Fuel System Monitoring

MONITORING STRUCTURE





Flow chart of the fuel system monitoring function

GENERAL DESCRIPTION

Mixture Pilot Control

The air mass taken in by the engine and the engine speed are measured. These signals are used to calculate an injection signal. This mixture pilot control follows fast load and speed changes.

Lambda-controller

The ECM-controller compares the oxygen sensor signal of the sensor upstream the catalyst with a reference value and calculates a correction factor for the pilot control.





Ranges of Learning Correction Coefficients tra, fra and dtv

Adaptive pilot control

Drifts and faults in sensors and actuators of the fuel delivery system as well as not measured air leakage influence the pilot control. This causes increasing deviations of the air/fuel ratio. The adaptive pilot control effects the controller correction in three different ranges.

Lambda deviations in range 1 are compensated by an additive correction value multiplied by an engine speed term. By this an additive correction per time unit is created.

Lambda deviations in range 2 are compensated by a multiplication a factor.

Lambda deviations in range 3 are compensated by an additive correction per injection.

A combination of all three ranges will be correctly separated and compensated.

Each value is adapted in its corresponding range only. But each adaptive value corrects the pilot control within the whole load/speed range. At the next start the stored adaptive values are included in the calculation of the pilot control just before the closed loop control becomes active.

Abbreviations for the fuel delivery system

QU1 upper air flow threshold range 1
NU1 upper engine speed threshold range 1
TLARN upper engine load threshold f(n) range 2
TLL2 lower engine load threshold range 2

tra additive per time unit learning correction coefficient (range 1)
TRADN lower diagnosis threshold of tra
TRADX upper diagnosis threshold of tra

fra multiplicative learning correction coefficient (range 2)
FRADN lower diagnosis threshold of fra
FRADX lower diagnosis threshold of fra

dtv additive per revolution learning correction coefficient (range 3)
DTVDN lower diagnosis threshold of dtv
DTVDX upper diagnosis threshold of dtv

QL2 lower air flow threshold range 2
QU3 upper air flow threshold range 3
NL3 lower engine speed threshold range 3
TLL3 lower engine load threshold range 3

Diagnosis of fuel delivery system

Faults in the fuel delivery system can occur which cannot be compensated for by the adaptive pilot control.
In this case the adaptive values leave a predetermined range.
If the adaptive value is outside a plausible range then the MIL is illuminated and the fault is stored.