Hybrids Don’t Save Much Gas, or Emissions
Not the kind on the market today, anyway.
So says a study done by General Motors which is to be presented to the Society of Automotive Engineers World Congress this coming April.
Conducted by three of GM’s top hybrid engineers, the study sought to ascertain the relative real world benefits of the different flavors of hybrid vehicles currently on the market and those which are expected over the next several years. The study was based on a model generated from the real-world driving behavior of 600 Southern California drivers, rather than on any EPA driving cycle, city or highway.
(more after the jump)
In most discussions, the word “hybrid” is used generically, without any effort to distinguish the very real differences in the blend of systems used to create the hybrid powertrain. While all hybrids use both electric and internal combustion drive systems, there are substantial differences between hybrid systems, depending on how much of each system is used.
For example, consider the so-called “full hybrid,” such as the Toyota Prius: The “full hybrid” moniker is somewhat misleading, because it suggests that there’s something special about the car. In reality, there’s not. A “full hybrid” is just a car with a conventional internal combustion engine that also has battery-powered electric motors which can power the car independently of the engine at low speeds, such as parking, and when extra power is needed, such as during acceleration. In those circumstances, the electric motors augment the gasoline engine’s output.
Then there’s the “conversion plug-in hybrid,” such as those being marketed by several independent companies based on a Prius. These are basically identical to the “full hybrid,” except that the batteries are larger. While a “full hybrid” relies on such energy capturing measures as regenerative braking for some of the power needed to recharge its batteries, the “conversion plug-in hybrid” allows drawing power from an external source to add to the battery power supply.
Next up is the “urban capable hybrid electric vehicle.” Such a vehicle does not yet exist, but the concept is that it is akin to a “full hybrid,” but with bigger batteries, such that it is able to run more on the battery and less with the internal combustion engine. (Think of it as a Prius with better batteries – likely what Toyota intended for the next-generation Prius, back when they thought they’d be able to make lithium ion batteries work.)
Last, but certainly not least, there is the Volt – er, well, not actually the Volt. Technically, it’s the “extended-range electric vehicle.” But, it is exactly what GM is planning for the Volt and it is what GM is talking about when it uses the term “E-Flex” to describe a powertrain.
GM wants you to think of this car as electric, not hybrid. That’s because the car is driven all of the time by the electric motors. The engine exists to recharge the batteries that provide power to the motors. The vehicle gets its extended range because the engine cuts in automatically to recharge the battery when the battery charge drops below a certain level. Until that time, the batteries are charged either regeneratively or by plugging in to an external source of electricity.
Of course, the advantage of the “extended range electric vehicle,” the E-REV, is that it provides the economy of electric motors with the range of a gasoline powered vehicle. That’s why GM’s so keen on the concept and so confident that it has a winner with “E-Flex.”
The chart accompanying this post summarizes the findings.
There is, however, an important sidelight to the study.
Not only do current types of hybrids not save much gas, they don’t do much for emissions, either.
Here’s why: the dirtiest moments in the internal combustion engine’s operation are when it is starting. The more times that the internal combustion engine in a hybrid turns off and the restarts, the more times you’re running that engine through its dirtiest phase of operation. On ordinary internal combustion vehicles, a catalytic converter ensures that the emissions components of the initial start exhaust are cleaned up. Hybrids, however, don’t use catalytic converters.
In contrast, the E-REV is designed so that it runs exclusively on electric power in urban operation and has an “extended” range that allows it to travel some distance before battery depletion causes the internal combustion engine to start. Once started, however, the engine continues to run – it doesn’t shut off and then restart because it is not powering the car, only charging the battery – until the battery has been sufficiently recharged. Hence, the dirty phase of the internal combustion engine’s cycle occurs only once.
Studies by the employees of a company that prove the company’s products to be superior to those of the competition are, of course, always suspect. As Harry S. Truman is reputed to have said, “[t]here are lies, damned lies, and statistics.” Yet, the logic behind the study’s conclusions seems self-evident: substantial improvements in fuel economy and emissions levels over those of an internal combustion engine are correlated to the extent that you don’t use one.
So, the next time some smarmy, politically correct Prius-type tries to lord it over you at a cocktail party because you drive a, say, Z4 – give him a lecture on how little he’s accomplishing with his hybrid and then tell him to call a Chevy dealer and get on the waiting list for a Volt.