Abstract:
A transmission having two clutches connected between a drive and respective transmission input shafts, one being hollow which supports the other within. A hollow countershaft which supports another countershaft therein. A main shaft arranged coaxially between the inner input shaft and an output shaft. Shifting elements can engage a variety of transmission connections in which transmission elements of the main group couple transmission elements of the range group which can couple the output shaft. The hollow countershaft has three fixed wheels which engage respective loose wheels, and the countershafts are rigidly coupled by a shifting element. With respect to this shifting element: an adjacent loose wheel rotates on and can rigidly couple the main shaft; a remote loose wheel rotates on and can rigidly couple the inner input shaft; and a central loose wheel rotates on and can rigidly couple at least one of the inner input and main shafts.

Description:
[0001]    This application is a National Stage completion of PCT/EP2012/072660 filed Nov. 15, 2012, which claims priority from German patent application serial no. 10 2011 088 396.7 filed Dec. 13, 2011. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention concerns a dual-clutch transmission. 
       BACKGROUND OF THE INVENTION 
       [0003]    Dual-clutch transmissions having two clutches, whose input sides are connected to a drive input shaft and whose output sides are connected respectively to one of two transmission input shafts arranged coaxially with one another, are known in various versions. In these, one transmission input shaft is in the form of an outer, hollow shaft radially inside which the other transmission input shaft, in the form of a solid shaft, is arranged. Furthermore, in such a dual-clutch transmission it is known to arrange a drive output shaft coaxially with respect to the drive input shaft and to provide one or two countershafts. Such dual-clutch transmissions have the advantage that in a sequential series of gearshifts they can basically be powershifted, since in each case a gear associated with one of the clutches is active while a subsequent gear associated with the other clutch is pre-selected, and the gearshift is carried out by opening and closing the two clutches with a time overlap. In this way dual-clutch transmissions enable gearshifts to take place largely without traction force interruption and with a high level of driving comfort. 
         [0004]    Dual-clutch transmissions are also known which have upstream splitter groups and/or downstream range groups, by virtue of which the number of gears in the main transmission can be multiplied. These group transmission designs are particularly appropriate for commercial vehicles, for example long-haul trucks, which on the one hand need a large number of gears with a correspondingly large transmission spread and on the other hand should provide a good level of driving comfort and high operational reliability. However, in transmissions designed in this way not all the gears can be powershifted. In particular, when—as is usual—the range group is designed to be shifted between two gear ranges, although it is true that most or all of the gears within the two gear ranges are made as powershift gears, the process of shifting between the range groups themselves cannot as a rule be carried out while maintaining the traction force. Moreover, since this shifting operation takes a comparatively long time, the gearshift in the main transmission and the shift in the range group, including the requisite synchronization processes, result, in the case of the gearshifts concerned, in on the whole lengthy shift phases in which the traction force is reduced or interrupted, these phases having a noticeably adverse effect on driving comfort. 
         [0005]    From DE 10 2010 003 924 A1 a dual-clutch transmission is known, which has two transmission input shafts arranged coaxially with one another, a main shaft coaxial with and axially behind the input shafts, an upstream splitter group and a downstream range group. In this transmission two countershafts are arranged with mutually parallel axes. The range group is in the form of a simple planetary gearset in which the sun gear is connected to the output end of the main shaft and the planetary carrier is coupled on the output side to a drive output shaft. To engage a lower gear group with a short gear ratio in the slow range, the ring gear can be coupled to a positionally fixed component, and to engage an upper group with a direct transmission between the main shaft and the drive output shaft, the ring gear can be coupled to the planetary carrier. A radially inner one of the two transmission input shafts can be connected directly to the input end of the main shaft. On the main shaft is additionally arranged a hollow shaft on which at least one loose wheel of a forward gear is mounted to rotate, which loose wheel can be connected in a rotationally fixed manner to the main shaft by means of a shifting element. The hollow shaft can be connected by means of shifting elements to the main shaft and/or to the planetary carrier. The gears of this known transmission can at least predominantly be powershifted. In particular, by virtue of the connectable hollow shaft the range group can also be powershifted. 
