11/02/2023
AIR FLOW SENSORS
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Read More:
VEHICLE SENSORS: FUNCTIONS AND TYPES - https://bit.ly/3uxllDn
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Air flow sensors measure either the volume or the mass of air flowing in a channel. In an automobile, the primary use of an air flow sensor is to determine the amount of air drawn into the engine through the intake manifold.
There are two main types of air flow sensors: volume air flow sensors, which measure the effect of moving air on a pinwheel or deflecting plate, and mass air flow sensors, which measure the mass of air as it passes through the sensor.
As the load on an internal combustion engine varies, it is necessary to determine how much air is entering the cylinders in order to determine how much fuel to inject and how to adjust the engine timing.
Because the stoichiometry of the air-fuel reaction depends fundamentally on the mass (proportional to the number of molecules) of the air, rather than the volume, the use of mass air flow sensors (MAFs) is much more widespread.
The first airflow sensors to appear in cars measured the deflection of a plate placed in the airflow path. Later, another style of volume air flow sensor, the Karman Vortex airflow sensor, was introduced.
This sensor determined the velocity of the airflow by monitoring the frequency of an artificially induced turbulence using optical sensors. The ECM combines volume airflow information with air temperature measurements to calculate the mass airflow.
There are several types of mass air flow sensors.
The most common designs use a thin resistive wire (usually platinum) that hangs down into the airflow. This wire is heated to a specified temperature, usually 100's of degrees Fahrenheit above the ambient temperature detected by the intake air temperature (IAT) sensor.
As the air moving through the sensor cools the hot wire, the current flow through the wire changes. This current is detected by the sensor, which then relays this information to the ECM.
Other types of mass airflow sensors include "cold-wire" sensors (which detect the varying inductance of a circuit connected to thin metallic strips that vibrate as the air goes by) and membrane sensors (MEMS devices that use the change in temperature of a heated membrane to detect air flow in a manner similar to the "hot wire" sensor).
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A device in the throttle body, the mass airflow, or MAF, sensor helps the engine computer determine the proper air-fuel mixture by measuring the mass of the air flowing past it. Because a precise mixture is crucial to efficiency and clean combustion, the MAF sensor accounts for differences in air density, which varies with temperature and altitude. A failed MAF sensor is one of many events that will trigger a check engine light. It may also result in rough running, stalling or a drop in gas mileage.
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