Abstract:
The transmission has a plurality of members that can be utilized in powertrains to provide at least eight forward speed ratios and one reverse speed ratio. The transmission includes four planetary gear sets having seven torque-transmitting mechanisms, four fixed interconnections, and a stationary (grounded) member. The powertrain includes an engine and torque converter that is selectively connected to at least one of the planetary gear members and an output member that is continuously connected with another one of the planetary gear members. The seven torque-transmitting mechanisms provide interconnections between various gear members and with the transmission housing, and are operated in combinations of two to establish at least eight forward speed ratios and at least one reverse speed ratio.

Description:
TECHNICAL FIELD 
     The present invention relates to a family of power transmissions having four planetary gear sets that are controlled by seven torque-transmitting devices to provide at least eight forward speed ratios and at least one reverse speed ratio. 
     BACKGROUND OF THE INVENTION 
     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. 
     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. 
     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-, 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 
     It is an object of the present invention to provide an improved family of transmissions having four planetary gear sets controlled to provide at least eight forward speed ratios and at least one reverse speed ratio. 
     The electrically variable transmission family of the present invention has four planetary gear sets, each of which includes a first, second and third member, which members may comprise a sun gear, a ring gear, or a planet carrier assembly member, in any order. 
     In referring to the first, second, third and fourth gear sets in this description and in the claims, these sets may be counted “first” to “fourth” in any order in the drawings (i.e., left to right, right to left, etc.). Additionally, the first, second or third members of each gear set may be counted “first” to “third” in any order in the drawings (i.e., top to bottom, bottom to top, etc.) for each gear set. 
     Each carrier member can be either a single-pinion carrier member (simple) or a double-pinion carrier member (compound). 
     A first interconnecting member continuously connects the first member of the first planetary gear set with the first member of the second planetary gear set and with the first member of the third planetary gear set. 
     A second interconnecting member continuously connects the second member of the first planetary gear set with the second member of the third planetary gear set and with the first member of the fourth planetary gear set. 
     A third interconnecting member continuously connects the third member of the first planetary gear set with the second member of the fourth planetary gear set. 
     A fourth interconnecting member continuously connects the second member of the second planetary gear set with the third member of the third planetary gear set. 
     The input shaft is selectively connected with at least one member of the planetary gear sets. The output shaft is continuously connected with at least one member of the planetary gear sets. 
     A first torque transmitting device, such as an input clutch, selectively interconnects a member of the fourth planetary gear set with the input member. 
     A second torque transmitting device, such as an input clutch, selectively connects a member of the first planetary gear set with the input member. 
     A third torque transmitting device, such as a brake, selectively connects a member of the fourth planetary gear set with a stationary member (transmission housing/casing). 
     A fourth torque transmitting device, such as a brake, selectively connects the third interconnecting member with a stationary member (transmission housing/casing). 
     A fifth torque transmitting device, such as a brake, selectively connects the second interconnecting member with a stationary member (transmission housing/casing). 
     A sixth torque transmitting device, such as a brake, selectively connects the fourth interconnecting member with a stationary member (transmission housing/casing). 
     A seventh torque transmitting device, such as a brake, selectively connects a member of the second planetary gear set with a stationary member. 
     The seven torque-transmitting mechanisms are selectively engageable in combinations of two to yield at least eight forward speed ratios and at least one reverse speed ratio. 
     This transmission arrangement ensures that no more than one input clutch is open during operation, leading to low transmission spin losses. 
     A variety of speed ratios and ratio spreads can be realized by suitably selecting the tooth ratios of the planetary gear sets. 
     The above features 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   a  is a schematic representation of a powertrain including a planetary transmission in accordance with the present invention; and 
         FIG. 1   b  is a truth table and chart depicting some of the operating characteristics of the powertrain shown in  FIG. 1   a.    
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawing, there is shown in  FIG. 1   a  a powertrain  10  having a conventional engine and torque converter  12 , a planetary transmission  14 , and a conventional final drive mechanism  16 . The engine  12  may be powered using various types of fuel to improve the efficiency and fuel economy of a particular application. Such fuels may include, for example, gasoline; diesel; ethanol; dimethyl ether; etc. 
