Page 220 - Mechanic Diesel - TT

MECHANIC DIESEL - CITS

Working principle of self-starter motor

Fleming’s right hand rule

Construction of self starter
The structure of Self Starter is almost similar to that of a dynamo and like a dynamo, it also has pole shoe, field
coil, armature, commutator and bush etc. The windings of a self-starter are usually series wound. Their field
coil and armature winding are made of thick insulated copper wire or thin copper strips. Because more power is
required to rotate the crank shaft, it is made by this type of winding.
In this, the resistance remains very low and a higher current of about 400 to 500 amps can be obtained, due to
which it is capable of rotating the crankshaft with sufficient power. Due to excessive current flowing in the self-
starter, it gets heated quickly, hence it should not be run for more than 30 seconds at a time, otherwise there is a
danger of its winding getting burnt.

Apart from this, only two carbon brushes are used in dynamo, but four carbon brushes are used in self-starter,
which are made of a mixture of graphite and copper, due to which they can handle more current. Can also bear
it. All its remaining parts are similar to those of a dynamo, only the armature. The shaft is kept relatively longer,
because a pinion is fitted on it, which connects to the fly wheel and rotates it.
Starter drive mechanisms
All types of self-starters are almost the same, but Starter Drive Mechanism or the difference between them lies
only in the drive mechanism connecting the flywheel and the self-starter. Many types of driving mechanisms are
used. These have a gear ratio of 15:1 between the self-armature and the flywheel i.e. when the self-pinion
When 15 revolutions are completed then the flywheel is able to rotate one revolution. This gear ratio of the driving
mechanism provides powerful torque to the engine, but it is necessary to break the connection between the self-
armature and the flywheel as soon as the engine starts running, otherwise the self-armature etc. start rotating with
the speed of the engine, due to which there is a danger of breaking the commutator segment and connections etc.
lives. For this purpose, special types of mechanisms are used to provide drive, which are as follows-
1 Lever or over running clutch type driving mechanism
2 Bendex type drive mechanism
3 Axial type driving mechanism
1 Lever or Over Running Clutch Type Mechanism

Hand operated lever assist with self-starter in some older vehicles The connection between the drive pinion
and the flywheel is established. In this system, there is a lever installed near the driving seat, which is related to
the shift lever. When the self has to be rotated, this lever is pressed. Due to this, the shift lever simultaneously
depresses the starting switch and also connects the drive mechanism to the flywheel. As soon as the pressure is
removed from the lever, the starting switch closes (OFF).
The connection between the drive mechanism and the flywheel also breaks. over running in picture The structure
of clutch drive mechanism is shown-

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CITS : Automotive - Mechanic Diesel - Lesson 62 - 66