Audi A4

since 1994 release

Manual of the car

Audi A4
+ Running gear
+ Regular servicing
+ Engines
+ Turbo-supercharging
+ System of an exhaust
+ Cooling system
+ Fuel tank and fuel pump
+ Air filter and channels of absorption
+ System of injection
+ Coupling
+ Transmission and main transfer
+ Suspension bracket of wheels and steering
+ Brakes
+ Wheels and tires
+ Electrotechnical equipment
- System of ignition
   What provides ignition
   When there is an ignition of fuel-air mix?
   Different systems of ignition
   So there is an ignition spark
   Executive body
   System brain
   The signals coming to the control unit
   Adjustment of a detonation
   Be careful in the address with ignition
   Works on system of ignition
   Search of malfunctions in ignition
   Ignition distributor
   Knot of high voltage
   Replacement of spark plugs
   Right choice of spark plugs
   Check of the moment of ignition
+ Lighting
+ Alarm equipment
+ Tools and devices
+ Heating and ventilation
+ Body details
+ Salon
Search of malfunctions
Technical characteristics


The signals coming to the control unit

Hall's sensor

The disassembled Hall's sensor of the engine with a working volume of 1,8 l. The major details are integrated system of Hall (in the case with the socket) and a diaphragm rotor.

Very simply it is possible to tell: Hall's sensor provides inclusion and switching off of current to the ignition coil (a bypass way via the control unit and the terminal cascade). It is called in honor of an opener of effect of Hall who is used in this sensor.

Hall's sensor consists of the following details: from a diaphragm rotor, for example, with four dredging (depending on the number of cylinders), a permanent magnet and the direct integrated system of Hall located opposite to it. All this works as a light lock, only here instead of light work with electromagnetic radiation.

If the diaphragm of a rotor is in the electromagnetic field, then Hall's sensor starts up current to the control unit. When the diaphragm leaves from an air gap between integrated system of Hall and a permanent magnet, current does not come to the control unit. These are signals for ignition. Hall's sensor settles down:

  • in the 74 kW engine under the distributor;
  • in the 92 kW engine and in the 110 kW four-cylinder engine ahead at the left on a head of the block of cylinders;
  • in the six-cylinder engine behind on the left head of the block of cylinders.

Sensor of speed and sensor of the moment of ignition

In addition to Hall's sensor information comes to the control unit from the sensor of speed of the engine and the sensor of the moment of ignition (the last only in the six-cylinder engine). Both are so-called induction sensors.

The sensor of speed of the engine functions as follows: in the sensor the coil and a magnet are placed. The interfaced detail is formed by gear heights on a gear wreath of a flywheel behind on the crankshaft. Every time when the tooth passes under the sensor, changes magnetic field of a permanent magnet, and in the coil tension appears. This small signal in the form of tension is enough for the subsequent processing in the control unit. Available also information on the frequency of rotation of the crankshaft.

To define exact position of the crankshaft, in a certain place on perimeter of a flywheel the steel pin was placed. When the pin passes under the sensor, there is tension peak that is used by the control unit for definition of position of the crankshaft.