PLD fuel quantity control function

W07.15-1363-79

1 Crankshaft

2 Camshaft

3 Unit pump cam

4 Roller tappets in the unit pump

5 High pressure chamber in the unit pump

β Delivery angle

a Start of delivery, e.g. for a 5° crankshaft angle before the top dead center (OT)

b End of delivery, e.g. for a 5° crankshaft angle after top dead center (OT), if the delivery angle (β) is 10°

A Scheme start of delivery

B Scheme end of delivery

TDC Top dead center

UT Bottom dead center [BDC]

General information

The fuel quantity (and thus also the injected quantity) is controlled via the delivery angle (β):

The delivery angle (β) is the angle by which the crankshaft (1) turns on a running engine between start of delivery (a) and end of delivery (b) for a unit pump.

The volume of fuel which is delivered by the respective unit pump and injected over the injection nozzle into the corresponding cylinder will change according to the size of the delivery angle (β).

The engine control (MR) will increase the delivery angle (β) when the volume of fuel injected must be increased, for example if there is a demand for power and the actual engine torque is less than the specified engine torque. It does this by actuating the solenoid valves in the unit pumps for longer and thus shifting the stopping delivery point (b) to a later point in time.

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The range within which control of the fuel quantity can take place is governed by the design of the unit pumps and the camshaft (2):

If, for example, the roller tappets in the unit pump (4) are in the base circle of the unit pump cam (3) then no injection takes place on actuation of the solenoid valve.

That is the max. control range is determined by the stroke of the unit pump cam (3) (about a 65.5° camshaft angle) and the max. quantity range by the respective displacement volumes in the high pressure chamber of the unit pump (5).

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Function

The engine control (MR) first calculates the required injection or fuel quantity which it needs to regulate the engine speed. Factors are taken into account here which enter into the calculation and later controlling of the delivered volume according to the operating and loading condition of the engine.

The fuel quantity can be limited, in particular during the start process during which the injected volume is independent of the accelerator pedal position, but also while driving, for example over a smoke limiting performance map in order to avoid increased smoke production.

Furthermore, altitude correction also avoids the situation where too much fuel is injected and increased smoke production results.

Once the engine control (MR) has calculated the required fuel quantity and the resulting delivery angle (β) for each unit pump (start of delivery (a) was already determined within the injection beginning control), it actuates the solenoid valve in the unit pump whose cylinder is within the compression stroke and thus initiates the delivery stroke on this unit pump.

The subsequent holding time of the solenoid valve, that is the time within which the solenoid valve in the unit pump is actuated, determines the fuel quantity and thus the period of injection or injected amount.

This means that fuel will be injected into the combustion chamber until the engine control (MR) interrupts actuation of the solenoid valve and initiates end of delivery (b).