Automatic transmission

An automatic transmission comprising:

• a double-pinion planetary gearset including:
• a first sun gear;
• a first ring gear constantly held stationary;
• and
• a first planet-pinion carrier arranged to carry a first planet pinion set in mesh with the first sun gear and the first ring gear;
• a first single-pinion planetary gearset including:
• a second sun gear, wherein the second sun gear is constantly coupled to the first sun gear so as to constitute a first rotor unit;
• a second ring gear;
• and
• a second planet-pinion carrier arranged to carry a second planet pinion set in mesh with the second sun gear and the second ring gear;
• a second single-pinion planetary gearset including:
• a third sun gear;
• a third ring gear, wherein the third ring gear is constantly coupled to the first planet-pinion carrier so as to constitute a second rotor unit;
• and
• a third planet-pinion carrier arranged to carry a third planet pinion set in mesh with the third sun gear and the third ring gear;
• an input shaft;
• an output shaft constantly coupled to the third planet-pinion carrier;
• a first coupling member arranged to be selectively applied to couple the second planet-pinion carrier to the first rotor unit;
• a second coupling member arranged to be selectively applied to couple the second planet-pinion carrier to the second rotor unit;
• a third coupling member arranged to be selectively applied to couple the input shaft to the second planet-pinion carrier;
• a fourth coupling member arranged to be selectively applied to couple the second ring gear to the third sun gear;
• a fifth coupling member arranged to be selectively applied to couple the second ring gear to the third planet-pinion carrier;
• and
• a sixth coupling member arranged to be selectively applied to couple the input shaft to the third sun gear;
• wherein at least first to eighth forward gear ratios and one reverse gear ratio are obtained between the input shaft and the output shaft by simultaneous application of three of the first to sixth coupling members.