The high-pressure fuel delivery function is described on engine 926.9 (6 cylinders) as an example.
Shown on cylinder 1 |
2 | High pressure pipe |
3 | Connection fitting |
4 | Fuel injectors with nozzle holder assemblies |
Y600 | Cylinder 1 single injection pump |
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Function
High-pressure fuel delivery by the pump-line-nozzle system takes place by way of the single injection pumps for cylinders 1 to 6 (Y600 to Y605), each one of which is assigned to a cylinder. The single injection pumps for cylinders 1 to 6 are powered by the camshaft by means of roller tappets; they are connected to the fuel injectors with a nozzle holder assembly (4) by means of short high-pressure lines (2) as well as connection fitting (3).
Each single injection pump for cylinders 1 to 6 has a fast-acting solenoid valve (7). This solenoid valve regulates the start of delivery and controls the quantity delivered. Solenoid valves (7) are actuated by the engine management (MR) control unit (A6), which calculates the start of delivery and quantity delivered according to the operating condition of the engine as soon as the engine is started and/or the engine is running.
For this purpose, the engine stop button (S11) must not be pressed when the engine is started via the engine start button (S10) as, in this case, no activation of solenoid valves (7) takes place either.
Depending on the position of the camshaft, each of the single injection pumps for cylinders 1 to 6 has the following power strokes:
Intake stroke
Initial stroke
Delivery stroke
Residual stroke
Together these power strokes form a working cycle, which is repeated with every additional rotation of the camshaft at the single injection pumps for cylinders 1 to 6 until the engine is switched off.
As soon as the engine is switched off, the engine management (MR) control unit stops actuation of solenoid valves (7). The single injection pumps for cylinders 1 to 6 deliver the almost depressurized fuel to the fuel return of the fuel low-pressure circuit (D) and the engine switches off.
Intake stroke, shown on cylinder 1 |
2 | High pressure pipe |
3 | Connection fitting |
4 | Fuel injectors with nozzle holder assemblies |
5 | Pump element |
6 | Supply passage |
7 | Solenoid valve |
8 | High pressure chamber |
Y600 | Cylinder 1 single injection pump |
B | Fuel feed |
D | Fuel return |
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The induction stroke begins after the vertex of the cam is exceeded and the pump element (5) moves downwards under the force of the restoring spring.
Owing to the continuous fuel overpressure of about 2.0 to 6.5 bar in the fuel low-pressure circuit, high-pressure chamber (8) is filled with fuel via supply passage (6) and open solenoid valve (7).
Therefore, the pressure in high-pressure chamber (8) filled with fuel is the same as the pressure in the fuel low-pressure circuit.
Initial stroke, shown on cylinder 1 |
2 | High pressure pipe |
3 | Connection fitting |
4 | Fuel injectors with nozzle holder assemblies |
5 | Pump element |
6 | Supply passage |
7 | Solenoid valve |
8 | High pressure chamber |
9 | Diversion chamber |
10 | Return flow passage |
Y600 | Cylinder 1 single injection pump |
B | Fuel feed |
D | Fuel return |
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After the intake stroke, pump element (5) continues to remain in the low stop position, and the roller tappet of the cylinder 1 single injection pump rolls off on the base circle of the unit pump cam. The pre-stroke begins only when the camshaft rotates further and the pump element (5) begins to move in the upward direction owing to the rising unit pump cam.
Due to the upward movement of pump element (5) and still open (de-energized) solenoid valve (7), the fuel in high-pressure chamber (8) is first pushed into a diversion chamber (9) and then into return channel (10).
Delivery stroke, shown on cylinder 1 |
2 | High pressure pipe |
3 | Connection fitting |
4 | Fuel injectors with nozzle holder assemblies |
5 | Pump element |
6 | Supply passage |
7 | Solenoid valve |
8 | High pressure chamber |
9 | Diversion chamber |
10 | Return flow passage |
11 | Anchor plate |
12 | Float needle |
13 | Injection nozzle |
Y600 | Cylinder 1 single injection pump |
B | Fuel feed |
C | Fuel high pressure |
D | Fuel return |
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The initial stroke has been completed and the delivery stroke starts as soon as the engine management control unit (MR) activates the cylinder 1 single injection pump. Solenoid (1) in the cylinder 1 single injection pump activates the anchor plate (11) with the float needle (12), which then locks the connection between high-pressure chamber (8) and return channel (10).
If solenoid valve (7) is closed, the fuel in high-pressure chamber (8) is compressed due to the upward movement of pump element (5) (start of delivery).
With the further upward movement of pump element (5), the pressure in high-pressure chamber (8) increases and thereby the pressure in high-pressure line (2), connection fitting (3) and injection nozzle (13) also increases further.
At a pressure of about 330 bar, injection nozzle (13) opens and the fuel is injected into the combustion chamber (start of injection). The fuel pressure can rise to up to 1800 bar.
As long as pump element (5) is moving upward and solenoid valve (7) is closed, the cylinder 1 single injection pump is in the delivery stroke. The holding time of the solenoid valve (7) determines the quantity delivered and / or injected.
Residual stroke, shown on cylinder 1 |
2 | High pressure pipe |
3 | Connection fitting |
4 | Fuel injectors with nozzle holder assemblies |
5 | Pump element |
6 | Supply passage |
7 | Solenoid valve |
8 | High pressure chamber |
9 | Diversion chamber |
10 | Return flow passage |
11 | Anchor plate |
12 | Float needle |
13 | Injection nozzle |
Y600 | Cylinder 1 single injection pump |
B | Fuel feed |
D | Fuel return |
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If activation of the cylinder 1 single injection pump is interrupted by the engine management control unit (MR), float needle (12) of the solenoid valve spring is pushed back into its starting position to the shut-off stop. The solenoid valve (7), and thereby the connection between the high pressure chamber (8) and the return flow passage (10) is opened. As a result, the fuel pressure in high-pressure chamber (8) and injection nozzle (13) falls sharply. Injection nozzle (13) closes and the process of injection concludes (end of delivery).