The fuel quantity PLN function is described by way of example on engine 926.9 (6 cylinder).
G07.15-A029-79
A3 | Drive control (CPC) control unit | Y602 | Cylinder 3 single injection pump | |
A6 | Engine management (MR) control unit | Y603 | Cylinder 4 single injection pump | |
CAN 4 | Drive train CAN | Y604 | Cylinder 5 single injection pump | |
Y600 | Cylinder 1 single injection pump | Y605 | Cylinder 6 single injection pump | |
Y601 | Cylinder 2 single injection pump | B | Output signals |
Start of delivery, shown on single injection pump for cylinder 1 |
1 | Crankshaft |
2 | Camshaft |
3 | Pump cam |
4 | Roller tappet |
5 | High pressure chamber |
6 | Solenoid valve |
7 | Injection nozzle |
Y600 | Cylinder 1 single injection pump |
OT | Top dead center |
UT | Bottom dead center |
a | Start of delivery (e.g. for a 5° crankshaft angle before the top dead center (OT)) |
G07.15-A032-82
End of delivery, shown on single injection pump for cylinder 1 |
1 | Crankshaft |
2 | Camshaft |
3 | Pump cam |
4 | Roller tappet |
5 | High pressure chamber |
6 | Solenoid valve |
7 | Injection nozzle |
Y600 | Cylinder 1 single injection pump |
OT | Top dead center |
UT | Bottom dead center |
b | End of delivery (e.g. for a 5° crankshaft angle after top dead center (OT), if the delivery angle (c) is 10°) |
c | Delivery angle |
G07.15-A033-82
General
The fuel quantity (and thus also the injected quantity) is controlled via the delivery angle (c).
The delivery angle (c) is the angle by which the crankshaft (1) turns on a running engine between start of delivery (a) and end of delivery (b) for the respective single injection pump of cylinders 1 to 6.
The volume of fuel which is delivered by the respective single injection pump of cylinders 1 to 6 and injected via injection nozzle (7) into the corresponding cylinder will change according to the size of the delivery angle (c).
The engine management (MR) control unit will increase the delivery angle (c) when the injection quantity must be increased, for example if there is a demand for power and the actual engine torque is less than the target engine torque. The engine management (MR) control unit does this by actuating solenoid valves (6) in the single injection pumps for cylinders 1 to 6 for longer and thus shifting the stopping delivery point (b) to a later point in time.
The range within which control of the fuel quantity can take place is governed by the design of the single injection pumps for cylinders 1 to 6 and camshaft (2).
If, for example, roller tappet (4) is in the base circle of pump cam (3) then no injection takes place on actuation of solenoid valve (6). That means that the max. control range is determined by the stroke of pump cam (3) (about a 65.5° camshaft angle) and the max. quantity range by the respective displacement volumes in high pressure chamber (5).
Function
The engine management (MR) control unit 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 may be limited, in particular during the start process in which the injection quantity is independent of the accelerator pedal position, but also while driving via a smoke-limiting characteristics map, for example, 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. The altitude correction adjusts the exhaust gas recirculation rate, the start of actuation and the actuation period (injection quantity) of the single injection pumps for cylinders 1 to 6, depending on the established limit values for the air/fuel ratio (Lambda).
The engine management (MR) control unit calculates the fuel quantity and the resulting delivery angle (c) for each single injection pump for cylinders 1 to 6 (the start of delivery (a) was determined as part of the start of injection regulation). The engine management (MR) control unit also actuates the respective solenoid valve (6) in the single injection pumps for cylinders 1 to 6, the cylinders of which are in the compression stroke, and thereby initiates the delivery stroke on this single injection pump for cylinders 1 to 6.
The following holding time of the respective solenoid valve (6), that is the time within which the respective solenoid valve (6) in the single injection pumps for cylinders 1 to 6 is actuated, determines the fuel quantity and thus the injection period or injection quantity. Fuel will be injected into the combustion chamber until the engine management (MR) control unit interrupts actuation of the respective solenoid valve (6) and initiates end of delivery (b).