Engine Speed Detection DDE7

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 OT 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 synchronization and is only performed when the engine is started. Effects of faults on the signals:
- Camshaft signal not OK: Engine start possible, but requiring an extended start duration, no impact when engine is running
- Crankshaft signal not O.K. Engine start possible via camshaft sensor signal, when engine is running, the camshaft sensor signal is used and torque is limited

Brief component description

Crankshaft sensor
The crankshaft sensor is mounted at the rear of the crankcase. The DDE control unit provides the sensor with an earthing point (M_KWG) and a supply voltage of 5 V (U_KWG). The crankshaft sensor is designed as a Hall effect 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.
N57: The crankshaft sensor on N57 is also able to identify the direction of rotation of the engine. This enables a faster engine start.

Camshaft sensor
The camshaft sensor is mounted at the top rear of the cylinder head cover. The DDE control unit provides the sensor with an earthing point (M_NWG). Via the activated terminal 87, the camshaft sensor is supplied with onboard 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).