Abstract:
A transmission is provided having at least three planetary gearsets, each having respective first, second, and third members, and six selectively engageable torque transmitting devices configured to selectively interconnect selected members of the planetary gearsets for unitary rotation thereby to provide at least six forward speed ratios and at least one reverse speed ratio between an input member and an output member.

Description:
TECHNICAL FIELD 
     This invention relates to transmissions having planetary gear arrangements. 
     BACKGROUND OF THE INVENTION 
     Passenger vehicles include a powertrain that is comprised of an engine, a multi-speed transmission, and a differential or final drive. The multi-speed transmission increases the overall operating range of the vehicle by permitting the engine to operate through its torque range a number of times. The number of forward speed ratios that are available in the transmission determines the number of times the engine torque range is repeated. Early automatic transmissions had two speed ranges. This severely limited the overall speed range of the vehicle and therefore required a relatively large engine that could produce a wide speed and torque range. This resulted in the engine operating at a specific fuel consumption point other than the most efficient point during cruising. Therefore, manually-shifted (countershaft transmissions) were the most popular. 
     With the advent of three- and four-speed automatic transmissions, the automatic shifting (planetary gear) transmission increased in popularity with the motoring public. These transmissions improved the operating performance and fuel economy of the vehicle. The increased number of speed ratios reduces the step size between ratios and therefore improves the shift quality of the transmission by making the ratio interchanges substantially imperceptible to the operator under normal vehicle acceleration. 
     It has been suggested that the number of forward speed ratios be increased to six or more. Six-speed transmissions are disclosed in U.S. Pat. No. 4,070,927 issued to Polak on Jan. 31, 1978; and U.S. Pat. No. 6,422,969 issued to Raghavan and Usoro on Jul. 23, 2002. 
     Six-speed transmissions offer several advantages over four- and five-speed transmissions, including improved vehicle acceleration and improved fuel economy. While many trucks employ power transmissions having six or more forward speed ratios, passenger cars are still manufactured with three- and four-speed automatic transmissions and relatively few five or six-speed devices due to the size and complexity of these transmissions. 
     Seven-speed transmissions are disclosed in U.S. Pat. No. 6,623,397 issued to Raghavan, Bucknor and Usoro. Eight speed transmissions are disclosed in U.S. Pat. No. 6,425,841 issued to Haka. The Haka transmission utilizes three planetary gear sets and six torque transmitting devices, including two brakes and two clutches, to provide eight forward speed ratios and a reverse speed ratio. One of the planetary gear sets is positioned and operated to establish two fixed speed input members for the remaining two planetary gear sets. Seven-, eight- and nine-speed transmissions provide further improvements in acceleration and fuel economy over six-speed transmissions. However, like the six-speed transmissions discussed above, the development of seven-, eight- and nine-speed transmissions has been precluded because of complexity, size and cost. 
     SUMMARY OF THE INVENTION 
     A transmission includes an input member, an output member, a stationary member, and first, second, and third planetary gearsets. Each of the planetary gearsets has a respective first, second, and third member. The first member of the first planetary gearset is continuously operatively connected to the input member for unitary rotation. The second member of the first planetary gearset is continuously operatively connected to the stationary member. The first member of the second planetary gearset is continuously operatively connected to the first member of the third planetary gearset for unitary rotation. The third member of the second planetary gearset is continuously operatively connected to the second member of the third planetary gearset for unitary rotation. The third member of the third planetary gearset is continuously operatively connected to the output member for unitary rotation. 
     The transmission also includes first, second, third, fourth, fifth, and sixth torque transmitting devices operative to selectively connect members of the planetary gearsets with the input member, the stationary member, or with other members of the planetary gearsets to provide at least six forward speed ratios. 
