Exhaust-Gas Recirculation Actuator
Exhaust-Gas Recirculation Actuator
Exhaust-gas recirculation actuator
The exhaust-gas recirculation is a measure to reduce the formation of nitrogen oxide (NOx). Nitrogen oxides are created in great quantities when combustion runs with an air surplus and at very high temperature. Here, the oxygen combines with the nitrogen of the combustion air to form nitrogen monoxide (NO) and nitrogen dioxide (NO2). On the diesel engine, exhaust-gas recirculation is sometime required at idle speed and always in the part-load range, because a particularly high air surplus is used there. The recirculated exhaust gas, to which fresh air is added and which has the same properties as inert gas, achieves the following:
- Lower residual oxygen content in the cylinder
- Lowering of the maximum combustion temperature by up to 500 °C. This effect is enhanced further if the recirculated exhaust gases are cooled.
Functional description
The exhaust-gas recirculation actuator is opened or closed electrically by the DDE control unit. To ensure optimized control of the exhaust-gas recirculation rate, the exact position must be continuously detected. The position of the exhaust-gas recirculation actuator is monitored by a non-contact hall effect sensor.
The mean quantity adaptation serves to adapt the exhaust-gas recirculation more precisely to tolerance in the fuel injection rates. The air ratio measured by the oxygen sensor and the air mass measured by the hot-film air-mass meter are used to determine a mean fuel injection rate across all cylinders. This value is compared with the fuel injection rate specified by the DDE control unit. If there is a deviation, the air mass is adapted to the actual fuel injection rate by adjusting the exhaust-gas recirculation actuator in such a way that the correct air ratio is set. The mean quantity adaptation is not a rapid control operation, rather an adaptive learning procedure. That means that the fuel injection rate error is learned in an adaptive characteristic map that is stored permanently in the DDE control unit.
Structure and inner electrical connection
The servomotor for the exhaust-gas recirculation actuator is a direct current motor. The position sensor is a hall effect sensor. The hall effect sensor determines the revolutions of the servomotor. This is used to calculate the position of the exhaust-gas recirculation actuator.
Schematic overview and nominal values
The hall effect sensor is supplied with 5 Volts and ground by the DDE.
A bridge circuit (H bridge) is used to activate the servomotor. This permits activation of the servomotor in the opposite direction. The bridge circuit is monitored diagnostically. H-bridge designates an electrical gearshift with 5 shift elements in the shape of a capital H for shifting between.
Observe the following nominal values for the exhaust-gas recirculation actuator:
Variable Value
Servomotor supply voltage 12 Volts
Activation frequency for 1300 Hz
servomotor
Blocking current for servomotor 5 A
Hall effect sensor supply voltage 4.5 to 5.5 V
Power consumption of hall effect 20 mA
sensor
Temperature range of hall effect -40 °C to 140 °C
sensor and servomotor
Diagnosis instructions
Failure of the component
If the hall effect sensor fails, the following behavior is to be expected:
- Fault entry in the engine control unit
- Emergency operation with substitute value (limited engine torque)
- Check Control message
If the servomotor fails, the following behavior is to be expected:
- Fault entry in the engine control unit
- No exhaust-gas recirculation
- Check Control message
General notes
If the exhaust-gas recirculation (EGR) valve is renewed, the following service function must be run before the replacement:
- Adaptation of exhaust-gas recirculation actuator
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