Planetary gear train of automatic transmission for vehicle

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

• an input shaft for receiving an engine torque;
• an output shaft for outputting a shifted torque;
• a first planetary gear set including a first rotation element, a second rotation element, and a third rotation element;
• a second planetary gear set including a fourth rotation element, a fifth rotation element, and a sixth rotation element;
• a third planetary gear set including a seventh rotation element, an eighth rotation element, and a ninth rotation element;
• a fourth planetary gear set including a tenth rotation element, an eleventh rotation element, and a twelfth rotation element;
• a first shaft fixedly interconnecting the first rotation element and the fourth rotation element and fixedly connected with the input shaft such that the first and fourth rotation elements always rotate at a speed of the input shaft;
• a second shaft fixedly connected with the second rotation element and fixedly connected with the output shaft, such that the second rotation element always rotate at a speed of the output shaft;
• a third shaft fixedly connected with the third rotation element;
• a fourth shaft fixedly interconnecting the fifth rotation element and the ninth rotation element, such that the fifth and ninth rotation speed always rotate at a same speed;
• a fifth shaft fixedly connecting the sixth rotation element and the tenth rotation element such that the sixth and tenth rotation element always rotate at a same speed, and selectively connectable with the second shaft and the third shaft;
• a sixth shaft fixedly connected with the seventh rotation element;
• a seventh shaft fixedly connecting the eighth rotation element and the eleventh rotation element such that the eighth and eleventh rotation element always rotate at a same speed, and selectively connectable with at least one of the first shaft and a transmission housing;
• and
• an eighth shaft fixedly connected with the twelfth rotation element and selectively connectable with the third shaft.