Hot-film air mass meter
The SIMAF GT2 hot film air mass meter by Siemens is used. The hot film air mass meter features planar resistors on glass. Its accuracy at all temperatures has been increased and its sensitivity to water and pulsation has been reduced.
The hot film air mass meter is secured to the air intake hose on the intake silencer and is a combined sensor. The hot film air mass meter detects the actual amount of air independently from the air pressure. The Digital Motor Electronics (DME) calculates the quantity of fuel to be injected in conjunction with other sensors. 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.
An electrically heated measuring cell protrudes into the air flow. The measuring cell is maintained at a constant temperature continuously. 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 μs). Pulsations due to the uneven firing interval on a cylinder bank also mean that negative air mass flows occur during driving. These negative air mass flows are included in the calculation.
| Item | Explanation |
|---|---|
| 1 | Hot-film air mass meter |
| 2 | 4-pin plug connection |
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 air mass signal is temperature-dependent. High accuracy is required to precisely determine the air mass. This is why the air mass signal received by the Digital Motor Electronics (DME) must be corrected using the signal from the intake air temperature sensor.
| Item | Explanation |
|---|---|
| 1 | Period |
| 2 | Characteristic curve for hot film air mass meter |
| 3 | Air mass |