PLD start of injection control function

W07.15-1278-79

Components for determination and regulation of the optimal start of injection

1 Engine CAN bus

A3 Drive control (FR) control unit

A6 MR/PLN control unit

B1 Foot throttle actuator

B10 Fuel temperature sensor
- Only on engine 541.9 up to engine end no. 094097 and
engine 542.9 up to engine end no. 094246

B15 Crankshaft angle position sensor

B16 Cylinder 1 TDC sensor

B65 Coolant temperature sensor

B111 Charge air combination sensor (temperature, pressure)

Y6-Y13 Unit pumps on cylinders 1 to 8 (engine 542)

Scatter of NOx and HC issue depending on the start of injection

X Start of injection in °CA

Y Emission in %

α Optimal start of injection

- advanced

+ retarded

Parameters which are included in regulation of the optimal start of injection (α)

A Engine speed and position of the crankshaft (crankshaft angle)

B Position of the camshaft

C Effective start of injection

D Fuel temperature

e Engine temperature

F Load condition (partial load, full load)

* Engine 541.9 up to engine end no. 094097 and engine 542.9 up to engine end no. 094246
(determination based on values from the fuel temperature sensor)

** Engine 541.9 as of engine end no. 094098 and engine 542.9 as of engine end no. 094247
(determination over a performance map)

General information

Regulation of the start of injection primarily occurs through adjusting the ignition retard and through securing ignition in the area of top dead center, that is for the highest compression temperature.

If the start of injection is not regulated the result would be that the ignition retard (time from start of injection to start of ignition), particularly in the higher engine speed range, would have a negative effect upon the combustion cycle. The pollutant emission and noise development would increase while the performance of the engine would drop.

Thus start of injection is primarily dependent upon the rotational speed of the engine and is set in the direction "advanced" with increasing engine speed to avoid the disadvantage of ignition retard in the higher engine speed range.

-----------------------------------------------------------------------------------------

The fact that the start of injection is a purely calculated parameter means that the engine control (MR) can consider parameters other than the engine speed (A) such as fuel temperature (D), engine temperature (E) and load condition (F). These parameters also have effects on the ignition retard and can therefore also contribute to increased pollutant emission.

Exact calculation and appropriate shifting of the start of injection allows the engine control (MR) to compensate for these effects and to lower the pollutant emissions. This allows nitrogen oxides (NOx), which were previously generated through advanced start of injection, and hydrocarbons (HC), which are generated through later start of injection, to be reduced significantly.

-----------------------------------------------------------------------------------------

1 Regulation of the start of injection

Start of injection is regulated over the start of delivery and constantly adjusted to match current operating conditions of the engine.
The start of delivery which previously occurred as the effective start of injection is the point in time at which the solenoid valve in the unit pump is fully closed and the fuel can be compacted or delivered. The start of delivery can be freely regulated within mechanical limits (only limited by the cam form) by the engine control (MR).
Limits (max. start of delivery 25° crankshaft angle before through to 5° crankshaft angle after top dead center) are stored on the MR/PLN control unit (A6) through which also calculation and appropriate actuation of the individual solenoid valves in the unit pumps for cylinders 1 to 8 (Y6-Y13) take place.
The start of delivery is recalculated for every injection process due to constantly changing operating conditions of the engine.

-----------------------------------------------------------------------------------------

2 Calculation of the start of delivery

Signals from the crankshaft angle position sensor (B15) are of primary importance for calculating the start of delivery. This allows the current engine speed and position of the crankshaft (A) to be determined. It is only during the starting procedure or if the crankshaft angle position sensor (B15) fails that additional signals of the TDC sensor on cylinder 1 (B16) are used. They give an indication of the current position of the camshaft (B) and thus when the 1st cylinder is in its compression stroke.
The effective start of injection (C), the fuel temperature (D), engine temperature (E) and load condition (F) are finally used to make the final calculation of the start of delivery.

 Effective start of injection (C)
The effective start of injection (C) is determined with the aid of impact or closing recognition and serves to compensate for scatters and tolerances in the manufacture of unit pumps through performance map regulation.

-----------------------------------------------------------------------------------------

 Fuel temperature (D)
For engine 541.9 up to engine end no. 094097 and for
engine 542.9 up to engine end no. 094246 the fuel temperature (D) is determined over the fuel temperature sensor (B10).
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.

 Engine temperature (E)
The engine temperature (E) is determined from values from the coolant temperature sensor (B65) and the charge air combination sensor (temperature, pressure) (B111).

 Load condition (F)
The load condition (F) is deduced from a number of factors including the engine speed and the position of the foot throttle actuator (B1).