Abstract:
A transmission is provided having four planetary gearsets, each having respective first, second, and third members, and a plurality of selectively engageable torque transmitting devices configured to selectively interconnect selected members of the four planetary gearsets 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 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, a stationary member, and first, second, third, and fourth planetary gearsets. Each of the gearsets has respective first, second, and third members. The first member of the first planetary gearset is continuously connected to the first member of the third planetary gearset for unitary rotation. The first member of the second planetary gearset is continuously operatively connected to the second member of the third planetary gearset for unitary rotation. The second member of the first planetary gearset is continuously operatively connected to the second member of the second planetary gearset for unitary rotation. The second member of the third planetary gearset is continuously operatively connected to the first member of the fourth planetary gearset for unitary rotation. The third member of the third planetary gearset is continuously operatively connected to the third member of the fourth planetary gearset for unitary rotation. The second member of the first planetary gearset is continuously operatively connected to the input member for unitary rotation. The second member of the fourth planetary gearset is continuously operatively connected to the output member for unitary rotation.  
         [0008]     First, second, third, fourth, fifth, and sixth torque transmitting devices are operative to selectively connect members of the planetary gearsets with the input member, the stationary member, or with other members of the planetary gearsets. The transmission thus described enables at least six forward speed ratios and two reverse speed ratios according to one torque transmitting device engagement sequence, and seven forward speed ratios and one reverse speed ratio according to another torque transmitting device engagement sequence. The transmission provided enables low internal loading, slow internal speeds, and only one overdrive in the arrangement for transversely mounted engines.  
         [0009]     In an exemplary embodiment, the first torque transmitting device is configured to selectively couple the second member of the first planetary gearset and the second member of the second planetary gearset with 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 stationary member. The third torque transmitting device is configured to selectively couple the first member of the fourth planetary gearset with the stationary member. The fourth torque transmitting device is configured to selectively couple the third member of the second planetary gearset with the stationary member. The fifth torque transmitting device is configured to selectively couple the third member of the third planetary gearset and the third member of the fourth planetary gearset with the stationary member. The sixth torque transmitting device is configured to selectively couple the second member of the first planetary gearsert and the second member of the second planetary gearset with a member of the third planetary gearset for unitary rotation.  
         [0010]     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  
       [0011]      FIG. 1  is a schematic representation of a planetary transmission in accordance with the present invention;  
         [0012]      FIG. 2  is a ratio chart and truth table depicting a first shift logic for use with the transmission of  FIG. 1 ;  
         [0013]      FIG. 3  is a ratio chart and truth table depicting a second shift logic for use with the transmission of  FIG. 1 ;  
         [0014]      FIG. 4  is a schematic representation of a second embodiment of a planetary transmission in accordance with the present invention;  
         [0015]      FIG. 5  is a ratio chart and truth table depicting a shift logic for use with the transmission of  FIG. 4 ; and  
         [0016]      FIG. 6  is a schematic representation of a third embodiment of a planetary transmission in accordance with the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     Referring to  FIG. 1 , a vehicle transmission  10  is schematically depicted. The transmission  10  includes four planetary gear sets  12 ,  14 ,  16 ,  18 . Each of the planetary gear sets includes respective first, second and third members. More specifically, planetary gear set  12  includes sun gear member  20 , ring gear member  22  and planet carrier assembly member  24 . Planetary gearset  12  is compound and thus planet carrier assembly member  24  rotatably supports a first set of planet gear members  26   a,  which meshingly engage sun gear member  20 . Planet carrier assembly member  24  also rotatably supports a second set of planet gears  26   b,  which meshingly engage the first set of planet gears  26   a  and ring gear member  22 .  
         [0018]     Planetary gear set  14  includes sun gear member  28 , ring gear member  30 , and planet carrier assembly member  24 . Planet carrier assembly member  24  is common to both planetary gear sets  12  and  14 , and thus the planet carrier assembly member of the first planetary gearset  12  is connected to the planet carrier assembly member of the second planetary gearset  14  for unitary rotation. Alternatively, and within the scope of the claimed invention, planetary gearsets  12 ,  14  may include individual planet carriers that are interconnected for unitary rotation. Planet carrier assembly member  24  rotatably supports a first set of planet gear members  32   a,  which meshingly engage sun gear member  28 , and a second set of planet gear members  32   b,  which meshingly engage the first set of planet gear members  32   a  and ring gear member  30 .  
