Abstract:
A transmission comprising three parallel shafts and gearwheels carried by the shafts, which intermesh with one another in pairs for transmitting torque either between the first shaft and the third shaft, or between the second shaft and the third shaft. At least one gearwheel in each pair of intermeshing gearwheels is rotatably supported on its shaft and can be locked to or disengaged from its shaft by means of associated clutch members. Gearwheels on the first shaft and second shaft are coordinated by clutch members, by means of which at least two gearwheels on each shaft can be disengaged from their shaft but coupled together for rotation together in order to permit the transmission of torque from the first shaft via the third and the second shaft back to the third shaft, and from the second shaft via the third and the first shaft back to the third shaft.

Description:
BACKGROUND AND SUMMARY  
       [0001]     The present application is a continuation of International Application PCT/SE2004/001717, filed Nov. 24, 2004, which claims priority to SE 0303530-0, filed Dec. 22, 2003. 
     
    
       [0002]     A transmission comprising first, second and third parallel shafts and gearwheels which are carried by the shafts.  
         [0003]     The present invention relates to a transmission, comprising first, second and third parallel shafts, rotatably supported in a casing, and gearwheels which are carried by the shafts and which intermesh with one another in pairs for transmitting torque either between the first shaft and the third shaft, or between the second shaft and the third shaft, and of which at least one gearwheel in each pair of intermeshing gearwheels is rotatably supported on its shaft and can be locked to or disengaged from its shaft by means of associated clutch members.  
         [0004]     The use of transmissions of the type described above in vehicle gearboxes of having two concentrically supported input shafts, which can each be drive-connected to the output shaft of an internal combustion engine via its own disk clutch, is already known. In such a “power shift” gearbox the first and second shafts form two intermediate shafts, the third shaft usually forming the output shaft, to which torque is transmitted alternately via the one or the other intermediate shaft through alternating engagement of the disk clutches. When driving in a selected gear, the next gear is usually pre-selected by engagement of the relevant gearwheel on the currently non-driven intermediate shaft prior to the actual gearshift, so that the actual gearshift can, in principle, take place without interruption of the torque through simultaneous disengagement of the currently engaged disk clutch and engagement of the other disk clutch.  
         [0005]     Such “power shift” gearboxes are often used in heavier trucks and plant vehicles and commonly have a total of ten or more gear ratios. The more gear ratios the gearbox is designed to have, the more gearwheels and clutches it requires and the more difficult it becomes to achieve suitable steps between the various gears in combination with an optimum span between the highest and the lowest gear ratio. A known method of minimizing the number of input shafts with associated clutch members is to have some or all gearwheels on the output shaft mesh with corresponding gearwheels on the two intermediate shafts. This means that the freedom to select steps between the various gears is more limited the greater the number of gearwheels on the intermediate shafts that mesh with common gearwheels on the output shaft. Maximum freedom, on the other hand, is obtained if each intermediate shaft gearwheel meshes with its own gearwheel on the output shaft, but this is then achieved at the expense of an increased number of requisite components.  
         [0006]     It is desirable to provide a transmission of the type specified in the introductory part, which having few constituent components permits a large number of gear ratios with even steps between the gears.  
         [0007]     According to an aspect of the present invention, at least two gearwheels rotatably supported on the first shaft and two gearwheels rotatably supported on the second shaft are coordinated by clutch members, which have neutral positions, in which both gearwheels are disengaged from their shaft and from one another, first engagement positions, in which the gearwheels are disengaged from the shaft but are coupled together for rotation together, and second engagement positions, in which one of the gearwheels is disengaged and one is locked to the shaft, and that the two gearwheels mesh with gearwheels on the third shaft in order to permit the transmission of torque from the first shaft via the third and the second shaft to the third, or from the second shaft via the third and the first shaft to the third shaft.  
         [0008]     In a preferred embodiment of the transmission according to the invention three gearwheels are used on the first and the second shaft, the gearwheels being coordinated by clutch members, which have first engagement positions, in which either the first and the second or the second and the third gearwheel are disengaged from the associated shaft but are coupled together for rotation together.  