         [0006]    From the previously unpublished DE 10 2011 005 028 A1 a dual-clutch transmission which has two clutches is known, the input sides of which clutches are connected to a drive input shaft while their output sides are connected, respectively, to one of two transmission input shafts arranged coaxially with one another, and in which two countershafts arranged coaxially with one another and a range group are also provided. The two countershafts are respectively in the form of a hollow shaft and a solid shaft, with the solid shaft arranged radially inside the hollow countershaft. The clutches with the input shafts form in each case a partial transmission with a plurality of gears that can be engaged. The gears can be coupled to a drive output shaft via the associated countershaft of the partial transmission concerned and via a main shaft connected to a sun gear of the range group. The drive output shaft is positioned coaxially with the two transmission input shafts and is connected to a planetary carrier of the range group. On the input side, the planetary carrier is connected to a non-shiftable loose wheel of a wheel plane axially adjacent to the range group. The non-shiftable loose wheel meshes with a shiftable loose wheel arranged on the radially inner of the two countershafts. Thereby, at least one gear can be coupled to the drive output shaft independently of the range group. In this way a power path to the drive output is produced, which is independent of a range group shift so that all the forward gears can in particular one involving a range group shift in a sequential gearshift series be powershifted. With seven wheel planes, this dual-clutch transmission provides nine forward gears and two reversing gears. 
         [0007]    From DE 10 2007 047 671 A1 a further dual-clutch transmission with two clutches is known, whose input sides are connected to a drive input shaft and whose output sides are connected, respectively, to one of two transmission input shafts arranged coaxially with one another. The dual-clutch transmission also comprises two countershafts arranged coaxially with one another and a range group in the form of a planetary gearset. The two countershafts are respectively in the form of a hollow and a solid shaft with the hollow shaft mounted to rotate on the solid shaft. By means of a shifting device that can be actuated on two sides, depending on the shift position of the shifting device, either the outer countershaft can optionally be connected to the inner countershaft in a rotationally fixed manner, or a loose wheel can be coupled, again in a rotationally fixed manner, to the inner countershaft. An element of the main group of the transmission, preferably a gearwheel, and an element of the range group of the transmission, preferably a planetary carrier, can be connected to one another by means of a coupling device. A drive output shaft is connected rotationally fixed to the planetary carrier. A gear of a lower gear range of the range group and a gear of an upper gear range of the range group can be formed at the same time, in such manner that the respective shifting clutches are closed but the associated powershift clutches, namely the input clutches of the dual clutch, are still open. The two transmission gears from the lower and upper gear ranges can also be engaged at the same time, in which case the powershift clutches are closed and the drive torque is transmitted in parallel by the gears in such manner that one of the two gears is selected, which then remains engaged, while the other transmission gear is disengaged. In this case a shift in the range group takes place under load. 
         [0008]    A comparable dual-clutch transmission, but with two axis-parallel countershafts, is also known from DE 10 2008 036 165 A1. 
         [0009]    Two further, similar dual-clutch transmissions, but respectively with one countershaft or with two countershafts arranged coaxially behind one other, are also known from U.S. Pat. No. 7,621,839 B2 and from U.S. Pat. No. 7,913,581 B2 respectively. 
       SUMMARY OF THE INVENTION 
       [0010]    Against this background the purpose of the present invention is to propose a dual-clutch transmission with a range group, whose forward gears including one involving a range group shift can all be powershifted and which, in relation to the number of gears, requires fewer components and has a compact structure. 
         [0011]    The invention is based on the recognition that in a dual-clutch transmission with a main group and with a range group in drive connection downstream from the main group, the range group can be shifted between two gears that belong respectively to a lower gear range and an upper gear range without traction force interruption in the drive-train if, by means of a shifting device, a supporting gear between the two gear ranges is produced, which bridges across the range group between the main transmission and the drive output of the transmission. By virtue of shiftable shaft connections and the range group, in a compact structure with a range group that can be bridged across in such a manner it should be possible to produce as many usable gears as possible in a powershiftable vehicle transmission, for example for commercial vehicles. 
         [0012]    Accordingly, the invention starts from a dual-clutch transmission having two clutches, whose input sides are connected to a drive input shaft and whose output sides are connected, respectively, to one of two transmission input shafts, wherein one transmission input shaft is in the form of a radially inner solid shaft which is fitted and able to rotate inside the axially shorter, second transmission input shaft in the form of a hollow shaft, having also at least two countershafts one of which is a radially inner, solid shaft fitted and able to rotate inside an axially shorter, outer hollow shaft, having also a drive output shaft coaxial with and arranged behind the drive input shaft, having also a main shaft arranged coaxially between the inner transmission input shaft and the drive output shaft, having also a multiple-gear main group comprising a plurality of forward gearwheel planes, having also a multiple-gear range group in drive connection downstream from the main group and having a plurality of shifting elements for shifting transmission elements and/or for forming transmission element connections in which a first transmission element of the main group is connected to a first transmission element of the range group and in which a second transmission element of the main group can be connected by means of a shifting element to a second transmission element of the range group, which element is or can be connected to the drive output shaft. 
