Abstract:
A multi-speed transmission offers seven forward speed ratios with a pleasing ratio step progression, with the seventh forward speed ratio offering a relatively large percentage of the ratio spread, relatively low pinion speeds and only light torque loading on gear members carrying torque in the seventh forward speed ratio due to a brake-type torque transmitting mechanism engaged in the seventh forward speed ratio.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to a multi-speed transmission having multiple planetary gear sets and at least six torque-transmitting mechanisms engagable in different combinations to provide seven forward speed ratios and a reverse speed ratio. 
       BACKGROUND OF THE INVENTION 
       [0002]    Wide ratio transmissions such as seven or eight speed transmissions offer several advantages including improved vehicle acceleration performance and potentially improved fuel economy over four, five and six speed transmissions. However, increasing the number of speed ratios presents challenges in packaging additional clutches, drive mechanisms for the various gear members, and hydraulic circuit feed paths, and in ensuring an overall axial length that is acceptable. 
       SUMMARY OF THE INVENTION 
       [0003]    A multi-speed transmission offers seven forward speed ratios with a pleasing ratio step progression, with the seventh forward speed ratio offering a relatively large percentage of the ratio spread, relatively low pinion speeds and only light torque loading on gear members carrying torque in the seventh forward speed ratio due to a brake-type torque transmitting mechanism engaged in the seventh forward speed ratio. 
         [0004]    More specifically, a multi-speed transmission within the scope of the invention has a first planetary gear set having a first, a second, and a third member. The first planetary gear set is representable as a three-node lever having a first, a second, and a third node corresponding with the first, the second, and the third member, respectively. The transmission also has a second, a third, and a fourth planetary gear set that have a fourth, a fifth, a sixth, a seventh, and an eighth member, with at least two of the second, third and fourth planetary gear sets intermeshing as a compound planetary gear set such that the fourth, fifth, sixth, seventh and eighth members rotate in fixed relation to one another and are representable by a five-node lever having a fourth, a fifth, a sixth, a seventh and an eighth node corresponding with the fourth, fifth, sixth, seventh and eighth members, respectively. As used herein, gear members that “rotate in fixed relation to one another” are interconnected such that their rotational speeds relative to one another are fixed. The first through eighth members are sun gear members, carrier members and ring gear members. The first node is grounded to a stationary member, such as the transmission housing or casing. The third node is continuously connected for common rotation with the input member. The seventh node is continuously connected for common rotation with the output member. Six torque-transmitting mechanisms are selectively engagable in different combinations to establish seven forward speed ratios and a reverse speed ratio between the input member and the output member. Optionally, selective engagement of two of the torque-transmitting mechanisms establishes an additional forward speed ratio between the input member and the output member for a total of eight forward speed ratios. 
         [0005]    The seven forward speed ratios include a first, a second, a third, a fourth, a fifth, a sixth and a seventh speed ratio between the input member and the output member. Preferably, the seventh forward speed ratio may be established by a single transition shift from the fourth, the fifth and the sixth speed ratios. Shifts between successive speed ratios also require single transition shifts. Thus, there is a simple, quick and appropriate transmission response to nearly any sudden throttle input. Only two torque-transmitting mechanisms are engaged in each speed ratio, and only one is a rotating-type torque-transmitting mechanism in any given speed ratio. Minimizing the number of rotating-type clutches required enables simpler hydraulic controls. 
         [0006]    There are many different transmission embodiments within the scope of the invention in which the planetary gear sets may include simple planetary gear sets, dual-pinion planetary gear sets, and a compound planetary gear set made up of two or three of the four planetary gear sets included in the transmission. In some embodiments, a first and a second interconnecting member connect different members of the planetary gear sets for common rotation. In some embodiments, the third brake-type torque-transmitting mechanism is positioned closer to the output member than any of the other torque-transmitting mechanisms. 
         [0007]    Preferably, the six torque-transmitting mechanisms include a first rotating-type torque-transmitting mechanism that is selectively engagable to connect the second node for common rotation with the eighth node. A second rotating-type torque-transmitting mechanism is selectively engagable to connect the third node for common rotation with the sixth node. A third rotating-type torque-transmitting mechanism is selectively engagable to connect the second node for common rotation with the fourth node. A first brake-type torque-transmitting mechanism is selectively engagable to ground the fourth node to the stationary member. A second brake-type torque-transmitting mechanism is selectively engagable to ground the sixth node to the stationary member. A third brake-type torque-transmitting mechanism selectively engagable to ground the fifth node to the stationary member. 
         [0008]    The seventh speed ratio is significantly higher than the sixth speed ratio, (with the exact percentage increase in speed ratio depending on the specific ring gear member to sun gear member speed ratios selected), and thus increases the overall speed ratio of the transmission by the same amount. The seventh speed ratio can thus be used to provide lower highway engine speeds and/or better performance at low speeds. The torque-transmitting mechanisms engaged in the seventh (top) speed ratio handle relatively low amounts of torque and can thus be sized very compactly. The specific ring gear member to sun gear member tooth ratios may be selected to ensure a good ratio progression, low sun gear torques and low pinion speeds. 
