Abstract:
A dual clutch transmission for motor vehicles has first and second input shafts, two clutches configured to selectively couple the input shafts to an engine, two intermediate shafts arranged parallel to the input shafts, gearwheel pairs of which a fixed gearwheel is arranged on one of the input shafts and a freely rotating gearwheel is arranged on one of the intermediate shafts, freely rotating output gearwheels arranged on each of the two intermediate shafts and meshing with a differential wheel, and coupling devices configured to selectively couple the freely rotating gearwheels to the respective intermediate shaft, of which at least the coupling devices for the output gearwheels are of double acting design. A dual clutch transmission of this kind makes a large number of gears possible without significantly increasing the dimensions of the transmission or the weight thereof.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims foreign priority benefits under 35 U.S.C. § 119(a)-(d) to DE 10 2016 202 914.2 filed Feb. 25, 2016, which is hereby incorporated by reference in its entirety. 
       TECHNICAL FIELD 
       [0002]    The invention relates to a dual clutch transmission for motor vehicles having a first input shaft and a second input shaft, two clutches, by means of which the first input shaft and the second input shaft can be selectively coupled to the engine, two intermediate shafts arranged parallel to the transmission input shafts, gearwheel pairs of fixed wheels and freely rotating wheels, of which a first gearwheel is arranged on one of the input shafts and a second gearwheel is arranged on one of the intermediate shafts, coupling devices, by means of which the freely rotating wheels can be selectively connected to the respective intermediate shaft, and an output gearwheel arranged on each of the two intermediate shafts, wherein the output gearwheels of both intermediate shafts mesh with the differential wheel and can each be alternately connected for conjoint rotation to the respective intermediate shaft by means of one of the coupling devices. 
       BACKGROUND 
       [0003]    There is an effort in the automotive industry to adapt the operating state of the engine in an optimum manner, during driving, to the current driving state of the motor vehicle in order to reduce emissions. This can be accomplished, for example, if the transmission has a large number of gears. In this case, selection is performed in such a way that the engine speed is held as low as possible, even at high driving speeds. Another aim is to keep down the masses which corotate under no load in order thereby to effect a further reduction in emissions. 
         [0004]    In a conventional design, a large number of gears necessarily implies a relatively large number of transmission gearwheels and therefore a relatively large overall length, although this is not desired in modern motor vehicle engineering, as well as a relatively high weight of the transmission and relatively high associated power losses. 
         [0005]    Known transmissions of the type stated at the outset (WO 2012/084250 A1; DE 10 2013 216 387 A1) are therefore already taking a step in the desired direction by providing the possibility of the power flowing both via a gearwheel stage associated with the first transmission input shaft and via a gearwheel stage associated with the second transmission input shaft. 
         [0006]    In the case of such dual clutch transmissions, the transmission input shafts are designed as an inner shaft and an outer shaft, wherein the inner shaft and the outer shaft can be driven selectively. The additionally selected gears can then be routed along an indirect path which runs via gearwheels that are arranged on the respective undriven transmission input shaft. 
         [0007]    These known dual clutch transmissions, by means of which it is possible, in addition to the existing gearwheel pairs and the gears that result therefrom, to select further gears, require hollow shaft devices for this purpose on the intermediate shafts and, in some cases, also on the transmission input shafts, on which hollow shaft devices in each case at least two gearwheels are arranged, wherein the hollow shafts corotate freely on the transmission input shafts and intermediate shafts but can be connected thereto for conjoint rotation when required. 
         [0008]    The use of such hollow shaft arrangements represents not only a high additional weight contribution but also leads to an increase in overall lengths and overall heights and to poorer efficiency of the transmission. 
         [0009]    It is therefore the underlying object of the invention to provide a dual clutch transmission which allows a large number of gears without enlarging the dimensions of the transmission and without significantly increasing the weight thereof. 
       SUMMARY 
       [0010]    According to the invention, this object is achieved by virtue of the fact that all the gearwheels arranged on the intermediate shafts are designed as freely rotating wheels and that at least the coupling devices provided for the output gearwheels of the intermediate shafts are of double-acting design. 
