On Newsstands August 13
R & D
< WHAT WORKS >
W W W. B U S I N E S S 2 . C O M
Gentlemen, Engage Your Planetary Gears
Normal driving
Managing power
C O U R T E S Y O F T O Y O TA ; I N F O G R A P H I C S B Y J E F F B E R L I N
way. While that seems counterintuitive,
the Prius actually performs more efficiently in the city because the Toyota
Hybrid System (THS) relies more on
the electric motor at lower speeds. Various levels of hybridization can be
matched with other technologies in the
pursuit of higher fuel efficiency.
Manufacturers can take advantage of
hybrid technology’s flexibility to create
vehicles specifically for a target market.
Ford, Chrysler, and General Motors all
The Prius can be powered by its 1.5-liter,
four-cylinder gas engine, its electric
motor, or both. A system called the planetary gear set splits the engine’s power
between the ring gear, which powers the
wheels, and the sun gear, which drives
the Prius’s electrical generator. The ring
gear can also be run by the electric
motor, allowing the car’s electronic control system (featuring four computers
and six chips) to determine the most efficient use of gas and electric power.
At low speeds and during light acceleration, the Prius runs entirely on electrical power. Once the car’s acceleration re-
Main Components of the Toyota Hybrid System
In the Toyota Hybrid System (THS), a controller coordinates the function of a gasoline engine, an electric
BATTERY
1.5-liter, 16-valve, 4-cylinder engine capable of
motor, a generator, and a storage battery so that they work together, boosting fuel economy while
up to 70 horsepower at 4,500 rpm. Provides
lowering emissions. A unique power-splitting device drives the wheels through any of the power-
The 110-pound battery is composed of 38
the majority of the car's power at cruising
generating components—individually or together, depending on driving conditions.
nickel-metal hydride (Ni-MH) modules sealed
speed and at full power. Also provides the
in a steel case behind the rear seat. Unlike
power for recharging the battery.
traditional lead-acid batteries, Ni-MH is
nonflammable and noncaustic.
ELECTRIC MOTOR
Permanent magnet motor that can produce up to 44
GENERATOR
horsepower at 1,040 to 5,600 rpm. Provides power during
Converts power from the gas
early acceleration and at low speeds and assists the engine
engine into electricity to recharge
as needed. Also converts vehicle’s forward motion during
the battery and supplies power to
braking into more electricity for the battery.
Drivetrain
Full power
Engine
Engine
Battery
With a hybrid car, you can hit the road instead of the gas station. B Y J O H N S O U S A N I S
GAS ENGINE
Starting
plan to introduce sport-utility vehicles
with limited hybridization by 2004.
HOW IT WORKS
Two hybrid electric vehicles (HEVs) on the market combine the convenience and performance of cars that have traditional gasoline engines with the environmental friendliness and low-speed efficiency of those powered by electric motors. The electric power of HEVs is generated by a system that reclaims energy
that a regular car would otherwise waste.
The first hybrid to hit the U.S. market was the Honda Insight, a two-seater with
an unparalleled EPA fuel economy of 61 miles per gallon city/68mpg highway, in
December 1999. Honda has sold about 6,700 Insights (MSRP $18,980) as of July.
The Toyota Prius, introduced in Japan in 1997 and the United States in July 2000,
is the world’s first mass-produced HEV. Toyota has sold about 13,000 of this
model (MSRP $20,450).
Using an onboard system of electronic controls to optimize the balance of gas and
electric power, the Prius achieves an EPA fuel economy of 52mpg city/45mpg high-
Hybrid System Power Management
Engine
Battery
Battery
Drivetrain
Drivetrain
Motor
Motor
Motor
When first starting, the electric motor
drives the car under battery power
while the gas engine remains off.
As the car accelerates, the gas engine
kicks in to power the car and run the
generator, which in turn powers the
electric motor and charges the battery.
Under full-power, the battery kicks in
to provide additional power to the
electric motor.
Cruising
Charging
Braking
Engine
Engine
Battery
Drivetrain
Battery
Motor
Battery
Drivetrain
Drivetrain
On the highway, the gas engine provides
most of the power, due to its increased
efficiency at high speeds; the electric
motor comes on only intermittently.
Engine
Motor
Motor
When power demand on the gas engine During deceleration and braking, the
is low (e.g., when cruising), the
electric motor converts forward motion
generator converts excess engine power into more power to recharge the battery.
to charge the battery.
quirements exceed 10 kilowatts, or 13.4
horsepower (for example, during faster
acceleration), the gas engine kicks on,
and the two power sources work simultaneously. When the car reaches cruising speed, the engine takes over, operating at or very near peak efficiency made
possible by the electronically controlled
continuously variable transmission
(CVT). The generator converts excess
power created by the engine to electrical
energy that is stored in the battery. Once
the vehicle dips below 40mph, the en-
gine stops powering the car.
As the vehicle slows, “regenerative
braking” begins, a process that converts
the car’s kinetic energy into electrical
energy, also stored in the battery. When
more braking power is needed, regenerative braking is aided by conventional
hydraulic brakes. When the driver resumes acceleration, the computer reengages the engine. ✦
John Sousanis is a freelance writer based in
Detroit.
drive the electric motor.
POWER
SPLIT DEVICE
Planetary gear unit that
connects the gas engine,
electric motor, and
generator to the drivetrain
of the car. It also allows
the engine and motor to
operate the car
independently or together.
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