Advanced Design for Bypass Type of Hot-Wire Air Flow Meter

This report introduces an advanced flow passage design for bypass type of hot-wire air flow meter. The design was employed in an air flow meter integrated into a throttle body i.e. an integral type air flow meter. Features of the design are (1) configuration integrated on a single piece die-cast body employing a two dimensional L-shaped bypass passage and (2) a wide bypass inlet with oval profile. This design yields better performance and is more economical.

This paper describes the features of this new flow passage configuration with respect to measurement accuracy and signal noise. That is, it deals with relations between the passage configuration and the signal output deflections due to throttle valve position or distortion on inlet airflow. It also deals with the effects on signal noise caused by turbulence in upstream flow and by fluctuation in bypass air due to flow confluence at the bypass outlet.

In addition, this paper includes a basic flow analysis of a bypass-type air flow meter and some examples of three dimensional numerical flow analysis.