Page 213 - Mechanic Diesel - TT

MECHANIC DIESEL - CITS

MODULE 9 : Starting System

LESSON 62 - 66: Study about starting system and its

components. Importance of checking

starter circuit for proper functioning

Objectives

At the end of this lesson you shall be able to
• explain About starting system and its components
• demonstrate importance of checking starter circuit for proper functioning.

Study of starting system and its components starting system
Internal combustion engines are not capable of starting automatically. Hence various systems to start these
engines; Like starter motor, self-start etc. are used. Some large engines used in trucks, tractors, and industrial
plants are operated by compressed air or a small starting engine, but automotive engines (spark ignition and
diesel) are operated by a small but powerful electric motor, which can prevent cracking or Starting motor (cranking
or starting motor) An ideal starting system includes the battery, starting motor, drive mechanism, ignition switch,
starter relay and all the wiring that helps in starting the engine. Facts like components of starting system, starting
circuit, various starting systems, starter driving mechanism, other methods of starting the engine etc. are described.
The Starting System: In an automobile, starting system cranks the engine initially. It has replaced manual effort
to crank the engine with the help of cranking rod that was used in ancient days. Initially, the engine requires
cranking but once the cycle is completed it starts and runs on its own. In two wheelers, it is common to ‘kick start’
the engine but in recent times a number of manufacturers have introduced ‘button start’. For initial cranking an
electric motor is provided that gets electric current as input from battery.

The mechanical energy, in the form of rotation of shaft, is transmitted to engine. This provides initial movement of
crankshaft, connecting rod and piston. As soon as spark occurs the fuel is ignited and output becomes available
from engine. No more cranking is needed and starting system stops working and engine runs on its own. The
starting system makes starting of vehicle convenient.
Requirements of the starting system
An internal combustion engine requires

• A combustible mixture,
• Compression stroke,
• A form of ignition, and
• The minimum initial starting speed (about 100 rpm) in order to start and continue running.
To meet the first three of these requirements the minimum starting speed must be attained. This is where
the electric starter comes in. The attainment of this minimum speed is again dependent on a number of
factors, such as;
1 The rated voltage of the starting system.

2 The lowest possible temperature at which the engine can still be started. This is known as the starting limit
temperature.
3 The torque required to crank the engine at its starting limit temperature (including the initial stalled torque).
4 The battery characteristics.

5 The voltage drop between the battery and the starter.
6 The starter to ring gear ratio.
7 The characteristics of the starter.

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