Description And Operation
DESCRIPTION
The Exhaust Gas Recirculation (EGR) system includes the following components (location illustration is 3.6L typical):
| 1. | Refer to EGR VALVE . |
| 2. | Refer to EGR PIPE . |
| 3. | Refer to EGR TEMPERATURE SENSOR . |
| 4. | Refer to EGR COOLER . |
The Exhaust Gas Recirculation (EGR) System recirculates exhaust gases back into the Intake Manifold to be mixed with the incoming fuel/air mixture. This helps reduces combustion chamber temperatures improving emissions and fuel economy. The hot exhaust gases are cooled by the EGR Cooler before reaching the EGR Valve. The Exhaust Gas Recirculation (EGR) Temperature Sensor is positioned between the EGR Cooler and EGR Valve. The feedback signal from the sensor is used to monitor the cooling efficiency of the recirculated exhaust gases passing through the EGR Cooler Assembly. The EGR System does not operate at idle. It typically operates during steady state speeds. A Stuck or leaking EGR Valve can cause engine stumble, sags, hesitation, rough idle, engine stalling and driveability concerns.
| Refer to COMPONENT INDEX . |
OPERATION:
The cooled Exhaust Gas Recirculation (EGR) Valve Assembly contains an electric Direct Current (DC) Motor and a gear box. An eccentric drive translates the gearbox output from a rotating motion (DC Motor) to a linear stroke (output shaft). The full range of travel of the shaft is approximately 5.0 mm from a fully closed to fully open position. An internal return spring ensures that the valve returns back to its closed position as a fail safe. The EGR Valve is controlled by the Powertrain Control Module (PCM) using an internal H-Bridge driver . The H-Bridge operates the EGR Valve using a Pulse Width Modulation (PWM) control to help reduce current draw. This helps protect the DC Motor from overheating and reduces electrical load on the system voltage.
The EGR Valve is operated and monitored in the following manner:
- During the initial opening of the EGR Valve the PCM drives the PWM duty cycle high resulting in a higher current draw. After the valve is fully opened the PCM duty cycle is reduced to maintain the EGR Valve position. This reduces the current draw and protects from overheating the EGR Valve DC Motor.
- The PCM monitors the temperature and current draw of the DC Motor inside the EGR Valve and will adjust the duty cycle to prevent the EGR Valve windings from overheating. Typically the peak current draw, by the EGR Valve, occurs during opening the valve and the maximum current load for a typical application is approximately 6.0 amps. The duty cycle is adjusted after opening the valve so that the typical average current draw is approximately 0.5 amps while holding the valve open.
- The PCM also applies a current in the closing direction to fulfill the required dynamic performance. This is done to control the closing speed of the shaft near the stop. This ensures that the valve does not close too fast causing the valve disk to be forced into the stop harshly which may damage the internal gearbox.
- When the EGR Valve is in the closed position the PCM will press the poppet into the seat with a -10% duty cycle to clean soot from the disc and seat.
There is a position sensor located on the output shaft. The sensor operates as a typical three wire sensor, with a 5-Volt Supply, Sensor Signal, and Sensor Ground circuit. Full range of travel of the output shaft will result in a change of approximately 3.9 volts in the position sensor reading. During normal operation the sensor signal will range between approximately 0.5 volts and 4.3 volts.
See the figures below for a typical current draw on the DC Motor and voltage reading of the sensor during the EGR Valve opening and closing. The red line represents current draw of the DC Motor and the black line represents the position sensor voltage.
| Refer to COMPONENT INDEX . |
The EGR pipe transfers the cooled exhaust gases from the EGR Cooler back to the Intake Manifold.
| Refer to COMPONENT INDEX . |
The EGR Temperature Sensor is positioned between the EGR Cooler and EGR Valve. The feedback signal from the sensor is used to monitor the cooling efficiency of the recirculated exhaust gases passing through the EGR Cooler assembly. At lower temperatures the signal feedback voltage will read closer to the upper operating parameter. As the recirculated exhaust gas temperature increases, the signal feedback voltage will decrease toward the lower operating parameter.
| Refer to COMPONENT INDEX . |
The EGR Cooler is located on the left side of the engine. The EGR Cooler uses engine coolant to reduce the temperature of the exhaust gas that is recirculated to the Intake Manifold, which in turn helps reduce NOx emissions.