         [0009]     By thus using three gearwheels with associated clutch members on the first and second shaft, it is possible, by way of a total of just eleven gearwheels, to transmit torque from the first or second shaft to the third shaft or vice-versa, with ten different gear ratios. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The invention will be described in more detail with reference to exemplary embodiments shown in the drawings attached, in which:  
         [0011]     FIGS.  1  to  5  show schematic longitudinal sections through an embodiment of a transmission according to the present invention with the torque transmission in the various gears marked. 
     
    
     DETAILED DESCRIPTION  
       [0012]     The transmission has a first shaft  1 , which is rotatably supported in a casing (not shown) and has a gearwheel  2  fixedly connected to the shaft, and three gearwheels  3 , 4  and  5  which are rotatably supported on the shaft and which are coordinated by three clutch devices  6 , 7  and  8 , which each comprise a hub  9 ,  10  and  11  fixedly connected to the shaft  1 , a clutch sleeve  12 ,  13  and  14 , supported so that it is axially displaceable on the respective hub  9 - 11 , and synchromesh devices not shown in more detail.  
         [0013]     The transmission furthermore has a second shaft  15 , which is rotatably supported in the casing and has a gearwheel  16  fixedly connected to the shaft, and three gearwheels  17 ,  18  and  19  which are rotatably supported on the shaft and which are coordinated by three clutch devices  20 ,  21  and  22 , which each comprise a hub  23 ,  24  and  25  fixedly connected to the shaft, a clutch sleeve  26 ,  27  and  28 , supported so that it is axially displaceable on the respective hub  23 - 25 , and synchromesh devices not shown in more detail.  
         [0014]     A third shaft  30  rotatably supported in the casing has two gearwheels  31  and  32  fixedly connected to the shaft, a first pair of gearwheels  33  and  34  which are connected to one another and are capable of rotating together on the shaft, and a second pair of gearwheels  35  and  36 , which are connected to one another and are capable of rotating together on the shaft. The pairs of gearwheels  33 ,  34  and  35 ,  36  are each coordinated by their clutch device  37  and  38  respectively, which each comprise a hub  39  and  40  fixedly connected to the shaft  30 , a clutch sleeve  41  and  42  respectively, supported so that it is axially displaceable on the respective hub  39 , 40 , and synchromesh devices not shown in more detail.  
         [0015]     The clutch device  6  on the shaft  1  has two positions, that is a neutral position, in which it disengages the gearwheel  3  from the shaft  1 , and an engagement position, in which it locks the gearwheel  3  to the shaft  1 .  
         [0016]     The clutch  7  on the shaft  1  has three positions, that is a neutral position, in which it disengages the gearwheels  3  and  4  from the shaft  1  and from one another, a first engagement position, in which it disengages the gearwheels  3  and  4  from the shaft  1  but keeps them coupled together, and a second engagement position, in which it disengages the gearwheel  3  from the shaft  1  and locks the gearwheel  4  to the shaft  1 .  
         [0017]     The clutch  8  on the shaft  1  has three positions, that is a neutral position, in which it disengages the gearwheels  4  and  5  from the shaft  1  and from one another, a first engagement position, in which it disengages the gearwheels  4  and  5  from the shaft but keeps them coupled together, and a second engagement position, in which it disengages the gearwheel  4  from the shaft  1  and locks the gearwheel  5  to the shaft  1 .  
         [0018]     The clutch  20  on the shaft  2  has three positions, that is a neutral position, in which it disengages the gearwheels  17  and  18  from the shaft  2  and from one another, a first engagement position, in which it disengages the gearwheels  17  and  18  from the shaft  2  but keeps them coupled together, and a second engagement position, in which it disengages the gearwheel  18  from the shaft and locks the gearwheel  17  to the shaft  2 .  
         [0019]     The clutch  21  on the shaft  2  has three positions, that is a neutral position, in which it disengages the gearwheels  18  and  19  from the shaft  2  and from one another, a first engagement position, in which it disengages the gearwheels  18  and  19  from the shaft but keeps them coupled together, and a second engagement position, in which it disengages the gearwheel  19  from the shaft and locks the gearwheel  18  to the shaft  2 .  
