Ignition Hall Effect Sensor: Description and Operation

The hall sensor generates a square wave signal which the ECU monitors. This signal is used as a reference for calculating the ignition timing, and engine speed.

THE HALL EFFECT

The Hall Effect:

The hall sensor contains a semiconductor wafer element, and a permanent magnet. When the current flowing through the sensor element in the direction of one axis (call it the X axis) is subjected to a magnetic field whose lines of flux cross perpendicular to the direction of current flow (call it the Z axis), electrons (charge carriers) in the current flow are deflected along an axis (call it the Y axis) perpendicular to the "X-Z" plane defined by the direction of current and lines of flux. The resulting difference in the concentration of electrons along opposite edges of the element creates a voltage potential (hall voltage) which can be measured. When the distributor is turning, vanes of a metal rotor, called a trigger wheel, alternately pass and block the lines of flux from the permanent magnet. When a vane passes between the magnet and sensor, the lines of flux permeate the metal vane and do not reach the sensor element. The flux density through the sensor element is negligible and the hall voltage is too small to measure (effectively zero). When no vanes are present between the magnet and sensor, the lines of flux pass through the hall sensor creating the hall effect. The signal generated by the hall sensor describes the relative position of the crankshaft. At the instant the hall sensor voltage goes high, a specific number of degrees of crankshaft rotation remain before TDC of the next power stroke. The ECU uses this information, compared with information from other sensors, to calculate the ignition timing. Turbo models have separate engine speed and crankshaft position sensor located on the rear of the engine block. These sensors directly signal the exact speed and position of the crankshaft at any time. By comparing these signals with that of the hall sensor, the ECU can determine if the distributor basic setting is correct or not. If the signals do not agree, once each revolution of the crankshaft, then a fault code is stored. For this reason it is important for the distributor to be set properly, even though the ignition timing is not actually adjustable.