Honda was technically the first name in hybrids in the U.S. market—with the original 1999 Honda Insight two-seat hatchback.
But in recent years Honda’s Integrated Motor Assist (IMA) ‘mild hybrid’ system has been overshadowed, and outperformed, by Toyota’s Hybrid Synergy Drive in the Prius family and other cars.
Soon, Honda will have a better alternative for its small cars: It will introduce a new-generation hybrid system that will supplant IMA in favor of a new ‘i-DCT’ single-motor system, operating with a seven-speed dual-clutch automated gearbox.
Promising fuel-economy gains of 30 percent or more compared to IMA, as well as improved acceleration and responsiveness, the new setup should allow future Honda small hybrids to be nearly as fuel-efficient as those Toyotas--but considerably more fun to drive.
The older IMA system debuted in the 1999 Insight, and was later rolled out in the Honda Civic Hybrid, current Insight, and CR-Z, as well as other models not sold in the U.S. It's been through at least nine generations.
Versus IMA, much-expanded electric-only range
One key to the improved mileage is that i-DCD permits two very fuel-saving things that IMA never allowed: electric-only launches and more efficient coasting.
With a thin yet strong (20 kilowatts or more) electric motor built into the dual-clutch gearbox, the system has the ability to decouple the engine and gearbox while using power from the electric motor, or regenerating it when coasting or braking.
i-DCD offers two main modes: engine assist operation, and EV operation. Under acceleration and high-speed cruising, the electric motor system helps out the engine and aids efficiency.
And under initial takeoff, deceleration, and low- or medium-speed cruising, the system can operate using the electric motor only, with the gasoline engine decoupled through the gearbox clutch.
Different from IMA on the road
That full decoupling is one of the keys to the substantial fuel-efficiency gains, according to engineers; so is the very wide gear-ratio span of the dual-clutch gearbox. Meanwhile, the gasoline engine itself is a fuel-saving Atkinson-cycle 1.5-liter four-cylinder engine, and the air conditioning and water pump are both electric, for better energy management.
At Honda’s R&D facility in Japan we got an early opportunity to drive a Honda Fit test mule with the system and found it to be a completely different kind of system than IMA.
Gentle takeoffs in electric-only mode were smooth, and at low speeds if you lift off the throttle even more to coast or maintain speed, the system will stay in electric mode yet the transmission will ready whatever gear is appropriate for the moment the gasoline engine starts up. Moderate acceleration from a standing start uses only the electric motor for the initial takeoff, starting up the gasoline engine a moment later and using the two power sources together.
Promise: smoothness, responsiveness
One other perhaps unintended advantage of configuring the hybrid system this way is that, accelerating moderately or rapidly, the motor system actually helps smooth shifts—by producing an added boost just before and during the shift itself.
That helps keep downshifts more seamless, too, and even in these prototype units we only experienced a little bit of hesitation when rolling back onto the throttle at moderate speeds.
Although Honda hasn’t yet detailed which cars i-DCD is going into, or how far from market it is, we anticipate it will be the Honda system that will likely see the broadest application, although two other hybrid systems are on the way as well..
One is the dual-motor i-MMD hybrid (and plug-in hybrid) system that will make its debut in the 2014 Honda Accord Hybrid and Accord Plug-In Hybrid. Then, later in that calendar year, the Acura RLX will follow with a new three-mode Super-Handling All-Wheel Drive hybrid system.
Otherwise, for the Civic Hybrid, Insight, CR-Z and any other small cars Honda has in the works--even the Fit--the new i-DCD could make a big difference.
It could put Honda back into competition among the most mileage-minded shoppers.