![]() This screw controls the air-fuel mixture by letting a metered amount of air flow past the air flap, thereby leaning or richening the mixture. Many VAF sensors have an air-fuel adjustment screw, which opens or closes a small air passage on the side of the VAF sensor. A voltage is applied to the potentiometer and a voltage appears on the output terminal of the potentiometer proportional to the angle the vane rotates, or the movement of the vane may directly regulate the amount of fuel injected, as in the K-Jetronic system. The vane moves in proportion to the airflow. ![]() The VAF (volume air flow) sensor measures the air flow into the engine with a spring-loaded air vane (flap/door) attached to a variable resistor ( potentiometer). Moving vane meter Intake-air flap type flowmeter Since around 2012, some MAF sensors include a humidity sensor. Also see manifold absolute pressure sensor ( MAP sensor). The MAF sensor provides the open-loop controller predicted air flow information (the measured air flow) to the ECU, and the oxygen sensor provides closed-loop feedback in order to make minor corrections to the predicted air mass. When a MAF sensor is used in conjunction with an oxygen sensor, the engine's air/fuel ratio can be controlled very accurately. Vehicles prior to 1996 could have MAF without an IAT. Both sensor designs output a 0.0–5.0 volt or a pulse-width modulation (PWM) signal that is proportional to the air mass flow rate, and both sensors have an intake air temperature (IAT) sensor incorporated into their housings for most post on-board diagnostics (OBDII) vehicles. However, with additional sensors and inputs, an engine's ECU can determine the mass flow rate of intake air.īoth approaches are used almost exclusively on electronic fuel injection (EFI) engines. Neither design employs technology that measures air mass directly. These are the vane meter and the hot wire. There are two common types of mass airflow sensors in use on automotive engines. In automotive applications, air density varies with the ambient temperature, altitude and the use of forced induction, which means that mass flow sensors are more appropriate than volumetric flow sensors for determining the quantity of intake air in each cylinder. Air changes its density with temperature and pressure. ![]() The air mass information is necessary for the engine control unit (ECU) to balance and deliver the correct fuel mass to the engine. MAF sensor in a 2006-2015 automotive diesel engineĪ mass (air) flow sensor ( MAF) is a sensor used to determine the mass flow rate of air entering a fuel-injected internal combustion engine.
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