         [0020]     The clutch  22  on the shaft  2  has two positions, that is a neutral position, in which it disengages the gearwheel  19  from the shaft  2 , and an engagement position, which locks the gearwheel  19  to the shaft  2 .  
         [0021]     The clutches  37  and  38  on the shaft  30  have two positions, that is a neutral position, in which the gearwheel pairs  33  and  34 ,  35  and  36  are disengaged from the shaft  30 , and an engagement position, in which the gearwheel pairs  33  and  34 ,  35  and  36  are locked to the shaft  30 .  
         [0022]     In one embodiment of the transmission according to the invention the gearwheels  2  and  16  on the shafts  1  and  15  respectively are designed to be driven alternately by a pair of input shafts, each via its disk clutch (not shown). The shafts  1  and  15  then form a pair of intermediate shafts and the shaft  30  and output shaft.  
         [0023]     In such a transmission of the so-called power shift type torque is transmitted via the one intermediate shaft in all odd gears and via the other intermediate shaft in all even gears.  
         [0024]     FIGS.  1  to  5  illustrate the torque transmission path of the various transmission steps in a transmission having ten gears. By connecting the transmission to a clutch and reverse unit of the type shown and described in SE 0300497-5, a gearbox with ten forward gears and ten reverse gears is obtained.  
         [0025]      FIG. 1  illustrates the torque transmission in 1 st  and 2 nd  gear. The clutch  6  is in its neutral position, the clutch  7  is in its first engagement position and the clutch  8  is in its second engagement position. The clutches  37  and  38  on the shaft  30  are in their neutral positions, whilst the clutch  20  on the shaft  15  is in its second engagement position and locks the gearwheel  17  to the shaft. The clutch  21  is in its first engagement position and the clutch  22  in its neutral position.  
         [0026]     When driving the shaft  1  with the shaft  15  disengaged, torque is transmitted in 1 st  gear from the shaft  1  to the shaft  30  via the gearwheels  5 ,  35 ,  36 ,  19 ,  18  and  31 . By disengaging the shaft  1  and engaging the shaft  15  the gear is disengaged. Through the clutch positions described above the 2nd gear is pre-selected and when the shaft  15  is driven torque is transmitted in 2 nd  gear from the shaft  15  to the shaft  30  via the gearwheels  17 ,  34 ,  33 ,  3 ,  4  and  31 . In and gears, therefore, all three shafts are involved in the torque transmission, the clutches  7  and  21  being used to transmit torque between adjacent gear wheels without the gearwheels being locked to the associated shaft.  
         [0027]      FIG. 2  illustrates the torque transmission in 3 rd  and 4 th  th gear. As in 1 st  gear, when transmitting torque in 3 rd  gear the clutch  8  is in its second engagement position and locks the gearwheel  5  to the shaft  1 , but instead of serving only as intermediate gear, the gearwheel  35  is now locked to the shaft  30  by the clutch  38  for transmitting torque directly from the shaft  1  to the shaft  30  via the gearwheels  5  and  35 . As in 2 nd  gear, when transmitting torque in 4 th  gear the clutch  20  is in its second engagement position and locks the gearwheel  17  to the shaft  15  for transmitting torque directly from the shaft  15  to the shaft  30  via the gearwheels  17  and  34 , which are locked to the shaft  30  by the clutch  37 .  
         [0028]      FIG. 3  illustrates the torque transmission in 5 th  and 6 th  gear. When transmitting torque in 5 th  gear the shaft  1  drives, the clutches  6  and  8  are in their neutral positions and the clutch  7  is in its second engagement position and locks the gearwheel  4  to the shaft  1 . Via the gearwheel  31  fixed to the shaft  30 , torque is transmitted directly to the shaft  30 . When transmitting torque in 6 th  gear the shaft  15  drives, the clutches  20  and  22  are in their neutral positions and the clutch  21  is in its second engagement position and locks the gearwheel  18  to the shaft  15 . Via the gearwheel  31  fixed to the shaft  30 , torque is transmitted directly to the shaft  30 .  
