Plug-ins on the line

摘要

Carmakers are hard at work developing the next generation of vehicles. Many, such as General Motors, Toyota and Ford, see plug-in hybrid electric vehicles as playing an important role in the future. The technology means that we can drive further using less fuel, and in some cases we would be able to drive purely on the electric power stored in the car, simply recharging the vehicle overnight while we sleep.rnThis idea raises issues for emissions testing procedures. How do you test a vehicle that, depending on how it is driven, could produce zero emissions? In the US, the Environmental Protection Agency (EPA) is working on a new test cycle that fits better with the way such cars work.rnAt present all vehicles have to go through the Federal Test Procedure. It is a city driving cycle that allows the EPA to test NOx levels, particulate matter and CO_2 emissions. It also measures a vehicle's fuel economy.rnAdd to this the Supplementary Federal Testing Procedure, which incorporates testing with the air conditioning switched on and more aggressive driving, and emissions can be tested for all driving styles. Even with the introduction of conventional hybrids such as the Toyota Prius, the procedure did not require significant changes.rnEPA light duty vehicle group manager Linc Wehrly says: "The biggest thing with the hybrids is the battery's state of charge. We test hybrids just like any other car, but the state of charge has to stay within +1 or -1%. We're assuming the state of charge fundamentally doesn't change." This is the problem that faces the EPA and carmakers. To meet this criterion, the vehicles will have to switch on their engines to maintain a constant battery charge - increasing emissions.