Hybrid Innovations

There are many ways to blend the internal combustion (IC) engine and electric power. These technologies have much in common—and many points of differentiation. In addition to Toyota's Hybrid Synergy Drive (HSD) system, other manufacturers have devised alternative means of propelling cars and trucks with a blend of fossil fuel and electricity.

Hybrid Vehicles
Hybrid vehicles are commonly categorized as being arranged in series and parallel configurations. WW II-era diesel submarines are a good example of the series arrangement. In this layout, an internal combustion (IC) engine spins an electric generator. Power from that generator is routed to storage batteries and to one or more electric motors. The electric motor(s) alone drive the vehicle. There is no direct mechanical link between the IC engine and the propulsion of the vehicle. So far, all vehicle makers seem to agree that the series configuration is impractical for automotive use due to its lower efficiency.


The parallel layout provides a means of linking two power sources—typically a gasoline engine and one or more electric motors—to the vehicle's drive wheels. Each source may or may not be able to drive the wheels independently of the other, and therein lays another point of distinction.


The most common parallel hybrid system is currently offered in the two-passenger Honda Insight, five-passenger Civic Hybrid, and the new Accord Hybrid. Honda positions an electric motor-generator (MG) in place of its IC engine's flywheel; this system is called Integrated Motor Assist. The MG bears some propulsion responsibility, it starts the internal combustion (IC) engine, and it charges the batteries, but it doesn't power the vehicle independently of the IC engine. Since it doesn't function on electric power alone, Honda's Integrated Motor Assist is best described as a mild hybrid system.


Efficiency gains in the Honda IMA system are less than those achieved by Toyota's HSD. Honda's Civic Hybrid offers 25-45-percent better fuel mileage than a conventional Civic. There is no other Toyota model comparable in size to the Prius, but as a point of reference, it beats the combined EPA estimated fuel economy rating of the smaller Corolla LE sedan with automatic transmission by 72 percent.