AutoNews.com: How the Honda Accord's innovative hybrid system works

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by Richard Truett of www.autonews.com

MARYSVILLE, Ohio -- Most of the attention for Honda's Accord hybrid will come from its eye-popping 50-mpg EPA city rating and under-$30,000 starting price. But those with an eye for engineering will see a creative combination of new technology with elements from the Chevrolet Volt, Toyota Prius and Ford Fusion Hybrid.

"Honda put in all we had," said Koji Ninomiya, chief engineer for the Accord Hybrid, through an interpreter. "We did our best, and we ended up at 50 mpg."

The car, which gets to dealerships in late October, uses three drive modes to crack the 50-mpg figure -- something no other mid-sized car, including the European diesels, can match.

Ninomiya said 50 mpg or any specific number was not the goal when Honda engineers began nearly a decade ago studying a new hybrid powertrain to replace its current design.

"We considered everything, [including] driving resistance and regenerative braking. We made the powertrain all new, and the biggest purpose of this was to aim for the most efficient system in the world. As we tried to optimize the efficiency, we decided two motors will be best," he said.

Here's how the two electric motors work in the Accord Hybrid's three drive modes, EV, Hybrid and Engine.

• EV mode: The car is propelled only by an electric motor powered by the lithium ion battery pack. The top speed is about 60 mph, but the range is very limited, just a few miles. Once the battery is depleted, the car automatically switches to Hybrid mode.

• Hybrid mode: The Accord Hybrid works a lot like a Chevrolet Volt. The 2.0-liter gasoline engine powers a generator to create electricity for the electric motor. Honda calls the generator a motor, hence two motors. Only the electric motor, fed by the generator, moves the car in Hybrid mode.

• Engine mode: The electric motor is decoupled, and the Accord's Atkinson cycle gasoline engine drives the wheels directly through a one-gear transmission. In that highway gear -- similar in efficiency to a sixth gear on a manual transmission -- the gasoline engine runs in its sweet spot, delivering both strong acceleration when needed and high fuel economy.

Ford and Toyota hybrids also use Atkinson cycle engines. The Accord's Atkinson cycle 2.0-liter gasoline engine is a first for Honda.




In an Atkinson cycle engine, the intake valves remain open briefly during the compression stroke. That pushes some of the air in the cylinders into the intake manifold, which lowers the compression ratio. That enables fast, smooth starts, which is ideal for hybrids. The downside is that it reduces power.

To solve that problem, Honda engineers installed VTEC, a system that electronically controls the timing of the valves with camshafts that have two sets of lobes. One set of lobes is for the Atkinson cycle; the other is for normal combustion. The engine's computer switches back and forth between the two sets of lobes, based on engine speed and load.

Other new technologies include the car's innovative regenerative brakes, which send electricity to the battery. Regeneration begins the instant a driver's foot leaves the accelerator, not when the brake pedal is pressed as it does on other hybrids.

The air-cooled lithium ion battery pack fits in a compact case between the rear seat and the trunk. The pack does reduce trunk space. The hybrid's trunk is 12.7 cubic feet, while the regular Accord's trunk is 15.8.

Honda will offer three versions of the Accord Hybrid. The base model starts at $29,155; a midlevel E-XL version, at $31,905; and the loaded Touring, at $34,905. The prices exclude shipping; figures haven't been announced.

Honda is assembling the Accord Hybrid at its Marysville plant; it is the first time the Accord Hybrid has been built in North America.

The car's innovative powertrain could help win back some former Honda fans who deserted the brand for other makes with more advanced engines and transmissions.

In the past, Honda had stuck with nickel-metal hydride batteries in its hybrids while other automakers developed more efficient gasoline-electric powertrains that use lighter, stronger lithium ion batteries.

And in its gasoline-powered cars, the company has been slow to shift to automatic transmissions with more than four speeds.

The result of that strategy: middle-of-the-pack fuel economy ratings and a string of misfires dating back nearly a decade, including the failed 2004-06 Accord Hybrid, a slow selling Civic Hybrid and dismal sales for the Insight and CR-Z hybrids.

The Accord Hybrid's 50 mpg is "a pretty strong statement," said California dealer Dave Conant. He is CEO of The C.A.R. Group, which owns 13 stores, including four Honda outlets.

"For a long time Honda sort of owned the territory," he said. "I think a 50-mpg Accord is going to absolutely swing people back to thinking of Honda as a fuel economy leader. It's long overdue, honestly."

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http://www.autonews.com/article/20130930/OEM06/309309954/how-the-honda-accords-innovative-hybrid-system-works#axzz2gNmxMhbV