Quantity control in idle speed range - function

In the idling speed range, the fuel delivery quantity must be constantly adapted to the operating state of the engine:

If, for example, the load take-off at the engine changes or (due to low outside temperatures) a high fuel requirement exists, then the MR/PLN control unit adjusts the delivery quantity (over the delivery angle) within prescribed limits.

The delivery angle is dependent on performance maps in the MR/PLN control unit and is basically dependent on the following input parameters:

 Engine speed

 Air mass

 Engine temperature

 Fuel temperature

The last parameter is only determined on engine 541.9 up to engine end no. 094097 and on engine 542.9 up to engine end no. 094246 over a fuel temperature sensor. The fuel temperature for all other engines (engine 541.9 as of engine end no. 094098 and engine 542.9 as of engine end no. 094247) is determined over a performance map.

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The individual cylinder torque control, altitude correction and smoke limitation in the engine control (MR) can additionally influence the delivery angle:

Individual cylinder torque control

Individual cylinder torque control balances out delivery quantity differences between individual unit pumps:

Tolerances and wear on the individual unit pumps can cause differing torque development in the various cylinders. This leads to rough running of the engine,

which means that the rotational speed of the crankshaft increases and decreases slightly. One can particularly feel this when idling. The individual cylinder torque control on the engine control (MR) can react to rough running since it actuates each unit pump individually. It balances out the rotational speed fluctuation through a slightly different injection quantity for individual cylinders until all cylinders have the same torque.

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Altitude correction

There is an atmospheric pressure sensor inside the MR/PLN control unit. It determines the air pressure of the ambient air from which the engine control (MR) deduces the altitude correction.

The altitude correction prevents too much fuel being injected at high altitudes.

Smoke limit

The quantity of fuel is limited in over a smoke limitation map so that no output of smoke occurs.