Tokyo — Honda is preparing a successor to the Integrated Motor Assist hybrid system for small vehicles, and we were able to sample an early prototype in a Honda Fit. The Sport Hybrid i-DCD system combines a 1.5-liter inline-four gasoline engine, a seven-speed dual-clutch transmission, and an electric motor/generator attached to the transmission.
The 1.5-liter engine uses the more-efficient Atkinson cycle and lacks any belts, as the water pump and air conditioning are both driven electrically. It still has a large pulley at the end of the crankshaft, but that’s in place merely to act as a dampener for the engine. The engine can be disconnected from the transmission when the car is driving on electrical power or braking.
Compared to its current small-car hybrid powertrains, Honda expects Sport Hybrid i-DCD to use 30 percent less fuel while offering 15 percent better acceleration. Honda believes that dual-clutch transmissions inject a dose of sportiness and fun into the otherwise efficiency-minded driving experience. The Honda Fit prototype is said to be capable of driving at 43 mph on electric power alone, for a total of 1.5 to 3 miles of all-electric driving range. That increased performance is possible because the new system uses a higher capacity lithium-ion battery, instead of the old nickel metal-hydride batteries in the current IMA.
We were only able to drive the Sport Hybrid i-DCD prototype briefly, but it demonstrated brisk and reasonably smooth acceleration. The dual-clutch transmission changes gear so quickly and smoothly it’s hard to tell unless you pay attention to the tachometer, and it’s easy to drive gently on electrical power alone. The transmission also downshifts promptly by two gears or more if you put your foot down at cruising speeds. It’s not as sporty as Honda would have you believe, but it’s definitely more responsive and more interesting to drive than current Honda small hybrids.
For now, Sport Hybrid i-DCD is just an engineering prototype and Honda has yet to determine actual vehicle applications. Yet given that it is touted as a powertrain for small cars that replaces IMA, we expect to see this new hybrid setup in future versions of the Honda Insight and Civic Hybrid — but it’s probably at least two or three years away.
Honda also let us try a Fit with a non-hybrid, direct-injected 1.5-liter inline-four engine and continuously variable transmission. It’s one of Honda’s first commercial direct-injection engines and falls under the Earth Dreams banner, Honda’s name for its fuel-sipping new powertrains. The engine has a variety of other fuel-saving measures like special low-tension piston rings, auto stop-start, and intake ports designed to make the air “tumble” into the cylinder. The CVT, for its part, has a wider range of ratios, less friction, and lower weight than an equivalent current CVT. Put together, Honda says a vehicle with this powertrain would be 10 percent more efficient and offer 15 percent better acceleration than a similarly equipped existing vehicle.
We drove the Fit with this powertrain on a high-speed oval at Honda’s R&D facility, which wasn’t necessarily the best test of the economy-minded setup. Nevertheless, it was immediately apparent that this CVT behaves more like a traditional automatic transmission, with discernible ratios steps and a direct acceleration feel (as opposed to the lethargic, rubber band-like drone of many CVTs). The Fit with this powertrain was sprightly and responsive but not especially quick. This will almost certainly be the standard engine and transmission choice in the next-generation Honda Fit, expected to debut by 2014.