EGR Valve
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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 illustrations 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.