Distributor (Crank Angle and #1 TDC Sensors)

Crank Angle And #1 TDC Sensor Location:

The Distributor consists of a housing, shaft, drive gear, distributor cap and rotor, and houses the crankshaft angle and the No.1 cylinder TDC sensors. The drive gear (mounted on the end of the distributor shaft) drives the shaft at cam shaft speed. On the other end of the shaft the rotor is mounted. When properly timed the rotor carries current from the coil tower in the distributor cap to the correct spark plug electrode for the designated firing order.

Crank Angle And #1 TDC Sensor:

The crankshaft angle sensor and the No.1 cylinder TDC sensor are composed of a disc and unit assembly. The disc is a metal disc which has four light-transmission slits located 90° apart around its circumference. There is also one additional slit located inward from these four. The inner slit is for the No.1 cylinder TDC sensor, and the outer slits are for the crankshaft angle sensor.
The disc is affixed to the distributor shaft. When the shaft rotates, the slits in the disc are optically read by the unit assembly. The unit assembly, in order to be able to detect the two types of slits, incorporates two luminous diodes and two photo diodes. There is a very slight clearance between the luminous diodes and the photo diodes, and the disc rotates within this space.

Crank Angle And #1 TDC Sensor System:

The light emitted from the luminous diodes reaches the photo diodes each time the disc turns. When the photo diodes receive the light transmitted, they become conductive in the direction opposite to that of ordinary diodes, with the result that current flows as shown by the broken-line arrow in the crank angle and #1 TDC sensor system image, and approximately 5v is applied to the comparator. When this happens, 5v is transmitted from terminal 2 to the ECU. Because the light to the photo diodes is interrupted when the slit passes, the current shown by the broken line stops flowing, and terminal 2 becomes O volts. In this way, then, the pulses from the unit assembly are sent to the ECU as signals.

Photoelectric Signal Pattern:

No.1 Cylinder TDC Signal:
Top dead center is detected by the signal obtained through the one inner slit of the disc. The ECU, based upon this signal, determines which of the four pulses from crank angle sensor is the signal for the #1 cylinder.
Crankshaft Angle Signal:
The four slits located at the outer circumference of the disc serve to detect the position of the crankshaft (and, therefore, the piston) relative to top dead center. The ECU, based on this signal, determines the fuel injection timing, and also calculates the amount of intake-air, the timing of the ignition signal, etc. for each revolution of the engine.