Saturday, October 13, 2012

BMW i3

The i3’s story begins with its LifeDrive architecture. According to BMW, experience with the Mini E and BMW  Active E (the electric 1-series coupe) has proven that creating an electric car out of a structure designed to house an internal-combustion engine results in wasteful excess weight and imperfect packaging. As a result, the i3  is made up of two separate modules, which BMW calls Drive and Life.
The Drive portion, made of extruded and cast aluminum pieces, carries all the driveline and chassis components. For an optimized center of gravity, the i3’s large and flat battery, roughly the size of the floor, sits low in this section. It’s encased in aluminum and has a capacity of roughly 21 kWh. Because the car is still a few years from production, the exact specs have yet to be nailed down.

Back inside the Drive structure, the i3 uses a 168-hp electric motor that’s 40 percent more compact than that of a Mini E, allowing it to fit right above the rear axle. Power is delivered to the wheels via a direct-drive single-speed transaxle. Yes, one speed. That means the car will never shift on its way up to a computer-limited top speed of 93 mph, which BMW has determined to be the point at which the batteries begin to drain too quickly. The company says the i3 will run 0 to 62 mph in 7.9 seconds. In terms of passing power, accelerating from 50 to 75 mph should take just six seconds.
Peak torque is 184 lb-ft. Range is estimated at 80 to 100 miles, and a full charge from a 240-volt source will take about six hours. With a special high-speed charger, the i3 is said to be capable of reaching an 80-percent charge in just an hour, meaning medium-range drives can be done with just a long coffee break in the middle. But wait, there’s more, as the infomercial folks might say.

Among the i3’s other energy-saving details are familiar concepts like the “air curtain” first seen on the updated 2011 1-series, which smoothes airflow around the front wheels, as well as narrow, drag-reducing tires. Like the accelerator in a Tesla Roadster, the i3’s go pedal is tuned so that the car will still coast if the driver lifts just slightly, while lifting entirely off the pedal will engage regenerative braking based on pedal position. BMW predicts that, in around-town driving, this will allow the brake pedal to go untouched 75 percent of the time.
Beyond that, a button-activated Eco Pro mode changes throttle response so that the same pedal travel delivers less power. In this mode, speed is capped anywhere between 56 and 74 mph, and climate-control output is reduced. However, because the batteries use the climate system to stay at an operating temperature of 68 degrees, the system always remains running to some extent. Eco Pro can extend range by as much as 20 percent. Truly distressed drivers will be able to fall back on Eco Pro +, a mode that shuts down daytime running lights and any other non-vital energy drains, limits climate control functions to a minimum, caps speed at 56 mph, and tells the driver to get bent when he dives into the accelerator. Oh brave new world, with such vehicles in it.

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