6.Starting System

7/27/2019 6.Starting System

1/13

Session 1Session Name: Automotive Starting System

Author Name: Satyajit R. Patil


2/13

Page 2 Ver 1:.01 Automotive Starting SystemSatyajit R. Patil, KESRIT

Session Objectives

At the end of this session, the learner will be able to:

Understand need of automotive starting system.

Write requirements of starting system.

List various components of starting system.

Understand working of the same.

Draw schematic of the same.

J ustify type of motor used.Identify probable faults in the starting system.

Teaching Learning Material

White Board and Markers

Overhead projector


3/13

Automotive Starting System Page 3Satyajit R. Patil, KESRIT

Session Plan

Time(in min)

ContentLearning Aid

andMethodology

FacultyApproach

Typical StudentActivity

Skill andCompetencyDeveloped

05

Introduction:Automotive StartingSystem

Chalk & Talk Explains ComprehendsKnowledgeIntrapersonal

15Need for AutomotiveStarting System

Chalk & TalkNumericalExamples

FacilitatesExplains

ComprehendsParticipates

ComprehensionIntrapersonalLinguisticApplication

20

Starting System:Layout andComponents

OHP FacilitatesExplains

ObservesComprehends

KnowledgeIntrapersonalSpatial

06 Types of Motors Chalk & Talk Explains ComprehendsKnowledgeIntrapersonal

10Probable Faults Group Discussion

FacilitatesModerates

ParticipatesObservesComprehends

ApplicationIntrapersonalInterpersonalLinguistic

04Conclusion

Question andAnswer

Questions AnswersComprehensionIntrapersonalLinguistic


4/13


Session Inputs

Introduction: Automotive Starting System

We may rec all the classification of automotive electrical systems

that we learnt in earlier session, one out of which is the starting

system. Then we may tell the learners about hand crank

method, used in the earlier days.

The Automotive Electrical systems are classified as follows:

Automotive storage and generation system

Automotive starting system

Automotive lighting systemAutomotive ignition system

Automotive Auxiliaries

We have already learnt about storage and generation system. The electric

energy is stored in the battery and generated using a generator oralternator. When the generator is generating the current, demand of

electrical load will be met by this current. However, if the vehicle is not

moving or moving at very low speed, the generator will not be operational

and the current will be extracted from the battery; and the battery will be

drained. Today, we will see how a vehicle gets started.

Earlier days, initial cranking was provided by using hands. The driver would

crank the engine shaft by revolving the handle, the engine would get started

and then he would come and occupy his seat to drive the vehicle. This is

called hand cranking and was very inconvenient and time consuming.

Ultimately, the need was felt for more sophisticated means to start the

vehicle. The system should be convenient to the driver and efficient.

Need for Automotive Starting System

Before going into the system, the need for Automotive Starting

System should be explained. We can explain the need with the

help of a numerical demonstration.


5/13


Suggested Activity: Numerical Examples

The need can be demonstrated with the help of a numerical example. Thisexample will illustrate the need for a starting system required in a vehicle.

The minimum cranking speed required to crank a petrol engine can be

taken as 100 rpm, while the motor speed can be taken as 1600 rpm. Hence

the reduction of the order of 16:1 is required. This shall also help in providingthe torque at the flywheel which will help starting the engine. These facts

are to be explained to the learners.

Finally the learners can be asked to come up with more examples on

similar lines.

An I. C. engine cannot be started on its own. It uses an electric

motor, called the cranking motor or the starting motor which

provides the initial drive to the crankshaft of an engine. As the

crankshaft starts rotating, the engine will start running and

combustion of the air fuel mixture will take plac e in the

combustion chamber. This will further provide power to the

engine. However, an electric motor will be required for cranking

the engine. Here, an electric motor uses current to produce the

mechanical energy.

Lets try to understand the need for a starting system with the help of an

illustration. Lets take a minimum cranking speed of an engine to be 100 rpm,i.e. the engine can be cranked at 100 rpm or more than that. The c ranking

motor speed will be 1600 rpm.

Also, in order to start the engine, a heavy torque is required. This torque is

much more than the torque required to keep the engine running. We know

that the torque is inversely proportional to the speed. Thus, in order to get a

heavy torque, the speed should be low.

If we apply this relationship to our motor engine case, we will have to have a

speed reduction mec hanism, since the motor speed is 1600 rpm and theengine cranking minimum speed is 100rpm. Thus, we should have a provision

for reduction of the order of 16:1 so that the motor speed of 1600 rpm can be

converted to 100 rpm of engine. This is made possible by a gear pair whosereduction ratio generally varies from 8:1 to 16:1; in our case it has to be 16:1.

This speed reduction also helps to provide the torque at the flywheel which is

mounted on an engine crankshaft.


6/13


But when the engine starts running, its speed will go on increasing and then it

will try to drive the motor. The important thing to be understood here is that,instead of speed reduction, now speed increment will occur. Thus, if the

engine has reached upto 2000 rpm, it will try to drive the cranking motor at

2000*16=32000 rpm. The motor, off course, will not be able to withstand this

high rpm owing to the resulting high centrifugal forces and will fail. Thus, there

has to be a mechanism with the help of which we should be able todisengage the gears mounted on the engine shaft and the motor output

shaft when the engine speeds up. At the same time, it will be essential to

bring these gears in mesh when we want to start the engine. Thus, the starting

mechanism connec ts and disconnects the engine from the c ranking motor

when required.

Starting System: Layout and Components

The layout of the starting system components can be shown withthe help of a transparency or diagram on blackboard. The role of

the individual components and overall functioning of the system is

then explained.

