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Ignition Systems. Identify the components in the following diagram. Next >. Sort the components into the following sections. Primary circuit. Secondary circuit. Secondary coil windings King lead Distributor cap Rotor button Spark plug leads Spark plugs. Battery/power supply
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Sort the components into the following sections. Primary circuit Secondary circuit Secondary coil windings King lead Distributor cap Rotor button Spark plug leads Spark plugs • Battery/power supply • Ignition switch • ballast resistor, • Primary coil windings • Switching device Next >
The Electrical power supplyis used to store and supply electrical current to all electrical systems including the ignition system. Next >
The ignition switchis the drivers master control switch. Next >
Ballast Resistor Ballast resistor is a wire resistor that reduces the voltage in the primary circuit of the ignition system that uses breaker points as the switching device Next >
Ignition Coil Dual output (wasted spark) Conventional Oil filled Direct output Next >
Coil Basic Functions The primary coil windings of the coil receives 12 volts from the battery and this is increased up to 30-50kv by electromagnetic induction. Soft iron core Next >
Switching devices. There are several forms of switching devices used in motor vehicles. • Contact breaker points. • Hall effect generator. • Pulse generator. • Optical pulse generator.
Contact breaker points Next >
Capacitor. The capacitor is fitted for two reasons: • It reduces arcing of the contacts. • It ensures a quicker collapse of the magnetic field. Next >
The dwell angle Next >
The dwell period • The dwell period on an engine with electronic ignition is controlled by the current limiting circuit within the amplifier or ECU • This is the time period that the ignition coil primary is switched on with current flowing in the winding. • It dictates the amount of stored energy in the ignition coil. Next >
Electronic earth switch Points – mechanical earth switch Trigger signal Electronic Ignition SystemsOperating principles Next >
Inductive pulse generator. • Note; the air gap is critical, and must be set using a plastic feeler gauge. Next >
AC output signal voltage Pick-up coil Permanent magnet Air gap Trigger Signal Inductive Inductive triggers do not require a separate power supply. The trigger signals are self-induced by the movement of the rotor. The rotor is rotated by a driven shaft (typically distributor shaft). The rotor has a number of teeth which correspond to the number of engine cylinders. A pickup coil is positioned near to the rotor. Next >
+ - Trigger Signals - Inductive
Trigger Signals – Inductive AC output signal voltage Next >
Hall effect generator Note three wires, as a supply voltage is needed Next >
Switch circuit voltage high - Open circuit Power supply Amplifier 5 volts Trigger Signals – Hall Effect
Power supply Amplifier 5 volts Switch circuit voltage low – Earth circuit Trigger Signals – Hall Effect Next >
Switch circuit voltage Time Hall effect signal waveform Trigger Signals – Hall Effect Next >
Optical pulse generator Next >
The amplifier receives the trigger signal, analogue or digital. The amplifier uses the trigger signal to switch the primary circuit in a similar manner to the set of points, although via a transistor rather than a mechanical set of points. Electronic earth switch Trigger signal
Ignition Timing The distributor is usually fitted with a mechanical advance mechanism and a vacuum advance mechanism. When the speed of the engine increases and the engine load increases, the ignition timing has to be altered to allow for propagation of the flame through the cylinder combustion chamber. When the engine speed increases, the ignition timing has to be advanced to allow time for the propagation of the flame though the cylinder.
What is the purpose of the contact breaker points? • They provide a switching mechanism to enable control of current flow through the primary (low-tension) circuit • What effect does the iron core have on the magnetic force generated by the primary coil when the points are closed? • It amplifies it • Does current flow through the secondary circuit whist the points closed? • No
Secondary circuit. • secondary windings of the ignition coil • high tension leads • rotor • distributor cap • spark plugs
HT leads are constructed of; • A conductor of fibreglass impregnated with carbon and synthetic rubber to provide sufficient tensile strength and to suppress television and radio interference. • The conductor is insulated with a thick rubber coating and is further insulated by a silicon based outer casing. • A metal fitting on each end is designed to clip on to either the distributor cap or spark plug. These are insulated by rubber boots.
The distributor capis made from injection moulded epoxy resin which has high heat resistance and good insulating properties. • In the centre of the cap a carbon contact is mounted on a spring to keep it in contact with the rotor. • Around the outside of the cap there is a metal contact for each cylinder that receives the spark from the rotor. • The rotor.The rotor is also made from epoxy resin and carries a metal bar that connects the centre electrode to each of the cylinder contacts as it turns. • What turns or drives the rotor? • Distributor shaft or the end of the camshaft • At what speed does the rotor turn? • Half the speed of the crankshaft
Spark plugs. • What temperatures must the spark plug operate in? • 400-800º C 2. Give 2 reasons why the ribs are formed on the outside of ceramic insulator. • Increase the length of the ‘flashover path’ • Improve the fitting of the spark plug leads
Spark plug identification • Thread size; this relates to the pitch and diameter of the thread. • Reach. The length of the thread is known as the ‘reach’ of the spark plug. • Heat range. The temperature that a spark plug will reach depends on the distance the heat must travel from the insulator to reach the outer shell of the plug and enter the cylinder head and the water jacket.
