by the distributor. The high voltage forces a current
Q6-20.
When performing maintenance on the
across the spark plug electrodes, creating a spark that
charging system, which of the following tasks
ignites the air-fuel mixture in the cylinder.
should be performed before the actual testing
begins?
A battery ignition system consists of two
c i r c u i t s -- p r i m a r y a n d s e c o n d a r y. T h e s y s -
1.
Perform a good visual inspection
tem may be conventional, contact-controlled, or
2.
Perform a good cleaning of the equipment
transistor-controlled magnetic pulse. Some compo-
3.
Perform a post-operational inspection
nents of these circuits may differ, but in both cases the
4.
Perform a load-test on the equipment
purpose is the same--to create the high voltage
Q6-21.
Which of the following conditions will cause a
necessary to fire the spark plug and to deliver high
battery excessive self-discharge?
voltage to the correct spark plug at the right time.
1.
Improperly secured battery
Conventional Ignition Systems
2.
Dirt and electrolyte on top of the battery
3.
Broken battery post
The conventional ignition system (fig. 6-41) was
4.
Warped battery case
the only type available for many years. And, although it
is gradually being replaced by the transistorized
IGNITION SYSTEMS
system, many are still in use.
LEARNING OBJECTIVES: Identify the
IGNITION RESISTOR.--An ignition resistor
components in an ignition system. Identify
(also known as a ballast resistor) is used in all
procedures for inspecting, testing, and
conventional ignition systems to help control current.
troubleshooting ignition system components.
The ignition resistor limits current flow across the
There are two methods used to ignite the fuel-air
breaker points during low-speed operation, when less
mixture in the cylinders of internal combustion
current is needed. This tends to prolong breaker point
engines. Heat of compression is one method, and it is
life.
used in diesel engines. The second method is the
During starting, the ignition resistor is bypassed to
electric spark, and it is used in gasoline engines. This
allow full current to the primary ignition circuit. This
section of the chapter deals with electrical spark
ensures a strong spark for starting. After the engine is
ignition systems. After completing this section, you
started, the resistor circuit is energized.
should be familiar with the purpose and operation of
electrical spark ignition systems.
IGNITION COIL.--The primary winding of the
ignition coil consists of a few hundred turns of heavy
Spark ignition may be subdivided into two
wire wrapped around a laminated soft-iron core. When
classes--battery and magneto. With either, the
current flows in the primary circuit, a magnetic field
fundamental job is to step up low voltage to a much
sets up around this coil. The secondary winding
higher value (15,000 to 20,000 volts) and to deliver the
consists of thousands of turns of very fine wire around
high voltage to the spark plugs at the proper time. The
the primary coil. The magnetic field from the primary
high voltage is capable of pushing current from one
coil surrounds or "links" the turns of wire on the
spark plug electrode to the other through the high
secondary winding by induction.
resistance set up by the gas pressure in the combustion
chamber.
If the flux linking a coil varies or changes in any
way, an electromotive force is induced in the turns of
BATTERY IGNITION SYSTEMS
the coil. This is the basic principle upon which the
induction coil works. In an induction coil (such as an
The voltage of the vehicle battery is not high
ignition coil), a magnetic field is set up by current from
enough to force a current across the spark plug
the battery flowing through the primary circuit. Unless
electrodes. To obtain the high voltage necessary (about
this current flow is changing to vary the strength of the
20,000 volts), a step-up pulse transformer (ignition
magnetic field, no voltage is induced in the secondary
coil) is used. The high voltage created is then delivered
winding.
to the spark plug of the correct cylinder at the right time
6-36
