• Feb 29, 2008

Part I: The New Fuel Cell Stack

In June of 2005, Honda became the first car company in the world to lease a hydrogen fuel cell powered car to Jon Spallino, of Redondo Beach, Calif. During the 2005-2006 auto show season, they showed off a concept version of their first purpose-built fuel cell powered car. Earlier this year they announced that the car would go into low volume production in 2008 and recently they allowed a group of journalists to drive the first two prototypes at the Laguna Seca racetrack along with the two of the current generation FCX cars. I was there.

The day began with a technical presentation of where Honda's fuel cell development has been and where it's going. Unlike most other car-makers working on hydrogen power, Honda is designing and building their own fuel cell stacks. The previous generations of stacks have been laid out much like the ones from companies like Ballard where the gases flow horizontally through the stack. This horizontal flow is what has led to one of the problems with fuel cells in cars, cold weather performance.

In a horizontal stack, the hydrogen and oxygen produce electricity and water, some of which condenses and sticks to the plates in the stack and eventually drips down and is drained out. The plates have horizontal channels which can make the drainage problematic, sometimes leaving liquid water in the stack which, if allowed to freeze, can damage it. The horizontal layout was chosen because of the size of stacks and the need to keep the center of gravity of the car low.

The major innovation of the new FCX concept is the new V-Flow fuel cell stack, where V stands for vertical. In this stack, the hydrogen and oxygen enter from the top and flow down through the stack. The channels in the plates are now vertical, and allow the water to flow out much more freely. Water on the plates reduces the electrical generating capacity and makes it inconsistent. In the new stack, the lack of standing water on the plates allows for much higher and more consistent power generation, and the better drainage means much lower operating temperature capability.

The end result is a power generation unit that has a power/volume density ratio 50 percent higher than the previous generation introduced in 2003 and a 67 percent improvement in power/weight ratio. Compared to the unit from 1999 those numbers are up by a factor of four. So they now have a stack that is small enough and powerful enough to fit upright in the center tunnel of the car.

This desich allows the floorpan and seats to now be moved much lower, allowing for vastly improved design flexibility. The current generation FCX is based on the design of the EV+ electric car built in the 90s, making it a tall four seat hatchback with the ultra capacitor (instead of a battery) sitting under the floor. The new FCX has the fuel cell mounted in the center tunnel between the driver and front passenger seat, and is a remarkably sleek-looking four door, four passenger sport sedan. The two cars are like night and day.

Part II: Styling and Powertrain

The new Honda FCX concept is a four-door, four seat sports sedan with a profile reminiscent of the Lamborghini Portofino concept of the late 1980s. It has an extreme cab-forward stance, with a sharply raked windshield, and a fairly tall rear deck. The A-pillars stretch way out toward the front corners with a fixed quarter window between the pillars and the leading edge of the doors. This design element is also reminiscent of another late 80s vehicle, the unfortunate first generation GM mini-vans. However, on this car the whole design seems to work much better.

The roof line sweeps back from the front bumper to trailing edge of the trunk lid one continuous sweep. The total effect is futuristic and slightly aggressive. It definitely doesn't have the top-heavy, slightly clunky look of the current FCX. The 2008 production version will look almost identical to the current prototypes, the main difference likely to be in the front bumper area. The front styling is expected to be maintained but the structure will be modified.

The insanely short nose is made possible by the redesigned and very compact power-train that Honda has devised. The previous FCX had the the electric motor and transaxle in two different planes. The new design has the gearbox and motor mounted in-line on the same axis, making the whole package almost nine inches shorter than the old one. In addition to being smaller the new motor is has an output increased from 107 to 127 hp. As with other electric power-trains, the gearbox is just a reduction gear-set, but is otherwise direct drive.

The fuel cell power-plant is 400 lbs lighter than the unit in the 2005 model. One of the pitfalls of previous fuel cells has been cold-weather start up performance. The Ford Focus FCV that was recently evaluated here needed to be kept above 40 degrees Fahrenheit to start. The 2006 FCX can start up at -4F and the new car with the vertical V Flow fuel cell stack can start-up at -22F. The current model also uses an ultracapacitor instead of a battery. The new version is equipped with a newly designed lithium-ion battery pack to supply supplemental power and also to run the air compressor necessary to get the fuel cell started. The battery is 40 percent lighter and 43 percent smaller in volume than the ultracapacitor while having much more power capacity.

The battery gets recharged by a combination of the fuel cell and regenerative braking. The regen braking is accomplished thanks to an electro-hydraulic brake system that handles the blending of regen and friction braking. In place of the electrically powered vacuum pump used for brake assist on the current car, the new one features hydraulic brake boost. Unlike some systems that integrate the booster with the slip control system, this one uses two separate units. The brake system includes disc brakes at all four corners with an electronic park brake system all suspended by double wishbones in the now classic Honda configuration.

For fuel storage, the new car replaces the two smaller hydrogen cylinders of the current car with a single larger capacity tank. Capacity of the tank is now 4kg (8.8 lbs) of hydrogen gas at 5000 psi. The combination of increased fuel capacity and more efficient powertrain yields a thirty percent improvement in range compared to the 2006 model. The current car goes 210 miles on the EPA combined test mode while the new one goes 270 miles and is expected to improve even more by the time production starts in 2008.

Click Here For Part III: Construction and Interior and Part IV: Driving at Laguna Seca



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