     In an exemplary embodiment, the first torque transmitting device is configured to selectively couple the input member and the first member of the first planetary gearset with the third member of the second planetary gearset and the second member of the third planetary gearset for unitary rotation. The second torque transmitting device is configured to selectively couple the third member of the first planetary gearset with the second member of the second planetary gearset for unitary rotation. The third torque transmitting device is configured to selectively couple the second member of the third planetary gearset and the third member of the second planetary gearset with the stationary member. The fourth torque transmitting device is configured to selectively couple the third member of the first planetary gearset with the third member of the second planetary gearset and the second member of the third planetary gearset for unitary rotation. The fifth torque transmitting device is configured to selectively couple the first member of the first planetary gearset with a member of the second planetary gearset for unitary rotation. The sixth torque transmitting device is configured to selectively couple a member of the second planetary gearset with the stationary member. 
     The transmission may further include a seventh torque transmitting device configured to selectively couple the second member of the second planetary gearset with the stationary member to provide at least seven forward speed ratios and at least one reverse ratio. 
     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 
         FIG. 1  is a schematic representation of a first transmission according to the present invention; 
         FIG. 2  is a ratio chart and truth table depicting a shift logic sequence for use with the transmission of  FIG. 1 ; 
         FIG. 3  is a schematic representation of a second transmission according to the present invention; 
         FIG. 4  is a ratio chart and truth table depicting a shift logic sequence for use with the transmission of  FIG. 3 ; 
         FIG. 5  is a schematic representation of a third transmission according to the present invention; 
         FIG. 6  is a ratio chart and truth table depicting a shift logic sequence for use with the transmission of  FIG. 5 ; 
         FIG. 7  is a schematic representation of a fourth transmission according to the present invention; 
         FIG. 8  is a ratio chart and truth table depicting a shift logic sequence for use with the transmission of  FIG. 7 ; 
         FIG. 9  is a schematic representation of a fifth transmission according to the present invention; 
         FIG. 10  is a ratio chart and truth table depicting a shift logic sequence for use with the transmission of  FIG. 9 ; 
         FIG. 11  is a schematic representation of a sixth transmission according to the present invention; 
         FIG. 12  is a ratio chart and truth table depicting a shift logic sequence for use with the transmission of  FIG. 11 ; 
         FIG. 13  is a ratio chart and truth table depicting another shift logic sequence for use with the transmission of  FIG. 11 ; 
         FIG. 14  is a schematic representation of a seventh transmission according to the present invention; and 
         FIG. 15  is a ratio chart and truth table depicting a shift logic sequence for use with the transmission of  FIG. 14 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , a transmission  10  is schematically depicted. The transmission  10  includes a first planetary gearset  12 , a second planetary gearset  14 , and a third planetary gearset  16 . Each of the first, second, and third planetary gearsets have respective first, second, and third members. More specifically, the first planetary gearset includes a sun gear member  18 , a ring gear member  20 , and a planet carrier assembly member  22 . Planet carrier assembly member  22  rotatably supports a plurality of planet gear members  24  that meshingly engage sun gear member  18  and ring gear member  20 . The second planetary gearset  14  includes a sun gear member  26 , a ring gear member  28 , and a planet carrier assembly member  30 . Planet carrier assembly member  30  rotatably supports a plurality of planet gear members  32  that meshingly engage sun gear member  26  and ring gear member  28 . The third planetary gearset  16  includes a sun gear member  34 , a ring gear member  36 , and a planet carrier assembly member  38 . Planet carrier assembly member  38  rotatably supports a plurality of planet gear members  40  that meshingly engage sun gear member  34  and ring gear member  36 . 
     Shaft  42  is an interconnecting member that continuously connects sun gear members  26  and  34  for unitary rotation. Input member  44  is connectable to an engine (not shown), either directly or through a torque convertor. Output member  46  is connectable to the final drive system of a vehicle to drive wheels or other tractive device. Interconnecting member  48  continuously interconnects the input member  44  and sun gear member  18  for unitary rotation. Transmission  10  also includes a stationary member such as transmission housing  50 . 
     Ring gear member  20  is continuously grounded to the housing  50  to prevent rotation of ring gear member  20 . Planet carrier assembly member  30  is continuously connected to ring gear member  36  for unitary rotation. Output member  46  is continuously connected to planet carrier assembly member  38  for unitary rotation. 
