Abstract: A compact hot-wire type air flow meter for an internal combustion engine with a high measuring accuracy is provided with a primary flow path forming an intake air passage and an auxiliary flow path incorporating therein a hot-wire element for measuring the intake air. The auxiliary flow path is defined by a flow path in an axial direction of the primary flow path and a flow path in a radial direction of the primary flow path.

Abstract: An air-fuel ratio detecting system detects the air-fuel ratio of the mixture supplied to an engine by means of titania whose electric resistance value varies in response to the oxygen content of the exhaust gases. The titania is connected in series with a reference resistor and a fixed voltage is applied to the junction of the titania and the reference resistor so as to generate a voltage corresponding to a change in the electric resistance of the titania. The detection voltage generated at the junction indicates the air-fuel ratio of the mixture and it is compared with a reference voltage for determining whether the air-fuel ratio is equal to the stoichiometric air-fuel ratio. The electric resistance of the titania varies with its operating temperature and the detection voltage varies correspondingly.