Abstract:
A transmission includes a housing, an input member connectable to an engine output member, and a launch clutch assembly connected to the input member. A first and a second countershaft are rotatably supported within the transmission housing. A plurality of co-planar gear sets are connected to the input member and the first and second countershafts. A plurality of torque transmitting mechanisms are provided for coupling various components of the co-planar gear sets to the input member and countershafts. The selective engagement of the launch clutch assembly and the torque transmitting mechanisms establishes at least one of six forward speed ratios and a reverse speed ratio.

Description:
FIELD 
       [0001]    The present disclosure relates to transmissions for motor vehicles and more particularly to automatic transmissions having one or more layshafts and having a compact design and which provides six, seven, or eight forward speeds or gears. 
       BACKGROUND 
       [0002]    The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
         [0003]    Dual clutch transmissions are a relatively recent addition to the stable of motor vehicle transmissions which previously included manual, continuously variable and automatic transmissions. Dual clutch transmissions or DCT&#39;s as they are now commonly known, combine good fuel economy with rapidly executed shifts. From a performance standpoint, therefore, they closely duplicate the feel and operation of a conventional mechanical transmission. Additionally, they may be configured to operate as an essentially automatic or manual transmission and thus exhibit exceptional versatility. 
         [0004]    Structurally, dual clutch transmissions typically include an input shaft which drives a pair of mutually exclusively engaged input clutches. The input clutches drive a pair of countershafts which each include a plurality of gears freely rotatably disposed on the countershafts and associated synchronizer clutches. The pluralities of gears are in constant mesh with gears secured to an output shaft. Activation of a synchronizer clutch synchronizes and couples a selected gear to its countershaft. Then, the input clutch associated with that countershaft is engaged to transmit torque from the input shaft to the output shaft. Because clutches, gears and synchronizers are disposed or stacked along the countershafts, the axial length of dual clutch transmissions can create packaging issues, particularly in smaller vehicles. 
         [0005]    While there are various ways to classify or categorize dual clutch transmissions, one approach to classification relates to the type of clutch utilized in the transmission: wet or dry. A wet dual clutch transmission contains lubricating transmission fluid not only in the gear and synchronizer section but also in the input clutches. A dry dual clutch transmission, of course, includes transmission fluid in the gear and synchronizer section but not in the clutches. While wet dual clutch transmissions offer slightly better durability and longer clutch life because of the cooling provided by the transmission fluid, they exhibit higher spin losses. Moreover, the incorporation of a lubrication pump which provides pressurized lubricating and cooling fluid further affects overall efficiency. Accordingly, wet dual clutch transmissions, all other parameters being equal, typically exhibit slightly lower fuel economy than dry dual clutch transmissions. 
         [0006]    From the foregoing, it is apparent that improvements addressing both packaging and efficiency issues of dual clutch transmissions are both desirable and possible. The present invention is so directed. 
       SUMMARY 
       [0007]    A layshaft automatic transmission is provided. The transmission includes a transmission housing, an input member connectable to an engine output member, a sleeve member at least partially concentric with the input member and at least partially surrounds the input member, a launch clutch assembly connected to the input member and to the sleeve member, wherein the launch clutch is selectively engageable to transmit torque from the input member to the sleeve member, a first drive gear rotatably fixed for common rotation with the sleeve member, and a second drive gear rotatably fixed for common rotation with the input member. A first countershaft is rotatably supported within the transmission housing and is spaced apart from and parallel with the input member and the sleeve member. A second countershaft is rotatably supported within the transmission housing and is spaced apart from and parallel with the input member and the sleeve member. A first driven gear is rotatably fixed for common rotation with the first countershaft and is in mesh with the first drive gear, a second driven gear is selectively connectable for common rotation with the first countershaft and is in mesh with the second drive gear, a third driven gear is selectively connectable for common rotation with the second countershaft and is in mesh with the second drive gear, a fourth driven gear is selectively connectable for common rotation with the second countershaft and in mesh with a transfer gear, a first output gear is selectively connectable for common rotation with the first countershaft, a second output gear is selectively connectable for common rotation with the first countershaft, a third output gear is selectively connectable for common rotation with the second countershaft, and a fourth output gear is selectively connectable for common rotation with the second countershaft. A plurality of torque transmitting mechanisms are provided for coupling various combinations of the drive gears, driven gears, and output gears to the input member, sleeve member, and countershafts. The selective engagement of the launch clutch assembly and the torque transmitting mechanisms establishes at least one of six forward speed ratios and a reverse speed ratio. 
