The charge-air-pressure control ensures setting of the right charge-air pressure at any point in time. Depending on the operating point, the charge-air pressure is controlled or regulated. In controlled operation, the charge-air pressure actuator is activated depending on the operating point with pulse duty factors predefined in characteristic maps.
In regulated operation, the actual charge-air pressure is picked up via the charge-air pressure sensor. The DDE control unit uses this to calculate the required pulse duty factor to achieve the specified target charge-air pressure.
A turbocharger with variable turbine geometry and without a ”wastegate” valve is used for turbo pressure control.
On the exhaust side there are adjustable blades on the outside of the turbine on rotating bearings. Those blades vary the force applied to the turbine by the exhaust, thereby altering, as required, the charge-air pressure generated by the turbocharger.
An adjusting lever on the turbine housing activates the adjustable guide vanes.
The adjusting lever is operated by means of an electrical charge-air pressure actuator (electric motor with worm gear and control electronics). The charge-air pressure actuator is mounted directly on the turbocharger and cannot be replaced separately.
The DDE provides the electrical charge-air pressure actuator with a pulse-modulated signal. The operating range of the signal lies between 10 % and 95 %, whereby 10 % means guide vanes opened and 95 % means guide vanes closed.
The electronics in the charge-air pressure actuator convert the PWM signal into a setting angle and activate the actuator motor.
The charge-air pressure actuator itself is self-diagnosable and reports faults to the DDE.
The adjusting lever must adjust between minimum and maximum activation by 35° to 45° angle of rotation. Adjustment must take place rapidly.
The charge-air-pressure control is monitored for the following faults:
Consequences of fault occurring in the charge-air-pressure control system:
Charge-air-pressure control is also deactivated when the following faults occur:
The charge-air pressure sensor registers the absolute pressure (total of charge-air pressure and ambient pressure) in the exhaust system and serves as a sensor for the charge-air-pressure control.
The charge-air pressure sensor is mounted directly on the air collector for intake air. The DDE control unit supplies the charge-air pressure sensor with earth (signal M_LDF) and a supply voltage of 5 V (signal U_LDF).
The pressure is picked up by a hole in the sensor and a corresponding measurement voltage (signal A_LDF) is sent to the DDE control unit.
If a defect is detected on the charge-air pressure sensor, the DDE control unit reacts as follows:
The charge-air temperature sensor detects the temperature of the intake air compressed by the turbocharger and cooled by the charge-air cooler.
The charge-air temperature sensor is located on the charge-air pipe between the charge-air cooler and the throttle valve.
The DDE control unit detects the of the charge-air temperature by the variable impedance of the sensor.
The following table shows the resistance characteristics of the charge-air temperature sensor:
Charge-air temperature |
Resistance |
-20 °C |
21.8 kOhm |
0 °C |
7.35 kOhm |
20 °C |
2.8 kOhm |
40 °C |
1.2 kOhm |
60 °C |
560.1 Ohm |
80 °C |
282.9 Ohm |
100 °C |
152.9 Ohm |
If a defect is detected on the charge-air temperature sensor, the DDE control unit reacts as follows: