High Pressure Cooled EGR Monitor (HPEGR): Notes

Prior to the inclusion of Variable Cam Timing (VCT) systems, EGR systems were primarily used to control tailpipe NOx emissions by reducing peak combustion temperatures. Modern day engines with VCT are starting to use external EGR systems to improve vehicle fuel economy by

• Reducing pumping losses
• Reducing heat transfer losses due to lower combustion temperatures
• Potential for high load enrichment reduction
• Potential for compression ratio increase

Starting in 2018 MY Ford will employ a High Pressure Cooled EGR system for fuel economy and emission reduction. This system includes the following components:

• An H-bridge motor controlled EGR valve & position sensor
• Delta PFE sensor to measure EGR flow
• EGR gas cooler (exhaust to coolant heat exchanger)
• EGR gas temperature sensor
• EGR/exhaust gas pressure sensor

High Pressure Cooled/Uncooled EGR will be used on both boosted and naturally aspirated engines:

• 2.7L GTDI 2018 MY
• 2.0L GTDI 2019 MY (uses EGR Temp Sensor post EGR valve)
• 3.3L 2018 MY

Courtesy of FORD MOTOR CO.

The High Pressure Cooled EGR Monitor has a series of electrical tests and functional tests that monitors various aspects of EGR system operation.

The Exhaust Gas Recirculation Pressure sensor (EGRP) measures the pressure differential across an orifice in the EGR system.

The EGRP sensor is a Delta Pressure Feedback EGR (DPFE) sensor measuring the pressure differential across a fixed orifice. The sensor contains two hoses on either side of the orifice and these hoses must be connected to properly measure the EGR flow. Therefore, a set of hose tests are provided to detect Upstream/Downstream hose disconnections and swapped hoses. The use of Stop/Start on some applications requires these hose tests to run during off-idle conditions because Stop/Start vehicles have limited idle opportunities. Hence, these diagnostics run continuously during both idle and off-idle operation.

Courtesy of FORD MOTOR CO.

The hose diagnostics execute in the vehicle operation range shown in the graph above. It shows the measured EGRP sensor delta pressure (Y-Axis) versus the full operation range of pressures seen in the intake manifold (XAxis). The normal expected range of EGRP sensor measurements are shown in blue with both a minimum and maximum calibration range (Y-Axis dotted lines at -1 kPa and 5 kPa). When the measured EGRP pressure is outside of this calibration range then a hose fault may be present. Notice that swapped hoses will be measured as negative flow (negative delta pressure) by the EGRP resulting in a mirrored delta pressure copy of the blue samples shown above (mirrored below the minimum calibration dotted line at -1 kPa). Both the upstream (UPS) and downstream (DNS) hose disconnections are detected when the EGRP measures are in the four quadrants beyond the calibrated limits (vertical dotted lines at -8 kPa and 5 kPa in the above figure).

The Exhaust Gas Recirculation Valve Control (EGRVC) actuator is used to provide a defined amount of EGR back into the intake manifold. The EGR valve actuator requires an ECU with an H-bridge output and position feedback. The EGR valve actuator is equipped with a non-contacting hall effect position sensor. This sensor is free of mechanical wear, is high-temperature capable, and provides very accurate position feedback.

After the vehicle has warmed up and normal EGR rates are being commanded by the PCM, the low flow check and the high flow check is performed. The EGR flow diagnostics execute once-per-driving cycle and are designed to set a fault when the total mass flow error results in a tailpipe emissions increase above the CARB defined level.

This is achieved by first calculating error tolerance bands around the commanded EGR mass flow and accumulating any error between the measured mass flow and these tolerance bands. This gives separate error accumulations for both insufficient and excessive EGR mass flow. These accumulated errors are then ratio'ed against an accumulation of the total commanded EGR mass flow and compared to a threshold. The threshold is set to represent the point in the drive where an unacceptable emissions level may result (calibrated to the FTP cycle emissions).

Courtesy of FORD MOTOR CO.

If the calculated insufficient flow rate is above a calibrated ratio when compared to actual flow rate a low flow malfunction is indicated (P0401). If the calculated excess flow rate is above a calibrated ratio when compared to actual flow rate a high flow malfunction is indicated (P0402).