Mass air flow sensors are typically applied to measure the amount of air entering the air intake tract of an internal combustion engine. So as to reduce pollution and to provide a cleaner and more complete fuel combustion, the mass air flow sensor signal is provided to a specialized computing device (sometimes called an engine control unit or ECU) that utilizes the air flow signal, among other measured signals, to calculate and regulate the proper amount of fuel to deliver to the engine for efficient combustion.
It is known that air density varies with temperature and pressure (often affected by the altitude at which the vehicle engine operates). The mass air flow sensor is applied to measure the mass flow of air in the intake tract to the engine under a variety of operating conditions.
Various types of mass air flow sensors are known. One type provides a vane or paddle projecting into the intake air stream and supported on a spring-loaded arm. The vane moves in proportion to the airflow and this displacement is calibrated and utilized to generate a mass flow signal.
Another type in wide use is the hot wire mass air flow sensor. This sensor has an electrically heated wire suspended in a portion of the engine intake air stream. The resistance of the wire varies with temperature, and wire temperature varies with the air flow over the wire. As air flow increases, the wire resistance decreases (decreasing wire temperature due to conduction cooling effect of the air) and therefore more current must be supplied by the sensor electronics to restore the wire temperature. In such a system, variations in the electric current supplied to heat the hot wire sensor are related to changes in air flow.
Other types of mass air flow sensors are known, however, these few are sufficient introductory examples for our discussions herein.
Mass air flow sensors are calibrated to have an output signal indicative of the quantity of air flowing in the air intake tract. This mass air flow calibration can be affected in undesired ways by the presence of vortices that may be present in the air flow stream. Vortices are a characteristic of turbulent fluid flow (herein we include air and other gases as fluids). A vortex is a spinning, often turbulent flow of fluid, swirling around a center. The fluid velocities in these vortices can be detected by the mass air flow sensor and contribute to measurement errors in the intake air flow with the result that the mass air flow sensor becomes a less reliable indicator of the quantity of air flow into the engine.
It is typical practice to install the mass air flow sensor after (downstream of) the air filter into the air intake tract between the air filter and the engine. Installation after the air filter is advantageous as the air filter removes contaminants from the air stream before they can build up upon and affect the calibration of the mass air flow sensor. The geometry of the air filter may contribute to the generation of shear layers in the air flow at the outlet side of the air filter, which may result in the generation of vortices in the air stream entering the mass air flow sensor and the resultant reduction in mass air flow sensor signal quality.
It is known within the prior art to install straightening vanes or flow aligned tubular honeycomb structures to reduce turbulence in the air intake tract. While such solutions are serviceable, they are disadvantageous from a total system cost point of view. Therefore a lower cost and more easily implemented solution is desirable.