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Technology and Features


While the FCX Clarity incorporates a plethora of interesting and often novel technologies, the real star of the show is the fuel cell power source and electric drivetrain. The fuel cell itself is the culmination of nearly a decade of research. It produces 100 kW of output, displaces 52 L of volume and weighs a mere 147 lbs (67 kg). Compared to the first stack that Honda was using in 1999, the new V Flow FC Stack represents a power improvement of 67%, a weight reduction of better than 67% and a size reduction of better than 60%. For a more real world comparison, imagine a typical tower style personal computer and double its depth front to back - that's about the size of the V Flow FC Stack.

In order to improve the efficiency of the stack Honda has made a number of innovations in its fundamental design. First and foremost, they have moved to a vertical flow layout (hence V-Flow) for hydrogen and air which allows the resulting byproduct (water) to drain more efficiently for improved power production and consistency. Just as importantly, by using gravity to drain the cell, the depth of flow channels was reduced which significantly reduced the size of the stack. Honda has also implemented a "wave flow" design for the flow channel separators. This results in better diffusion of hydrogen and air for more efficiency, plus it provides a means for cooling channels to be compactly interlaced among the flow channels. More power, reduced size and improved efficiency. There is much, much more, but since fuel cells are still relatively "black box" technology for most of us, we'll leave at this - Honda has improved the design and manufacturing of their fuel cell substantially and it shows in the size and output of the V-Flow FC Stack.

Supplementing the fuel cell stack during acceleration as well as absorbing power during regenerative braking is the responsibility of a compact Lithium Ion battery (about half the size and weight of the previous FCX's ultracapacitor). This battery actually has lower energy density than commercially available Li-Ion units, but much higher output density - necessary for handling the large and rapidly changing power demands during acceleration and regeneration.

The V-Flow FC Stack and Li-Ion battery work together to power the compact 100 kW electric motor. By passing the drive axle through the center of the motor, the size of the motor and transmission have been substantially reduced. The overall height of the motor, transmission and Power Drive Unit (basically overall power control for the motor) is less than 30" and the width front to back is about 12". The motor produces 189 lbs-ft of torque from approximately 0-2500 rpm and 134 hp from approximately 3500-8000 rpm. The approximate figures are due to a lack of exact data from Honda at this point. What we can say is that the motor is producing peak power from approximately 35 mph to 80 mph according to Honda figures.

Body and Structure

The design of the FCX Clarity is focused on the propulsion system and hydrogen storage tank. Because of the distributed drive system, designers were given more freedom (they state that as long as they had 4 wheels, the rest was up to them), but they were also constrained by safety concerns. The V-Flow FC Stack is located in the center of the car, low and between the passengers, while the motor is up front and the Li-Ion battery under the rear seat. The hydrogen storage tank is positioned between the rear wheels and suspension structure.

With this basic structure outlined, the designers were able to create a completely flat underbody for improved aerodynamic performance (no hot exhaust gasses makes this much easier). And the small size of the motor up front meant that the cabin could be pushed very far forward relative to traditional front engined gasoline vehicles. Careful obsevers will also note a slight narrowing of the body from front to rear, especially in the greenhouse area. This teardrop shape is highly efficient from an aerodynamic standpoint (see the Honda Insight for an early application of this shape on production cars), and Honda's designers have incorporated it without compromising interior space.

Finally, the structure of the car is designed to not only protect the occupants, but also the hydrogen tank and V-Flow FC Stack. Crash forces are routed around critical components and occupants and critical areas are reinforced. Honda has already performed extensive crash testing on the FCX Clarity (front, side and rear impact).


There is of course, great concern that hydrogen powered vehicles may pose additional safety risks, and not just during crashes. In addition to the specially designed structure, Honda has also implemented special measures to protect occupants and rescue responders in the event of component failure or accidental damage. First, both hydrogen and high voltage lines (the V-flow FC Stack operates at 288 Volts nominal) are isolated from the passenger cabin so that the chance of contact or leakage in the passenger compartment are minimized. The vehicle also contains numerous hydrogen sensors throughout which, if hydrogen is detected, will trigger a warning light, or in more serious cases, activate cut-off valves and switch on ventilation systems in the cabin. Other sensors will disconnect all high voltage lines in the event of a crash or accidental grounding. Interestingly, the 12 Volt battery under the hood is not just for accessory power. In our discussions with Honda engineers working with fire departments to educate them on FCX Clarity safety issues, we were told that the 12V battery actually powers the activation switch for the car so that all an emergency responder needs to do to cut power is disconnect the 12V battery.

Luxury and Special Features

Honda has chosen to make the FCX Clarity a premium vehicle, and as such has equipped it with many high end features not found on other vehicles in this class. Along with traditional VSA and TCS, Honda has included Adaptive Cruise Control, previously found on the Acura RL.

A relatively new technology called Motion Adaptive Electric Power Steering has also been adapted to the FCX Clarity. This system works with the VSA and TCS systems to change steering effort in response to road conditions and vehicle attitude. For example, in cases of understeer, the EPS will decrease steering effort as the point of the limit of adhesion is reached to communicate the decreased grip to the driver. If the driver persists in applying too much steering input, the system will increase steering effort to discourage the driver from applying more steering lock and making the understeer worse. In cases of oversteer, as the limit of adhesion is reached at the rear, the steering effort will be increased to discourage additional steering input. If oversteer occurs, the effort remains higher in order to prevent the driver from overcorrecting and spinning in the opposite direction.

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11-28-2007 07:52 Total efficiency   (Score: 1, Normal) Dren
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