         [0013]    To achieve the stated objective, in this transmission the invention furthermore provides that on the outer countershaft at least three fixed wheels are arranged, each of which meshes with a respective loose wheel and the two countershafts can be connected to one another in a rotationally fixed manner by means of a shifting element that can be actuated on one side, wherein the loose wheel closest to the shifting element is mounted to rotate on the main shaft and can be connected thereto in a rotationally fixed manner, the loose wheel farthest from the shifting element is mounted to rotate on the inner transmission input shaft and can be connected rotationally fixed thereto, and a central loose wheel is arranged and able to rotate axially between the other two loose wheels and can be connected rotationally fixed to the inner transmission input shaft, to the main shaft, or to both those shafts. 
         [0014]    Thus, the invention describes a dual-clutch gear system which comprises few components and wheel planes, wherein all the forward gears in a sequential series of gearshifts can be powershifted, including a range group shift. In this way range shifts with a long shifting time, which affect driving comfort adversely, can advantageously be avoided. The number of forward gears that can be powershifted exceeds twice the number of forward gearwheel planes in the main group, without the need for an upstream splitter group or an additional hollow shaft fitted on the main shaft. 
         [0015]    A particularly compact structure with numerous shifting options is achieved with this transmission in that one of the two transmission input shafts is in the form of a radially inner solid shaft and the other transmission input shaft is an axially shorter, outer hollow shaft arranged coaxially over the inner transmission input shaft in such manner that the inner transmission input shaft projects out of the outer transmission input shaft on both sides. Furthermore a main shaft is provided, which is arranged coaxially with and axially between the inner transmission input shaft and the drive output shaft. In addition, one of the two countershafts is in the form of a radially inner solid shaft and the other countershaft is an axially shorter, outer hollow shaft fitted coaxially over the inner countershaft in such manner that the inner countershaft projects out of the outer, hollow countershaft on both sides and the two countershafts can be coupled to one another by means of a shifting element that can be actuated on one side. 
         [0016]    This arrangement enables an effective multiple use of the shifting elements, gearwheels and shaft connections provided. Basically, in each case a plurality of fixed and/or loose wheels can be arranged on the two countershafts, with the countershaft formed as a hollow shaft supporting at least three fixed wheels. Preferably, only fixed wheels are arranged on the two countershafts apart from the one-side-acting shifting element for coupling the two countershafts to one another, whereas all the shifting elements of the main group are arranged on the transmission input shaft and the main shaft. The arrangement of the countershafts coaxially one over the other limits the radial diameter of the transmission. 
         [0017]    The invention makes available a transmission gear arrangement which, with only five forward gearwheel planes and a two-stage range group, provides eleven powershiftable forward gears of which at least one forward gear can be engaged and used independently of the shift condition of the range group. To be specific, the first forward-gear gearwheel plane comprises two meshing fixed wheels which form an input constant, wherein the first fixed wheel is connected rotationally fixed to the outer transmission input shaft and the second fixed wheel is connected rotationally fixed to the inner countershaft, the second forward-gear gearwheel plane comprises a loose wheel which meshes with a fixed wheel, wherein the loose wheel is mounted to rotate on the inner transmission input shaft but can be connected rotationally fixed thereto by means of a shifting element, whereas the associated fixed wheel is arranged rotationally fixed on the outer countershaft, the third forward-gear gearwheel plane comprises a loose wheel which meshes with a fixed wheel, wherein the loose wheel is positioned and can rotate axially between the inner transmission input shaft and the main shaft and can be connected rotationally fixed by a shifting element to the inner transmission input shaft and also, by another shifting element, to the main shaft, the associated fixed wheel being arranged rotationally fixed on the outer countershaft, the fourth forward-gear gearwheel plane comprises a loose wheel which meshes with a fixed wheel, wherein the loose wheel is mounted to rotate on the main shaft but cab be connected rotationally fixed thereto by a shifting element, whereas the associated fixed wheel is arranged rotationally fixed on the outer countershaft, and the fifth forward-gear gearwheel plane comprises a loose wheel which meshes with a fixed wheel, wherein the loose wheel is mounted to rotate on the main shaft and can be connected rotationally fixed thereto by a shifting element, whereas the associated fixed wheel is arranged on the inner countershaft in a rotationally fixed manner. 
