It is calculated from the signals of crankshaft position sensor and camshaft position sensor. The crankshaft position sensor can know which cylinder piston is at the top dead center, and the camshaft position sensor can know which cylinder piston is in the compression stroke.
When the light beam of the light emitting diode hits the photosensitive diode, the photosensitive diode generates voltage; When the light beam of the LED is blocked, the voltage of the photodiode is 0. These voltage signals are shaped and amplified by the circuit and sent to the electronic control unit when the crank angle is 1 and 120. The electronic control unit calculates the engine speed and crankshaft position according to these signals.
Extended data:
Magnetoelectric induction speed sensor and crankshaft position sensor are installed on the upper and lower floors of the distributor. The sensor consists of permanent magnet induction detection coil and rotor (timing rotor and speed rotor), and the rotor rotates with the distributor shaft. The timing rotor has one, two or four teeth, while the speed rotor has 24 teeth. The permanent magnet induction detection coil is fixed on the distributor body.
If we know the speed sensor signal, the crankshaft position sensor signal and the working sequence of each cylinder, we can know the crankshaft position of each cylinder. The rotor signal disk of the magnetoelectric induction speed sensor and the crankshaft position sensor can also be installed on the crankshaft or camshaft.
Baidu Encyclopedia-Crankshaft Position Sensor