Operation of the contactless ignition system (VAZ-2109)

When the ignition is turned on, contacts "30" and "87" of relay 1 are closed (figure 110) ignition and the supply voltage is supplied to terminal "4" of switch 5 and the contactless sensor in the ignition distributor sensor 6. The camshaft rotates the shaft of the ignition distributor sensor and the contactless sensor produces voltage pulses (see figure 108, II) to terminal "6" of the switch. In turn, the switch converts them into current pulses in the primary winding of ignition coil 4.



The current flowing through the primary winding of the ignition coil creates a magnetic field around the winding turns. At the moment of current interruption, the magnetic field decreases sharply and, crossing the turns of the secondary winding, induces an EMF of about 22...25 kV in it. The high-voltage current goes to the spark plugs and closes along the path: secondary winding of the ignition coil, high-voltage wire, central terminal of the cover, central and outer contacts of the rotor, side electrode of the ignition distributor cover, spark plug, "ground". Then, through parallel circuits, the current passes through the battery, generator, all switched-on consumers, to contacts "87" and "30" of the ignition relay, to terminal "+B" and to the secondary winding of the ignition coil.



High voltage supplied to the central electrode of the spark plug breaks the air gap between the electrodes, and a spark jumps between them, igniting the working mixture in the engine cylinder.

To obtain maximum power and efficiency of the engine, it is necessary to ignite the working mixture a little earlier than the piston reaches TDC, so that combustion ends when the crankshaft turns 10...15° after TDC. In order for the fuel to burn in a timely manner, each engine speed requires its own ignition advance angle. When the crankshaft speed decreases, the ignition advance angle should decrease, and when it increases, it should increase.

At high rotation speed, weights 1 (figure 111) under the action of centrifugal forces they rotate relative to their axes, rest against the driven plate 3 and, overcoming the tension of the springs, rotate it together with the screen 9 (see figure 107) in the direction of rotation of the ignition distributor sensor shaft by angle "A" (figure 111, b). Now the screen slot at angle "A" passes through the sensor gap earlier and it gives out a pulse earlier, i.e. the ignition advance increases. When the rotation speed decreases, the centrifugal forces decrease, and the springs turn the driven plate 3 together with the screen against the direction of rotation of the shaft, i.e. the ignition advance decreases.




When the engine load changes, the residual gas content in the engine cylinders changes. At high loads, when the carburetor throttle valves are fully open, the residual gas content in the working mixture is low, so the mixture burns faster and ignition should occur later. When the engine load decreases, (throttle cover) the amount of residual gases increases, the working mixture burns longer and ignition must occur earlier. The ignition advance angle is adjusted depending on the engine load by the vacuum ignition advance regulator.

At aperture 20 (see figure 107) This regulator operates under vacuum, transmitted from the area above the throttle valve of the primary chamber of the carburetor. When the throttle valve is closed (engine idle), the hole from which the vacuum comes is higher than the edge of the throttle valve, above which there is no vacuum, so the vacuum regulator does not work.

When the throttle valve opens slightly, a vacuum appears in the hole area, which is transmitted to the vacuum regulator. Diaphragm 20 bends and, with the help of rod 21, turns the sensor support plate against the direction of rotation of the ignition distributor sensor shaft. The ignition advance increases. As the throttle valve opens further, (increase in load) the vacuum decreases and the spring presses the diaphragm back to its original position. The sensor support plate rotates in the direction of the shaft rotation, and the ignition advance decreases.

(The article is copied from the website: «www.VazBook.ru»)