Electronically-controlled CVT

The E-CVT saw first commercial automotive use in Toyota's Hybrid Synergy Drive system. This system is not a true CVT, having a fixed gear ratio, but behaves very similar to a true CVT. In this system, the transmission is an integral part of the hybrid powertrain and is actually a torque combiner. The gear train is a permanently-engaged, fixed-ratio, 3-way planetary gear. The engine is attached to one input, the driveshaft and the main electric motor to another, and then a smaller motor-generator controls the differential's third input to create a continuously-variable ratio between engine speed and wheel speed, with the variation taken by the electric motor and generator.

The advantage of the system is its mechanical simplicity - no clutches, torque converters or shifting gears. A disadvantage is that continuous electrical power transmission between the two motor-generators is needed even during cruise, with resulting conversion losses, but the total effect is to increase the net efficiency through four methods:
The ICE engine may be completely shut down, rather than idle.
The electric motor operates during high torque demands required to put the vehicle in motion.
The ICE engine operates mostly at higher power demands, where it is more efficient.
Energy may be recovered through the generation function when the vehicle is slowing or coasting downhill, with the energy (stored in the battery) applied to the initial acceleration of the vehicle and when high power demands require a that both the ICE engine and the electric motor operate.

The design of the system may be optimized for efficiency or for performance, as appropriate for the marketing segment for which the vehicle is targeted.