DaimlerChrysler presented an update on what it is learning from its F 500 Mind—a diesel-hybrid research car first unveiled at the Tokyo Motor Show last year (mentioned briefly in an earlier post).

The F 500 MIND is a platform for a number of technology innovations; tempting as it might be to explore those, I'm just going to focus on the diesel hybrid drive.

The F500 MIND is a full-size luxury fastback sedan concept—larger than the S-Class. Its full parallel hybrid drive system pairs a 184 kW (250 hp) 4-liter V8 diesel engine with a 50 kW electric motor to produce a combined output of 234 kW (313 hp) and a total peak torque of 860 Nm. That output makes it, according to DaimlerChrysler, the most powerful hybrid drive to be fitted in a rear-wheel-drive passenger car at the present time. The vehicle uses a 300V Lithium-Ion battery.

The F500 features stop-start functionality and regenerative braking. The electric drive takes over completely in slow-moving stop-go traffic, for acceleration or for parking. The combination of these functions reduces fuel consumption by some 20% compared to a comparable conventional diesel in the NEDC (New European Driving Cycle) test cycle and emissions by 15–20%. The latter is also a result of the sensor-controlled exhaust treatment system.

However, once the DCX researchers took to the road under practical operating conditions, the results changed.

“The actual fuel consumption of the hybrid drive on longer interurban or motorway journeys is actually higher than with the standard Mercedes diesel model.”

Dr Herbert Kohler, Vice President, Body and Powertrain Research
Chief Environmental Officer for DaimlerChrysler

The road trials confirmed that the hybrid drive’s primary area of use will be for inner-city driving where the benefits offered by engine shut-off at traffic lights and energy recovery during frequent braking can be fully utilized. Now the DCX researchers are now more closely comparing the hybrid system vis-à-vis a comparable diesel engine to better define a future application scenario for the hybrid drive.

“We are looking to fine tune the hybrid drive and deploy it in such a way that its benefits outweigh the tremendous technical effort involved. As a result of the practical tests that have been held so far, we now know that the diesel engine holds a greater overall potential for reducing fuel consumption and levels of CO₂ emissions.”

Dr Herbert Kohler

Relevant to this discussion and these results are some comments that came in from a Green Car Congress reader—a European engineer—in a private email. His observation was that hybridization of the diesel engine might be only way to meet the next generation of more stringent EURO5 diesel emission levels without sacrificing fuel economy. (More exacting standards require more add-on emissions control systems, which in turn increase consumption, which eats up the efficiency improvements in the engine.) Nevertheless, he concludes, a diesel meeting CAFE SULEV standards very likely will not show the kind of mileage we know from current diesels—even with hybridization.

DaimlerChrysler also has in the works a diesel hybrid version of its Vision Grand Sport Tourer, and has shown an early production model. (Earlier post.) I’m looking for some clarification from DCX on these results from the F 500, and any impact that might have on their plans for the Vision GST Hybrid—or if there are comparable test results from that vehicle as well.