Intake air amount detecting system

摘要

An intake air amount detecting system includes a branch pipe disposed in the intake manifold of the engine and having two passages each provided therein with a temperature responsive resistor. One of the two passages is provided with an electric heater and a voltage is applied to the electric heater so that the temperature difference in the two passages measured by the two temperature responsive resistors is maintained at a predetermined value irrespective of the amount of air flow through the intake manifold. An A-D converter is further provided and includes a time constant circuit and a capacitor for producing across the capacitor a reference voltage which has a waveform representing a predetermined relationship between the voltage applied to the electric heater and the amount of intake air flow. The voltage actually applied to the heater is compared with the reference voltage at a voltage comparater in the A-D converter and the A-D converter produces a pulse signal having a time width corresponding to a period from the rise of the reference voltage until the reference voltage reaches the actual voltage, and hence corresponding to the amount of intake air flow.