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

Description:
TECHNICAL FIELD 
     The present invention relates to a power transmission having three planetary gear sets that are controlled by six torque-transmitting devices to provide eight forward speed ratios and 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 transmission having three planetary gear sets controlled to provide eight forward speed ratios and one reverse speed ratio. 
     The transmission family of the present invention has three 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 and third gear sets in this description and in the claims, these sets may be counted “first” to “third” in any order in the drawing (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 drawing (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). Embodiments with long pinions are also possible. 
     A first interconnecting member continuously connects the third member of the first planetary gear set with the third member of the second planetary gear set. 
     A second interconnecting member continuously connects the second member of the second planetary gear set with the first member of the third planetary gear set. 
     A first torque transmitting device, such a brake, selectively connects the first member of the first planetary gear set with a stationary member (transmission housing/casing). 
     A second torque transmitting device, such as a brake, selectively connects the third member of the second planetary gear set with a stationary member (transmission housing/casing). 
     A third torque transmitting device, such as a brake, selectively connects the second member of the second planetary gear set with a stationary member (transmission housing/casing). 
     A fourth torque transmitting device, such as a clutch, selectively connects the second member of the first planetary gear set with the second member of the second planetary gear set. 
     A fifth torque transmitting device, such as a clutch, selectively connects the second member of the first planetary gear set with the second member of the third planetary gear set. 
     A sixth torque transmitting device, such as a clutch, selectively connects the first member of the second planetary gear set with the second member of the third planetary gear set. 
     The six torque-transmitting mechanisms are selectively engageable in combinations of three to yield eight forward speed ratios and one reverse speed ratio. 
     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 DRAWING 
         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.    
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings, 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 member  17  continuously connected with the engine  12 , a planetary gear arrangement  18 , and an output member  19  continuously connected with the final drive mechanism  16 . The planetary gear arrangement  18  includes three planetary gear sets  20 ,  30  and  40 . 
     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  rotatably mounted on a carrier member  39  and disposed in meshing relationship with both the ring gear member  34  and the sun gear member  32 . 
     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  mounted on a carrier member  49  and disposed in meshing relationship with both the ring gear member  44  and the sun gear member  42 . 
     The planetary gear arrangement also includes six torque-transmitting mechanisms  50 ,  52 ,  54 ,  55 ,  56  and  57 . The torque-transmitting mechanisms  50 ,  52  and  54  are a stationary-type torque-transmitting mechanism, commonly termed brakes or reaction clutches. The torque-transmitting mechanisms  55 ,  56  and  57  are rotating-type torque-transmitting mechanisms, commonly termed clutches. 
     The input member  17  is continuously connected with the sun gear member  32  of the planetary gear set  30 . The output member  19  is continuously connected with the ring gear member  44  of the planetary gear set  40 . The first interconnecting member  70  continuously connects the ring gear member  24  of the planetary gear set  20  with the ring gear member  34  of the planetary gear set  30 . The second interconnecting member  72  continuously connects the planet carrier assembly member  36  of the planetary gear set  30  with the sun gear member  42  of the planetary gear set  40 . 
     A first torque transmitting device, such as brake  50 , selectively connects the sun gear member  22  of the planetary gear set  20  with the transmission housing  60 . A second torque transmitting device, such as brake  52 , selectively connects the ring gear member  34  of the planetary gear set  30  with the transmission housing  60 . A third torque transmitting device, such as brake  54 , selectively connects the planet carrier assembly member  36  of the planetary gear set  30  with the transmission housing  60 . A fourth torque transmitting device, such as clutch  55 , selectively connects the planet carrier assembly member  26  of the planetary gear set  20  with the planet carrier assembly member  36  of the planetary gear set  30 . A fifth torque transmitting device, such as clutch  56 , selectively connects the planet carrier assembly member  26  of the planetary gear set  20  with the planet carrier assembly member  46  of the planetary gear set  40 . A sixth torque transmitting device, such as clutch  57 , selectively connects the sun gear member  32  of the planetary gear set  30  with the planet carrier assembly member  46  of the planetary gear set  40 . 
     As shown in  FIG. 1   b , and in particular the truth table disclosed therein, the torque-transmitting mechanisms are selectively engaged in combinations of three to provide eight forward speed ratios and one reverse speed ratio all with single transition shifts with a double overdrive. 
