Engine speed detection DDE7

Engine speed detection DDE7

Two sensors are used to detect the engine speed and the position of the camshaft and the crankshaft:

• Crankshaft sensor
  The DDE control unit uses the crankshaft signal to calculate the precise engine speed and detect the TDC positions of the crankshaft.
  
• Camshaft sensor
  The DDE control unit uses the camshaft signal to determine whether a cylinder is at TDC on the compression or exhaust stroke.
  

For starting the engine, the DDE control unit checks the following conditions:

• the two signals must not have any faults
  
• the signals must be detected in a specific chronological sequence
  

This process is referred to as synchronisation and is only performed when the engine is started. Effects of faults on the signals:

• Camshaft signal not OK:
  engine start possible, however with extended start time;
  no effect with the engine running
  
• Crankshaft signal not OK:
  engine start via camshaft signal possible;
  with the engine running, the camshaft signal is used and the torque is limited
  

Brief description of components

Crankshaft sensor

The crankshaft sensor is mounted at the rear of the crankcase. The DDE control unit supplies the sensor with earth (M_KWG) and a supply voltage of 5 V (U_KWG). The crankshaft sensor is designed as a Hall sensor.

On the crankshaft there is an increment gear which has 58 small permanent magnets around its perimeter. As the crankshaft rotates, these magnets move past the crankshaft sensor, thereby producing the crankshaft signal.

Camshaft sensor

The camshaft sensor is mounted at the top rear of the cylinder head cover. The DDE control unit supplies the sensor with earth (M_NWG). Via the activated terminal 87, the camshaft sensor is supplied with on-board supply voltage. The camshaft sensor is designed as a Hall sensor.

There are three different segments at the back of the camshaft and these move past the camshaft sensor. The DDE control unit evaluates the resulting voltage signal (three different square-wave signals per camshaft revolution).