     The planetary transmission  14  includes an input shaft  17  continuously connected with the engine  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 four planetary gear sets  20 ,  30 ,  40  and  50 . 
     The planetary gear set  20  includes a sun gear member  22 , a ring gear member  24 , and a 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 . 
     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 ,  38  rotatably mounted on a carrier member  39 . The pinion gears  37  are disposed in meshing relationship with the ring gear member  34 . The pinion gears  38  are disposed in meshing relationship both the sun gear member  32  and the respective pinion gear  37 . 
     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 ,  48  rotatably mounted on a carrier member  49 . The pinion gears  47  are disposed in meshing relationship with the ring gear member  44 . The pinion gears  48  are disposed in meshing relationship with both the sun gear member  42  and the respective pinion gear  47 . 
     The planetary gear set  50  includes a sun gear member  52 , a ring gear member  54  and a planet carrier assembly member  56 . The planet carrier assembly member  56  includes a plurality of pinion gears  57  rotatably mounted on a carrier member  59  and disposed in meshing relationship with both the sun gear member  52  and the ring gear member  54 . 
     The planetary gear arrangement also includes seven torque-transmitting mechanisms  80 ,  82 ,  84 ,  85 ,  86 ,  87  and  88 . The torque-transmitting mechanisms  80  and  82  are rotating-type torque-transmitting mechanisms, commonly termed clutches. The torque-transmitting mechanisms  84 ,  85 ,  86 ,  87  and  88  are stationary-type torque-transmitting mechanisms, commonly termed brakes or reaction clutches. 
     The output shaft  19  is continuously connected with the ring gear member  24 . The first interconnecting member  70  continuously connects the ring gear member  24  of the planetary gear set  20  with the sun gear member  32  of the planetary gear set  30  and with the ring gear member  44  of the planetary gear set  40 . A second interconnecting member  72  continuously connects the planet carrier assembly member  26  of the planetary gear set  20  with the sun gear member  42  of the planetary gear set  40  and with the ring gear member  54  of the planetary gear set  50 . A third interconnecting member  74  continuously connects the sun gear member  22  of the planetary gear set  20  with the planet carrier assembly member  56  of the planetary gear set  50 . A fourth interconnecting member  76  continuously connects the ring gear member  34  of the planetary gear set  30  with the planet carrier assembly member  46  of the planetary gear set  40 . 
     A first torque transmitting device, such as clutch  80 , selectively connects the planet carrier assembly member  56  with the input member  17 . A second torque transmitting device, such as clutch  82 , selectively connects the planet carrier assembly member  26  with the input member. A third torque transmitting device, such as brake  84 , selectively connects the sun gear member  52  with the transmission housing  60 . A fourth torque transmitting device, such as brake  85 , selectively connects the sun gear member  22  and the planet carrier assembly member  56  via interconnecting member  74  with the transmission housing  60 . A fifth torque transmitting device, such as brake  86 , selectively connects the planet carrier assembly member  26 , sun gear member  42  and the ring gear member  54  via interconnecting member  72  with the transmission housing  60 . A sixth torque transmitting device, such as brake  87 , selectively connects the ring gear member  34  and the planet carrier assembly member  46  via interconnecting member  76  with the transmission housing  60 . A seventh torque transmitting device, such as brake  88 , selectively connects the planet carrier assembly member  36  with the transmission housing  60 . 
     As shown in  FIG. 1   b , and in particular the truth table disclosed therein, the torque-transmitting mechanisms are selectively engaged in combinations of two to provide eight forward speed ratios and two reverse speed ratios. 
