8-speed automatic transmission for vehicle

An eight-speed automatic transmission for a vehicle, comprising a single pinion planetary gear set, a double pinion planetary gear set, a compound planetary gear set, a first clutch, a second clutch, a third clutch, a fourth clutch, a first brake, a second brake, and a one-way clutch, wherein:

• an input shaft is disposed for receiving power of an engine;
• the single pinion planetary gear set comprises a first ring gear fixedly connected to the input shaft, a first sun gear fixedly connected to a housing, and a first planet carrier;
• the double pinion planetary gear set comprises a second ring gear variably fixed to the housing by the first brake or the one-way clutch that are disposed in parallel, a second sun gear fixedly connected to the first planet carrier, and a second planet carrier variably connected to the second ring gear by the second clutch;
• and
• the compound planetary gear set comprises a short sun gear variably connected to the second sun gear by the first clutch, a short pinion engaged with the short sun gear, a long sun gear fixedly connected to the second planet carrier, a long pinion engaged with the short pinion and the long sun gear and variably connected to the input shaft by the third clutch, and a third ring gear that is engaged with the long pinion, is variably connected to the second planet carrier and the long sun gear by the fourth clutch, and is connected to an output shaft, wherein
• the second brake variably fixes the second planet carrier and the long sun gear to the housing,
• the single pinion planetary gear set, the double pinion planetary gear set, and the compound planetary gear set are disposed in a sequence of the single pinion planetary gear set, the double pinion planetary gear set, and the compound planetary gear set from the engine to the output shaft, and
• the first clutch and the third clutch are disposed between the compound planetary gear set and the output shaft.