Ignition and Electrical Systems

Module (b)

City & Guilds3905 / IVQ in Motor Vehicle Engineering

Unit 1 Engine Systems 1

Table of Content

1. Introduction to Basic Electricity2. 1.1b & 1.2b Spark ignition systems3. 1.3b Ignition Timing4. 1.4b Electrical Systems

Introduction to basic Electricity

Introduction to basic Electricity• After studying this chapter you will know about:

– Electrons & their flow

– Electricity

– Current, its flow & types

– Voltage

– Resistance

– Ohm’s Law

Matter

Solid Liquid Gas

•Everything in the world is made of matter

•Matter is anything that has mass (weight) and occupies space

• All matter (solid, liquid & gas) have molecules

• All molecules can be further divided into atoms

• Each atom has a nucleus which contains:– Neutron (no charge)– Proton (positive charge)– Electron (negative charge) Moves around nucleus

Inside Nucleus

• Element– A chemical element is a pure chemical substance

consisting of one type of atom

• Compound– A chemical compound is a pure chemical

substance consisting of two or more different elements

• Atom

• Molecules

O Atom is the smallest particle into which an element or substance can be divided, without losing its property

• Atom Construction

• Electrons– They have (–)ve charge

– Free to move around nucleus, unlike protons and neutrons which are fixed in the center

– (+)ve charge in the nucleus by proton attracts (–)ve electron

– The closer, the stronger force of attraction

• Simplest atom of hydrogen

• Now lets see a more complex atom of copper

Introduction to basic Electricity• Copper

– Most commonly used

– Atomic number is 29 (i.e. 29 protons & 29 electrons)

– 2, 8, 18, 1 electrons in 1st to 4th ring

• Conductors have < 4 electrons in outer ring

• Insulators have > 4 electrons in outer ring

• Semi-conductors = 4 electrons in outer ring

• Electron Flow

– Electrons farther from the nucleus are loosely held

– They start moving freely from atom to atom

– They are also called free electrons

– When atom looses electron, it gains another one from the adjacent atom

• Current & Electricity

– The directed flow of electron from one atom to another in a conductor

– Measured in amperes (A)

– Free electrons, unless directed, can not produce current

• Current Flow1. Conventional (we will study this type)

Positive to negative

2. Electron theory Negative to positive

• Current flow– Types

1. A.C

2. D.C

• Voltage1. A force that causes electrons to move in an electrical

circuit

2. Also called1. EMF (electromotive force)

2. Electrical pressure

3. Potential difference (Difference in potential between two points)

• Resistance (Ohms)

1. Resistance restricts the flow of electric current.

2. Energy is used up as the voltage drives the current through the resistor

3. This energy appears as heat in the component.

• Ohm’s Law

1.1b & 1.2bSpark Ignition Systems

(Identification, Components & Function)

Spark ignition systems

• In this section we will study about:

1. Spark ignition system components2. Contact Breaker3. Contact Breakerless4. Ignition switch5. Ignition coil6. Ballast resistor7. Spark advance devices8. Spark plugs

1.1b & 1.2b

Spark ignition systems• Ignition System

1.1b & 1.2b

• Ignition System

– Provides high-intensity sparks at the spark plugs to ignite the air-fuel mixture in the combustion chamber

– Spark should be at the right time

– Energy is obtained from the battery & alternator

– Can produce 40,000 or more volts by the ignition coil

1.1b & 1.2b

• Components1. Battery2. Low-tension cables3. Ignition coil4. Distributor5. Coil high-tension cable6. Spark plug cables7. Spark plugs

1.1b & 1.2b

Spark ignition systems 1.1b & 1.2b

Spark Ignition Systems

Contact BreakerContact

Breakerless / Electronic

Direct

• Types

We will only talk about the contact-breaker & contact-breakerless types in detail

1.1b & 1.2b

1. Contact Breaker Ignition Systems

1.1b & 1.2b

There are two parts to the system

1. Primary Section

i. Battery

ii. Ignition switch

iii. Ballast resistor

iv. Primary winding of the ignition coil

v. Primary section of the distributor

1.1b & 1.2b

2. Secondary Section

i. Secondary windings of the ignition coil

ii. Secondary side of the distributor

iii. Spark plug cables

iv. Spark plugs

1.1b & 1.2b

• Activity in the primary section

1. Step 1

i. Battery is connected to terminal B of the ignition switch

ii. Ignition switch is turned to S for starting

iii. Ignition switch is turned to IG once the engine is running

1.1b & 1.2b

2. Step 2i. Breaker points are closed

ii. To energies primary windings, current flows from:

Battery Ballast resistor

Primary windings

of ignition coil

Points Earth

1.1b & 1.2b

3. Step 3i. Breaker points are opened and closed by the action of

cam in the distributor as it rotates

ii. Primary windings are de-energized when points are open, and a high voltage is induced in the secondary windings

1.1b & 1.2b

• Activity in the Secondary Section

1. Step 1

i. Secondary winding of the coil are connected to the rotor of the distributor by the coil high-tension cable

ii. The rotor rotates to distribute the high-tension voltage to the segments in the distributor cap

