Abstract:
A transmission is provided having a planetary gearset having respective first, second, and third members, and a compound gearset having respective first, second, third, and fourth members. The transmission also includes a plurality of selectively engageable torque transmitting devices configured to selectively interconnect selected members of the planetary gearset and the compound gearset for unitary rotation thereby to provide a plurality of forward speed ratios and at least one reverse speed ratio between an input member and an output member.

Description:
TECHNICAL FIELD  
       [0001]     This invention relates to power transmissions having planetary gear arrangements.  
       BACKGROUND OF THE INVENTION  
       [0002]     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.  
         [0003]     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.  
         [0004]     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.  
         [0005]     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.  
         [0006]     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  
       [0007]     A transmission is provided having an input member, an output member, and a stationary member. A planetary gearset includes respective first, second, and third members. A compound gearset includes respective first, second, third, and fourth members. The first member of the planetary gearset is continuously operatively connected to the input member for unitary rotation therewith. The second member of the planetary gearset is continuously grounded to the stationary member. The first member of the compound gearset is continuously operatively connected to the output member for unitary rotation therewith.  
         [0008]     The transmission further includes first, second, third, fourth, fifth, and sixth torque transmitting devices that are operative to selectively connect members of the planetary gearset and the compound gearset with the stationary member or with other members of the planetary gearset or the compound gearset to provide at least eight forward speed ratios and one reverse speed ratio.  
         [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 a schematic representation of a transmission in accordance with the present invention;  
         [0011]      FIG. 2  is a ratio chart and truth table depicting a shift logic for use with the transmission of  FIG. 1 ; and  
         [0012]      FIG. 3  is a schematic representation of a second embodiment of a transmission in accordance with the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]     Referring to  FIG. 1 , a transmission  10  for a vehicle is schematically depicted. The transmission  10  includes planetary gearsets  14 ,  16 ,  18 . Planetary gearset  14  includes a sun gear member  22 , a ring gear member  26 , and a planet carrier assembly  28 . Planet carrier assembly  28  includes a planet carrier member  30 , which rotatably supports a plurality of planetary pinion gear members. Planetary gearset  14  is compound, and therefore planet carrier member  30  rotatably supports a first set of planetary pinion gear members  34   a  that meshingly engage ring gear member  26 , and a second set of planetary pinion gear members  34   b  that meshingly engage the first set of planetary pinion gear members  34   a  and sun gear member  22 .  
         [0014]     Planetary gearsets  16 ,  18  together form a compound gearset  34 , and more particularly, compound gearset  34  is a Ravigneaux gearset. Planetary gearset  16  includes sun gear member  38  and ring gear member  42 . Planet carrier assembly  46  includes planet carrier member  50 , which rotatably supports planetary pinion gear members  54 . Planetary gearset  16  further includes planet carrier member  50  and planetary pinion gear members  54 , which meshingly engage ring gear member  42  and sun gear member  38 .  
         [0015]     Planetary gearset  18  includes sun gear member  58  and ring gear member  42 . Planet carrier assembly  46  further includes planetary pinion gear members  62 , which are rotatably mounted to planet carrier member  50 . Planetary gearset  18  further includes planet carrier member  50  and planetary pinion gear members  54 ,  62 . Planetary pinion gear members  62  meshingly engage sun gear member  58  and planetary pinion gear members  54 .  
         [0016]     It should be noted that, where used in the claims, first, second, third, and fourth members of a planetary gearset or a Ravigneaux gearset do not necessarily refer to a member of a particular type; thus, for example, a first member may be any one of a ring gear member, sun gear member, or planet carrier member.  
