Apparatus for measuring a flow rate of intake air for an engine

摘要

An apparatus for measuring a flow of intake air to an engine includes a bridge circuit including a heat resistor placed in an intake air path of the engine, a resistor for sensing the temperature of the intake air, and a plurality of balance resistors. A heating current is supplied to this bridge circuit through a transistor controlled by a periodical current-passage control signal generated by a microcomputer. A signal Vh, representing a temperature change of the heat resistor heated by the heating current, is detected by the microcomputer. A first correction value is computed by using a difference between the detected value from the microcomputer and a signal Vho, representing temperature of the heat resistor when the bridge circuit is balanced at normal temperature. A time width correction value DELTA Do1 is computed from a table on the basis of the first correction value. The correction signal DELTA Do1 is used for correcting the current passage time. The current passage time width as corrected is used for computing a flow of the intake air.