The Ford Fusion Energi. Credit: Ford

Ford unveiled its new Fusion Energi plug-in hybrid at the North American International Auto Show in Detroit this week. It didn't say much about the car, except that it will get something like 100 miles per gallon equivalent (MPGe), which is better than the Chevrolet Volt or the upcoming Toyota Prius plug-in, and that it will go on sale toward the end of this year.

Of course, 100 miles per gallon equivalent sounds impressive. Unfortunately, the MPGe figure is not very meaningful. It's useful as a way of comparing the efficiency of cars when they are operating in electric mode, but for a plug-in hybrid, which can run part time on gasoline, it doesn't tell drivers what they really want to know: how much gas the car will use and how much it will cost to operate.

According to the U.S. Environmental Protection Agency definition, MPGe is meant to describe the efficiency of the vehicle when operating using electricity alone, which in a plug-in hybrid is typically only a relatively short range—the Chevrolet Volt can go about 35 miles on the electricity stored in its battery. MPGe refers to how many miles the car can go on an amount of electricity equivalent to a gallon of gasoline.

Based on the figure of 100 MPGe, we know that the Fusion Energi will be slightly more efficient in electric mode than the Volt (93 MPGe) and the all-electric Leaf (99 MPGe).

But drivers need to know how far the car can go on electricity and under what conditions the gas engine will come on, to figure out how much gas they'd use. The Chevrolet Volt can go 35 miles on battery power before using the gas engine. The upcoming Toyota plug-in Prius will only get about a dozen miles on a charge. If your commute is 30 miles round trip, you could get away without using any gasoline with the Volt, but not with the Prius. If your commute is much longer than the Volt electric range, you may want to consider the Prius, which gets 49 miles per gallon after the electricity is gone, rather than 37 miles per gallon for the Volt.

So we don't know how far the Fusion Energi will go on battery power. We don't even know if it will be able to achieve highway speeds on electricity alone. And there's no way for drivers to know how much gas it would use, or whether it would make more or less sense to buy than its competitors.

Credit: GM

Today GM announced that it will introduce changes to the Chevrolet Volt to guard against fires like the ones that occurred after crash tests last year.

New Volts will incorporate the changes, including steel reinforcements, starting this month. The approximately 12,000 cars that have already been built (about 8,000 have been sold so far) can also be retrofitted at dealerships starting in February. The retrofits will be part of a voluntary program, not an official product recall.

GM has also confirmed what caused a handful of Volt battery fires in testing last year. A side-impact test caused part of the Volt's structure to break into the battery casing, and a small coolant leak was exacerbated when, as part of the test procedure, the battery was slowly turned over. When the battery pack was upside down, the coolant leaked onto a circuit board, which caused a short, and then the fully charged battery caught fire.

The fires could likely have been avoided if the batteries had simply been drained of charge after the test—much as a conventional vehicle would have its gas tank drained. The fires didn't start right after the crash tests, so there would be plenty of time to do this. But the changes to the Volt are meant to prevent coolant leaks as the result of a side-impact collision.

Much has been made of the fact that the Volt battery pack isn't encased in metal, while the pack for the Nissan Leaf electric car is. But the Volt pack is, in fact, well protected by a steel tunnel built into the floor of the car.

Battery Reinforcements: Engineers add steel brackets to the undercarriage of the Chevrolet Volt. Credit: GM

GM is adding extra steel braces to the steel tunnel to further protect the battery. The company says tests show this will prevent coolant leaks. GM is also adding coolant level sensors and a special tamper proof cover meant to prevent overfilling of the coolant.

Mary Barra, GM's senior vice president of global product development, said today that the fires were not the result of a problem the battery cells inside the battery pack. She also said no changes will be made to the manufacture of the battery pack itself. And she expressed confidence in the safety of the lithium-ion chemistry GM is using, saying that the cells had been subjected to rigorous tests, including driving nails through them.

Despite all of those tests, apparently the cells—at least when fully charged—are still not robust enough to keep from catching fire after a short caused by a coolant leak.

It's not clear whether a more stable battery chemistry, such as the lithium-iron phosphate materials used by companies such as A123 Systems, could have prevented the fires.

Having a few electric vehicle charging stations here and there isn't a big deal. But if they ever become common in cities, they'll be an eyesore, with their long, tangled black cords clumped onto their sides or sprawling across parking spaces to the outlet on the side of a car. Charging stations could also be a tempting target for vandals.

A much more elegant solution would be to bury inductive chargers under parking spots, a concept that Daimler has started testing. The chargers could be invisible and protected from vandals. And they could make charging easier—just pull into a parking spot, and the car can start charging.

Daimler, along with Conductix-Wampfler, a company based in Germany, has only recently started testing cars equipped with the inductive charging coils. But the initial results look positive.

The system is 90 percent efficient, which isn't as good as charging with a cable, but is better than some other inductive charging systems. The companies say that when you count efficiency losses within the car, the system is almost as good as plugging in.

Daimler has modified a E-Cell plug-in hybrid concept vehicle like this one to allow it to charge without having to plug in. So what will we call plug-in hybrids now? Credit: Daimler

In initial tests, after two or three practice runs, drivers have been able to successfully park their cars so that they're centered over the charging coils.

An object detection system is supposed to avoid the potential problem of the buried coils heating up a piece of metal left on the road. The prototypes are based on a wireless charging system developed for electric buses that has been operating since 2003.

It will be interesting to see how the cost of the system compares to conventional chargers, and whether it will still be necessary to install a post for communications gear, to allow drivers to pay for the charge with their credit cards, for example. Ultimately, cities will have to decide whether the better looks and convenience are worth the sacrifice in energy efficiency.

The company WiTricity is developing chargers that could be more convenient still, charging efficiently at distances greater than is allowed by inductive charging. We featured the technology as one of our 10 Emerging Technologies of 2008.