Understanding Hybrid Electric Vehicles
Understanding how hybrid vehicles work will help you evaluate the choices in the market and choose the best vehicle for your needs.
Hybrid electric vehicles combine an internal combustion engine with an electric motor powered by batteries. This combination is more efficient and cuts down on fuel use. However, not all hybrid vehicles are the same. There are different degrees of hybridization and different drivetrains utilized depending on which hybrid you're looking at.
Hybridization:
Idle-off capability
The Idle-off feature enables a vehicle to turn off its gas engine when stopped in order to save fuel. In a well designed system, the engine will be ready to go again almost instantly. All hybrids have this feature, but so do some conventional vehicles, so having this feature doesn't make a vehicle a hybrid.
Regenerative Braking
In a regular car, the friction of the brakes is what stops the car. Regenerative braking takes over some of the stopping duties from the friction brakes and uses the electric motor to help the car stop. The electric motor operates as a generator, recovering some of the kinetic energy and converting it into electricity that is stored in the battery so it can be used later to help drive the vehicle.
Power Assist and Engine Downsizing
A hybrid vehicle is one that uses two methods of providing power to the wheels. The ability of an electric motor to help share the load with a gasoline engine is the technology that truly qualifies a vehicle as a hybrid. A vehicle meets this classification only if it has a large enough motor and battery pack that the motor can supplement the engine to help accelerate the vehicle while driving.
Electric-only-drive
This technology allows the vehicle to drive using only the electric motor and battery, taking full advantage of electric part of the dual system. This is a full hybrid. The greater flexibility of full hybrids allows the vehicle to spend more time operating its engine only when it is at its most efficient. At low speeds and at launch, the electric motor and battery powers the car and at high speeds the engine takes over.
Extended Battery-Electric Range
The final level of hybridization extends the electric motor's capacity to drive the car by recharging the battery by plugging it in. A plug-in hybrid can operate solely as a battery-electric vehicle for as much as 20-60 miles, improving the environmental performance.
Drivetrains:
The drivetrain of a vehicle is composed of the components that are responsible for transferring power to the drive wheels of your vehicle. With hybrids there are three possible setups for the drivetrain: the series drivetrain, the parallel drivetrain, and the combined series/parallel drivetrain.
Series Drivetrain
In a series hybrid, the electric motor is the only means of providing power to turn the wheels. The motor receives electric power from either the battery pack or from a generator run by a gasoline engine. A computer determines how much of the power comes from the battery or the engine/generator set. Both the engine/generator and regenerative braking recharge the battery pack.
Parallel Drivetrain
With a parallel hybrid vehicle, both the engine and the electric motor generate the power that drives the wheels. The addition of computer controls and a transmission allow these components to work together. Parallel hybrids can use a smaller battery pack and therefore rely mainly on regenerative braking to keep it recharged. Since the engine is connected directly to the wheels, it eliminates the inefficiency of converting mechanical power to electricity and back, which makes these hybrids very efficient on the highway.
Series/Parallel Drivetrains
This drivetrain merges the parallel and series drivetrains. By combining the two designs, the engine can both drive the wheels directly and be effectively disconnected from the wheels so that only the electric motor powers the wheels. As a result of this dual drivetrain, the engine operates at near optimum efficiency more often.
Published on WEDNESDAY, February 11, 2009 - Email to a friend
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