     The transmission  10  further includes a plurality of selectively engageable torque transmitting devices, or clutches C 1 -C 7 . Clutch C 1  selectively couples sleeve  48 , input member  44 , and sun gear member  18  to sun gear member  26  and sun gear member  34  for unitary rotation. Clutch C 2  selectively couples sleeve  48 , input member  44 , and sun gear member  18  to planet carrier assembly member  30  and ring gear member  36  for unitary rotation. Clutch C 3  selectively couples planet carrier assembly member  22  with ring gear member  28  for unitary rotation. Clutch C 4  is a brake that selectively couples ring gear member  28  to the housing  50 . Clutch C 5  is a brake that selectively couples ring gear member  36  and planet carrier assembly member  30  to the housing  50 . Clutch C 6  selectively couples planet carrier assembly member  22  to planet carrier assembly member  30  and ring gear member  36  for unitary rotation. Clutch C 7  is a brake that selectively couples sun gear member  26  and sun gear member  34  to the housing  50 . 
     Referring to  FIG. 2 , a shift logic sequence for clutches C 1 -C 7  is depicted that provides eight forward speed ratios and one reverse speed ratio between the input member  44  and the output member  46 . Referring to  FIGS. 1 and 2 , a first forward speed ratio is achieved when clutches C 3  and C 7  are engaged. A second forward speed ratio is achieved when clutches C 6  and C 7  are engaged. A third forward speed ratio is achieved when clutches C 3  and C 6  are engaged. A fourth forward speed ratio is achieved when clutches C 1  and C 6  are engaged. A fifth forward speed ratio is achieved when clutches C 1  and C 3  are engaged. A sixth forward speed ratio is achieved when clutches C 1  and C 2  are engaged. A seventh forward speed ratio is achieved when clutches C 2  and C 3  are engaged. An eighth forward speed ratio is achieved when clutches C 2  and C 4  are engaged. A reverse speed ratio is achieved when clutches C 3  and C 5  are engaged. It should be noted that the omission of clutch C 4  yields a six clutch/seven speed transmission, i.e., speed ratios  1 - 7 . 
     In the embodiment depicted, ring gear members  20 ,  28 , and  36  each have 81 teeth, sun gear member  18  has 51 teeth, sun gear member  26  has 49 teeth, and sun gear member  34  has 31 teeth. 
     Referring to  FIG. 3 , an alternative transmission  110  is schematically depicted. The transmission  110  includes a first planetary gearset  112 , a second planetary gearset  114 , and a third planetary gearset  116 . Each of the first, second, and third planetary gearsets have respective first, second, and third members. More specifically, the first planetary gearset includes a sun gear member  118 , a ring gear member  120 , and a planet carrier assembly member  122 . Planet carrier assembly member  122  is compound and thus rotatably supports a first set of planet gear members  124   a  that meshingly engage sun gear member  118 . Planet carrier assembly member  122  also rotatably supports a second set of planet gear members  124   b  that meshingly engage the first set of planet gear members  124   a  and ring gear member  120 . 
     The second planetary gearset  114  includes a sun gear member  126 , a ring gear member  128 , and a planet carrier assembly member  130 . Planet carrier assembly member  130  rotatably supports a plurality of planet gear members  132  that meshingly engage sun gear member  126  and ring gear member  128 . The third planetary gearset  116  includes a sun gear member  134 , a ring gear member  136 , and a planet carrier assembly member  138 . Planet carrier assembly member  138  rotatably supports a plurality of planet gear members  140  that meshingly engage sun gear member  134  and ring gear member  136 . 
     Shaft  142  is an interconnecting member that continuously connects sun gear members  126  and  134  for unitary rotation. Interconnecting member  148  continuously interconnects the input member  144  and sun gear member  118  for unitary rotation. Transmission  110  also includes a stationary member such as transmission housing  150 . 
     Planet carrier assembly member  122  is continuously grounded to the housing  150  to prevent rotation of planet carrier assembly member  122 . Planet carrier assembly member  130  is continuously connected to ring gear member  136  for unitary rotation. Output member  146  is continuously connected to planet carrier assembly member  138  for unitary rotation. 
