Abstract:
A six-speed transmission includes an input shaft, an output shaft, and a planetary gear arrangement having first, second and third planetary gear sets, each planetary gear set having first, second and third members. First and second interconnecting members continuously interconnect members of the planetary gear sets. The six torque-transmitting mechanisms are engaged in combinations of two to establish six forward speed ratios and at least one reverse speed ratio between the input shaft and the output shaft. The second and third sun gears hold the reaction torque in the first through fourth speeds, resulting in low planetary gear loading, which provides small gear sets, reduced clutch loading, reduced internal speeds, and low losses.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to a six-speed transmission having six torque-transmitting mechanisms which are engaged in combinations of two to provide at least one reverse speed ratio and six forward speed ratios.  
       BACKGROUND OF THE INVENTION  
       [0002]     Passenger vehicles include a powertrain that is comprised of an engine, 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 during cruising, other than the most efficient point. 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; U.S. Pat. No. 6,071,208 issued to Koivunen on Jun. 6, 2000; U.S. Pat. No. 5,106,352 issued to Lepelletier on Apr. 21, 1992; and U.S. Pat. No. 5,599,251 issued to Beim and McCarrick on Feb. 4, 1997.  
         [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. The Polak transmission provides six forward speed ratios with three planetary gear sets, two clutches, and three brakes. The Koivunen and Beim patents utilize six torque-transmitting devices including four brakes and two clutches to establish six forward speed ratios and a reverse ratio. The Lepelletier patent employs three planetary gear sets, three clutches and two brakes to provide six forward speeds. One of the planetary gear sets is positioned and operated to establish two fixed speed input members for the remaining two planetary gear sets.  
       SUMMARY OF THE INVENTION  
       [0006]     The invention provides an improved six-speed transmission having relatively low sun gear loading, which enables small gear sets, reduced clutch loading, reduced internal speeds, and reduced losses.  
         [0007]     The six-speed transmission includes six torque-transmitting mechanisms that are engaged in combinations of two to provide at least one reverse speed ratio and six forward speed ratios. The transmission is arranged to provide two dual clutch rotating modules to ensure good cooling on every shift. Medium, wide and narrow overall ratios are available with the different embodiments described. Also, because planetary gear loading is low, a fine tooth quiet planetary module design is achieved.  
         [0008]     More specifically, the invention provides a six-speed transmission including an input shaft, an output shaft, and a planetary gear arrangement having first, second and third planetary gear sets, each planetary gear set having first, second and third members. The input shaft is continuously connected with the first member of the first planetary gear set, and the output shaft is continuously connected with the second member of the second planetary gear set. A first interconnecting member continuously connects the first member of the second planetary gear set with the second member of the third planetary gear set. A second interconnecting member continuously connects the third member of the second planetary gear set with the third member of the third planetary gear set. The third member of the first planetary gear set is continuously connected with a stationary member. A first torque-transmitting mechanism selectively connects the first member of the first planetary gear set with the first member of the third planetary gear set. A second torque-transmitting mechanism selectively connects the first member of the first planetary gear set with the first member of the second planetary gear set. A third torque-transmitting mechanism selectively connects the second member of the first planetary gear set with the second member of the third planetary gear set. A fourth torque-transmitting mechanism selectively connects the second member of the first planetary gear set with the first member of the third planetary gear set. A fifth torque-transmitting mechanism selectively connects the second member of the third planetary gear set with the stationary member. A sixth torque-transmitting mechanism selectively connects the third member of the third planetary gear set with the stationary member.  
         [0009]     A first forward speed ratio is established with the engagement of the fourth and sixth torque-transmitting mechanisms; a second forward speed ratio is established with the engagement of the third and sixth torque-transmitting mechanisms; a third forward speed ratio is established with the engagement of the first and sixth torque-transmitting mechanisms; a fourth forward speed ratio is established with the engagement of the second and sixth torque-transmitting mechanisms; a fifth forward speed ratio is established with the engagement of the second and first torque-transmitting mechanisms; a sixth forward speed ratio is established with the engagement of the second and fourth torque-transmitting mechanisms; and a reverse speed ratio is established with the engagement of the fourth and fifth torque-transmitting mechanisms.  
