Crankshaft Position Sensor: Description and Operation

Crank angle sensor
The crank angle sensor detects engine rpm and the crank angle (piston position). It also sends a signal to the control unit to control various operations. This sensor is built into the distributor.





Signal rotor plate
The signal rotor plate has 360 slits at 1° intervals on its outer periphery. It also has four slits at 90° intervals.
These four slits are used to detect the crank angle, that is, the position of each piston. The teeth are used to provide the 1° signal that is necessary to control engine rpm and ignition timing.





Crank angle sensor operation
The crank angle sensor has two diodes and a wave forming circuit. When a signal rotor plate passes the space between the Light Emitting Diode (L.E.D.) and Photo Diode, the slit of the signal rotor plate alternately cuts the light which is sent to the photo diode from the L.E.D. This causes an alternative voltage and it is then converted into an on-off pulse by the wave forming circuit, which is sent to the control unit.








Detection of (1) signal (For detecting of engine rpm and ignition timing control)
Diodes (1) and (3) are used to detect the 1° signal which is created by 360 slits on the rotor plate. When a slit reaches the space between the L.E.D. and photo diode, the photo diode receives the light from the LE.D. and this causes an alternative voltage. Thus, each wave from each diode is compounded. Then, the compound wave is converted into an on-off pulse. This 1° on-off signal is sent to the control unit.

Detection of 180° signal
(For detecting piston T.D.C.)
Diode (2) is used to detect the 180° signal which is created by 90° slits on the rotor plate. When a slit reaches the space between the L.E.D. and photo diode, the photo diode catches the light from the L.E.D. and this causes an alternative voltage. At this time, a signal on-off pulse is generated. Since engine rpm is twice that of the distributor, the rotor plate has four slits at 90° intervals.