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A hybrid car or hybrid electric vehicle is a vehicle which relies not only on batteries but also on an internal combustion engine which drives a generator to provide the electricity and may also drive the wheels directly.
A hybrid car uses more than one power source, almost always an internal-combustion engine and an electric motor. In the hybrid design, the combustion engine is the final source of the energy used to power the car, though an alternative motor assists when more power is demanded using stored energy. This contrasts with all-electric cars which use batteries charged by an external source. Benefits of the hybrid design include the following:
The first successful hybrid electric car was engineered by Ferdinand Porsche in 1928. Since then, hobbyists have continued to build such cars but none was put into production by a major manufacturer until the waning years of the twentieth century.
Automotive hybrid technology became commercially successful in the 1990s when the Honda Insight and Toyota Prius became available. These vehicles have a direct linkage from the internal combustion engine to the driven wheels, so the engine can provide acceleration power. Prototypes of plug-in hybrid cars, with larger battery packs that can be re-charged from the power grid, have been built in the U.S., and one production PHEV, the Renault Kangoo, went on sale in France in 2003. DaimlerChrysler is currently building a small number of PHEVs based on the Sprinter van.
Earlier hybrid designs tended to use the electric motor for all power, due to simplicity. The engine would charge batteries from which the motor drew power, running only when needed to charge them back up. The engine would only run at its most efficient speed when doing so. However, this design was actually less efficient because of losses accrued in converting the kinetic energy of the engine into electrical energy, and back into kinetic energy at the wheels.
More modern designs reverse this to some degree, using the gasoline engine for primary power, but using one that is smaller than would otherwise be needed. The electric motor is essentially a very large starter motor, which operates not only when the engine needs to be turned over, but also when the driver "steps on the gas" and requires extra power. Instead of the engine solely charging the batteries, the motor acts as a generator during braking, using the momentum of the car to generate electricity. Thus the energy that would normally be lost when stopping is used to speed the car back up. Since the amount of electrical power needed is much smaller, the size of the battery systems is reduced.
Such designs were released in the late 1990s in the Honda Insight and Toyota Prius. The Insight sold poorly due to its high price and small size, but the Prius has been in high demand since its introduction. Newer designs are considerably more conventional and slightly cheaper, often appearing and performing identically to their non-hybrid counterparts while delivering 50% better fuel efficiency. The Honda Civic Hybrid appears identical to the non-hybrid version, for instance, but delivers about 50 mpg (US). The redesigned 2004 Toyota Prius improved passenger room, cargo area, and power output, while increasing energy efficiency and reducing emissions. The Honda Insight is still on sale and has a devoted base of owners, similar to the phenomenon observed with Apple computer.
2004 should see the first hybrid SUV's. Ford Motor Company is making the first hybrid SUV, the Ford Escape Hybrid. Toyota announced model year 2005 hybrid versions of the Toyota Highlander and Lexus RX 400h. Honda has also announced that they would release a hybrid version of the Accord.
An R.L. Polk & Co. Survey of 2003 automobiles showed that hybrid car registrations in the United States rose to 43,435 automobiles, a 25.8 percent increase from 2002 numbers. California had the most hybrid vehicles registered with 11,425, which may be partially due to its higher gasoline prices and emissions rules, which hybrids generally have little trouble passing.
One particularly interesting combination uses a diesel engine for power. Diesels are excellent at delivering constant power for long periods of time, suffering less wear while delivering higher efficiency. However, the engines also suffer from poor acceleration due to having a limited RPM range. This poor acceleration can be addressed with the hybrid technique, and such designs may offer performance in a car of over 100 mpg (2.35 liter/100km).
Diesel hybrid have the advantage they can use 100% pure biofuels (biodiesel), so they don´t need petroleum at all.
However, there are no diesel production models as of 2003.