         [0018]    In order to provide a relatively large overall spread of the transmission, an essentially geometric gradation can be realized, which is adapted to the higher gears in the direction of a partially progressive gradation variation. 
         [0019]    Moreover, it can be provided that the range group is in the form of a planetary gearset with a central sun gear, an outer ring gear and a planetary carrier, wherein the planetary carrier guides a plurality of planetary gearwheels that mesh with the sun gear and with the ring gear. In this case the sun gear functions as a first transmission element of the range group which is connected to the main shaft that functions as the first transmission element of the main group, whereas the planetary carrier functions as the second transmission element of the range group, which is connected rotationally fixed to the drive output shaft and can be connected by means of a shifting element arranged between the range group and an adjacent forward-gear gearwheel plane to a loose wheel of the forward-gear gearwheel plane which is mounted to rotate on the main shaft and can be connected rotationally fixed thereto by a shifting element, which functions as the second transmission element of the main group, and in which the ring gear can be connected by a shifting element to a positionally fixed component and can also be coupled by a shifting element to the planetary carrier. 
         [0020]    By virtue of the shiftable coupling of a loose wheel or gearwheel to the drive output shaft via the planetary carrier a drive torque is transmitted to the drive output, independently of a shift in the range group between a lower and an upper gear range. In this way the range group can be bridged in a particular gear in a powershifted manner. Since in the gear the range group is not involved in the power flow, in that gear it can be shifted while free from load, without traction force interruption. In the next gear the power flow then takes place again by way of the range group in the then engaged upper or lower gear range. 
         [0021]    In an example shifting sequence of the eleven-gear transmission according to the invention, the powershifted bridging of the range group can be realized in that the eighth forward gear can be engaged by forming a connection between the planetary carrier of the range group and the adjacent loose wheel of the fifth forward-gear wheel plane. Thus, the eighth gear acts as a supporting gear during a range group shift. 
         [0022]    In addition, it can be provided that the seventh forward gear can be used as the highest gear of the lower gear range by forming a direct connection between the inner transmission input shaft and the main shaft and by engaging a lower transmission stage in the range group. 
         [0023]    Thus in the seventh gear the drive power in the main group is transmitted directly from the associated transmission input shaft to the main shaft and converted in the range group. In that gear the conversion therefore takes place only by the range group. In the eighth gear the range group can then be shifted to the upper gear range. Conversely, starting from the ninth gear the range group can be shifted to the lower gear range in the eighth gear. 
         [0024]    Furthermore, it can be provided that the eleventh forward gear can be used as a direct gear by forming a direct connection between the inner transmission input shaft and the main shaft and by engaging an upper transmission stage in the range group. This enables a direct, powershiftable straight-through connection to the drive output, which has a high efficiency. 
         [0025]    In addition a reversing-gear wheel plane can be provided, which is arranged axially between the fourth and fifth forward-gear wheel planes and which comprises a loose wheel, a fixed wheel and a gearwheel for reversing the rotation direction, which is mounted to rotate freely and which meshes with both the loose wheel and the fixed wheel. The loose wheel of this reversing-gear wheel plane is mounted to rotate on the main shaft and can be connected thereto in a rotationally fixed manner by a shifting element, whereas the associated fixed wheel is arranged rotationally fixed on the inner countershaft. 
         [0026]    In this way, in combination with the two clutches and by coupling the two countershafts and the range group, a total of six reversing gears can be used, most of which can be powershifted. Accordingly, the reversing-gear wheel plane provided can advantageously be connected upstream from the last of the forward-gear wheel planes, so that the last forward-gear wheel plane can be engaged for the direct coupling of the main group to the drive output, i.e. for bridging the range group. 
