fixed to shaft  12  for free rotation therewith. A hydraulic clutch, preferably a multi-plate clutch  26 , is also mounted on input shaft  12 . Clutch  26 , when engaged, locks first gear  24  to shaft  12  so that they rotate conjointly. When clutch  26  is disengaged, input gear  24  can turn freely on the shaft. A torque converter  28  is also mounted on and driven by input shaft  12 . The input side  30  of the torque converter is fluidly coupled to output side  32  of the torque converter in the conventional manner. A first gear of a drop gear set, shown in FIG. 1 as second gear  34 , is also mounted on shaft  12  and is coupled to the output side  32  of the torque converter to rotate conjointly therewith. First gear  24  is driven by the engine  23  whenever the forward high range clutch  26  is engaged. Clutch  26 , like all the other clutches in transmission  10 , is designed to provide conjoint rotations, and not to slip for any extended period of time. Thus, gear  24  rotates at substantially the same speed as engine  23 . Although we have not shown it in FIG. 1, one or more reduction gears could easily be disposed between engine  23  and input shaft  12  without violating the spirit of the present invention. Engine  23  also drives input side  30  of torque converter  28  which, in turn, is fluidly coupled to the output side  32  of the torque converter and drives it. Since the output side of the torque converter is fixed to and rotates conjointly with second gear  34 , gear  34  rotates with the input shaft. Gear  34  is fluidly coupled to the input shaft whenever the forward high range clutch  26  is engaged. Unlike gear  24 , gear  34  is fluidly coupled to engine  23 , and therefore does not always rotate at the same speed as engine  23 , as does gear  24 . These two gears, both located on input shaft  12 , provide the dual power flows for transmission  10 . For the high range of forward gears, power flows from engine  23  through gear  24  and thence to the rest of the transmission and driven wheels or tracks. For the low range of forward gears and the reverse gears, power flows from the engine through torque converter  28  and to gear  34 . From gear  34 , this power is coupled to the remaining portions of the transmission. For this reason, clutch  26  is termed the “forward high range” clutch. When it is engaged, power is provided to the forward high range of gear ratios.  
         [0014]    Transmission  10  also includes a first counter shaft  14  on which gears  35 ,  36  and  38  are mounted. Gear  35  is mounted on counter shaft  14  for free rotation thereon. Transmission  10  includes a second clutch  40  that is also mounted on counter shaft  14  and, when engaged, fixes third gear  35  to rotate conjointly with counter shaft  14 . When clutch  40  is disengaged, gear  35  rotates freely about counter shaft  14 . Clutch  40 , when engaged, enables the transmission to provide all of the reverse gear ratios. As shown by dotted lines  37 , gear  35  is in continuous mesh with gear  60  on the output shaft. When clutch  40  is engaged, power flow bypasses the second counter shaft  16  and goes to output shaft  18 , thus reversing the direction of rotation of output shaft  18 . It is this reversal of rotation of the output shaft that causes the transmission, and hence the vehicle, to operate in reverse. For this reason, clutch  40  is called the “reverse clutch” or “reverse master clutch”.  
         [0015]    Gear  36  is also mounted on counter shaft  14  for free rotation therewith. A third clutch, clutch  42 , is mounted on counter shaft  14  and, when engaged, fixes gear  36  to rotate conjointly with counter shaft  14 . When clutch  42  is disengaged, gear  36  rotates freely about counter shaft  14 . Clutch  42  is the forward low range clutch. When it is engaged transmission  10  can operate in a low range of forward gear ratios. Reverse clutch  40  and the forward low range clutch  42  are not simultaneously engaged in any of the gear ratios of transmission  10 .  
         [0016]    The second gear of the drop gear set, fifth gear  38 , is mounted on counter shaft  14  to rotate conjointly therewith. Second gear  34  on input shaft  12  and fifth gear  38  on first counter shaft  14  together comprise drop gear set  33  and jointly serve to transfer the engine power from torque converter  28  to first counter shaft  14 . Gears  34  and  38  are in constant meshing engagement at all times during transmission operation. In a similar fashion, gears  24  (on shaft  12 ) and  36  (on shaft  14 ) are also in constant meshing engagement.  
         [0017]    Clutch  42  is called the “forward low range clutch” because when it is engaged, it enables the transmission to operate in the forward low range gear ratios. It is always engaged when the transmission is in these forward gear ratios.  
         [0018]    Power from engine  23  goes through torque converter  28  to gear  34 , the first gear of the drop gear set, which transmits power to the second gear of the drop gear set, gear  38 . Since gear  38  is fixed to the first counter shaft  14 , this causes counter shaft  14  to rotate the “gear” side of clutch  26 , the forward high range clutch. However, clutch  26  is always disengaged when clutch  42  is engaged, thus permitting gear  29  to spin freely on shaft  12 . Power is transmitted from gear  38  to counter shaft  14  and thence through clutch  42  to gear  36 . This power flow provides all the forward low range gear ratios. All of these low range gear ratios therefore couple the engine to the wheels or tracks through torque converter  28 . Once engine power has been supplied to gear  36  in this manner, gear  36  transmits the power to shaft  16  through gear  48  with which it continuously meshes.  
