PLD start of injection control function

 The start of injection control PLN function is described using engine 926.9 (6 cylinders) as an example.

G07.15-A031-79

General

The start of injection is primarily regulated to compensate for the ignition delay and to ensure ignition in the area of top dead center, i.e. at the highest compression temperature.

If start of injection were not controlled then this would result in ignition delay (time from start of injection to start of ignition) having a negative effect on the combustion cycle, particularly at high engine speeds. Pollutant emissions and noise development would increase while the power output of the engine would reduce.

Thus start of injection is primarily dependent on the engine speed and is adjusted in the direction "advanced" with increasing engine speed in order to avoid the disadvantages of ignition delay in the upper rpm range.

To determine the start of injection, the engine management (MR) control unit reads in the following sensors:

 Fuel temperature sensor (fuel temperature)

 Crankshaft position sensor (engine speed)

 Camshaft position sensor (engine speed)

 Coolant temperature sensor (engine temperature)

 Charge air pressure and temperature sensor (engine temperature and load condition)

Exact calculation and appropriate shifting of the start of injection allows the engine management (MR) control unit to lower emissions. This allows one to significantly reduce nitrogen oxides (NOx) which is generated when start of injection occurs too early and hydrocarbons (HC), which are generated when the start of injection occurs too late.

Function

Start of injection is controlled over the start of delivery and is constantly adjusted to the current operating conditions of the engine.

Start of delivery, which takes place somewhat earlier than the actual start of injection is the point in time at which the respective solenoid valve in the single injection pumps for cylinders 1 to 6 is fully closed and the fuel can be compressed or delivered.

Start of delivery can be regulated completely freely within mechanical limits (limited by the design of the cam) by the engine management (MR) control unit.

The limit values (max. start of delivery at a crankshaft angle of between 25° before top dead center and 5° after top dead center) are stored in the engine management (MR) control unit, through which the calculation is also performed and the individual solenoid valves in the single injection pumps for cylinders 1 to 6 are actuated accordingly.

The constantly changing operating conditions of the engine means that the start of delivery must be recalculated after every injection process.

Signals from the crankshaft position sensor are decisive for calculating the start of delivery. These make it possible to determine the current engine speed and the position of the crankshaft. It is only during the starting procedure or when the crankshaft position sensor fails that signals from the camshaft position sensor are also used. They provide information about the current position of the camshaft and therefore when cylinder 1 is on the compression stroke.

For the final calculation of the start of delivery, the actual start of injection, the fuel temperature, the engine temperature and the load condition are used.

The actual start of injection is determined with the aid of the impact or closing recognition and serves to balance out scatters and tolerances in the manufacture of the single injection pumps for cylinders 1 to 6 using performance map regulation.