Eight speed powertrain of automatic transmission for vehicle

An eight-speed powertrain of an automatic transmission, comprising:

• a first planetary gear set comprising operational elements of a first sun gear, a first ring gear, and a first planet carrier;
• a second planetary gear set comprising operational elements of a second sun gear, a second ring gear, and a second planet carrier;
• a third planetary gear set comprising operational elements of a third sun gear, a third ring gear;
• a third planet carrier;
• and
• a fourth planetary gear set comprising operational elements of a fourth sun gear, a fourth ring gear, a fourth planet carrier;
• an input shaft, at least one output gear, and a transmission case;
• wherein:
• the first sun gear is fixedly connected to the transmission case so as to operate as a fixed element;
• the first planet carrier is fixedly connected to the second ring gear;
• the second sun gear is fixedly connected to the input shaft so as to operate as an input element,
• the third ring gear and the fourth ring gear are formed together and fixedly connected to the output gear so as to operate as an output element,
• the first ring gear is variably connected to the third sun gear via a first clutch,
• the second ring gear is variably connected to the input shaft via a second clutch,
• the first ring gear is variably connected to the fourth sun gear via a third clutch,
• the fourth planet carrier is variably connected to the input shaft via a fourth clutch,
• the fourth sun gear is variably connected to the input shaft via a fifth clutch,
• the second planet carrier is variably connected to the transmission case via a first brake, and
• the third sun gear is variably connected to the transmission case via a second brake.