Ignition Systems

Question 1

Magneto Principle

Answer 1

AC generator,transformer and distribution system providing high voltage current to spark plugs

Question 2

Contact Breaker

Answer 2

Interrupt primary winding current to initiate a rapid collapse of primary winding magnetic field

Converts AC into pulses

Collapse of magnetic field in primary produces surge of energy in secondary winding

4 cylinder = 4 points
6 cylinders = 6 points

Question 3

Primary Winding

Answer 3

Low tension circuit
Few thick turns of wire

Question 4

Secondary Winding

Answer 4

High tension cable
Turns of fine wire
Step up transformer

Connects spark plug to distributor and transmits the current

Question 5

Role of a capacitor / condenser

Answer 5

+ Prevent arching at contact breaker point (path of least resistance)

+ Ensure highest possible voltage induced in secondary circuit

! Without engine will not start

Fitted in parallel to contact breaker

(High current flow after collapsing magnetic field)

Question 6

Distributor

Answer 6

Distributes electrical pulses to each spark plug at appropriate sequence.

• Rotor arm driven by the engine

HT current fed to rotor and passes to each spark plug
Rotor rotates at 1/2 engine speed

Question 7

Ignition switch on/off

Answer 7

On switch on = primary circuit broken making ignition live
Off switch = primary coil earthed so no output to spark plugs

Question 8

Advantages of two spark plugs

Answer 8

Accelerate combustion process
Quicker peak cylinder pressure
More power

Question 9

Magneto checks what it means

Answer 9

If switching to one gives a complete dead cut indicating failure of one half of the ignition circuit

If no drop in RPM would show the ignition system is not being earthed

Question 10

Impulse Coupling Magneto

Answer 10

Spring loaded clutch between drive spindle from engine and magneto

Purpose - Retard the spark during engine starting via spring loaded clutch.

Provides a stronger spark at TDC for engine start

Rotate shingle winds up spring releases spinning up magneto

1/2 revs of engine to ensure strong spark

Question 11

High Tension Booster Coil

Answer 11

Battery used to boost voltage within primary winding
Field collapse an even greater voltage occurs in secondary winding
Used on large engines

Question 12

Magnetic Rotor

Answer 12

Induces an EMF within primary winding

Question 13

Steps for sparking a spark plug

Answer 13

Magnetic rotor/contact breaker and distributor driven by camshaft rotate 1/2 the crankshaft speed

Spark needed contact breaker opens to break primary circuit causing magnetic field to rapidly collapse

Collapse induces higher emf (low current) within the secondary winding

Sent to distributor

Distributor sends secondary current to spark plugs in correct sequence

Question 14

Starter Motor

Answer 14

Used to turn crank assembly on start

Question 15

Primary Winding

Answer 15

High Current
Low Voltage

Question 16

Secondary Winding

Answer 16

Low Current
High Voltage

Question 17

Design of Magento System

Answer 17

Makes it fail safe in the air
Allows the engine to continue to fire if the switch fails
Potential hazard on the ground

Question 18

Spark Plug gap

Answer 18

Too small - weak spark
Too large - no spark

Oil/carbon/lead can lead to plug fouling

Question 19

Arrangements of spark plugs

Answer 19

Each magneto drives 1 spark plug in each cylinder for redundancy
- quicker rise in peak cylinder pressure (power)

Question 20

Capacitor role

Answer 20

Momentarily store charge to prevent a large spark across the points (contact breaker) and reduce pitting of the points

Question 21

Purpose of HT cable

Answer 21

Connects the spark plug to the distributor and transmits the current from the secondary winding

Question 22

Ignition system is switched off by

Answer 22

Grounding both the primary and secondary circuits