Basic Ignition System

  An ignition system changes battery voltage to a very high voltage and then sends the high voltage to the spark plugs. The following parts are included, shown in Fig. 5. 3：

    ．Battery - provides power for system

    ．Ignition switch - allows driver to turn ignition and engine on and off

    ．Ignition coil - changes battery voltage into 30，000 volts or more during normaloperation. It has the potential to produce up to 60,000 volts

    ．Switching device - mechanical or electronic switch that operates the ignition coil

    ．Spark plug - uses high voltage from the ignition coil to produce an arc，ignitingthe fuel charge

    ．Ignition system wires - connect ignition system components

    When the ignition switch is on and the switching device is closed（conductingcurrent)，current flows through the ignition coil. When the piston is near TDV on its compression stroke，the switching device opens to stop current flow through the ignition coil. This causes the coil to produce a high-voltage surge，which flows through the spark plug wire and arcs across the spark plugs' electrodes.

    The electric arc，or spark，at the spark plug ignites the fuel mixture. The mixture begins to burn，forming pressure in the cylinder for the engine's power stroke.

    When the ignition key is turned off, the battery-to-coil circuit is broken. Without current to the ignition coil，an arc cannot be produced at the spark plugs and the engine stops running.

    An actual ignition system is much more complex than the one just discussed. Vehicleshave multiple-cylinder engines，and the timing of the spark must vary with operating conditions.

    There are two main circuits of an ignition system：the primary circuits and secondary circuits. The primary circuit includes all the components and wires operating on lowvoltage.  Thus ignition system primary voltage is normally below battery voltage.Conventional wire similar to the wire used in other electrical system is used.

    The secondary circuit of the ignition system is the high-voltage section. Its operating voltage can normally range from 4，000 to 30，000 volts，depending on system design. Itconsists of the wires and parts between the coil output and the spark plug ground. Thesecondary wire must have thick insulation to prevent electrical leakage（electricitytravelling through insulation from one component to another)．