What Makes it a Hybrid?
There are four different principles to Hybrid Vehicle designs
A Hybrid Vehicle is any vehicle that uses more then one source to propel it. Generally, these types of vehicles contain a petrol motor (Gasoline or Diesel) and a secondary electric motor. Most of the Hybrids on the road today use the electric motor to offset the use of the petrol motor, thus extending the MPG of the vehicle.
There are many people and grassroot organizations that are taking matters into their own hands by adding additional batteries to not only increase the MPG, but to run the vehicle directly on electric power. Plug-in kits and companies that supply them are gaining in popularity.
If you already have a Hybrid such as a Toyota Prius or Honda, you can extend your driving range while decreasing your MPG.
Below, we look at the different types of Hybrid Vehicle technology that are in use today.
Different Types of Hybrid Vehicles
·Parallel Hybrid Electric Vehicle 
Parallel Drivetrains.
In a parallel hybrid electric vehicle, both the engine and the motor can drive the wheels . Both the Honda Insight and the Honda Civic Hybrid are parallel hybrids.
Parallel drive trains are mechanically more complicated than series drive trains. For one thing, a transmission is required to allow the engine to drive the wheels. Then there must be a means of coupling the engine, motor, and transmission. Finally, the controller necessary to make all these components work together is more complex than in the series drive train.
· Series Drivetrains
In a series hybrid electric vehicle, an electric motor is the only means of driving the wheels . The motor obtains electricity either from a battery pack or from a generator powered by an engine in much the same way as a portable generator. A controller determines how power is shared between the battery and the engine/generator set.
· Split Parallel Hybrid
One special type of parallel hybrid uses a “split” drivetrain, in which the engine drives one set of wheels, while an electric motor drives another . This can provide 4-wheel drive, although recharging the batteries by the engine is then more complicated since it involves operating the front wheels in regenerative braking mode while the engine is driving the rear wheels. At one time, Daimler Chrysler planned to produce a Dodge Durango SUV with such a system.
· Series-Parallel Hybrid
Series/Parallel Drivetrains. The Toyota Prius made popular a new concept that combines many of the advantages of the parallel drive train with the series drive train’s ability to maintain engine operation near its most efficient operating point Variations on this design have shown up in the Nissan Tino Hybrid, which was sold for a short period in Japan, and is being incorporated into a hybrid vehicle developed by Paice Corporation