         [0010]     In one embodiment, each of the first members is a ring gear, each of the second members is a planet carrier assembly member, and each of the third members is a sun gear. In this embodiment, the ring gear of the first planetary gear set has 85 teeth, the sun gear of the first planetary gear set has 55 teeth; the ring gear of the second planetary gear set has 81 teeth; the sun gear of the second planetary gear set has 21 teeth; the ring gear of the third planetary gear set has 81 teeth; and the sun gear of the third planetary gear set has 29 teeth.  
         [0011]     In another embodiment of the invention, the first, second and third members of the first planetary gear set are a planet carrier assembly member, a ring gear and a sun gear, respectively, and the first, second and third members of the second and third planetary gear sets are a ring gear, a planet carrier assembly member and a sun gear, respectively. In this embodiment, the ring gear of the first planetary gear set has 81 teeth; the sun gear of the first planetary gear set has 41 teeth; the ring gear of the second planetary gear set has 81 teeth; the sun gear of the second planetary gear set has 23 teeth; the ring gear of the third planetary gear set has 81 teeth; and the sun gear of the third planetary gear set has 35 teeth.  
         [0012]     In a further embodiment, the first, second and third members of the first planetary gear set are a sun gear, a planet carrier assembly member and a ring gear, respectively, and the first, second and third members of the second and third planetary gear sets are a ring gear, a planet carrier assembly member and a sun gear, respectively. In this embodiment, the ring gear of the first planetary gear set has 85 teeth; the sun gear of the first planetary gear set has 55 teeth; the ring gear of the second planetary gear set has 81 teeth; the sun gear of the second planetary gear set has 31 teeth; the ring gear of the third planetary gear set has 81 teeth; and the sun gear of the third planetary gear set has 49 teeth.  
         [0013]     The first, second and third planetary gear sets may all be simple planetary gear sets. Alternatively, the first planetary gear set is a compound planetary gear set, and the second and third planetary gear sets are simple planetary gear sets.  
         [0014]     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  
       [0015]      FIG. 1   a  is a stick diagram of a transmission in accordance with the invention;  
         [0016]      FIG. 1   b  is a truth table corresponding with the transmission of  FIG. 1   a;    
         [0017]      FIG. 2   a  is a stick diagram of a transmission in accordance with a first alternative embodiment of the invention;  
         [0018]      FIG. 2   b  is a truth table corresponding with the transmission of  FIG. 2   a;    
         [0019]      FIG. 3   a  is a stick diagram of a transmission in accordance with a second alternative embodiment of the invention; and  
         [0020]      FIG. 3   b  is a truth table corresponding with the transmission of  FIG. 3   a.   
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]     Referring to  FIG. 1   a , a stick diagram is shown for a narrow or close ratio transmission in accordance with the invention. As shown in  FIG. 1   a , a powertrain  10  includes a conventional engine and torque converter  12 , a planetary transmission  14 , and a conventional final drive mechanism  16 .  
         [0022]     The planetary transmission  14  includes an input shaft  17  continuously connected with the engine and torque converter  12 , a planetary gear arrangement  18 , and an output shaft  19  continuously connected with the final drive mechanism  16 . The planetary gear arrangement  18  includes three planetary gear sets  20 ,  30  and  40 .  
         [0023]     The planetary gear set  20  includes a sun gear member  22 , a ring gear member  24  and planet carrier assembly member  26 . The planet carrier assembly member  26  includes a plurality of pinion gears  27  rotatably mounted on a carrier member  29  and disposed in meshing relationship with both the sun gear member  22  and the ring gear member  24 .  
         [0024]     The planetary gear set  30  includes a sun gear member  32 , a ring gear member  34  and a planet carrier assembly member  36 . The planet carrier assembly member  36  includes a plurality of pinion gears  37  rotatably mounted on a carrier member  39  and disposed in meshing relationship with both the sun gear member  32  and the ring member  34 .  