         [0009]    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 
         [0010]      FIG. 1  is an embodiment of a transmission in accordance with the invention shown in lever diagram form; 
           [0011]      FIG. 2  is a truth table showing an engagement schedule for the torque-transmitting mechanisms of the transmission of  FIG. 1  to establish seven forward speed ratios and a reverse speed ratio; 
           [0012]      FIG. 3  is a first embodiment in stick diagram form of the transmission of  FIG. 1 ; 
           [0013]      FIG. 4  is a second embodiment in stick diagram form of the transmission of  FIG. 1 ; 
           [0014]      FIG. 5  is a third embodiment in stick diagram form of the transmission of  FIG. 1 ; and 
           [0015]      FIG. 6  is a fourth embodiment in stick diagram form of the transmission of  FIG. 1 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]    Referring to the drawings, wherein like reference numbers refer to like components,  FIG. 1  illustrates a powertrain  10 , schematically in lever diagram form, mounted on and partially forming a vehicle (not shown). The powertrain  10  includes an engine  12  connected to a transmission  14 . The transmission  14  is designed to receive driving power from the engine  12 , as discussed below. The engine  12  powers an input member  16  of the transmission  14 . A final drive unit  19  is operatively connected to an output member  17  of the transmission  14 . 
         [0017]    The transmission  14  includes a three-node lever  20  representing a first planetary gear set having a first, a second and a third member, represented by nodes A, B and C, respectively. The members may be a ring gear member, a sun gear member and a carrier member, although not necessarily in that order. Nodes, A, B and C are referred to in the claims as the first, second and third nodes, respectively. As used herein, a “node” is a component of a transmission, such as a ring gear member, a carrier member, or a sun gear member, which is characterized by a rotational speed and which can act as a junction of torques applied to that component from other components and by that component to other components. The other components which may interact with a given node include other coaxial members of the same set of planetary gears which appear as other nodes on the same lever. The other components which may interact with a given node also include interconnections to members of other planetary gear sets which appear as nodes on another lever, a stationary member such as the transmission case, and other transmission members. 
         [0018]    The transmission  14  further includes a five-node lever  22  representing second, third and fourth planetary gear sets interconnected so as to be representable by nodes D, E, F, G and H, respectively. As those skilled in the art will readily understand, two or more planetary gear sets may be represented as a single lever in a lever diagram when two different members of one of the planetary gear sets are connected for common rotation with two different members of the other planetary gear set and/or when planetary gear sets intermesh as a compound planetary gear set. Each of the nodes D, E, F, G and H represent a ring gear member, a sun gear member, or a carrier member, although not necessarily in that order. Nodes D, E, F, G and H are referred to in the claims as the fourth, fifth, sixth, seventh, and eighth node, respectively. 
         [0019]    The input member  16  is connected for common rotation with node C. The output member  17  is connected for common rotation with node G. Node A is continuously grounded to a stationary member  24 . 
         [0020]    The transmission  14  also has selectively engagable torque-transmitting mechanisms that provide various speed ratios, as described below. Torque-transmitting mechanism  50 , a rotating-type clutch, is selectively engagable to connect node B for common rotation with node H. Torque-transmitting mechanism  52 , also a rotating-type clutch, is selectively engagable to connect node C for common rotation with node F. Another torque-transmitting mechanism  54 , a stationary clutch, also referred to as a brake-type toque-transmitting mechanism, is selectively engagable to ground node D to the stationary member  24 . Torque-transmitting mechanism  56 , a rotating-type clutch, is selectively engagable to connect node B for common rotation with node D. Torque-transmitting mechanism  57 , a stationary-type clutch, also referred to as a brake-type torque-transmitting mechanism, is selectively engagable to ground node F to the stationary member  24 . Torque-transmitting mechanism  58 , a stationary-type clutch, also referred to as a brake-type torque-transmitting mechanism, is selectively engagable to ground node E to the stationary member  24 . 
         [0021]    The torque-transmitting mechanisms  50 ,  52 ,  54 ,  56 ,  57  and  58  are selectively engagable in the different combinations of pairs, as illustrated in  FIG. 2 , to provide a reverse speed ratio (REV), and seven forward speed ratios (1st, 2nd, 3rd, 4th, 5th, 6th, and 7th). Each speed ratio established in  FIG. 2  may also be referred to as a “gear”. Those skilled in the art will readily recognize that the engagement of these different combinations of torque-transmitting mechanisms shown in  FIG. 2  will result in seven forward speed ratios having different numerical values, as well as a reverse speed ratio. 
