Mass air flow meter DDE7

Mass air flow meter DDE7

The mass air flow meter measures the mass of fresh air drawn in by the engine. The intake air temperature sensor is also integrated in the mass air flow meter.

The air mass serves as a measurement variable in the DDE control unit for the following functions:

• Exhaust gas recirculation
  
• Calculating limitation volume
  

Function of mass air flow meter

Power supply and signals

The mass air flow meter is supplied with power and earth as follows:

• The power supply of 12 V is applied via terminal 87 (signal name U_HR).
  
• The DDE control unit supplies the mass air flow meter with earth (signal name M_HFM). This output on the DDE control unit can be activated.
  NB: Only if the DDE control unit detects an engine speed of more than 50 rpm is the earth contact of the HFM enabled. With the engine at a standstill and terminal 15 On, the HFM is not supplied with earth, which means that in this state it does not issue any signals!
  This function is intended to prevent oil and dirt residues from burning into the sensor element of the HFM at terminal 15 On.
  

The mass air flow meter returns the air mass value via the signal T_HFM to the DDE control unit.

The signal is a square-wave signal with an amplitude of 5 V and frequency between 1.2 and 14 kHz. This frequency corresponds to a period duration of 0.8 - 0.07 ms.

The DDE control unit uses the frequency of this signal to calculate the air mass value with the unit mg/stroke.

Troubleshooting

Faults in the component 'mass air flow meter' result in one or more fault reactions:

• Exhaust gas recirculation is deactivated
  
• Deactivation of charge-air-pressure control
  
• Volume limitation
  
• Output of a substitute value dependent on engine speed
  

Function of the intake air temperature sensor

The intake air temperature sensor measures the temperature of the fresh air that is taken in by the engine.

Power supply and signals

The DDE control unit supplies the intake air temperature sensor with voltage and earth as follows:

The power supply output on the DDE can be activated.

The earth contact is across the cable M_HFM.

The intake air temperature sensor returns the intake-air temperature via the signal T_TANS to the DDE control unit.

The signal is a square-wave signal with an amplitude of 5 V and frequency of around 19 Hz. This frequency corresponds to a period duration of 53 ms.

The DDE control unit uses the pulse duty factor of this signal to calculate the intake-air temperature with the unit °C. The pulse duty factor can lie between 10 % and 90 %.

Troubleshooting

Faults in the component 'intake air temperature sensor' result in one or more fault reactions:

• Exhaust gas recirculation is deactivated
  
• Deactivation of charge-air-pressure control
  
• Volume limitation
  
• Output of a substitute value dependent on engine speed