Theory Of 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.
- During initial opening of the EGR Valve the PCM drives the Pulse Width Modulation (PWM) voltage high resulting in a high current draw. After the valve is fully opened the PCM voltage is reduced to maintain the EGR Valve position. This reduces the current draw and protects from overheating the DC motor.
- The PCM monitors the temperature and current draw of the DC motor inside 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 and the maximum current load for a typical application is approximately 6.0 amps. The duty cycle is adjusted after opening so that the typical average current draw is approximately 0.5 amps.
- The PCM also applies a current in the closing direction to fulfill the required dynamic performance. This is done to slow down 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.
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 sensor voltage.