PLD start of injection control function
General information
Regulation of the start of injection primarily takes place to adjust the ignition retard and to secure ignition in the top dead center area, which is at 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), above all in the upper engine speed range, would have a negative effect on the combustion cycle. The pollutant emission and the noise development would increase while the performance of the engine would drop.
Thus the start of injection is primarily dependent upon the rotational speed of the engine and is increasingly set in the direction of "advanced" with increasing engine speed in order to avoid the disadvantages of the ignition retard. The fact that the start of injection is purely calculated means that the engine control (MR) can take account of other 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 also contribute to increased pollutant emission. The exact calculation and appropriate shifting of the start of injection means that it is possible for the engine control (MR) to balance out these effects and to lower the pollutant emission. This allows one to significantly reduce the nitrogen oxides (NO x) which are generated through an advanced start of injection and hydrocarbons (HC) which are generated by a retarded start of injection.
Regulation of the start of injection
The start of injection is regulated over the start of delivery and constantly adjusted to the momentarily existing operating conditions of the engine. The start of delivery, which takes place somewhat earlier than the actual start of injection, is the point in time at which the solenoid valve in the unit pump is fully closed and the fuel compacted or delivered. The start of delivery can be regulated freely within the given mechanical limits (limited by the cam form) by the engine control (MR). The limits (max. start of delivery 25° crankshaft angle before up to 5° crankshaft angle after top dead center) are stored in the control unit for engine control (MR) (A6) through which the calculation and corresponding actuation of the individual solenoid valve also takes place in the unit pumps on cylinders 1 to 8 (Y6-Y13). The start of delivery is re-calculated after each fuel injection cycle because of the ever changing operating conditions of the engine.
Calculation of the start of delivery
Signals from the crankshaft position sensor (B15) which are primarily crucial for calculating the start of delivery. This allows the system to determine the current engine speed and the position of the crankshaft (A).
It is only for the starting procedure or if the crankshaft position sensor (B15) fails that additional signals from the camshaft position sensor (B16) are used. They provide an indication about the current position of the camshaft (B) and therefore when the 1st cylinder will be in its compression cycle.
Apart from the fuel temperature (D), the engine temperature (E) and the load condition (F), which can be deduced in a number of ways including from the engine speed and the position of the foot throttle actuator (B1), the final calculation of the start of delivery also requires determination of the effective start of injection (C). This occurs with the aid of opening/closing recognition which serves to determine the scatters and tolerances in manufacture of the unit pump and to balance these out using regulation based on a performance map.
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