A Field Guide to Hybrid Drive Systems
When reduced to its basics, there are four types of hybrid powertrains: (1) micro hybrids; (2) parallel hybrids; (3) power-split, two-mode or series-parallel hybrids; and (4) series hybrids. [The last in this series is more commonly known as an E-REV, or Extended-Range Electric Vehicle, and is best represented by the Chevy Volt/Cadillac ELR.]
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If this isn’t confusing enough, there also are “full” and “mild” hybrids. The former is capable of propelling the vehicle on just the engine, just the electric motor or on a combination of both. “Mild” hybrids offer start-stop capability, perhaps with a level of power assist to the combustion engine and regenerative braking. Unlike full hybrids, they can’t provide full-EV propulsion.
Micro hybrids are the first step between conventional internal combustion-powered vehicles and true hybrids. They add start-stop capability, shutting down the engine when the vehicle has come to a complete stop, and electrical load is low enough to allow it to be met without need for the alternator to recharge the battery. It provides its benefits by eliminating idling and quickly spinning the engine up once the brake pedal is released, allowing the driver to accelerate away from a stop normally. It is only starting to make its presence felt in North America due to the fact that the official EPA drive cycle doesn’t include much time where the test vehicle is stationary, so this option makes little difference in the mileage rating. Nevertheless, Ford offers stop-start on the 1.6-liter Fusion, and versions are offered by BMW, Porsche and Kia. Studies expect eight million U.S. vehicles by 2017 to use the technology, thanks to the new CAFE standards. It will expand as automakers upgrade electrical systems and batteries to allow engines to be shut off while the vehicle is coasting.