Crankshaft and Camshaft Sensors for Ignition System - Page 2486
The disc contains 360 slits around its circumference to indicate the crankshaft angle. An additional six light-transmission slits located 60° apart located
inward from the edge are used to indicate number one cylinder's top dead center position. The pick-up unit assembly uses two luminous diodes and two
photo diodes, in order to be able to detect the two different slits. There is a very slight clearance between the luminous diodes and the photo diodes, and
the disc rotates within this space. As the distributor shaft rotates the slits at the discs edge pass between the light and the optical reading part of the unit.
The light emitted from the luminous diodes pass through the slits to the photo sensing diodes. When the photo diodes receive the light, they become
conductive and generate a signal, which is sent to the Control Unit.
The Control Unit is able to detect number one cylinder TDC by the signal generated through the single inner slit on the disc.
The slits at the outer circumference of the disc serve to detect the position of the crankshaft (and, therefore, the piston) relative to top dead center.
Based on these signals, the Control Unit is able to determine the fuel injection pulse width, ignition timing, and also the intake air flow rate for each
revolution of the engine.
