BMW’s High MPG ActiveHybrid

by Todd Kaho

12/08/2008

EfficientDynamics is a principle BMW Group is using to define company efforts aimed at protecting the environment – efficiency combined with driving dynamics. From advanced technology clean diesel to powertrain efficiencies, weight saving technologies, and exploration of alternative fuel sources, the goal is a systemic approach for planned sustainability and reduced fuel consumption with lower emissions. From 1990 to 2005, this approach allowed BMW to reduce CO2 emissions by 12 percent and fuel consumption by 14 percent, which is significant considering the fleet grew during that timeframe to include larger sedans and SUVs.

Certainly, BMW isn’t locked into one technology or direction for improving environmental performance. The latest evidence was revealed at the recent L.A. Auto Show in the form of a mild hybrid version of the large 7 Series luxury sedan. The BMW 7 Series ActiveHybrid is currently a concept, but the car displayed in L.A. appears close to production-ready. The ActiveHybrid scheme is logical in a large luxury sedan, providing additional performance, improved economy, lower emissions, and more voltage for high-end electronics.

BMW 7 Series ActiveHybrid lithium-ion battery

The hybrid technology employed in the 7 Series was developed in collaboration with Daimler for use in upscale vehicles. It places a small, highly efficient electric motor inside the transmission housing. Electrical energy is stored in a compact, high performance lithium-ion battery mounted below the load floor in the trunk. In the concept, a clear panel trimmed in stainless provides a view of the power pack from above. Energy normally wasted during deceleration is captured through an aggressive Brake Energy Regeneration scheme and is fed back into the high capacity lithium-ion battery. The car also features an on-board 120 volt electrical network that operates in parallel with the 12 volt system.

The 15 kW motor in the transmission adds 20 horsepower and, more importantly, 155 lbs-ft of torque to the propulsion system. Combined with a twin-turbo V-8 internal combustion engine that delivers 407 horsepower and 442 peak ft-lbs of torque, total output comes to 427 horses and a whopping 597 lbs-ft of torque.

BMW 7 Series ActiveHybrid twin turbochargers

The 4.4-liter aluminum V-8 features twin turbochargers mounted in the ‘V’ between the cylinder banks to boost performance. Each turbo feeds four cylinders in the innovative design. Fuel is delivered by BMW’s second-generation direct injection technology known as High Precision Injection. The system utilizes piezo injectors to squirt fuel into the cylinders at 2,900 psi. Though the ActiveHybrid 7 is a large sedan, acceleration with the high performance V-8 and electric assist is impressive. Likewise, fuel economy is also improved, with independent testing showing a 15 percent improvement in the EU fuel economy cycle. That should translate to 27 mpg on the highway by U.S. EPA standards.

In Europe, this class of vehicle is known as a luxury saloon, defined by a flowing hoodline, long wheelbase, and generous cabin area which work together to produce substantial overall presence. BMW’s rendition is unique, managing to be both sporty and elegant. The concept has a different front end treatment with air intakes below the signature kidney-shaped dual grille openings that’s highlighted by a horizontal brushed aluminum band. Seven LED fog lamps are located at the outboard section of the intake. The design is balanced by a rear fascia duct, also trimmed with a brushed aluminum band that incorporates the exhaust outlets.

Front view of Efficient Dynamics BMW 7 Series ActiveHybrid

There’s no missing the fact that this car is part of the BMW EfficientDynamics strategy. The rich Blue Water metallic paint treatment is emblazoned with bold EfficientDynamics graphics and BMW ActiveHybrid identification along the flanks. Finishing touches include a slightly lower stance and lightweight 20 inch alloy wheels that are color matched to the body.

BMW’s 7 Series ActiveHybrid is much more than an interesting design exercise. It’s a bit of fresh thinking that succinctly illustrates the potential of clever engineering and underscores that no platform is off-limits when it comes to ‘green’ design. Will it see production? BMW isn’t saying, but count on several of the technologies developed here making their way into future generations as the company moves forward with its EfficientDynamics strategy.