Hybrids are everywhere these days and can be defined as, "any vehicle combining two or more sources of power which can directly or indirectly provide propulsion." Although all hybrid vehicles on the market today use batteries as one of the power sources, there are different mechanical layouts and operational approaches in the way electric motors function alongside gasoline combustion engines. Those that use a combustion engine to generate electrical power are described simply as "hybrids", while vehicles with larger battery packs that can also be recharged with an electrical cord are known as "plug-in hybrids". Vehicles with electric motors and without combustion engines are not considered hybrids, because they are "pure electric" vehicles. These so-called "EVs" are outside the scope of what we are covering here. In this article, we'll take a brief look at the different classifications of hybrid vehicles, how they work, and how they are laid out mechanically. We'll also discuss how hybrids save energy and save you money, how the EPA rates hybrids, and the projected costs one might anticipate if purchasing a hybrid.
Hybrid vehicles that use both combustion and electric motors are not a new invention. In fact, the first hybrid vehicle was created by Ferdinand Porsche in 1900 and featured a gasoline engine generating power for electric drive motors at both front wheels. While alternative energy vehicles have seen minor spurts of interest over the years, for example during the 1970s fuel crises, it's been within the last decade that technology has advanced the hybrid's practicality without a huge cost penalty. Toyota led the way in the late 1990's with the introduction of the Prius, which is far and away the world's best-selling hybrid. As people across the globe realize the importance of reducing pollution and conserving natural resources, the lower emissions and fossil fuel savings generated by hybrid vehicles have made them popular to purchase and to be seen in. Although diesel engines are not typically used in today's production hybrid vehicles, there will likely come a day when that is more common. Current diesel-electric hybrids such as Volkswagen's XL1 lightweight concept car powered by a compact electric motor and two-cylinder turbo-diesel have documented over 300 miles per gallon; Volvo's production V60 diesel-hybrid achieves 100 mpg; and full-size luxury cars such as Mercedes' recently-introduced E-class diesel-hybrid have been tested at 54 mpg.
Layouts of combustion engines and electric motors in hybrids vary greatly by manufacturer, and the art and science of hybrid engineering is a work in progress that's likely to see evolutionary improvements during the next decade. Terms used when describing a hybrid vehicle include:
PARALLEL HYBRID - A hybrid setup where a combustion engine and an electric motor are attached to one transmission and can power the car at the same time. Under most driving conditions, both motors are active. There can be electric-only operation at low speeds. A generator in between the engine and transmission serves to charge the battery. This setup is more fuel efficient during high-speed driving. (Example: Honda Insight).
SERIES HYBRID - A hybrid setup where electric motors provide all motive power to the wheels. A small combustion engine has no direct connection to the drive wheels and its only function is to recharge the battery pack. On short trips, the combustion engine may not even run at all. Larger electric motors necessitate battery packs which are larger, heavier, and more costly. This setup is more efficient during city driving. (Example: BMW i3)
SERIES-PARALLEL HYBRID - As its name implies, this hybrid setup is a combination of the two types described above. A power-split device is used to allow either mechanical or electrical power to the drive wheels. A smaller and more efficient combustion engine can be used. This setup maximizes the electric motor's torque at low speeds, and takes advantage of the gas engine's efficiency at high speeds. (Example: Toyota Prius)
PLUG-IN HYBRID - These can be either series or parallel hybrids, where a large battery pack powers electric motors to drive the wheels most of the time. The battery is designed to be recharged by plugging into normal household current (120V or 240V). A plug-in hybrid (PHEV) is designed to run for a longer time in electric-only mode due to its larger batteries. The combustion engine kicks in to extend its range if the battery runs down. (Examples: Chevrolet Volt, Ford C-Max)
FULL HYBRID - Any hybrid which can be propelled on just the combustion engine, just the batteries, or a combination of both, is a full hybrid. All the hybrid types described above are full hybrids. Manufacturers of supercars have recently realized strong performance gains from full hybrid setups thanks to the instant torque electric motors provide. This layout has already become a trend in performance-oriented vehicles. For example, gasoline and electric motors can be found in today's production Porsche 918s, McLaren P1s, and Ferrari LaFerraris (all achieving 0-60 times under 3 seconds) as well as upcoming Audi A8, Acura NSX, and BMW i8 models.
MILD HYBRID - A combustion-electric setup where the combustion engine propels the wheels at all times, with an electric motor assisting only when more power is needed. To save fuel, the vehicle may employ what is known as "start-stop", shutting off the engine during braking, coasting or idling. In mild hybrids, the electric motor is not capable of moving the vehicle on its own. (Example: Chevrolet Silverado, BMW 7-series)
Combustion engines are designed to be big and powerful enough to deliver peak power and great 0-60 mph times when the accelerator pedal is floored. Even though that kind of driving is done quite infrequently, internal combustion engines still burn fuel 100% of the time they're running. They are also very inefficient, with only 25% of their fuel consumption being used as energy to move the vehicle. Most vehicles need only 25 horsepower to maintain a steady cruising speed. Hybrids gain much of their efficiency by using smaller combustion engines sized for the lower horsepower demands of average driving. For example, vehicles that might normally be equipped with a V6 of 3.0 to 4.0 liters can be outfitted as hybrids with 2.0 liter 4-cylinder engines. Horsepower and torque lost from engine downsizing are compensated for by electric motors that provide additional thrust when needed.