         [0022]    Optionally, the transmission  14  may be operated as an eight-speed transmission if the torque-transmitting mechanisms  50  and  58  are engaged following the second speed ratio (2nd) to establish an additional forward speed ratio, not listed in the table of  FIG. 2 , for a total of eight forward speed ratios. 
         [0023]    A controller (not shown) is operatively connected with the torque-transmitting mechanisms and is programmed with an algorithm to select different ones of the speed ratios set forth in  FIG. 2  to provide seven forward speed ratios (1st, 2nd, 3rd, 4th, 5th, 6th, and 7th) and the reverse speed ratio. Alternatively, less than seven of the forward speed ratios may also be selected, such as to enable a five-speed or six-speed transmission with single-transition shifts. The speed ratios chosen or permitted by the controller may depend upon whether single-transition shifts are desired. As used herein, a “single-transition shift” in the context of speed ratios established with pairs of engaged torque-transmitting mechanisms means that one torque-transmitting mechanism remains engaged and another torque-transmitting mechanism is disengaged while a different torque-transmitting mechanism is engaged in shifting from one speed ratio to a subsequent speed ratio (whether in an upshift or a downshift). As is apparent from  FIG. 2 , the seven forward speed ratios 1st, 2nd, 3rd, 4th, 5th, 6th, and 7th, are operable in progression with single-transition shifts. Additionally, there are multiple single-transition upshifts (shifts from a lower numbered speed ratio to a higher numbered speed ratio (i.e., 1 st to 2nd), which are shifts from a higher numerical speed ratio to a lower numerical speed ratio. For example, a shift from the fourth (4th), fifth (5th) or sixth (6th) forward speed ratio to the seventh (7th) forward speed ratio is a single transition shift. 
         [0024]    The topology and ring gear member to sun gear member tooth ratios of a specific transmission embodiment implementing the lever diagram embodiment of  FIG. 1  will determine the most pleasing progression of the forward speed ratios for a given application and/or driving situation. Because each of the speed ratios established as set forth in  FIG. 2  require only two torque-transmitting mechanisms to be applied, and because most utilize only one rotating clutch (i.e., only one of torque-transmitting mechanisms  50 ,  52 , and  56 ), hydraulic leakage losses are minimized, as these are more commonly encountered with rotating-type than with stationary-type torque-transmitting mechanisms. 
         [0025]    Referring to  FIG. 3 , a powertrain  110  has a transmission  114  configured in accordance with and operable in like manner as the transmission  14  shown in lever diagram form in  FIG. 1 . The powertrain  110  includes engine  12  powering an input member  116  of the transmission  114 . Final drive unit  19  is operatively connected to an output member  117  of the transmission  114 . 
         [0026]    The transmission  114  includes simple planetary gear sets  130  and  140 , as well as planetary gear sets  150  and  160  interconnected to form a compound planetary gear set  150 ,  160 . Planetary gear set  130  includes a sun gear member  132 , a ring gear member  134 , and a carrier member  136  that rotatably supports a plurality of pinion gears  137  that mesh with both the ring gear member  134  and the sun gear member  132 . 
         [0027]    Planetary gear set  140  includes a sun gear member  142 , a ring gear member  144 , and a carrier member  146  that rotatably supports a plurality of pinion gears  147  that mesh with both the ring gear member  144  and the sun gear member  142 . 
         [0028]    Compound planetary gear set  150 ,  160  includes planetary gear set  150  having a sun gear member  152 , a ring gear member  154  and a carrier member  156  that rotatably supports a plurality of pinion gears  157  that mesh with both the sun gear member  152  and the ring gear member  154 . The pinion gears  157  are long pinion gears. The carrier member  156  also rotatably supports a second set of pinion gears  167  that are included in planetary gear set  160 . Gear set  160  also includes sun gear member  162 . Pinion gears  167  mesh with the pinion gears  157  and with the sun gear member  162 . 
         [0029]    The input member  116  is continuously connected for common rotation with the ring gear member  134 . Sun gear member  132  is continuously grounded to a stationary member  124 , such as a casing of the transmission  114 . Ring gear member  154  is continuously connected for common rotation with output member  117 . An interconnecting member  170  continuously connects ring gear member  144  for common rotation with sun gear member  152 . Interconnecting member  172  continuously connects sun gear member  142  for common rotation with carrier member  156 . 
