Planetary gear train of automatic transmission for vehicles

A planetary gear train of an automatic transmission for vehicles, comprising:

• an input shaft receiving torque of an engine;
• an output shaft outputting changed torque;
• a first planetary gear set having a first sun gear, a first planet carrier and a first ring gear;
• a second planetary gear set having a second sun gear, a second planet carrier and a second ring gear;
• a third planetary gear set having a third sun gear, a third planet carrier and a third ring gear;
• a fourth planetary gear set having a fourth sun gear, a fourth planet carrier and a fourth ring gear;
• a first rotational shaft having the first sun gear and selectively connected to a transmission housing;
• a second rotational shaft having the first planet carrier and directly connected to the input shaft;
• a third rotational shaft having the first ring gear, the second planet carrier, the third sun gear, and the fourth sun gear;
• a fourth rotational shaft having the second sun gear;
• a fifth rotational shaft having the second ring gear and selectively connected to the first rotational shaft and the second rotational shaft;
• a sixth rotational shaft having the fourth planet carrier and directly connected to the output shaft;
• a seventh rotational shaft having the third planet carrier, and the fourth ring gear and selectively connected to the fourth rotational shaft or selectively connected to the transmission housing;
• an eighth rotational shaft having the third ring gear and selectively connected to the fifth rotational shaft;
• and
• six friction elements each disposed to selectively connect the rotational shafts or selectively connect at least one of the rotational shafts with the transmission housing, the six friction elements comprising:
• a first clutch interposed between the second rotational shaft and the fifth rotational shaft;
• a second clutch interposed between the fourth rotational shaft and the seventh rotational shaft;
• a third clutch interposed between the first rotational shaft and the fifth rotational shaft;
• a fourth clutch interposed between the fifth rotational shaft and the eighth rotational shaft;
• a first brake interposed between the first rotational shaft and the transmission housing;
• and
• a second brake interposed between the seventh rotational shaft and the transmission housing.