In general, charge-air-pressure control leads to an calibration of the geometries of the guide vanes of the exhaust turbocharger or calibration of a bypass valve (if present). The charge-air pressure is regulated by the software with the aim of achieving clean combustion and favourable consumption. The function of the charge-air-pressure control is also intended to restrict the charge-air pressure to protect the engine and the turbocharger itself. The objectives are rapid charge-air-pressure build-up, harmonious pressure and torque characteristics across the entire engine speed range at all accelerator pedal settings as well as an overall efficiency rating that is as high as possible.
In the present engine, this is a pneumatically activated calibration of the turbine geometry (VTG turbocharger) without wastegate.
The DDE control module activates the electropneumatic pressure converter of the VTG controller by means of a 250 Hertz PWM signal with pulse duty factors (i.e. changeable pulse widths) between 0 % and 95 %. This enables a pilot vacuum of up to approx. 800 mbar. The pilot vacuum increase only takes place in exactly linear form with medium pulse duty factors. In line with this, the guide vanes of the turbocharger are only adjusted in exactly linear form with medium pulse duty factors. At a pulse duty factor of 95 %, the calibration of the guide vanes has the maximum angle of instance.
The power supply of the pressure converter is approx. 12.5 Volts. The operating voltage range lies between 10.8 Volts and 16 Volts. At 16 Volts, the current consumption is a maximum of approx. 1.6 Amperes.
The reaction of the component to activation by PWM signals takes place within fewer than 200 milliseconds if the component is functioning without faults. In the event of a longer reaction time, check the vacuum system for leak-tightness.
Depending on the engine speed and the injected fuel mass, a base target value for the charge-air pressure is determined. This base target value is corrected depending on the factors intake-air temperature, atmospheric pressure and coolant temperature. The charge-air pressure target value formation can determine an absolute and a relative charge-air pressure target value.
During the regeneration phase of the diesel particle filter, the charge-air-pressure control can be restricted.