How Hybrids Work
In theory hybrids work quite simply. How that theory is implemented in any particular vehicle can be somewhat complex, but that's a topic for another time.
By definition a hybrid uses two or more methods to convert stored energy into motion. By making the best use of each method, the idea is to make a vehicle that among other benefits is more economical to operate.
You may not be aware that hybrids have been a popular form of transportation since the early 1900's. Diesel locomotives, or more properly, diesel-electric locomotives are indeed a perfect example of hybrids. The first gas-electric locomotive was built by General Electric in 1910. GE also built the first commercial diesel-electric in 1918.
While those first locomotives are a far cry from what they have evolved into over the years, the idea is still the same. A gas or diesel engine turns a generator or alternator and creates electricity. That electricity powers electric motors attached to the drive wheels and moves the train.
Hybrid Cars - Gasoline and Electric
Some of the original proposals for hybrids cars were very much like diesel-eletric locomotives. A gasoline engine would drive a generator or alternator creating electricity. That electricity would charge a bank of batteries.(there's the difference) The electricity from those batteries would power electric motors attached to the drive wheels.
If not for the short life, the high maintenance, the expense, the weight and the environmental issues of those original batteries, many more of us would probably be driving hybrid cars today. Battery technology has certainly come a long way in last ten or fifteen years, but in the meantime the automotive designers and engineers have designed hybrid systems that are more similar to a conventional car. These systems rely less on the battery packs while still providing most of the benefits of those early hybrid designs.
Today's typical hybrid includes a transmission which receives its power from both a gas-powered engine and an electric motor. The flow of electricity to the electric motor is controlled by a computerized power box and derived from the smaller bank of batteries.
Electric Motor Functions
There are several ways the electric motor can assist the gas-powered engine in a hybrid vehicle. A particular hybrid may use one or a combination of several of these ways.
Powering the transmission: In most vehicles the transmission connects to the wheels, so whatever turns the transmission makes the wheels turn. The electric motor may at times power the transmission on it's own in some hybrids. This would occur at lower speeds and at these times the gas-powered engine would be in "stand-by" mode and use no gas.
Assisting the engine: Hybrid vehicles have smaller engines than gas-only vehicles because the electric motor is available to help power the transmission. This combination of motor and engine can provide the same power to the wheels while reducing gas consumption.
Restarting the engine: When a conventional vehicle is stopped in traffic, the engine idles, burning gasoline. In a hybrid the engine can be stopped when the vehicle is stopped. The electric motor then acts as a starter for the engine when needed again. The motor also keeps other systems like the air conditioning running when the engine is stopped.
Recharging the batteries: under certain conditions, braking, cruising, etc., the motors role is reversed and it actually recharges the batteries.
These functions of the motor can cause the hybrid to perform in ways equal to a conventional vehicle while still conserving gas. As these functions are combined in a hybrd vehicle it becomes more fuel efficient.
Batteries in Modern Hybrids
Today's hybrid vehicles store electricity in a high-tech pack of NiMH (nickel metal hydride) batteries. Some of the features that make them ideal for helping to power a vehicle:
No need to plug in: todays hybrid vehicles don't need to be plugged in to recharge the batteries. A hybrid can generate plenty of electricity while driving to recharge it's NiMH battery pack.
Reusing otherwise wasted energy: in conventional vehicles braking only generates heat, wasting the energy that was used to accelerate. Many hybrids instead generate electricity while braking, recharging the batteries and conserving energy.
No need to replace: unlike many types of rechargeable batteries, hybrid vehicle batteries retain their ability to recharge for many years. The electronic control system of most modern hybrids never allow the battery pack to fully charge or discharge. This keeps the batteries at the optimum charge, about half, extending their life beyond that of the typical vehicle.