         [0030]    The transmission  114  has six selectively engagable torque-transmitting mechanisms  50 A,  52 A,  54 A,  56 A,  57 A, and  58 A, as well as a free-wheeling one-way clutch F 1 A that is that is connected in parallel with torque-transmitting mechanism  57 A and permits rotation in only one direction. Torque-transmitting mechanism  50 A is a rotating-type clutch that is selectively engagable to connect carrier member  136  for common rotation with sun gear member  162 . Torque-transmitting mechanism  52 A is a rotating-type clutch that is selectively engagable to connect input member  116  and ring gear member  134  for common rotation with carrier member  156 . Torque-transmitting mechanism  54 A is a brake-type torque-transmitting mechanism that is selectively engagable to ground ring gear member  144  with stationary member  124 . Free-wheeling one-way clutch F 1 A prevents rotation of carrier member  156  in a direction opposite the input member  116 . Torque-transmitting mechanism  56 A a rotating-type clutch that is selectively engagable to connect carrier member  136  for common rotation with ring gear member  144  and sun gear member  152 . Torque-transmitting mechanism  57 A is a brake-type torque-transmitting mechanism that is selectively engagable to ground carrier member  156  to the stationary member  124 . Torque-transmitting mechanism  58 A is a brake-type torque-transmitting mechanism that is selectively engagable to ground carrier member  146  to the stationary member  124 . 
         [0031]    The members of transmission  114  correspond with the lever diagram transmission  14  of  FIG. 1  as follows: sun gear member  132  corresponds with node A; carrier member  136  corresponds with node B; ring gear member  134  corresponds with node C; interconnected ring gear member  144  and sun gear member  152  correspond with node D; carrier member  146  corresponds with node E; interconnected sun gear member  142  and carrier member  156  correspond with node F; ring gear member  154  corresponds with node G; and sun gear member  162  corresponds with node H. The torque-transmitting mechanisms  50 A,  52 A,  54 A,  56 A,  57 A, and  58 A correspond with torque-transmitting mechanisms  50 ,  52 ,  54 ,  56 ,  57 , and  58 , respectively, and are engagable according to the same schedule of  FIG. 2  to achieve seven forward speed ratios and a reverse speed ratio (and, optionally, an eighth forward speed ratio by engaging torque-transmitting mechanisms  50 A and  58 A). 
         [0032]    One exemplary set of gear tooth counts for the transmission  114  is as follows: ring gear member  134 : 89 teeth; sun gear member  132 : 49 teeth; ring gear member  144 : 97 teeth; sun gear member  142 : 57 teeth; ring gear member  154 : 87 teeth; sun gear member  152 : 43 teeth; and sun gear member  162 : 35 teeth. With the engagement schedule as set forth in  FIG. 2  for corresponding torque-transmitting mechanisms, the following speed ratios are attained: reverse speed ratio (REV): −3.137; first forward speed ratio (1st): 3.854; second forward speed ratio (2nd): 2.313; third forward speed ratio (3rd): 1.551; fourth forward speed ratio (4th): 1.167; fifth forward speed ratio (5th): 0.851; sixth forward speed ratio (6th): 0.669; and seventh forward speed ratio (7th): 0.560. The following corresponding ratio steps are achieved: REV/1st: −0.81; 1st/2nd: 1.67; 2nd/3rd: 1.49; 3rd/4th: 1.33; 4th/5th: 1.37; 5th/6th: 1.27; and 6th/7th: 1.19. This corresponds with an overall ratio spread (1st/7th) of 6.88. Depending on the tooth ratios utilized, the seventh speed ratio (7th) may be approximately 16 to 18 percent higher than the sixth speed ratio (6th), with the sun gear member  142  handling about 15 percent of the torque on the input member  116  and the torque-transmitting mechanism  58 A only about 43 percent of the torque on the input member  116 . 
         [0033]    The highest speed for each set of pinions in any of the speed ratios with respect to the speed of the input member is as follows: pinion gears  137 : 1.58; pinion gears  147 : 1.158; pinion gears  157 : 3.103; and pinion gears  167 : 2.968. Planetary gear set  140  is lightly loaded, with its members carrying torque only during the seventh forward speed ratio due to engagement of brake-type torque-transmitting mechanism  58 A. In the seventh forward speed ratio, the members of planetary gear set carry the following torque ratios with respect to the torque at the input member  116 : sun gear member  142 : 0.163; ring gear member  144 : 0.277; and carrier member  146 : −0.440. 
         [0034]    Referring to  FIG. 4 , a powertrain  210  has a transmission  214  configured in accordance with and operable in like manner as the transmission  14  shown in lever diagram form in  FIG. 1 . The powertrain  210  includes engine  12  powering an input member  216  of the transmission  214 . Final drive unit  19  is operatively connected to an output member  217  of the transmission  214 . 
         [0035]    The transmission  214  includes simple planetary gear set  230 , as well as planetary gear sets  240  and  250  interconnected to form a compound planetary gear set  240 ,  250 , and dual-pinion planetary gear set  260 . Planetary gear set  230  includes a sun gear member  232 , a ring gear member  234 , and a carrier member  236  that rotatably supports a plurality of pinion gears  237  that mesh with both the ring gear member  234  and the sun gear member  232 . 
