Crankshaft Position Sensor: Description and Operation

Top Dead Sensor Circuit:

LOCATION
The Crank Angle Sensor and the Top Dead Center Sensor are located within the distributor housing.

CONSTRUCTION
Both sensors are incorporated into one module; a disc and a pick-up module. The disc is affixed to the distributor shaft and the light-transmitting module is mounted stationary to the distributor housing.

Crank Angle And #1 TDC Sensor:

The disc contains slits around its circumference with a blank space 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 module assembly uses two luminous diodes and two photo diodes, in order to be able to detect the two different slits.


OPERATION
There is a very slight clearance between the luminous diodes and the photo diodes, and the disc rotates within this space. As the shaft rotates, the slits at the discs edge pass between the light and the optical receptor part of the module. 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 Module

The Control Module is able to detect number one cylinder TDC by comparing the signal generated through the inner slits on the disc and the blank space in the outer slits.

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 Module is able to determine the fuel injection pulse width, ignition timing, and also the intake air flow rate for each revolution of the engine.