     The reverse (Reverse) speed ratio is established with the engagement of the input clutch  80  and the brake  89 . The input clutch  80  connects the sun gear member  22  and the planet carrier assembly member  56  via interconnecting member  74  with the input member  17 . The brake  86  connects the planet carrier assembly member  26 , the sun gear member  42  and the ring gear member  54  via interconnecting member  72  with the transmission housing  60 . The sun gear member  22  and the planet carrier assembly member  26  rotate at the same speed as the input member  17 . The planet carrier assembly member  26 , sun gear member  42  and ring gear member  54  do not rotate. The ring gear member  24 , sun gear member  32  and ring gear member  44  rotate at the same speed as the output member  19 . The ring gear member  44  rotates at a speed determined by the speed of the planet carrier assembly member  46  and the ring gear/sun gear tooth ratio of the planetary gear set  40 . The ring gear member  24 , and therefore the output member  19 , rotates at a speed determined from the speed of the sun gear member  22  and the ring gear/sun gear tooth ratio of the planetary gear set  20 . The numerical value of the reverse speed ratio is determined utilizing the ring gear/sun gear tooth ratios of the planetary gear sets  20  and  40 . 
     The first forward speed ratio is established with the engagement of the input clutch  80 , and the brake  87 . The input clutch  80  connects the sun gear member  22  and the planet carrier assembly member  56  via interconnecting member  74  with the input member  17 . The brake  87  connects the ring gear member  34  and the planet carrier assembly member  46  via interconnecting member  76  with the transmission housing  60 . The sun gear member  22  and planet carrier assembly member  56  rotate at the same speed as the input member  17 . The ring gear member  34  and planet carrier assembly member  46  do not rotate. The planet carrier assembly member  26 , sun gear member  42  and ring gear member  54  rotate at the same speed. The speed of the sun gear member  42  is determined from the speed of the ring gear member  44  and the ring gear/sun gear tooth ratio of the planetary gear set  40 . The ring gear member  24 , sun gear member  32  and ring gear member  44  rotate at the same speed as the output member  19 . The speed of the ring gear member  24 , and therefore the output member  19 , is determined from the speed of the sun gear member  22 , the speed of the planet carrier assembly member  26  and the ring gear/sun gear tooth ratio of the planetary gear set  20 . The numerical value of the first forward speed ratio is determined utilizing the ring gear/sun gear tooth ratios of the planetary gear sets  20  and  40 . 
     The second forward speed ratio is established with the engagement of the input clutch  80  and the brake  88 . The input clutch  80  connects the sun gear member  22  and the planet carrier assembly member  56  with the input member  17 . The brake  88  connects the planet carrier assembly member  36  with the transmission housing  60 . The sun gear member  22  and the planet carrier assembly member  56  rotate at the same speed as the input member  17 . The planet carrier assembly member  26 , sun gear member  42  and ring gear member  54  rotate at the same speed. The sun gear member  42  rotates at a speed determined from the speed of the ring gear member  44 , the speed of the planet carrier assembly member  46  and the ring gear/sun gear tooth ratio of the planetary gear set  40 . The ring gear member  24 , sun gear member  32  and ring gear member  44  rotate at the same speed as the output member  19 . The speed of the ring gear member  24 , and therefore the output member  19 , is determined from the speed of the sun gear member  22 , the speed of the planet carrier assembly member  26  and the ring gear/sun gear tooth ratio of the planetary gear set  20 . The numerical value of the second forward speed ratio is determined utilizing the ring gear/sun gear tooth ratios of the planetary gear sets  20 ,  30  and  40 . 
     The third forward speed ratio is established with the engagement of the input clutch  82  and brake  87 . The input clutch  82  connects the planet carrier assembly member  26 , sun gear member  42  and ring gear member  54  with the input member  17 . The brake  87  connects the ring gear member  34  and planet carrier assembly member  46  with the transmission housing  60 . The planet carrier assembly member  26 , sun gear member  42  and ring gear member  54  rotate at the same speed as the input member  17 . The ring gear member  34  and planet carrier assembly member  46  do not rotate. The ring gear member  24 , sun gear member  32  and ring gear member  44  rotate at the same speed as the output member  19 . The speed of the ring gear member  44  is determined from the speed of the sun gear member  42  and the ring gear/sun gear tooth ratio of the planetary gear set  40 . The speed of the ring gear member  24 , and therefore the output member  19 , is determined from the speed of the sun gear member  22 , the speed of the planet carrier assembly member  26  and the ring gear/sun gear tooth ratio of the planetary gear set  20 . The numerical value of the third forward speed ratio is determined utilizing the ring gear/sun gear tooth ratios of the planetary gear sets  20  and  40 . 