         [0036]    Compound planetary gear set  240 ,  250  includes planetary gear set  240  having a sun gear member  242 , a ring gear member  244  and a carrier member  246  that rotatably supports a plurality of pinion gears  247  that mesh with both the sun gear member  242  and the ring gear member  244 . The pinion gears  247  are long pinion gears. The carrier member  246  also rotatably supports a second set of pinion gears  257  that are included in planetary gear set  250 . Gear set  250  also includes sun gear member  252 . Pinion gears  257  mesh with the pinion gears  247  and with the sun gear member  252 . 
         [0037]    Planetary gear set  260  is a dual-pinion planetary gear set that includes a sun gear member  262 , a ring gear member  264 , and a carrier member  266 . The carrier member  266  rotatably supports a first set of pinion gears  267  and a second set of pinion gears  268 . Pinion gears  267  mesh with both the sun gear member  262  and the second set of pinion gears  268 . Pinion gears  268  mesh with pinion gears  267  and ring gear member  264 . 
         [0038]    The input member  216  is continuously connected for common rotation with the ring gear member  234 . Sun gear member  232  is continuously grounded to a stationary member  224 , such as a casing of the transmission  214 . Carrier member  266  is continuously connected for common rotation with output member  217 . An interconnecting member  270  continuously connects ring gear member  244  for common rotation with carrier member  266 . Interconnecting member  272  continuously connects carrier member  246  for common rotation with ring gear member  264 . 
         [0039]    The transmission  214  has six selectively engagable torque-transmitting mechanisms  50 B,  52 B,  54 B,  56 B,  57 B, and  58 B, as well as a free-wheeling one-way clutch FIB that is that is connected in parallel with torque-transmitting mechanism  57 B and permits rotation in only one direction. Torque-transmitting mechanism  50 B is a rotating-type clutch that is selectively engagable to connect carrier member  236  for common rotation with sun gear member  252 . Torque-transmitting mechanism  52 B is a rotating-type clutch that is selectively engagable to connect input member  216  and ring gear member  234  for common rotation with carrier member  246 . Torque-transmitting mechanism  54 B is a brake-type torque-transmitting mechanism that is selectively engagable to ground sun gear member  242  with stationary member  224 . Free-wheeling one-way clutch F 1 B prevents rotation of carrier member  246  in a direction opposite the input member  216 . Torque-transmitting mechanism  56 B is a rotating-type clutch that is selectively engagable to connect carrier member  236  for common rotation with sun gear member  242 . Torque-transmitting mechanism  57 B is a brake-type torque-transmitting mechanism that is selectively engagable to ground carrier member  246  to the stationary member  224 . Torque-transmitting mechanism  58 B is a brake-type torque-transmitting mechanism that is selectively engagable to ground sun gear member  262  to the stationary member  224 . 
         [0040]    The members of transmission  214  correspond with the lever diagram transmission  14  of  FIG. 1  as follows: sun gear member  232  corresponds with node A; carrier member  236  corresponds with node B; ring gear member  234  corresponds with node C; sun gear member  242  corresponds with node D; sun gear member  262  corresponds with node E; interconnected carrier member  246  and sun gear member  264  correspond with node F; interconnected carrier member  266  and ring gear member  244  correspond with node G; and sun gear member  252  corresponds with node H. The torque-transmitting mechanisms  50 B,  52 B,  54 B,  56 B,  57 B, and  58 B correspond with torque-transmitting mechanisms  50 ,  52 ,  54 ,  56 ,  57 , and  58 , respectively, and are engagable according to the same schedule of  FIG. 2  to achieve seven forward speed ratios and a reverse speed ratio (and, optionally, an eighth forward speed ratio by engaging torque-transmitting mechanisms  50 B and  58 B). 
         [0041]    One exemplary set of gear tooth counts for the transmission  214  is as follows: ring gear member  234 : 89 teeth; sun gear member  232 : 49 teeth; ring gear member  244 : 87 teeth; sun gear member  242 : 43 teeth; sun gear member  252 : 35 teeth; ring gear member  264 : 79 teeth and sun gear member  262 : 35 teeth. With the engagement schedule as set forth in  FIG. 2  for corresponding torque-transmitting mechanisms, the following speed ratios are attained: reverse speed ratio (REV): −3.138; first forward speed ratio (1st): 3.868; second forward speed ratio (2nd): 2.317; third forward speed ratio (3rd): 1.551; fourth forward speed ratio (4th): 1.166; fifth forward speed ratio (5th): 0.851; sixth forward speed ratio (6th): 0.669; and seventh forward speed ratio (7th): 0.557. The following corresponding ratio steps are achieved: REV/1st: −0.81; 1st/2nd: 1.67; 2nd/3rd: 1.49; 3rd/4th: 1.33; 4th/5th: 1.37; 5th/6th: 1.27; and 6th/7th: 1.20. This corresponds with an overall ratio spread (1st/7th) of 6.94. 