         [0019]     Planetary gear set  16  includes sun gear member  34 , ring gear member  36  and planet carrier assembly member  38 . Planet carrier assembly member  38  rotatably supports planet gears  40 , which meshingly engage sun gear member  34  and ring gear member  36 . Planetary gear set  18  includes sun gear member  42 , ring gear member  44 , and planet carrier assembly member  46 . Planet carrier assembly member  46  rotatably supports planet gears  48 , which meshingly engage sun gear member  42  and ring gear member  44 .  
         [0020]     Sun gear member  34  and sun gear member  42  are continuously operatively connected for unitary rotation by an interconnecting member such as shaft  50 . Sleeve  52 , which is the transmission input member, is connected to planet carrier assembly member  24  for unitary rotation therewith. Input member  52  is connectable to the output member of an engine (not shown), such as a crankshaft, either directly or through a torque converter (not shown). Sleeve  54 , which is located radially outward from sleeve  52 , is connected to sun gear member  28  for rotation therewith. Sleeve  56 , which is radially outward from sleeve  54 , is connected to sun gear member  20  for rotation therewith. Interconnecting member  58  operatively connects ring gear member  36  and ring gear member  22  for unitary rotation. Ring gear member  30  is connected to planet carrier assembly member  38  for unitary rotation therewith. Planet carrier  38  is connected to the ring gear member  44  via sleeve  62  for unitary rotation. The transmission  10  includes an output member, such as output shaft  60 . Output shaft  60  is connected to planet carrier assembly member  46  for unitary rotation therewith. Output shaft  60  is connectable to a vehicle final drive system to drive vehicle wheels or other tractive device.  
         [0021]     It should be noted that, where used in the claims, first, second, and third members of planetary gearsets 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 assembly member. Similarly, as used in the claims, the respective first, second, or third members of two or more gearsets may or may not be the same type of member.  
         [0022]     The transmission  10  includes a plurality of selectively engagable torque-transmitting devices, or clutches, C 1 -C 8 . Clutch C 1  is selectively engageble to interconnect the planet carrier assembly member  24  and the input member  52  with shaft  50  and sun gear members  34 ,  42  for unitary rotation. Clutch C 2  is selectively engageable to interconnect planet carrier assembly member  24  and input member  52  with planet carrier assembly member  38  for unitary rotation. Planet carrier assembly member  38  is connected to ring gear member  44  for unitary rotation therewith by interconnecting member  62 . Thus engagement of clutch C 2  further causes the interconnection of ring gear member  44  with planet carrier assembly member  24  and input member  52  for unitary rotation. Clutch C 3  is a brake which is selectively engageable to ground sleeve  56  and sun gear member  20  to a stationary member such as housing  62 . Clutch C 4  is a brake that is selectively engageable to ground interconnecting member  58 , ring gear member  22 , and ring gear member  36  to housing  62 . Clutch C 5  is a brake that is selectively engageable to ground ring gear member  44  and planet carrier assembly member  38  to housing  62 . Clutch C 6  is a brake that is selectively engageable to ground sleeve  54  and sun gear member  28  to housing  62 . Clutch C 7  is a brake that is selectively engageable to ground shaft  50 , sun gear member  34  and sun gear member  42  to housing  62 . Clutch C 8  is selectively engageable to connect member  58 , ring gear member  22 , and ring gear member  36  with planet carrier assembly member  24  and input member  52  for unitary rotation.  
         [0023]     Sun gear member  20  preferably has 39 teeth, ring gear member  22  preferably has 81 teeth, sun gear member  28  preferably has 39 teeth, ring gear member  30  preferably has 81 teeth, sun gear member  34  preferably has 37 teeth, ring gear member  36  preferably has 81 teeth, sun gear member  42  preferably has 26 teeth and ring gear member  44  preferably has 81 teeth.  
         [0024]     Transmission  10  is characterized by two optimal shift logic sequences.  FIG. 2  depicts a first optimal shift logic sequence “A” to achieve seven forward speed ratios and two reverse ratios between the input member  52  and the output member  60 . Referring to  FIGS. 1 and 2 , a first speed ratio is achieved when clutches C 3  and C 7  are engaged and when C 1 , C 2 , C 4 -C 6 , and C 8  are disengaged. A second speed ratio is achieved when clutches C 6  and C 7  are engaged and clutches C 1 -C 5  and C 8  are disengaged. A third speed ratio is achieved when clutches C 8  and C 7  are engaged and when clutches C 1 -C 6  are disengaged. A fourth speed ratio is achieved when clutches C 2  and C 7  are engaged and clutches C 1 , C 3 -C 6 , and C 8  are disengaged. A fifth speed ratio is achieved when clutches C 2  and C 8  are engaged, and clutches C 1 , C 3 -C 7  are disengaged. A sixth speed ratio is achieved when clutches C 2  and C 3  are engaged and when clutches C 1 , and C 4 -C 8  are disengaged. A seventh speed ratio is achieved when clutches C 2  and C 4  are engaged and when clutches C 1 , C 3 , and C 5 -C 8  are disengaged. A first reverse speed ratio is achieved when clutches C 3  and C 5  are engaged and when clutches C 1 , C 2 , C 4 , and C 6 -C 8  are disengaged. A second reverse speed ratio is achieved when clutches C 8  and C 5  are engaged and when clutches C 1 -C 4 , and C 6 -C 7  are disengaged. The first shift logic sequence, i.e., shift logic A, as shown in  FIG. 2  is usable for transverse or rear drive. It should be noted that clutch C 1  is not employed in shift logic “A.” 