         [0027]    The eleven-gear transmission according to the invention needs only ten shifting elements, eight of them associated with the main group and two with the range group. So far as possible the shifting elements are combined two shifting elements at a time in shifting devices that can be actuated on both sides, in order to save both space and costs. For example, an arrangement with six shifting positions is possibly, wherein one shifting device is associated with the radially inner transmission input shaft, a second and a third shifting device with the main shaft, and a fourth shifting device with the range group. For the shiftable coupling of the main group to the range group, preferably a shifting element actuated on one side is provided. Likewise, for the coupling of the two countershafts a shifting element actuated on one side is present. The two shifting elements actuated on one side then form the fifth and sixth shifting positions of the dual-clutch transmission. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]    For the further clarification of the invention a drawing of an example embodiment is attached, which shows: 
           [0029]      FIG. 1 : A schematic view of a dual-clutch transmission according to the invention, and 
           [0030]      FIG. 2 : An example shifting scheme for the dual-clutch transmission in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0031]    According to these, the dual-clutch transmission shown in  FIG. 1  comprises a main group HG of countershaft design with a plurality of spur gear stages and shifting devices, and a range group GP of planetary design, which are arranged coaxially with respect to one another. In addition a dual clutch DK with two clutches K 1 , K 2  is provided, whose input sides are formed by a common clutch cage  15 . The clutch cage  15  is connected in a rotationally fixed manner to a driveshaft w_an of a drive engine (not shown). The output sides of the dual clutch DK are respectively connected to two transmission input shafts w_K 1 , w_K 2  arranged coaxially with one another. The transmission input shaft w_K 1  of the first clutch K 1  is in the form of an inner, solid shaft which projects on the transmission side out of the transmission input shaft w_K 2  of the second clutch K 2 , which is in the form of an outer, hollow shaft. Coaxially with the two transmission input shafts w_K 1 , w_K 2  and axially adjacent to the first transmission input shaft w_K 1  is arranged a main shaft w_HG associated with the main transmission HG. Furthermore there are two countershafts w_V 1 , w_V 2 , the first of which w_V 1  is in the form of a hollow shaft inside which the second countershaft w_V 2 , in the form of a solid shaft, is fitted to rotate and which projects axially on both sides out of the hollow shaft w_V 1 . 
         [0032]    The main group HG comprises five forward-gearwheel planes Z 1 , Z 2 , Z 3 , Z 4 , Z 5  and a reversing-gear wheel plane ZR, in each case with associated spur gears. In the first forward-gear wheel plane Z 1  a fixed wheel  1  fixed on the second transmission input shaft w_K 2  meshes with a fixed wheel  2  fixed on the second countershaft w_V 2 . The forward-gear wheel plane Z 1  acts as an input constant of the second clutch K 2  and the second transmission input shaft w_K 2 . In the second forward-gearwheel plane Z 2  a loose wheel  3  arranged on the first transmission input shaft w_K 1  meshes with a fixed wheel  4  fixed on the first countershaft w_V 1 . In the third forward-gear wheel plane Z 3  a second loose wheel  5  mounted to rotate on the first transmission input shaft w_K 1  and the main shaft w_HG meshes with a second fixed wheel  6  fixed on the first countershaft w_V 1 . In the fourth forward-gear wheel plane Z 4  a loose wheel  7  mounted to rotate on the main shaft w_HG meshes with a third fixed wheel  8  arranged rotationally fixed on the first countershaft w_V 1 . In the fifth forward-gear wheel plane Z 5  a loose wheel  9  mounted to rotate on the main shaft w_HG meshes with a fixed wheel  10  on the second countershaft w_V 2 , 
         [0033]    Between the fourth forward-gear wheel plane Z 4  and the fifth forward-gear wheel plane Z 5  is arranged a reversing-gearwheel plane ZR, in which a loose wheel  11  mounted to rotate on the main shaft w_HG and a fixed wheel  12  on the second countershaft w_V 2  mesh with a rotatably mounted rotation direction reversing gearwheel  13 . 
         [0034]    The range group GP comprises a central sun gear SR, an outer ring gear HR and a planetary carrier PT, which guides a plurality of planetary gearwheels PR that mesh with the sun gear SR and the ring gear HR. The sun gear SR is connected in a rotationally fixed manner to the output end of the main shaft w_HG. On the output side a drive output shaft w_ab is arranged coaxially with the main shaft w_HG and the two transmission input shafts w_K 1 , w_K 2 . The drive output shaft w_ab is connected rotationally fixed to the output end of the planetary carrier PT. 