1.1b & 1.2b

2. Step 2

i. Spark plug cables connect the segments of the distributor cap to the spark plug

ii. The cable should be connected in correct firing order

1.1b & 1.2b

3. Step 3

i. High voltage from coil causes a spark at the spark plug electrodes

ii. This ignites the air-fuel mixture in the combustion chamber

iii. Process is repeated for each power stroke of engine

1.1b & 1.2b

• Ignition Switch1. It controls the power by preventing accessories from

running down the car's battery when the car is parked for a long period of time

2. The ignition switch connects the starter to the battery, allowing the battery to send a powerful surge of electricity to the starter when the car is being started.

1.1b & 1.2b

1. Contact Breaker Ignition Systems• Ignition Switch

• Ignition Coil

– Primary winding consists of a few hundred turns of heavy wire

– Secondary winding consists of thousands of turns of fine wire

– Soft-iron core in the centre of the coil

– 12 volts of the battery are stepped up to the high voltage

1.1b & 1.2b

1. Contact Breaker Ignition Systems• Ignition Coil

1.1b & 1.2b

Spark ignition systems Types of Ignition Coil

1.1b & 1.2b

(a) conventional coil (b) coil-on-plug

Spark ignition systems Types of Ignition Coil

1.1b & 1.2b

(c) direct ignition, dual-spark coil (d) coil with exposed core

• Ballast Resistor

– Fitted between the ignition switch and the ignition coil

– Reduces voltage at the coil

– Coil is designed to operate on lower-than-battery voltage

1.1b & 1.2b

1. Contact Breaker Ignition Systems• Ballast Resistor

1.1b & 1.2b

• Distributor parts

1. Housing

2. Shaft with a cam

3. Advance mechanism

4. Breaker contact points

5. Capacitor

6. Rotor

7. Cap

1.1b & 1.2b

• Distributor

1.1b & 1.2b

• DistributorShaft is driven through gears by the camshaft

• Distributor has following three functions

1. To make and break the primary circuit of the ignition coil

2. To do this at the right time for each cylinder

3. To distribute the high voltage to the spark plugs

1.1b & 1.2b

• Action in the Distributor1. For a 4-cylinder engine the distributor has a cam with 4

lobes2. The cam rotates and contacts the fiber rubbing block of the

breaker arm3. This opens and closes the points4. When points open, a high voltage is induced in the ignition

coil5. A spark is produced at the spark plug

1.1b & 1.2b

• Cam angle and dwell1. It is the time that the points are closed2. Angle turned by the distributor cam from points

closed to points open3. Points must remain closed for a very short period to

build up the magnetic field

1.1b & 1.2b

1. Contact Breaker Ignition Systems• Cam angle or dwell

1.1b & 1.2b

• Capacitor / Condenser1. Made up of two strips of metal plates, with a strip

of insulating paper between them2. These are rolled into a cylinder and inserted into a

metal container3. The plates absorb current and stops it quickly4. It is a temporary reservoir of charge

1.1b & 1.2b

1. Contact Breaker Ignition Systems• Capacitor / Condenser

1.1b & 1.2b

1. Contact Breaker Ignition Systems• Spark-Advance Devices

Spark Advance Devices

Centrifugal Advance(Engine Speed)

Vacuum Advance(Engine Load)

1.1b & 1.2b

• Spark-Advance Devices1. Centrifugal Advance

I. At idle speed, spark is timed to occur at some degrees before TDC of compression stroke

II. At fast speed, spark has to occur much earlier to get the same result, as piston speed increases

III. It contains flyweights that throw outwards at high rpmIV. This turns the cam in relation to the distributor shaftV. So the spark occurs early

1.1b & 1.2b

• Centrifugal Advance

1.1b & 1.2b

• Centrifugal Advance

1.1b & 1.2b

• Spark-Advance Devices2. Vacuum Advance

I. Operated by intake manifold vacuumII. Intake manifold vacuum varies with engine loadIII. It consists of a diaphragm unitIV. One side connected to base plateV. Other side connect to a port in carburetor by a vacuum line, spring is

fitted at this sideVI. Rotating the base plate causes the contact points to open early and so

advances the spark

1.1b & 1.2b

Vacuum Advance

1.1b & 1.2b

• Spark-Advance Devices3. Vacuum Retard

I. Distributors may have a vacuum retard mechanismII. The retard mechanism is contained in the rear of the vacuum

diaphragm chamberIII. When the engine is operating under high-vacuum conditions

(deceleration or idle), intake manifold vacuum is applied to the retard mechanism

IV. The retard mechanism moves the breaker points mounting plate in the direction of distributor rotation, thereby retarding the ignition timing.

