Hybrid Innovations

To date, Honda's hybrids have used a three- or four-cylinder gasoline engine aided by an electric motor. For 2005, the concept will be extended to a larger Accord sedan that combines a 3.0-liter V-6 with electric assist. The Accord Hybrid V-6 engine is programmed to use only three cylinders while cruising and to shut off entirely when the vehicle is at a stop.


According to Toyota's Dave Hermance, "Toyota's Hybrid Synergy Drive (HSD) differs substantially from Honda's system in that it is a full hybrid system that, depending upon driving circumstances, exhibits both series and parallel characteristics. Like a series hybrid, the Prius gasoline engine powers a generator, which supplies electrical current to an electric drive motor. Like a parallel hybrid, both the IC engine and the electric motor are capable of providing power to the wheels." HSD allows each power source to drive the vehicle independently (see "Inside the HSD" for a complete explanation), which is something competitive mild hybrids can't do.


More than 250,000 (with both HSD and the earlier Toyota Hybrid System (THS)) Toyota Prius have been built and sold during the past seven years, all over the globe. Following that success, two other makers have devised their own variations of the series/ parallel theme. The new-for-2005 Ford Escape Hybrid has a powertrain that is similar to that of the Toyota Prius. Although Toyota does not directly supply any parts or software for the Escape Hybrid, a licensing agreement permits Ford to use technology patented by Toyota. Nissan has also signed an agreement with Toyota to use HSD in the future. Efforts are well underway to develop a Nissan Altima hybrid, a car that will combine a Nissan engine with HSD components supplied by Toyota.

Idle-Stop Strategies
Another emerging concept doesn't use electric power to propel the vehicle at all, but instead shuts off the IC engine when it's not needed, then quickly restarts the IC engine when power is required. (This same strategy is found in true hybrid systems, as well). In some GM fleet and future consumer trucks, an electric motor-generator device replaces the standard starter and alternator. It's wired to batteries that store energy. The batteries are charged by two means: During deceleration, the motor-generator switches to generator mode to convert unwanted vehicle momentum into an electrical charge that can be used later. If this charging means proves insufficient, the generator draws power from the engine. Since the motor-generator device does not help propel the vehicle, a conventional gasoline engine handles that job unaided.


Shutting off the gasoline engine at stops saves some fuel. Since the motor-generator is far more powerful than a conventional starter, it quickly and easily wakes up the sleeping engine when the accelerator is tapped after the stoplight turns green. Operation is automatic and relatively seamless, but the efficiency payoff is modest. According to EPA estimates, the benefit is about 10% in city driving, which is at most, about a 1-2 mpg gain. Also, it is worth noting that the California Air Resources Board (CARB) does not classify such systems as "hybrids" at all. To qualify as a hybrid, CARB requires that the electric motor assist in propelling the vehicle.