Hybrid Synergy Drive

Hybrid Synergy Drive is Toyota Motor Corporation's proprietary hybrid drivetrain technology, first introduced on the 1997 Prius, which replaces a conventional geared transmission with an electromechanical system combining a gasoline engine, two electric motor-generators and a planetary gearset that continuously varies the effective gear ratio like a continuously variable transmission. As a full hybrid it can run on electric power alone at low speed, a capability most competing hybrid systems of its era lacked, and by shutting the engine off at rest and keeping it near its efficient operating point it lets Prius models exceed 40 miles per gallon in city driving and reach 55 on the highway.