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05MAY 2012

i8 Concept / BMW

Posted in Design - Transport by FORMAKERS

The story of the i8 begins with its so-called LifeDrive architecture.

BMW says that its experiences in creating the Mini E and 1-series-based BMW ActiveE showed that adapting cars engineered for internal-combustion power to electric propulsion results in a lot of excess weight and compromises in packaging. As a result, both the i8 and i3 are built using two purpose-built modules: one to house passengers, dubbed “Life,” and one for propulsion and suspension components, called “Drive.

” Combine them, and you have a car—and marketing-friendly “LifeDrive” branding. While the i3 and i8 share the LifeDrive architectural philosophy, the cars differ in execution.

That’s because the i3 is fully electric, while this i8 is a plug-in hybrid. The i8’s powertrain is split between its two axles, with an electric motor and direct-drive transmission at the front axle and a gas engine and transaxle at the rear.

Interestingly, the battery packs in the i3 and i8 use different lithium-ion chemistries, as well as unique shapes.

The large, square pancake battery of the i3 is designed for longer distance travel—in other words, it has a lot of energy—and is located below the passenger compartment. In contrast, the i8’s lithium-ion cells protrude into the coupe’s Life space, where, as in the Chevrolet Volt, the liquid-cooled and -heated battery stack fills a hump that could be mistaken for a transmission tunnel.

The i8’s elongated pack is designed to deliver shots of power in short spurts; the final spec is yet to be decided, but it should have a capacity of around 8 kWh. Arranging the pack this way allowed BMW’s engineers to achieve yet another claim of perfect 50/50 weight distribution, thereby preserving peace in the city of Munich.

As in the i3, the i8’s Drive components are largely crafted of aluminum, while the Life module uses a carbon-fiber skeleton wrapped in thermoplastic exterior panels. So much lightweight material allows the i8 to use a smaller, lighter battery than would be needed if the car were made of heavier steel.

This frees up room in the cabin, and, more important, keeps the curb weight around a svelte 3300 pounds. The rigidity imparted by the carbon fiber also allows for long, dramatic doors that ease access to the two small rear seats.

While most other hybrids are based on existing front-drive vehicles, BMW had the luxury of starting from scratch.

As with all 50/50-balanced cars, the majority of braking forces occur at the front axle. So, in the effort to recoup as much energy from regenerative braking, it makes sense for BMW to fit the electric half of the powertrain up front.

The i8 uses a modified version of the i3's electric motor, with a peak output of 129 hp and 184 lb-ft of torque. It’s fed juice, of course, by those lithium-ions, and takes about two hours to charge from a 240-volt trough.

Battery topped off, the i8 will return 20 miles of all-electric driving..

Design team:
BMW

Status:
Proposal

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