GF47.00-W-3012MA | Fuel high pressure delivery, function | 5.8.04 |
ENGINE 900.9 in MODEL 970, 972, 975, 976 with BODY 972.890
ENGINE 902.9 in MODEL 950, 952, 953, 954 with BODY 940.890
ENGINE 902.9 in MODEL 970, 972, 974, 975, 976 with BODY 972.890
ENGINE 904.9 in MODEL 375.1 with BODY 375.850
ENGINE 904.9 in MODEL 958.0 with BODY 958.860
ENGINE 904.9 in MODEL 970, 972, 975, 976 with BODY 972.890
ENGINE 906.9 in MODEL 374.5 with BODY 374.860
ENGINE 906.9 in MODEL 375.3 with BODY 375.820
ENGINE 906.9 in MODEL 950, 952, 953, 954 with BODY 940.890
ENGINE 906.9 in MODEL 958.0 with BODY 958.860
ENGINE 906.9 in MODEL 958.2 with BODY 958.870
ENGINE 906.9 in MODEL 970, 972, 974, 975, 976 with BODY 972.890
ENGINE 924.9 in MODEL 958.0 with BODY 958.860
ENGINE 924.9 in MODEL 970, 972, 974 with BODY 972.890
ENGINE 926.9 in MODEL 950, 952, 953, 954 with BODY 940.890
ENGINE 926.9 in MODEL 958.2 with BODY 958.870
ENGINE 904.925 in MODEL 8AB390.053 /054
ENGINE 904.965 in MODEL 8AB390.053 /054
W07.15-1350-12
1 Unit pump
2 High pressure pipe
3 Pressure pipe connection
4 Nozzle holder combination
General information
The fuel high pressure delivery for the PLD system is accomplished using individual unit pumps (1), each of which is assigned to one cylinder. The unit pumps (1) are driven by the camshaft via roller tappets and are connected to the injection nozzles in the nozzle holder combinations (4) via short high pressure lines (2) and the pressure pipe connection (3).
Each unit pump (1) contains a fast-acting solenoid valve for regulation of the start of injection and control of the injection quantity. The solenoid valves are actuated by the control unit of engine control (MR), which calculates the start of delivery and quantity delivered according to the operating condition of the engine as soon as the engine is cranked and / or the engine is running.
However, the actuation requires that the immobilizer (WSP) in the control unit of engine control (MR) has detected a correct transponder code (from the ignition key), and has consequently been deactivated. Furthermore, the stop engine button must not be activated if the engine is started with the start engine button because in this case the solenoid valves will also not be activated.
Function
Depending on the position of the camshaft, each of the unit pumps (1) have the following power strokes:
Induction stroke
Pre-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 respective unit pumps (1), till the engine is turned off.
As soon as the engine is turned off, the control unit of engine control (MR) stops the actuation of the solenoid valves. The unit pumps (1) pump the fuel virtually unpressurized into the fuel return for the low-pressure fuel circuit and the engine dies.
The description of one operating cycle of a unit pump, given below, applies for all other unit pumps. A schematic illustration is given for better understanding.
W07.15-1358-82
Induction stroke
2 High pressure pipe
3 Pressure pipe connection
4 Nozzle holder combination
5 Pump element
6 Supply passage
7 Solenoid valve
8 High pressure chamber
B Fuel feed
D Fuel return
The induction stroke begins after the peak 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, the high pressure chamber (8) is filled with fuel via the supply passage (6) and the opened solenoid valve (7).
Therefore, the pressure in the high-pressure chamber (8) filled with fuel is the same as the pressure in the fuel low pressure circuit.
W07.15-1359-82
Pre-stroke
2 High pressure pipe
3 Pressure pipe connection
4 Nozzle holder combination
5 Pump element
6 Supply passage
7 Solenoid valve
8 High pressure chamber
9 Pressure reduction chamber
10 Return flow passage
B Fuel feed
D Fuel return
The pump element (5) initially stops at the bottom-most position, depending on the induction stroke and the roller tappet for the unit pump rolls along the base circuit of the unit pump cam. The fuel high pressure delivery for the PLD system is accomplished using individual unit pumps (1), each of which is assigned to one cylinder. 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.
The upward motion of the pump element (5) and still opened (de-energized) the solenoid valve (7), initially forces the fuel in the high pressure chamber (8), into the diversion control chamber (9) and then into the return flow passage (10).
W07.15-1360-82
Delivery stroke
2 High pressure pipe
3 Pressure pipe connection
4 Nozzle holder combination
5 Pump element
6 Supply passage
7 Solenoid valve
8 High pressure chamber
9 Pressure reduction chamber
10 Return flow passage
11 Solenoid
12 Armature plate
13 Float needle
14 Injection nozzle
B Fuel feed
C Fuel high-pressure
D Fuel return
The pre-stroke concludes, and the delivery stroke begins as soon as the control unit of engine control (MR) actuates the solenoid (11) in the unit pump . The solenoid (11) activates the anchor plate (12) with the float needle (13), which then locks the connection between the high-pressure chamber (8) and the return flow passage (10).
If the solenoid valve (7) is closed, the fuel in the high-pressure chamber (8) is compressed due to the upward movement of the pump element (5) (start of delivery).
With the further upward movement of the pump element (5), the pressure in the high pressure chamber (8), and thereby the pressure in the high pressure line (2), in the pressure pipe connection (3) and in the injection nozzle (14) also increases further.
At a pressure of about 330 bar, the injection nozzle (14) opens, and the fuel is injected into the combustion chamber (start of injection). The fuel pressure can rise up to 1800 bar during injection.
As soon as the pump element (5) is in the upward movement and solenoid valve (7) is closed, the unit pump is in the delivery stroke. The holding time of the solenoid valve (7) determines the quantity delivered and / or injected.
W07.15-1361-82
Residual stroke
2 High pressure pipe
3 Pressure pipe connection
4 Nozzle holder combination
5 Pump element
6 Supply passage
7 Solenoid valve
8 High pressure chamber
9 Pressure reduction chamber
10 Return flow passage
11 Solenoid
12 Armature plate
13 Float needle
14 Injection nozzle
B Fuel feed
D Fuel return
If the actuation of the solenoid (11) is stopped, the float needle (13) of the solenoid valve spring is pushed back in its starting position on 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 the high pressure chamber (8) and in the injection nozzle (14) falls sharply. The injection nozzle (14) closes and the process of injection concludes (end of delivery).
The remaining fuel delivered by the pump element (5) up to the peak of the unit pump cam flows through the diversion chamber (9) and return flow passage (10) back into the fuel low pressure circuit.The fuel high pressure delivery for the PLD system is accomplished using individual unit pumps (1), each of which is assigned to one cylinder.
The diversion chamber (9) is necessary as an expansion chamber for the pressure peaks of the unit pump during the residual stroke. This prevents the pressure behavior of the adjacent unit pumps being affected through the return flow passage (10).