Principle of Operation

PRINCIPLE OF OPERATION

The Saab 900 is fitted with a breakerless ignition system incorporating a Hall sensor.

Instead of mechanical contact-breaker points, the distributor incorporates a semiconductor transducer (Hall sensor) and a slotted rotor.

The Hall sensor is connected to an amplifier. The amplifier amplifies and converts the signal from the sensor. This signal is then used to control the charging and discharging of the ignition coil

Caution: The electronic ignition system has an ignition voltage of over 30,000 V and is within the power range that may be lethal to sensitive persons, such as those who have a pacemaker.


Distributor




The distributor is located on the camshaft cover and incorporates a slotted rotor, which rotates with the distributor shaft, and a Hall sensor fitted to a plate inside the distributor. The sensor consists of a semiconductor element and a magnet which acts on the semiconductor. The slotted rotor alternately interrupts and releases the magnetic field, thereby determining the ignition timing.





Note: The Hall sensor and the rotor cannot be removed separately. If the sensor unit is suspected of being defective, the entire distributor must be replaced.






Charging the ignition coil

The slotted rotor breaks the magnetic field. No voltage is generated in the Hall sensor. The amplifier is energised, the primary circuit is closed and the primary winding charges the ignition coil.


Firing instant

The slot in the rotor is in line with the Hall sensor. The voltage generated in the sensor is sensed by the amplifier, which breaks the primary circuit. The spark-firing voltage is now induced in the secondary winding of the coil.


Amplifier




The amplifier is mounted on a cooling plate, forward of the left-hand wheel housing.

The amplifier amplifies and converts the pulse from the distributor. The amplified and converted pulse is then used to control the charging and discharging of the coil.

The amplifier also monitors and controls the dwell angle.

The use of hybrid technology in the design of the module has made it possible to produce an extremely compact amplifier.


Ignition pulse amplifier




The ignition system is equipped with an ignition pulse amplifier (not included on cars without tachometer), to provide more reliable control of the electronic components affected by the ignition (the APC and LH systems), and to reduce the radio interference.

The ignition pulse amplifier is located in the electrical distribution box, in position D.