Page 218 - Mechanic Diesel - TT

MECHANIC DIESEL - CITS

The basic starting system includes the following components:

1 Battery.
2 Cable and wires.
3 Ignition switch.
4 Starter solenoid or relay.

5 Starter motor.
6 Starter drive and flywheel ring gear.
7 Starting safety switch.
Starter Motor: The starter motor is like any other electrical motor but it is designed to work under high electrical
overloads and produces very high power. Due to this, the motor can operate for short durations. High current is
needed to operate it that generates heat. Time is also required to dissipate this heat. Therefore, it is advisable that
the motor be given enough gaps between more than one starting attempts.
The motor has got field coils with pole shoes, armature and a housing that encloses them. Apart from these it
has brushes, bushings that make its operation efficient. The field coils and pole shoes produce strong stationary
electromagnetic fields as current is passed through them. Magnetic polarity (N or S) depends upon the direction
in which the current flows. The magnetic fields produced are opposite in nature.

The armature is located between drive and end frames. It has windings and the commutator mounted on the
armature shaft. The windings are made of a number of coils of a single loop each. These are insulated from each
other and fit into slots in the armature shaft. The commutator has heavy copper segments surrounding the shaft
but are insulated from each other and the shaft. The armature is surrounded by field coils. Current is supplied
to armature and it produces magnetic field in each conductor. The magnetic fields are also produced by field
coils. The reaction between these magnetic fields causes the rotation of armature. The rotation is transferred to
crankshaft of the engine through armature shaft. This causes cranking of engine.
The current from field coils to the armature is transferred through brushes. These brushes are held with the help
of springs against the commutator. The brushes can be from two to six in number for smooth motion and constant
torque delivery. Figure 7 represents starter motor

Types of starting system
Starting system is used to start the engine. When the starter switch is pressed or turned, the current flowing
through the battery causes the starter shaft to rotate. The drive pinion is coupled to the starter motor shaft. The
drive pinion rotates the engine’s flywheel until the engine starts. Various systems are used to start the engine,
which are as follows-

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CITS : Automotive - Mechanic Diesel - Lesson 62 - 66