     The reverse speed ratio is established with the engagement of the brake  52  and clutches  55 ,  56 . The brake  52  engages the ring gear member  34  and the ring gear member  24  via interconnecting member  70  with the transmission housing  60 . The clutch  55  engages the planet carrier assembly member  26  with the planet carrier assembly member  36  and the sun gear member  42  via interconnecting member  72 . The clutch  56  engages the planet carrier assembly member  26  with the planet carrier assembly member  46 . The sun gear member  32  rotates at the same speed as the input member  17 . The ring gear member  34  and ring gear member  24  do not rotate. The planet carrier assembly member  36 , planet carrier assembly member  26 , planetary gear set  40  and output member  19  rotate at the same speed. The speed of the planet carrier assembly member  36 , and therefore the output member  19 , is determined from the speed of the sun gear member  32  and the ring gear/sun gear tooth ratio of the planetary gear set  30 . The numerical value of the reverse speed ratio is determined utilizing the ring gear/sun gear tooth ratios of the planetary gear set  30 . 
     The first forward speed ratio is established with the engagement of the brakes  50 ,  52  and the clutch  56 . The brake  50  engages the sun gear member  22  with the transmission housing  60 . The brake  52  engages the ring gear member  34  and the ring gear member  24  via interconnecting member  70  with the transmission housing  60 . The clutch  56  engages the planet carrier assembly member  26  with the planet carrier assembly member  46 . The sun gear member  32  rotates at the same speed as the input member  17 . The ring gear member  34 , planetary gear set  20  and planet carrier assembly member  46  do not rotate. The planet carrier assembly member  36  and sun gear member  42  rotate at the same speed. The speed of the planet carrier assembly member  36  is determined from the speed of the sun gear member  32  and the ring gear/sun gear tooth ratio of the planetary gear set  30 . The ring gear member  44  and output member  19  rotate at the same speed. The speed of the ring gear member  44 , and therefore the output member  19 , 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 numerical value of the first forward speed ratio is determined utilizing the ring gear/sun gear tooth ratios of the planetary gear sets  30  and  40 . 
     The second forward speed ratio is established with the engagement of the brakes  50 ,  54  and clutch  56 . The brake  50  engages the sun gear member  22  with the transmission housing  60 . The brake  54  engages the planet carrier assembly member  36  and the sun gear member  42  via interconnecting member  72  with the transmission housing  60 . The clutch  56  engages the planet carrier assembly member  26  with the planet carrier assembly member  46 . The sun gear member  32  rotates at the same speed as the input member  17 . The planet carrier assembly member  36  and sun gear member  42  do not rotate. The ring gear member  34  and ring gear member  24  rotate at the same speed. The speed of the ring gear member  34  is determined from the speed of the sun gear member  32  and the ring gear/sun gear tooth ratio of the planetary gear set  30 . The sun gear member  22  does not rotate. The planet carrier assembly member  26  and planet carrier assembly member  46  rotate at the same speed. The speed of the planet carrier assembly member  26  is determined from the speed of the ring gear member  24  and the ring gear/sun gear tooth ratio of the planetary gear set  20 . The ring gear member  44  and output member  19  rotate at the same speed. The speed of the ring gear member  44 , and therefore the output member  19 , is determined from the speed of the planet carrier assembly member  46  and the ring gear/sun gear tooth ratio of the planetary gear set  40 . 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 brake  50  and the clutches  55 ,  56 . The brake  50  engages the sun gear member  22  with the transmission housing  60 . The clutch  55  engages the planet carrier assembly member  26  with the planet carrier assembly member  36  and the sun gear member  42  via interconnecting member  72 . The clutch  56  engages the planet carrier assembly member  26  with the planet carrier assembly member  46 . The sun gear member  32  rotates at the same speed as the input member  17 . The ring gear member  34  and ring gear member  24  rotate at the same speed. The planet carrier assembly member  36 , planet carrier assembly member  26 , planetary gear set  40  and output member  19  rotate at the same speed. The speed of the ring gear member  34  is determined from the speed of the sun gear member  32 , the speed of the planet carrier assembly member  36  and the ring gear/sun gear tooth ratio of the planetary gear set  30 . The speed of the planet carrier assembly member  26 , and therefore the output member  19 , is determined from the speed of the ring gear member  24  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  30 . 
     The fourth forward speed ratio is established with the engagement of the brake  50  and the clutches  56 ,  57 . The brake  50  engages the sun gear member  22  with the transmission housing  60 . The clutch  56  engages the planet carrier assembly member  26  with the planet carrier member  46 . The clutch  57  engages the sun gear member  32  with the planet carrier assembly member  46 . The sun gear member  32 , planet carrier assembly member  46  and planet carrier assembly member  26  via interconnecting member  72  rotate at the same speed as the input member  17 . The planet carrier assembly member  36  and sun gear member  42  rotate at the same speed. The ring gear member  34  and ring gear member  24  rotate at the same speed. The speed of the ring gear member  34  is determined from the speed of the sun gear member  32 , the speed of the planet carrier assembly member  36  and the ring gear/sun gear tooth ratio of the planetary gear set  30 . The sun gear member  22  does not rotate. The speed of the planet carrier assembly member  26  is determined from the speed of the ring gear member  24  and the ring gear/sun gear tooth ratio of the planetary gear set  20 . The ring gear member  44  and the output member  19  rotate at the same speed. The speed of the ring gear member  44 , and therefore the output member  19 , 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 numerical value of the fourth forward speed ratio is determined utilizing the ring gear/sun gear tooth ratios of the planetary gear sets  20 ,  30  and  40 . 
