Peugeot To Show First Production Diesel Hybrid, For Europe Only

Peugeot 3008 HYbrid4 Concept

We're pretty focused on the US car market here at GreenCarReports.com, so we don't write about cars we won't be able to buy all that often. Today, we're making an exception for a particularly significant technology advance.

Next month, at the Frankfurt Motor Show, French automaker Peugeot will unveil the 3008 HYbrid4 Concept, which will become the world's first diesel hybrid-electric vehicle when it goes into production next year as a 2011 model.

Gasoline only, until now

Starting with the groundbreaking 1997 Toyota Prius, all hybrids until now have used gasoline engines. "Full hybrids," which can run in all-electric mode for short distances, usually fit a gasoline engine that's modified to match the electric motor's low-end torque.

But in Europe, more than half the new cars sold are highly fuel efficient turbodiesels, from cars as small as the Mini D up to the largest luxury sedans. (Though it's worth noting that most of them wouldn't pass stringent US emissions requirements without added, and costly, exhaust treatment equipment like particle filters and additional catalysts.)

Peugeot (and its partner Citroen) have been working on diesel hybrids for most of the decade, and have shown several generations of concept vehicles.

The 3008 multi-purpose vehicle, or MPV (the European name for minivans and people movers), was launched this past January. For the 2011 model year, it will carry the world's first diesel hybrid powertrain offered for sale by any automaker.

Other carmakers have been studying diesel hybrids as well, and Volvo is rumored to be planning at least one vehicle for launch in 2012. Thus far, though, Peugeot clearly leads the pack--and it has never even offered a gasoline hybrid.

2009 peugeot 3008 official photos 022

Emissions as low as a subcompact

Peugeot expects the diesel hybrid to provide fuel savings of up to 35 percent over a non-hybridized engine with the same performance, and says the 3008 HYbrid4 concept emits just 99 grams per kilometer of carbon dioxide (CO2).

That's as good as the most efficient diesel subcompacts without hybrid systems, and better than the 109 g/km the company projected in January.

The new powertrain uses a full parallel hybrid design, in which the car can be moved by its 163-horsepower, 2.0-liter diesel engine powering the front wheels, the rear-mounted 37-hp electric motor powered by a lithium-ion battery pack, or both at the same time.

The combined mode is similar to the all-wheel-drive system used in the 2009 Toyota Highlander Hybrid and 2010 Lexus RX450h hybrid crossovers, which eliminates the weight and cost of mechanical drive.

(The tradeoff, though, is reduced ability: The controls shut down the electric motor if it overheats under a heavy load, such as it might experience while trying to move the vehicle out of a particularly boggy or slippery surface.)

As in all hybrids, the battery pack is recharged via regenerative brakes, which feed torque to the electric motor/generator to convert it back into stored energy, rather than wasting it as heat from conventional friction brakes.

Peugeot 3008 HYbrid4 Concept

Doctoring for diesel

In some ways, a diesel engine is not a terribly logical partner for the electric motor in a hybrid powertrain. For one thing, diesels develop their best torque at low speeds, just like electric motors.

In full hybrids, the gasoline engines are tuned to operate on what's called the Atkinson Cycle. It makes them very efficient, but with almost no low-end torque at all--a deficiency neatly remedied by the electric motor(s), which develop maximum torque from 0 rpm.

So diesels in hybrid applications have to be tuned to produce torque as high as possible in their limited range of engine speeds. Peugeot has no doubt spent quite some time doing just that.

Secondly, diesels are already more efficient than gasoline engines--a good rule of thumb is that diesels convert up to 35 percent of fuel energy into torque, whereas gasoline engines are closer to 25 percent. So adding hybrid gear to a diesel may improve fuel economy less, because it's starting from a more efficient base.

Finally, modern turbodiesels are 10 to 15 percent more costly to build than gasoline engines. Adding a battery pack, electric motor/generator(s), and power electronics to an expensive engine makes the whole package even pricier than a gasoline hybrid.

Still, Peugeot has as much experience with small, high efficiency turbodiesel engines as any European carmaker. And electric drive is very clearly one of the tools for further reducing fuel consumption and tailpipe emissions. If not Peugeot, then who?

2009 peugeot 3008 official photos 008

Not for the US

We're not likely to see diesel hybrids in the US market any time soon, however. Neither Peugeot nor Citroen has sold cars here for two decades. And diesels haven't sold well since the 1980s, despite decades of diesel models from Mercedes-Benz and Volkswagen.

We think the 2010 Volkswagen Golf TDI could be diesel's big winner in the US (because it's inexpensive), but that Audi, BMW, and other prestige brands may struggle in convincing buyers that diesels match their brand image.

Already BMW has added special incentives on its two diesel offerings, the 2009 BMW 335d and 2009 BMW X5 xDrive35i. Those are on top of IRS tax credits for the 335d and X5 diesel, but sales are still slower than BMW's projections.

Nonetheless, the 2010 Peugeot 3008 HYbrid4 will be a significant achievement when the first ones roll off the lots at French dealers. It's just one more sign that the proliferation of powertrain options to improve fuel efficiency and cut emissions isn't ending any time soon.