         [0008]    In one aspect of the present invention the torque transmitting mechanisms include two clutches and three synchronizer assemblies and a launch device. 
         [0009]    In another aspect of the present invention the torque transmitting mechanisms include two clutches, two synchronizer assemblies, a dog clutch and a launch device. 
         [0010]    In another aspect of the present invention the torque transmitting mechanisms include three synchronizers. 
         [0011]    In yet another aspect of the present invention the transmission includes a fifth driven gear for providing at least seven forward speed or gear ratios. 
         [0012]    In yet another aspect of the present invention the transmission provides at least eight forward speed or gear ratios. 
         [0013]    Further aspects, advantages and areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0014]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0015]      FIG. 1  is a diagrammatic view of an embodiment of a six speed layshaft transmission; and 
           [0016]      FIG. 2  is a diagrammatic view of another embodiment of a seven or eight speed layshaft transmission. 
       
    
    
       [0017]    It will be appreciated that in all of the drawings, certain components, for example, the output gears, the differential assembly and the output shafts or axles have been rotated out of radial position or gear sizes or shaft spacings have been altered in order to illustrate the components, their locations and interconnections more clearly. 
       DETAILED DESCRIPTION 
       [0018]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
         [0019]    With reference to  FIG. 1 , a six speed transmission is illustrated and generally designated by the reference number  10 . The six speed transmission  10  includes a housing  12  having various bores, openings, flanges and features that receive, locate, support and protect the components of the transmission  10 . The housing  12  rotatably supports a transmission input shaft  14 . The input shaft  14  is coupled at one end to a flywheel damper assembly  15 . The flywheel damper assembly  15  receives input torque from a prime mover (not shown), such as a combustion engine, a hybrid engine, or an electric motor. The input shaft  14  is coupled at an opposite end to a launch clutch  17 . The launch clutch  17  includes a first plurality of clutch plates or discs  19  coupled to the input shaft  14  for rotation therewith. Interleaved with the first plurality of clutch plates or discs  19  is a second plurality of clutch plates or discs  21  that are coupled to and rotate with a quill, sleeve shaft, or drive tube  23 . The launch clutch  17  is engageable to selectively transfer torque from the input shaft  14  to the drive tube  23 . 
         [0020]    A first, smaller input drive gear  16  is rotatably fixed to the drive tube  23  and a second, larger input drive gear  18  is fixed to the input shaft  14 . It should be appreciated that the terms “smaller” and “larger” with reference to gear sizes are utilized herein only in the most relative and general sense and primarily for the purpose of locating or identifying the gears in the respective drawing Figures. Accordingly, it should be understood that the actual gear sizes, and their relative sizes, may vary from such descriptions in order to achieve certain or specific gear ratios and/or speed changes. 
         [0021]    Also rotatably supported in the housing  12  is a first layshaft or countershaft  20  associated with first, second, fourth, and sixth gears and a second layshaft or countershaft  60  associated with third, fifth, and reverse gears. However, there may be arrangements that benefit from further mixing odd and even gears on a layshaft/countershaft and the above description by no means limits the scope of the invention. The first countershaft  20  and the second countershaft  60  are parallel to and spaced from the input shaft  14 . At one end of the first countershaft  20  is a first, wet input clutch assembly  22  having a first plurality of clutch plates or discs  24  coupled to the first countershaft  20  for rotation therewith. Interleaved with the first plurality of clutch plates or discs  24  is a second plurality of clutch plates or discs  26  that are coupled to and rotate with a first quill or drive tube  28 . The first wet clutch assembly  22  is engageable to selectively transfer torque from the first quill or drive tube  28  to the first countershaft  20 . 