     The fifth forward speed ratio is established with the engagement of the clutches  55 ,  56 ,  57 . In this configuration, the input member  17  is directly connected with the output member  19 . The numerical value of the fifth forward speed ratio is 1. 
     The sixth forward speed ratio is established with the engagement of the brake  50  and the clutches  55 ,  57 . The brake  50  engages the sun gear member  22  with the transmission housing  60 . The clutch  55  engages the planet carrier assembly member  26  with the planet carrier assembly member  36  and with the sun gear member  42  via interconnecting member  72 . The clutch  57  engages the sun gear member  32  with the planet carrier assembly member  46 . The sun gear member  32  and planet carrier assembly member  46  rotate at the same speed as the input member  17 . The planet carrier assembly member  26 , planet carrier assembly member  36  and sun gear member  42  rotate at the same speed. The ring gear member  34  and ring gear member  24  rotate at the same speed. The speed of the ring gear member  34  is determined from the speed of the sun gear member  32 , the speed of the planet carrier assembly member  36  and the ring gear/sun gear tooth ratio of the planetary gear set  30 . The sun gear member  22  does not rotate. The speed of the planet carrier assembly member  26  is determined from the speed of the ring gear member  24  and the ring gear/sun gear tooth ratio of the planetary gear set  20 . The ring gear member  44  and output member  19  rotate at the same speed. The speed of the ring gear member  44 , and therefore the output member  19 , 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 numerical value of the sixth forward speed ratio is determined utilizing the ring gear/sun gear tooth ratios of the planetary gear sets  20 ,  30  and  40 . 
     The seventh forward speed ratio is established with the engagement of the brakes  50 ,  54  and clutch  57 . The brake  50  engages the sun gear member  22  with the transmission housing  60 . The brake  54  engages the planet carrier assembly member  36  and sun gear member  42  via interconnecting member  72  with the transmission housing  60 . The clutch  57  engages the sun gear member  32  with the planet carrier assembly member  46 . The sun gear member  32  and planet carrier assembly member  46  rotate at the same speed as the input member  17 . The planet carrier assembly member  36 , sun gear member  42  and sun gear member  22  do not rotate. The ring gear member  34  and ring gear member  24  rotate at the same speed. The speed of the ring gear member  34  is determined from the speed of the sun gear member  32  and the ring gear/sun gear tooth ratio of the planetary gear set  30 . The ring gear member  44  and output member  19  rotate at the same speed. The speed of the ring gear member  44 , and therefore the output member  19 , is determined from the speed of the planet carrier assembly member  46  and the ring gear/sun gear tooth ratio of the planetary gear set  40 . The numerical value of the seventh forward speed ratio is determined utilizing the ring gear/sun gear tooth ratios of the planetary gear sets  30  and  40 . 
     The eighth forward speed ratio is established with the engagement of the brakes  50 ,  52  and the clutch  57 . The brake  50  engages the sun gear member  22  with the transmission housing  60 . The brake  52  engages the ring gear member  34  and ring gear member  24  via interconnecting member  70  with the transmission housing  60 . The clutch  57  engages the sun gear member  32  with the planet carrier assembly member  46 . The sun gear member  32  and planet carrier assembly member  46  rotate at the same speed as the input member  17 . The ring gear member  34  and planetary gear set  20  do not rotate. The planet carrier assembly member  36  and sun gear member  42  rotate at the same speed. The speed of the planet carrier assembly member  36  is determined from the speed of the sun gear member  32  and the ring gear/sun gear tooth ratio of the planetary gear set  30 . The ring gear member  44  and output member  19  rotate at the same speed. The speed of the ring gear member  44 , and therefore the output member  19 , 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 numerical value of the eighth forward speed ratio is determined utilizing the ring gear/sun gear tooth ratios of the planetary gear sets  30  and  40 . 
     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 and ratio steps that are available in the above described transmission. For example, the step ratio between the first and second forward speed ratios is 1.43, while the step ratio between the reverse speed ratio and first forward ratio is −0.59. 
     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.