In addition to traditional brakes, hybrids also use a regenerative braking effect when on-board sensors detect the vehicle is slowing. The physical resistance electric motors naturally have when they're not powering the vehicle allows them to act like a generator to recharge the battery. Additional fuel gains are made by using tires with a stiffer rubber compound, and inflating them to a higher psi. While these factors may result in a harsher ride, this type of "eco-plus" tire has much lower rolling resistance and creates roughly half as much drag as traditional tires do.
Hybrids with a combustion engine shut the engine down at low speeds or when the vehicle is stopped, so no fuel is wasted from an idling engine. This adds up to significant savings over time. Since combustion engines in hybrids are designed to be secondary power sources, those engines are designed to run at lower maximum rpms to allow use of lighter internal engine components that further improve efficiency.
Hybrid vehicles are full of state-of-the-art technology. In addition to the battery packs, there are electric motors, regenerative braking systems, and all the software to seamlessly operate the systems. Comparing suggested retail prices of 'gas-only' and hybrid versions of the same make and model may result in sticker shock once you realize that fuel-saving hybrids may cost $2,000 to $8,000 more.
With that kind of extra cost up front, figuring out how much money a hybrid will save gets trickier. Realizing how off-putting higher sticker prices of these vehicles can be, the U.S. Federal government has enacted a tax credit for buyers of pure electric and hybrid-electric vehicles ranging from $2,500 to $7,500, based on battery capacity. These credits expire once a vehicle manufacturer's model reaches a certain sales plateau. For more details on specific makes and models, the U.S. Department of Energy's Tax Incentives Information section is an excellent source of information. Their website also features a comparison calculator which allows a visitor to compare any hybrid model of their choice to a non-hybrid version of that same model, or to a completely unrelated one.
In a 2013 study by U.S. News & World Report, gas and hybrid-electric versions of five popular models were compared using then-current gasoline prices of $4 per gallon and an average of 15,000 miles driven per year. They found a hybrid version of the Volkswagen Jetta cost $8,300 more than the base model, added 156 miles to the range, added 55 horsepower, and saved $800 annually on fuel (42/48 mpg vs. 23/29). A Ford Fusion hybrid cost $5,500 more, added 185 miles to the cruising range, added 13 horsepower, and saved $850 annually on fuel (47/47 mpg vs. 22/34). A Toyota Highlander SUV hybrid cost $8,275 more than a V6 4-wheel-drive model, added 105 miles to cruising range, added 10 horsepower, and saved $860 annually on fuel (28/28 mpg vs. 17/22). Interestingly, Lincoln priced their MKZ hybrid the same as their V6 gas model. The hybrid added 181 miles to cruising range, lost 52 horsepower to the gas version, and saved $800 annually on fuel (45/45 mpg vs. 19/28).
According to the TrueCar Data firm, the fuel savings of a Ford Fusion hybrid would take six and a half years to offset its higher sticker price if gasoline cost $5 a gallon, and eight and a half years at $4. If gasoline were to climb to $6 per gallon, hybrid Hyundai Sonatas, Toyota Camry, and Kia Optimas would lead the way with a payback period of only four years. TrueCar also calculates that a buyer selecting a Nissan Leaf pure electric vehicle over a similarly sized Nissan Versa gas model wouldn't see a payback for eight and half years at $4 per gallon, and six years at $5 per gallon.
Another cost to take into consideration is the replacement of the battery pack. Initially, there was great concern about both the longevity of the battery as well as its price. With time, the industry has seen that the battery packs can last 10 years or more. Some hybrids used as taxis have approached 200,000 miles, still running on their original battery packs. The aftermarket has also responded with the availability of replacement hybrid batteries at a more reasonable cost.
In 2010, the United States Environmental Protection Agency (EPA) began assigning multiple economy ratings to plug-in hybrid vehicles (PHEV). Because fewer gallons of fuel are used to power the vehicle, additional ratings were developed to reflect how effectively a hybrid uses electricity. We'll take a look at these figures that are now mandated on new car window stickers such as kilowatt-hours per 100 miles (kWh/100m), mpg-equivalent (MPGe), combustion engine economy (if it's powering the vehicle by itself), annual electricity cost, and cruising range.
First, kilowatt-hours per 100 miles are based on a formula where 33.7 kilowatt hours equal one gallon of gasoline. Because the house or building you'll plug your vehicle into for charging is also billed in kilowatt hours, this makes it easier to figure typical dollar costs you'll face. An "MPGe" rating signifies how many miles the vehicle can go using the same energy content as a gallon of gasoline, with a small "e" designating energy content. This formula uses a common standard where 115,000 BTUs equal the heat energy that would be generated by burning one gallon of gasoline. Vehicles that can run on either electric or combustion are required to display both an MPGe rating (shown on a miles per gallon format) and a traditional MPG rating for the gasoline engine on its own. Range, especially the distance one can drive in "all electric" mode, is hyper-critical for buyers who want to maximize how far they can travel without burning fuel. Prospective purchasers of hybrid vehicles are well-advised to consider the full picture, including initial cost, intended driving range, local cost of electricity (for PHEVs) and future gasoline prices. This much is certain: the hybrid vehicle is here to stay, and technical advancements will make such a vehicle a more attractive option for a greater number of buyers in the future.