Engine Protection: Crankshaft Emergency-Running Mode (Dual Ignition) - Mercedes-Benz M 447 hLAG Service Manual

Natural gas engine egm engine control unit

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Table of Contents

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2.2.1.5 Engine protection: camshaft emergency-running mode

detect

and

evaluate

M 447 hLAG is equipped with two inductive speed sensors – one crankshaft sensor and one camshaft

sensor. Both speed sensors are evaluated and monitored by the engine control. As the resolution of the

crankshaft sensor is higher than that of the camshaft sensor (more tooth faces on the crankshaft gear),

the crankshaft signal is normally used for determining the crank angle. The camshaft signal is required for

system synchronisation and when the crankshaft signal fails. If the camshaft signal fails before "system

synchronisation" , the engine control switches into the crankshaft emergency-running mode. In the

crankshaft emergency-running mode the so-called dual ignition (two cylinders are ignited simultaneously)

takes place and the torque reduction is carried out as a function of the engine speed. If the camshaft

sensor fails after "system synchronisation" is carried out, engine operation is maintained without

restriction.

Note: To accelerate the engine run-up during starting, starting is carried out with dual ignition (cylinder-

selective gas injection and firing of two cylinders).