Injection Regulation, Function - GF07.10-D-1004HD
ENGINES 651.955/956/957 in MODEL 906
with CODE (XZ1) Model generation 1
with CODE (MZ0) Blue EFFICIENCY
Function requirements
- Circuit 87 ON
- Circuit 61 ON
General
The CDI control unit (N3/28) allocates fuel quantities to the engine as required. Based on a characteristics map, the CDI control unit calculates the injection time and rail pressure on the basis of the following sensors and signals:
- Engine oil level sensor (B40/6)
- Engine oil temperature sensor (B40/9)
- Hot film MAF sensor (B2/12), for the intake air mass
- Intake air temperature sensor (B2/12b1) (for model 906)
- Rail pressure sensor (B4/16)
- Boost pressure sensor (B5/6)
- Coolant temperature sensor (B11/17)
- Charge air temperature sensor (B17/13)
- Crankshaft sensor (L5/10), engine speed
- Accelerator pedal module (B37/3) (for model 906), engine load request from the driver
- Fuel temperature sensor (B50/5)
- Oxygen sensor (B85/2), to regulate the main injection quantity correction
- Temperature sensor upstream of exhaust gas turbocharger (B16/13), for controlling the wide open throttle
- Diesel particulate filter differential pressure sensor (B28/18), for the load condition of the diesel particulate filter (DPF)
- Temperature sensor upstream of diesel particulate filter (B19/17), to control the exhaust after treatment
- Knock sensor 1 (A16/5) and knock sensor 2 (A16/6), zero quantity calibration
- Atmospheric pressure sensor in CDI control unit, atmospheric air pressure for altitude adaptation
- Outside temperature sensor (B14), for measuring the ambient temperature
Function sequence
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 (Y74/5) regulation
- Quantity control valve (Y94/3) regulation
Pressure regulating valve regulation
The rail pressure is regulated by the pressure regulating valve after each engine start. At this time the quantity control valve is energized and therefore fully open so that the maximum fuel quantity is delivered to the high-pressure pump. M41/3
Pressure regulating valve regulation takes place under the following conditions:
- After each engine start at idle up to a fuel temperature of 10°C, with rising fuel temperature
- After each engine start at idle at a fuel temperature of 5°C and lower, with falling fuel temperature
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.
Quantity control valve regulation
The rail 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)
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 compress the fuel which the quantity control valve lets through to it as required by the current situation. The high-pressure pump therefore does not have to work as hard which reduces fuel consumption.
After switching off the engine, there is a residual pressure of about 50 to 80 bar in the high-pressure control circuit.
Therefore the high-pressure system may only be opened after completely relieving the pressure on safety grounds.
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 following injectors for preinjection is calculated by the CDI control unit according to the load.
- Cylinder 1 injector (Y76/14)
- Cylinder 2 injector (Y76/15)
- Cylinder 3 injector (Y76/16)
- Cylinder 4 injector (Y76/17)
Furthermore the last actuation begin of the main injection and the onboard power supply voltage determined by the battery (G1) are 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
- 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:
- Full load injection quantity limitation is active (engine speed > 4500 RPM)
- Fuel temperature limit exceeded
- Rail pressure is too low
- Engine is in the deceleration mode
- External intervention in quantity control is active, e.g. by the Electronic Stability Program (ESP®)
- Engine is switched off
Function sequence for post injection
Post injection serves to increase the exhaust temperature, to support the conversion of the exhaust gas components in the oxidation catalytic converter and to support DPF regeneration. To do this, the load condition of the DPF is detected by the DPF differential pressure sensor.
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.
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
Additional function requirements for injection quantity correction
- Engine speed from 1000 RPM up to 2600 RPM (deceleration mode or normal driving mode)
- Engine oil temperature higher than 80°C
Function sequence for injection quantity correction
Injection quantity correction is subdivided into 2 subareas:
D Zero quantity calibration
D 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 over time. This change in injection quantity can be corrected by altering the actuation duration (zero quantity calibration). The zero quantity calibration takes place with the aid of knock sensor 1 and knock sensor 2.
During normal engine operation or in deceleration mode, a pilot injection quantity is calibrated at defined intervals selectively for each cylinder. The pilot injection quantity causes the engine to vibrate at a certain frequency which can be detected by knock sensor 1 and knock sensor 2.
In order to calibrate the injection quantity, the actuation time is increased until the CDI control unit receives a signal from knock sensor 1 and knock sensor 2.
This actuation duration corresponds to a defined injection quantity. The difference between the new and nominal actuation duration is used for injection quantity correction.
Main injection quantity correction
With this function, the main injection quantity is corrected with the aid of an oxygen sensor.
Here the injection quantity is adjusted until the specified lambda value stored in the CDI control unit is reached.
The CDI control unit changes the exhaust gas recirculation rate (AGR rate) over the left exhaust gas recirculation controller (Y27/15) to prevent an increase in the emission values resulting from tolerances in the fuel injectors and the hot film mass air flow sensor. The residual oxygen content is monitored via the oxygen sensor.
| Component description for CDI control unit, | N3/28 | GF07.16-D-6000HD |
| Knock sensor, component description | A16/5 A16/6 |
GF07.04-D-6030HD |
| Component description for intake air temperature sensor | B2/12b1 | GF07.04-D-6070HD |
| Component description for hot film mass air flow sensor | B2/12 | GF07.07-D-6000HD |
| Component description for rail pressure sensor | B4/16 | GF07.04-D-6210HD |
| Component description for boost pressure sensor | B5/6 | GF07.04-D-6053HD |
| - | B5/9 Engine 651.955/957 |
GF07.04-D-6053HDA |
| Component description for coolant temperature sensor | B11/17 | GF07.04-D-6040HD |
| Component description for temperature sensor upstream of turbocharger | B16/13 | GF07.04-D-6109HD |
| Component description for charge air temperature sensor | B17/13 | GF07.04-D-6050HD |
| Component description for temperature sensor on diesel particulate filter | B19/17 | GF07.04-D-6111HD |
| Component description for the differential pressure sensor (DPF) | B28/18 | GF07.04-D-6122HD |
| Component description for an engine oil level sensor | B40/6 | GF18.40-D-4109HD |
| Component description for oil temperature sensor | B40/9 | GF18.30-D-2011HD |
| Component description for an oxygen sensor | B85/2 | GF07.04-D-6101HD |
| Component description for the crankshaft position sensor | L5/10 | GF07.04-D-6011HD |
| Component description for high-pressure pump | M41/3 | GF07.02-D-3010HD |
| Component description for exhaust gas recirculation controller | Y27/15 | GF14.20-D-4007HD |
| Component description for pressure regulating valve | Y74/5 | GF07.05-D-6020HD |
| Component description for fuel injectors | Y76/14, Y76/15, Y76/16, Y76/17 | GF07.03-D-6120HD |
| Component description for quantity control valve | Y94/3 | GF07.05-D-6010HD |