         [0025]     The planetary gear set  40  includes a sun gear member  42 , a ring gear member  44  and a planet carrier assembly member  46 . The planet carrier assembly member  46  includes a plurality of pinion gears  47  rotatably mounted on a carrier member  49  and disposed in meshing relationship with both the sun gear member  42  and the ring gear member  44 .  
         [0026]     In this embodiment, each of the planetary gear sets  20 ,  30  and  40  are simple planetary gear sets.  
         [0027]     The planetary gear arrangement  18  also includes six torque-transmitting mechanisms  80 ,  82 ,  84 ,  86 ,  88 ,  89 . The torque-transmitting mechanisms  80 ,  82 ,  84 ,  86  are rotating-type torque-transmitting mechanisms, commonly termed clutches. The torque-transmitting mechanisms  88 ,  89  are stationary-type torque-transmitting mechanisms, commonly termed brakes or reaction clutches.  
         [0028]     The input shaft  17  is continuously connected with the ring gear member  24 , and the output shaft  19  is continuously connected with the planet carrier assembly member  36 . A first interconnecting member  70  continuously connects the ring gear member  34  with the planet carrier assembly member  46 . A second interconnecting member  72  continuously connects the sun gear member  32  with the sun gear member  42 . The sun gear member  22  is continuously connected with the transmission housing  60 .  
         [0029]     As referred to in the claims, the planetary gear set  20  is the first planetary gear set, the planetary gear set  30  is the second planetary gear set, and the planetary gear set  40  is the third planetary gear set. Also referenced in the claims are first, second and third members of each planetary gear set. In this embodiment, each first member is a ring gear, each second member is a planet carrier assembly member, and each third member is a sun gear. Also, the torque-transmitting mechanism  80  is referred to as the first torque-transmitting mechanism, the torque-transmitting mechanism  82  is the second torque-transmitting mechanism, the torque-transmitting mechanism  84  is the third torque-transmitting mechanism, the torque-transmitting mechanism  86  is the fourth torque-transmitting mechanism, the torque-transmitting mechanism  88  is the fifth torque-transmitting mechanism, and the torque-transmitting mechanism  89  is the sixth torque-transmitting mechanism.  
         [0030]     The ring gear member  24  is selectively connectable with the ring gear member  44  through the clutch  80 . The ring gear member  24  is selectively connectable with the ring gear member  34  through the clutch  82 . The planet carrier assembly member  26  is selectively connectable with the planet carrier assembly member  46  through the clutch  84 . The planet carrier assembly member  26  is selectively connectable with the ring gear member  44  through the clutch  86 . The planet carrier assembly member  46  is selectively connectable with the transmission housing  60  through the brake  88 . The sun gear member  42  is selectively connectable with the transmission housing  60  through the brake  89 .  
         [0031]     As shown in the truth table of  FIG. 1   b , the torque-transmitting mechanisms  80 ,  82 ,  84 ,  86 ,  88 ,  89  are selectively engaged in combinations of two to provide six forward speed ratios and two reverse speed ratios. It should be noted that each of the speed shifts is a single transition shift.  
         [0032]     To establish the reverse # 2  speed ratio, the clutch  80  and brake  88  are engaged. The overall numerical value of the reverse # 2  speed ratio is −1.739, as indicated in the truth table of  FIG. 1   b.    
         [0033]     To establish the reverse # 1  speed ratio, the clutch  86  and brake  88  are engaged. The overall numerical value of the reverse # 1  speed ratio is −2.864, as indicated in the truth table.  
         [0034]     The first forward speed ratio is established with the engagement of the clutch  86  and the brake  89 . The overall numerical value of the first forward speed ratio is 2.817, as indicated in the truth table.  
         [0035]     The second forward speed ratio is established with the engagement of the clutch  84  and the brake  89 . The overall numerical value of the second forward speed ratio is 2.074, as indicated in the truth table.  
