Hybrid automobiles, or hybrid electric vehicles, are automobiles that use both a traditional fuel-burning internal combustion engine and an electric power train. Electrical power is stored in onboard batteries, which may be charged either by the internal combustion engine or (in the case of plug-in hybrids) by being plugged into a power source to draw electricity off the grid, as full-electric vehicles do. Most of today’s hybrids also make use of regenerative braking in order to improve energy efficiency and reduce waste heat. Hybrids in general have better fuel economy than similar conventional vehicles and use smaller internal combustion engines, without facing some of the disadvantages of full-electric vehicles.
In today’s infrastructural landscape, the main disadvantage of an electric car intended for mass production is the need to recharge the automobile’s batteries. While this may be possible at home—and even then, apartment dwellers among others may have difficulty recharging at home—it is far more difficult on the road, and except in California, recharging facilities are not common at U.S. gas stations.
Many hybrid cars use a start-stop system, which reduces the amount of time the engine spends idling by automatically shutting off the internal combustion engine when the car is stopped (such as in heavy stop-and-go traffic, in line at drive-throughs, or at traffic lights). Originally introduced for conventional internal combustion engine vehicles in the 1970s amid concerns about volatile gasoline prices, start-stop systems have become more common in hybrid vehicles. In particular, this improves fuel and energy efficiency in city driving, which is typically the least efficient mode of driving. Powered features like onboard radio and climate control are usually designed to run off the electric motor rather than stopping and starting with the engine.
While many drivers have absorbed the idea that every engine start induces wear on the engine, this is really only significantly true of cold starts (when the car has been stopped long enough for the engine to cool down), especially in cold weather. The short stops of a start-stop system do not weather the engine in the same way, as the oil that lubricates it has remained warm.
On the other hand, batteries do wear out faster when a start-stop system is used, especially the absorbent glass mat (AGM) lead acid batteries used by most automobile manufacturers—but even so, replacing a battery thus worn down is a much cheaper proposition.
Mazda in 2011 introduced an improved stop-start system, the i-ELOOP, which determines which piston in the internal combustion engine is in position for the fastest restart of the engine, resulting in a restart time of less than half a second, and which while decelerating into the stop converts kinetic energy to electricity that is stored in a double-layer capacitor that powers the car’s electrical system during the stop period.
Some hybrids have been called “electric assist” vehicles, or mild hybrids, because they lack a mode of propulsion that depends only on electricity, requiring the use of the internal combustion engine for that. The electric motors in mild hybrids are small and replace the starter and alternator of the conventional design, improving the car’s efficiency and making a start-stop system possible. Though regenerative braking is often used, it recovers far less energy than in full hybrids, and in general the fuel efficiency gains of a mild hybrid design are, as the name indicates, mild. Honda’s Integrated Motor Assist feature is an example of a major manufacturer’s mild hybrid design, as is the discontinued hybrid version of the Chevrolet Malibu.
Mild hybrids use motor-generators, power transducers that are also used by many other hybrid designs. Most manufacturers have developed proprietary motor-generators for use in their vehicles, with mild variations on the same fundamental design principles, such as Toyota’s Hybrid Synergy Drive. All such drives are electrical generators that can also function as motors. In the case of mild hybrids, their motor power is limited and powered by electricity generated by the internal combustion engine while it is in use.
Regenerative braking is a popular feature in hybrid cars and greatly assists in their energy efficiency and emissions. All braking systems work, by definition, by reducing the kinetic energy of the car’s forward motion. Conventional automobile brakes accomplish this by friction. Applying friction increases the amount of necessary force required to turn the wheels, which then slow down much faster than if the car were to simply coast to a stop (slowed by the friction of its contact with the road). Excess energy is converted into waste heat. Regenerative braking instead reclaims as much kinetic energy as possible, diverting it to operate an electric motor in order to generate electricity, which is then stored in the onboard batteries. Conventional brakes are still used as well, however, because regenerative braking does not function well at low speeds, at which point friction braking does the rest of the work. Regenerative brakes also do not work to keep cars from rolling down inclines.
The use of hybrid cars has been encouraged in the United States through various means in order to reduce America’s dependence on fossil fuels, America’s contributions to greenhouse gas emissions, and the impact of gasoline price volatility on the American economy. A federal income tax credit was offered from 2005 to 2010, for instance. The American Recovery and Reinvestment Act of 2009 opted to focus on infrastructure improvements rather than consumer incentives, but new legislation has added tax credits for plug-in electric vehicles. Several states (including Arizona, California, Florida, New York, and Virginia) also allow certain hybrid cars to use carpool/HOV lanes with only one passenger, based on the premise that hybrid car usage offers a fuel efficiency benefit comparable to that of carpooling. San Jose, California, formerly offered a free parking permit to hybrid vehicle owners whose cars had been purchased locally, and Los Angeles offers free parking in city-owned parking spaces for all hybrid or fully electric vehicles. Other cities have considered similar initiatives, though the 2008 financial crisis has tabled many such discussions.
Though hybrid designs were developed at the dawn of the 20th century, not until the end of the 1990s were any hybrid cars made widely available. The Toyota Prius and Honda Insight were the first major hybrids available in the United States and remain leading brands today. Though modern hybrids premiered on the Japanese market (and a larger percentage of the Japanese market is made up of hybrids), the United States has become the largest hybrid market in the world, with over 2.5 million hybrids sold by 2013.
Major hybrid vehicles in the 2010s include the Toyota Prius, Honda Insight, Cadillac ELR, and hybrid versions of the Toyota Camry, Ford Fusion, Volkswagen Jetta, and Honda Accord. Major launches have also been scheduled for a Toyota RAV4 hybrid, diesel hybrid Volvos, and hybrid versions of the Toyota Corolla, Hyundai Accent, and Mercedes-Benz E-Class.
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- Life Cycle Assessment of Greenhouse Gas Emissions From Plug-In Hybrid Vehicles: Implications for Policy.” Environmental Science and Technology, v. 42/9 (2008). ; . “
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