The components of a typical automotive starting system are:

Battery

Starter switchElectric motor

Pinion on motor shaft

Flywheel ring gearSolenoid switch

BatteryThe battery provides the heavy current required for the c ranking motor. One

battery terminal is connected to the motor terminal and the other is earthed.

When the switch is closed, the current from the battery will be delivered to

the motor. Heavy current of the order of 200-400 amperes can be extracted

from the battery when the starter switch is closed.

Starter SwitchIt has two positions, open and closed. When the switch is closed, the circuit is

made and when it is open, the c ircuit is broken.


7/13


Electric Motor

The function of a motor is to convert electrical energy into mechanical

energy. As the current stored in the battery is dc, the cranking motor shouldbe of dc type. Generally a four pole, series motor is used for engine cranking.

Pinion on Motor ShaftThis is a small gear mounted on the motor output shaft and revolves with the

motor speed.

Flywheel Ring Gear

This ring gear is mounted on the engine crankshaft and aside to the flywheel.

It takes drive from the pinion gear and makes the c rankshaft revolve.

Solenoid Switch

This will look after the engagement and disengagement of the motor pinionwith the ring gear. As the current flows through the solenoid, it energizes so as

to push the pinion into mesh with a ring gear. As the current stops flowing, it

de-energizes and the pinion will be brought out of the mesh with the ring

gear due to the spring pressure.

(The details of the driving mechanisms are out of scope of this lecture.)


8/13


Starting system: layout and components

Type of Motors

The types of motors, usually preferred for automotive starting

purposes are to be explained. The sketches showing the seriesshunt and compound type of motors may be drawn on the

blackboard. In this segment the reasons for the use of the series

motor as the cranking motor is explained.

The choice to be made is dc or ac motor. Since the battery is

being used as an energy storage device, which provides dc; the

motor to be used will also be of dc type.

The next choice is to be made between the series, the shunt or

the compound motor types. In the series motor, the field windings

and the armature windings are in series with each other;whatever amount of current flows through the field winding, the

same amount of current flows through the armature windings. In

the shunt motor, these windings are parallel to each other. Part ofthe current flows through the field windings and part of the

current flows through the armature windings. The compoundmotor uses both i.e. the series and the parallel connections for

field and armature windings.


9/13


The series motor, owing to its highest cranking torque is usually preferred for

the motor vehicles. Since the armature and the field windings are wound in

series, it draws maximum current, may be of the order of 200-400 amps,which results in more torque as compared to the shunt motor. This motor

may be a two pole motor or a four pole motor. With the four pole motor, the

distribution of magnetic flux will be more uniform, hence these are preferred

over the two pole motors.

The compound motor is widely used for industrial applications. However, the

large starter motors are often compound wound and operated in two

stages. The first stage involves the shunt winding being connected in series

with the armature. This connection allows for low meshing torque due to the

resistance of the shunt winding. When the pinion of the starter is fully in mesh

with the ring gear =, a set of contac ts causes the main supply to be passed

through the series winding and armature giving full torque. The shunt windingwill now be connected in parallel and will act in such a way as to limit the

maximum speed of the motor.

Nowadays, owing to their simple construction and compactness, permanent

magnet motors (PMDC ) motors are also used in vehicles as cranking motors.

Probable Faults

We want the learners to come up with the probable faults that

may appear in the starting system. Since, they already know thevarious components and their functions; we would expect themto come up with reasons behind the cause of the faults.

Suggested Activity: Group Discussion

Two groups of learners will be formed and they will be given a situation. The

situation is as follows:

The vehicle is not getting started though sufficient fuel is available and

there is no problem with the ignition system.

The learners will need to list out various causes due to which it is not getting

started. Group formation will take around 3 minutes and 5 minutes would

be given for discussion. Last 2 minutes are meant for conclusion of

discussion.


10/13


The group of learners will deliberate on the situation. The problem may be

attributed to the battery, the starting switch or the c ranking motor itself.

The battery voltage and terminals need to be checked. If the battery is

drained, the voltage would have reduced and it may not be sending current

to the motor. Also, the terminals should be cleaned as unclean terminals may

not establish proper contact. The starter switch also needs inspec tion. If the

windings of the motor get short circuited, the motor will not run and thus willbe unable to start the engine. The motor terminals also should be checked

for proper contact. The drive mechanism also should be checked for open

circuit or engagement of pinion and flywheel ring gear. If the meshing

doesnt take place, the drive from motor will not get transmitted to the

engine and it will not start.

At least one of the learners is expected to come up with reasons/faults dueto which the vehicle is not getting started.

Conclusion

For conclusion, a question-answer session will be conducted to

seek the correct answers from the learners. The faculty mayrequire to refine and reinforce the answers given by the learners.

Suggested Activity: Question and Answer

The following questions can be asked to the learners:

1. What is the range of the minimum cranking speed for SI and CI engines?2. Why pinion flywheel reduction is arranged in the starting system?3. Which type of motor is preferred and why?


11/13


Summary

In this session, we learnt to:

Understand need of automotive starting system.

Write requirements of starting system.

List various components of starting system.

Understand working of the same.

Draw schematic of the same.J ustify type of motor used.

Identify probable faults in the starting system.


12/13


Assignment1. Draw the schematic of typical automotive starting system.2. List elements of typical automotive starting system and write role of the

same in overall functioning of the system.

3.The learners can be divided in groups of 5 each. They are supposed tovisit any garage/service station nearby and observe starting system of any

three vehicles of preferably different categories. They are also required to

write the specifications of the stating system of the said vehicles.


13/13


ReferencesP. L. Kohli, Automotive Elec trical Equipment, Tata McGrawHill

Tom Denton, Automobile Electrical and Electronics Systems, SAE

International

6.Starting System

Documents

Transcript of 6.Starting System