         [0036]     The third forward speed ratio is established with the engagement of the clutch  80  and brake  89 . The overall numerical value of the third forward speed ratio is 1.710, as indicated in the truth table.  
         [0037]     The fourth forward speed ratio is established with the engagement of the clutch  82  and brake  89 . The overall numerical value of the fourth forward speed ratio is 1.259, as indicated in the truth table.  
         [0038]     The fifth forward speed ratio is established with the engagement of the clutches  80  and  82 . The overall numerical value of the fifth forward speed ratio is 1, as indicated in the truth table.  
         [0039]     The sixth forward speed ratio is established with the engagement of the clutches  82  and  86 . The overall numerical value of the sixth forward speed ratio is 0.816, as indicated in the truth table.  
         [0040]     As set forth above, the engagement schedules of the torque-transmitting mechanisms are shown in the truth table of  FIG. 1   b . This table also provides an example of speed ratios that are available using preferred ring gear/sun gear tooth ratios. The ring gear/sun gear tooth ratio of the planetary gear set  20  is preferably 85/55; the ring gear/sun gear tooth ratio of the planetary gear set  30  is preferably 81/21; and the ring gear/sun gear tooth ratio of the planetary gear set  40  is preferably 81/29. The truth table of  FIG. 1   b  also describes the ratio steps that are attained using the sample tooth ratios given. For example, the step ratio between the first and second forward ratios is 1.36. Again, as illustrated in the truth table of  FIG. 1   b , all of the single step forward ratio interchanges are of the single transition variety. The overall ratio of the transmission of  FIG. 1   a  is 3.453, as indicated in the truth table.  
         [0041]     Turning to  FIGS. 2   a  and  2   b , an alternative embodiment of a powertrain  110  is shown in accordance with the invention. This embodiment is in most respects similar to that of  FIG. 1   a , except that the first planetary gear set has been reconfigured as a compound planetary gear set. Like reference numbers are used to refer to like components in  FIGS. 1   a  and  2   a . As shown in  FIG. 2   a , a powertrain  110  includes a conventional engine and torque converter  12 , a planetary transmission  114 , and a conventional final drive mechanism  16 .  
         [0042]     The planetary transmission  114  includes an input shaft  17  continuously connected with the engine and torque converter  12 , a planetary gear arrangement  118 , and an output shaft  19  continuously connected with the final drive mechanism  16 . The planetary gear arrangement  118  includes three planetary gear sets  120 ,  130  and  140 .  
         [0043]     The planetary gear set  120  is a compound planetary gear set, and includes a sun gear member  122 , a ring gear member  124 , and a planetary gear set  126 . The planetary gear set  126  includes a plurality of pinion gears  127 ,  128  rotatably mounted on carrier member  129 . The pinion gears  127  are in meshing engagement with the ring gear member  124 , and the pinion gears  128  are in meshing engagement with the sun gear member  122 .  
         [0044]     The planetary gear set  130  includes a sun gear member  132 , a ring gear member  134 , and a planetary gear set  136 . The planet carrier assembly member  136  includes a plurality of pinion gears  137  rotatably mounted on a carrier member  139  and disposed in meshing relationship with both the sun gear member  132  and the ring gear member  134 .  
         [0045]     The planetary gear set  140  includes a sun gear member  142 , a ring gear member  144 , and a planet carrier assembly member  146 . The planet carrier assembly member  146  includes a plurality of pinion gears  147  rotatably mounted on a carrier member  149  in meshing engagement with the ring gear  144  and the sun gear member  142 .  
         [0046]     The planetary gear arrangement  118  also includes six torque-transmitting mechanisms  180 ,  182 ,  184 ,  186 ,  188 , and  189 . The torque-transmitting mechanisms  180 ,  182 ,  184  and  186  are rotating-type torque-transmitting mechanisms, and the torque-transmitting mechanisms  188  and  189  are brakes.  
