How does a hybrid car work?

Hybrid cars combine electric motors and smaller gasoline engines in an attempt to increase efficiency. Find out exactly how they work in this podcast from HowStuffWorks.com.

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Episode Transcript

Speaker 1 (00:00):
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Welcome to Brainstuff from how stuff works dot com where

(00:22):
smart Happens. Hi. I'm Marshall Brain with today's question, how
does a hybrid car work? We're all familiar with gasoline
powered cars, and most people have heard about our scene
electric cars. A hybrid car is a combination of the two.

(00:44):
Hybrid vehicle contains both a gasoline engine and an electric
motor in an attempt to get the best of both worlds.
The best way to understand the advantages of a hybrid
vehicle is to think about a car traveling down a
highway at the postage speed on level ground. In this case,
the engine is doing three things. First, it's overcoming rolling

(01:05):
resistance in the drivetrain. Second, it's overcoming air resistance, and
third it's powering accessories like the alternator and the air conditioner.
The engine might need to produce no more than twenty
horse power to carry this load. The reason why cars
have a hundred or two hundred or three hundred horsepower
engines is to handle acceleration from a standing stop, as

(01:25):
well as for passing and hill climbing. We only use
the maximum horsepower rating for one percent of the driving time.
The rest of the time we are carrying around the
weight and friction of that much larger engine, and that
wastes a lot of energy. In a pure hybrid vehicle,
you have a complete electric car. It includes an electric
motor to provide power to the wheels, as well as

(01:48):
batteries to supply the motor with electricity. Then you have
a completely separate gasoline engine powering a generator. The engine
is small, perhaps only twenty horsepower, and it's designed to
run it just one speed for maximum efficiency. The purpose
of this small, efficient engine is to provide enough power
for the car at its cruising speed. During times of acceleration,

(02:12):
the batteries provide the extra power necessary. When the car
is decelerating or standing still, the batteries recharge. This sort
of hybrid car is essentially an electric car with a
built in recharger for longer range. The advantage is that
the small, efficient gasoline engine gets great mileage. The only
problem with this traditional hybrid car is the weight. The

(02:35):
car has to carry the weight of the electric motor,
the generator, the gasoline engine, and the batteries. You don't
need as many batteries as a pure electric car, so
that saves some weight, but a full size electric motor
plus a ten kilowatt generator can weigh several hundred pounds.
Most hybrid vehicles, therefore, try to strike a compromise. They

(02:56):
use a larger gasoline engine that's connected directly to the
drive train, along with a smaller electric motor attached to
the engine or the transmission. The gasoline engine provides most
of the car's power, with the electric motor adding extra
power is needed for acceleration. Because the electric motor can
double as a generator during breaking and only has to

(03:17):
run part of the time, it can be extremely light.
The disadvantage of this approach is that the gasoline engine
must run at varying speeds, which reduces its efficiency. For
more on this and thousands of other topics, is It
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