     The transmission  110  further includes a plurality of selectively engageable torque transmitting devices, or clutches C 1 -C 7 . Clutch C 1  selectively couples sleeve  148 , input member  144 , and sun gear member  118  to sun gear member  126  and sun gear member  134  for unitary rotation. Clutch C 2  selectively couples sleeve  148 , input member  144 , and sun gear member  118  to planet carrier assembly member  130  and ring gear member  136  for unitary rotation. Clutch C 3  selectively couples ring gear member  120  with ring gear member  128  for unitary rotation. Clutch C 4  is a brake that selectively couples ring gear member  128  to the housing  150 . Clutch C 5  is a brake that selectively couples ring gear member  136  and planet carrier assembly member  130  to the housing  150 . Clutch C 6  selectively couples ring gear member  120  to planet carrier assembly member  130  and ring gear member  136  for unitary rotation. Clutch C 7  is a brake that selectively couples sun gear member  126  and sun gear member  134  to the housing  150 . 
     Referring to  FIG. 4 , a shift logic sequence for clutches C 1 -C 7  is depicted that provides eight forward speed ratios and one reverse speed ratio between the input member  144  and the output member  146 . The clutch engagement sequence of  FIG. 4  is identical to that of  FIG. 2 , but different speed ratios between input member  144  and output member  146  are achieved. In the embodiment depicted, ring gear member  120  has 80 teeth, sun gear member has 40 teeth, ring gear members  128  and  136  each have 81 teeth, sun gear member  126  has 41 teeth, and sun gear member  134  has 31 teeth. 
     Referring to  FIG. 5 , transmission  210  includes a first planetary gearset  212 , a second planetary gearset  214 , and a third planetary gearset  216 . Each of the first, second, and third planetary gearsets have respective first, second, and third members. More specifically, the first planetary gearset includes a sun gear member  218 , a ring gear member  220 , and a planet carrier assembly member  222 . Planet carrier assembly member  222  is compound and thus rotatably supports a first set of planet gear members  224   a  that meshingly engage sun gear member  218 . Planet carrier assembly member  222  also rotatably supports a second set of planet gear members  224   b  that meshingly engage the first set of planet gear members  224   a  and ring gear member  220 . 
     The second planetary gearset  214  includes a sun gear member  226 , a ring gear member  228 , and a planet carrier assembly member  230 . Planet carrier assembly member  230  rotatably supports a plurality of planet gear members  232  that meshingly engage sun gear member  226  and ring gear member  228 . The third planetary gearset  216  includes a sun gear member  234 , a ring gear member  236 , and a planet carrier assembly member  238 . Planet carrier assembly member  238  rotatably supports a plurality of planet gear members  240  that meshingly engage sun gear member  234  and ring gear member  236 . 
     Shaft  242  is an interconnecting member that continuously connects sun gear members  226  and  234  for unitary rotation. Interconnecting member  248  continuously interconnects the input member  244  and planet carrier assembly member  222  for unitary rotation. Transmission  210  also includes a stationary member such as transmission housing  250 . 
     Sun gear member  218  is continuously grounded to the housing  250  to prevent rotation of sun gear member  218 . Planet carrier assembly member  230  is continuously connected to ring gear member  236  for unitary rotation. Output member  246  is continuously connected to planet carrier assembly member  238  for unitary rotation. 
     The transmission  210  further includes a plurality of selectively engageable torque transmitting devices, or clutches C 2 -C 8 . Clutch C 1  as found in the transmissions  10 ,  110  of  FIGS. 1 and 3 , respectively, i.e., selectively interconnecting an input member and a member of the first planetary gearset with the sun gear members of the second and third planetary gearsets, is not present in transmission  210 . Clutch C 2  selectively couples sleeve  248 , input member  244 , and planet carrier assembly member  222  to planet carrier assembly member  230  and ring gear member  236  for unitary rotation. Clutch C 3  selectively couples ring gear member  220  with ring gear member  228  for unitary rotation. Clutch C 4  is a brake that selectively couples ring gear member  228  to the housing  250 . Clutch C 5  is a brake that selectively couples ring gear member  236  and planet carrier assembly member  230  to the housing  250 . Clutch C 6  selectively couples ring gear member  220  to planet carrier assembly member  230  and ring gear member  236  for unitary rotation. Clutch C 7  is a brake that selectively couples sun gear member  226  and sun gear member  234  to the housing  250 . Clutch C 8  selectively couples planet carrier assembly member  222 , member  248 , and input member  244  with ring gear member  228  for unitary rotation. 
