Theory Of Operation
The Cooled EGR Valve Assembly contains an electric 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). An internal return spring ensures that the valve returns back to its closed position as a fail safe. The Powertrain Control Module (PCM) controls the opening and closing of the DC motor with a PWM signal. As a fail safe, there is a return spring within the EGR Valve to ensure closing of the valve. 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 is done to ensure 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. The full range of travel of the shaft is approximately 7.0 mm from a fully closed to fully open position.
The PCM monitors the temperature and current draw of the EGR Valve and will adjust the duty cycle to prevent the EGR Valve windings from overheating. Typically, the peak current draw on by the EGR Valve occurs during opening and the maximum current load for a typical application is approximately 7.0 amps. The duty cycle is adjusted after opening so that the typical average current draw is approximately 0.5 amps.
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. A full range of travel in the output shaft will result in a change of approximately 3.0 volts in the position sensor reading. During normal operation the sensor signal will range between approximately 1.0 volts and 4.0 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.