         [0011]    The invention provides a solution with which it is possible, in a very simple and uncomplicated manner, using a small number of wheel sets, to provide a dual clutch transmission by means of which a high number of gears can be selected. One significant feature here is formed by the output gearwheels arranged on the intermediate shafts, which make it possible to provide “winding path gears”. The output gearwheels designed as freely rotating wheels can be connected to their respective intermediate shaft with the aid of coupling devices, wherein attention should be drawn particularly to the fact that at least the coupling devices provided for the output gearwheels of the intermediate shaft are of double-acting design, thus making it possible to use these coupling devices also to connect the respectively adjacent freely rotating wheel arranged on the intermediate shaft to its intermediate shaft in a fixed manner. 
         [0012]    The transmission can have four or more wheel sets. 
         [0013]    In a preferred illustrative embodiment, the transmission according to the invention is provided with four wheel sets and five coupling devices. In this case, the 1 st  and 4 th  gears are positioned on one intermediate shaft and the 2 nd  and 3 rd  gears are positioned on the other intermediate shaft. 
         [0014]    By means of such a transmission, eight forward gears and two reverse gears can be obtained. 
         [0015]    This is achieved, for example, by virtue of the fact that the 3 rd , 4 th , 5 th  and 6 th  forward gears can be selected as basic gears. 
         [0016]    The 1 st , 2 nd , 7 th  and 8 th  forward gears can then each be designed to be selectable as winding path gears via both intermediate shafts. 
         [0017]    In such a design, the 2 nd  to 7 th  forward gears can be selected without interrupting the tractive effort. 
         [0018]    As an alternative, the transmission can also have five wheel sets, and six coupling devices. 
         [0019]    In this case, the 1 st  and 3 rd  gears are positioned on one of the intermediate shafts and the 5 th  gear is positioned on the other intermediate shaft. The 2 nd  and 4 th  gears can be positioned either on the first or the second intermediate shaft. 
         [0020]    By means of a transmission of this kind, eleven forward gears and two reverse gears can be achieved. 
         [0021]    In this case, the 4 th  to 8 th  forward gears can be selected as basic gears, while the 1 st  to 3 rd  and the 9 th  to 11 th  forward gears can be selected as winding path gears via the gearwheel sets of both intermediate shafts. 
         [0022]    In such a design, the 4 th  to 9 th  forward gears can be selected without interrupting the tractive effort. 
         [0023]    The invention is illustrated by way of example in the drawing and described in detail below with reference to the drawing, in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  shows a first illustrative embodiment of the dual clutch transmission according to the invention, having four wheel sets, 
           [0025]      FIG. 2  shows a table illustrating the selection of eight forward gears and two reverse gears with the transmission shown in  FIG. 1 , 
           [0026]      FIG. 3  shows the power flow for the 1 st  gear, 
           [0027]      FIG. 4  shows the power flow for the 2 nd  gear, 
           [0028]      FIG. 5  shows the power flow for the 3 rd  gear, 
           [0029]      FIG. 6  shows the power flow for the 4 th  gear, 
           [0030]      FIG. 7  shows the power flow for the 5 th  gear, 
           [0031]      FIG. 8  shows the power flow for the 6 th  gear, 
           [0032]      FIG. 9  shows the power flow for the 7 th  gear, 
           [0033]      FIG. 10  shows the power flow for the 8 th  gear, 
           [0034]      FIG. 11  shows the power flow for the 1 st  reverse gear, 
           [0035]      FIG. 12  shows the power flow for the 2 nd  reverse gear, 
           [0036]      FIG. 13  shows a second illustrative embodiment of the dual clutch transmission according to the invention, having five wheel sets, 
           [0037]      FIG. 14  shows a table illustrating the selection of eleven forward gears and two reverse gears with the transmission shown in  FIG. 13 , 
           [0038]      FIG. 15  shows the power flow for the 1 st  gear, 
           [0039]      FIG. 16  shows the power flow for the 2 nd  gear, 
           [0040]      FIG. 17  shows the power flow for the 3 rd  gear, 
           [0041]      FIG. 18  shows the power flow for the 4 th  gear, 
           [0042]      FIG. 19  shows the power flow for the 5 th  gear, 
           [0043]      FIG. 20  shows the power flow for the 6 th  gear, 
           [0044]      FIG. 21  shows the power flow for the 7 th  gear, 
           [0045]      FIG. 22  shows the power flow for the 8 th  gear, 
           [0046]      FIG. 23  shows the power flow for the 9 th  gear, 
           [0047]      FIG. 24  shows the power flow for the 10 th  gear, 
           [0048]      FIG. 25  shows the power flow for the 11 th  gear, 
           [0049]      FIG. 26  shows the power flow for the 1 st  reverse gear, 
           [0050]      FIG. 27  shows the power flow for the 2 nd  reverse gear. 