     In the embodiment depicted, ring gear members  220 ,  228 , and  236  each have 81 teeth, and sun gear member  218  has 39 teeth, sun gear member  226  has 37 teeth, and sun gear member  234  has 26 teeth.  FIG. 6  depicts a preferred shift logic to provide seven forward speed ratios between the input member  244  and the output member  246 , and one reverse speed ratio. Referring to  FIGS. 5 and 6 ; a first speed ratio is achieved when clutchs C 3  and C 7  are engaged; a second speed ratio is achieved when clutches C 6  and C 7  are engaged; a third speed ratio is achieved when clutches C 8  and C 7  are engaged; a fourth speed ratio is achieved when clutches C 2  and C 7  are engaged; a fifth speed ratio is achieved when clutched C 8  and C 2  are engaged; a sixth speed ratio is achieved when clutches C 2  and C 3  are engaged; and a seventh speed ratio is achieved when clutches C 2  and C 4  are engaged. A reverse speed ratio is achieved when clutches C 3  and C 5  are engaged. Clutch C 4  may be omitted, whereby six forward speed ratios are provided. 
     Referring to  FIG. 7 , transmission  310  includes a first planetary gearset  312 , a second planetary gearset  314 , and a third planetary gearset  316 . Each of the first, second, and third planetary gearsets have respective first, second, and third members. More specifically, the first planetary gearset includes a sun gear member  318 , a ring gear member  320 , and a planet carrier assembly member  322 . Planet carrier assembly member  322  rotatably supports planet gear members  324  that meshingly engage sun gear member  318  and ring gear member  320 . 
     The second planetary gearset  314  includes a sun gear member  326 , a ring gear member  328 , and a planet carrier assembly member  330 . Planet carrier assembly member  330  rotatably supports a plurality of planet gear members  332  that meshingly engage sun gear member  326  and ring gear member  328 . The third planetary gearset  316  includes a sun gear member  334 , a ring gear member  336 , and a planet carrier assembly member  338 . Planet carrier assembly member  338  rotatably supports a plurality of planet gear members  340  that meshingly engage sun gear member  334  and ring gear member  336 . 
     Shaft  342  is an interconnecting member that continuously connects sun gear members  326  and  334  for unitary rotation. Interconnecting member  348  continuously interconnects the input member  344  and ring gear member  320  for unitary rotation. Transmission  310  also includes a stationary member such as transmission housing  350 . 
     Sun gear member  318  is continuously grounded to the housing  350  to prevent rotation of sun gear member  318 . Planet carrier assembly member  330  is continuously connected to ring gear member  336  for unitary rotation. Output member  346  is continuously connected to planet carrier assembly member  338  for unitary rotation. 
     The transmission  310  further includes a plurality of selectively engageable torque transmitting devices, or clutches C 1 -C 7 . Clutch C 1  selectively couples sleeve  348 , input member  344 , and ring gear member  320  to shaft  342 , sun gear member  326  and sun gear member  334  for unitary rotation. Clutch C 2  selectively couples sleeve  348 , input member  344 , and ring gear member  320  to planet carrier assembly member  330  and ring gear member  336  for unitary rotation. Clutch C 3  selectively couples planet carrier assembly member  322  with ring gear member  328  for unitary rotation. Clutch C 4  is a brake that selectively couples ring gear member  328  to the housing  350 . Clutch C 5  is a brake that selectively couples ring gear member  336  and planet carrier assembly member  330  to the housing  350 . Clutch C 6  selectively couples planet carrier assembly member  322  to planet carrier assembly member  330  and ring gear member  336  for unitary rotation. Clutch C 7  is a brake that selectively couples shaft  342 , sun gear member  326  and sun gear member  334  to the housing  350 . 