         [0022]    Disposed on the first countershaft  20  is a first, larger driven gear  32  in constant mesh with the first, smaller input drive gear  16 . Disposed on the first drive tube  28  is a second, smaller driven gear  34  in constant mesh with the second, larger input gear  18 . Disposed on the first countershaft  20  is a driven gear  31  that is adjacent the driven gear  32 . Disposed between the first, larger driven gear  32  and the second, smaller driven gear  34  is the first wet, input clutch assembly  22 . 
         [0023]    Freely rotatably disposed on the first countershaft  20  is a third drive gear  46  and a fourth, smaller drive gear  48  axially spaced from the third drive gear  46 . Disposed between the third, larger drive gear  46  and the fourth, smaller drive gear  48  is a first double synchronizer clutch assembly  52 . The first synchronizer clutch assembly  52  is rotationally coupled to the first countershaft  20  by a first interengaging synchronizer  54  and is free to translate axially along the first countershaft  20 . A shift actuator assembly (not shown) which may be mechanical, hydraulic, electric or pneumatic, bi-directionally translates the first synchronizer clutch assembly  52 . When translated to the right or left from a neutral center position, the first synchronizer clutch assembly  52  first synchronizes the speed of the adjacent gear, either the gear  48  to the right or the gear  46  to the left, and then positively couples the synchronized gear to the first countershaft  20 . 
         [0024]    At one end of the second countershaft  60  is a second, wet input clutch assembly  62  having a first plurality of clutch plates or discs  64  coupled to the second countershaft  60  for rotation therewith. Interleaved with the first plurality of clutch plates or discs  64  is a second plurality of clutch plates or discs  66  that are coupled to and rotate with a second quill or drive tube  68 . The second wet input clutch assembly  62  is engageable to selectively transfer torque from the second quill or drive tube  68  to the second countershaft  60 . 
         [0025]    Disposed on the second quill or drive tube  68  is a fifth, driven gear  72  in constant mesh with the second, larger input drive gear  18 . Freely rotatably disposed on the second countershaft  60  is a sixth, driven gear  74  in constant mesh with the driven gear  31 . Disposed between the fifth, driven gear  72  and the sixth, driven gear  74  is the second, wet input clutch assembly  62 . 
         [0026]    Disposed adjacent the sixth, driven gear  74  is a reverse dog clutch or single sided synchronizer clutch assembly  75 . The synchronizer clutch assembly  75  is rotationally coupled to the second countershaft  60  by a synchronizer  77  and is free to translate axially along the second countershaft  60 . A shift actuator assembly (not shown) which may be hydraulic, electric or pneumatic, engages and bi-directionally translates the synchronizer clutch assembly  75 . When translated to the right from a neutral center position, the synchronizer clutch assembly  75  first synchronizes the speed of the adjacent gear  74  and then positively couples the synchronized gear  74  to the second countershaft  60 . 
         [0027]    Freely rotatably disposed on the second countershaft  60  is a seventh, larger drive gear  84  and an eighth, smaller drive gear  86  axially spaced from the seventh drive gear  84 . Disposed between the seventh, larger drive gear  84  and the eighth, smaller drive gear  86  is a second double synchronizer clutch assembly  88 . The second synchronizer clutch  88  is rotationally coupled to the second countershaft  60  by synchronizer  92  and is free to translate axially along the second countershaft  60 . A second shift actuator assembly (not shown) which may be mechanical, hydraulic, electric or pneumatic, engages and bi-directionally translates the second synchronizer clutch assembly  88 . When translated to the right or left from a neutral center position, the second synchronizer clutch assembly  88  first synchronizes the speed of the adjacent gear, either the gear  86  to the right or the gear  84  to the left, and then positively couples the synchronized gear to the second countershaft  60 . 
