Patent ID: 8864618

Claim:
A planetary gear train of an automatic transmission for a vehicle comprising: an input shaft receiving torque of an engine; an output shaft outputting a changed torque; a first planetary gear set having three rotation elements and disposed on the input shaft; a second planetary gear set having three rotation elements and disposed at a rear of the first planetary gear set on the input shaft; a third planetary gear set having three rotation elements and disposed at a rear of the second planetary gear set on the input shaft; a fourth planetary gear set having three rotation elements and disposed at a rear of the third planetary gear set on the input shaft; a first rotation shaft provided with a first rotation element of the first planetary gear set and a first rotation element of the second planetary gear set directly connected to the first rotation element of the first planetary gear set, and selectively connected to a transmission housing; a second rotation shaft provided with a second rotation element of the first planetary gear set; a third rotation shaft provided with a third rotation element of the first planetary gear set and directly connected to the input shaft; a fourth rotation shaft provided with a second rotation element of the second planetary gear set and selectively connected to the second rotation shaft or the transmission housing; a fifth rotation shaft provided with a third rotation element of the second planetary gear set, a first rotation element of the third planetary gear set and a first rotation element of the fourth planetary gear set; a sixth rotation shaft provided with a second rotation element of the fourth planetary gear set and selectively connected to the input shaft or the second rotation shaft; a seventh rotation shaft provided with a second rotation element of the third planetary gear set and a third rotation element of the fourth planetary gear set, and connected to the output shaft; an eighth rotation shaft provided with a third rotation element of the third planetary gear set and selectively connected to the transmission housing; and six frictional elements interposed between the rotation shafts or between the rotation shaft and the input shaft or the transmission housing.