         [0029]      FIG. 4  illustrates the torque transmission in 7 th  and 8 th  gear. When transmitting torque in 7 th  gear the shaft  1  drives, the clutches  7  and  8  are in their neutral positions and the clutch  6  is in its engagement position and locks the gearwheel  3  to the shaft  1 . The clutch  37  is in its engagement position and locks the gearwheel pair  33 ,  34  to the shaft  30  for transmitting torque from the shaft  1  to the shaft  30  via the gearwheel  3  and the gearwheel pair  33 ,  34 . When transmitting torque in 8 th  gear the shaft  15  drives, the clutches  20  and  21  are in their neutral positions and the clutch  22  is in its engagement position and locks the gearwheel  19  to the shaft  16 . The clutch  38  is in its engagement position for locking the gearwheel pair  35 ,  36  to the shaft  30  and transmitting torque from the shaft  15  to the shaft  30 .  
         [0030]      FIG. 5  illustrates the torque transmission in 9 th  and 10 th  gear. When transmitting torque in 9 th  gear the shaft  1  drives. As in 7 th  gear, the clutch  7  is in its neutral position, whilst the clutch  6  is in its engagement position and locks the gearwheel  3  to the shaft  1 . 10 th  gear is pre-selected in that the clutch  8  is in its first engagement position. The clutches  37  and  38  are in their neutral positions, whilst the clutch  20  on the shaft  15  is in its first engagement position and locks the gearwheels  17  and  18  together at the same time that these are disengaged from the shaft  15 . The torque is now transmitted from the gearwheel  3  on the shaft  1  via the disengaged gearwheel pair  33 ,  34  on the shaft  30  and the disengaged gearwheel pair  17 ,  18  on the shaft  16  to the fixed gearwheel  31  on the shaft  30 . When transmitting torque in 10 th  gear the shaft  15  drives. The gearwheels  17  and  17  are disengaged from the shaft  15  by the clutches  20  and  21 , whilst the clutch  22  is in its engagement position and locks the gearwheel  19  to the shaft  15 . The clutches  37  and  38  are in their neutral positions, whilst the clutch  8  on the shaft  1  is in its first engagement position and locks the gearwheels  4 , 5  together at the same time that these are disengaged from the shaft  1 . The torque is now transmitted from the gearwheel  19  on the shaft  15  via the disengaged gearwheel pair  35 ,  36  on the shaft  30  and the disengaged gearwheel pair  4 , 5  on the shaft  1  to the fixed gearwheel  31  on the shaft  30 .  
         [0031]     In the transmission according to the invention clutches  7 ,  8 ,  20  and  21  are therefore used, which in addition to the usual functions for transmission clutches of locking and disengaging gearwheels on an associated shaft here also have the further function of being able to lock adjacent gearwheels to the shaft together without locking the gearwheels on the shaft. Coupled gearwheels of different diameters can thereby be used to transmit torque with a gear ratio step from a driving shaft via an output shaft to a third shaft and thence back to the output shaft. This gives great freedom in selecting the gear ratio of the various gears compared to torque transmission between the shafts via a single common gearwheel. This makes it possible, using few constituent gearwheels and clutches, to produce a transmission having a large number of gear ratios with a large span between top and bottom gear. In the embodiment described a ten-gear transmission is achieved using just eleven gearwheels, except for the primary drive gearwheels.  
         [0032]     In the present application, the use of terms such as “including” is open-ended and is intended to have the same meaning as terms such as “comprising” and not preclude the presence of other structure, material, or acts. Similarly, though the use of terms such as “can” or “may” is intended to be open-ended and to reflect that structure, material, or acts are not necessary, the failure to use such terms is not intended to reflect that structure, material, or acts are essential. To the extent that structure, material, or acts are presently considered to be essential, they are identified as such.  
         [0033]     While this invention has been illustrated and described in accordance with a preferred embodiment, it is recognized that variations and changes may be made therein without departing from the invention as set forth in the claims.