Engine Speed Sensor: Description and Operation

Crankshaft Position And Speed Sensor:

PURPOSE AND LOCATION
The crankshaft position sensor (1) supplies the ECU (3) with information on crankshaft position and engine speed. The sensor is mounted close to the flywheel (2).

CONSTRUCTION (A)
The sensor (1) consists of a permanent magnet (4), a pole tip (5) which concentrates a magnetic field at the end of the device and a coil (6). The magnet creates a magnetic field which varies in strength depending on whether a hole or "tooth" is passing the tip.

OPERATION
An altering voltage is induced in the sensor when one of the "windows" on the flywheel passes the tip. This variable signal is transmitted to the ECU.

In effect, the sensor supplies the ECU with a unique altering voltage (an electrical picture) from which the ECU can determine both the crankshaft position and speed.

SIGNAL (B)
The frequency (7) of the signal is used to determine the engine speed.

To provide a referance signal for the crankshaft position, one or more "teeth" on the flywheel circumference are made longer than others. The ECU detects the crankshaft position by sensing the interruption in the signal (8) which occurs as a long "tooth" passes the sensor. This referance is used to determine the top dead center (TDC) position.