         [0025]     Referring to  FIGS. 1 and 3 , the second shift logic sequence “B” is depicted. Using shift logic B, a first speed ratio is achieved when clutches C 3  and C 7  are engaged and when clutches C 1 , C 2 , C 4 -C 6 , and C 8  are disengaged. A second speed ratio is achieved when clutches C 6  and C 7  are engaged and when clutches C 1 -C 5  and C 8  are disengaged. A third speed ratio is achieved when clutches C 3  and C 6  are engaged and when clutches C 1 , C 2 , C 4 , C 5 , C 7 , and C 8  are disengaged. A fourth speed ratio is achieved when clutches C 1  and C 6  are engaged and when clutches C 2 -C 5 , and C 7 -C 8  are disengaged. A fifth speed ratio is achieved when clutches C 1  and C 3  are engaged and when clutches C 2 , and C 4 -C 8  are disengaged. A sixth speed ratio is achieved when clutches C 1  and C 2  are engaged and when clutches C 3 -C 8  are disengaged. A seventh speed ratio is achieved with clutches C 2  and C 3  are engaged and when clutches C 1 , and C 4 -C 8  are disengaged. An eighth speed ratio is achieved when clutches C 2  and C 4  are engaged and when clutches C 1 , C 3 , and C 5 -C 8  are disengaged. A reverse ratio is achieved when clutches C 3  and C 5  are engaged and when clutches C 1 , C 2 , C 4 , and C 6 -C 8  are disengaged. Referring again to  FIG. 2 , is should be noted that by omitting clutch C 4 , six speed ratios are achievable, i.e., speed ratios 1-6. Referring again to  FIG. 3 , it should be noted that clutch C 8  is not employed in shift logic “B.” Further, clutch C 4  may be omitted whereby seven speed ratios are achieved in shift logic “B,” i.e., speed ratios 1-7.  
         [0026]     Referring to  FIG. 4 , wherein like reference numbers refer to like components from  FIG. 1 , an alternative transmission  10 ′ for use with transverse or rear drive is schematically depicted. Transmission  10 ′ is similar to the transmission  10  of  FIG. 1 , except the arrangement of planetary gearset  16  has been modified to move clutch C 7  between planetary gearsets  16  and  18  so the input member  52 ′ can be located in line with the output member  60 ′. Clutch C 1  is eliminated. Input member  52 ′ is a shaft that is coextensive with the centerline of the transmission  10 ′ and the axis of rotation. Interconnecting member  64  operatively connects ring gear member  30  with planet carrier assembly member  38  and sun gear member  44  for unitary rotation. Interconnecting member  62 ′ is a shaft that is coextensive with the centerline of the transmission  10 ′ and interconnects ring gear member  44  and planet carrier  38 .  FIG. 5  depicts a shift logic sequence identical to shift logic sequence A of  FIG. 1  that is preferably employed with transmission  10 ′, but with different speed ratios achieved. Because of the absence of clutch C 1  in transmission  10 ′, shift logic B as shown in  FIG. 3  is not usable in transmission  10 ′. Transmission  10 ′ is characterized by low sun gear loading, which allows for fine pitch helical gearing, uniform ratio steps, reduced clutch torques, which improves frictional spin losses, and planet and carrier speeds that are conducive to high-speed engines.  
         [0027]     Referring to  FIG. 6 , wherein like reference numbers refer to like components from  FIGS. 1 and 4 , another alternative transmission  10 ″ is schematically depicted. Transmission  10 ″ is similar to transmission  10  of  FIG. 1 , except that the input member  52 ″ extends between clutch C 3  and planet carrier assembly member  24 , which results in the removal of clutch C 8 . With the absence of clutch C 8 , shift logic sequence “B” of  FIG. 2  is preferably employed with transmission  10 ″.  
         [0028]     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.