DV11
Operation and Maintenance
125
Common Rail Fuel-injection System
Printed in Mar. 2005 PS-MMA0608-E1A
z This indirect control of the nozzle needle using a hydraulic force-amplification
system is applied because the forces which are necessary for opening the needle
very quickly cannot be directly generated by the solenoid valve. The so-called
control quantity needed for opening the nozzle needle is in addition to the fuel
quantity which is actually injected, and it is led back to the fuel-return line via the
control chamber's orifices. In addition to the control quantity, fuel is also lost at the
nozzle-needle and valve plunger guides. These control and leak-off fuel quantities
are returned to the fuel tank via the fuel return and the collector line to which
overflow valve, high pressure pump, and pressure control valve are also
connected.
1) Method of operation
The injector's operation can be subdivided into four operating states with the
engine running and the high pressure pump generating pressure.
- Injector closed (with high pressure applied)
- Injector opens (start of injection)
- Injector opened fully, and
- Injector closes (end of injection)
These operating states result from the distribution of the forces applied to the
injector's components. With the engine at standstill and no pressure in the rail, the
nozzle spring closes the injector.
Nozzle & needle
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