GF07.10-P-1004OGG Injection Regulation, Function
GF07.10-P-1004OGG Injection Regulation, Function
- as of model year 09
Function requirements for CDI injection regulation, general points
^ Circuit. 87 ON (engine control ON)
^ Engine running
CDI injection regulation, general
The engine receives the fuel quantity required in each case from the CDI control unit (N3/9).
Using the performance map, the CDI control unit calculates the injection time and rail pressure on the basis of the following sensors and signals:
- Oil temperature sensor (B1)
- 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)
- Rail pressure sensor (B4/6)
- Charge pressure sensor (B5/1)
- Coolant temperature sensor (B11/4)
- Charge air temperature sensor (B17/8)
- Pressure sensor downstream of air filter (B28/5)
- Accelerator pedal sensor (B37), driver engine load request
- Accelerator pedal sensor, accelerator pedal operation fast or slow (when accelerating)
- Fuel temperature sensor (B50)
- Crankshaft Hall sensor (B70), engine speed
- Fuel filter condensation sensor with heating element (B76/1) (with code (U41) Fuel/water separator and lubrication package or code (U42) BlueTec (SCR) diesel exhaust gas cleaning for monitoring the water level in the fuel main filter
- O2 sensor upstream of CAT (G3/2)
- Temperature sensor upstream of turbocharger (B19/11)
- Pressure differential sensor (DPF) (B28/8), for the load condition of the diesel particulate filter (DPF) for vehicles with code (474) particulate filter
- Temperature sensor upstream of diesel particulate filter (B19/9), to control the exhaust after treatment on vehicles with code (474) particulate filter
- Altitude pressure sensor in CDI control unit, atmospheric pressure for altitude adaptation
Function sequence for CDI injection regulation
The injection regulation is described at the following points:
^ Function sequence for rail pressure regulation
^ Preinjection function sequence
^ Main injection function sequence
^ Post injection function sequence
^ 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) regulation
^ 2-regulator concept regulation
^ Quantity control valve (Y94) regulation
Pressure regulator valve regulation
The rail pressure is controlled by the pressure regulating valve after each engine start. Here the quantity control valve is energized and therefore fully open so that the maximum fuel quantity is delivered to the high-pressure pump.
Pressure regulator valve regulation takes place under the following conditions:
- After each engine start at idle up to a fuel temperature of 10 °C, for a rising fuel temperature
- After each engine start at idle up to a fuel temperature of 5 °C, for a 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.
2-regulator concept regulation
The rail pressure is jointly regulated in idle and in deceleration mode by the pressure regulator valve and quantity control valve.
Quantity control valve regulation
The rail pressure is controlled 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)
In this case, the pressure regulating valve remains energized (closed), thereby performing a locking 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 depending on the situation. Thus the high-pressure pump is relieved and the fuel consumption reduced.
After switching off the engine, there is a residual pressure of about 50 to 80 bar in the high-pressure control circuit. The high-pressure system may only be opened on safety grounds after successful pressure reduction by the CDI control unit.
Preinjection function sequence
The objective of preinjection is to reduce combustion noise and exhaust emissions. This is achieved by 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 (Y76) during preinjection is calculated by the CDI control unit according to the load. The position of the throttle valve actuator (M16/6), the last actuation begin of the main injection and the on-board electrical system voltage delivered by the battery (G1) are also taken into account.
Preinjection is not initiated by the CDI control unit if one of the following statuses is present:
- The preinjection time is exceeded
- The preinjection quantity is too low
- The detected engine speed is too high
- The quantity of main injection is too low
- The rail pressure is too low
- The engine is switched off
Main injection function sequence
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:
- Fuel temperature limit exceeded
- Full load injection quantity limitation is active (engine speed > 4500 rpm)
- The rail pressure is too low
- Engine is in the deceleration mode
- External access to quantity control is occurring, e.g. by the Electronic Stability Program (ESP)
- The engine is switched off
Post injection function sequence
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 status of the diesel particulate filter DPF is detected by the pressure differential sensor (DPF). The 2nd post injection 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:
- The preinjection time is exceeded
- The detected engine speed is too high
- The calculated quantity of post-injection is too small
- The quantity of main injection is too low
- The rail pressure is too low
- The engine is switched off
Additional function requirements Injection quantity correction
^ Engine speed between 1200 rpm and 3000 rpm (deceleration mode or normal driving mode)
^ Engine oil temperature >80 °C
^ Fuel temperature 30 to 50 °C
Function sequence for injection quantity correction
The injection quantity correction is subdivided into 2 partial areas:
^ Zero quantity calibration
^ Quantity mean value adaptation
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 adaptation of the actuation time (zero quantity calibration).
This actuation time corresponds to a defined injection quantity. The difference between the new and nominal actuation time is used for injection quantity correction.
The 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 motor speed evaluated. If the respective motor speed deviates from the stored specified value then the calibration value is adapted and stored in the CDI control unit.
Quantity mean value adaptation
Quantity mean value adaptation is a teach-in function of the CDI control unit, which is used to adjust the exhaust gas recirculation (EGR) rate so that the emission levels do not deteriorate because of the tolerances of the fuel injectors, left hot film mass air flow sensor and right hot film mass air flow sensor.
To do this, the CDI control unit reads in information from the following sensors:
- Left hot film MAF sensor
- Right hot film MAF sensor
- O2 sensor upstream TWC
The CDI control unit alters the AGR rate via left exhaust gas recirculation positioner (Y27/9) and the throttle valve actuator. The residual oxygen content is monitored via the O2 sensor upstream of catalytic converter.
