Abstract:
A transmission is provided that utilizes three planetary gear sets and three layshaft gear sets, as well as four rotating-type clutches and one brake that are engagable in different combinations to provide eight forward speed ratios between an input member and an output member of the transmission. By combining features of a layshaft transmission with those of a planetary transmission, the low spin losses and packaging convenience typical of a layshaft transmission are available while still achieving the high torque capacity typical of a planetary transmission.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 60/947,150, filed Jun. 29, 2007, and which is hereby incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to a multi-speed transmission having planetary gear sets and layshaft gear sets, and that can achieve eight forward speed ratios between an input member and an output member. 
       BACKGROUND OF THE INVENTION 
       [0003]    Automatic transmissions often use planetary gear sets through which torque can be split to achieve a high overall torque ratio. Depending on the number of planetary gear sets and the number of selectively engagable torque-transmitting mechanisms, a high number of speed ratios with a pleasing ratio progression can be achieved. 
         [0004]    Layshaft transmissions, also referred to as countershaft transmissions, utilize parallel layshafts with gears intermeshing to selectively distribute torque between the layshafts as synchronizers are engaged to connect the gears with the respective layshafts. Layshaft transmissions may offer a lower number of shifting elements and a more compact arrangement than an automatic transmission with planetary gear sets. The suitability of an automatic transmission versus a layshaft transmission for a given application typically involves a tradeoff between the efficiency and compactness of a layshaft transmission with the high torque capacity of a planetary transmission. Current front-wheel drive automatic transmissions are typically six-speed transmissions that have three planetary gear sets. There is difficulty in achieving more forward speed ratios than six in front wheel-drive applications due to transmission axial length restrictions. For rear wheel-drive applications, eight speed transmissions are known, but typically require four planetary gear sets. The axial length required to package four planetary gear sets may be too large for an on-axis passenger vehicle (i.e., a vehicle having a transmission with the transmission input member aligned with the transmission output member). 
       SUMMARY OF THE INVENTION 
       [0005]    A transmission is provided that utilizes three planetary gear sets and three layshaft gear sets, as well as four rotating-type clutches and one brake that are engagable in different combinations to provide eight forward speed ratios between an input member and an output member of the transmission. By combining features of a layshaft transmission with those of a planetary transmission, the low spin losses and packaging convenience typical of a layshaft transmission are available while still achieving the high torque capacity typical of a planetary transmission. 
         [0006]    Specifically, a multi-speed transmission is provided with an input member and an output member spaced parallel to one another to establish first and second axes of rotation. Three layshaft gear sets (a first, a second and a third layshaft gear set) are included in the transmission, each having a first gear concentric about the first axis of rotation and a second gear intermeshing with the first gear and concentric about the second axis of rotation. Furthermore, the transmission has a first, a second, and a third planetary gear set, each having a ring gear member, a sun gear member, and a carrier member and a set of pinion gears that intermesh with both the sun gear member and the ring gear member. The carrier member of each planetary gear set rotatably supports the respective set of pinion gears. Each of the planetary gear sets is concentric about either the first or the second axis of rotation. At least one of the planetary gear sets is concentric about the first axis of rotation and at least one other of the planetary gear sets is concentric about the second axis of rotation. The ring gear member of the first planetary gear set is continuously connected for common rotation with the first gear of the first layshaft gear set. The second gear of the first layshaft gear set is continuously connected for common rotation with the sun gear member of the second planetary gear set. The sun gear member of the first planetary gear set is continuously connected for common rotation with the first gear of the third layshaft gear set. An interconnecting member continuously connects the carrier member of the third planetary gear set for common rotation with the carrier member of the second planetary gear set. 