     The fourth forward speed ratio is established with the engagement of the input clutch  82  and the brake  88 . The input clutch  82  connects the planet carrier assembly member  26  and the sun gear member  42  with the input member  17 . The brake  88  connects the planet carrier assembly member  36  with the transmission housing  60 . The planet carrier assembly member  26 , sun gear member  42  and ring gear member  54  rotate at the same speed as the input member  17 . The sun gear member  22  and planet carrier assembly member  56  rotate at the same speed. The ring gear member  34  and planet carrier assembly member  46  rotate at the same speed. The speed of the planet carrier assembly member  46  is determined from the speed of the sun gear member  42 , the speed of the ring gear member  44  and the ring gear/sun gear tooth ratio of the planetary gear set  40 . The planet carrier assembly member  36  does not rotate. The speed of the sun gear member  32  is determined from the speed of the ring gear member  34  and the ring gear/sun gear tooth ratio of the planetary gear set  30 . The ring gear member  24 , sun gear member  32  and ring gear member  42  rotate at the same speed as the output member  19 . The speed of the ring gear member  24 , and therefore the output member  19 , rotates at a speed determined from the speed of the sun gear member  22 , the speed of the planet carrier assembly member  26  and the ring gear/sun gear tooth ratio of the planetary gear set  20 . The numerical value of the fourth forward speed ratio is determined utilizing the ring gear/sun gear tooth ratio of the planetary gear sets  20 ,  30  and  40 . 
     The fifth forward speed ratio is established with the engagement of the input clutches  80  and  82 . In this configuration, the input shaft  17  is directly connected with the output shaft  19 . The numerical value of the fifth forward speed ratio is 1. 
     The sixth forward speed ratio is established with the engagement of the input clutch  82  and the brake  84 . The input clutch  82  connects the planet carrier assembly member  26 , the sun gear member  42  and ring gear member  54  with the input member  17 . The brake  84  connects the sun gear member  52  with the transmission housing  60 . The sun gear member  52  does not rotate. The planet carrier assembly member  26 , sun gear member  42  and ring gear member  54  rotate at the same speed as the input member  17 . The sun gear member  22  and planet carrier assembly member  56  rotate at the same speed. The speed of the planet carrier assembly member  56  is determined from the speed of the ring gear member  54  and the ring gear/sun gear tooth ratio of the planetary gear set  50 . The ring gear member  34  and planet carrier assembly member  46  rotate at the same speed. The speed of the planet carrier assembly member  46  is determined from the speed of the ring gear member  44 , the speed of the sun gear member  42  and the ring gear/sun gear tooth ratio of the planetary gear set  40 . The ring gear member  24 , sun gear member  32  and ring gear member  44  rotate at the same speed as the output member  19 . The speed of the ring gear member  24 , and therefore the output member  19 , is determined from the speed of the sun gear member  24 , the speed of the planet carrier assembly member  26  and the ring gear/sun gear tooth ratio of the planetary gear set  20 . The numerical value of the sixth forward speed ratio is determined utilizing the ring gear/sun gear tooth ratios of the planetary gear sets  20 ,  40  and  50 . 
