Although the first successful hybrid car was developed back in 1900, the more recent wave of eco-friendly hybrid vehicles arrived largely thanks to a number of technological innovations. Without advances in mechanical systems, electronics and materials, hybrid designs would have remained impractical and costly. Each innovation solved key technical challenges, resulting in cars with very high fuel efficiency.
A lightweight, high-capacity battery is essential to a hybrid, as it stores the energy needed to propel the car. Lead-acid batteries, long used to start traditional cars and trucks as well as to run golf carts and other short-range vehicles, are inexpensive and practical but heavy. Batteries with lithium-ion or nickel-metal hydride chemistries have good energy storage capacity and significant weight savings compared to lead-acid designs.
Virtually all hybrid cars reap significant energy savings through a technology called regenerative braking. A traditional braking system dissipates a car's motion through simple friction -- rubbing a brake pad against a metal disk. This works well, but wastes the energy of movement as heat. Regenerative braking recovers the energy as electricity, using the wheels to turn a motor/generator. The braking system recharges the battery with this electricity.
Hybrid cars are so called because they have two sources of power: a traditional internal combustion engine and an electric motor. The addition of the motor, battery and other components means extra weight, so car designers strove to minimize the additional mass. One strategy employed was the use of the rare-earth metal neodymium in the electric motor's magnets. Neodymium makes the strongest permanent magnets known to science, producing powerful forces from a relatively small amount of material. This allows automakers to produce compact, lightweight motors with enough power to propel the car.
Running a hybrid car means controlling dozens of complex variables involving the battery charge, vehicle speed and many other factors. Fortunately, the same tiny microprocessors that power every device from toaster ovens to Web servers can rapidly compute the best combination of electric and gasoline power for different circumstances. An array of sensors feed the processors with data in real time, forming an accurate, responsive control system. The chips are lightweight and draw little power of their own, allowing the car to run at high efficiency.
The transmission of a traditional car manages the engine's power and torque for a given revolutions-per-minute rate and vehicle speed. A hybrid's transmission has a more sophisticated mechanism, combining the output of the engine and electric motor to suit the needs of the moment. The transmission handles the different torque characteristics of the engine and motor, producing net power that runs the vehicle. In addition to fulfilling the mechanical requirements, the transmission is also lightweight, reliable and doesn't add excessive cost to the car.
Chicago native John Papiewski has a physics degree and has been writing since 1991. He has contributed to "Foresight Update," a nanotechnology newsletter from the Foresight Institute. He also contributed to the book, "Nanotechnology: Molecular Speculations on Global Abundance."