Patent ID: 8574112

Claim:
A gear train of an automatic transmission for vehicles, comprising: a first planetary gear set having a first sun gear, a first planet carrier, and a first ring gear as rotation elements of the first planetary gear set; a second planetary gear set having a second sun gear, a second planet carrier, and a second ring gear as rotation elements of the second planetary gear set; a third planetary gear set having a third sun gear, a third planet carrier, and a third ring gear as rotation elements of the third planetary gear set; and frictional elements including a plurality of clutches and a plurality of brakes, each of the plurality of clutches connecting at least a rotation element of the first, second, and third planetary gear sets to another rotation element of the first, second, and third planetary gear sets or to an input shaft, and each of the plurality of brakes connecting at least a rotation element of the first, second, and third planetary gear sets to a transmission housing, wherein the rotation elements of the first planetary gear set are operated as first, second and third rotation elements of the gear train, with the first rotation element always operated as a fixed element, the second rotation element forming a first intermediate output path through which a reduced rotational speed is output, the third rotation element connected to an input shaft thereby forming an input path and the third rotation element forming a second intermediate output path through which a rotational speed of the input shaft is output, wherein a rotation element in the rotation elements of the second planetary gear set is fixedly connected to a rotation element in the rotation elements of the third planetary gear set and another rotation element in the rotation elements of the second planetary gear set is selectively connected to another rotation element in the rotation elements of the third planetary gear set such that the second and third planetary gear sets operate as a compound planetary gear set having four rotation elements, and wherein the four rotation elements of the operating compound planetary gear set are operated as fourth, fifth, sixth and seventh rotation elements of the gear train, with the fourth rotation element selectively connected to the first or second intermediate output paths and selectively connected to the transmission housing thereby forming a first variable input path so as to be operated as a selective fixed element, the fifth rotation element selectively connected to the input shaft or selectively connected to the transmission housing thereby forming a second variable input path so as to be operated as a selective fixed element, the sixth rotation element connected to an output gear and forming a final output path, and the seventh rotation element fixedly connected to the first intermediate output path thereby forming an intermediate input path, wherein each of the first, second and third planetary gear sets is a simple planetary gear set including one sun gear, one planet carrier and one ring gear.