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What Makes A Hybrid

Hybrids Under the Hood

[Original Source: subsequently modified by Green Huddlers]


A hybrid electric vehicle combines an internal combustion engine and an electric motor, merging the best features of combustion engine cars and electric vehicles. The combination allows the electric motor to help the conventional engine operate more efficiently, cutting down on combustible fuel use. Simultaneously providing long distance driving and fast refueling capability via the gasoline-fueled combustion engine. In the end, this hybridization gives you the ability to drive hundreds of miles using less fuel. Gasoline-fueled HEVs are among a select few vehicle technologies that can dramatically increase fuel economy and extremely lower levels of smog-forming and cancer causing emissions, while delivering the safety and performance the public has come to expect. But that all depends on how well automakers apply the technology.


To help you navigate the hybrid market, let's take a closer look at what's under the hood that sets hybrids apart. But remember, when looking at hybrids, no matter what the technology, the clearest and most direct way to evaluate the environmental performance of a hybrid electric vehicle is by its fuel economy and emissions. So don't just trust an automaker when they tell you it is a hybrid, check the fuel economy and emissions to make sure the vehicle is significantly cleaner and more efficient than its conventional counterparts. A small light fuel efficient non-hybrid can be a far better for the environment (and your checkbook), than a giant SUV with the hybrid badge. Always check the fuel economy and emissions data available at Hybrid Consumer Center.


How we classify Hybrids: Understanding the technology

Not all hybrids are created equal. In fact, there are degrees of hybridization such as "mild" and "full" and even different drive-trains utilized depending on which hybrid you're looking at. If we approach hybrids by looking at the technological steps that separate conventional vehicles from battery electric vehicles, we can better evaluate how a particular hybrid operates.  


4 Levels of Hybridization

  1. Idle-off capability
  2. Power Assist and Engine downsizing (at this step you reach a "mild" hybrid)
  3. Electric-only drive (at this step you reach a "full" hybrid)
  4. Extended battery-electric range (at this step you become a "plug-in" hybrid)


1) Idle-Off

Like the switch that turns off the refrigerator light bulb when the door is closed, this feature allows a vehicle to turn off its gasoline engine when stopped, saving fuel. In a well-designed system, the engine will turn back on and be ready to go in less time than it takes for you to move your foot from the brake to the gas pedal. However, while hybrids use a full function electric motor operating above 100 Volts to accomplish this, conventional vehicles accomplish this same thing by using a beefed up starter motor (often called an integrated starter-generator). This ability alone does not qualify a vehicle as a hybrid even though all hybrids can do this.

A "muscle hybrid" is a vehicle that uses hybrid technology to increase power and performance rather than significantly increasing fuel economy--leading to an expensive vehicle with very low cost-effectiveness.

Some automakers are trying to take advantage of idle-off provided by beefed up starter-motors to claim they are actually putting hybrids on the road, garnering an undeserved green image. Claiming these vehicles are hybrids simply rings hollow because they don't take the next two steps, which are necessary to qualify as a real hybrid. Be wary, these are, at best, half-hearted attempts at hybridization.  Find out more information in our Hybrid Watchdog.


2) Power Assist and Engine Downsizing

The most basic definition of a hybrid drive-train is that it uses two methods of providing power to the wheels. As a result, the ability of an electric motor to help share the load with a combustion engine is the technology step that, on top of the first two, truly qualifies a vehicle as a hybrid. A vehicle meets this classification only if it has a large enough motor and battery pack such that the motor can actually supplement the engine to help accelerate the vehicle while driving. This power assist ability, combined with downsizing the engine, allows the vehicle to achieve the same performance as a vehicle with a larger engine while achieving superior fuel economy. Typically vehicles containing these first three features are categorized as a "mild" hybrid like the Insight, Civic, and Accord hybrids from Honda.


3) Electric-only-drive

This technology step allows the vehicle to drive using only the electric motor, thus taking full advantage of electric side of the dual system. With this step, we separate out "full" hybrids such as the Toyota Prius and Ford Escape Hybrid. This is the reason why Prius owners are sometimes shocked when they start their car and don't even realize it's on—only the quiet battery system is operating the car rather than the traditional rumble of the combustion engine. 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 propels the car; while at high speed the combustion engine takes over. Depending on the model, this switch over can happen anywhere from 15 to 60 MPH.


4) Extended Battery-Electric Range (Plug-in)

The final level of hybridization extends the electric motor's capacity to drive the car by charging the battery pack from the energy grid (i.e. "plug in"). This allows the hybrid to operate solely as a battery-electric vehicle for some range, such as 10-60 miles. These are designated PHEV (Plug-in Hybrid Electric Vehicle) followed by the electric range in miles. For example, PHEV that can go 10 miles on electric only after charging up is referred to as a PHEV-10. Thus improves their environmental performance even with today's "dirty" grid1. The biggest challenge with PHEVs is cost—they have the highest up-front costs because they require larger battery packs to ensure good vehicle performance and sufficient all-electric range. To-date automakers have not offered any PHEV passenger vehicles, though several have been announced and are expected in 2009-2010.


Regenerative Braking

While regenerative braking is not required in a hybrid vehicle, this article would be remiss if did not include this important feature.  The energy associated with a car in motion is called kinetic energy—the faster a car moves, the more kinetic energy it has. To slow down or stop a car, you have to get rid of that energy. In a conventional car, you use the friction of your mechanical brakes to stop, turning the kinetic energy into hot brakes and thereby throwing away the energy. "Regen" or regenerative braking takes over some of the stopping duties from the friction brakes and instead uses this to power a generator while still stopping the car. In many models the same electric motor used to propel the car can operates as a generator.  The generator recovers some of the kinetic energy and converts it into electricity that is stored in the battery pack so it can be used later to help drive the vehicle down the road. In order for the system to actually improve fuel economy, however, the vehicle must have a large enough electric motor operating at a high enough voltage to efficiently capture the braking energy. Also, the vehicle requires a battery pack with enough capacity to store this energy until it is needed. Some automakers claim to have regenerative braking on conventional vehicles with integrated starter-generators, but their system cannot recover enough energy to actually help power the vehicle or cut fuel use beyond what is achieved with their idle-off ability.


What it All Means

All of these features are a means to a end: a more fuel efficient greener vehicles. A plug-in vehicle will allow you to have some of your transportation fueled by the grid (or your solar panels), that will make it cheaper to operate it too. However it is likely to cost more to purchase. Consider all the options listed above and your driving habits and needs. Do you walk, ride, a bike or use public transportation and only rarely drive? If so, your vehicle choice is likely not worth the additional cost of a plug-in. However, if you're a road warrior, the addition fuel savings will pay back the cost quickly.



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Green Options › Articles › What Makes A Hybrid