A solid-state air flow sensor for automotive use

Abstract

A new wire-wound type hot-wire air flow sensor was designed for automotive applications. The sensing probe of the sensor is formed from a small platinum wire-round resistor and installed in the bypass of the measuring air stream in order to protect the sensing probe from surface contamination by dust and mechanical damage by a burst reverse flow which are common in such applications. In the design of the bypass passage, its length and the pressure loss in it are selected to get precise measurements in pulsating flow conditions. A new electronic control method was applied to the solid-state hot-wire sensor to allow the dynamic range to be increased from full scale/40 to full scale and the operating temperature range from −40 to 125 °C. An electronic control circuit for the hot-wire sensor is fabricated on an alumina substrate using thick film technology, and the sensing probes are connected to this substrate directly. This integrated solid-state air flow sensor shows a deviation of the measured mass air flow value of less than 4% of the indicated value.