Hot-Film Air Mass Meter
Hot-Film Air Mass Meter
Hot-film air mass meter
The hot film air mass meter is secured to the intake silencer.
The hot film air mass meter is a combined sensor. The hot film air mass meter detects the actual amount of air independently from the air pressure. In conjunction with other sensors, the engine control unit calculates the amount of fuel to be injected. An intake air temperature sensor is integrated into the hot film air mass meter. This sensor measures the temperature of the intake air before the exhaust turbocharger.
Functional description
An electrically heated measuring cell protrudes into the air flow. The temperature of the measuring cell is always kept constant. The air flow draws heat from the measuring cell. The greater the air mass flow the more energy must be deployed to keep the temperature of the measuring cell constant.
The characteristic curve of the hot film air mass meter is extended in the negative value range of the air mass flow (range greater than 550 �s). Pulsations due to the uneven firing interval on a bank also mean that negative air mass flows occur during driving. These negative air mass flows are included in the calculation.
Structure and inner electrical connection
The sensor is operated with a voltage of 12 Volts. The intake air temperature sensor is supplied with 5 Volts by the engine control.
Evaluation electronics evaluate the measured data in the hot film air mass meter. This enables exact detection of the air mass flowing through, including the direction of flow. The sensor element only detects part of the air mass flow. The total air mass flowing through the measuring tube is determined on the basis of a calibration.
Signal shape and setpoint values
The hot film air mass meter has a frequency-coded output signal. The sensor is designed in such a way that return flows (dynamic pulsation in the intake pipe) can be detected and processed both with regard to their amount and direction of flow.
The signal quality for the air mass is temperature-dependent. High accuracy is required to precisely determine the air mass. This is why the air mass signal received in the engine control unit must be corrected with the signal of the intake air temperature sensor.
Observe the following setpoint values for the hot film air mass meter:
Size Value
Voltage range 7.5 to 17 volts
Maximum power consumption Less than 0.1 A
Measuring range of hot film air -60 bis 850 kg/h
mass meter
Measuring range of intake air -40 °C to 110 °C
temperature
Frequency range 1 to 15 kHz
Temperature range -40 °C to 120 °C
Diagnosis instructions
Failure of the component
If the hot film air mass meter fails, the following behavior is to be expected:
- Fault entry in the engine control unit
- Emergency operation with substitute value
General notes
The hot film air mass meter has a self-diagnosis facility that detects internal sensor faults. Furthermore, the two digital output signals - air mass and temperature signal - are examined electrically and with regard to faults in the value range. If the hot film air mass meter detects an internal fault, the air mass signal is set for a sustained period to Low and the temperature signal is set for a sustained period to High.
We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.