Charging System
The charging system is needed to recharge (re-energize)
the battery after starting system or other electrical system
operation. The battery can become discharged (run down)
after only a few minutes of starter motor operation. The
charging system also provides all of the vehicle’s electrical
needs while the engine is running. Basically, the charging
system consists of the alternator and a voltage regulator.
Look at Figure 1-25.
The alternator produces the electricity to recharge the
battery. It is driven by a belt from the engine crankshaft
pulley. The alternator sends current through the battery to
reactivate the chemicals in the battery. This again prepares
the battery for starting or other electrical loads.
The voltage regulator controls the electrical output of
the alternator. It ensures that about 14.5 volts are produced
by the alternator. Current then flows back into the battery,
since battery voltage is only about 12.5 volts.
Fuel System
The fuel system must meter the right amount of fuel
(usually gasoline or diesel oil) into the engine for efficient
combustion under different conditions. At low speeds, it
must meter a small amount of fuel into the airstream. As
engine speed and load increase, the fuel system must
meter more fuel into the airstream. The fuel system must
also alter the fuel metering with changes in engine temper-
ature and other variables.
There are two basic types of automotive fuel systems
in current use—gasoline injection and diesel injection. A
third type of fuel system—carburetion—has not been
commonly used since the mid 1980s.
Gasoline Injection System
A gasoline injection system uses fuel pump pressure
to spray fuel into the engine intake manifold, usually near
the cylinder head’s intake port. A basic system is pictured
in Figure 1-26.
An electric fuel pump forces fuel from the fuel tank to
the fuel injector. A constant pressure is maintained at the
injector. The fuel injector is simply an electrically-operated
fuel valve. When energized by the control module, it
opens and squirts fuel into the intake manifold or the com-
bustion chamber. When not energized, it closes and pre-
vents fuel entry into the engine.
Modern gasoline injection systems open the injector
when the engine intake valve opens. Then, fuel is partially
or completely forced into the combustion chamber by
pump pressure. This helps control how much fuel enters
the cylinder and also increases combustion efficiency, as
you will learn in later chapters.
A control module (computer) is used to regulate when
and how long the injector opens. It uses electrical informa-
tion from various sensors to analyze the needs and operating
conditions of the engine. The engine sensors monitor
various operating conditions, such as engine temperature,
speed, load, and so on. In this way, the computer can deter-
mine whether more or less fuel is needed and whether the
injector should be opened for a longer or shorter period of
time based on the current operating conditions.
A throttle valve controls airflow, engine speed, and
engine power. It is connected to the accelerator pedal. When
the pedal is pressed, the throttle valve opens to allow more air
into the combustion chambers. In turn, the control module
holds the injectors open for a longer period of time, allowing
more fuel into the combustion chamber. The increase in air
and fuel results in an increase in engine power output.
As the accelerator pedal is released, the throttle valve
closes, reducing the amount of air allowed into the
combustion chamber. The control module, in turn, reduces
the amount of time the injectors are open, thus reducing
the amount of fuel released into the injection chamber.
The decrease in air and fuel results in a decrease in engine
power output.
Diesel Injection System
A diesel injection system forces fuel directly into the
engine’s combustion chamber, as shown in Figure 1-27.
The heat resulting from highly compressed air, not an elec-
tric spark plug, ignites and burns the fuel. When the intake
valve opens, a full charge of air is allowed to flow into the
cylinder. Then, on the compression stroke, the air is
squeezed until it is at a high temperature. As soon as the
fuel is injected into the hot air, the fuel burns and expands.
A diesel injection system basically consists of an
injection pump, injector, and glow plug system. The
injection pump is a high-pressure, mechanical pump. It is
powered by the engine and forces fuel to the diesel
injector under very-high pressure. A conventional fuel
pump feeds fuel from the tank to the injection pump.
Chapter 1 Review of Engine Operation 21
Battery
Voltage
regulator
Main fuse
Charging system
wiring harness
Charge
indicator
Alternator
Alternator
belt
Figure 1-25. The charging system recharges the battery and
provides the vehicle’s electrical needs while the engine is
running. (Honda)