Component description for fuel injectors - GF07.03-P-6120P
ENGINES 642 in MODEL 164.1/8, 203.0/2, 221.0/1, 251.0/1 up to Model Year 08/Modification Year 07
ENGINES 642 in MODEL 209.3/4, 211.0/2/6, 219.3
ENGINES 642 in MODEL 461.3, 463.3
Shown on cylinder 1, except OM 642.920/940/950 with code (494) USA version and without model 461.3
Location
The fuel injectors (Y76) are respectively screwed into the top of the cylinder head.
All fuel injectors have a 7-digit code, the injector quantity compensation coding on the upper side of the injector. This code describes the quantity characterization of the respective injector. If an injector is replaced, this code must be given to the CDI control unit (N3/9) via STAR DIAGNOSIS.
Task
Fuel injectors have the task of injecting the fuel under high pressure into the respective cylinders. Injection timing and the injection period which determine the injection quantity are decided by the following factors:
- Actuation period of the piezoceramic
- Opening and closing rate of the nozzle needle
- Height of the needle lift
- Nozzle geometry
Design, except model 211.022 with OM 642.920 and with code (494) USA version
The fuel injectors in model 211.022 with OM 642.920 and with code (494) USA version, in model 211.024 with OM 642.920 and in model 211.022/222 with OM 642.920 and with code (498) Japan version have a 7-hole nozzle module.
Function
- Engine off, fuel injectors not actuated
The injection system is filled with fuel but is unpressurized (atmospheric pressure). The valve spring on the valve group holds the valve bolt, the nozzle spring and the nozzle needle closed. No injection takes place.
- Engine runs, fuel injectors not actuated
The rail pressure generated by the high pressure pump is applied above the feed restrictor in the control chamber as well as above the rail at the injector and thus at the nozzle needle. The nozzle needle remains closed because of the pressure differentials and no injection takes place.
- Fuel injectors actuated
Upon activating the piezo actuator, this gets longer and thus presses via the coupler module on the valve bolt and closes the bypass. The pressure in the control chamber drops via the outlet restrictor, the nozzle needle opens and inject begins. The opening speed of the nozzle needle is determined by the cross-sectional area of the outlet restrictor and feed restrictor.
The diverted fuel quantity passes via the fuel return back into the tank.
Maintaining the actuation voltage determines the injection period and injection quantity.
- Activating fuel injectors
The piezo actuator is discharged and shortens. The valve bolts frees up the bypass and closes the control chamber. The pressure in the control chamber rises via the outlet restrictor, feed restrictor and bypass to the rail pressure level and the nozzle needle closes. The injection process is complete. A particularly rapid closing of the needle can be achieved in that the control chamber has the rail pressure applied to it at the same time via the feed restrictor, outlet restrictor and bypass.