The current invention discloses a dual-mode electro-mechanical variable speed transmission. Said transmission includes an input shaft, an output shaft
system, a planetary
gear system having at least three co-axial rotating members, two electric machines along with the associated controllers for the electric machines, and at least a
clutch. Said planetary
gear system has at least three branches; each
branch corresponds to a co-axial rotating member. The first
branch couples to the first
electric machine with a fixed speed ratio; another
branch couples to the input shaft with a fixed speed ratio; and yet anther branch couples to the output shaft
system with a fixed speed ratio; the second
electric machine couples selectively to two of the branches in the planetary
gear system with different speed ratios. Said two branches are not the first branch and one of the said two branches is connected to the output shaft
system. Said dual-mode electro-mechanical variable speed transmission is capable of providing at least two power splitting operation
modes, including an output power splitting mode. Different operation
modes cover different speed ratio regimes. At the
mode switching point, the corresponding
clutch or clutches is automatically synchronized. Thus the speeds of the rotation members of the transmission are continuous, and the transmission is free from shock loads at the operating
mode switching point. In addition, said transmission is capable of providing operations with at least a fixed input-to-output speed ratio.