Air Flow Meter/Sensor: Description and Operation

Optical Karman-vortex Air Flow Meter:

Pulse Width To Air Flow Chart:

The Optical Karman-Vortex Air Flow Meter, located in the right front portion of the engine compartment, precisely measure air flow into the engine and relays this information to the ECU. The air flow meter is fitted with a vortex generator (basically, an obstruction in the air stream). As air flows past the vortex generator, vortices (turbulent air flow) are generated in direct proportion to the air flow.

At the top of the vortex generator there is a thin metal foil (the mirror) mounted to a leaf spring. A luminous diode shines infrared light on the mirror, the reflected light is detected by the photo transistor mounted below. The vortices created by the air flow cause the mirror to vibrate, the photo transistor detects the vibration as an interruption of the reflected light and inputs this signal to the ECU. As air flow increases there is a proportional increase in mirror vibration and, therefore, an increase in the signal frequency to the ECU.