         [0007]    Five torque-transmitting mechanisms are engaged in different combinations to establish eight forward speed ratios between the input member and the output member. A first of the torque-transmitting mechanisms is selectively engagable to ground the sun gear member of the first planetary gear set to a stationary member, such as the transmission casing. A second of the torque-transmitting mechanisms is selectively engagable to connect the ring gear member of the first planetary gear set and the first gear of the first layshaft gear set for common rotation with the first gear of the second layshaft gear set. A third of the torque-transmitting mechanisms is selectively engagable to connect the carrier member of the first planetary gear set for common rotation with the first gear of the second layshaft gear set. A fourth of the torque-transmitting mechanisms is selectively engagable to connect the ring gear member of the second planetary gear set for common rotation with the second gear of the second layshaft gear set and the sun gear member of the third planetary gear set. A fifth of the torque-transmitting mechanisms is selectively engagable to connect the ring gear member of the third planetary gear set for common rotation with the second gear of the third layshaft gear set. The gear sets and selective and continuous interconnections described above result in a compact transmission with low spin losses and high torque capacity. 
         [0008]    The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic illustration in lever diagram form of a combined planetary and layshaft transmission within the scope of the invention; 
           [0010]      FIG. 2  is a schematic illustration in stick diagram form of the transmission of  FIG. 1 ; 
           [0011]      FIG. 3  is a schematic illustration of the transmission of  FIGS. 1 and 2  showing the component layout about axes of rotation established by the input member and the output member; and 
           [0012]      FIG. 4  is a truth table illustrating the clutch engagement schedule for the transmission of  FIGS. 1-3 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0013]    Referring to the drawings, wherein like reference numbers refer to like components,  FIG. 1  shows a transmission  10  in lever diagram form. The transmission  10  has an input member  12  adapted to receive power from an engine (not shown) and an output member  14 . The input member  12  and output member  14  are spaced parallel to one another to establish two different axes of rotation, as will be made apparent in the stick diagram representation in  FIG. 3 . 
         [0014]    The transmission  10  includes a first, a second and a third planetary gear set, represented in lever diagram form as three different three-node levers  20 ,  30 , and  40 , respectively. The first lever  20  has a first node A, representing a carrier member, a second node B representing a ring gear member, and a third node C, representing a sun gear member of the first planetary gear set. The second lever  30  has a first node D, representing a sun gear member, a second node E, representing a carrier member, and a third node F, representing a ring gear member of the second planetary gear set. The third lever  40  has a first node G, representing a carrier member, a second node H, representing a sun gear member, and a third node I, representing a ring gear member of the third planetary gear set. 
         [0015]    The transmission  10  includes a first, a second, and a third layshaft gear set represented in lever diagram form as three different three-node levers  50 ,  60 , and  70 , respectively. Each of the levers  50 ,  60 , and  70  has two nodes representing intermeshing first and second gears, and a grounded node therebetween, as those skilled in the art will recognize is an accurate representation in lever form of two intermeshing gears concentric about different parallel layshafts and aligned to intermesh. The levers  50 ,  60 ,  70  for the layshaft gear sets are shown as dashed lines. The lever  50  has a first node J representing a first gear, a second node K, representing a second gear, and a third node L grounded to a stationary member  80  to indicate that the first and second gears intermesh. The stationary member  80  is preferably the casing of the transmission  10 . The lever  60  has a first node M, representing a first gear, a second node N, representing a second gear, and a third node P grounded to the stationary member  80  to indicate that the first and second gears intermesh. The lever  70  has a first node Q, representing a first gear, a second node R, representing a second gear, and a third node S grounded to the stationary member  80  to indicate that the first and second gears intermesh. 
         [0016]    The input member  12  is connected for common rotation with node A. The output member  14  is connected for common rotation with node E and is spaced from and generally parallel to the input member  12 . An interconnecting member  82  connects node E (i.e., the carrier member of the second planetary gear set) for common rotation with node G (i.e., the carrier member of the third planetary gear set). A hub  84  connects node C for common rotation with node Q. A hub  86  connects node B for common rotation with node J. A hub  88  connects node D for common rotation with node K. A hub  89  connects node H for common rotation with node N. 
         [0017]    A first torque-transmitting mechanism  90 , which is a brake, also referred to as a stationary-type clutch, is selectively engagable to ground node C to the stationary member  80 . A second torque-transmitting mechanism  92 , which is a rotating-type clutch, is selectively engagable to connect node J (as well as node B, due to hub  86 ) for common rotation with node M. A third torque-transmitting mechanism  94 , which is a rotating-type clutch, is selectively engagable to connect node A for common rotation with node M. A fourth torque-transmitting mechanism  96 , which is a rotating-type clutch, is selectively engagable to connect node F for common rotation with node H (as well as node N, due to hub  89 ). A fifth torque-transmitting mechanism  98 , which is a rotating-type clutch, is selectively engagable to connect node I for common rotation with node R. 
