Engine Speed Detection Digital Diesel Electronics (DDE7): Notes

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