     In the embodiment depicted, ring -gear members  320 ,  328 , and  336  each have 81 teeth, and sun gear member  318  has 51 teeth, sun gear member  326  has 41 teeth, and sun gear member  334  has 29 teeth.  FIG. 8  depicts a shift logic sequence to provide eight forward speed ratios between the input member  344  and the output member  346 , and one reverse speed ratio. The clutch engagement for the shift logic of  FIG. 8  is identical to the clutch engagement shown in  FIG. 2 . 
     Referring to  FIG. 9 , transmission  410  includes a first planetary gearset  412 , a second planetary gearset  414 , and a third planetary gearset  416 . Each of the first, second, and third planetary gearsets have respective first, second, and third members. More specifically, the first planetary gearset includes a sun gear member  418 , a ring gear member  420 , and a planet carrier assembly member  422 . Planet carrier assembly member  422  is compound and thus rotatably supports a first set of planet gear members  424   a  and a second set of planet gear members  424   b . The first set of planet gear members  424   a  meshingly engage sun gear member  418 , and the second set of planet gear members  424   b  meshingly engage the first set of planet gear members  424   a  and ring gear member  420 . 
     The second planetary gearset  414  includes a sun gear member  426 , a ring gear member  428 , and a planet carrier assembly member  430 . Planet carrier assembly member  430  rotatably supports a plurality of planet gear members  432  that meshingly engage sun gear member  426  and ring gear member  428 . The third planetary gearset  416  includes a sun gear member  434 , a ring gear member  436 , and a planet carrier assembly member  438 . Planet carrier assembly member  438  rotatably supports a plurality of planet gear members  440  that meshingly engage sun gear member  434  and ring gear member  436 . 
     Shaft  442  is an interconnecting member that continuously connects sun gear members  426  and  434  for unitary rotation. Input member  444  is continuously connected to sun gear member  418  for unitary rotation. Transmission  410  also includes a stationary member such as transmission housing  450 . 
     Planet carrier assembly member  422  is continuously grounded to the housing  450 . Planet carrier assembly member  430  is continuously connected to ring gear member  436  for unitary rotation. Output member  446  is continuously connected to planet carrier assembly member  438  for unitary rotation. 
     The transmission  410  further includes a plurality of selectively engageable torque transmitting devices, or clutches C 1 -C 6 . Clutch C 1  selectively couples input member  444  and sun gear member  418  to shaft  442 , sun gear member  426  and sun gear member  434  for unitary rotation. Clutch C 2  selectively couples input member  444  and sun gear member  418  to planet carrier assembly member  430  and ring gear member  436  for unitary rotation. Clutch C 3  selectively couples ring gear member  420  with ring gear member  428  for unitary rotation. Clutch C 4  is a brake that selectively couples ring gear member  428  to the housing  450 . Clutch C 5  is a brake that selectively couples ring gear member  436  and planet carrier assembly member  430  to the housing  450 . Clutch C 6  selectively couples ring gear member  420  to planet carrier assembly member  430  and ring gear member  436  for unitary rotation. 
     In the embodiment depicted, ring gear members  420 ,  428 , and  436  each have 81 teeth, and sun gear member  418  has 35 teeth, sun gear member  426  has 35 teeth, and sun gear member  434  has 31 teeth.  FIG. 10  depicts a shift logic sequence to provide seven forward speed ratios between the input member  444  and the output member  446 , and one reverse speed ratio. A first speed ratio is achieved when clutches C 1  and C 5  are engaged; a second speed ratio is achieved when clutches C 1  and C 4  are engaged; a third speed ratio is achieved when clutches C 1  and C 6  are engaged; a fourth speed ratio is achieved when clutches C 1  and C 3  are engaged; a fifth speed ratio is achieved when clutches C 1  and C 2  are engaged; a sixth speed ratio is achieved when clutches C 2  and C 3  are engaged; and a seventh speed ratio is achieved when clutches C 2  and C 4  are engaged. A reverse speed ratio is achieved when clutches C 3  and C 5  are engaged. 
     Referring to  FIG. 11 , transmission  510  includes a first planetary gearset  512 , a second planetary gearset  514 , a third planetary gearset  516 , and a fourth planetary gearset  554 . Each of the first, second, third, and fourth planetary gearsets have respective first, second, and third members. More specifically, the first planetary gearset includes a sun gear member  518 , a ring gear member  520 , and a planet carrier assembly member  522 . Planet carrier assembly member  522  rotatably supports a plurality of planet gear members  524  that meshingly engage sun gear member  518  and ring gear member  520 . 