         [0028]    The third, larger drive gear  46  and the seventh, larger drive gear  84  both are in constant mesh with and drive a first output or ring gear  98  that is associated with and is an input member to a differential assembly  100 . Similarly, the fourth, smaller drive gear  48  and the eighth, smaller driven gear  86  both are in constant mesh with and drive a second output or ring gear  102  that is also associated with and is an input member to the differential assembly  100 . The differential  100  is coupled to a respective pair of axles or output shafts  106  and  108 . 
         [0029]    In the embodiment illustrated in  FIG. 1 , the first driven gear  32  is associated and active with first gear and fourth gear, the second driven gear  34  is associated and active with second and sixth gears, the third drive gear  46  is associated and active with first and second gears, and the drive gear  48  is associated and active with fourth and sixth gears. The fifth driven gear  72  is associated and active with third and fifth gears, the sixth driven gear  74  and the drive gear  31  are associated and active with reverse, the seventh drive gear  84  is associated and active with third gear and reverse, and the drive gear  86  is associated and active with fifth gear. 
         [0030]    For example, to engage first gear, the first double synchronizer clutch assembly  52  is translated to the left to synchronize and connect the gear  46  to the first countershaft  20 . The launch clutch  17  is then engaged to transfer drive torque from the input shaft  14 , through the gears  16  and  32  to the first countershaft  20 , and from the first countershaft  20  through gear  46  to the output gear  98 , the differential assembly  100  and the axles or output shafts  104  and  106 . 
         [0031]    To engage second gear, the first double synchronizer clutch assembly  52  is translated to the left to synchronize and connect the gear  46  to the first countershaft  20 . The first input clutch assembly  22  is then engaged to transfer drive torque from the input shaft  14 , through the gears  18  and  34  to the first countershaft  20 , and from the first countershaft  20  through gear  46  to the output gear  102 , the differential assembly  100  and the axles or output shafts  104  and  106 . 
         [0032]    To engage third gear, the second double synchronizer clutch assembly  88  is translated to the left to connect the gear  84  to the second countershaft  60 . The second input clutch assembly  62  is then engaged to transfer drive torque from the input shaft  14 , through the gears  18  and  72  to the second countershaft  60 , and from the second countershaft  60  through gear  84  to the output gear  98 , the differential assembly  100  and the axles or output shafts  104  and  106 . 
         [0033]    To engage fourth gear, the first double synchronizer clutch assembly  52  is translated to the right to connect the gear  48  to the first countershaft  20 . The launch clutch assembly  17  is then engaged to transfer drive torque from the input shaft  14 , through the gears  16  and  32  to the first countershaft  20 , and from the first countershaft  20  through gear  48  to the output gear  102 , the differential assembly  100  and the axles or output shafts  104  and  106 . 
         [0034]    To engage fifth gear, the second synchronizer clutch assembly  88  is translated to the right to engage the gear  86  and connect it to the second countershaft  60 . The second input clutch assembly  62  is then engaged to transfer drive torque from the input shaft  14 , through the gears  18  and  72  to the second countershaft  60 , and from the second countershaft  60  through gear  86  to the output gear  102 , the differential assembly  100  and the axles or output shafts  104  and  106 . 
         [0035]    To engage sixth gear, the first double synchronizer clutch assembly  52  is translated to the right to connect the gear  48  to the first countershaft  20 . The first input clutch assembly  22  is then engaged to transfer drive torque from the input shaft  14 , through the gears  18  and  34  to the first countershaft  20 , and from the first countershaft  20  through gear  48  to the output gear  102 , the differential assembly  100  and the axles or output shafts  104  and  106 . 
         [0036]    Reverse is achieved by translating the synchronizer clutch assembly  77  to the right to engage the gear  74  and connect it to the second countershaft  60  and translating the second synchronizer clutch assembly  88  to the left to engage the gear  84  and connect it to the second countershaft  60 . It is also possible to use a dog clutch or a sliding reverse configuration in place of the synchronized reverse. The launch clutch  17  is then engaged to transfer drive torque from the input shaft  14 , through the gears  16  and  32  to the first countershaft  20 , and from the first countershaft  20  through gear  31  to gear  74 , and from gear  74  to the second countershaft  60 , and through gear  84  to the output gear  98 , the differential assembly  100  and the axles or output shafts  104  and  106 . 
