Air Mass Equalisation DDE 4.1

Due to the dual air supply system on the 8-cylinder engine, an additional control facility for the two turbocharges with respect to each other, i.e. so-called air mass equalisation, is necessary to ensure effective engine operation. Air mass equalisation is implemented by a software function in the DDE, the equalisation controller.

Function

The two mass air flow sensors measure the volume of fresh air drawn in on both sides of the air guide system. To ensure load is distributed evenly over the two turbochargers and they are protected against excessively high speeds at high engine loads and speeds, the equalisation controller attempts to maintain equalisation of the air masses drawn in on the left and right sides. This is achieved by setting the pulse duty factors for the left and right boost pressure adjuster such that equal air masses are drawn in on both sides.

Components

The following components influence air mass equalisation:

• All components of the air guide system such as intake snorkel, air cleaner, air hoses, intercooler, etc.
  
• Air mass meter
  
• Exhaust gas recirculation valves, pressure converter for exhaust gas recirculation valves and the exhaust pipes to the valves
  
• Turbochargers with variable nozzle turbines and electric boost pressure adjusters
  

Fault monitoring

The following points are monitored for the purpose of detecting faults in the air mass system:

• The DDE control unit calculates the difference in the measured air masses. If the difference exceeds a defined value, fault code 1E30 "boost pressure control", defect type "equalisation controller" is stored.
  
  

The following monitoring procedure is conducted throughout the entire operating range in order to detect serious faults in the air mass system:

• The DDE control unit calculates the air mass index from the air masses measured. If the absolute value exceeds a defined limit, defect code 3620 "air mass system fault" is stored. In this case, the cause is in all probability attributed to a serious fault in the air mass system, e.g. detached charge air hose.
  
  

As a response to the two faults, the injection volume is reduced resulting in a considerable reduction in power output, as well as deactivation of boost pressure control and activation of the turbochargers with fixed pulse duty factors. Fault code 3620 "air mass system fault" additionally causes the EGR control to be deactivated.

Effect of a defective turbocharger adjustment on one side:

In order to protect the turbochargers from further damage, both units are operated with relatively low pulse duty factors. If the adjustment of one turbocharger is blocked this means that it can no longer respond correctly to activation with the low pulse duty factor (= lower boost pressure and air throughput). This means that higher air mass will be measured on the side of the defective turbocharger.

Before replacing a turbocharger, the adjustment of both turbochargers must always be checked first.