     The second planetary gearset  514  includes a sun gear member  526 , a ring gear member  528 , and a planet carrier assembly member  530 . Planet carrier assembly member  530  rotatably supports a plurality of planet gear members  532  that meshingly engage sun gear member  526  and ring gear member  528 . The third planetary gearset  516  includes a sun gear member  534 , a ring gear member  536 , and a planet carrier assembly member  538 . Planet carrier assembly member  538  rotatably supports a plurality of planet gear members  540  that meshingly engage sun gear member  534  and ring gear member  536 . 
     The fourth planetary gearset  554  includes a sun gear member  556 , a ring gear member  558 , and planet carrier assembly member  538 . Planet carrier assembly member  538  is common to the third and fourth planetary gearsets  516 ,  554 , and thus the planet carrier assemblies of the third and fourth planetary gearsets  516 ,  554  are continuously connected for unitary rotation. Alternatively, and within the scope of the claimed invention, the third and fourth planetary gearsets may employ separate, interconnected planet carrier assembly members. Planet carrier assembly  538  rotatably supports a plurality of planet gear members  560  that meshingly engage sun gear member  556  and ring gear member  558 . 
     Shaft  542  is an interconnecting member that continuously connects sun gear members  526 ,  534 , and  556  for unitary rotation. Input member  544  is continuously connected to sun gear member  518  for unitary rotation. Transmission  510  also includes a stationary member such as transmission housing  550 . 
     Ring gear member  520  is continuously grounded to the housing  550 . Planet carrier assembly member  530  is continuously connected to ring gear member  536  for unitary rotation. Output member  546  is continuously connected to planet carrier assembly member  538  for unitary rotation. 
     The transmission  510  further includes a plurality of selectively engageable torque transmitting devices, or clutches C 1 -C 7 . Clutch C 1  selectively couples input member  544  and sun gear member  518  to shaft  542 , sun gear member  526 , sun gear member  534 , and sun gear member  556  for unitary rotation. Clutch C 2  selectively couples input member  544  and sun gear member  518  to planet carrier assembly member  530  and ring gear member  536  for unitary rotation. Clutch C 3  selectively couples planet carrier assembly member  522  with ring gear member  528  for unitary rotation. Clutch C 4  is a brake that selectively couples ring gear member  528  to the housing  550 . Clutch C 5  is a brake that selectively couples ring gear member  536  and planet carrier assembly member  530  to the housing  550 . Clutch C 6  selectively couples planet carrier assembly member  522  to planet carrier assembly member  530  and ring gear member  536  for unitary rotation. Clutch C 7  is a brake that selectively couples ring gear member  558  to the housing  550 . 
     In the embodiment depicted, ring gear members  520 ,  528 ,  536 , and  558  each have 85 teeth, and sun gear member  518  has 55 teeth, sun gear member  526  has 37 teeth, sun gear member  534  has 29 teeth, and sun gear member  556  has 45 teeth.  FIG. 12  depicts a shift logic sequence to provide eight forward speed ratios between the input member  544  and the output member  546 , and one reverse speed ratio. A first speed ratio is achieved when clutches C 1  and C 5  are engaged; a second speed ratio is achieved when clutches C 1  and C 7  are engaged; a third speed ratio is achieved when clutches C 1  and C 4  are engaged; a fourth speed ratio is achieved when clutches C 1  and C 6  are engaged; a fifth speed ratio is achieved when clutches C 1  and C 3  are engaged; a sixth speed ratio is achieved when clutches C 1  and C 2  are engaged; a seventh speed ratio is achieved when clutches C 2  and C 3  are engaged; and an eighth speed ratio is achieved when clutches C 2  and C 4  are engaged. A reverse speed ratio is achieved when clutches C 3  and C 5  are engaged. 
