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A new type hot wire probe has been developed for measurement of intake mass air flow rate in electronic fuel injection systems. The probe was composed of a coiled platinum wire covered with a glass-ceramic composite material. Improvement in response time has been achieved through the reduction of heat transfer from the hot wire probe to the leading wires, resulting from low thermal conductivity of the covering material. The decrease of the longitudinal heat flow rate has been revealed by the measurement of temperature distribution in the probe.

This report outlines the developmental status of the Hitachi hot wire air flow meter. It describes the newly developed hot wire probe and the air flow meter body to realize an improved cost performance ratio. In addition, it covers approaches to improve response time when the air flow rate is changed and to avoid deterioration in measurement accuracy caused by dirt deposits on the hot wire probe.