August 31 2009   Source: Bryan Joslin via BMW


BMW's Frankfurt Concept Combines Efficiency and Sportiness

For months the rumors have been rampant about BMW's "green supercar" project. A combination of factors — last year's record fuel prices, a global recession, new fuel economy regulations in it biggest market (the US) — have forced BMW to look at the future through more realistic lenses. It has stepped up its EfficientDynamics development program, which combines high efficiency and minimal emissions with traditional BMW driving dynamics. The new Vision EfficientDynamics concept car, which will be shown on the company's stand at the Frankfurt Motor Show starting next week, embodies the spirit of BMWs to come.

The goal for BMW's designers was to create an exciting package in which the performance of an M car could co-exist with a sustainable technology ensemble. The resulting Vision EfficientDynamics coupe features a 2+2 seating arrangement with gullwing doors and a turbo-diesel and electric hybrid drivetrain powering all four wheels.

The unique hybrid drive system employs a 1.5-liter, three-cylinder turbo-diesel engine that uses the most current engine technology available, including common-rail direct injection and a variable-geometry turbocharger. Boasting an output of 163 hp and 214 lb-ft, the little diesel sets a new standard for specific output at 109 hp/liter. The engine is mounted mid-ship, as in the BMW M1, where it is mated to a six-speed dual-clutch gearbox.

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Two electric motors assist the diesel engine. The main motor is sandwiched between the engine and the gearbox, and can be used in conjunction with or independently from the engine to drive the rear wheels. It also acts as an electric generator under braking or on when coasting. On its own it is capable of making up to about 50 hp — plenty for cruising — and a hefty 214 lb-ft of torque.

The second motor applies power to the front axle. As much as 140 hp and 162 lb-ft can be pushed through the single-speed front gearbox. As with the rear motor, the front one can run in tandem or independently from the engine.

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Power for the electric motors is stored in a 98-cell lithium-polymer battery pack. The cells are contained in a chassis element that runs through the center of the car and combined weigh just 187 pounds. Surprisingly, the need for active cooling of the battery array has been eliminated through the use of an energy management and operating strategy that prevents overheating. The batteries can be charged either through the onboard generator or through a domestic-standard (220-volt) wall outlet that recharges in just two and a half hours.

A sophisticated power management system controls which drive units are employed based on the demand for performance and the charging status of the lithium-polymer batteries. In fully electric mode, the Vision coupe can cover a little over 30 miles on a single charge, enough for an intra-urban commute. However, when the road opens up, the system can release as much as 351 hp and 590 lb-ft, allowing the 3076-pound coupe to achieve 0-to-60 mph performance of around 4.6 seconds. It is expected the concept would achieve 62.5 mpg on the EU combined test cycle and achieve a CO2 output of just 99 grams/km. With a diesel fuel tank of just 4.6 gallons the Vision is capable of a combined (electric and diesel) range of 435 miles.

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Lightweight construction and advanced aerodynamics help to achieve these performance figures. The chassis and suspension, for instance, are made entirely of aluminum, while the roof and the transparent door skins are of polycarbonate instead of glass. The seat shells are made of Kevlar. By employing knowledge gained from its Formula 1 racing program, BMW was able to achieve a drag coefficient of just 0.22.

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It's too early to start calling the BMW Vision EfficientDynamics the next-generation M1. Instead, what BMW is hoping to achieve with this concept is progress in the thinking of a what a "green car" can be as well as what sports car can be. Its goal is to convince the show-going public today — and the buying public in the very near future — that the two don't have to be mutually exclusive.