       
    
    
     DETAILED DESCRIPTION 
       [0051]    As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
         [0052]    The transmission illustrated in  FIGS. 1 to 12  is a dual clutch transmission having four gearwheel pairs of fixed wheels and freely rotating wheels, in which the four gearwheel pairs are indicated by the numbers 1 to 4 and the reverse gear is indicated by R, in each case with a square boundary. 
         [0053]    The dual clutch transmission  1  illustrated in  FIG. 1  comprises two friction clutches  2  and  3  known per se, said clutches transmitting the power flow supplied by an engine  4  selectively to two input shafts. The input shafts are designed as an inner shaft  5  and an outer shaft  6 , wherein the inner shaft  5  extends coaxially through the outer shaft  6 . 
         [0054]    Two gearwheels  7  and  8  are arranged for conjoint rotation on the outer shaft  6 . 
         [0055]    The inner shaft  5  projects by a certain amount from the outer shaft  6  within the transmission case (not shown in the drawing), wherein two gearwheels  11  and  17  connected for conjoint rotation to the inner shaft  5  are arranged on the end of the inner shaft  5  which projects from the outer shaft  6 . 
         [0056]    Two intermediate shafts  13  and  14  are furthermore provided, on which shafts gearwheels are likewise arranged. The gearwheels arranged on the intermediate shafts  13 ,  14  are rotatably mounted as freely rotating wheels and can be connected for conjoint rotation to the intermediate shafts  13  and  14  by means of coupling devices according to the selection of the desired gear. 
         [0057]    In the illustrative embodiment shown, gearwheel  8 , which is seated on the outer shaft  6 , meshes with a gearwheel  24 , which is arranged rotatably on the first intermediate shaft  13 , while the gearwheel  7  of the outer shaft  6  is in engagement with a gearwheel  9  rotatably mounted on the second intermediate shaft  14 . 
         [0058]    The gearwheel  17  of the inner shaft  5  meshes with a gearwheel  19  arranged rotatably on the first intermediate shaft  13 , while gearwheel  11 , which is seated on the inner shaft  5 , is in engagement with a gearwheel  10  rotatably mounted on the second intermediate shaft  14 . 
         [0059]    On the right-hand side in the drawing, the first intermediate shaft  13  is provided with an output gearwheel  26  mounted loosely thereon and, on the same side, the second intermediate shaft  14  has an output gearwheel  21  mounted loosely thereon. On the left-hand side, the first intermediate shaft  13  is fitted with a gearwheel  15  arranged for conjoint rotation thereon, which is in engagement, for reverse gear, with a gearwheel  12  seated rotatably on the second intermediate shaft  14 . The engagement of these two gearwheels  15  and  12  is indicated by a dashed line  33 . 
         [0060]    The output gearwheels  21  and  26  mounted on the right-hand side of the intermediate shafts  13  and  14  both mesh with the differential gearwheel  23 , via which the power flow is transmitted to the wheels of the vehicle. 
         [0061]    Five coupling devices are provided to shift the transmission, namely one coupling device  27  between the output gearwheel  26  seated on the first intermediate shaft  13  and the gearwheel  24  likewise arranged thereon, and one coupling device  20  between the gearwheels  24  and  19  of the first intermediate shaft  13 . 
         [0062]    On the second intermediate shaft  14  there is a coupling device  22  between output gearwheel  21  and the adjacent gearwheel  9 , another coupling device  16  between the two gearwheels  9  and  10 , which are likewise arranged on the second intermediate shaft  14 , and a third coupling device  18  between gearwheel  10  and the gearwheel  12  seated at the left-hand end and provided for reverse gear. 
         [0063]    All five coupling devices are of double-acting design. In the case of the coupling devices  22  and  27  provided for output gearwheels  21  and  26 , for example, this has the effect that output gearwheels  21  and  26  can be connected to their intermediate shafts  13  and  14 , respectively, and that an additional winding path gear can be selected in the leftward-shifted position of coupling devices  22  and  27 , while, at the same time, output gearwheels  21  and  26  can rotate freely around their respective intermediate shafts  13  and  14 . 
         [0064]    By means of a transmission of this kind, having four gearwheel pairs and five coupling devices, it is possible to select eight forward gears, these being illustrated in the table shown in  FIG. 2 . Here, K 1  and K 2  signify the clutches indicated by 2 and 3 in the drawing, wherein the number “1” denotes the clutch as closed and “0” denotes the clutch as open. IS  1  and IS  2  denote the intermediate shafts  13  and  14  shown in the drawing, and S 1 , S 2 , S 3 , S 5  and S 6  denote the five coupling devices  20 ,  16 ,  18 ,  22  and  27 . 
