Fuel System Monitoring (HFM-System)
Fuel System Monitoring (HFM-System)
Mixture adaptation
In the ECU the injection time is calculated from: 1) an HFM based basic load signal, 2) an additive correction of the mixture adaptation, 3) a multiplicative correction from the lambda controller, and 4) a multiplicative correction of the mixture adaptation. All correction factors are calculated at any time during engine operation.
The mixture adaptation of the first lambda loop control has three adaptation ranges: idle, medium load, very high load. The learning integrators are thus activated in different speed and load ranges. The deviation of the lambda controller from it`s neutral value (1 or 0 (0 for Range 2)) is learned in one of the integrators at idle, medium load/speed and very high load/speed. The diagnosis of the fuel delivery system conducts a check of the output values of the mixture adaptation. If one integrator exceeds its error threshold, a malfunction is detected. If a pending code is stored the similar conditions were set (red field). The pending will be erased at the end of the next driving cycle in which similar conditions have been encountered without an exceedance of the malfunction criteria. The MIL illuminates, if two faults in any range are found consecutively.
The offset adaptation of the second lambda loop control trims the multiplicative correction from the lambda controller of the first lambda loop control system to achieve a exact lambda.
If the offset adaptation of the second control loop reaches the allowed limit, the fault code for the trim control is set.
Description of the Threshold Evaluation Function
The flow chart on illustrates the Fuel System Monitoring Function. The three-adaptation integrators are evaluated. If they surpass a threshold, after having been activated for a certain period, the MIL is illuminated.
If range 4 is activated, a time counter counts the active time. After it has passed a threshold the cycle flag is set and, if the adaptation factor exceeds a threshold, the MIL illuminated.
If range 2 is activated, there are two possibilities to set the cycle flag either the:
1) adaptation factor stable, or
2) the adaptation factor active for a minimum time. If the adaptation factor exceeds a threshold, after the cycle flag has been set, the MIL is illuminated.
If range 1 is activated and the cycle flag of range 2 has been previously set, the adaptation factor is checked for stability. If the adaptation factor is stable the cycle flag is set. If the cycle flag from range 2 is not set but the flag for minimum time is set, the cycle flag can also be set, if the adaptation range 1 has been activated for a certain period. It is now dependent on the values of the adaptation-integrator, whether or not the MIL is illuminated.