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Chapterhaptehapter
30SystemsStarting
After studying this chapter, you will be able to:
❚ Explain the principles of 12-volt dc and high-
voltage ac electric motors.
❚ Describe the construction and operation of
conventional 12-volt and high-voltage start-
ing motors and circuits.
❚ Sketch a simple computer-controlled starting
system circuit.
❚ Explain the operation and location of starting
motor solenoids and HV contactors.
❚ List and describe the purpose of major start-
ing circuit components.
❚ Compare different types of starting motor
drive mechanisms.
❚ Describe starting system safety features,
especially with high-voltage hybrid starting
systems.
❚ Compare 12-volt engine starting circuits with
HV starting circuits.
❚ Correctly answer ASE certifi cation test ques-
tions that require a knowledge of both 12-volt
and HV starting system fundamentals.
An engine starting system must crank or spin
the engine until fuel combustion forces the pistons
down and the engine begins to operate on its own
power. When the driver turns the ignition key or
presses the start button, electrical energy is sent to
the starting circuit to energize the 12-volt starting
motor mounted on the engine block. A small gear on
the starting motor engages and rotates a large gear
on the engine fl ywheel. This spins the engine crank-
shaft, pulls air into the cylinders, and operates the
spark plugs to fi re up the engine.
The starting system in today’s hybrids and
ECM-controlled starting circuits can also shut the
engine off when it is not needed. This feature saves
a tremendous amount of gasoline that is normally
wasted when a car is sitting idle at stoplights or
intersections.
The starting system has helped make the mod-
ern automobile a reliable and convenient means of
transportation. It provides an effortless method of
cranking and starting multi-cylinder engines. Few
car owners would be physically capable of starting a
multi-cylinder engine using a hand crank. The elec-
tric starting motor is designed to crank the engine
with the simple turn of a key or press of a button.
This chapter provides the information needed to
understand how any starting system is supposed to
function. You will learn about the operation of con-
ventional 12-volt starting circuits before studying
more complex hybrid high-voltage starting systems.
You will also learn about electronic starter disen-
gagement systems.
12-Volt Starting System Principles
The 12-volt starting system uses battery power
and an electric motor to turn the engine crankshaft
for engine operation. The main parts of a starting
system include:
• Battery—The battery is a source of electrical
energy for the starting circuit.
• Ignition switch—The ignition switch, or start
switch, allows the driver to control starting
system operation.
• Starter solenoid—The starter solenoid is a
high-current contactor for connecting the bat-
tery to the starting motor.
• Starter relay—The starter relay is a low-current
relay that operates the starter solenoid.
Engine