         [0019]    Referring now to second counter shaft  16 , a sixth gear, gear  44  is mounted on second counter shaft  16  for free rotation thereon. A seventh gear  46  is also mounted on second counter shaft  16  for conjoint rotation therewith. An eighth gear  48  is mounted on second counter shaft  16  for conjoint rotation therewith. A ninth gear  50  is mounted on second counter shaft  16  for free rotation thereon.  
         [0020]    A fourth transmission clutch  52  is mounted on second counter shaft  16  to connect sixth gear  44  to shaft  16  for conjoint rotation therewith. A fifth clutch  54  is mounted on second counter shaft  16  to connect ninth gear  50  to shaft  16  for conjoint rotation therewith. Eighth gear  48  is in continuous meshing engagement with fourth gear  36 . Second countershaft  16  receives power from engine  23  in three different ways. In each of the forward gear ranges, the high range through gear  24  and gear  36 , and the low range through gear  34 , gear  38  and thence to gear  36 , counter shaft  16  is driven by gear  48  which is in constant meshing engagement with gear  36  on first counter shaft  14 . Thus, in all forward gear ratios, second counter shaft  16  receives power through gear  48 . For the low range forward gear ratios, the power goes through torque converter  28 . For the high range of gear ratios, power is transmitted through clutch  26 . In the high range of forward gears, clutch  42  is not engaged, and hence gear  36  rotates freely on shaft  14  and serves merely to transfer power from gear  24  to gear  48 . In the forward lower range of gear ratios, clutch  42  is engaged and serves to transmit power from shaft  14  to gear  36  and thence to shaft  16  through gear  48  with which it continuously meshes.  
         [0021]    Referring now to first output shaft  18 , a tenth gear  56  is mounted on output shaft  18  for conjoint rotation therewith. An eleventh gear  58  is mounted on output shaft  18  for free rotation therewith. A twelfth gear  60  is mounted on output shaft  18  for free rotation therewith. Twelfth gear  60  is also fixed to eleventh gear  58  such that gears  58  and  60  rotate conjointly at all times. A thirteenth gear  62  is mounted on output shaft  18  for free rotation therewith. A fourteenth gear  64  is mounted on output shaft  18  for conjoint rotation therewith. A fifteenth gear  66  is mounted on output shaft  18  for conjoint rotation therewith.  
         [0022]    A sixth transmission clutch  68  is mounted on output shaft  18  to connect eleventh gear  58  and twelfth gear  60  to output shaft  18  for conjoint rotation therewith. A seventh clutch  70  is mounted on output shaft  18  to connect thirteenth gear  62  to output shaft  18  for conjoint rotation therewith.  
         [0023]    Tenth gear  56  on output shaft  18  is coupled to sixth gear  44  on second counter shaft  16  for continuous meshing engagement therewith. Eleventh gear  58  on output shaft  18  is coupled to seventh gear  46  on counter shaft  16  for continuous meshing engagement therewith. Twelfth gear  60  on output shaft  16  is engaged with third gear  35  on first counter shaft  14  for continuous meshing engagement therewith. Thirteenth gear  62  on output shaft  18  is connected to eighth gear  48  on second counter shaft  16  for continuous meshing engagement therewith. The fourteenth gear  64  on output shaft  18  is connected to ninth gear  50  on second counter shaft  16  for continuous meshing engagement therewith.  
         [0024]    We will now describe the engagement of the speed clutches to provide each of the forward and reverse gear ratios. The speed clutches are the two clutches,  52  and  54  on shaft  16  and  68  and  70  on shaft  18 . Clutch  52  is the first and fifth gear clutch. Clutch  54  is the second and sixth gear clutch. Clutch  68  is the third and seventh gear clutch, and clutch  70  is the fourth and eighth gear clutch.  
         [0025]    Starting with the forward gear ratios and going from the lowest gears to the highest gears, the power flow in first gear forward is as follows. First, clutch  42 , the forward low range clutch, is engaged. Power flows from the engine through the torque converter and the drop gear set  33  to shaft  14 . With clutch  42  engaged, the fourth transmission gear, gear  36  rotates conjointly with shaft  14 . Gear  36  is in constant meshing engagement with eighth gear  48  on shaft  16 . Thus, for any of the forward low range gear ratios, shaft  16  is driven through the torque converter.  
         [0026]    With first/fifth gear clutch  52  engaged, gear  44  rotates together with driven shaft  16  and transmits its power to output shaft  18  through gear  56  with which it is in constant meshing engagement. Gear  56  is fixed to shaft  18  and therefore rotates the output shaft.  
         [0027]    For the second gear, second/sixth gear clutch  54  is engaged and the other three speed range clutches are disengaged. Again, shaft  16  is driven by gear  48 . Gear  50  rotates jointly with shaft  16  when clutch  54  is engaged. Gear  50  also meshes continuously with gear  64  on output shaft  18 . Since gear  64  is fixed to rotate conjointly with output shaft  18 , this causes output shaft  18  to rotate.  
