The two-mode system in the BMW Concept X6 ActiveHybrid combines two compact, high-performance electric motors with a electrical continuously variable transmission (ECVT) transmission using fixed transmission ratios. These drive systems are connected to one another by three planetary gearsets allowing a power split covering the drive forces of the combustion engine and the electric motors in two transmission ranges, thereby providing optimum power and maximum efficiency under all driving conditions and power requirements from the driver.

In the power split drive mode, also referred to as the output branched concept, one of the two electric motors acts as a generator, converting some of the engine’s power into electrical current subsequently fed to the battery or the second electric motor. The second electric motor then converts such power coming from the first electric motor or from the battery back into mechanical power for the output drive shaft on the transmission.

Where GM is using the full-range optimization of the two-mode drive system to enhance towing capabilities of its full-size SUVs that are its initial targets for the system, BMW is highlighting the potential for enhanced performance and driving dynamics, along with reduced fuel consumption.

BMW Concept X6 ActiveHybrid can be driven on electric power only, on the combustion engine alone, or with a combination of both power units. When operating in all-electric mode, the underfloor protection panel moves up to cover the two tailpipes on the exhaust system as long as they are not required for their normal purpose.

Daimler’s Mercedes-Benz also introduced a two-mode SUV at Frankfurt. The ML 450 Hybrid is due to be launched on the market in 2009 as a gasoline hybrid using the two-mode hybrid drive. With a combined system output of 250 kW (340 hp) and a combined maximum torque of 480 Nm, the ML 450 Hybrid consumes 7.7 liters per 100 kilometers (30.5 mpg US)—equivalent to CO2 emissions of 185 g/km. (Earlier post.)

In parallel to the Global Hybrid Cooperation effort with GM and DaimlerChrysler, BMW has also entered into yet another joint venture with DaimlerChrysler to develop components for a mild hybrid drive in luxury performance sedans. (Earlier post.)