         [0065]    The letter “L” used in the table stands for a displacement of the respective coupling device to the left, the letter “R” stands for a displacement to the right and “0” stands for the neutral position, in which the respective coupling device is set to an inactive state. 
         [0066]    This table in  FIG. 2  furthermore also shows the shift positions for the two reverse gears R 1  and R 2 . 
         [0067]    Each of the following  FIGS. 3 to 12  illustrates the power flows associated with the individual gears, wherein the respective power flow is indicated by thick solid lines, while the inactive transmission components are shown in thin lines. 
         [0068]      FIG. 3  illustrates the power flow for the 1 st  gear. Here, the engine  4  drives the inner shaft  5  via friction clutch  2 . In this case, gearwheel  17 , which is seated in a fixed manner on the inner shaft  5 , meshes with gearwheel  19 , which is seated on the first intermediate shaft  13  and which is connected for conjoint rotation to the first intermediate shaft  13  by means of coupling device  20 . 
         [0069]    In the same way, gearwheel  24 , which is seated on the first intermediate shaft  13 , is connected for conjoint rotation to the first intermediate shaft  13  by means of coupling device  27  and meshes with gearwheel  8 , which is seated on the idly corotating outer shaft  6 . Here, the gearwheel  7  of the outer shaft  6  meshes with gearwheel  9 , which is seated on the second intermediate shaft  14  and which is connected for conjoint rotation to the second intermediate shaft  14  by means of coupling device  16 . 
         [0070]    In this selected gear, coupling device  22  is shifted to the right and connects output gearwheel  21  for conjoint rotation to the second intermediate shaft  14 . 
         [0071]    Since both output gearwheels  21  and  26  mesh with the differential gearwheel  23 , and output gearwheel  26 , which is seated on the first intermediate shaft  13 , freely corotates, the differential gearwheel  23  is driven via the output gearwheel  21  of the second intermediate shaft  14  and transmits the power flow to the wheels. 
         [0072]    The selection of this 1 st  gear involves a winding path gear, during which the power flows from the inner shaft  5 , via the first intermediate shaft  13  and the second intermediate shaft  14 , and from there to the differential gearwheel  23 . 
         [0073]      FIG. 4  illustrates the power flow which defines the 2 nd  gear. This too is a winding path gear since the power flow is transmitted from the engine  4  to the outer shaft  6  via friction clutch  3  and, from there, initially from gearwheel  7 , via both gearwheels  9  and  10 , which are connected for conjoint rotation to the second intermediate shaft  14  by means of coupling devices  16  and  22 , to gearwheels  11  and  17 , which are seated on the idly corotating inner shaft  5 . From there, the power flows onward to the first intermediate shaft  13 , namely via the gearwheel  17  of the inner shaft  5  to gearwheel  19 , which meshes with the latter and which is connected for conjoint rotation to the first intermediate shaft  13  by means of coupling device  20 . In this design of the 2 nd  gear, output gearwheel  26  is connected in a fixed manner to the first intermediate shaft  13  by means of coupling device  27 , allowing output gearwheel  26  to transmit the torque to the differential gearwheel  23 . 
         [0074]      FIGS. 5 to 8  illustrate the four basic gears, gears three to seven. In these illustrations, the power flows respectively from the engine  4 , via one of the two friction clutches  2  or  3 , to the inner shaft  5  or the outer shaft  6  and, from there, directly to the differential gearwheel  23  via one of the two intermediate shafts  13  or  14 . 
         [0075]      FIGS. 9 and 10  illustrate gears  7  and  8 , which, once again, are selected as winding path gears via both intermediate shafts  13  and  14 . 
         [0076]      FIGS. 11 and 12  illustrate the power flows for the two reverse gears, which, once again, are selected as winding path gears since the power flows pass via both intermediate shafts  13  and  14 . 
         [0077]      FIG. 13  shows a second illustrative embodiment of the invention, in which the transmission has five wheel sets and six coupling devices. 
         [0078]    In this figure, the same reference numbers are used for identical components as in  FIG. 1 . 
