Electrically variable transmissions have been proposed in many forms including at least one two-mode compound-split transmission form. The U.S. Pat. No. 5,931,757, issued to Schmidt on Aug. 3, 1999, and assigned to the assignee of the present invention, describes a compound-split power transmission. The transmission described therein is an electrically variable transmission, which employs two electric power units that are controlled in a variable speed manner to distribute power to an output portion of the transmission. The transmission also includes a prime mover, such as an internal combustion engine, which distributes power to either one or more of the electric units and to the transmission output. During the first mode of operation, the power transmission provides an input split of power and during the second mode of operation or range, the transmission provides a compound-split of power distribution.
The prior art transmission has two working planetary gearsets and one reduction planetary gearset. Of the two working planetary gearsets, the engine or prime mover is connected to one member of one planetary unit, a first of the electrical units is connected to a member of each of the planetary units, and the second electrical unit is connected to one member of the one of the planetary units. The transmission output shaft is connected to members of both planetary units during the compound-split mode of operation of the transmission.