Exhaust Gas Recirculation (EGR) System Monitor

EXHAUST GAS RECIRCULATION (EGR) SYSTEM MONITOR

The EGR system is a closed loop EGR control system that uses an air system model EGR to estimate the percent of EGR in the cylinder. Air flow into the engine is modeled using a mass air flow sensor (MAF) and a model of air flow over the throttle restriction. EGR mass flow is then calculated as the difference between the cylinder charge from the speed density equation and this model of the mass air flow after the throttle. This model value of the actual EGR flow based on measured values is compared with the estimated EGR rate computed by the EGR rate controller. The EGR rate controller calculates the mass flow based on an open area estimate at the EGR valve and a modeled value of mass flow per open area. EGR open area estimate uses a combination of the area calculated from the modeled EGR rate and a calibrated curve of the expected open area based on EGR valve position.

Once the engine is warm and the system in closed loop EGR control, the monitor awaits calibrated engine speed/load conditions selected for robust detection of high flow and low flow concerns. When the engine enters the operational regime for robust detection, the calculated rate deviation (modeled controller estimate) is compared to thresholds that are calibrated as a function of speed and load. An up/down counter is used that counts upward when the rate deviation exceeds the calibrated threshold and counts downward when the deviation falls below the threshold for the case of high flow. Similarly, the up/down counter counts upward when the rate deviation falls below a calibrated threshold and counts downward when it rises above the threshold for the case of low flow. Once the debounce counter exceeds a calibrated threshold for either high or low flow a concern is detected and DTC P0401 sets for a low flow concern while DTC P0402 sets for a high flow concern.

The typical EGR low flow monitor entry conditions include:
- Engine torque is 100 - 600 Nm (74 - 443lb-ft)
- Engine RPM is between 600 RPM and 2500 RPM
- Engine coolant temperature is 70 - 100°C (158 - 212°F)
- EGR valve position between 40% and 60%
- EGR rate desired value between 0% and 100%

DTC P0401 sets when the delivered EGR is 28% less than expected for the operating conditions. EGR rates are specified as a function of engine RPM and indicated torque setpoint.

The typical EGR high flow monitor entry conditions include:
- Engine torque between 100 Nm (74 lb-ft) and 600 Nm (443 lb-ft)
- Engine RPM is between 600 RPM and 2500 RPM
- Engine coolant temperature between 70°C (158°F) and 100°C (212°F)
- EGR valve position between 0% and 6%
- EGR rate desired value between 0% and 15%

DTC P0402 sets when the delivered EGR is 15% greater than expected for the operating conditions. EGR rates are specified as a function of engine RPM and indicated torque setpoint.