       FIG. 13  depicts a shift logic sequence for use with the transmission  510  of  FIG. 11  that does not employ clutches C 6  and C 7 . Referring to  FIGS. 11 and 13 , a first speed ratio is achieved when clutches C 1  and C 5  are engaged; a second speed ratio is achieved when clutches C 1  and C 4  are engaged; a third speed ratio is achieved when clutches C 1  and C 3  are engaged; a fourth speed ratio is achieved when clutches C 1  and C 2  are engaged; a fifth speed ratio is achieved when clutches C 2  and C 3  are engaged; and a sixth speed ratio is achieved when clutches C 2  and C 4  are engaged. A reverse speed ratio is achieved when clutches C 3  and C 5  are engaged. 
     Referring to  FIG. 14 , transmission  610  includes a first planetary gearset  612 , a second planetary gearset  614 , a third planetary gearset  616 , and a fourth planetary gearset  654 . Each of the first, second, third, and fourth planetary gearsets have respective first, second, and third members. More specifically, the first planetary gearset includes a sun gear member  618 , a ring gear member  620 , and a planet carrier assembly member  622 . Planet carrier assembly member  622  rotatably supports a first set of planet gear members  624   a  that meshingly engage sun gear member  618 ; planet carrier assembly member  622  also rotatably supports a second set of planet gear members  624   b  that meshingly engage the first set of planet gear members  624   a  and ring gear member  620 . 
     The second planetary gearset  614  includes a sun gear member  626 , a ring gear member  628 , and a planet carrier assembly member  630 . Planet carrier assembly member  630  rotatably supports a plurality of planet gear members  632  that meshingly engage sun gear member  626  and ring gear member  628 . The third planetary gearset  616  includes a sun gear member  634 , a ring gear member  636 , and a planet carrier assembly member  638 . Planet carrier assembly member  638  rotatably supports a plurality of planet gear members  640  that meshingly engage sun gear member  634  and ring gear member  636 . 
     The fourth planetary gearset  654  includes a sun gear member  656 , a ring gear member  658 , and planet carrier assembly member  638 . Planet carrier assembly member  638  rotatably supports a plurality of planet gear members  660  that meshingly engage sun gear member  656  and ring gear member  658 . 
     Shaft  642  is an interconnecting member that continuously connects sun gear members  626 ,  634 , and  656  for unitary rotation. Input member  644  is continuously connected to sun gear member  618  for unitary rotation. Transmission  610  also includes a stationary member such as transmission housing  650 . 
     Planet carrier assembly member  622  is continuously grounded to the housing  650 . Planet carrier assembly member  630  is continuously connected to ring gear member  636  for unitary rotation. Output member  646  is continuously connected to planet carrier assembly member  638  for unitary rotation. 
     The transmission  610  further includes a plurality of selectively engageable torque transmitting devices, or clutches C 1 -C 7 . Clutch C 1  selectively couples input member  644  and sun gear member  618  to shaft  642 , sun gear member  626 , sun gear member  634 , and sun gear member  656  for unitary rotation. Clutch C 2  selectively couples input member  644  and sun gear member  618  to planet carrier assembly member  630  and ring gear member  636  for unitary rotation. Clutch C 3  selectively couples ring gear  620  with ring gear member  628  for unitary rotation. Clutch C 4  is a brake that selectively couples ring gear member  628  to the housing  650 . Clutch C 5  is a brake that selectively couples ring gear member  636  and planet carrier assembly member  630  to the housing  650 . Clutch C 6  selectively couples ring gear member  620  to planet carrier assembly member  630  and ring gear member  636  for unitary rotation. Clutch C 7  is a brake that selectively couples ring gear member  658  to the housing  650 . 
     In the embodiment depicted, ring gear members  620  has 80 teeth and ring gear members  628 ,  636 , and  658  each have 85 teeth; sun gear member  618  has 35 teeth, sun gear member  626  has 24 teeth, sun gear member  634  has 29 teeth, and sun gear member  656  has 47 teeth.  FIG. 15  schematically depicts a shift logic sequence for use with the transmission  610  of  FIG. 14  to achieve eight forward speed ratios and one reverse speed ratio between the input member  644  and the output member  646 . The clutch engagement sequence of  FIG. 14  is identical to the clutch engagement sequence of  FIG. 12 . 
     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.