         [0018]    Referring to  FIG. 2 , the transmission  10  of  FIG. 1  is shown in stick diagram form in which it is referred to as transmission  10 A. It should be appreciated that transmission  10  and transmission  10 A are different representations (lever and stick diagrams, respectively) of the same transmission. Similarly, equivalent components of those depicted in  FIG. 1  in the transmission  10  are referred to using the same reference number followed by an “A” in the stick diagram version of the transmission  10 A. The input member  12 A defines a first axis  13  about which it concentrically rotates. The output member  14 A is spaced parallel to the input member  12 A. 
         [0019]    The first planetary gear set  20 A is shown in fragmentary form, with only that portion on one side of axis  13  about which it concentrically rotates being depicted. A sun gear member  22 , a ring gear member  24 , and a carrier member  26  rotatably supporting pinion gears  27  are concentric about the axis  13 . The pinion gears  27  mesh with both the sun gear member  22  and the ring gear member  24 . The sun gear member  22  corresponds with node C, the carrier member  26  corresponds with node A, and the ring gear member  24  corresponds with node B. 
         [0020]    The second planetary gear set  30 A is shown in fragmentary form, with only that portion on one side of axis  15  about which it concentrically rotates being depicted. A sun gear member  32 , a ring gear member  34 , and a carrier member  36  rotatably supporting pinion gears  37  are concentric about the axis  15 . The pinion gears  37  mesh with both the sun gear member  32  and the ring gear member  34 . The sun gear member  32  corresponds with node D, the carrier member  36  corresponds with node E, and the ring gear member  34  corresponds with node F. 
         [0021]    The third planetary gear set  40 A is shown in fragmentary form, with only that portion on one side of axis  15  about which it concentrically rotates being depicted. A sun gear member  42 , a ring gear member  44 , and a carrier member  46  rotatably supporting pinion gears  47  are concentric about the axis  15 . The pinion gears  47  mesh with both the sun gear member  42  and the ring gear member  44 . The sun gear member  42  corresponds with node H, the carrier member  46  corresponds with node G, and the ring gear member  44  corresponds with node I. 
         [0022]    A first layshaft gear set  50 A, corresponding with lever  50  of  FIG. 1 , includes a first gear  52  intermeshing with a second gear  54 , and corresponding with nodes J and K of  FIG. 1 , respectively. The first gear  52  is concentric about axis  13 , and the second gear  54  is concentric about axis  15 . A second layshaft gear set  60 A, corresponding with lever  60  of  FIG. 1 , includes a first gear  62  intermeshing with a second gear  64 , and corresponding with nodes M and N of  FIG. 1 , respectively. The first gear  62  is concentric about axis  13 , and the second gear  64  is concentric about axis  15 . A third layshaft gear set  70 A, corresponding with lever  70  of  FIG. 1 , includes a first gear  72  intermeshing with a second gear  74 , and corresponding with nodes Q and R of  FIG. 1 , respectively. The first gear  72  is concentric about axis  13 , and the second gear  74  is concentric about axis  15 . 
         [0023]    The input member  12 A is connected for common rotation with the carrier member  26 . The output member  14 A is connected for common rotation with the carrier member  46 . A gear  99  is shown connected with the output member  14 A. Gear  99  is a first gear of a final drive gear set shown in more detail in  FIG. 3 . An interconnecting member  82 A connects the carrier member  36  for common rotation with the carrier member  46 . A hub  84 A connects sun gear member  22  for common rotation with first gear  72 . A hub  86 A connects ring gear member  24  for common rotation with first gear  52 . A hub  88 A connects sun gear member  32  for common rotation with second gear  54 . A hub  89 A connects sun gear member  42  for common rotation with second gear  64 . 
