Hybrid-Electric Drive

The drivesystem in a conventional car consists of an internal-combustion engine mechanically coupled to the drive wheels through the transmission, driveshaft, and so on. This is an ingenious but complex and inherently inefficient way of converting fuel into traction at the wheels. A much better way is to have the engine (or other power source) generate electricity from the fuel, which then powers motors that turn the wheels. Such a "hybrid-electric" drivesystem offers several advantages over conventional systems.

Most importantly, the engine needs to handle only the maximum continuous load, not the peak load. Unlike the mechanical torque generated by a conventional system, the hybrid's electricity can be stored temporarily in a small battery or other similar device until it's needed for extra acceleration. Result: the engine can shrink to a fraction of the current normal size, reducing weight, cost, and fuel consumption; and it can always run at or very near its "sweet spot," typically doubling drivesystem efficiency. It can even turn off automatically whenever it's not needed.

Additionally, the electric motors of a hybrid vehicle can recover part of the braking energy that would otherwise be lost as heat in the brakes. They become generators, slowing the vehicle by using its kinetic energy to make electricity that is stored until needed. Some experimental vehicles have demonstrated up to 70-percent peak energy recovery, but recovery of about 50 percent is seen by many experts as a more realistic goal.

And finally, hybrid-electric drive opens the door to other exciting new electrical power sources, such as fuel cells.

The exact workings of hybrid drivesystems vary. There are two basic configurations: parallel and series. For more details on these, see the Hybrid Vehicle Propulsion Program On-Line Resource Center (http://hevdev.nrel.gov).

Many auto manufacturers are now developing or selling hybrid-electric cars, which is a huge leap forward in its own right. However, thanks to the principle of mass decompounding, hybrid-electric drive works better and costs less if you reduce the vehicle's weight and drag first.

Don't confuse hybrid-electric vehicles with battery-electric vehicles. Hybrids generate their own electricity onboard, so they don't have to haul around hundreds of extra pounds of storage batteries, nor do they suffer from the short driving ranges and long recharging times of battery cars.