         [0037]    It should be clear that there are instances where a stepped gear configuration can be used, for example to achieve a proper reverse gear while maintaining an optimum package. The direction reversal necessary for reverse is achieved by engagement of the first, driven gear  32  and the sixth, driven gear  74 , as noted above. 
         [0038]    Turning to  FIG. 2 , an embodiment of a seven speed transmission is illustrated and generally indicated by reference number  200 . The transmission  200  is similar to the transmission  10  shown in  FIG. 1  and like components are indicated by like reference numbers. However, the transmission  200  further includes a driven gear  202  freely rotatably disposed on the second countershaft  60 . The driven gear  202  is in constant mesh with the gear  16 . The driven gear  202  is rotationally coupled to the second countershaft  60  by a double sided synchronizer  75 ′ which replaces the single sided synchronizer  75 . Finally, disposed adjacent the driven gear  32  is a reverse dog clutch or single sided synchronizer clutch assembly  204 . The synchronizer clutch assembly  204  is rotationally coupled to the first countershaft  20  by a synchronizer  206  and is free to translate axially along the first countershaft  20 . A shift actuator assembly (not shown) which may be hydraulic, electric or pneumatic, engages and bi-directionally translates the synchronizer clutch assembly  204 . When translated to the right from a neutral center position, the synchronizer clutch assembly  204  first synchronizes the speed of the adjacent gear  32  and then positively couples the synchronized gear  32  to the first countershaft  20 . 
         [0039]    In the embodiment illustrated in  FIG. 2 , the first driven gear  32  is associated and active with first gear, the second driven gear  34  is associated and active with second and fifth gears, the third drive gear  46  is associated and active with fifth gear, and the drive gear  48  is associated and active with first and second gears. The fifth driven gear  72  is associated and active with fourth and seventh gears, the sixth driven gear  74  and the drive gear  31  are associated and active with reverse, the driven gear  202  is associated and active with third and sixth gears, the seventh drive gear  84  is associated and active with sixth and seventh gears, and the drive gear  86  is associated and active with third and fourth gears and reverse. 
         [0040]    For example, to engage first gear, the single sided synchronizer clutch assembly  204  is translated to the right to synchronize and connect the gear  32  to the first countershaft  20  and the first double synchronizer clutch assembly  52  is translated to the right to synchronize and connect the gear  48  to the first countershaft  20 . The launch clutch  17  is then engaged to transfer drive torque from the input shaft  14 , through the gears  16  and  32  to the first countershaft  20 , and from the first countershaft  20  through gear  48  to the output gear  102 , the differential assembly  100  and the axles or output shafts  104  and  106 . 
         [0041]    To engage second gear, the first double synchronizer clutch assembly  52  is translated to the right to synchronize and connect the gear  48  to the first countershaft  20 . The first input clutch assembly  22  is then engaged to transfer drive torque from the input shaft  14 , through the gears  18  and  34  to the first countershaft  20 , and from the first countershaft  20  through gear  48  to the output gear  102 , the differential assembly  100  and the axles or output shafts  104  and  106 . 
         [0042]    To engage third gear, the second double synchronizer clutch assembly  88  is translated to the right to connect the gear  86  to the second countershaft  60  and the third double synchronizer clutch assembly  75 ′ is translated to the left to connect the gear  202  to the second countershaft  60 . The launch clutch assembly  17  is then engaged to transfer drive torque from the input shaft  14 , through the gears  16  and  202  to the second countershaft  60 , and from the second countershaft  60  through gear  86  to the output gear  102 , the differential assembly  100  and the axles or output shafts  104  and  106 . 