         [0024]    A first torque-transmitting mechanism  90 A, which is a brake, is selectively engagable to ground sun gear member  22  and first gear  72  to the stationary member  80 A. A second torque-transmitting mechanism  92 A, which is a rotating-type clutch, is selectively engagable to connect ring gear member  24  and first gear  52  for common rotation with first gear  62 . A third torque-transmitting mechanism  94 A, which is a rotating-type clutch, is selectively engagable to connect carrier member  26  for common rotation with first gear  62 . A fourth torque-transmitting mechanism  96 A, which is a rotating-type clutch, is selectively engagable to connect sun gear member  42  for common rotation with ring gear member  34 . A fifth torque-transmitting mechanism  98 A, which is a rotating-type clutch, is selectively engagable to connect ring gear member  44  for common rotation with second gear  74 . 
         [0025]    Referring to  FIG. 3 , a transmission  100  is shown in stick diagram form and corresponds with the transmission  10  of  FIG. 1  and the transmission  10 A of  FIG. 2 . It should be appreciated that transmission  100  is a different representation of the same transmission  10  and  10 A. Components identical to those of  FIG. 1  are represented by the same reference numbers raised by 100. An input member  112  receives power from an engine output member  116  through a flywheel or flexplate  117  driving the input member  112  through a damper mechanism  118 . An engine-driven pump  119  is driven off of the input member  112 . Although not shown, optionally, a torque converter may be used between the engine output member  116  and the input member  112 . 
         [0026]    The input member  112  is integrally connected with a first layshaft  121  with which it defines a first axis of rotation  113 . The output member  114  is spaced parallel to the input member and partially defines a second axis of rotation  115  with a second layshaft  123  with which it is axially aligned. 
         [0027]    The first planetary gear set  120  includes a sun gear member  122 , a ring gear member  124 , and a carrier member  126  rotatably supporting pinion gears  127 , each of which concentrically rotates about axis  113 . The sun gear member  122  corresponds with sun gear member  22  and node C of  FIGS. 1 and 2 , the carrier member  126  corresponds with carrier member  26  and node A, and the ring gear member  124  corresponds with ring gear member  24  and node B of  FIGS. 1 and 2 . The pinion gears  127  mesh with both the sun gear member  122  and the ring gear member  124 . 
         [0028]    The second planetary gear set  130  includes a sun gear member  132 , a ring gear member  134 , and a carrier member  136  rotatably supporting pinion gears  137 , each of which concentrically rotates about axis  115 . The sun gear member  132  corresponds with sun gear member  32  and node D of  FIGS. 1 and 2 , the carrier member  136  corresponds with carrier member  36  and node E of  FIGS. 1 and 2 , and the ring gear member  134  corresponds with ring gear member  34  and node F of  FIGS. 1 and 2 . The pinion gears  137  mesh with both the sun gear member  132  and the ring gear member  134 . 
         [0029]    The third planetary gear set  140  includes a sun gear member  142 , a ring gear member  144 , and a carrier member  146  that rotatably supporting pinion gears  147 , each of which concentrically rotates about the axis  115 . The sun gear member  142  corresponds with sun gear member  42  and node H of  FIGS. 1 and 2 , the carrier member  146  corresponds with carrier member  46  and node G of  FIGS. 1 and 2 , and the ring gear member  144  corresponds with ring gear member  44  and node I of  FIGS. 1 and 2 . The pinion gears  147  mesh with both the sun gear member  142  and the ring gear member  144 . 
         [0030]    A first layshaft gear set  150 , corresponding with layshaft gear set  50 A of  FIG. 2  and lever  50  of  FIG. 1 , includes a first gear  152  intermeshing with a second gear  154 , and corresponding with nodes J and K of  FIG. 1 , and first gear  52  and second gear  54  of  FIG. 2 , respectively. The first gear  152  is concentric about axis  113 , and the second gear  154  is concentric about axis  115 . A second layshaft gear set  160 , corresponding with layshaft gear set  60 A of  FIG. 2  and with lever  60  of  FIG. 1 , includes a first gear  162  intermeshing with a second gear  164 , and corresponding with nodes M and N of  FIG. 1 , and gears  62  and  64  of  FIG. 2 , respectively. The first gear  162  is concentric about axis  113 , and the second gear  164  is concentric about axis  115 . A third layshaft gear set  170 , corresponding with lever  70  of  FIG. 1  and layshaft gear set  70 A of  FIG. 2 , includes a first gear  172  intermeshing with a second gear  174 , and corresponding with nodes Q and R of  FIG. 1 , and gears  72  and  74  of  FIG. 2 , respectively. The first gear  172  is concentric about axis  113 , and the second gear  174  is concentric about axis  115 . 