Because battery technology has not advanced dramatically enough to enable battery-only vehicles to have range on a single charge comparable to gasoline cars, and because major automakers have not been interested in marketing vehicles that have enough range for daily commuting and errands but not for interstate journeys, all major automakers involved in such research have since given up, and moved to fuel cells and hybrids. Toyota has announced that it intends that all its vehicles will have a hybrid electric version by 2012. It appears many European companies, where diesel is much more common, will follow Toyota's lead and move in the same direction.
In the earliest hybrid cars, prior to the Prius and Insight, the internal combustion engine only serves as an on-board generator to supply power to the electric motor which provide the sole driving force to the wheels. This is referred to as a "Series Hybrid" system.
In the second generation, the internal combustion engine drives the wheels directly with the electric motor serving as a power assist when extra power is needed, and to recapture the kinetic energy usually lost during braking. This is known as a "Parallel Hybrid" system. The extra power from the electric motor enables the manufacturers to reduce the engine size to achieve fuel economy. Either approach has its limitations.
Starting from 2004 model year, the Toyota Prius uses the third-generation hybrid design. In this new design, the wheels can be driven by either the internal combustion engine or the electric motor using a planetary gear system to draw power from either source. The on-board computer optimizes the fuel usage by shutting off the internal combustion engine when the electric motor is sufficient to provide the power. The internal combustion engine starts up whenever extra power is needed or the battery needs recharging. The electric motor serves as the main driving force and a generator. The more efficient new design enabled Toyota to build the new Prius as a mid-size car without sacrificing fuel economy.
A "full hybrid", sometimes also called the "strong hybrid", is a vehicle that can run on just the engine, just the batteries, or a combination of both. The Prius and the Escape are examples of this. A large, high voltage battery pack is usually needed for battery-only operation.
Assist hybrids use a battery and electric motors to accelerate the car, but only in combination with the internal combustion engine. The Honda Insight is an example of an assist hybrid.
These are full hybrids, able to run in electric-only mode, with larger batteries and the ability to recharge from the electric power grid (some call it griddable hybrid.) Their benefit is that they can be gasoline-independent for daily commuting, while they have the extended range of a hybrid for long trips. The Electric Power Research Institute's research indicates a lower total cost of ownership for PHEVs due to reduced service costs and gradually improving batteries. Some critics argue that unless the electric power is generated by clean energy source (such as solar, wind, hydro, geo-thermal etc.), a gasoline hybrid car may be cleaner and more energy efficient than a PHEV when the entire powerplant-to-tailpipe energy conversion cycle is considered.
A hydraulic hybrid vehicle uses hydraulic and mechanical components instead of electrical ones. A variable displacement pump replaces the motor/generator, and a hydraulic accumulator replaces the batteries. The hydraulic accumulator, which is essentially a pressure tank, is potentially cheaper and more durable than batteries. Hydraulic hybrid technology is being actively developed by Eaton and several other companies, primarily in heavy vehicles like buses, trucks and military vehicles. Many cities, including New York City and Seattle, Washington have purchased hybrid electric/diesel buses.
There is another kind of cars that are marketed as hybrids, but technically they are not. The critics called these mild hybrid cars to distinguish from a real hybrid design. One upcoming example is the 2005 Chevrolet Silverado Hybrid fullsize pickup truck. Some people argue that it is not really hybrid since the electric motor/generator does not drive the wheels at all. In these mild hybrid cars, an oversize, large starter motor spins up the engine to operating rpm before fuel is injected into the combustion chambers. At high rpm, an engine can be restarted efficiently and cleanly. This allows the car to shut down the internal combustion engine whenever the car is coasting, braking, or stopped but the accessories can continue to run on electrical power. The motor/generator is also used to recapture energy through regenerative braking. Chevrolet was able to get a 10% improvement on the Silverado's fuel efficiency by shutting down and restarting the engine on demand. Mild hybrids often use 48 Volt systems to supply the power needed for the startup motor, as well as to compensate for the increasing number of electronic accessories on modern vehicles. These vehicles do not achieve the fuel mileage of "true" hybrid models.
Government agencies in the US offer benefits to encourage the purchase of certain qualifying hybrid or electrical vehicles.
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