2013 Honda Fit EV applies ‘lessons learned’ from fuel-cell Clarity

  • 20-Nov-2012 05:30 EST
2013 Honda Fit EV.jpg

Leveraging knowledge gained on Honda’s previous electrified-vehicle programs, the 2013 Fit EV boasts a combined adjusted EPA mpg-equivalency rating of 118 mpg-e, in addition to an estimated EPA combined city/highway driving range of 82 mi (132 km).

Honda began developing battery-electric powertrains for automobiles in 1988, with that early research culminating in the 1997 EV Plus—a four-passenger electric vehicle (EV) utilizing nickel metal-hydride (NiMH) batteries. A range of electrified vehicles has since followed, including the 2000 Insight hybrid, the 2002 FCX fuel-cell car, the 2008 FCX Clarity dedicated fuel-cell vehicle, and the latest addition, the 2013 Fit EV.

“It’s this continuum of improvement,” Steve Ellis, Manager of Fuel Cell Vehicle Sales and Marketing at American Honda Motor Co., explained to AEI. “As I’ve said over the years, we never stopped developing electric vehicles: through transition from EV Plus to the first FCX, which was the fuel-cell vehicle based on the EV Plus—it used the same drivetrain, and that was with the Ballard stack. The next fuel-cell vehicle was the Honda stack FCX, and that led to Clarity. Right up till today, we’ve continued developing electric vehicles.”

Inevitably, each successive electrified vehicle borrows from its forebears and builds upon lessons learned. And the Fit EV is no exception. For example, Bio-Fabric seating material pioneered in the FCX Clarity finds its way into the Fit EV, albeit a different formulation derived from a different feedstock. The Fit EV's seat fabric is polyethylene terephthalate (PET) based on sugarcane-derived ethanol, while the initial Clarity’s Bio-Fabric was a polytrimethylene terephthalate (PTT) material made by fermenting corn.

The ethanol for the Fit EV’s PET is produced using bagasse, the fibrous matter that remains after sugarcane stalks are crushed to extract their juice. Honda notes that since bagasse is not foodstuff—unlike corn—its use does not adversely affect food supply.

Inside Honda's 92-kW electric machine

The most obvious influence on the Fit EV is in the powertrain. “The Fit EV actually utilizes the drive motor and the electronics control from the FCX Clarity. Some will say, ‘It’s derived from…’ [but] it’s the actual components,” Ellis shared. “Now the difference is that we can electronically tune those for power output.”

In the 2011 FCX Clarity, power output from the ac synchronous permanent-magnet motor is 100 kW; in the Fit EV, output is 92 kW in the Sport driving mode (75 kW in Normal mode; 47 kW in Econ). The electric machine's rotor and stator feature a combined reluctance-torque, low-loss magnetic circuit and full-range, full-digital vector control. Honda claims that the average motor efficiency in the EPA city test cycle is 94.6%.

The car's driveshaft passes through the center of the hollow rotor shaft in a coaxial configuration, which allows the motor and gearbox to be combined into a single compact unit. The rotor features an interior permanent magnet (IPM) to lower inductance, improving reluctance torque and delivering the same high torque rating (256 N·m/189 lb·ft) as the Clarity.

Compared to the rotor designs in the EV Plus and FCX Clarity, the shape of the magnet in the Fit EV rotor has been optimized to increase energy conversion efficiency, according to Honda. And the Fit EV's motor housing is a more rigid structure to minimize noise and vibration.

The new EV’s Toshiba-produced, 20-kW·h SCiB lithium-ion battery is air-cooled and positioned under the passenger compartment.

“A lot of things like the Li-ion battery, for example, are both in the [Fit EV] and in our hybrids. Our first application of Li-ion batteries in a production car was in this [FCX Clarity],” said Ellis, noting that the previous FCX fuel-cell car had ultracapacitors for energy capturing and regenerative braking.

All-new regen braking system

“The advancements of the regenerative braking system [in the Fit EV] are a result of, again, lessons learned from Clarity,” Ellis continued. “It’s an all-new system, but when we have vehicles with all-electric drive and incorporating regen braking, we can keep improving that. So feedback from customers, lessons learned from Clarity and even our hybrids led to the development of that system.”

Advanced cooperative control between the electric powertrain and the newly developed electric servo brake system results in an 8% increase in energy recovery compared to conventional regenerative braking, according to Honda. A distinctive feature of the new brake system is that in addition to the master cylinder, all slave cylinders are also individually controlled.

With “brakes off,” the servo motor provides no pressure in the brake lines to eliminate any loss. During regenerative braking, the servo motor applies no pressure; the pedal force simulator provides the driver with the desired linear brake-pedal feel. With friction braking, the servo motor provides brake pressure according to the brake-pedal stroke. When the driver releases the throttle pedal, regenerative braking is initiated.

As the driver steps on the brake pedal, the drive motor switches to generator mode to maximize energy recovery. Before the vehicle comes to a full stop, braking is gradually apportioned from regenerative to friction braking for a smooth stop.

Regenerative braking is further increased when selecting the new “B” (Brake) shift position—a helpful feature when controlling the Fit EV’s following distance behind a car, or when driving downhill. To reduce brake-pedal operation in downhill driving, the Fit EV’s braking system incorporates “regenerative grade logic” that automatically increases regeneration to help limit vehicle speed.

The system regulates speed when the driver first releases the accelerator pedal and also helps maintain constant vehicle speed after the driver initiates brake-pedal inputs—functionality similar to engine braking in a gasoline-engine vehicle.

The continuity that Ellis referenced applies not only to Honda’s electrified vehicles, but also to the entire vehicle development team. Ellis’ history at Honda stretches back to the original EV Plus, and also includes alt-fuel vehicles such as the Civic GX natural gas vehicle.

“Even though my title is on the marketing side, my background is very technical. I’m not an engineer, but I’m accused of it,” he quipped.

Ellis noted that the three Japan-based Honda R&D engineers who were present at a Fit EV media event this past summer—Sachito Fujimoto, Chief Engineer and Large Project Leader (LPL); Kenichiro Kimura, Powertrain Assistant LPL; and Hideo Sakai, Dynamic Assistant LPL—have similar backstories.

“All three of them had a direct role with EV Plus previously, and all three of them worked on the FCX Clarity program,” Ellis said. “It’s not like they were taken off of one [program] and put onto another; we’re doing parallel development of the next-generation fuel-cell vehicle from Honda and, of course, Fit EV.”

The Fit EV uses the standardized SAE J1772 charging port. When connected to a standard 120-V AC outlet, the car can be fully recharged in less than 15 h, claims Honda. With a 240-V AC Level 2 Electric Vehicle Supply Equipment device connected to the Fit EV’s onboard 6.6-kW charger, the charge time is said to be less than 3 h.

Currently available for lease only ($389/month for 36 months) in select markets in California and Oregon, the Fit EV will expand to select East Coast markets in spring 2013. Honda anticipates production of approximately 1100 vehicles in MY2013-2014.

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