         [0028]    For the third gear, third/seventh gear clutch  68  is engaged and all the other speed clutches ( 52 ,  54 ,  70 ) are disengaged. Power is transmitted, again, from gear  48  to shaft  16 , thence to gear  46  which is fixed on shaft  16  and to gear  58  with which gear  46  is in continuous meshing engagement. With clutch  68  engaged, gear  58  rotates conjointly with shaft  18 . Thus, shaft  18  is driven by shaft  16 .  
         [0029]    Finally, for fourth gear, fourth/eighth gear clutch  70  is engaged to lock gear  62  with respect to shaft  18 . Power flows from gear  48  directly to gear  62  with which it is in constant meshing engagement. Clutch  70  fixes gear  62  with respect to output shaft  18  and thus causes output shaft  18  to rotate conjointly with gear  62 .  
         [0030]    The forward high range gear ratios, gear ratios five through eight, are also driven in a similar manner through gear  48 . For the high range of forward gear ratios, clutch  26  on the input shaft is engaged, thus causing gear  24  to rotate conjointly with input shaft  12 . This power is transmitted from gear  24  to gear  36 , which is in constant meshing engagement with gear  24  and thence to gear  48  which is in constant meshing engagement with gear  36 . Clutch  42  is always disengaged in these gear ratios, permitting shaft  14  to spin freely driven by drop gear set  33 . In this manner power is transmitted to shaft  16  through gear  48  and the higher range forward gears (gear ratios  5 - 8 ) are engaged in the same manner as the lower range forward gear ratios (gears  1 - 4 ) described immediately above.  
         [0031]    For the reverse gear ratios, power is not supplied directly to shaft  16  through gear  48 , but is supplied through reverse master clutch  40  on shaft  14  through gear  35  and thence to gear  60  on output shaft  18  with which gear  35  is in continuous engagement. This “bypassing” of shaft  16  and the continuous meshing engagement of gears  35  and  60  are indicated by dashed line  37  in FIG. 1.  
         [0032]    This bypassing of shafts  14 ,  16 , and  18  do not lie in the same plane, as the FIGURE would seem to show, but are in a substantially triangular axial relationship. Thus, the distance between shaft  14  and  16  is generally the same as the distance between shafts  16  and  18 , which is generally the same as the distance between shaft  18  and shaft  14 . These relationships have been “flattened” in FIG. 1 to permit the easy illustration of the gear shafts and clutches of transmission  10 .  
         [0033]    In the lowest reverse gear ratio, first gear reverse, power is transmitted through torque converter  28  through the drop gear set and thence to shaft  14 . Reverse clutch  40  on shaft  14  is engaged to transfer power to gear  35  and thence to gear  60  on shaft  18 . Power flows from gear  60  to gear  58  with which it always rotates conjointly, and thence to gear  46 . Clutch  52  is engaged, and therefore gear  44  is fixed with respect to shaft  16  and drives gear  56  fixed on output shaft  18 , causing output shaft  18  to rotate.  
         [0034]    In a similar fashion, in the second reverse gear, gear  58  drives gear  46  which causes shaft  16  to rotate. Unlike first gear reverse, clutch  54 , the second gear clutch, is the only speed clutch engaged, causing gear  50  to rotate conjointly with shaft  16 . Since gear  50  is in continuous meshing engagement with gear  64 , which, in turn, is fixed to rotate conjointly with shaft  18 , gear  50  causes output shaft  18  to rotate.  
         [0035]    For the third reverse gear, clutch  68  is engaged, causing gear  60  to be fixed with respect to shaft  18 . Since gear  60  is driven by gear  35  on shaft  14 , shaft  18  is caused to rotate.  
         [0036]    The final gear ratio, fourth gear reverse, is provided by engaging clutch  70  on shaft  18 . Power transmitted to gear  60  is transmitted to gear  58  which rotates shaft  16  through gear  46 . Gear  48 , in turn, is fixed to shaft  16  and is in continuous meshing engagement with gear  62  on shaft  18 . Clutch  70  fixes gear  62  to rotate conjointly with shaft  18  thereby causing output shaft  18  to rotate.  
         [0037]    The description above explains how each of the gear ratios are provided, and how power flows in dual paths through transmission  10 .  
         [0038]    The remaining shaft in the transmission is the mechanical front wheel drive output shaft  20 . Sixteenth gear  72  is mounted on MFD output shaft  20  for free rotation therewith. Eighth clutch  74  is mounted on shaft  20  to connect sixteenth gear  72  to output shaft  20  for conjoint rotation.  
         [0039]    While the embodiments illustrated in the FIGURES and described above are presently preferred, it should be understood that these embodiments are offered by way of example only. The invention is not intended to be limited to any particular embodiment, but is intended to extend to various modifications that nevertheless fall within the scope of the appended claims.