Planetary gear train of automatic transmission for vehicle

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 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 shaft including the first sun gear;
• a second rotation shaft including the first planet carrier and the second ring gear;
• a third rotation shaft including the first ring gear and the third sun gear;
• a fourth rotation shaft including the second sun gear and selectively connected to the input shaft;
• a fifth rotation shaft including the second planet carrier and selectively connected to the input shaft or selectively connected to the transmission housing;
• a sixth rotation shaft including the third planet carrier and the fourth ring gear and directly connected to the output shaft to be continuously operated as an output element;
• a seventh rotation shaft including the third ring gear and selectively connected to the transmission housing;
• an eighth rotation shaft including the fourth sun gear and selectively connected to the third rotation shaft;
• a ninth rotation shaft including the fourth planet carrier and directly connected to the input shaft to be continuously operated as an input element;
• and
• six friction elements disposed to selectively connect the rotation shafts with each other and selectively connect the rotation shafts with the transmission housing.