by Sam Domett

Created on: January 10, 2011

The simplest hybrid drive system is the series hybrid, where an engine drives an electric motor and/or charges a battery. This is very common in locomotives and in early experiments with electric vehicles, but is not commonly used today in cars.

Toyota Prius Hybrid Synergy Drive

The second type is the series-parallel, as in the Toyota Prius, where there is a petrol engine, an electric motor, and a storage battery. Either the petrol engine or the electric motor can move the car, or both can operate at the same time, when extra acceleration is needed.

The Prius uses Toyota’s Hybrid Synergy Drive, in which the electric motor is connected to the drivetrain through a planetary gearbox, which allows the engine to move the car, the electric motor to move the car, or both to move the car.

Honda Insight Ecological Drive Assist System

The Honda hybrid system – Eco Assist - is different in that the starter motor has been replaced by an electric motor sandwiched between the engine and the gearbox. Like the Prius, the Honda system can use the electric motor, engine, or both to move the car.

Stop Start Systems in Cars

Most hybrid vehicles have a stop/start system as part of the drivetrain, which means the engine shuts down when the car comes to a stop, further saving fuel. When the driver presses the throttle, depending on conditions, the engine will start, or the electric motor will push the car, or if the driver is really in a hurry, both motor and engine will activate.

What Batteries do Hybrids Use?

The most common type of battery being used today is the nickel metal hydride battery, but lithium-ion batteries, such as the ones in cell phones, promise more storage capacity and power, and research is under way into integrating this type of battery into a hybrid system. Several hurdles have to be overcome, such as increased price, and the higher operating temperature of Lithium- ion batteries.

What is Regenerative Braking?

It’s important to note that most hybrid vehicles offer the best performance in urban areas, where the car can use regenerative braking. An electric motor can operate in two ways. If electricity is supplied to it, it will turn, but if the motor turns – as when the car slows down and the wheels are turning the motor - the motor becomes a generator, producing electricity. This electricity is then delivered back into the battery pack.

Driving on highways doesn’t involve much slowing down, so the benefit of regenerative braking is not as strong, and therefore a hybrid will get much lower mileage when driven long distances at speed than when it is driving in traffic that stops and starts periodically.

Some new cars, notably the latest BMW 1-Series, are now coming out with a mild hybrid system that uses regenerative braking only, which feeds power into the cars standard battery, reducing the amount of work the alternator has to do in producing electricity to run the car’s systems, and so saving fuel.

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