         [0047]     The input shaft  17  is continuously connected with the planet carrier assembly member  126 , and the output shaft  19  is continuously connected with the planet carrier assembly member  136 . A first interconnecting member  170  continuously connects the ring gear member  134  with the planet carrier assembly member  146 . A second interconnecting member  172  continuously connects the sun gear member  132  with the sun gear member  142 . The sun gear member  122  is continuously connected with the transmission housing  160 .  
         [0048]     As referred to in the claims, the first, second and third planetary gear sets are the planetary gear sets  120 ,  130  and  140 , respectively. The planet carrier assembly member  126  is the first member of the first planetary gear set  120 , the ring gear member  124  is the second member of the first planetary gear set  120 , and the sun gear member  122  is the third member of the first planetary gear set  120 . In the planetary gear sets  130 ,  140 , the first, second and third members are ring gear members, planet carrier assembly members, and sun gear members, respectively.  
         [0049]     The planet carrier assembly member  126  is selectively connectable with the ring gear member  144  through the clutch  180 . The planet carrier assembly member  126  is selectively connectable with the ring gear member  134  through the clutch  182 . The ring gear member  124  is selectively connectable with the planet carrier assembly member  146  through the clutch  184 . The ring gear member  124  is selectively connectable with the ring gear member  144  through the clutch  186 . The planet carrier assembly member  146  is selectively connectable with the transmission housing  160  through the brake  188 . The sun gear member  142  is selectively connectable with the transmission housing  160  through the brake  189 .  
         [0050]     The reverse # 2 , reverse # 1 , first, second, third, fourth, fifth and sixth speeds are achieved by the clutching engagements shown in the truth table shown in  FIG. 2   b , which is the same as that of  FIG. 1   b  described previously. The truth table of  FIG. 2   b  also provides examples of speed ratios that are available using preferred ring gear/sun gear tooth ratios. The speed ratios illustrated in  FIG. 2   b  correspond with the following ring gear/sun gear tooth ratios: the ring gear/sun gear tooth ratio of the planetary gear set  120  is 81/41; the ring gear/sun gear tooth ratio of the planet carrier assembly member  130  is 81/23; and the ring gear/sun gear tooth ratio of the planet carrier assembly member  140  is 81/35. The truth table of  FIG. 2   b  also describes the ratio steps that are attained utilizing the sample tooth ratios given. For example, the step ratio between the first and second forward speed ratios is 1.43. The overall ratio for this transmission is 4.68 as indicated in the truth table. Like the embodiment of  FIG. 1   b , it can also be readily determined from the truth table of  FIG. 2   b  that all of the single step forward ratio interchanges are of the single transition variety.  
         [0051]     Turning to  FIGS. 3   a  and  3   b , a second alternative embodiment of the invention is shown. This embodiment is similar to that of  FIG. 1   a , except that the connections for the first planetary gear set have been rearranged. The sequence of operation described in the truth table of  FIG. 3   b  is the same as that of  FIGS. 1   b  and  2   b . Again, like reference numbers are used to refer to like components in  FIGS. 1   a ,  2   a  and  3   a.    
         [0052]     As shown in  FIG. 3   a , a powertrain  210  includes a conventional engine and torque converter  12 , a planetary transmission  21 , and a conventional final drive mechanism  16 .  
         [0053]     The planetary transmission  214  includes an input shaft  17  continuously connected with the engine and torque converter  12 , a planetary gear arrangement  218 , and output shaft  19  continuously connected with the final drive mechanism  16 . The planetary gear arrangement  218  includes three planetary gear set  220 ,  230  and  240 .  
         [0054]     The planetary gear set  220  includes a sun gear member  222 , a ring gear member  224 , and a planet carrier assembly member  226 . The planet carrier assembly member  226  includes a plurality of pinion gears  227  rotatably mounted on a carrier member  229  and disposed in meshing relationship with both the sun gear member  222  and the ring gear member  224 .  
