A Conversation for Four-Stroke Internal Combustion Engines

Operation of the Ignition System

Post 1

Kandyman - Keeper of Old Buses

Just read the excellent section on the 4-stroke engine and would like to make a few comments if I may.

My understanding of the way a car's ignition system works is as follows:-

Low tension (12V) DC from the car battery is applied to through the ignition coil primary winding to earth via the points in the distributor. The points are opened and closed by a 4 point cam driven from the engine camshaft. As the points open and close the voltage at the "earthy" side of the coil primary winding alternates between 12v and 0V, simulating an AC waveform. The transformer effect induces a high tension voltage in the coil secondary winding and this is transferred to the distributor centre terminal via a high tension lead. The high tension voltage is then transferred to the relevant spark plug via the rotor arm (which rotates on the end of the distributor cam) and the associated spark plug ht lead. Synchronisation of the spark distribution is achieved by having the distributor driven from the engine camshaft.

As engine speed increase it is advantageous to have the spark plug fire slightly earlier in the cycle. The small tube between the carb and the distributor (vacuum advance/retard pipe) achieves this as follows:-

Increased engine speed = more vacuum in carb venturi. The points are mounted on a plate which can rotate a small distance in relation to the distributor cams. The level of vacuum in the carb venturi effectively sucks the points plate round and they open slightly earlier thus advancing the point in the cycle when the spark occurs.

Another small point, in the section "Basic Anatomy ......"

You don't mention the flywheel which conserves the momentum of the firing strokes and helps smooth out the power obtained from the engine.

Hope the above is of some help. Please feel free to use it if you agree with what I've said, or come come back to me and tell me I've got it wrong.

Keep up the great work

Kandyman


Operation of the Ignition System

Post 2

RadoxTheGreen - Retired

Found this site a while back. It has really good animated engine cutaways.smiley - smiley

http://www.keveney.com/Engines.html


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