         [0043]    To engage fourth gear, the second double synchronizer clutch assembly  88  is translated to the right to connect the gear  86  to the first countershaft  20 . The second input clutch assembly  62  is then engaged to transfer drive torque from the input shaft  14 , through the gears  18  and  72  to the second countershaft  60 , and from the second countershaft  60  through gear  86  to the output gear  102 , the differential assembly  100  and the axles or output shafts  104  and  106 . 
         [0044]    To engage fifth gear, the first synchronizer clutch assembly  52  is translated to the left to engage the gear  46  and connect it to the first countershaft  20 . The first input clutch assembly  22  is then engaged to transfer drive torque from the input shaft  14 , through the gears  18  and  34  to the first countershaft  20 , and from the first countershaft  20  through gear  46  to the output gear  98 , the differential assembly  100  and the axles or output shafts  104  and  106 . 
         [0045]    To engage sixth gear, the second double synchronizer clutch assembly  88  is translated to the left to connect the gear  84  to the second countershaft  60  and the third double synchronizer clutch assembly  75 ′ is translated to the left to connect the gear  202  to the second countershaft  60 . The launch clutch assembly  17  is then engaged to transfer drive torque from the input shaft  14 , through the gears  16  and  202  to the second countershaft  60 , and from the second countershaft  60  through gear  84  to the output gear  98 , the differential assembly  100  and the axles or output shafts  104  and  106 . 
         [0046]    To engage seventh gear, the second double synchronizer clutch assembly  88  is translated to the left to connect the gear  84  to the second countershaft  60 . The second input clutch assembly  62  is then engaged to transfer drive torque from the input shaft  14 , through the gears  18  and  72  to the second countershaft  60 , and from the second countershaft  60  through gear  84  to the output gear  98 , the differential assembly  100  and the axles or output shafts  104  and  106 . 
         [0047]    Reverse is achieved by translating the third synchronizer clutch assembly  75 ′ to the right to engage the gear  74  and connect it to the second countershaft  60  and translating the single sided synchronizer clutch assembly  204  to the right to engage the gear  32  and connect it to the first countershaft  20 , and translating the second synchronizer clutch assembly  88  to the right to engage the gear  86  and connect it to the second countershaft  60 . The launch clutch  17  is then engaged to transfer drive torque from the input shaft  14 , through the gears  16  and  32  to the first countershaft  20 , and from the first countershaft  20  through gear  31  to gear  74 , and from gear  74  to the second countershaft  60 , and through gear  86  to the output gear  102 , the differential assembly  100  and the axles or output shafts  104  and  106 . 
         [0048]    It should be appreciated that the transmission  200  may also be configured as an eight speed transmission without departing from the scope of the present invention. For example, engagement of the single sided clutch  204 , the first synchronizer clutch assembly  52 , and the launch clutch  17  may be associated with an additional forward gear. In this embodiment, the first driven gear  32  is associated and active with first and fifth gears, the second driven gear  34  is associated and active with second and sixth gears, the third drive gear  46  is associated and active with fifth and sixth gears, and the drive gear  48  is associated and active with first and second gears. The fifth driven gear  72  is associated and active with fourth and eighth gears, the sixth driven gear  74  and the drive gear  31  are associated and active with reverse, the driven gear  202  is associated and active with third and seventh gears, the seventh drive gear  84  is associated and active with seventh and eighth gears, and the drive gear  86  is associated and active with third and fourth gears and reverse. 
         [0049]    The layshaft transmissions  10  and  200  according to the present invention provide many features and benefits. For example, there are fewer planes of gears compared to an equivalent dual clutch transmission. Additionally, the input clutches are disposed on the axes of the quills and countershafts. All of these features permit a more axially compact transmission. In fact, the nominal axial distance between the input shaft and the center of the differential is smaller than in most dual clutch transmission configurations. 
         [0050]    The solid input shaft improves hydraulic pump packaging and provides the potential for improved hybridization. The gear sets between the input shaft and the gears on the quills reduce quill, clutch and countershaft speeds and thus reduce spin losses in both the gears and the input clutches relative to conventional dual clutch transmission configurations. 
         [0051]    The description of the invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.