         [0055]     The planetary gear set  230  includes a sun gear member  232 , a ring gear member  234 , and a planet carrier assembly member  236 . The planet carrier assembly member  236  includes a plurality of pinion gears  237  rotatably mounted on a carrier member  239  and disposed in meshing relationship with both the sun gear member  232  and the ring gear member  234 .  
         [0056]     The planetary gear set  240  includes a sun gear member  242 , a ring gear member  244 , and a planet carrier assembly member  246 . The planet carrier assembly member  246  includes a plurality of pinion gears  247  rotatably mounted on a carrier member  249  and disposed in meshing relationship with both the sun gear member  242  and the ring gear member  244 .  
         [0057]     Each of the planetary gear sets  220 ,  230  and  240  is a simple planetary gear set.  
         [0058]     The planetary gear arrangement  218  also includes six torque-transmitting mechanisms  280 ,  282 ,  284 ,  286 ,  288 , and  289 . The torque-transmitting mechanisms  280 ,  282 ,  284  and  286  are rotating-type torque-transmitting mechanisms, commonly termed clutches, and the torque-transmitting mechanisms  288 ,  289  are stationary-type torque-transmitting mechanisms, commonly termed brakes or reaction clutches.  
         [0059]     The input shaft  17  is continuously connected with the sun gear member  222 , and the output shaft  19  is continuously connected with the planet carrier assembly member  236 . A first interconnecting member  270  continuously connects the ring gear member  234  with the planet carrier assembly member  246 . A second interconnecting member  272  continuously connects the sun gear member  232  with the sun gear member  242 . The ring gear member  224  is continuously connected with the transmission housing  260 .  
         [0060]     As referred to in the claims, the first, second and third planetary gear sets are the planetary gear sets  220 ,  230  and  240 , respectively. The sun gear member  222  is the first member of the first planetary gear set, the planet carrier assembly member  226  is the second member of the first planetary gear set, and the ring gear member  224  is the third member of the first planetary gear set. In the planetary gear sets  230  and  240 , the first, second and third members are the ring gear member, planet carrier assembly member, and sun gear member, respectively.  
         [0061]     The sun gear member  222  is selectively connectable with the ring gear member  244  through the clutch  280 . The sun gear member  222  is selectively connectable with the ring gear member  234  through the clutch  282 . The planet carrier assembly member  226  is selectively connectable with the planet carrier assembly member  246  through the clutch  284 . The planet carrier assembly member  226  is selectively connectable with the ring gear member  244  through the clutch  286 . The planet carrier assembly member  246  is selectively connectable with the transmission housing  260  through the brake  288 . The sun gear member  242  is selectively connectable with the transmission housing  260  through the brake  289 .  
         [0062]     As shown in the truth table of  FIG. 3   b , the torque-transmitting mechanisms  280 ,  282 ,  284 ,  286 ,  288  and  289  are selectively engaged in combinations of two to provide six forward speed ratios and two reverse speed ratios, in the same sequence of engagement described previously with respect to  FIGS. 1   b  and  2   b . The table also provides an example of speed ratios that are available using the following ring gear/sun gear tooth ratios, given by way of example: the ring gear/sun gear tooth ratio of the planetary gear set  220  is 85/55; the ring gear/sun gear tooth ratio of the planetary gear set  230  is 81/31; and the ring gear/sun gear tooth ratio of the planetary gear set  240  is 81/49. The truth table of  FIG. 3   b  also describes the ratio steps that are attained utilizing the sample tooth ratios given. For example, the step ratio between the first and second forward ratios is 1.60. The overall ratio for this wide ratio six speed is 7.218, as indicated in the truth table.  
         [0063]     Accordingly, the various embodiments of the invention described by way of example provide wide, medium and narrow ratio transmissions which are compatible with high speed, low torque engines. Because the sun gears of the second and third planetary gear sets are grounded in the first through fourth speed ratios, planetary gear loading is low, enabling fine tooth quiet planetary module design. Clutch loading is also very low, enabling a compact design and a small transmission diameter.  
         [0064]     While the best modes for carrying out the invention have been described in detail, the 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.