     The seventh forward speed ratio is established with the engagement of the input clutch  82  and the brake  85 . The input clutch  82  connects the planet carrier assembly member  26 , sun gear member  42  and ring gear member  54  with the input member  17 . The brake  85  connects the sun gear member  22  and planet carrier assembly member  56  with the transmission housing  60 . The sun gear member  22  and planet carrier assembly member  56  do not rotate. The planet carrier assembly member  26 , sun gear member  42  and ring gear member  54  rotate at the same speed as the input member  17 . The ring gear member  24 , sun gear member  32  and ring gear member  44  rotate at the same speed as the output member  19 . The ring gear member  34  and planet carrier assembly member  46  rotate at the same speed. The speed of the planet carrier assembly member  46  is determined from the speed of the sun gear member  42 , the speed of the ring gear member  44  and the ring gear/sun gear tooth ratio of the planetary gear set  40 . The speed of the ring gear member  24 , and therefore the output member  19 , is determined from the speed of the planet carrier assembly member  26  and the ring gear/sun gear tooth ratio of the planetary gear set  20 . The numerical value of the seventh forward speed ratio is determined utilizing the ring gear/sun gear tooth ratios of the planetary gear sets  20  and  40 . 
     The eighth forward speed ratio is established with the engagement of the input clutch  80  and the brake  84 . The input clutch  80  connects the sun gear member  22  and the planet carrier assembly member  56  with the input member  17 . The brake  84  connects the sun gear member  52  with the transmission housing  60 . The sun gear member  52  does not rotate. The sun gear member  22  and planet carrier assembly member  56  rotate at the same speed as the input member  17 . The planet carrier assembly member  26 , sun gear member  42  and ring gear member  54  rotate at the same speed. The speed of the ring gear member  54  is determined from the speed of the planet carrier assembly member  56  and the ring gear/sun gear tooth ratio of the planetary gear set  50 . The ring gear member  34  and planet carrier assembly member  46  rotate at the same speed. The ring gear member  24  sun gear member  32  and ring gear member  44  rotate at the same speed as the output member  19 . The speed of the ring gear member  44  is determined from the speed of the sun gear member  42 , the speed of the planet carrier assembly member  46  and the ring gear/sun gear tooth ratio of the planetary gear set  40 . The speed of the ring gear member  24 , and therefore the output member  19 , is determined from the speed of the sun gear member  22 , the speed of the planet carrier assembly member  26  and the ring gear/sun gear tooth ratio of the planetary gear set  20 . The numerical value of the eighth forward speed ratio is determined utilizing the ring gear/sun gear tooth ratio of the planetary gear sets  20 ,  40  and  50 . 
     As set forth above, the engagement schedule for the torque-transmitting mechanisms is shown in the truth table of  FIG. 1   b . This truth table also provides an example of speed ratios that are available utilizing the ring gear/sun gear tooth ratios given by way of example in  FIG. 1   b . The N R1 /S R1  value is the tooth ratio of the planetary gear set  20 ; the N R2 /S R2  value is the tooth ratio of the planetary gear set  30 ; and the N R3 /S R3  value is the tooth ratio of the planetary gear set  40 . Also, the chart of  FIG. 1   b  describes the ratio steps that are attained utilizing the sample of tooth ratios given. For example, the step ratio between the first and second forward speed ratios is 1.64, while the step ratio between the reverse speed ratio (Reverse) and first forward ratio is −0.56. It should be noted that the single step forward ratio interchanges are of the single transition variety. 
     The powertrain  10  may share components with a hybrid vehicle, and such a combination may be operable in a “charge-depleting mode”. For purposes of the present invention, a “charge-depleting mode” is a mode wherein the vehicle is powered primarily by an electric motor/generator such that a battery is depleted or nearly depleted when the vehicle reaches its destination. In other words, during the charge-depleting mode, the engine  12  is only operated to the extent necessary to ensure that the battery is not depleted before the destination is reached. A conventional hybrid vehicle operates in a “charge-sustaining mode”, wherein if the battery charge level drops below a predetermined level (e.g., 25%) the engine is automatically run to recharge the battery. Therefore, by operating in a charge-depleting mode, the hybrid vehicle can conserve some or all of the fuel that would otherwise be expended to maintain the 25% battery charge level in a conventional hybrid vehicle. It should be appreciated that a hybrid vehicle powertrain is preferably only operated in the charge-depleting mode if the battery can be recharged after the destination is reached by plugging it into an energy source. 
     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.