BMW AG and DaimlerChrysler AG, both holdouts in joining the hybrid-electric vehicle segment, agree to collaborate on the development of mild-hybrid powertrains for rear-wheel-drive premium cars.

Mild hybrids generally feature a starter/alternator unit for engine start-stop capability, along with a small battery pack for power boosts and capturing energy from regenerative braking. The vehicles are not capable of running on electric power only and usually do not produce the same fuel savings as full hybrids.

“This collaboration will allow us to broaden our technological base in the area of future hybrid-drive systems for the premium class and will allow the two companies to pool their innovative resources,” says Klaus Draeger of BMW’s management board.

“The distinct identities of the different brands will not be affected, since the relevant technologies will be tailored to fit the specific character of the different vehicles.”

Both auto makers plan to market their respective systems within the next three years, DC says, declining to indicate which models are being targeted for hybridization.

The project will complement the work accomplished through the auto makers’ 3-way alliance with General Motors Corp. for the development of Two-Mode full-hybrid systems and advanced batteries.

GM and DC’s Chrysler Group already have announced several applications for their full-hybrid systems, such as fullsize trucks and SUVs.

And twice in the last two months, Chrysler President and CEO Tom LaSorda has hinted at future hybrid programs, one of which involves mild-hybrid technology.

But BMW and Mercedes-Benz have been mum on what they planned to do with their part of the technology.

Gasoline powertrains initially will be targeted by BMW under the new agreement due to the potential for greater fuel savings over diesels, Reuters reports, but the auto maker plans to look at the feasibility of both gasoline and diesel hybrids in the future.