The ActiveHybrid 7, a hybrid version of BMW’s 7-series luxury sedan due out in the spring of 2010, takes a very different approach. It has only a small electric motor positioned between the engine and transmission, and it comes with only a small lithium-ion battery pack. The following figure shows that the battery pack is located to the side of the trunk, leaving plenty of space for golf bags. (BMW says that four standard bags will still fit, which I suppose is a critical specification for 7-series customers.) (via CNET)
To me this always seemed like the most intuitive placement for an electric motor in a hybrid drivetrain. The service range of the electric motor is (in my observation) about the same as a torque convertor making for good serviceability.
However, does the mere 20hp this setup is currently capable of producing really offset the added weight and complication? An additional 20hp added to a 4,900 lb car is like driving with a strong tailwind.
