Introduction
to How Car Engines Work
Internal
Combustion
Parts
of an Engine
What
Can Go Wrong
Engine
Subsystems
As you can see in the previous descriptions under
"What Can Go Wrong," an engine has a number
of systems that help it do its job of converting
fuel into motion. Most of these subsystems can be
implemented using different technologies, and better
technologies can improve the performance of the
engine. Here's a look at all of the different subsystems
used in modern engines:
Valve train
The valve train consists of the valves and a mechanism
that opens and closes them. The opening and closing
system is called a camshaft. The camshaft
has lobes on it that move the valves up and down,
as shown in fugure - 5.
Fugure - 5 The camshaft
Most
modern engines have what are called overhead
cams. This means that the camshaft is located
above the valves, as you see in Figure 5. The cams
on the shaft activate the valves directly or through
a very short linkage. Older engines used a camshaft
located in the sump near the crankshaft. Rods
linked the cam below to valve lifters above
the valves. This approach has more moving parts
and also causes more lag between the cam's activation
of the valve and the valve's subsequent motion.
A timing belt or timing chain links the crankshaft
to the camshaft so that the valves are in sync with
the pistons. The camshaft is geared to turn
at one-half the rate of the crankshaft. Many high-performance
engines have four valves per cylinder (two for intake,
two for exhaust), and this arrangement requires
two camshafts per bank of cylinders, hence the phrase
"dual overhead cams."
See
How Camshafts Work for details.
Ignition
system
The ignition system (Figure 6) produces a
high-voltage electrical charge and transmits it
to the spark plugs via ignition wires. The
charge first flows to a distributor, which
you can easily find under the hood of most cars.
The distributor has one wire going in the center
and four, six, or eight wires (depending on the
number of cylinders) coming out of it. These
ignition wires send the charge to each spark
plug. The engine is timed so that only one cylinder
receives a spark from the distributor at a time.
This approach provides maximum smoothness.
See
How Automobile Ignition Systems Work for more details.
Cooling
system
The cooling system in most cars consists of the
radiator and water pump. Water circulates through
passages around the cylinders and then travels through
the radiator to cool it off. In a few cars (most
notably Volkswagen Beetles), as well as most motorcycles
and lawn mowers, the engine is air-cooled instead
(You can tell an air-cooled engine by the fins adorning
the outside of each cylinder to help dissipate heat.).
Air-cooling makes the engine lighter but hotter,
generally decreasing engine life and overall performance.
See How Car Cooling Systems Work for details.
Air
intake system
Most cars are normally aspirated, which means
that air flows through an air filter and directly
into the cylinders. High-performance engines are
either turbocharged or supercharged,
which means that air coming into the engine is first
pressurized (so that more air/fuel mixture can be
squeezed into each cylinder) to increase performance.
The amount of pressurization is called boost.
A turbocharger uses a small turbine attached
to the exhaust pipe to spin a compressing turbine
in the incoming air stream. A supercharger
is attached directly to the engine to spin the compressor.
See How Turbochargers Work for details.
Starting
system
The starting system consists of an electric starter
motor and a starter solenoid. When you turn
the ignition key, the starter motor spins the engine
a few revolutions so that the combustion process
can start. It takes a powerful motor to spin a cold
engine. The starter motor must overcome:
Because
so much energy is needed and because a car uses a
12-volt electrical system, hundreds of amps of electricity
must flow into the starter motor. The starter solenoid
is essentially a large electronic switch that can
handle that much current. When you turn the ignition
key, it activates the solenoid to power the motor.
Lubrication system
The lubrication system makes sure that every moving
part in the engine gets oil so that it can move easily.
The two main parts needing oil are the pistons (so
they can slide easily in their cylinders) and any
bearings that allow things like the crankshaft and
camshafts to rotate freely. In most cars, oil is sucked
out of the oil pan by the oil pump, run through the
oil filter to remove any grit, and then squirted under
high pressure onto bearings and the cylinder walls.
The oil then trickles down into the sump, where it
is collected again and the cycle repeats.
Fuel
system
The fuel system pumps gas from the gas tank and
mixes it with air so that the proper air/fuel mixture
can flow into the cylinders. Fuel is delivered in
three common ways: carburetion, port fuel injection
and direct fuel injection.
-
In
carburetion, a device called a carburetor
mixes gas into air as the air flows into the engine.
-
In
a fuel-injected engine, the right amount
of fuel is injected individually into each cylinder
either right above the intake valve (port fuel
injection) or directly into the cylinder (direct
fuel injection).
See
How Fuel Injection Systems Work for more details.
Exhaust system
The exhaust system includes the exhaust pipe and
the muffler. Without a muffler, what you would hear
is the sound of thousands of small explosions coming
out your tailpipe. A muffler dampens the sound.
The exhaust system also includes a catalytic converter.
See How Catalytic Converters Work for details.
Emission
control system
The emission control system in modern cars consists
of a catalytic converter, a collection of
sensors and actuators, and a computer to monitor
and adjust everything. For example, the catalytic
converter uses a catalyst and oxygen to burn off
any unused fuel and certain other chemicals in the
exhaust. An oxygen sensor in the exhaust stream
makes sure there is enough oxygen available for
the catalyst to work and adjusts things if necessary.
Electrical
system
The electrical system consists of a battery
and an alternator. The alternator is connected
to the engine by a belt and generates electricity
to recharge the battery. The battery makes 12-volt
power available to everything in the car needing
electricity (the ignition system, radio, headlights,
windshield wipers, power windows and seats, computers,
etc.) through the vehicle's wiring.
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