Injection Regulation, Function - GF07.10-D-1004TSC

Engine 642.8 in model 907 

Block diagram 

Function requirements for CDI injection regulation, general points 

• Circuit 87 (engine timing ON)
• Engine running.

CDI injection regulation, general 

The CDI control unit (N3/28) allocates the required fuel quantity in each case to the engine.

Based on a characteristics map, the CDI control unit calculates the fuel quantity and injection period and fuel pressure on the basis of the following sensors and signals:

• Engine oil sensor (B40/8)
• Hot film mass air flow sensor (B2/14) for the intake air mass
• Fuel pressure sensor (B4/17)
• Boost pressure sensor (B5/8)
• Rpm sensor (B6/24)
• Coolant temperature sensor (B11/19)
• Charge air temperature sensor (B17/15)
• Intake manifold pressure sensor (B28/19)
• Accelerator pedal module (A68), engine load request from driver
• Accelerator pedal sensor, fast or slow accelerator pedal application
• Accelerator pedal sensor, accelerator pedal operation fast or slow (when accelerating)
• Fuel temperature sensor (B50/6)
• Crankshaft position sensor (B70/1), engine speed
• Oxygen sensor (B85/4)
• Temperature sensor upstream of diesel particulate filter (B19/9)
• Temperature sensor upstream of ATL (B16/11)
• DPF differential pressure sensor (B28/16), load condition of the diesel particulate filter
• Atmospheric pressure sensor in CDI control unit, atmospheric pressure for altitude adaptation

Function sequence for CDI injection regulation 

The injection regulation is described in the following steps:

• Function sequence for rail pressure regulation
• Function sequence for preinjection
• Function sequence for main injection
• Function sequence for post injection
• Function sequence for injection quantity correction

Function sequence for rail pressure regulation 

Rail pressure regulation is subdivided into the following regulation strategies:

• Pressure regulating valve regulation
• 2-control concept regulation
• Quantity control valve regulation

Pressure regulating valve regulation 

The fuel pressure is regulated by the pressure regulating valve (Y74/6) after each engine start. At this time the quantity control valve is deenergized and therefore fully open so that the maximum fuel quantity is delivered to the high-pressure pump.

Pressure regulating valve regulation takes place under the following conditions:

• Up to 5 s in neutral after every manual engine start
• Up to a fuel temperature of 20 °C

Pressure regulating valve regulation causes the cold fuel to be heated rapidly by the fuel being forced at high pressure through a narrow gap in the pressure regulating valve.

2-control concept regulation 

If the conditions for the pressure regulating valve regulation are no longer fulfilled, the fuel pressure is regulated jointly by the pressure regulating valve (Y74/6) and the quantity control valve (Y94/4) at a speed of ≤ 12 km/h or at a speed of > 12 km/h in overrun mode.

Quantity control valve regulation 

If the conditions for the pressure regulating valve regulation and the 2-control-concept-regulation are not fulfilled, the rail pressure is regulated by the quantity control valve (Y94/4).

The pressure regulating valve is closed in a controlled manner and thus performs a retention function.

The advantage of quantity control valve regulation is that the high-pressure pump only needs to compact the fuel which the quantity control valve lets through to the high-pressure pump as required by the current situation. The high-pressure pump is thus relieved and the fuel consumption is reduced. The fuel system high-pressure circuit is unpressurized after switching off the engine. During the automatic engine stop, a fuel pressure of approx. 250 bar is maintained in the high-pressure fuel circuit.

Function sequence for preinjection 

The objective of preinjection is to reduce combustion noise and exhaust emissions. This is achieved by injecting fuel one or two times before the main injection starts to make the combustion run smoother.

The start of actuation of the fuel injectors (Y76) for preinjection is calculated by the CDI control unit operating point dependent. In addition, the ambient condition and the engine temperature, the last beginning of actuation of the main injection and the on-board electrical system voltage determined by the on-board electrical system battery (G1) are taken into account.

The preinjection is suppressed by the CDI control unit if one of the following conditions exists:

• Preinjection timing point is exceeded.
• The calculated preinjection quantity is too low.
• Detected engine speed is too high.
• Main injection quantity is too low.
• The fuel pressure is too low.
• The engine is switched off.

Function sequence for main injection 

The main injection is performed immediately after preinjection and generates power and torque. Main injection is controlled by the start of actuation (injection timing point) and the actuation duration (injection period).

The main injection is suppressed by the CDI control unit if one of the following conditions exists:

• The fuel temperature limit is exceeded.
• Engine speed > 4,500 RPM
• The fuel pressure is too low.
• Engine is in the deceleration mode
• External interference in the quantity control is present, e.g. as a result of the Electronic Stability Program (ESP®)
• The engine is switched off.

Function sequence for post injection 

The post injection serves to increase the exhaust gas temperature and support the conversion process of the exhaust gas components in the oxidation catalytic converter and the regeneration of the diesel particulate filter (DPF).

For this purpose, the load condition of the DPF is detected with the aid of the differential pressure sensor (DPF) (B28/16). The 2nd post injection further increases the exhaust gas temperature and triggers the regeneration process. The soot particles in the exhaust gas are then burnt subsequently.

The post injection is suppressed by the CDI control unit if one of the following conditions exists:

• Preinjection timing point is exceeded.
• Detected engine speed is too high.
• the calculated post-injection is too low.
• Main injection quantity is too low.
• The fuel pressure is too low.
• The engine is switched off.

Additional function requirements for injection quantity correction 

• Engine speed between 1200 and 3000 RPM (Decel mode or normal driving operation)
• Engine oil temperature > 80 °C
• Fuel temperature 30 to 50 °C

Function sequence for injection quantity correction 

Injection quantity correction is subdivided into 2 subareas:

• Zero quantity calibration
• Quantity mean value adaptation

Zero quantity calibration 

Due to friction and the associated wear during opening and closing of the fuel injectors a change in injection quantity takes place over the runtime. This change in injection quantity can be corrected by adaptation of the actuation duration (zero quantity calibration).

This actuation duration corresponds to a defined injection quantity. The difference between the new and nominal actuation duration is used for injection quantity correction.

Zero quantity calibration is conducted for various prescribed injection pressures in deceleration mode. The fuel injectors are actuated one after the other in this phase using a calibration value and the respective engine speed evaluated. If the respective engine speed deviates from the stored specified value then the calibration value is adapted and stored in the CDI control unit.

Quantity mean value adaptation 

The quantity mean value adaptation is a learning function of the CDI control unit, with the help of which the exhaust gas recirculation rate is corrected so that the emissions values are not degraded by the tolerances of the fuel injectors and the hot film mass air flow sensor (B2/14).

To do this, the CDI control unit reads in information from the following sensors:

• Hot film mass air flow sensor (B2/14)
• Oxygen sensor (B85/4)

The CDI control unit alters the exhaust gas recirculation rate via the exhaust gas recirculation positioner (Y27/17) and the throttle valve actuator (M16/48). The residual oxygen content is monitored via the oxygen sensor.

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