1.1b & 1.2b

• Spark-Advance Devices4. Combined centrifugal and vacuum advance

I. At any time there will be centrifugal advance due to engine speed and vacuum advance due to engine load

II. If a car is going up a hill at full throttle and the speed falls off, the manifold vacuum will become less, both advance (centrifugal and vacuum) will be reduced

III. Both will automatically adjust to suit the driving conditions of speed and load

1.1b & 1.2b

1. Contact Breaker Ignition Systems• Spark Plugs– It sparks to ignite the air–fuel mixture in the

combustion chamber

1.1b & 1.2b

Spark Plugs construction

1. Metal shell2. Ceramic insulator3. Electrode (special alloy wire)4. Earth electrode5. Threads6. Terminal7. Gasket

1.1b & 1.2b

1. Contact Breaker Ignition Systems• Spark Plugs Identification

1. Thread size (diameter)2. Reach (length of thread)3. Heat range (operating temperature)

1.1b & 1.2b

1. Contact Breaker Ignition Systems• Spark Plugs Identification

1. Thread size (diameter)1. Thread size vary from 10 mm, 12 mm, 14 mm, or 18 mm

diameter2. Commonly 14 mm diameter plugs are used

1.1b & 1.2b

• Spark Plugs Identification2. Reach (length of thread)

1. It varies from 9 mm, 11 mm, or 13 mm2. It shouldn’t be too long because preheating will damage the

plug or even strike the piston3. It shouldn’t be too short because this will effect smooth

running and performance of engine4. Thread on the plug should be same length as the thread in the

cylinder head.

1.1b & 1.2b

• Spark Plugs Identification3. Heat range (operating temperature)

1. Heat range should be between 400oC and 800o C, this is the self-cleaning temperature range

2. If less then this range then soot and carbon will form which will cause plug failure

3. If more then this range, then it will damage the plug and pre-ignition may occur.

1.1b & 1.2b

Spark ignition systemsSpark Plugs Identification

1.1b & 1.2b

1. Contact Breaker Ignition Systems• Hot and Cold Spark Plugs

1. Temperature of a plug depends on the distance that the heat travels from the plug to the cylinder head

2. If heat path is long, plug is hotter, and known as hot plug and vice versa

Insulator Outer Shell

Cylinder head

Water jacket

HEAT PATH

1.1b & 1.2b

HEAT PATH

Heat range of spark plugs – the longer the heat path, the hotter the temperature at which the plug operates

• Firing Order

1. Sequence in which the power stroke occur2. So it is the order in which the ignition system must provide a

spark at the spark plugs3. Determined by the shape of crankshaft, arrangement of

cams on camshaft and the ignition distributor timings4. High-tension cables between the distributor cap and the

spark plugs must be connected to the spark plugs in the correct firing order

1.1b & 1.2b

• Suppression (Spark plug cables)

1. Ignition system circuit uses TV & Radio Suppression (TVRS) cable to carry high voltage, also known as resistance cable

2. It suppresses the electrical pulses of the ignition system to minimize interference with reception on your car radio or TV

3. Cable connects each spark plug to distributor cap and the coil to center tower of the cap

1.1b & 1.2b

• Spark plug cables

1. High-tension cables link the distributor cap, the spark plug and the high tension terminal of the ignition coil

2. These are heavily insulated because they carry high voltage3. Insulation should withstands effects of high temperature, oil and

moisture4. Core is made up of carbon-impregnated linen or fiberglass5. These resistance cables prevent the ignition system to interfere with

radio and television reception

1.1b & 1.2b

• Spark plug cables

1.1b & 1.2b

Spark ignition systems2. Breakerless (Electronic) Ignition Systems

1.1b & 1.2b

2. Breakerless (Electronic) Ignition Systems1. Electronic ignition has no breaker contact points and is

also known as breakerless ignition2. Instead of contact points, it uses pulse generator in the

distributor and an electric control3. The generated pulse are used as signals to the

electronic control unit, which makes and breaks the primary circuit

4. Together, the pulse generator and electrical control unit perform the same function as a set of breaker points

5. Distributor has no points to wear, ignition is precise and sparks are of high intensity

2. Breakerless (Electronic) Ignition Systems

2. Breakerless (Electronic) Ignition Systems• Pulse generator– It has a stator and a rotor unit

• Stator1. Stator has a permanent magnet and a small

induction (pickup) coil2. Pickup coil is connected to the electronic control

unit by two leads

2. Breakerless (Electronic) Ignition Systems• Pulse generator• Rotor

1. Rotor (signal rotor or reluctor) is made up of soft iron and has number of teeth equal to the number of cylinder of the engine

2. As each tooth rotates past the pickup coil, a very small voltage is induced into the coil

3. This small electrical pulse is used as a precisely timed signal for action in the electronic control unit

1.1b & 1.2b

• Electronic control unit1. It is also known as igniter or ignition module2. It can be inside or outside of the distributor3. It has transistors, diodes and resistors4. Transistors act as switching devices for the ignition-coil primary

circuit5. When pulse generator gives signal to ECU, it opens the primary

circuit6. Magnetic field of the primary windings in the ignition coil collapse,

and a high voltage in the secondary windings is induced

1.1b & 1.2b

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