         [0031]    The input member  112  is connected for common rotation with the carrier member  126 . The output member  114  is connected for common rotation with the carrier member  146 . A gear  199  is shown connected with the output member  114 . Gear  199  corresponds with gear  99  of  FIG. 2 , and is a first gear of a final drive gear set  200  that includes a differential  201  to deliver tractive power from the output member  114  to front wheel axles  202  and  204 , establishing the transmission  100  as a front wheel-drive transmission. 
         [0032]    An interconnecting member  182  connects the carrier member  136  for common rotation with the carrier member  146  and corresponds with interconnecting members  82  and  82 A of  FIGS. 1 and 2 , respectively. A hub  184  connects sun gear member  122  for common rotation with first gear  172 , and corresponds with hubs  84  and  84 A of  FIGS. 1 and 2  respectively. A hub  186  connects ring gear member  124  for common rotation with first gear  152 , and corresponds with hubs  86  and  86 A of  FIGS. 1 and 2 , respectively. A hub  188  connects sun gear member  132  for common rotation with second gear  154 , and corresponds with hubs  88  and  88 A of  FIGS. 1 and 2 , respectively. A hub  189  connects sun gear member  142  for common rotation with second gear  164 , and corresponds with hubs  89  and  89 A of  FIGS. 1 and 2 , respectively. 
         [0033]    A first torque-transmitting mechanism  190 , which is a brake corresponding to torque-transmitting mechanisms  90  and  90 A, is selectively engagable to ground sun gear member  122  and first gear  172  to stationary member  180 , which is depicted as the transmission casing, and corresponds with stationary members  80  and  80 A of  FIGS. 1 and 2 , respectively. A second torque-transmitting mechanism  192 , which is a rotating-type clutch corresponding to torque-transmitting mechanisms  92  and  92 A of  FIGS. 1 and 2 , respectively, is selectively engagable to connect ring gear member  124  and first gear  152  for common rotation with first gear  162 . A third torque-transmitting mechanism  194 , which is a rotating-type clutch corresponding to torque-transmitting mechanisms  94  and  94 A of  FIGS. 1 and 2 , respectively, is selectively engagable to connect carrier member  126  for common rotation with first gear  162 . A fourth torque-transmitting mechanism  196 , which is a rotating-type clutch corresponding to torque-transmitting mechanisms  96  and  96 A of  FIGS. 1 and 2 , respectively, is selectively engagable to connect sun gear member  142  for common rotation with ring gear member  134 . A fifth torque-transmitting mechanism  198 , which is a rotating-type clutch corresponding to torque-transmitting mechanisms  98  and  98 A of  FIGS. 1 and 2 , respectively, is selectively engagable to connect ring gear member  144  for common rotation with second gear  174 . 
         [0034]    Referring to  FIG. 4 , a truth table shows the engagement schedule to achieve a reverse speed ratio (REV) and eight forward speed ratios (1st, 2nd, 3rd, 4th, 5th, 6th, 7th, and 8th), (with N representing neutral). Each column represents the engagement status of a particular torque-transmitting mechanism. An “X” indicates that the torque-transmitting mechanism of that column is engaged in the speed ratio indicated in the row. The reference numbers of corresponding torque-transmitting mechanisms of each of  FIGS. 1-3  are shown above the appropriate column.  FIG. 4  indicates that the torque-transmitting mechanisms are engaged in combinations of three to establish a given speed ratio.  FIG. 4  also indicates that shifts between subsequent forward speed ratios are single transition shifts. Each arrow extending between one row and the next extends from the torque-transmitting mechanism that is disengaged to the torque-transmitting mechanism that is engaged to establish a ratio change (gear shift) via a single transition shift (i.e., only one torque-transmitting mechanism is disengaged and another is engaged while two others remain engaged to establish a speed ratio change). 
         [0035]    While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.