         [0035]    To engage the transmission elements in the form of loose wheels  3 ,  5 ,  7 ,  9 ,  11  and shiftable planetary gearset components HR, PT, and to form connections of the shiftable transmission elements in the form of shafts w_K 1 , w_K 2 , w_V 1 , w_V 2 , four double-sided or alternately actuated shifting devices S 1 , S 2 , S 3 , S 4  with eight shifting elements A, B, C, D, F, G, I, J and two shifting devices E, H that act on one side are provided. 
         [0036]    In the example embodiment shown, the shifting elements A, B, C, D, E, F, G, H of the main group HG are designed with synchronizers and the shifting elements I, J of the range group are in the form of claw clutches. 
         [0037]    The first shifting device S 1  serves alternatively for coupling the loose wheel  3  of the second forward-gear wheel plane Z 2  to the first transmission input shaft w_K 1  by means of the first shifting element A and for coupling the loose wheel  5  of the third forward-gear wheel plane Z 3  to the first transmission input shaft w_K 1  by means of the second shifting element B. 
         [0038]    The second shifting device S 2  serves alternatively for coupling the loose wheel  5  of the third forward-gear wheel plane Z 3  to the main shaft w_HG by means of the third shifting element C and for coupling the loose wheel  7  of the fourth forward-gear wheel plane Z 4  to the main shaft w_HG by means of the fourth shifting element D. By engaging the second shifting element B and the third shifting element C, a direct connection of the first transmission input shaft w_K 1  to the main shaft w_HG can be formed. 
         [0039]    The third shifting device S 3  serves alternatively for coupling the loose wheel  11  of the reversing-gear wheel plane ZR to the main shaft w_HG by means of the sixth shifting element F and for coupling the loose wheel  9  of the fifth forward-gear wheel plane Z 5  to the main shaft w_HG by means of the seventh shifting element G. 
         [0040]    The fourth shifting device S 4  associated with the range group GP serves alternatively for coupling the ring gear HR to a positionally fixed component or housing component  14  by means of the ninth shifting element I and for coupling the ring gear HR to the planetary carrier PT by means of the tenth shifting element J. By virtue of the coupling with the housing  14 , a short gear ratio of the planetary transmission GP is engaged, for the use of a lower gear range. By the coupling to the planetary carrier PT the planetary gearset GP is blocked, so that a direct gear or direct connection between the main shaft w_HG and the drive output shaft w_ab is obtained. 
         [0041]    The fifth shifting element E, which only acts on one side, can be used as a coupling device for the rotationally fixed coupling of the two countershafts w_V 1  w_V 2 . 
         [0042]    The eighth shifting element H, which also acts on only one side, is designed for the direct coupling of the loose wheel  9  of the fifth forward-gear wheel plane Z 5  to the planetary carrier PT and thereby for the direct coupling of the loose wheel  9  to the drive output shaft w_ab. By means of this shifting element H, independently of the shifting conditions of the associated shifting device S 4  the range group GP can be bridged to the drive output shaft w_ab. In that case the power is transmitted by way of the second clutch K 2 , the first forward-gear wheel plane Z 1  as the driving spur gear stage, the second countershaft w_V 2  and the fifth forward-gear wheel plane Z 5  as the driven spur gear stage. The planetary gearset GP rotates in a neutral position of the associated shifting device S 4  and with the connection between the first transmission input shaft w_K 1  and the main shaft w_HG, or open first clutch K 1 , also in the lower transmission ratio when the shifting element I is activated and in the upper transmission ratio when the shifting element J is activated, without power transmission, and can therefore be shifted while free from load. 
         [0043]    The dual-clutch transmission described above enables at least eleven powershiftable forward gears V 1 , V 2 , V 3 , V 4 , V 5 , V 6 , V 7 , V 8 , V 9 , V 10 , V 11 , and six partly powershiftable reversing gears R 1 , R 2 , R 3 , R 4 , R 5 , R 6 . The attached  FIG. 2  shows an example of a shifting scheme for this. In the table of  FIG. 2  the shifting elements activated in each case are marked by as dot. According to the table, the shifts take place in alternation by way of the two clutches K 1 , K 2 , beginning with the first clutch K 1  In the first seven gears the lower transmission ratio of the range group GP is activated, as made clear by the dots in column I. As necessary, the two countershafts w_V 1 , w_V 2  are coupled to one another, which is done by engaging the shifting element E. Gearshifts within the main group HG take place without traction force interruption in a known manner by preselecting the respective next gear and then, with a time overlap, opening the clutch K 1  or K 2  of the active gear and closing the clutch K 2  or K 1 , respectively, of the new gear. 