         [0042]    The highest speed for each set of pinions in any of the speed ratios with respect to the speed of the input member is as follows: pinion gears  237 : 1.58; pinion gears  247 : 3.145; pinion gears  257 : 2.950; pinion gears  267 : −3.142; and pinion gears  268 : −3.142. Planetary gear set  260  is lightly loaded, with its members carrying torque only during the seventh forward speed ratio due to engagement of brake-type torque-transmitting mechanism  58 B. In the seventh forward speed ratio, the members of planetary gear set  260  carry the following torque ratios with respect to the torque at the input member  216 : sun gear member  262 : −0.443; ring gear member  264 : 1.000; and carrier member  266 : −0.557. Depending on the tooth ratios utilized, the seventh speed ratio (7th) may be approximately 18 to 23 percent higher than the sixth speed ratio (6th), with the sun gear member  262  and the torque-transmitting mechanism  58 B handling only about 44 percent of the torque on the input member  116 . 
         [0043]    Referring to  FIG. 5 , a powertrain  310  has a transmission  314  configured in accordance with and operable in like manner as the transmission  14  shown in lever diagram form in  FIG. 1 . The powertrain  310  includes engine  12  powering an input member  316  of the transmission  314 . Final drive unit  19  is operatively connected to an output member  317  of the transmission  314 . 
         [0044]    The transmission  314  includes simple planetary gear set  330 , as well as planetary gear sets  340 ,  350  and  360  interconnected to form a compound planetary gear set  340 ,  350 ,  360 . Planetary gear set  330  includes a sun gear member  332 , a ring gear member  334 , and a carrier member  336  that rotatably supports a plurality of pinion gears  337  that mesh with both the ring gear member  334  and the sun gear member  332 . 
         [0045]    Compound planetary gear set  340 ,  350 ,  360  includes planetary gear set  340  having a ring gear member  344  intermeshing with a first set of pinion gears  347 . Planetary gear set  350  has a sun gear member  352 , a ring gear member  354  and a carrier member  356  that rotatably supports a second set of pinion gears  357  that mesh with both the sun gear member  352 , the ring gear member  354  and the pinion gears  347 . Carrier member  356  also rotatably supports the pinion gears  347 . The pinion gears  357  are long pinion gears. The carrier member  356  also rotatably supports a third set of pinion gears  367  that are included in planetary gear set  360 . Gear set  360  also includes sun gear member  362 . Pinion gears  367  mesh with the pinion gears  357  and with the sun gear member  362 . 
         [0046]    The input member  316  is continuously connected for common rotation with the ring gear member  334 . Sun gear member  332  is continuously grounded to a stationary member  324 , such as a casing of the transmission  314 . Ring gear member  354  is continuously connected for common rotation with output member  317 . 
         [0047]    The transmission  314  has six selectively engagable torque-transmitting mechanisms  50 C,  52 C,  54 C,  56 C,  57 C, and  58 C, as well as a free-wheeling one-way clutch F 1 C that is that is connected in parallel with torque-transmitting mechanism  57 C and permits rotation in only one direction. Torque-transmitting mechanism  50 C is a rotating-type clutch that is selectively engagable to connect carrier member  336  for common rotation with sun gear member  362 . Torque-transmitting mechanism  52 C is a rotating-type clutch that is selectively engagable to connect input member  316  and ring gear member  334  for common rotation with carrier member  356 . Torque-transmitting mechanism  54 C is a brake-type torque-transmitting mechanism that is selectively engagable to ground sun gear member  354  with stationary member  324 . Free-wheeling one-way clutch F 1 C prevents rotation of carrier member  356  in a direction opposite the input member  316 . Torque-transmitting mechanism  56 C a rotating-type clutch that is selectively engagable to connect carrier member  336  for common rotation with sun gear member  352 . Torque-transmitting mechanism  57 C is a brake-type torque-transmitting mechanism that is selectively engagable to ground carrier member  356  to the stationary member  324 . Torque-transmitting mechanism  58 C is a brake-type torque-transmitting mechanism that is selectively engagable to ground ring gear member  344  to the stationary member  324 . 
         [0048]    The members of transmission  314  correspond with the lever diagram transmission  14  of  FIG. 1  as follows: sun gear member  332  corresponds with node A; carrier member  336  corresponds with node B; ring gear member  334  corresponds with node C; sun gear member  352  corresponds with node D; ring gear member  344  corresponds with node E; carrier member  356  corresponds with node F; ring gear member  354  corresponds with node G; and sun gear member  362  corresponds with node H. The torque-transmitting mechanisms  50 C,  52 C,  54 C,  56 C,  57 C, and  58 C correspond with torque-transmitting mechanisms  50 ,  52 ,  54 ,  56 ,  57 , and  58 , respectively, and are engagable according to the same schedule of  FIG. 2  to achieve seven forward speed ratios and a reverse speed ratio (and, optionally, an eighth forward speed ratio by engaging torque-transmitting mechanisms  50 C and  58 C). 
