Internal Combustion-Electric Hybrids
By Carey Russ (c) 2003
One automotive ``technology of the future'' is an accepted
technology of the present. Gasoline-electric hybrid vehicles, if not
commonplace, are readily available from several manufacturers.
They combine an internal-combustion engine with batteries and an
electric motor to produce motive power. Depending on the system
design, hybrid vehicles can operate on internal combustion or
purely electric power, or a combination of each. The electric motor
may do double duty as the internal combustion engine's starter
motor. During deceleration, it also functions as a generator, to
recharge the storage batteries. As an added benefit, magnetic drag
produced in generator mode contributes to the braking efficiency
of the vehicle.
Broadly speaking, there are two ways to categorize hybrid systems.
Series designs use the internal combustion engine to charge
batteries, which provide power to the electric motor or motors that
turn the wheels. In parallel systems, the internal combustion engine
is used to both provide tractive power and charge the batteries, and
the electric motor also provides tractive power. Depending on
conditions, the vehicle may operate under purely internal
combustion power, purely electric power, or a combination of
both.
Toyota was the first to market with the first-generation Prius in
Japan in the late 1990s. Although Toyota brought a few early
Priuses to the U.S. for evaluation, Honda beat them to market here
when it introduced the Insight in late 1999. The American-spec
Prius debuted a few months later. For the 2003 model year, they
were joined by the Honda Civic Hybrid. Toyota debuted the
second American-generation Prius recently, and has announced
that a hybrid model of the popular Lexus RX330 SUV will be
available in the future. Ford has announced that a hybrid version of
its Escape SUV will be offered in about a year, with a hybrid
model of its upcoming Futura mid-sized sedan planned. General
Motors has a number of hybrids in development, including full-
sized pickups, SUVs and sedans of all sizes, and even a diesel-
electric bus. Other manufacturers are working on hybrids as well.
All current automotive hybrid systems are parallel in nature,
although they vary in complexity. Honda's ``Integrated Motor
Assist'' (IMA) is among the simplest. The electric motor assists the
gasoline engine when extra power is needed; an Insight or Civic
Hybrid never operates as a purely electric vehicle. Despite its
simplicity, IMA does significantly improve efficiency, primarily
because a smaller, more-efficient gasoline engine can be used than
if there was no IMA. The Prius and other announced hybrids are
considerably more complex. Although they normally operate under
a combination of gasoline and electric power, they can run (rarely)
as purely gasoline or (more commonly) purely electric vehicles.
It is also possible to drive one set of wheels with an internal-
combustion engine and the other with electric power in a hybrid
four-wheel drive system. There is also absolutely no reason that
the gasoline engine in a hybrid cannot be replaced by a diesel for
even greater efficiency. The next ten years are going to be very
interesting in terms of hybrid technology.
A little off-topic, but.... Hybrid systems are not found only on
roads. In the 1930s, to reduce air pollution caused by steam
locomotives in urban environments, General Electric developed
diesel-electric switching locomotives in which the diesel engine
was used to run a generator to charge storage batteries that drove
the traction motors. At 300 horsepower, they were strong enough
for the light-duty requirements of their day, but quickly became
obsolete.
All railroad-sized diesel locomotives in use in North America
today are diesel-electric designs, but they differ significantly from
automotive hybrids in that no storage batteries are used. Electric,
rather than mechanical or hydraulic (torque converter) power
transmission is used because electric traction motors can stand up
to the power necessary to move a heavy train. And, as with
regenerative braking in hybrid cars, the traction motors can be used
to help slow a train, although the energy generated is converted to
heat and dissipated through heavy-duty resistors. Mechanical and
hydraulic transmission systems have been used successfully in
small industrial switching locomotives with a few hundred
horsepower, but were abject failures in main-line service in
locomotives with 4,000 horsepower and many, many lb-ft of
torque.