         [0079]    n contrast to the illustrative embodiment shown in  FIG. 1 , an additional gearwheel  38  is arranged on the inner shaft  5 , being connected in a fixed manner to said shaft and being in engagement with a gearwheel  37  rotatably mounted on the first intermediate shaft  13 . 
         [0080]    A further coupling device  36  is arranged between gearwheel  37 , which is mounted on the first intermediate shaft  13 , and gearwheel  24 , which is arranged to the right thereof in the drawing, which coupling device is of double-acting design and selectively connects either gearwheel  24  or gearwheel  37  for conjoint rotation to the first intermediate shaft  13 . 
         [0081]    In the illustrative embodiment shown in  FIG. 13 , gearwheel pairs  1 ,  3  and  4  extend along the first intermediate shaft  13 , and gearwheel pairs  5  and  2  extend along the second intermediate shaft  14 . 
         [0082]    By means of the transmission illustrated in  FIG. 13 , eleven forward gears and two reverse gears can be selected. 
         [0083]      FIG. 14  shows the shift pattern for the transmission illustrated in  FIG. 13 . The two friction clutches K 1  and K 2  are once again shown on the left-hand side, bearing the reference numbers  2  and  3 , wherein the number “1” denotes the clutch as closed and “0” denotes the clutch as open. 
         [0084]    In the central area, the positions of the coupling devices (CD) are illustrated, wherein “L”=left-hand position, “R”=right-hand position and “0”=neutral position. 
         [0085]    Forward gears  1  to  11  and the two reverse gears R 1  and R 2  are shown in the following right-hand column. 
         [0086]    The 1 st  to 3 rd  gears are winding path gears, in which there is an interruption in the tractive effort. The 4 th  to 8 th  gears are the five basic gears which can be selected without an interruption in the tractive effort by means of the available gearwheel pairs. The 9 th  gear is once again a winding path gear but without an interruption in the tractive effort. The 10 th  and 11 th  gears are once again winding path gears but with an interruption in the tractive effort. 
         [0087]    The following  FIGS. 15 to 27  illustrate the power flow for each individual gear in thick solid lines, while the inactive regions of the transmission are illustrated in thin lines. 
         [0088]      FIG. 15  shows the selection of the 1 st  gear, which is a winding path gear with an interruption in the tractive effort. In this 1 st  gear, the power flows from the engine  4 , via friction clutch  3 , to the outer shaft  6  and, from there, via gearwheel  7 , which is seated in a fixed manner on the outer shaft, to gearwheel  9 , which is seated on the second intermediate shaft  14  and which is connected for conjoint rotation to the intermediate shaft  14  by means of coupling device  22 . Via gearwheel  10 , which is likewise connected for conjoint rotation to the second intermediate shaft  14  by means of coupling device  16 , the power flows via gearwheel  11  to the idly corotating inner shaft  5  and, from there, passes via gearwheel  17  and via gearwheel  19 , which meshes with the latter, to the second intermediate shaft  14 , wherein gearwheel  19  is connected for conjoint rotation to the first intermediate shaft  13  by means of coupling device  20 . 
         [0089]    In this selection, output gearwheel  26 , which is seated on the first intermediate shaft  13 , is connected for conjoint rotation to the first intermediate shaft  13  by means of coupling device  27 , with the result that the power is transmitted from output gearwheel  26  to the differential gearwheel  23 , while output gearwheel  21 , which is seated on the second intermediate shaft  14 , is decoupled and idly corotates. 
         [0090]      FIGS. 16 and 17  illustrate the shifts for the 2 nd  and 3 rd  gears, wherein it is clear from the power flow that these are likewise winding path gears, especially since the power flows via both intermediate shafts  13  and  14 . 
         [0091]      FIGS. 18 to 22  illustrate the power flow for the 4 th  to 8 th  gears. These are the five basic gears, which are derived from the five gearwheel pairs. In each case, the power only ever flows via one of the two intermediate shafts  13  and  14 . 
         [0092]      FIGS. 23 to 25  illustrate the power flows in the 9 th  to 11 th  gears. These are once again winding path gears since the respective power flow is via both intermediate shafts  13  and  14 . 
         [0093]      FIGS. 26 and 27  illustrate the respective power flow for the two reverse gears, and these are likewise winding path gears since the respective power flow is once again via both intermediate shafts  13  and  14 . 
         [0094]    As is apparent from the two illustrative embodiments, relatively large numbers of gears are possible with relatively few wheel sets, wherein there are only relatively small jumps between the individual gears and the intervals can be set in an optimum manner. 
         [0095]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.