         [0049]    One exemplary set of gear tooth counts for the transmission  314  is as follows: ring gear member  334 : 89 teeth; sun gear member  332 : 49 teeth; ring gear member  344 : 79 teeth; sun gear member  352 : 39 teeth; ring gear member  354 : 79 teeth; sun gear member  352 : 39 teeth; and sun gear member  362 : 33 teeth. With the engagement schedule as set forth in  FIG. 2  for corresponding torque-transmitting mechanisms, the following speed ratios are attained: reverse speed ratio (REV): −3.141; first forward speed ratio (1st): 3.712; second forward speed ratio (2nd): 2.265; third forward speed ratio (3rd): 1.551; fourth forward speed ratio (4th): 1.174; fifth forward speed ratio (5th): 0.851; sixth forward speed ratio (6th): 0.669; and seventh forward speed ratio (7th): 0.500. The following corresponding ratio steps are achieved: REV/1st: −0.85; 1st/2nd: 1.64; 2nd/3rd: 1.46; 3rd/4th: 1.32; 4th/5th: 1.38; 5th/6th: 1.27; and 6th/7th: 1.34. This corresponds with an overall ratio spread (1st/7th) of 7.42. Depending on the tooth ratios utilized, the seventh speed ratio (7th) may be approximately 29 to 38 percent higher than the sixth speed ratio (6th), with the ring gear member  344  and the torque-transmitting mechanism  58 C handling only about 50 percent of the torque on the input member  316 . 
         [0050]    The highest speed for each set of pinions in any of the speed ratios with respect to the speed of the input member are as follows: pinion gears  337 : 1.58; pinion gears  347 : −3.950; pinion gears  357 : 3.950; and pinion gears  367 : 3.958. Planetary gear set  340  is lightly loaded, with its members carrying torque only during the seventh forward speed ratio due to engagement of brake-type torque-transmitting mechanism  58 C. In the seventh forward speed ratio, the members of planetary gear set  340  carry the following torque ratios with respect to the torque at the input member  316 : ring gear member  344 : −0.500. The sun gear member  352  of planetary gear set  350 : 0.247; and carrier member  356  of planetary gear set  350  is 0.253. 
         [0051]    Referring to  FIG. 6 , a powertrain  410  has a transmission  414  configured in accordance with and operable in like manner as the transmission  14  shown in lever diagram form in  FIG. 1 . The powertrain  410  includes engine  12  powering an input member  416  of the transmission  414 . Final drive unit  19  is operatively connected to an output member  417  of the transmission  414 . 
         [0052]    The transmission  414  includes simple planetary gear set  430 , as well as planetary gear sets  440  and  450  interconnected to form a compound planetary gear set  440 ,  450 , and dual-pinion planetary gear set  460 . Planetary gear set  430  includes a sun gear member  432 , a ring gear member  434 , and a carrier member  436  that rotatably supports a plurality of pinion gears  437  that mesh with both the ring gear member  434  and the sun gear member  432 . 
         [0053]    Compound planetary gear set  440 ,  450  includes planetary gear set  440  having a sun gear member  442 , a carrier member  446  that rotatably supports a plurality of pinion gears  447  that mesh with the sun gear member  442 . The pinion gears  447  are long pinion gears. The carrier member  446  also rotatably supports a second set of pinion gears  457  that are included in planetary gear set  450 . Gear set  450  also includes a sun gear member  452  and a ring gear member  454 . Pinion gears  457  mesh with the pinion gears  447  and with the sun gear member  452 . 
         [0054]    Planetary gear set  460  is a dual-pinion planetary gear set that includes a sun gear member  462 , a ring gear member  464 , and a carrier member  466 . The carrier member  466  rotatably supports a first set of pinion gears  467  and a second set of pinion gears  468 . Pinion gears  467  mesh with both the sun gear member  462  and the second set of pinion gears  468 . Pinion gears  468  mesh with pinion gears  467  and ring gear member  464 . The transmission  414  is very compact radially because sun gear member  462  can be incorporated directly into output member  417 , rather than spinning around it. 
         [0055]    The input member  416  is continuously connected for common rotation with the ring gear member  434 . Sun gear member  432  is continuously grounded to a stationary member  424 , such as a casing of the transmission  414 . Ring gear member  454  and sun gear member  462  are continuously connected for common rotation with output member  417 . An interconnecting member  470  continuously connects ring gear member  464  for common rotation with carrier member  446 . Interconnecting member  472  continuously connects ring gear member  454  for common rotation with sun gear member  462 . 
