7 Series E65 730d (M57T2) SAL
The piezo injectors do not leak when closed (in contrast to conventional fuel injectors).
The rail pressure regulating valve is therefore open when de-energised in engines with piezo injectors. This
ensures that the pressure is equalised after the engine has been turned off. If the pressure is not equalised,
bubbles will form when the engine cools down. These bubbles will slow down the pressure build-up when the
engine is next started.
The piezo injector allows multi-port injections with a maximum of 4 injection processes.
The multi-port injections can consist of:
•
Pre-injection(s)
•
Main injection(s)
•
Post injection(s)
The pre-injection improves the noise level due to a gentler combustion process. A double pre-injection is
possible when the engine is idle and when engine speed is no greater than approximately 2000 rpm.
The post injection is applied during regeneration of the diesel particulate filter. A double post injection is possible
with light engine load and at low engine speed.
Zero quantity adaptation and mean quantity adaptation
Zero-quantity adaptation is the adaptation process that guarantees that a defined pre-injection is available for
each piezo injector after the running-in phase (approx. 1500 km). For the engine to comply with the EURO 4
exhaust emission regulations, the pre-injection quantity, which is very small, must be precisely metered.
Because of the deviation in the injection quantity over the running time, the zero-quantity adaptation is performed
continuously by the DDE control module.
For each cylinder, a small quantity of fuel is injected in overrun mode. This quantity is continuously adjusted until
the DDE recognises increasing torque.
The irregular rotation from the crankshaft is used to calculate the torque. The crankshaft sensor measures
irregular rotation. The DDE can thus recognise the activation duration from which the respective cylinder starts
to work.
During zero-quantity adaptation, the amount of fuel injected is used by the DDE as a correction value for the pre-
injection characteristic map.
Zero-quantity adaptation takes place alternately from one cylinder to the next during each overrun phase: Engine
speed: 1500 to 2500 rpm (engine at operating temperature)
Zero-quantity adaptation has no effect on fuel consumption, as only a very small amount of fuel (approx. 1 mm
3
) is injected into each cylinder.
Mean quantity adaptation is the adaptation process in which the fuel-to-air ratio is corrected (partial-load range).
The exhaust gas recirculation valve carries out this correction by adjusting the recirculated volume of exhaust
gas.
While the injection quantity compensation and zero-quantity compensation do not require additional
components, an oxygen sensor is required for mean quantity adaptation.
The oxygen sensor is a broadband oxygen sensor with continuous characteristic curve. LSU 4.9
Mean quantity adaptation is not a "quick" adjustment, but rather an intelligent learning process.
An oxygen sensor variance is "learnt" in a characteristic map and is permanently stored in the DDE control unit
(EEPROM).
The characteristic map must be reset (deleted) in the EEPROM if any of the following components is replaced:
•
Mass air flow sensor
•
Piezo injector
SBT M57TU2 and M67TU diesel engines E65, E66
BMW AG - TIS
03.02.2013 15:11
Issue status (12/2007) Valid only until next DVD is issued
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