Page 248 - Mechanic Diesel - TT

MECHANIC DIESEL - CITS

Current is permitted to flow through the timer coil to the electronic control unit, where the primary current flows.
As a result, the ignition coil builds up a strong magnetic field.
As the reluctor wheel rotates slightly further, the reluctor tooth moves away from the timer coil. The air gap be-
comes wider offering a high reluctance. This results in a weaker magnetic field for the timer coil and the induced
voltage reverses. The flow of current to the primary circuit is stopped.
The magnetic field in the ignition coil collapses and enough high voltage is produced for producing spark at the
spark plug.
The reluctor wheel in the figure has six teeth. This wheel is used for a six-cylinder engine. The reluctor wheel has
the same number of teeth as there are cylinders in the engine.

Hall effect sensor
The hall effect was named after the scientist who dis- covered the effect. Magnetic sensors used in electronic
distribution utilize the principle of Hall effect.
As shown there is magnetism in the air gap between the two poles of a magnet. When a steel shutter is placed or
moved between these poles, the magnetism in the air gap is cut off. This principle is called Hall effect.
A rotor with curved plates is used in the Hall effect distributor of an electronic ignition system. These curved plates
are called shutters. The shutters are curved in such a way that they can move between the two poles of the
magnetic sensor with the movement of the rotor.
The number of shutters is the same as the number of cylinder in the engine.
Whenever a shutter passes between the two poles of the magnetic sensor, it outs off the magnetism in the air gap
between the poles. This send a signal to the electronic control unit.
When a shutter moves away from the air gap, the magnetic sensor develops a voltage. ECU then receives a
single from the magnetic sensor, to permit the current to pass through the primary winding of the ignition coil.
However, when a shutter passes between the poles, the magnetic field is cut off and the signal voltage comes to
zero.

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CITS : Automotive - Mechanic Diesel - Lesson 71 - 75