Porsche Hybrid Slims Down

Porsche’s first fully hybrid production model SUV, the 2011 Cayenne S Hybrid, touts some impressive power and performance numbers.

Its supercharged 3.0-liter V6 gas engine and electric motor, combined, can deliver up to 380 hp. Reports say it can go from 0 to 60 mph in 6.5 seconds. And it has a top speed of 150 mph. Yet, quite remarkable, the two and a half ton SUV still has an estimated EPA fuel economy of 23 mpg city, 26 mpg highway.

How did Porsche accomplish this? Like any auto maker converting a gasoline or diesel model to hybrid, Porsche had to make some design tradeoffs. Specifically, it had to address the increased weight when adding the electric drivetrain to an existing gasoline powered SUV.

In general, the additional weight factor can be significant. The main components of an electric drivetrain, its motor and batteries, can weight several hundred pounds. This is bad in a few ways. For any vehicle, the more weight, the slower it moves with a given horsepower gas engine or electric motor. And the more weight, the lower the fuel economy.

To offer good fuel economy and keep performance in line with what’s expected in a Porsche, weight tradeoffs had to be made. Just how much does reducing a vehicle’s weight help? According to the U.S. Department of Energy, “for every 10 percent of weight eliminated from a vehicle’s total weight fuel economy improves by seven percent.”

To trim weight from the Cayenne S Hybrid, Porsche “jettisoning the conventional 4×4 drivetrain and [went] with much lighter all-wheel-drive system,” according to the Wall Street Journal. The company also increased the use of aluminum (replacing heavier steel elements) in the SUV’s body. 

Combined, these changes saved about 400 pounds. Even with that reduction, the Cayenne S Hybrid still weights about 465 pounds more than the gasoline powered Cayenne V6.

Going forward, as automakers try to push up the fuel economy of hybrids, weight is going to be an ongoing problem.

Certainly, this is not a new issue. For years, automakers have reduced vehicle weight using aluminum for steel for select body frame parts. And they have made extensive use of composite plastics for interior elements as well as door panels, bumpers, and other body parts. However, there is a potential problem with this approach. Namely, many customers want their hybrid cars and SUVs to be green. Unfortunately, the traditional plastic composites are not.

Automakers have been trying to address this issue by using more recycled plastics and bio-degradable materials. For example, about “5 to 10 percent of the plastics currently used in GM vehicles are made of recycled materials – a number that’s considerably higher than it was five years ago,” according to an AOL Autos article.

On the biodegradable front, Ford, Honda, Toyota, and others have been replacing some parts traditionally made from plastics with parts made from more environmentally-friendly materials. Materials being explored are based on a variety of plants including coconut, flax, hemp, nut shells, and soybeans. Most of these replacement efforts have focused on interior parts including seat foam, seat coverings, and interior panels.