BMW is expected to unveil its third hybrid model at the 2010 Geneva Motor Show this March. It will be a mild-hybrid version of the all-new 2011 BMW 5-Series sedan line it has just unveiled, which will go on sale in June.

The ActiveHybrid 5 will follow in the footsteps of the 2010 BMW ActiveHybrid 7, its fullsize hybrid luxury sports sedan, and use much of the same hybrid system.  In the 7-Series, a three-phase synchronous electric motor is connected to the crankshaft of the car's 4.4-liter gasoline V-8 engine and drives through a new 8-speed automatic transmission.

The car is a mild hybrid, so while its electric motor restarts the gasoline engine after it shuts off at stops--and adds torque to assist the  engine as well--it cannot travel on electric power alone, as do such full hybrids as the 2010 BMW ActiveHybrid X6 "sports activity coupe".

The combined output of the hybrid system in the larger 7-Series hybrid is 455 horsepower and 516 pound-feet of torque, sending the ActiveHybrid 7 from 0-60 mph in just 4.8 seconds while offering fuel economy that's 15 percent better than the similarly powerful 750i.

In November, Peter Tünnermann, project manager for the ActiveHybrid X6, told the British magazine Autocar that BMW would introduce its third hybrid within 12 months. The ActiveHybrid 5 was widely expected to be that car, and it is now confirmed.

Tünnermann said, "Volume models like the 3-, 5- and 7-series are clearly more suited towards a mild hybrid set-up on the basis of their packaging and broad appeal." This obviously leaves open the possibility of a BMW ActiveHybrid 3 to come.

It's unclear whether the BMW ActiveHybrid 5 will be launched with the rest of the 2011 BMW 5-Series range in the U.S. next fall, or whether it will lag a year and be offered as a 2012 model. We'll bring you more details from Geneva when we have them.

[Automotive News (subscription required) via MotorAuthority]