         [0056]    The transmission  414  has six selectively engagable torque-transmitting mechanisms  50 D,  52 D,  54 D,  56 D,  57 D, and  58 D, as well as a free-wheeling one-way clutch F 1 D that is that is connected in parallel with torque-transmitting mechanism  57 D and permits rotation in only one direction. Torque-transmitting mechanism  50 D is a rotating-type clutch that is selectively engagable to connect carrier member  436  for common rotation with sun gear member  452 . Torque-transmitting mechanism  52 D is a rotating-type clutch that is selectively engagable to connect input member  416  and ring gear member  434  for common rotation with carrier member  446 . Torque-transmitting mechanism  54 D is a brake-type torque-transmitting mechanism that is selectively engagable to ground sun gear member  442  with stationary member  424 . Free-wheeling one-way clutch F 1 D prevents rotation of carrier member  446  in a direction opposite the input member  416 . Torque-transmitting mechanism  56 D is a rotating-type clutch that is selectively engagable to connect carrier member  436  for common rotation with sun gear member  442 . Torque-transmitting mechanism  57 D is a brake-type torque-transmitting mechanism that is selectively engagable to ground carrier member  446  to the stationary member  424 . Torque-transmitting mechanism  58 D is a brake-type torque-transmitting mechanism that is selectively engagable to ground carrier member  466  to the stationary member  424 . 
         [0057]    The members of transmission  414  correspond with the lever diagram transmission  14  of  FIG. 1  as follows: sun gear member  432  corresponds with node A; carrier member  436  corresponds with node B; ring gear member  434  corresponds with node C; sun gear member  442  corresponds with node D; carrier member  466  corresponds with node E; interconnected carrier member  446  and ring gear member  464  correspond with node F; interconnected sun gear member  462  and ring gear member  454  correspond with node G; and sun gear member  452  corresponds with node H. The torque-transmitting mechanisms  50 D,  52 D,  54 D,  56 D,  57 D, and  58 D correspond with torque-transmitting mechanisms  50 ,  52 ,  54 ,  56 ,  57 , and  58 , respectively, and are engagable according to the same schedule of  FIG. 2  to achieve seven forward speed ratios and a reverse speed ratio (and, optionally, an eighth forward speed ratio by engaging torque-transmitting mechanisms  50 D and  58 D). 
         [0058]    One exemplary set of tooth ratios for the transmission  414  is as follows: ring gear member  434  to sun gear member  432 : 1.82; ring gear member  454  to sun gear member  442 : 2.06; ring gear member  454  to sun gear member  452 : 2.62; and ring gear member  464  to sun gear member  462 : 1.80. With the engagement schedule as set forth in  FIG. 2  for corresponding torque-transmitting mechanisms, the following speed ratios are attained: reverse speed ratio (REV): −3.192; first forward speed ratio (1st): 4.060; second forward speed ratio (2nd): 2.370; third forward speed ratio (3rd): 1.549; fourth forward speed ratio (4th): 1.157; fifth forward speed ratio (5th): 0.853; sixth forward speed ratio (6th): 0.673; and seventh forward speed ratio (7th): 0.556. The following corresponding ratio steps are achieved: REV/1st: −0.79; 1st/2nd: 1.71; 2nd/3rd: 1.53; 3rd/4th: 1.34; 4th/5th: 1.36; 5th/6th: 1.27; and 6th/7th: 1.21. This corresponds with an overall ratio spread (1st/7th) of 7.31. 
         [0059]    The highest speed for each set of pinions in any of the speed ratios with respect to the speed of the input member  416  are as follows: pinion gears  437 : 1.574; pinion gears  447 : 3.109; pinion gears  457 : 3.044; pinion gears  467 : 5.294; and pinion gears  468 : 5.294. Planetary gear set  460  is lightly loaded, with its members carrying torque only during the seventh forward speed ratio due to engagement of brake-type torque-transmitting mechanism  58 B. In the seventh forward speed ratio, the members of planetary gear set  460  carry the following torque ratios with respect to the torque at the input member  416 : sun gear member  462 : −0.556; ring gear member  464 : 1.000; and carrier member  466 : −0.444. Depending on the tooth ratios utilized, the seventh speed ratio (7th) may be approximately 20 to 100 percent higher than the sixth speed ratio (6th), with the sun gear member  462  and the torque-transmitting mechanism  58 D handling only about 56 and 44 percent of the torque on the input member  116 , respectively. 
         [0060]    Thus, there are several exemplary stick-diagram embodiments of transmissions  114 ,  214 ,  314  and  414  corresponding with the embodiment of transmission  14  in lever diagram form in  FIG. 1 . Each embodiment offers seven forward speed ratios with an evenly-spaced ratio progression, a good overall ratio spread, relatively low pinion speeds, and relatively low torque on the brake-type-torque transmitting mechanism loaded in the seventh forward speed ratio and the planetary gear set with a member grounded thereby. 
         [0061]    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.