         [0017]     The transmission includes an input member such as input shaft  66 . Input shaft  66  is continuously connected to planet carrier member  30  for unitary rotation therewith. Input shaft  66  is connectable to an engine output member (not shown) such as a crankshaft, either directly or through a torque converter (not shown). Sleeve  70  is concentrically positioned around input shaft  66 , and is continuously connected to sun gear member  58  for unitary rotation therewith. Sleeve  74  is concentrically positioned around sleeve  70 , and is continuously connected to sun gear member  38  for unitary rotation therewith. An output member, such as output shaft  78 , is continuously connected to ring gear member  42  for unitary rotation therewith. Output shaft  78  is connectable to a vehicle final drive system (not shown) to drive vehicle wheels (not shown) or other tractive device.  
         [0018]     The transmission  10  includes a plurality of selectively engagable torque-transmitting devices, or clutches, C 1 -C 6 . Clutch C 1  is selectively engageable to couple ring gear member  26  to sleeve  70  and sun gear member  58  for unitary rotation. Clutch C 2  is a brake which is selectively engageable to ground planet carrier member  50  to a stationary member such as transmission housing  80 . Clutch C 3  is a brake which is selectively engageable to ground sleeve  74  and sun gear member  38  to housing  80 . Clutch C 4  is selectively engageable to couple ring gear member  26  to sleeve  74  and sun gear member  38  for unitary rotation. Clutch C 5  is selectively engageable to couple planet carrier member  30  to sleeve  74  and sun gear member  38  for unitary rotation. Clutch C 6  is selectively engageable to couple the input shaft  66  and planet carrier member  30  to planet carrier member  50  for unitary rotation.  
         [0019]     An electronic control unit (not shown) is preferably employed to control the engagement of the torque transmitting devices C 1 -C 6  via hydraulic actuation in a manner understood by those skilled in the art.  
         [0020]     Referring to  FIG. 2 , a shift logic sequence for clutches C 1 -C 6  is depicted that provides eight forward speed ratios and one reverse speed ratio between the input member  66  and the output member  78 . Referring to  FIGS. 1 and 2 , a first forward speed ratio is achieved when clutches C 1  and C 2  are engaged. A second forward speed ratio is achieved when clutches C 1  and C 3  are engaged. A third forward speed ratio is achieved when clutches C 1  and C 4  are engaged. A fourth forward speed ratio is achieved when clutches C 1  and C 5  are engaged. A fifth forward speed ratio is achieved when clutches C 1  and C 6  are engaged. A sixth forward speed ratio is achieved when clutches C 5  and C 6  are engaged. A seventh forward speed ratio is achieved when clutches C 4  and C 6  are engaged. An eighth forward speed ratio is achieved when clutches C 3  and C 6  are engaged. A reverse speed ratio is achieved when clutches C 2  and C 4  are engaged.  
         [0021]     It should be noted, as apparent from  FIG. 2 , that transmission  10  is characterized by single step speed ratio interchanges between adjacent forward speed ratios being accomplished by single transition shifting. It should be further noted that clutch C 2  may be used for friction launch to eliminate a torque converter between an engine output member and the input shaft  66 . Planetary gearset  14  generates an underdrive ratio.  
         [0022]     Referring to  FIG. 3 , wherein like reference numbers refer to like components from  FIG. 1 , an alternative transmission  10 ′ is schematically depicted. Transmission  10 ′ is similar to the transmission shown at  10  in  FIG. 1  except for the arrangement of the compound gearset. Compound gearset  34 ′ of transmission  10 ′ includes sun gear members  38 ,  58  and planet carrier member  50 . Compound gearset  34 ′ further includes a member, such as drum  82 , which rigidly interconnects ring gear members  42   a  and  42   b.  Planet carrier member  50  rotatably supports planetary pinion gear member  54   a,    54   b,  and  62 . Planetary pinion gear member  54   a  is meshingly engaged with ring gear member  42   a  and with sun gear member  38 . Planetary pinion gear member  54   b  is meshingly engaged with ring gear member  42   b. Planetary pinion gear member  58  is meshingly engaged with sun gear member  58  and planetary pinion gear member  42   b.  Output shaft  78  is continuously connected to drum  82  for unitary rotation therewith.  
         [0023]     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.