Planetary gear train for automatic transmission of vehicle

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

• an input shaft receiving torque of an engine;
• an output shaft outputting changed torque of the engine;
• a first planetary gear set including a first sun gear, a first planet carrier, and a first ring gear;
• a second planetary gear set including a second sun gear, a second planet carrier, and a second ring gear;
• a third planetary gear set including a third sun gear, a third planet carrier, and a third ring gear;
• a fourth planetary gear set including a fourth sun gear, a fourth planet carrier, and a fourth ring gear;
• a first rotation shaft including the first and second sun gears and selectively connected to a transmission housing;
• a second rotation shaft including the first planet carrier;
• a third rotation shaft including the first and fourth ring gears and selectively connected to the transmission housing;
• a fourth rotation shaft including the second planet carrier and directly connected to the input shaft;
• a fifth rotation shaft including the second ring gear and the third and fourth sun gears;
• a sixth rotation shaft including the third planet carrier and selectively connected to the second rotation shaft;
• a seventh rotation shaft including the third ring gear and selectively connected to the second and fourth rotation shafts;
• an eighth rotation shaft including the fourth planet carrier and selectively connected to the sixth rotation shaft, and directly connected to the output shaft;
• and
• six friction elements disposed to selectively connect the rotation shafts to each other and selectively connect the rotation shafts to the transmission housing.