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The
growing need to reduce fuel consumption and lower emissions in the
United States transportation sector has spurred urban transit bus
operators to pioneer the adoption of alternate fuels and new drive
system technologies. One of the most promising technologies to receive
attention is hybrid-electric drive, which consists of two or more
onboard fuels that supply energy to electric traction motors that
in turn drive the wheels. By contrast, conventional drive employs
an internal combustion engine to generate rotational force that
is then only mechanically transferred to drive the wheels.
A
growing number of companies are developing and beginning to supply
commercial hybrid-electric drive products to the truck and bus markets.
Most of these commercially-available hybrid buses combine an internal
combustion engine and traction battery, although there are many
possible drive system configurations.
The
electric drive improves drive system efficiency, reduces energy
consumption, recovers energy, reduces emissions, and improves driveability.
Hybrid systems are being used in transit bus applications where
pure battery-electric drivetrain is not yet feasible because the
power and energy requirements associated with typical urban transit
bus drive cycles exceed the performance capabilities -- primarily,
range -- of current battery technologies. Transit operators are
implementing hybrid buses since the hybrid drive systems can easily
meet and exceed the urban transit bus drive cycle requirements while
still improving fuel economy and emissions.
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