         [0044]    The seventh forward gear is designed to be the highest gear of the lower gear range. In that gear the transmission input shaft w_K 1  is directly connected to the main shaft w_HG by means of the relevant activated shifting elements B, C. The gear ratio of that gear corresponds to the lower transmission ratio of the range group GP. 
         [0045]    In the eighth forward gear V 8  the range group GP is bridged by engaging the shifting element H. The power flow passes by way of the second clutch K 2 , the first forward-gear wheel plane Z 1 , the fifth first forward-gear wheel plane Z 5  and via the planetary carrier PT coupled by the eighth shifting element H to the fifth first forward-gear wheel plane Z 5 , to the drive output shaft w_ab. In this eighth forward gear V 8  the range group is not involved in the power flow and can therefore be shifted while free from load to the upper gear range or the block rotation for the next (ninth forward gear V 9 ). The ninth forward gear V 9  is then activated without traction force interruption by closing the first clutch K 1  and opening the second clutch K 2 , comparably to a gearshift within the main group HG. 
         [0046]    The tenth and eleventh forward gears V 10 , V 11  are in turn engaged within the main group HG, the eleventh gear V 11  being designed as a direct gear and obtained by engaging the shifting elements B and C while the shifting element J is also engaged. 
         [0047]    The six reversing gears R 1 , R 2 , R 3 , R 4 , R 5 , R 6  are formed by the reversing-gear wheel plane ZR, wherein the two countershafts w_V 1 , w_V 2  are mutually coupled. The change between the third reversing gear R 3  and the fourth reversing gear R 4 , during which the range group GP is shifted, takes place with traction force interruption since both of the gears R 3 , R 4  are supplied with torque by way of the same clutch K 1 . The other reversing gearshifts can be carried out as powershifts. 
       INDEXES 
       [0000]    
       
           1  Fixed wheel on the second transmission input shaft 
           2  Fixed wheel on the second countershaft 
           3  Loose wheel on the first transmission input shaft 
           4  Fixed wheel on the first countershaft 
           5  Loose wheel on the first transmission input shaft 
           6  Fixed wheel on the first countershaft 
           7  Loose wheel on the main shaft 
           8  Fixed wheel on the first countershaft 
           9  Loose wheel on the main shaft 
           10  Fixed wheel on the second countershaft 
           11  Loose wheel on the main shaft 
           12  Fixed wheel on the second countershaft 
           13  Gearwheel for reversing the rotation direction 
           14  Positionally fixed component 
           15  Dual clutch cage 
         A Shifting element 
         B Shifting element 
         C Shifting element 
         D Shifting element 
         E Shifting element 
         F Shifting element 
         G Shifting element 
         H Shifting element 
         I Shifting element 
         J Shifting element 
         DK Dual clutch 
         GP Range group 
         HG Main group 
         HR Ring gear 
         PR Planetary gearwheel 
         PT Planetary carrier 
         SR Sun gear 
         K 1  First clutch 
         K 2  Second clutch 
         R 1  First reversing gear 
         R 2  Second reversing gear 
         R 3  Third reversing gear 
         R 4  Fourth reversing gear 
         R 5  Fifth reversing gear 
         R 6  Sixth reversing gear 
         S 1  First shifting device 
         S 2  Second shifting device 
         S 3  Third shifting device 
         S 4  Fourth shifting device 
         V 1  First forward gear 
         V 2  Second forward gear 
         V 3  Third forward gear 
         V 4  Fourth forward gear 
         V 5  Fifth forward gear 
         V 6  Sixth forward gear 
         V 7  Seventh forward gear 
         V 8  Eighth forward gear 
         V 9  Ninth forward gear 
         V 10  Tenth forward gear 
         V 11  Eleventh forward gear 
         Z 1  First forward-gear wheel plane 
         Z 2  Second forward-gear wheel plane 
         Z 3  Third forward--gear wheel plane 
         Z 4  Fourth forward-gear wheel plane 
         Z 5  Fifth forward-gear wheel plane 
         ZR Reversing-gear wheel plane 
         w_an Drive input shaft 
         w_ab Drive output shaft 
         w_HG Main shaft 
         w_K 1  First transmission input shaft 
         w_K 2  Second transmission input shaft 
         w_V 1  First countershaft 
         w_V 2  Second countershaft