GF07.16-P-2014OHL | CDI injection control, function | 5.5.08 |
ENGINE 642.9 in MODEL 221.0 as of Model Year 09 /Modification Year 08
ENGINE 642.9 in MODEL 221.1 as of Model Year 09 /Modification Year 08
General function requirements
Circuit 61 ON
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Common rail diesel injection, injection control (CDI) - general
Injection regulation has the task of injecting the required injection quantity at the required point in time into the respective cylinder.
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The CDI control unit (N3/9) reads in signals from the following sensors for injection regulation:
- Rail pressure sensor (B4/6/)
- Charge pressure sensor (B5/1)
- Coolant temperature sensor (B11/4)
- Charge air temperature sensor (B17/8)
- Crankshaft Hall sensor (B70), for the engine speed
- Pressure sensor downstream of air filter (B28/5), for absolute pressure (vacuum) in the intake tract
- Accelerator pedal sensor (B37), for the accelerator pedal position
- Fuel temperature sensor (B50)
- O2 sensor upstream of CAT (G3/2), to regulate the exhaust aftertreatment
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- Temperature sensor upstream of diesel particulate filter (B19/9), on vehicles with code (474) particulate filter, to control the exhaust aftertreatment
- Temperature sensor upstream of turbocharger (B19/11), to control the exhaust aftertreatment
- Pressure differential sensor (DPF) (B28/8), on vehicles with code (474) particulate filter, for the load condition of the diesel particulate filter (DPF)
- Left hot film mass air flow sensor (B2/6), for the suctioned in air mass
- Intake air temperature sensor (B2/6b1)
- Right hot film mass air flow sensor (B2/7), for the suctioned in air mass
- Intake air temperature sensor (B2/7b1)
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Here one must differentiate between the following function sequences according to the injection timing point:
Function sequence: Preinjection
Function sequence: Main injection
Function sequence: Post injection
Function sequence: Preinjection
The objective of preinjection is to reduce combustion noise. This is achieved by injecting fuel up to 2 times before the main injection starts to make the combustion run smoother.
Preinjection also leads to reduction of the particulate matter (particles) (PM) in the exhaust gas.
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The start of actuation of the fuel injectors (Y76) during preinjection is calculated by the CDI control unit according to the load. The last start of actuation of main injection and the system voltage supplied by the on-board electrical system battery (G1) are also taken into account.
Preinjection is not initiated by the CDI control unit if one of the following statuses is present:
- Preinjection timing point exceeded
- Calculated preinjection quantity is too low
- Detected engine speed too high
- Main injection quantity is too low
- Rail pressure is too low
- Engine is switched off
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Function sequence: Main injection
Main injection follows preinjection. Main injection is controlled by the start of actuation (injection timing point) and the actuation duration (injection period). Main injection for the fuel injectors is not initiated by the CDI control unit if one of the following statuses is present:
- Full load injection quantity limitation is active (engine speed > 4500 rpm)
- Fuel temperature limit exceeded
- Rail pressure is too low
- The engine is in deceleration mode
- An external intervention in the quantity regulation, e.g. by the Electronic Stability Program (ESP) exists
- Engine is switched off
Function sequence: Post injection
Post-injection follows main injection. Secondary injection serves to increase the exhaust gas temperature and to support the conversion process of exhaust gas components in the oxidation catalytic converter.
On vehicles with code (474) particulate filter, a further injection is made for the purpose of DPF regeneration. To do this, the load condition of the DPF is detected through the DPF differential pressure sensor. The 2nd post injection increases the exhaust temperature and the regeneration process is triggered. The PM are then burnt in the exhaust.
Post-injection is not initiated by the CDI control unit if one of the following statuses is present:
- Preinjection timing point exceeded
- Detected engine speed too high
- Calculated post injection quantity too low
- Main injection quantity is too low
- Rail pressure is too low
- Engine is switched off