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

Engine 651 in model 907 

Block diagram 

Function requirements for CDI injection regulation, general points 

• Circuit 87M ON (Engine management ON)
• Engine running

CDI injection regulation, general 

The CDI control unit allocates fuel quantities to the engine as required. The powertrain control unit receives the "Engine running" information via the engine CAN from the CDI control unit.

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

• Engine oil temperature sensor
• Hot film MAF sensor, for the aspirated air mass
• Intake air temperature sensor
• Fuel pressure sensor
• Boost pressure sensor
• Low-pressure turbocharger boost pressure sensor
• Rpm sensor
• Coolant temperature sensor
• Charge air temperature sensor
• Pressure sensor downstream of air filter
• Crankshaft position sensor, engine speed

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 therefore relieved which reduces fuel consumption.

After switching off the engine, there is a residual pressure of about 50 to 80 bar. The high-pressure fuel circuit may only be opened on safety grounds after the pressure has been reduced by the CDI control unit.

Function sequence for preinjection 

The objective of preinjection is to reduce combustion noise and exhaust emissions. This is achieved by pre-injecting fuel up to 2 times before the main injection starts to make the combustion run smoother. The start of actuation of the fuel injectors for preinjection is calculated by the CDI control unit according to the load. Furthermore, the position of the throttle valve actuator, the last actuation start time of the main injection and the on-board electrical system voltage transferred by the on-board electrical system battery (G1) are taken into account.

Preinjection is not initiated by the CDI control unit if one of the following statuses is present:

• Accelerator pedal module, engine load request from the driver
• Accelerator pedal module, accelerator pedal operation fast or slow (when accelerating)
• Fuel temperature sensor
• Temperature sensor upstream of the diesel particulate filter, to regulate the exhaust aftertreatment
• Temperature sensor upstream of turbocharger
• Diesel particulate filter differential pressure sensor, for the load condition of the diesel particulate filter (DPF)
• 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 fuel pressure control 
• Function sequence for preinjection 
• Function sequence for main injection 
• Function sequence for post injection 
• Function sequence for injection quantity correction 
• Function sequence for combustion pressure control 

Function sequence for fuel pressure control 

The fuel pressure control is subdivided into the following control 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 after each engine start. The quantity control valve is deenergized here 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:

• After each engine start at idle speed up to a fuel temperature of 10 °C (if the fuel temperature is rising)
• After each engine start at idle speed up to a fuel temperature of 5 °C (the fuel temperature is falling)

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. In extreme driving conditions, the fuel temperature can be up to 150 °C.

2-control concept regulation 

The fuel pressure is jointly regulated in idle and in deceleration mode by the pressure regulating valve and quantity control valve.

Quantity control valve regulation 

The fuel pressure is regulated by the quantity control valve as soon as the following conditions exist:

• Fuel temperature > 10 °C
• One-off rail pressure request > 310 bar (e.g. abrupt acceleration or driving off)

• 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). Main injection for the fuel injectors is not initiated by the CDI control unit if one of the following statuses is present:

• Wide open throttle injection quantity limitation is active.
• The fuel temperature limit is exceeded.
• The fuel pressure is too low.
• Engine is in the deceleration mode.
• An external quantity intervention occurs, for example by the ESP®.
• The engine is switched off.

Function sequence for post injection 

Post injection serves to increase the exhaust temperature as well as to support the conversion of the exhaust gas components in the oxidation catalytic converter and to support DPF regeneration.

For this purpose, the load condition of the DPF is recorded by the differential pressure sensor (DPF). The 2nd post injection further increases the exhaust temperature and the regeneration process is triggered. The soot particles in the exhaust gas are then burnt subsequently.

Post injection is not initiated by the CDI control unit if one of the following statuses is present:

• 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 1000 RPM and 2600 RPM (deceleration mode or normal driving mode)
• 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 
• Main injection quantity correction 

Zero quantity calibration 

The possible friction caused when the fuel injectors are opened and closed results in a change in injection quantity operating time. This change in injection quantity can be corrected by adaptation of the actuation duration (zero quantity calibration).

During normal engine operation or in deceleration mode, a pilot injection quantity is calibrated at defined intervals selectively for each cylinder.

Main injection quantity correction 

For this function, the main injection quantity is corrected using the oxygen sensor upstream of the catalytic converter.

Here the injection quantity is adjusted until the specified lambda specified value stored in the CDI control unit is reached.

The CDI control unit changes the exhaust gas recirculation rate (EGR rate) over the exhaust gas recirculation actuator (Y27/9) to prevent an increase in the emission levels resulting from tolerances in the fuel injectors and the hot film mass air flow sensor. The residual oxygen content is monitored by the oxygen sensor upstream of catalytic converter.

Function sequence for combustion pressure control 

The actuation profile for pre-injection and post injection results in identical heating patterns for all the cylinders. The load monitoring, operating condition and the rate of cylinder pressure exert an individual influence on each cylinder. The tolerance and wear are compensated for each specific cylinder throughout the engine's entire service life.

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