Hybrid cars built to conserve fuel

With current gas prices, we're hearing a lot right now about hybrid cars because of their excellent gas mileage. Last week, I received a question from a reader that gets at the essence of hybrid car technology. The question was, "How can a hybrid car be any more efficient than a normal car, given that the engine has to charge the batteries?" In other words, since the engine has to burn gas to charge the battery anyway, why doesn't the mileage of a hybrid car work out to be the same as a normal car?

Let's explore the technology of hybrid cars using the Toyota Prius as an example. The Prius has both a small gasoline engine and an electric motor. There is also a battery pack for the motor, a special transmission that lets the engine and the motor work together and a computer that controls the whole thing.

When you are sitting still in a Prius, for example at a traffic light, the gasoline engine does not need to run at all. By eliminating the idling, you automatically save gas. If you are traveling slowly in a Prius, for example inching forward in bumper-to-bumper traffic, the electric motor can do the driving and the engine does not need to run. Once you get above 15 mph, the gas engine kicks in. Bumper-to-bumper driving is a huge gas-waster for a normal engine. When you rev the engine to travel at 5 miles per hour and then stop again, there is no better way to waste gasoline.

When you drive a hybrid car in bumper-to-bumper traffic and it is time to recharge the batteries, the engine can run at a consistent, optimal speed to spin the generator. There is no revving and stopping. So the engine is always being used as efficiently as possible. That makes a hybrid car like the Prius much more efficient in city driving.

Add to that the fact that the gasoline engine in a hybrid car can be very small and light compared to a normal car engine. That makes the engine more efficient all the way around. Then you add to that the fact that most hybrid cars like the Prius are very aerodynamic. They also have special tires, etc. to make them more efficient. Many hybrid cars use regenerative braking to capture the car's energy during braking and store it in the batteries. Finally, there is the car's computer and display. The display tells the driver when he or she is wasting gas (for example, by accelerating too fast), and this helps the driver do a better job.