With a prohibitively limited driving range and far longer "refueling" times than conventional ICE (internal combustion engine) vehicles, it's no surprise the expensive battery electric vehicle (EV) isn't yet a market-viable transportation solution. Those disadvantages are why EVs were beaten out by ICEs in the industry's early days, and why they have not been able to compete effectively ever since.
But today's "hybrid" electric vehicles (HEVs) marry EV and ICE power sources in a single vehicle that combines their best attributes. A typical hybrid can operate at low speeds on more efficient, emissions-free electric power yet offer the range and performance of an ICE. The engine charges its batteries on the fly, and it can be quickly refueled almost anywhere.
Hybrids come in two basic types: Parallel and series. A parallel hybrid blends power from an electric motor and an ICE through a complex transmission that drives the vehicle's wheels. "Full" parallel hybrids, such as Toyota's Synergy Drive and Ford's essentially identical system, can run on electric alone for short distances before the ICE kicks in, while "2-Mode" hybrids -- offered by GM, Chrysler and (soon) BMW and Mercedes-Benz -- add a second power mode that saves fuel at highway as well as city speeds. So-called "mild" parallel hybrids, such as Honda's Integrated Motor Assist (IMA) and GM's simpler and less expensive Saturn and Chevrolet hybrids, use an electric motor to automatically restart the engine after it shuts down (to save fuel at rest) and assist it to boost acceleration, but not to drive the wheels.
Series hybrids power their wheels with electric motors only, while ICEs (or other power sources) drive on-board generators to provide the necessary volts. The best-known example is a diesel/electric locomotive, which uses diesel-driven generators to pump electric power to its batteries, which in turn power its motor-driven wheels.
GM experimented with a variety of hybrids during its 1990s EV program, including one design that used a high-efficiency gas turbine to drive its generator. And GM's Chevrolet Volt, scheduled for a late 2010 debut, should be the first production series hybrid and the first that is plug-in rechargeable. GM says Volt's "E-Flex" powertrain system will provide roughly 40 miles of range on its (lithium-ion) batteries alone before a small gasoline engine starts to keep it going. Future variations will use alternate-fuel and diesel ICEs, and maybe someday even fuel cells, as range extenders.
Because electric propulsion is three times as efficient (in terms of how much stored energy gets to the wheels) as the typical ICE, the more a hybrid's motor propels it, the more fuel it saves and the fewer emissions it generates. A hybrid can maximize fuel economy (Toyota's Prius), enhance performance by using the motor to "boost" the ICE's output (Honda's now-discontinued Accord Hybrid) while retaining good fuel economy, or achieve a desired balance of both. Hybrids also save fuel by recapturing energy through regenerative braking -- the motor becomes a generator that charges the battery during coasting and braking, which slows the vehicle and saves the regular brakes -- and shutting off the ICE when it's not needed.
While hybrids are more expensive to purchase than comparable ICE vehicles, they save money over time by consuming less fuel -- some more than others, depending upon their design and the vehicle size and type. Compared to conventional ICE vehicles, they offer:
- Lower operating costs due to increased fuel economy, especially in city driving
- Reduced tailpipe emissions
- Recaptured energy and reduced brake wear due to regenerative braking
- Federal income tax credits (up to $3,400; see http://www.fueleconomy.gov/).
We recommend that potential buyers do the math (how many gas dollars will be saved per year vs. the hybrid's higher price), think through each one's pros and cons before deciding what to buy and not get carried away into a hasty decision by today's pain at the pump.
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