With the research and development of hybrids, Toyota introduced the Hybrid Synergy Drive (HSD), this system is made up of two electric motors and one motor. Directly connected to the engine and one electric motor, not directly connected to another engine. This system is the most critical design is a compound planetary gear transmission. Engine and electric motor combine to form a connected drive units, formed the second electric motor drive unit. These two units by the on-board computer deployed flexibly through the gearbox on the drive wheel transmission.
When the first power unit through the gearbox to the wheels of power transmission; in pure electric mode, the second power unit replaced the engine and the electric motor alone to power the wheels, engine and electric motor are connected in a closed state. Vehicle deceleration, HSD hybrid system of electric motor into a generator to charge the battery pack.